LifePO4 batteries for use with Midnite Classic 150?

[Sunking]

I see how that would be annoying if you are trying to design an EV. Below the threshold, the only way to drain the battery completely is to use fewer and fewer amps.

Every battery has some Ri, and I know I can 100% drain the 400wh lithium battery in my electric bicycle. So what did they do? Design the battery so the max amp draw is lower than the threshold? Is there a proper name for the "threshold"?

I am not real familiar with the E-Bike crowd bu tI have looked at the equipment you guys use so I have a clue. When I look @ online E-Bike supplies in batteries, I am seeing the same LiPo's we use in RC airplanes. Yes I fly RC 3D Planes. Here is what I am driving at Any Lithium battery you buy has C-Rates listed. One for Continuous, and one for Burst (maybe be called Pulse, Intermittent .....)

There is no defined method for the C-Ratings crazy as that sounds. It is an arbitrary number the manufacture feels comfortable with. It is related to Ri, however it is not a performance specification, it is a THERMAL specification one in which the Manufacture is comfortable with.

Back to E-Bike Batteries. LiPo's used in RC Hobby are extremely low Ri and thus have very high C-rates. Smallest out there is 20/40 and many as high as 100/200. For RC planes, heli's, quads it is extremely important to keep them light in weight as possible and they require very high power to weight ration motor to get them off the ground. A 2.5 pound airplane or heli will use a 500 to 700 watt motor @ 3S or 4S. That requires an operating current of 50 to 65 amps. Well if you were to use LiFePo4 would mean a 3S 30 AH 10 pound battery in a plane with a gross max flying weight of 2.5 pounds. Does not compute. However LiPo's have much higher energy density and much higher C-Rates. So that plane of heli can use a 1/2-pound 3S 2200 mah 30/60 C-rate battery. Not much fly time of roughly 5 to 6 minutes, but does work.

Back to E-Bike again. Unlike a EV you are very restricted in space and weight and LiFePo4 is just not a good option. So they tend to use LiPo's for the same reasons RC aircraft use them. LiPo's have two huge negatives Very Expensive and Very short Cycle Life. . A LiPo with 150 cycles is a very tired old fat puffy battery. Sound familiar?

[karrak]

Lithium batteries do not go out of balance. The only metric that throws them out of balance is differencand e in leakage current which takes months to accumulate.

Yes, it takes months to accumulate but it does accumulate. At present my battery goes out of balance by at least 1% per year. I am sure it was more when it was newer but have only started keeping data on the imbalance recently.

Karrak you came here for one purpose and one purpose only. To harass me. You even conspired on another forum to bring others here to help you. You found one poor soul. At least he had enough common sense to give up and leave.

If trying to counter some of the misinformation, incorrect information and what I see as bad advice that you sometimes post is deemed as harassment, then yes I am here to harass you. I have not conspired on any other forum and did not ask for anyone to come on this forum to counter your misinformation. If you mean wb9k, who runs the warranty lab at A123 Systems as the poor soul, I am sure he has better things to do with his time than put up with your rudeness and abuse. Shame for the rest of us that he is not around this forum anymore. He probably has far more knowledge and experience with LFP batteries than anyone posting on this forum. It is worth reading what he had to say, his first post is here https://www.solarpaneltalk.com/forum...629#post247629 My post three post before this is what he had to say on the other forum, if anyone has the time it is worth reading all the other posts that he wrote in that thread.

[createthis]

That cannot happen as it is physically impossible. Think of it like a sling shot, You put your marble in, draw it back, and let it go.

However if you draw to high of a C-Rate for too long, then yes you can and will have thermal damage. Short the cell out and it can explode. Note on your battery specs. If i remember correctly maximum continuous rate is 3C (300 amps), and Pulse is 10C (1000 amps for 10 seconds)

I see how that would be annoying if you are trying to design an EV. Below the threshold, the only way to drain the battery completely is to use fewer and fewer amps.

Every battery has some Ri, and I know I can 100% drain the 400wh lithium battery in my electric bicycle. So what did they do? Design the battery so the max amp draw is lower than the threshold? Is there a proper name for the "threshold"?

[Sunking]

What if the voltage does sag below 10 volts for some reason, but then bounces back to 10 volts. Would that damage the battery? Or does it only damage the battery when the voltage bounces back to under 10 volts?

That cannot happen as it is physically impossible. Think of it like a sling shot, You put your marble in, draw it back, and let it go.

However if you draw to high of a C-Rate for too long, then yes you can and will have thermal damage. Short the cell out and it can explode. Note on your battery specs. If i remember correctly maximum continuous rate is 3C (300 amps), and Pulse is 10C (1000 amps for 10 seconds)

[createthis]

Well lets fix that for you right now. Short Story it effects how fast you can charge and discharge. Don't concern yourself with Charge because you will never need or be able to go fast enough for it to be a problem if you charge at C/2 (50 amps or less). Even if you did, the batteries just slows it down by physics and self regulates. So don't waste anytime worrying about it.

Where it might become a problem is on discharge in the form of Voltage Sag. We need to talk a little math to understand

Voltage = Current x Resistance.

Simple enough equation if either current or resistance goes up, so does voltage. Resistance is pretty much fixed, so voltage will vary with current. With me so far?

So your battery as Internal Resistance we will call Ri GBS is fairly high. For each cell roughly .005 Ohms. Wire all of them up in seires coupled with connector resistance you have roughly .021 Ohms. So you charge up your battery fully, and are seeing 14 volts Open Circuit voltage. That means no current or 0 amps. You have a 1000 watt Inverter with a 1000 watt light bulb and turn it on. While doing this you are watching the battery voltage right on the battery term post. You observe the voltage of the battery falls from 14 volts to 12 volts. What happened. Th ebattery is rated for 3C or 300 amps.

You had voltage sag from high battery Ri. Use the Equation. 100 amps x .02 Ohms = 2 volts. 14 volts - 2 volts = 12 volts. Keep that light on for 20 minutes or less and the Inverter will trip off from LVD set to 11 volts despite you still having 50 to 70% capacity left in it. When the Inverter trips off you battery voltage jumps back up to 13 volts.

Another catch is the battery wire between battery and Inverter also adds voltage sag compounding the problem. If the wire is too long or too small for the length, the Inverter might very well shut off immediately despite having a fully charged up battery.

Understand now? In an EV that just sucks acceleration way down. That is one reason why I ditched the GBS them. Will it be a problem for you? I cannot say except it might if you have heavy loads left on for any period of time. Good news is it does not hurt the batteries. Your Inverter LVD will trip before it becomes a problem.

When you get your Cellpro Power Lab 8 and use the Balance plug, you can measure Ri of each cell. Without the Balance Plug it can only read the total pack RI. RI is your health meter of a battery. To be useful it has to be done at a specific SOC and temperature. Best method is 50% SOC and Room Temp cells. Keep a log. When you see Ri go up, you will know they are aging and loosing capacity. Also keep Capacity logged.

Same thing can be applied to your LiPo's on your Quads.

I've read the GBS cells quoted at between 1.5 and 1.8 mohms or 0.0018 ohms. I'll be sure to measure and log it per cell in order to keep an eye on things. This particular battery will mostly be used to charge laptops, small 12V devices, and personal electric vehicles like boosted boards and electric bicycle batteries that charge at under 300 watts, so I'll be surprised if it's a problem in the immediate future. I'm kicking around a few future projects in the back of my head where I'm sure Ri will be an issue, but they're just ideas for now.

What if the voltage does sag below 10 volts for some reason, but then bounces back to 10 volts. Would that damage the battery? Or does it only damage the battery when the voltage bounces back to under 10 volts?

[createthis]

Now you are talking. Do you have a good 12 to 80 VDC 60 amp power supply to use with the Cellpro? It will make short work of balancing the batteries.

I've got a 12V 33 ah AGM battery. I can cycle it until the job is done. If that gets tedious, maybe I can use my truck's starter battery or something. I saw a guy using the regen capability of the cellpro to bottom balance an LFP cell and charge a lead acid battery on Youtube. Figured I'd read the manual when the cellpro arrives, do the math, and go from there.

[Sunking]

I was aware of the greater internal resistance of the GBS cells before I made the purchase, though I admit I don't fully understand how it will affect my system in practice yet. .

Well lets fix that for you right now. Short Story it effects how fast you can charge and discharge. Don't concern yourself with Charge because you will never need or be able to go fast enough for it to be a problem if you charge at C/2 (50 amps or less). Even if you did, the batteries just slows it down by physics and self regulates. So don't waste anytime worrying about it.

Where it might become a problem is on discharge in the form of Voltage Sag. We need to talk a little math to understand

Voltage = Current x Resistance.

Simple enough equation if either current or resistance goes up, so does voltage. Resistance is pretty much fixed, so voltage will vary with current. With me so far?

So your battery as Internal Resistance we will call Ri GBS is fairly high. For each cell roughly .005 Ohms. Wire all of them up in seires coupled with connector resistance you have roughly .021 Ohms. So you charge up your battery fully, and are seeing 14 volts Open Circuit voltage. That means no current or 0 amps. You have a 1000 watt Inverter with a 1000 watt light bulb and turn it on. While doing this you are watching the battery voltage right on the battery term post. You observe the voltage of the battery falls from 14 volts to 12 volts. What happened. Th ebattery is rated for 3C or 300 amps.

You had voltage sag from high battery Ri. Use the Equation. 100 amps x .02 Ohms = 2 volts. 14 volts - 2 volts = 12 volts. Keep that light on for 20 minutes or less and the Inverter will trip off from LVD set to 11 volts despite you still having 50 to 70% capacity left in it. When the Inverter trips off you battery voltage jumps back up to 13 volts.

Another catch is the battery wire between battery and Inverter also adds voltage sag compounding the problem. If the wire is too long or too small for the length, the Inverter might very well shut off immediately despite having a fully charged up battery.

Understand now? In an EV that just sucks acceleration way down. That is one reason why I ditched the GBS them. Will it be a problem for you? I cannot say except it might if you have heavy loads left on for any period of time. Good news is it does not hurt the batteries. Your Inverter LVD will trip before it becomes a problem.

When you get your Cellpro Power Lab 8 and use the Balance plug, you can measure Ri of each cell. Without the Balance Plug it can only read the total pack RI. RI is your health meter of a battery. To be useful it has to be done at a specific SOC and temperature. Best method is 50% SOC and Room Temp cells. Keep a log. When you see Ri go up, you will know they are aging and loosing capacity. Also keep Capacity logged.

Same thing can be applied to your LiPo's on your Quads.

[inetdog]

You are definitely acquiring a dangerous thing.

Yeah but he is into a cool hobby. I enjoy flying RC but never got into racing quads.

Mine goes up and has come down hard a couple of times.

I was referring to a little knowledge....
But it applies to the batteries too.

[Sunking]

250 sized racing quads typically use 1000mah 4S batteries, and the 50W B6AC V2 works great for those:

Well yes but that is a tiny battery 14.8 volts @ 1 AH or 14.8 watt hours. Your charger is capable of charging them at 3C. But your 4S GBS 100 AH is roughly 100 times larger and best your charger can do is what 3 to 4 amps on a 4S LFP? That is C/33 to C/25 or 100 times slower.

Interestingly enough, I hadn't read this post before I made the purchase, but I did indeed buy a Power Lab 8. Weird that you and I are on the same page for once, eh?

Now you are talking. Do you have a good 12 to 80 VDC 60 amp power supply to use with the Cellpro? It will make short work of balancing the batteries.

When you get your batteries use the busbars and wire all 4 in parallel and walk away for a couple of hours. The decide on Top or Bottom, your choice. If you Bottom discharge them to 2.5 volts, let them rest, repeat until when at rest they are at 2.5 vpc an dlet them rest 12 hours. Your target is anywhere from 2.4 to 2.5 range.

If you decide on Top Balance charge to 3.65 volts and hold until charge current drops to C/33. With all 4 cells in parallel that is 400 AH / 33 Hours = 12 amps. Additionally buy yourself a 4 S JST Balance Plug from any Hobby Shop. When you wire the batteries in series you can do your maintenance and Top Balance checks with your Cellpro 8. You will thank me later for that advice once you realize what it can do. Trick is you will need a good 1500 watt 18 volt DC power Supply to take full advantage of the Cellpro Power Lab 8. If you are not aware it will do bidirectional charging from one battery to another of any chemistry know today and all future types.

Good luck.

[Sunking]

I don't think it's so sinister as that. I don't think it's about money. I think it's about uneducated consumers not understanding the technology, like you said..

True, very true, but that makes consumers easy pigeons to pluck.

Here is what Top vs Bottom Balance comes down too pure and simple Risk and picking the lessor of the two evils.

Top Balance maximizes pack capacity and is best used for infrequent applications like power tools. The down side is stressing the cells charging cells to 100%, and you destroying weaker cells if fully discharged. To run Top Balance requires cell level monitor and control provide by a BMS.

Bottom Balance eliminates the risk of over discharging cells. Down side is it has a risk of over charging the weakest cell if you push the pack SOC level too high. It requires no cell level monitoring or extra equipment to implement, just sound strategy and sacrificing of few percentage points of total pack AH capacity.

LFP batteries are sensitive to over discharge (cell reversal) and over charge. However LFP is fairly tolerant of over charge up to 4.0 vpc before you risk thermal runaway, whereas LiCo is extremely sensitive and cannot tolerate any over charge. Take them to 100% or 105% you only loose cycle life. On the other hand no LFP type will tolerate over discharge to cell reversal. One time is all it takes.

So you choose which path you like. I choose the low risk option and sacrifice 3 to 5 AH out of each 100 AH of battery. With a cutoff voltage of 3 vpc per pack, I never ever get close to going over the cliff at 2.0 vpc. On a 12 volt system I would set LVC at 12 volts, the cliff is at 8 volts. No Inerter or gizmo is going to work down to 8 volts. On the charge side on a 12 volt system, you stop at 13.4 volts and hold. Well below 14.6 volts upper limit..That only cost you 3 to 5% capacity and doubles cycle life.

It is not that hard to understand.

[SunEagle]

You are definitely acquiring a dangerous thing.

Yeah but he is into a cool hobby. I enjoy flying RC but never got into racing quads.

Mine goes up and has come down hard a couple of times.

[createthis]

However I do agree you need to use top balance because you do not know the technology and how it works. It is not for consumers like yourself who need to rely automation to protect your batteries.Bottom balance is very simple and requires very little automation. Manufactures do not like or approve because it does not make them money if they cannot sell you a BMS.

I don't think it's so sinister as that. I don't think it's about money. I think it's about uneducated consumers not understanding the technology, like you said.

Frankly, I would have been pretty content to remain one of those uneducated consumers. I don't really mind paying a little extra to have the technology manage itself and stay out of my way. Again, I think if Midnite Solar had a LifePO4 charging profile, we wouldn't be having this conversation and I'd be happily using one of those automated batteries.

I watched a video on Youtube a few months ago about a guy who made a sandwich from scratch. Like, he milked the cow and made the cheese and grew the lettuce and baked the bread. I think it took him something like six months to make the stupid thing. When he finally ate it, he hated the way it tasted. Six months of his life, just to be dissatisfied.

I don't think consumerism is the problem here. I think it's a lack of adoption.

[inetdog]

Am I actually starting to sound like I know what I'm talking about?

You are definitely acquiring a dangerous thing.

[createthis]

No sir it is not

"Top balance means capacities are off at the top and over charging is a risk."

That part is half correct, At the top, all cells are at maximum capacity, but capacity is not equal. The only thing that is equal at the top is SOC voltage of 3.6 volts. Both over charge and over discharge are is highly likely without a BMS.


"Bottom balancing means capacities are off at the bottom and over discharge is a risk. It's really a personal preference thing."

None of this statement is correct and leading you to the wrong conclusions. When you BB all cells both AH capacity and SOC voltages are equal in all cells. Capacity = 0 AH, and SOC Voltage = 2.5 volts. Over discharge risk is minimized to almost impossible. Like Top Balance, over charge is possible with BB system if you try to push the weak cell to high. The magic of BB systems is capacity is equal in all cells at all SOC levels. You stop charging when the weak cell reaches 80 to 90% SOC. So in the proceeding example if the weak cell is 97 AH and you charge the weak cell to 90% capacity, all cells have 87.3 AH. The weak cell will have ever so slightly higher voltage than all others when charged up. But the voltage difference is very small roughly .05 volts or less. The weak cell should be up around 3.41 to 3.43 volts at rest, and the others around 3.36 3.38 volts so in a 4S pack totals roughly 13.5 volts.

I think I was tired at this point. My second statement is clearly not correct. In bottom balancing, the capacity and SOC of each cell is zero at the bottom. Over discharge is less of a risk than top balancing because the other cells have no opportunity to cannibalize the lowest voltage cell (a process I admittedly do not fully understand, but I've heard you talk about a lot). It's still possible to damage the cell if bottom balanced by over discharging. It's just not as much of a risk as with top balancing. Over charging is the greatest risk with bottom balancing, which we mitigate by setting the charge controller to a voltage lower than 14.6V, thereby providing a buffer area.

In top balancing, the greatest risk is over discharge because of the (admittedly not well understood) cannibalization effect. Over charging is still a risk, if the BMS current shunt things cannot offload enough current to keep up, but it's less of a risk than in bottom balancing situations because all cells have equal SOC at the top. In addition, top balancing features the added risk of BMS failure. If this happens, the battery will be destroyed by overcharging.

I decided to start out with bottom balancing because I know LifePO4 and lithium cells in general do not like to be charged 100%, so I'm hoping to get a little extra life out of my cells by avoiding that SOC range.

I may try top balancing at some point in the future if I feel like, and that's no ones business but my own, especially if I end up destroying my pack in the process.

Am I actually starting to sound like I know what I'm talking about?

[createthis]

Never heard of a RC hobby charger limited to 50 watts, especially if you are running RC heli's. Those guys use large 6S 6000 mah packs and larger. A 50 watt charger would take 3 hours to charge a 6S@6000 mah pack. Ever consider getting a Cellpro Power Lab 8? It would make short work of maintaining and Gross Balance your new cells with either top or bottom balance @ 60 amps charge or discharge current.

250 sized racing quads typically use 1000mah 4S batteries, and the 50W B6AC V2 works great for those: http://www.getfpv.com/lumenier-1000m...tery-xt60.html
250s are actually aging now too. It's actually been a while since I've charged any of my batteries (which may have destroyed them), so I don't remember exactly, but I think I used to charge those at 1A, just to be safe. Yeah, it took a long ass time, but better that than a bloated pouch cell. The charger is capable of 6A charging, so this was nowhere near the upper limit.

150s and even 122 sized quads are quickly becoming the standard, and these quads use even smaller ah batteries.

The B6AC top balances, BTW. There's that.

Interestingly enough, I hadn't read this post before I made the purchase, but I did indeed buy a Power Lab 8. Weird that you and I are on the same page for once, eh?