LiFeP04 Batteries for Solar & BMS

[tasman]

In the photo, there are 64 x 40amp cells to make 12v x 640amps. The active balancers are connected to each cell line and about to take out my pack to make some adjustments and changes to it, by adding a couple more relays to switch back charge when it drops to 3.4v, from 3.6v. Instead of having to do it myself. But as I've said, yet to reach either top or bottom charge parameters so am really doing this for added security and improve my knowledge.

So what would you call my connection technique and is a good one, or not. To me it looks like a ladder because it connections across and along each cell line, rather than each line being separate until the end where they connect across the lines in parallel.

[Sunking]

In the photo, there are 64 x 40amp cells to make 12v x 640amps. The active balancers are connected to each cell line and about to take out my pack to make some adjustments and changes to it, by adding a couple more relays to switch back charge when it drops to 3.4v, from 3.6v. Instead of having to do it myself. But as I've said, yet to reach either top or bottom charge parameters so am really doing this for added security and improve my knowledge.

So what would you call my connection technique and is a good one, or not. To me it looks like a ladder because it connections across and along each cell line, rather than each line being separate until the end where they connect across the lines in parallel.

4 Balance boards right? Connected like the diagram for ladder right? Sounds like 4S16P t o me making 12 volts. It will work but 12 volts was a very poor voltage selection unless you have a special reason like an RV.

[tasman]

4 Balance boards right? Connected like the diagram for ladder right? Sounds like 4S16P t o me making 12 volts. It will work but 12 volts was a very poor voltage selection unless you have a special reason like an RV.

Yep 4 active balance boards, connected to a dedicated off grid BMS.

My apologies, thought using "MH" for motorhome would be ok, but can see you call them RV's. My house pack is also 12v, because it uses a 3000-6000w inverter for all house requirements. A friend set his house up using 12v and an inverter, found it used less energy than running either 24v or 48v for his house, plus apppliances are cheaper and easy to get down here than dc ones. So changed all our lght globes to 240v LED and reconnected the house wiring to the inverter. Haven't had a problem since, The only things using power at night are the freezers, big LED TV and a linux pc. During the day we run our band studio on it with no problems at all, all it takes is good energy management.

Forgot, we also connect our MH to the house when not travelling, which gives us another 1000w of solar and 480ah extra lifepo4.

[Sunking]

A friend set his house up using 12v and an inverter, found it used less energy than running either 24v or 48v for his house,.

That is not possible. 24 volts is 200% more efficient than 12 volts and 48 volts is 400% more efficient than 12 volts.

[tasman]

That is not possible. 24 volts is 200% more efficient than 12 volts and 48 volts is 400% more efficient than 12 volts.

You'll have to explain how that works, as I said I'm not that up on the technicalities of different voltage use, just go by what others have said and what I've picked up myself.

Was told using 24volts for the house would halve my pack ah capacity and on the surface that's how it looks. if you can explain how you get 200% extra energy out of half the ah capacity, I'd be most appreciative. Can understand the extra power for EV's by upping the voltage, but not how you can get 200% more energy out of a 24v system, by halving the amperage of a 12v one. Especially when using it through an inverter.

[Sunking]

if you can explain how you get 200% extra energy out of half the ah capacity, I'd be most appreciative.

I did not say that, I said 200% more efficient. Big difference.

Let's assume two simple circuits of a 12 and 24 volt battery 100 feet of copper 4 AWG wire, and 2 500 watt Gizmos one rated for 12 volts and the other rated for 24 volts. The 12 volt battery and 24 volt have the exact same capacity. The 12 volt is 320 AH = the 24 volt is 160 AH. We use the exact same two 12 volt 160 AH batteries.

On the 12 volt system the gizmo draws 42 amps and looses 1.2 volts or 10% of its power (50 watts)
On the 24 volt system the gizmo draws 21 amps and looses .6 volts or 2.5% of its power (12.5 watts)

Having said that we could make the 12 volt system just as efficient as the 24 volt system. We would have to use 2/0 AWG copper cable instead of #4 AWG. 100 feet of #4 AWG cost roughly $70, and 100 feet of #2/0 cost $220. Which system do you use?

I would not use either of them. I would use 48 volts and only loose 1.25% of the power or 6.25 watts. I could use a little smaller battery and panel wattage saving me more money. Now you know why utilities use very high voltages.

[tasman]

I did not say that, I said 200% more efficient. Big difference.

Let's assume two simple circuits of a 12 and 24 volt battery 100 feet of copper 4 AWG wire, and 2 500 watt Gizmos one rated for 12 volts and the other rated for 24 volts. The 12 volt battery and 24 volt have the exact same capacity. The 12 volt is 320 AH = the 24 volt is 160 AH. We use the exact same two 12 volt 160 AH batteries.

On the 12 volt system the gizmo draws 42 amps and looses 1.2 volts or 10% of its power (50 watts)
On the 24 volt system the gizmo draws 21 amps and looses .6 volts or 2.5% of its power (12.5 watts)

Having said that we could make the 12 volt system just as efficient as the 24 volt system. We would have to use 2/0 AWG copper cable instead of #4 AWG. 100 feet of #4 AWG cost roughly $70, and 100 feet of #2/0 cost $220. Which system do you use?

I would not use either of them. I would use 48 volts and only loose 1.25% of the power or 6.25 watts. I could use a little smaller battery and panel wattage saving me more money. Now you know why utilities use very high voltages.

Now your using and very distorted example, I already knew and understand the efficiency of higher voltages over distance and energy medium carrying capacity with energy loss. However that doesn't equate when you are using an inverter, within a metre or two of the supply, nor in any situation with short wiring runs in a MH.

I believe efficiency is determined by the cost and return of a system, so it's not very efficient to use 24v-48v when you have short runs less than a few metres, with 6 BS wiring, 12v is much cheaper because you lose capacity by increasing voltage. The loses would be very minimal and you double your ah capacity with lower voltages, making your system much more efficient in it's use of stored energy. Higher voltages only become more efficient when you have long runs and seeking high HP energy outputs.

Wouldn't it be more reasonable to say, it is more effective to use higher voltages and wiring for long runs, but not more efficient because of capacity loses and cost. The cost if a 48v 500amp pack, is 4 times the price of a 12v pack and won't provide any more than a 500amp 12v pack over the distances and situations we are talking about.

Off course if you have 10-30m between your supply, and your storage or usage, then it makes sense to us higher voltages and wiring capacity. Our 350w wind generator pumps high voltages to the controller over about 20m, which is very efficient and sensible. But when it comes to storage capacity, to me it's much more efficient to get the most out of your pack and by doubling or 4 times the energy availability, to me is very efficient use of a system. Correct me if I'm wrong

[Sunking]

Now your using and very distorted example, I already knew and understand the efficiency of higher voltages over distance and energy medium carrying capacity with energy loss. However that doesn't equate when you are using an inverter, within a metre or two of the supply, nor in any situation with short wiring runs in a MH.

I believe efficiency is determined by the cost and return of a system, so it's not very efficient to use 24v-48v when you have short runs less than a few metres, with 6 BS wiring, 12v is much cheaper because you lose capacity by increasing voltage. The loses would be very minimal and you double your ah capacity with lower voltages, making your system much more efficient in it's use of stored energy. Higher voltages only become more efficient when you have long runs and seeking high HP energy outputs.

Wouldn't it be more reasonable to say, it is more effective to use higher voltages and wiring for long runs, but not more efficient because of capacity loses and cost. The cost if a 48v 500amp pack, is 4 times the price of a 12v pack and won't provide any more than a 500amp 12v pack over the distances and situations we are talking about.

Off course if you have 10-30m between your supply, and your storage or usage, then it makes sense to us higher voltages and wiring capacity. Our 350w wind generator pumps high voltages to the controller over about 20m, which is very efficient and sensible. But when it comes to storage capacity, to me it's much more efficient to get the most out of your pack and by doubling or 4 times the energy availability, to me is very efficient use of a system. Correct me if I'm wrong

Have forgot about the wiring between panels and controller, or systems that use 12 volt DC appliances like an RV. Even th e short wiring between battery and inverter use the exact same model I have used here. A 1000 watt inverter at 12 volts needs 100 amps or 25 amps at 48 volts. If given the choice higher voltage wins every single time. Go above 1000 watts and using 12 volts is extremely dangerous and expensive.

[Sunking]

I believe efficiency is determined by the cost and return of a system, so it's not very efficient to use 24v-48v when you have short runs less than a few metres, with 6 BS wiring, 12v is much cheaper because you lose capacity by increasing voltage.

Beg your pardon. I do not know who told you this or where you picked that up from is FALSE.

12 volts @ 100 AH = 24 volts @ 50 AH = 48 volts @ 25 AH = 1200 watt hours every day of the week any time of day. All three can be made with the same 4-12 volt 25 AH batteries. At higher voltages I can use much smaller less expensive wire at higher efficiency.

Same applies to charge controllers. At 1000 watts you have to use a $600 80 amps controller on a 12 volt battery with much larger wiring. At 48 volts all I need is a 20 amps $200 controller and small inexpensive wire. No matter how you want to spin it higher voltage = higher efficiency and lower cost.

[tasman]

Beg your pardon. I do not know who told you this or where you picked that up from is FALSE.

12 volts @ 100 AH = 24 volts @ 50 AH = 48 volts @ 25 AH = 1200 watt hours every day of the week any time of day. All three can be made with the same 4-12 volt 25 AH batteries. At higher voltages I can use much smaller less expensive wire at higher efficiency.

Same applies to charge controllers. At 1000 watts you have to use a $600 80 amps controller on a 12 volt battery with much larger wiring. At 48 volts all I need is a 20 amps $200 controller and small inexpensive wire. No matter how you want to spin it higher voltage = higher efficiency and lower cost.

I understand what you're saying and the perceived savings, but it doesn't compute when looking at the real economic facts. I have 2x60amp programmable mppt solar chargers on my MH, (1000w), total cost was less than $300, 4x 60amp on my house (2000w) and will add more as I increase panels.

My theory is rather than use a single big controller, much better to use a couple of smaller ones, then if one packs it in, you still have energy input, even if it is limited. Also have two spares in the MH and two at home and as I bought them all together, got a great deal. My set up allows me to switch off sections of the panel grid if necessary, it's aligned with my battery pack charge cut off. People have commented on my set up, but there have been a number of occasions where we've come across other travellers who were experiencing energy problems because of controller break downs. It happened to us when we first set the system up, one of the controllers failed, just switched off half the panels and changed over the controller. It was a production fault so was replaced quickly by the suppliers. These mppt controllers have been operating for years without a problem, first on L/A, then gel, now lifepo4. That's when we switched to MPPT. after seeing the difference between what goes into a battery with PWM, compared to a MPPT on another MH in shade.

The availability of 24v and 48v appliances and accessories is virtually nil. So 24 and 48v is useless for using low voltage appliances, it's the same with lighting. Try finding 24v or 48v lights or appliances and you enter the non existent, or expensive zone down here. My panels on the MH are 12v and on the house, 24v, because of the distance between the panels and controller, plus they are cheaper here than 12v panels.

Which means for off road and off grid, you have to use an inverter, or stick with pure 12v, meaning you can utilise your energy better and cheaper. Why add cost to break down 24-48v to a usable 12v, when there is no need and it's cheaper. We have lots of 12 volt charged, or operated stuff which would be impossible to obtain using higher voltages. Then you have to go to 240V AC and transform the power back to 12 volts. It may be different in the USA or Europe, but in Aus and especially Tasmania, we are very restricted in choice.

When you have a system that's been running for nearly 2 years on lifepo4, used daily and has yet to reach top or bottom charge parameters, to me that's a very efficient system, with a good fail safe backup.

[Mike90250]

.....Correct me if I'm wrong

Lower voltage systems have more losses, and as Sunking says, over 1000W delivered AC, the current density just gets insane and becomes dangerous.

And then you have the issues with parallel batterys to get the enormous Ah required to support the loads.

[tasman]

Lower voltage systems have more losses, and as Sunking says, over 1000W delivered AC, the current density just gets insane and becomes dangerous.

And then you have the issues with parallel batterys to get the enormous Ah required to support the loads.

Every MH I've come across using L/A or lifepo4 batteries uses 12v through 1000+w inverters and most off grid homes using inverters do the same.

Why do they sell so many 1000+w 12v inverters if they are dangerous and inefficient, most I've seen use 1-2.5kw 12v inverters in MH's and 3+kw 12v inverters in their homes with no problems at all. There are only loses when energy has a long distance to travel to the storage or load, aren't there.

[Sunking]

Why do they sell so many 1000+w 12v inverters if they are dangerous and inefficient,

Because consumers are trapped in 12 volt boxes, and ignorant. Same reason you can buy plug-in Grid Tied Inverters that are not legal to use, marijuana, cigarettes, tobacco, and automatic weapons. There is a lot of money to made off from fools. It is that simple. 12 volt cost more to install, operate, and are dangerous about 1000 watts. One can even argue 1000 watts is way too much. 12 volts is for toys and RV's. End of story. In an off-grid you would not use DC power on anything. You would use 24 or 48 volt battery with a 240/120 VAC inverter. 240/120 volt appliances and gizmos are a lot cheaper and way more efficient than a 12 volt toy model.

[Living Large]

Why do they sell so many 1000+w 12v inverters if they are dangerous and inefficient, most I've seen use 1-2.5kw 12v inverters in MH's and 3+kw 12v inverters in their homes with no problems at all. There are only loses when energy has a long distance to travel to the storage or load, aren't there.

250 Amps DC, for a 3kW+ inverter @12V? It may be common somewhere, but I wouldn't want it in my house. When you start talking about 2000 or 3000 Watts, at 12V, the current becomes unwieldy and all the wiring associated with the PV and batteries is going to have to increase to larger sizes. And it requires larger current capacity charging equipment too. I'm new to this, but those are my thoughts.

[Sunking]

250 Amps DC, for a 3kW+ inverter @12V?

Copper cable the size of your wrist and takes a $3000 15-ton hydraulic compression tool to terminate that kind of cable.