Does my MPPT SCC and 120V charger choice make sense for my LiFeMnPO4 batteries?

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2. This is how I would do it because it is cheap. You do just like above but use Power Resistors. So here is how you do it. For each 100 watt resistor is roughly 1.5 Ohms a common resistor value. at 12 volts, a 1.5 ohm resistor will draw 8 amps. So say you buy 5 100 watt power resistors and wire them in parallel. You just made a 40 amp discharger. Once you get the voltage bleed down, you can them start removing resistor to lower the drain for more control. Careful though we are talking some HEAT, an dif you leave at the wrong time and let ig to far you could do damage. But you have a extra set of eyes. Use your Elite and LVD to shut it down.

Sounds like an excellent solution to me! For something I'm probably only going to use once a year (or less), it's easier to stomach the $89 investment for the iCharger than the $275 for the CellPro 8.

First that is the difference between a Distributive BMS (Elite), and a Centralised BMS (Orion) Get it? Secondly it is the quality of the parts. Elite is Chi-Com and I do not know what chip set if any they use. Orion uses a TI Chip set you can program and good ole USA made. OK for plus an minuses a Centralised BMS requires 2-wires for every cell. Not a big deal on a 4S system, a cable management problem on a 100S system. Distributive requires a Vampire Board on every cell and a loop signal cable to Control Unit. Understand?

Easy to program. The Orion is tailored to a low voltage EV of 8 to 16S. You get a coulomb counter, CANBUSS to work with a Motor Controller. The advantage is like you noted you can program Trigger points. Or if it sees a problem with any cell it can react and do something, whatever you want it to do. In an EV if it sees a cell go low, it can reduce power or Limp Home Mode, or operate the LVD to save the battery. It has Diagnostics, data logging, bells and whistles. More than what you probable need and unless you are a code bug the Elite will probably work OK for you. The Orion just does a lot more and flexible.

It seems to me like the Elite is a good compromise for my application...no programming required, everything is set up to work in an RV setting as I plan to use it. Perhaps later in life when I have more time to play with BMS's I'll give something like the Orion a try.

Thanks again for all the help! I will be starting to buy parts soon and will report back.

[Sunking]

I have decided on bottom balance approach. I looked into the CellPro Multi4 and it does not have discharge capability. I'm guessing there are others available if not using a light bulb or something to draw power. That's research for another day, but at a glance the $89 iCharger 106B+ may do I what I need for less than half the cost of the CellPro 8.

I owned an Icharger 106B+ some time ago. Good little charger but I think I should point out some things you may not be aware of. Here is the one big limitation. Max discharge current is 7 amps or 20 watts, whichever comes first. What that means is If the charger has to dissipate more than 20 watts, you wil not get the full 7 amps without a Ballast resistor. Example say a 20 volt battery would limit you to just 1 amp. 20 volts x 1 amp = 20 watts. You woul dhave to use a 350 watt resistor to take the heat off the Icharger to get 7 amps. Now at 3.2 volts of LFP is no problem at 7 amps.

Now here is the kicker when you get your cells and parallel them up you will have a 3.2 volt 800 AH Battery. Lets say they arrive at 60% SOC that means they have 480 amp hours you need to bleed off. See the problem? It would take you 480 AH / 7 amps = 68.5 hours to discharge them, almost 3 days.

The PL8 is not much better at 10 amps 100 watt imit. So what is a guy to do then?

Well cheer up there are a couple of ways. I won't leave you down and out for the count.

1. Connect the batteries in series to make your 12 volt battery. Make you a plug if you want to use say the Icharger to monitor cell voltages, or use a DMM. Go down to Wally World and buy some cheap Car Head Lights. Most are around 50 to 70 watts, so you would want a few of them. Current = Power / Voltage. So at 200 watts / 12 volts = 16.6 amps. You can go up to 1000 watts if you can afford it.

2. This is how I would do it because it is cheap. You do just like above but use Power Resistors. So here is how you do it. For each 100 watt resistor is roughly 1.5 Ohms a common resistor value. at 12 volts, a 1.5 ohm resistor will draw 8 amps. So say you buy 5 100 watt power resistors and wire them in parallel. You just made a 40 amp discharger. Once you get the voltage bleed down, you can them start removing resistor to lower the drain for more control. Careful though we are talking some HEAT, an dif you leave at the wrong time and let ig to far you could do damage. But you have a extra set of eyes. Use your Elite and LVD to shut it down.

Sound good?

With the Elite, you cannot adjust the voltage at which the boards start shunting, it is set at 3.55V. Additionally, over-voltage triggers when the highest cell voltage hits 3.8V (gulp) and undervoltage triggers when the lowest cell hits 2.8V. That would be unacceptable to me except that I plan for the solar cc and shorepower charger to stop charging well before that, so 3.8V would only be achieved if all hell broke loose and my chargers somehow did not automatically stop charging.

No problem assuming your batteries are in good health and you only charge to 13.8 volts you should not trigger, but it is possible. Example for whatever reason a cell fails, deteriorates, or become really unbalanced it is possible for a cell to go over 3.6 volts. Example 3 cells charging at 3.3 volts an done faulty cell at 3.6 volts = 13.5 volts with a charger set at 13.8 volts. It is possible, but that is what you have a monitor and eyes for.

There is a CANBUS option on the Elite BMS but I have no idea how it would interact with the programmable Magnum inverter/charger. Maybe this would be a good time to talk about what the Orion Jr has to offer. The BMS comparison website you sent me indicating that the Orion Jr also uses shunt-based passive cell balancing, only there are no vampire boards attached to each cell as the Jr does it internally. Does this make it any better than the Elite?

First that is the difference between a Distributive BMS (Elite), and a Centralised BMS (Orion) Get it? Secondly it is the quality of the parts. Elite is Chi-Com and I do not know what chip set if any they use. Orion uses a TI Chip set you can program and good ole USA made. OK for plus an minuses a Centralised BMS requires 2-wires for every cell. Not a big deal on a 4S system, a cable management problem on a 100S system. Distributive requires a Vampire Board on every cell and a loop signal cable to Control Unit. Understand?

How complex is the setup on a Jr and what are some of the advantages? I can't seem to find much information on it, and particularly not for use in a boat or RV.
You've provided me a lot of great information, so thanks again!

Easy to program. The Orion is tailored to a low voltage EV of 8 to 16S. You get a coulomb counter, CANBUSS to work with a Motor Controller. The advantage is like you noted you can program Trigger points. Or if it sees a problem with any cell it can react and do something, whatever you want it to do. In an EV if it sees a cell go low, it can reduce power or Limp Home Mode, or operate the LVD to save the battery. It has Diagnostics, data logging, bells and whistles. More than what you probable need and unless you are a code bug the Elite will probably work OK for you. The Orion just does a lot more and flexible.

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I think you have a decent MOP going for you. The real challenge for you is when you receive the cells how you will implement the initial Balance Act being it Top, Middle or Bottom.

I have decided on bottom balance approach. I looked into the CellPro Multi4 and it does not have discharge capability. I'm guessing there are others available if not using a light bulb or something to draw power. That's research for another day, but at a glance the $89 iCharger 106B+ may do I what I need for less than half the cost of the CellPro 8.

So I have a suggestion and I do not know if your Elite System can do this or not. I know the Orion can. You want it to send a signal to the charger to either Turn off, or lower the voltage to Float when the first cell reaches 3.55 volts. At the cell with your low charge rate wil be roughly 95% SOC and that is all she's got Scotty. That is when you want to terminate. After a few times via trial and error you can find the right Absorb voltage.

With the Elite, you cannot adjust the voltage at which the boards start shunting, it is set at 3.55V. Additionally, over-voltage triggers when the highest cell voltage hits 3.8V (gulp) and undervoltage triggers when the lowest cell hits 2.8V. That would be unacceptable to me except that I plan for the solar cc and shorepower charger to stop charging well before that, so 3.8V would only be achieved if all hell broke loose and my chargers somehow did not automatically stop charging. There is a CANBUS option on the Elite BMS but I have no idea how it would interact with the programmable Magnum inverter/charger. Maybe this would be a good time to talk about what the Orion Jr has to offer. The BMS comparison website you sent me indicating that the Orion Jr also uses shunt-based passive cell balancing, only there are no vampire boards attached to each cell as the Jr does it internally. Does this make it any better than the Elite? How complex is the setup on a Jr and what are some of the advantages? I can't seem to find much information on it, and particularly not for use in a boat or RV.

Good luck, keep doing homework, and I will be happy to answer questions. If I do not know the answer, I know where to find them.

You've provided me a lot of great information, so thanks again!

[Sunking]

I am pretty sold on the concept of bottom balancing and monitoring for voltage drift (easy to do when it's all spelled-out for you on the LCD screen), but I doubt the bleeder boards will be doing any cell balancing with the conservative charger settings we are using.

When it comes down to it I will basically be using the BMS as my battery monitor (cell voltages, temp, overall voltage and amps in/out) and more importantly as a source for a backup LVC/HVC if my chargers/inverter do not shut down on their own. The cost for all of that is $345 (plus the LVC/HVC contactors, which I would buy anyway), and I will NOT have to buy the Victron BMV702 as my energy monitor (which costs $205), so the difference in cost between no-BMS + BMV702 and the full-system just described is only $140. If I went with no BMS I would have to figure out a way to have that secondary LVC/HVC control.

I think you have a decent MOP going for you. The real challenge for you is when you receive the cells how you will implement the initial Balance Act being it Top, Middle or Bottom.

Here is a little tib bit if you have not already discovered it. When you Bottom Balance you are making a known reference point of 0 AH or 0% SOC. The cell voltages will only be equal at the Bottom. But here is the catch. On the first couple of charges you need to watch the cell voltages. You are looking for the weakest cell, or the cell with the lowest AH Capacity. That cell wil be the one with the highest voltage when they approach being fully charged. That cell will be full before the others. So you need to watch and note when it gets to roughly 3.5 volts. From 3.5 to 3.6 volts is a fast ride and happens quickly.

So I have a suggestion and I do not know if your Elite System can do this or not. I know the Orion can. You want it to send a signal to the charger to either Turn off, or lower the voltage to Float when the first cell reaches 3.55 volts. At the cell with your low charge rate wil be roughly 95% SOC and that is all she's got Scotty. That is when you want to terminate. After a few times via trial and error you can find the right Absorb voltage.

Good luck, keep doing homework, and I will be happy to answer questions. If I do not know the answer, I know where to find them.

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Tell me more about the Vampire Boards. What functions do they perform? Is it bleeding only? Or do they also measure the voltage and temp also? I suspect they do it all if I remember correctly. Been a while since I looked. Don't worry to much about them because essentially if your charger never goes above 13.8 volts, they should never trigger the bleeders. And if you ask me nicely I can tell you how to disable them. They have a power resistor to burn the power off when turned on. Cut one end of it and open it up. Think of it like a washed out bridge.

Thanks for the info on the GBS vs CALB, I will consider this further.

Here are the specs on the Elite BMS:
Main Screen Display: Pack Voltage, Pack Current, Battery Capacity, Alarm Message
Individual Cell Screen: Cell number, voltage and temperature
Computer Input Power: 9-20V, 120mA
Battery Voltage: 12-500V
Shunt Input: 500A = 50mV
Pack Voltage Resolution: 0.2V
Current Resolution: 0.1A
Temperature Measurement Range: -99F to +199F or -146 to +92C
Video Output: Composite Video, Color, NTSC, RS-170
Measurement accuracy: Better than 1% of Full Scale
Maximum number of cells supported: 140
Balancing Threshold: 3.55V
Balancing Current: 0.5A
Alarm Output Current: 4A surge for 100mS, 2A continuous*
Optional Data Interface: CAN
Ground Fault Detection: 2mA (5000 Ohm/Volt)

I am pretty sold on the concept of bottom balancing and monitoring for voltage drift (easy to do when it's all spelled-out for you on the LCD screen), but I doubt the bleeder boards will be doing any cell balancing with the conservative charger settings we are using.

When it comes down to it I will basically be using the BMS as my battery monitor (cell voltages, temp, overall voltage and amps in/out) and more importantly as a source for a backup LVC/HVC if my chargers/inverter do not shut down on their own. The cost for all of that is $345 (plus the LVC/HVC contactors, which I would buy anyway), and I will NOT have to buy the Victron BMV702 as my energy monitor (which costs $205), so the difference in cost between no-BMS + BMV702 and the full-system just described is only $140. If I went with no BMS I would have to figure out a way to have that secondary LVC/HVC control.

[Sunking]

I like the GBS/Elite system for several reasons. I like the packaging as it fits where I want it to go, I like that the cells are banded together, the 4-screw terminals and the caps that cover the I terminals.

I did too and paid up for it just like you. What I did not realize at the time is the Internal Resistance of the cells. For an EV we need to be able to draw very high amounts of current in short bust of 10 to 15 seconds to accelerate. Example I was trying to pull 600 amps from 100 AH cells aka 6C. Well the cells can do that but due to high resistance the voltage collapses. OK do not panic because you will not ever make that demand because with a 1000 watt Inverter at 12 volts the most you can possible pull is 100 amps. On a 200 AH pack is only C/2 well within its capability. However I do not think they will last as long as CALB. Hard to say because I have never been able to test them under cream puff conditions of solar with low demand.

Tell me more about the Vampire Boards. What functions do they perform? Is it bleeding only? Or do they also measure the voltage and temp also? I suspect they do it all if I remember correctly. Been a while since I looked. Don't worry to much about them because essentially if your charger never goes above 13.8 volts, they should never trigger the bleeders. And if you ask me nicely I can tell you how to disable them. They have a power resistor to burn the power off when turned on. Cut one end of it and open it up. Think of it like a washed out bridge.

Don't worry about the Orion Jr. Go on with your plans.

Anyway to see where GBS batteries fall on the ole quality scale click this link. It is one of the pages I already gave you from David. It is called a Short Discharge Time. It is a theoretical time it would take to fully discharge any battery type or any capacity with a dead fault short. Not something you can really do but is based entirely on the Internal Resistance of the battery. Tells a designer the quality and if the battery is a good match for his application The shorter the time, the better the battery is. You can clearly see where all the Chi-Coms fall at the bottom of the list. Don't freak out because it is tailored to EV. Search around David site. Try using the BMS Selector tool. The Elite is in there and you can compare it to other options.

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And I was just feeling confident about my equipment purchase and you had to throw down a post like that. <--Note the smiley. As a summary, this is an electrical system being placed into service in a high roof Sprinter van. 200 aH of lithium batteries, single 305W LG solar panel(32.5 Vmpp, 9.26 lmpp), Victron 75/15 solar charge controller as primary source of charging, Magnum MMS1012 1000W pure sine inverter/charger/transfer switch (confirmed that this unit has fully customizable charge settings)--keep in mind this unit will charge the house batteries when plugged into 120V shorepower and I will also have the capability to use a second 600W pure sine inverter that will be used to feed alternator power to the Magnum inverter/charger to charge the batteries when driving. Even though there are two electrical losses in the inverters, the ability to run small gauge AC wires from the front of the van to the rear where the house batteries are located is a big plus. Also needed is a battery monitoring system to track useage.

I like the GBS/Elite system for several reasons. I like the packaging as it fits where I want it to go, I like that the cells are banded together, the 4-screw terminals and the caps that cover the I terminals. I like that many RVs and boats are using this system with good feedback and I have a personal friend using this system. Because it's a complete package, tech support is available if I run into install problems. I love the way the LCD displays battery SOC, charging/discharge rate, individual cell voltage and temperature. Basically, I didn't have anything to not like until you brought up the vampire board issue. It sounds to me like this is one of the bigger issues you have with the components I'm looking at, and I get the impression that use of the Orion Jr TI chipset resolves this issue. What it means to me is trying to figure out how to get all of the above working with the Orion Jr, as the Elite system comes with everything I need (including the LVD and HVC contactors) and installation is well-documented since it is designed for use in boats and RVs.

I searched around and found pretty extensive use of the Orion Jr in EVs, but not RVs. You have me interested, but perhaps you can tell me how achievable the Orion Jr method would be considering my needs.

As always, I'm enjoying the dialogue!

[Sunking]

I thought you were leaning towards no-BMS, but thanks for clarifying. I am sure you and I both are aware of quite a few YouTubers that are anti-BMS. I just happen to not be one of them.

No I am not anti-BMS as some may lead you to believe. They have their place on larger systems, and for people who do not care to learn anything about Lithium batteries. Great example if you have watched the news is a fire in an apartment complex killing a little girl. The BMS malfunctioned. Those Hoover Boards now have 120 fires to their credit and 1 death. Just a fact. Damn Chi-Coms cheap junk.

You have a 4S system, not 45S or 100S like an EV. You are using LFP which is fairly safe and moderately tolerant to over charge voltages up to 4.2 volts per cell before you run into the danger of THERMAL RUNAWAY like on the HOOVER BOARDS and EV's that do not use LFP. Couple that with the 2.0 volts minimum on a 4S system gives you a operational Window of safety of 8 to 16.8 volts. You will not even come close to those limits if your Inverter LVD is set for 12 volts and Charger set to 13.8 volts. It you see your battery voltage less than 12 volts, you know you got a problem and do not need a BMS to tell you that.

FWIW you cannot define a BMS, there is no Industry definition. A simple Volt meter qualifies. So does a Cell Level Voltage Monitor

I am not seeing the advantage of the Orion Jr over the Elite Power BMS. Both are capable of LVD and HVC, both passively cell-balance. The Elite system includes a shunt and provides cell-level voltages, temperature, pack SOC, charge rate/discharge rate, all on a nice 7" LCD monitor. This is similar to the functionality of the Victron BM702 that everyone loves, however the Elite system provides more information. The only differences I can tell between the Elite and Orion Jr systems is one has the vampire boards (500mA spec) on the battery terminals while the Orion Jr does it internal to the BMS unit and is rated at 200mA shunt rate. Beyond capabilities I do not require, is there something I am missing?

The Orion can do everything the Elite can do and more. The Orion is Program Loop Controller you can fully customize. Lot's of EV guys use them with Bottom Balance to monitor everything you can with the Elite. An EV uses them also for a speedometer and Fuel Gauge as the Orion has a Coulomb Counter. A Coulomb Counter measures Amp Hour in and Amp Hours Out. It tells you pretty much exactly what the battery SOC is. The Orion also uses CAN BUS. It just does a lot more, fully programmable, data logging, trouble codes, and can communicate with other electronics via the Can Bus. It is tailored to EV's

From the Orion literature: "The Orion BMS uses passive balancing to remove charge from the most charged cells in order to maintain the balance of the pack. The passive shunt resistors dissipate up to 200mA per cell. While that amount may seem small, that current is more than sufficient for maintaining balance in very large battery packs."

It seems to me that the method the BMS uses for cell-balancing is almost a moot issue if I am successful in setting my solar charge controller and my 120V shorepower charger to never let the batteries reach a SOC that would trigger cell-balancing. LVD and HVC are obviously very important.

OK both the Elite and Orion use the exact same methods to balance, they bleed the cells or Shunt. Only the shunt currents are different. The Orion is a Centralized Active BMS and fully programmable because they use a TI Chip Set. Your Elite, not certain, but I do not think you can program what voltage it triggers on, nor can you disable it. On the Orion you can program the Shunt Balance to any voltage you want, or disable it so it never turns on. I suspect the Elite you have no control over and is just a passive Bleeder Board. Those have a tendency to fail Shorted out Bleeding your cell to death. That is where the bad reputation comes from.

I am sorry you are having to spoon-feed me. I am trying to read up on the technology BEFORE I buy the batteries, SCC, inverters, etc., but quite frankly this thread has helped me far more than anything I have read elsewhere, so thank you.

No Sir I am happy to do it.

You can use a BMS if you want an extra set of eyes. Just be aware of the danger using one with passive Bleeded Boards. They do not use chip sets that the industry uses. Most are Chi-Com like Hoover Boards. I am not saying DO NOT USE them. All I am saying is for a 4S battery they are not needed if you know what you are doing. The biggest flaw with a BMS is they use Top Balance topology, which requires you to fully charge the battery to 100% SOC. Charging any lithium battery to 100% SOC shortens battery cycle life and runs a much higher risk of thermal runaway. That is precisely why commercial EV manufacture do not allow you the customer to fully charge the EV battery. Like the Orion they use a TI Chip Set to control the SOC and not allow you to fully charge. It only monitors the cells and rarely ever does any balancing except when necessary and never 100%, some where in the MIDDLE. They can do that because they use matched cells.

If it were me in your shoes, I would use a cell level monitor, no Balancing. Use the right hardware and you can use it as a secondary fail safe in the event your Inverter LVD fails, or for whatever reason the Charger goes stupid and supplies more than 14 volts. Example if any cell drops below 2.6 volts for more than 15 seconds, disconnect the battery. If any cell goes above 3.6 volts disconnect the charger. I know both the Orion and Cell Pro can do that on their own. I do not know if the Elite can or cannot. Last time I looked at it a few years ago I was not impressed.

FWIW A few years ago being an engineer I was in the camp of: One Must Use BMS. Not today, I got educated from bad experiences living in that camp. Damn Bleeder Boards sent me packing..

EDIT NOTE:

If you have not bought your batteries as of yet I sugest you use CALB over GBS from Elite. CALB are less expensive, higher quality and last a lot longer. If something does go wrong you have a batter chance on warranty claim with CALB. EV guys like myself learned that lesson the hard way. My first LFP for my cart was GBS, I got rid of them after 6-months for CALB. But I do not have the CALBS anymore either. Sold them to a friend who still uses them in his cart. The GBs were sold to another person and they died in 6 months. Today I use Leaf Modules going on two years now.

Here is a GOLD MINE web site ran by a friend and fellow EV Designer. Every BMS and Lipo battery is there. David owns his own company and makes BMS systems out of Boulder CO. We don;t always agree, but I do not hold that against him as he smokles dope like cigarettes. That is why he live in Boulder. He offered me a job some years back when I wanted to retire for the 2nd time. His BMS uses a Custom IC he designed and manufactured by Atmel if I remember correctly.

[ASprinter]

OK let's get one thing straight, I am NOT telling you cannot use a BMS. OK?

I thought you were leaning towards no-BMS, but thanks for clarifying. I am sure you and I both are aware of quite a few YouTubers that are anti-BMS. I just happen to not be one of them.

If you are going to use anything, all you need is cell voltages and guess what you can use? Either a Cell Pro 8 or better for you it smaller brother Cell Pro Multi4. Use the LVD to protect over discharge, limit charge voltage to 13.6 to 13.8, and so you can sleep at night a cell monitor to keep an eye on voltages.

Thank you for pointing out a less expensive option for bottom-balancing.

One word of caution. If you bottom balance you must know about lithium batteries. So far you are doing your homework. If you really want a BMS look at an Orion Jr. It will work up to 16S and you do no thave to use the Balance Feature, Just use it to monitor cell voltage and temps. It can even interface to a LVD and HVC if you want. Just do your homework.

I am not seeing the advantage of the Orion Jr over the Elite Power BMS. Both are capable of LVD and HVC, both passively cell-balance. The Elite system includes a shunt and provides cell-level voltages, temperature, pack SOC, charge rate/discharge rate, all on a nice 7" LCD monitor. This is similar to the functionality of the Victron BM702 that everyone loves, however the Elite system provides more information. The only differences I can tell between the Elite and Orion Jr systems is one has the vampire boards (500mA spec) on the battery terminals while the Orion Jr does it internal to the BMS unit and is rated at 200mA shunt rate. Beyond capabilities I do not require, is there something I am missing?

From the Orion literature: "The Orion BMS uses passive balancing to remove charge from the most charged cells in order to maintain the balance of the pack. The passive shunt resistors dissipate up to 200mA per cell. While that amount may seem small, that current is more than sufficient for maintaining balance in very large battery packs."

It seems to me that the method the BMS uses for cell-balancing is almost a moot issue if I am successful in setting my solar charge controller and my 120V shorepower charger to never let the batteries reach a SOC that would trigger cell-balancing. LVD and HVC are obviously very important.

I am sorry you are having to spoon-feed me. I am trying to read up on the technology BEFORE I buy the batteries, SCC, inverters, etc., but quite frankly this thread has helped me far more than anything I have read elsewhere, so thank you.

[Sunking]

OK let's get one thing straight, I am NOT telling you cannot use a BMS. OK?

I am saying it is not required. As Mike points out most system you can buy are Chi-Com and quality is questionable. What I am saying is with a 4S battery or 12 volts it is blatantly obvious if a cell voltage goes out of whack. With LFP you are most concerned with over discharge.

Let's use a Bible tactic, a parable. Peter, A DIY EV uses a 45S 144 volt battery. The operating voltage range is 162 volts down to 113 volts. If Peter looks at the volt meter on the controller and sees say 150 volts all is good right? Not necessarily because Peter could have 1, 2, 3 or even more cells setting at less than 2.5 volts and destroying them and never know it until it is too late.

But John uses a 4S 12 volt system with a operating range of 13.8 to 12 volts. If John has a week cell he knows immediately right?

See what I am driving at?

EV manufactures do something you cannot. They use matched cells, within 1% capacity tolerance. Rarely if ever do they Balance the cells. In fact none of them would ever allow you to fully charge the EV pack. If they did, they could not offer the long warranties. The lithium cells they use only have 500 cycle in them if fully charged up. EV limit the customer to 90/10 at most. Some even tighter limits. at 80/20.

OK you can mimic what commercial EV manufacturers do by Bottom Balance and run in the middle. The real dander of LFP is over discharge. When you Bottom Balance you eliminate over discharge and you do it passively requiring nothing more than setting your Inverter LVD to 12 volts if it allows it. If not most Inverters default at 10.5 volts which will also work. When you Bottom Balance all cells wil be 2.5 volts when discharged. That is 10 volts. Damage is at 2 volts per cell or 8 volts.

If you are going to use anything, all you need is cell voltages and guess what you can use? Either a Cell Pro 8 or better for you it smaller brother Cell Pro Multi4. Use the LVD to protect over discharge, limit charge voltage to 13.6 to 13.8, and so you can sleep at night a cell monitor to keep an eye on voltages.

One word of caution. If you bottom balance you must know about lithium batteries. So far you are doing your homework. If you really want a BMS look at an Orion Jr. It will work up to 16S and you do no thave to use the Balance Feature, Just use it to monitor cell voltage and temps. It can even interface to a LVD and HVC if you want. Just do your homework.

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If you were designing the electrical system for a recreational vehicle with a LiFeMnPO4 battery, how would you do it? You are really helping me understand how all of the various components work together, however without a BMS how would you devise an automatic LV/HV cutoff in case the inverters and chargers didn't do it on their own? I want that second line of defense but I'm unsure how to get there without the BMS.

I'm not sure how the top-end cell balance works on my Nissan Leaf, but I know the canbus tells my charger to reduce charging amperage significantly once the battery hits near 100% and cell balancing initiates. (That takes 40 min after the battery hits 100%.) The BMS that comes with my GBS batteries obviously isn't that sophisticated.

[Sunking]

Sorry for the confusion, yes, there will only be 4 cells. The 12-cell pic above is simply a photo I stole off the internet.

THX. I knew something was not right.

You are correct, the BMS applies a 0.5A load when cell voltage hits 3.55V to cell balance. I suspect doing a cell balance before putting this into use will be critical because with the charge settings being recommended to me it sounds like the cells are unlikely to hit the 3.55v required to initiate cell balancing.

You are correct, before the Vampire Boards turn on, they must reach the trigger point. To use the BMS would require you to set the Controller to 14.4 volts or 4 x 3.6 volts per cell. At 13.6 to 13.8 no cell should get high enough to trigger them on if they are BALANCED. So keep your eyes on the cell voltages near the top and bottom. Look for the one higher than the others at the TOP, or a cell with lower voltage at the BOTTOM. The spread from high to low should be no greater than 0.1 volts at the top or bottom. In the middle should be less than .05. They should always be between 3 and 3,45 volts.

But back to Mike's point and what DIY EV builders have experienced is two fold failures. If you have say a 20 amp charger, and the By Pass boards can only shunt .5 amps, when the first cell triggers it is very possible charge current will still be 20 amps or at least more than the shunt can bypass leaving the remainder still flowing through a fully charged cell. Once that cell reaches 4.2 volts you go into thermal run-away. Now in theory that should not happen if the cells are balanced to start with will reach 3.6 volts at roughly the same time.

However it takes a special charger to work with the bypass boards. It needs a signal to tell the charger the first By Pass Board has turned on, and then the controller cuts back charge current to .5 amps. Understand?

But the real problem with Bypass Boards with monitors have a nasty failure mode and parasitic loads. Bypass boards have a nasty habit of failing shorted. That means they never unlatch and keep BLEEDING .5 amps. Unless you are on top of your game, you will not catch it until it over discharges a cell. Lithium batteries do not tolerate being over discharged. The stronger cells will eat the bad cell by reverse polarity and destroys the cel instantly making a dead Short Circuit. That is when the Magic Smoke escapes followed by spewing gel and flames.

I would likely do a bottom balance. If I have to buy equipment (CellPro 8) at least I don't also have to buy a DC power supply.

Well you do not need the Cell Pro to do that. You just need a load to discharge the cells. There is a catch though. You had better be there to catch the moment when the voltage drops to 2.5 volts. Once it goes below 2.0 volts is death. With the Cell Pro you can program it to stop discharging at any voltage you want automatically. You start by setting it to say 10 amps discharge and stop at 2.5 volts. First time around the cell voltage will rebound up above 2.5 volts. You keep lowering the current. What I do is set the voltage to 2.4 volts. Your goal is after rested no cell above 2.5 volts or lower than 2.4 volts. Takes a while. Once you get there that is 0 AH capacity at 10 volt pack voltage. Set your LVD to 12 volts. At 12 volts you stil have around 10% capacity left in the tank.

With Lithium Batteries STAY AWAY FROM THE KNEE CURVES at both TOP and BOTTOM. Makes no difference what point you balance at, Top, Bottom, or Middle. Stay away from fully charged and discharged.

[ASprinter]

Mike,
I appreciate the insight on use of BMS. I am purchasing the batteries as a kit that also includes the BMS, vampire boards, two contactors and the shunt-based battery monitor with the LCD display. I like the idea of having the BMS as a backup to perform the LV and HV cutout in the event some other part of my system fails. I know there are other ways to do it, but I think this is a good way for a newbie like myself to go.

OK you got me confused. Is this a 12 volt battery?

Sorry for the confusion, yes, there will only be 4 cells. The 12-cell pic above is simply a photo I stole off the internet.

Anyway I do Bottom Balance as do most folks who customize EV and Golf Carts. But here is the deal, you cannot use the BMS to perform your Initial Bulk Balance. A BMS is designed to only keep a Top Balanced pack in Balance, thus very small minor corrections. The reason is the Vampire Boards aka Balance Boards can only bleed a very small current. Not sure what your boards are rate dat but typical is 300 to 500 Milli-amps. New batteries will have a significant difference. 10 to 20 AH difference depending on capacity of the cell. With Solar only have a average 4 Sun Hours it can take days or weeks. A 500 milli-amp board can only correct up to 2 AH per day, and if the th ecell range difference is 20 AH you are talking 10 days.

You are correct, the BMS applies a 0.5A load when cell voltage hits 3.55V to cell balance. I suspect doing a cell balance before putting this into use will be critical because with the charge settings being recommended to me it sounds like the cells are unlikely to hit the 3.55v required to initiate cell balancing.

I do have a Cell Pro 8 and a few others. Great charger to have. Not only will it do Lithium, but any battery chemistry on the face of earth today and tomorrow in the future. To Top Balance you would also need a DC Power Supply to go with that Cell Pro. Bottom Balance you do not need a DC Supply because you will only discharge and not charge.

I can get you started. If you Top, Bottom or Mid Balance you connect all cells in Parallel to start with.

If you Mid Balance you just walk away over night. Next day install them in series. Use Option 1 or 2.

Bottom Balance after you walk away for the night, then discharge them so at rest the finale voltage falls no higher than 2.5 volts, and no lower than 2.4 volts. Connect them is series and charge until one cell reaches 3.55 volts then terminate the charge. Note charge voltage and use that as you rset point using option 1 as the high point. Float will still be 13.6 volts.

If you go with Top Balance, you need to build a Balance Plug for the Cell Pro. After leaving them in parallel over night, install them with your Balance Plug you made for the Cell Pro. assuming a 12 volt configuration set the charger up for LiFe 4S. Charge at as high of a rate as youR DC Power Supply will let you go assuming you do not go over the Cell Pro limit which I think is 50-Amps off the top of my head. Terminate when the current tapers off to 3% of C. So if the total capacity is 100 AH, terminate at 3 amps.

If you go with Top Balance let me know because you wilL want to use your BMS to disconnect the batteries if any cell drops to 2.6 to 2.9 volts under load. Use option 1 or 2 to charge.

I would likely do a bottom balance. If I have to buy equipment (CellPro 8) at least I don't also have to buy a DC power supply.

[Sunking]

That is great to know, thank you! I see no reason to buy a more expensive charge controller.

And SunKing, thanks again for the recommendations. You did a great job explaining what happens under each of the scenarios, so I will probably try option 1 as a learning exercise but have option 2 in my back pocket as well.

I will be using a BMS, seems like a cheap insurance policy in case something else goes awry. It will have low voltage cutoff, high voltage cutout and top-end shunt-type cell balancing. I will be able to see the voltage of each of the 4 cells, so my plan is to watch it when I charge it and if there is a large cell inbalance I will stop and do a bottom balance. Bottom balancing looks really straight-forward, I am just not sure how I would do it without spending $280 on a CellPro Powerlab 8 (which seems to be how everyone does it.)

OK you got me confused. Is this a 12 volt battery?

Why am I seeing 12 cells? I should only see 4 Cells.

Even if your configuration is 4S3P I should only see 4 cell voltages.

Anyway I do Bottom Balance as do most folks who customize EV and Golf Carts. But here is the deal, you cannot use the BMS to perform your Initial Bulk Balance. A BMS is designed to only keep a Top Balanced pack in Balance, thus very small minor corrections. The reason is the Vampire Boards aka Balance Boards can only bleed a very small current. Not sure what your boards are rate dat but typical is 300 to 500 Milli-amps. New batteries will have a significant difference. 10 to 20 AH difference depending on capacity of the cell. With Solar only have a average 4 Sun Hours it can take days or weeks. A 500 milli-amp board can only correct up to 2 AH per day, and if the th ecell range difference is 20 AH you are talking 10 days.

I do have a Cell Pro 8 and a few others. Great charger to have. Not only will it do Lithium, but any battery chemistry on the face of earth today and tomorrow in the future. To Top Balance you would also need a DC Power Supply to go with that Cell Pro. Bottom Balance you do not need a DC Supply because you will only discharge and not charge.

I can get you started. If you Top, Bottom or Mid Balance you connect all cells in Parallel to start with.

If you Mid Balance you just walk away over night. Next day install them in series. Use Option 1 or 2.

Bottom Balance after you walk away for the night, then discharge them so at rest the finale voltage falls no higher than 2.5 volts, and no lower than 2.4 volts. Connect them is series and charge until one cell reaches 3.55 volts then terminate the charge. Note charge voltage and use that as you rset point using option 1 as the high point. Float will still be 13.6 volts.

If you go with Top Balance, you need to build a Balance Plug for the Cell Pro. After leaving them in parallel over night, install them with your Balance Plug you made for the Cell Pro. assuming a 12 volt configuration set the charger up for LiFe 4S. Charge at as high of a rate as youR DC Power Supply will let you go assuming you do not go over the Cell Pro limit which I think is 50-Amps off the top of my head. Terminate when the current tapers off to 3% of C. So if the total capacity is 100 AH, terminate at 3 amps.

If you go with Top Balance let me know because you wilL want to use your BMS to disconnect the batteries if any cell drops to 2.6 to 2.9 volts under load. Use option 1 or 2 to charge.

[Mike90250]

Pitfalls of attaching a BMS
1) it's got lots of parts, usually made as cheap as possible in China, and seldom has proper engineering behind it. More parts, wires, connections = more ways things can go wrong on you
2) top end shunt. Unless the shunt can bypass your charger entire current ( a 30A charger needs 30A shunts) you still have a very high chance of cooking a cell or three, If you have 30A charger, and your BMS has 2 A shunts, your "full" cells will only be overcharged by 28A instead of a 30A overcharge, Big Whoopee, so what, You need at least a 25A shunt, and then you only cook your cell with 5A. Still going to kill the cell.

In solar applications, high charging current is needed to replace the consumed power in the short 3 or 5 hour solar day. you are not going to trickle charge the battery with 5 amps.