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Off-Grid 24v 400AH Battery Pack Help
#1
Hi everyone.  I've been spending $$ and hours trying to make sure that I build my battery pack correctly.   I have recently purchased 16 3.2v 200ah LifoP04 batteries, and will be configuring them into a 24v 400ah battery pack for my cabin that will be recharged using an existing solar array.

Would the attached diagram be correct?  I wasn't sure about the separate BMS setup, I have two 8s version I purchased.  

Thoughts?

Thank you.

David


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#2
Here's a sample wiring from Midnite Solar's official docs - its what I used to wire mine up.  


A couple of topics based on this
1)  Note that DC Ground Fault that may be required for your local codes.    I use the Midnite Classic Controller which has it built in.  No sure about your controller.
2) You don't show a circuit breaker coming into the MPPT Charge controller from the Solar Farm - but its recommended for sure.
     (And you don't show a surge protector at Solar Farm - but maybe its in your Solar Farm combiner box)
3)  This has shunt - you might add one later.
4) The wiring should be in a box (for protection) per our local codes

Tip: Fuses are functional but I find circuit breakers easier to shut things off to work on things - i.e. just flip a switch.


NOTE: I did a previous post that was 'just wrong' in this spot, so I've replaced it with an actual real world wiring diagram and hopefully some helpful comments Smile
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#3
For my camp I have moved as much stuff over to 12V LED and fans to limit the need for AC power. This allows me less inverter losses and the ability to keep the power in the battery.

I run a Buck converter from 7s (li-ion) 24V down to 13.7V DC for all those loads.

As for the Image looks good I just don;t use Victron so am unfamiliar with all the Devices. Any reason specifically for using 2 separate BMS's Why not just Parallel up 2x8 instead of 2x 1x8
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******Hi My name is Jason and I have SOCD (Solar Obsessive Compulsive Disorder)*******
Current Powerwall - 1400 Cells 7s200p (modular 40p packs) ~ 12kWh of storage     4x 315W Canadian Solar Panels

Working on the next 7s40p packs     ~2.5kWh

Waiting on 2000 Cells of unused Sony vt4 (2000mah 30A) ~ 15kWh      hehehehehe  More Power
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#4
OffGridInTheCity and jdeadman Thank you so much for your responses! Very helpful. I am completely new to this and have no idea what I am doing other than reading online what others have done. Really just trying to avoid killing myself or burning down my cabin. I am reviewing what you both wrote...

(08-29-2019, 01:02 AM)jdeadman Wrote: For my camp I have moved as much stuff over to 12V LED and fans to limit the need for AC power.    This allows me less inverter losses and the ability to keep the power in the battery.

I run a Buck converter from 7s (li-ion) 24V down to 13.7V DC for all those loads. 

As for the Image looks good I just don;t use Victron so am unfamiliar with all the Devices.  Any reason specifically for using 2 separate BMS's  Why not just Parallel up 2x8  instead of 2x 1x8

I'm not sure what you mean regarding the BMS 2X 1X8 vs 2X8.  It basically is 16 3.2v 200ah LifoPo4 batteries in two groups of 8 that will be parallel to give me a 24v 400ah battery.  Unless I"m doing this wrong.  Don't you want a separate BMS wire going to each battery?  So with 16 batteries, that was why I got two BMS 8s models.

(08-28-2019, 08:58 PM)Wedgies Wrote: Hi everyone.  I've been spending $$ and hours trying to make sure that I build my battery pack correctly.   I have recently purchased 16 3.2v 200ah LifoP04 batteries, and will be configuring them into a 24v 400ah battery pack for my cabin that will be recharged using an existing solar array.

Would the attached diagram be correct?  I wasn't sure about the separate BMS setup, I have two 8s version I purchased.  

Thoughts?

Also gleaned a lot from this guy: https://www.youtube.com/watch?v=_PgthByAYz4&t=1433s

Thank you.

David


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#5
That is a totally Fine way of doing it but What I was suggesting is to Parallel into 2 Cell groups then series those 8 groups of 2 for a 8s2p setup  See Image    This would allow for a single BMS to be used.  If you are using Matched cells (they have the same capacity) then balancing is rarely needed. 

But there is no problem with 2 separate batteries
Ibiza likes this post
******Hi My name is Jason and I have SOCD (Solar Obsessive Compulsive Disorder)*******
Current Powerwall - 1400 Cells 7s200p (modular 40p packs) ~ 12kWh of storage     4x 315W Canadian Solar Panels

Working on the next 7s40p packs     ~2.5kWh

Waiting on 2000 Cells of unused Sony vt4 (2000mah 30A) ~ 15kWh      hehehehehe  More Power
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#6
On your diagram I would put the relay between the solar panel and the controller, this way if it triggers the controller won't lose power and still be connected to the panel, this will cause the controller to cycle back and forth when it doesnt see a battery connected. If panel is disconnected the controller will think is night time and thats no big deal.

Like someone mention you only need one bms. For solar I recommend the chargery bms8t, it aint cheap at about 100 dollars but its worth it. I been using one on my 220ah 4s system. It uses mechanical relays to shutoff power. The reason this is important is if the bms shutsoff charging, the bms mosfets (electronic relays) will act like a diode, the controller will see a battery but it won't be able to charge it, this causes voltage surges as the controller tries to forcibly charge the battery. Voltage surges are very bad, will destroy anything that can't handle overvoltage.
I use 2 x 30 amp automotive relays to disconnect the panel, one controlled by the chargery bms8t, and one by the overvoltage protection relay as shown in my diagram.


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#7
(08-29-2019, 03:51 AM)jdeadman Wrote: That is a totally Fine way of doing it but What I was suggesting is to Parallel into 2 Cell groups then series those 8 groups of 2 for a 8s2p setup  See Image    This would allow for a single BMS to be used.  If you are using Matched cells (they have the same capacity) then balancing is rarely needed. 

But there is no problem with 2 separate batteries

OK.  I think I see where you're going here.  So it looks like with an 8s2p, what your saying is it would be grouping the batteries into cells of two 3.2v batteries = 6.4v each, then running those in series to bring up to 24v.  The BMS's I have are 8S models, so it has a black wire that goes to the main negative, and 8 red wires that are supposed to go to each positive terminal of each of the individual batteries.  So I guess I don't understand how you can only use one BMS and still make sure the batteries are protected?

(08-29-2019, 03:03 PM)Wedgies Wrote:
(08-29-2019, 03:51 AM)jdeadman Wrote: That is a totally Fine way of doing it but What I was suggesting is to Parallel into 2 Cell groups then series those 8 groups of 2 for a 8s2p setup  See Image    This would allow for a single BMS to be used.  If you are using Matched cells (they have the same capacity) then balancing is rarely needed. 

But there is no problem with 2 separate batteries

OK.  I think I see where you're going here.  So it looks like with an 8s2p, what your saying is it would be grouping the batteries into cells of two 3.2v batteries = 6.4v each, then running those in series to bring up to 24v.  The BMS's I have are 8S models, so it has a black wire that goes to the main negative, and 8 red wires that are supposed to go to each positive terminal of each of the individual batteries.  So I guess I don't understand how you can only use one BMS and still make sure the batteries are protected?

Also, are there advantages to grouping the batteries that way?

(08-29-2019, 05:37 AM)jonyjoe505 Wrote: On your diagram I would put the relay between the solar panel and the controller, this way if it triggers the controller won't lose power and still be connected to the panel, this will cause the controller to cycle back and forth when it doesnt see a battery connected. If panel is disconnected the controller will think is night time and thats no big deal.

Like someone mention you only need one bms. For solar I recommend the chargery bms8t, it aint cheap at about 100 dollars but its worth it. I been using one on my 220ah 4s system. It uses mechanical relays to shutoff power. The reason this is important is if the bms shutsoff charging, the bms mosfets (electronic relays) will act like a diode, the controller will see a battery but it won't be able to charge it, this causes voltage surges as the controller tries to forcibly charge the battery. Voltage surges are very bad, will destroy anything that can't handle overvoltage.
I use 2 x 30 amp automotive relays to disconnect the panel, one controlled by the chargery bms8t, and one by the overvoltage protection relay as shown in my diagram.




I thought it could destroy the charge controller to have it connected to a solar array without it having a connection to the battery bank?  That at least is what I am hearing from here:  https://www.youtube.com/watch?v=_PgthByAYz4

(08-29-2019, 03:51 AM)jdeadman Wrote: That is a totally Fine way of doing it but What I was suggesting is to Parallel into 2 Cell groups then series those 8 groups of 2 for a 8s2p setup  See Image    This would allow for a single BMS to be used.  If you are using Matched cells (they have the same capacity) then balancing is rarely needed. 

But there is no problem with 2 separate batterie

Ok ignore my original description of what you are proposing,  what you meant was 8 sets of two 3.2v in parallel to up to 40ah, then run those in series to up to 24v.  Duuu.  LOL
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#8
Yea the Latter. There is good reason to increase your Capacity of Each cell and Lower complexity and wiring in general. Also if you test the cells alone you can group them to make a better balanced Battery so you need less overall balancing.

Also makes a cleaner install
Wedgies likes this post
******Hi My name is Jason and I have SOCD (Solar Obsessive Compulsive Disorder)*******
Current Powerwall - 1400 Cells 7s200p (modular 40p packs) ~ 12kWh of storage     4x 315W Canadian Solar Panels

Working on the next 7s40p packs     ~2.5kWh

Waiting on 2000 Cells of unused Sony vt4 (2000mah 30A) ~ 15kWh      hehehehehe  More Power
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#9
I watch the youtube video, in it he mentions to use the bms to control the charging and the "victron battery protect" to control the discharging. 

The bms should be the last line of defense in case the charging system doesnt stop charging or battery goes out of balance during charging. The controller if it is in the proper setting will hopefully not let the battery get too high. On my system I have an overvoltage protection relay that will trip if the battery voltage gets too high. You never want the bms to stop the charging, thats when the battery is disconnected from the controller (while still connected to the panel), I think that is what he mention about the controller being destroyed. Mine never got destroyed but you get the controller cycling back and forth and voltage surges which can destroy equipment that is connected to system. I lost many fans and pumps from voltage surges.

overall voltage charging (recommend active balancers to keep battery in balance)
1. solar controller (set low enough so battery never reaches full charge triggering bms)
2. overvoltage protection relay (set to disconnect panel at voltage below bms activation)
3. bms (only activates if above 2 fails, will cause voltage surges if activated)

Since your system is relying on overall voltage to control charging I highly recommend active balancers, these will keep the battery in perfect balance so overall voltage is always accurate. 

active balancers I use, the 4s model cost 92 dollars. This is the only way that you safely charge using overall voltage. Lithium batteries have a tendency to go out of balance when fast charging near the top end. These balancers balance at up to 6 amps, they can keep up when your charging at higher amps. If the bms trips early to stop charging you will never get a full charge and your controller will be producing voltage surges. 


This a picture of the chargery bms8t I use, I paid 86 dollars for it, this is the best bms for solar that I found. balances at 1.2 amps, SOC, lcd screen, audible alarms, 2x temp sensors, programmable cutoffs, amps is only limited by the size of your mechanical relay. With this bms and overvoltage protection relay you can leave system running 24/7 and rarely need to do adjustments.




To use one bms, just connect both of your 8s batteries together with y connectors. The main power connectors, and the balance connectors, once connected the batteries will equalize and you will have a giant battery. Connect the bms to this battery. Just make sure both batteries are the same voltage before connecting together. Thats how I have my 220ah battery connected, its actually 2x 110ah 4s20p lifepo4 connected together.
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#10
(08-29-2019, 06:23 PM)jonyjoe505 Wrote: I watch the youtube video, in it he mentions to use the bms to control the charging and the "victron battery protect" to control the discharging. 

The bms should be the last line of defense in case the charging system doesnt stop charging or battery goes out of balance during charging. The controller if it is in the proper setting will hopefully not let the battery get too high. On my system I have an overvoltage protection relay that will trip if the battery voltage gets too high. You never want the bms to stop the charging, thats when the battery is disconnected from the controller (while still connected to the panel), I think that is what he mention about the controller being destroyed. Mine never got destroyed but you get the controller cycling back and forth and voltage surges which can destroy equipment that is connected to system. I lost many fans and pumps from voltage surges.

overall voltage charging (recommend active balancers to keep battery in balance)
1. solar controller (set low enough so battery never reaches full charge triggering bms)
2. overvoltage protection relay (set to disconnect panel at voltage below bms activation)
3. bms (only activates if above 2 fails, will cause voltage surges if activated)

Since your system is relying on overall voltage to control charging I highly recommend active balancers, these will keep the battery in perfect balance so overall voltage is always accurate. 

active balancers I use, the 4s model cost 92 dollars. This is the only way that you safely charge using overall voltage. Lithium batteries have a tendency to go out of balance when fast charging near the top end. These balancers balance at up to 6 amps, they can keep up when your charging at higher amps. If the bms trips early to stop charging you will never get a full charge and your controller will be producing voltage surges. 


This a picture of the chargery bms8t I use, I paid 86 dollars for it, this is the best bms for solar that I found. balances at 1.2 amps, SOC, lcd screen, audible alarms, 2x temp sensors, programmable cutoffs, amps is only limited by the size of your mechanical relay. With this bms and overvoltage protection relay you can leave system running 24/7 and rarely need to do adjustments.




To use one bms, just connect both of your 8s batteries together with y connectors. The main power connectors, and the balance connectors, once connected the batteries will equalize and you will have a giant battery. Connect the bms to this battery. Just make sure both batteries are the same voltage before connecting together. Thats how I have my 220ah battery connected, its actually 2x 110ah 4s20p lifepo4 connected together.

I see.  This was very helpful!  Thank you.  It sounds like my original wiring plans are "ok", but it can be better and more efficient.
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