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What do I need to make a 600Ah 25.6v battery pack? (BMS and balancing)

trougnouf

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Aug 15, 2021
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Hello all,

I am trying to design a battery pack that will be much more cost efficient than 3x Victron's 200Ah 25.6v batteries (4000 euros each).

This is all new and a bit overwhelming to me. I get that I need 16* 304Ah cells (which can be found on Alibaba); 8S and 2P. The BMS and balancing aspects are foreign though.

BMS:
- From what I understand, the BMS sends a charge and/or load disconnect signal when appropriate. I read that parallel configurations sometimes require multiple BMS (8S2P). Is it possible to still have only one connect/disconnect signal ? I don't need the redundancy of having a part of the battery pack as a backup and one signal seems easier to handle.
- (I think this is my main question) In 2P8S (one BMS), how is the BMS connected to the cells? What do I need to look for in a BMS that handles this configuration?
- Do some BMS handle the load/charge disconnect instead of sending a signal? (I don't necessarily need that but curious about what I am looking at sometimes)

Load balancing:
- I'm just starting to discover these devices. Will it make a difference whether I have my battery packs in parallel one way or the other? (eg with the 8S2P "Fortune cells layout" which uses only one BMS). How is it connected and what do I need to look for to get a compatible load balancer?

I don't really care about the cost so far since it will be far below the cost of 3 Victron batteries, I want to make what's theoretically best for the battery pack's safety and longevity. I've attached a diagram of my system's current planning stage (before looking into DIY battery) for reference.
 

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If you have 8s2p then you need two BMS. The exception to that is if you want to spend the big bucks on a BMS like Batrium, which can work across batteries.

The ideal situation is that your charge devices cut off charging long before your BMS has to step in. That's how my system is configured and I would guess most forum members have do it also.

For a 2p8s configuration, the BMS doesn't know you have parallel cells. It sees the pair of cells as a single entity. That lack of granularity is what pushed me away from that configuration. I went 4s2p instead.

I have not found the need to balance between my two batteries. My cells stay pretty closely balanced, as do the batteries. My BMS (Overkill Solar, aka JBD) does an excellent job of keeping the cells in balance. If you were to purchase less than Grade A cells, maybe more powerful cell balancer would be needed.
 
8S2P it is then. I guess I would make two separate batteries.

The multiple signal cables seemed problematic but I was stuck in victron world and I read the "BMS Type Summary.pdf" guide; there are BMS with built-in cutoff so no need for signaling, and I can get a hybrid BMS if I stick with the Victron combination inverter/charger (where the same ports must share charge/load). The ANT BMS was recommended, I can't find it in stock anywhere but I guess I will find something similar now that I know better what I am looking for.

I guess it's pretty standard for the BMS to balance its cells so no need for a balancer?

Thank you!
 
I haven't seen a lot of implementations with the ANT BMS. Yes, it's mentioned a few times on the forum, just not a lot of use compared to other BMS brands. I'm not knocking ANT, just saying that the number of folks that have detailed knowledge might be sparse.

Most of us have no signal cables. Quality devices for charge and discharge can be programmed to stop the charge/discharge at acceptable voltage levels.

I use Victron solar charge controllers and shunt. I'll eventually upgrade my old school inverter to a Victron.
 
I haven't seen a lot of implementations with the ANT BMS. Yes, it's mentioned a few times on the forum, just not a lot of use compared to other BMS brands. I'm not knocking ANT, just saying that the number of folks that have detailed knowledge might be sparse.

Most of us have no signal cables. Quality devices for charge and discharge can be programmed to stop the charge/discharge at acceptable voltage levels.

I use Victron solar charge controllers and shunt. I'll eventually upgrade my old school inverter to a Victron.
I will try to maximize usage of the 24v system directly (eg heating / cooling, lights) so I will need some way to stop these dumb devices. If the BMS itself can cut off power then it's perfect. It should only occur in case of failure anyway, since I will set the battery charger to kick in when the batteries reach a threshold low voltage (I think the Victron Quattro + GX device can do that.)

Do you have any BMS recommendation? (Ideally with worldwide/EU availability)

I see Daly a lot on Aliexpress, the "BMS Type Summary" beginner guide mentions that those are not suited for hybrid charger/inverter (because separate charge/load ports), but from the images shown there appears to be only one port so maybe they updated their design and the pdf is out of date? edit: Daly doesn't seem to be recommended in the forum.
 
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I have the Overkill Solar (aka JBD) BMS. It has been reliable for me and if you poke around on the forum, there aren't a lot of failures. The Daly has a lot of problem posts.

The problem with Overkill Solar at this time is their offering became too popular. They ran out of inventory and couldn't keep up with demand. So there are a few folks that couldn't get a BMS or when they had questions/issues, couldn't get an answer. A second vendor on the forum is now offering the same (JBD) BMS.

Victron sells the Battery Protect device that can be used to cut off loads. It's NOT designed to be used with an inverter (heavy loads). You would be more likely to put it in a circuit where there are lights and other low amp loads.
 
Thank you. I've been seeing the JBD products on here, it's too bad they have such relatively low Amp ratings (120A seems to be the max) but I will do 3 parallel batteries with smaller cells instead of two with 304Ah cells if that gets me the most safe and reliable results.

Those do have built-in switches right?

The Battery Protect is what I had in mind on my original design which is based on Victron's signaling BMS but I guess it's not necessary with a BMS that cuts the load off since they cut off at exactly the same point.
 
I will try to maximize usage of the 24v system directly (eg heating / cooling, lights) so I will need some way to stop these dumb devices. If the BMS itself can cut off power then it's perfect. It should only occur in case of failure anyway, since I will set the battery charger to kick in when the batteries reach a threshold low voltage (I think the Victron Quattro + GX device can do that.)

Do you have any BMS recommendation? (Ideally with worldwide/EU availability)

I see Daly a lot on Aliexpress, the "BMS Type Summary" beginner guide mentions that those are not suited for hybrid charger/inverter (because separate charge/load ports), but from the images shown there appears to be only one port so maybe they updated their design and the pdf is out of date? edit: Daly doesn't seem to be recommended in the forum.
you could take a look at the seplos bms'es.

they are smart , so the can communicate with your inverter/victron system to throttle down charging when almost full ( helps enormpus with cell balancing)

they are stackable up to 6 ( batteries communicate with eachother and report to inverter.

they are well build

they have a 1 amp balancing

they have precharge build in ( protects you inverters capacitors)
 
Thank you. I've been seeing the JBD products on here, it's too bad they have such relatively low Amp ratings (120A seems to be the max) but I will do 3 parallel batteries with smaller cells instead of two with 304Ah cells if that gets me the most safe and reliable results.

Those do have built-in switches right?

The Battery Protect is what I had in mind on my original design which is based on Victron's signaling BMS but I guess it's not necessary with a BMS that cuts the load off since they cut off at exactly the same point.

It depends on what you mean by a "switch".

The Battery Protect is programmable, so you can set the cutoff to whatever you want.
 
you could take a look at the seplos bms'es.

they are smart , so the can communicate with your inverter/victron system to throttle down charging when almost full ( helps enormpus with cell balancing)

they are stackable up to 6 ( batteries communicate with eachother and report to inverter.

they are well build

they have a 1 amp balancing

they have precharge build in ( protects you inverters capacitors)
Looks good! It seems to be limited to 100A (so still three smaller batteries rather than 2) for 24v systems but the features including Victron compatibility are peace of mind.

It depends on what you mean by a "switch".

The Battery Protect is programmable, so you can set the cutoff to whatever you want.
I was only ever looking at the remote pin, never realized that (even the non smart) battery protect could have a set cutoff voltage. That's much more useful, thank you :)
 
Looks good! It seems to be limited to 100A (so still three smaller batteries rather than 2) for 24v systems but the features including Victron compatibility are peace of mind.


I was only ever looking at the remote pin, never realized that (even the non smart) battery protect could have a set cutoff voltage. That's much more useful, thank you :)
i have the 200a 48v , and never realy looked at 24v to be honest.
then again..
you can stack them together, so 3 would be fine.
 
i have the 200a 48v , and never realy looked at 24v to be honest.
then again..
you can stack them together, so 3 would be fine.
The stack means different series / batteries will communicate together?

They actually have a 24v 200Ah version on their Alibaba so I can stick to two batteries afterall :)
edit: nvm, the specs listed are that of a 48v battery o_O so the title seems wrong.
 
I'm looking at the 123SmartBMS system now, I like that it's European rather than Alibaba so probably better tested and supported, + I believe it might be what's in Victron's batteries.
I could either go with one module per two cells (I guess balancing by group of two is most likely ok?) or two battery packs with separate BMS (probably best, a bit pricey, close to 1000 euros, but the manual mentions that it's supported and that the charge/load signals can be connected in series).
 
Now looking at the ElectroDacus.

123SmartBMS looked great but one of the functions I want (relay to turn on the charger from a given voltage up to a set threshold) requires configuration with a Windows-only software, that's a bit too restrictive to me.

The ElectroDacus is open-source and seems significantly less expensive. There is a lot of good documentation on usage. I don't think I will be able to modify the firmware but it's a peace of mind knowing that I won't ever be locked in entirely and it seems I can work around some potentially missing functionalities with an external Arduino.

I briefly investigated the diyBMS too but as the name implies it's diy and I don't trust myself to do a good enough soldering job when my life might depend on it.

edit: I ordered the ElectroDacus
 
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Now looking at the ElectroDacus.

123SmartBMS looked great but one of the functions I want (relay to turn on the charger from a given voltage up to a set threshold) requires configuration with a Windows-only software, that's a bit too restrictive to me.

The ElectroDacus is open-source and seems significantly less expensive. There is a lot of good documentation on usage. I don't think I will be able to modify the firmware but it's a peace of mind knowing that I won't ever be locked in entirely and it seems I can work around some potentially missing functionalities with an external Arduino.

I briefly investigated the diyBMS too but as the name implies it's diy and I don't trust myself to do a good enough soldering job when my life might depend on it.

edit: I ordered the ElectroDacus
you should go to these two sites that cover Electrodacus. I used one a few months ago and am very pleased. The implementation is a bit different than the FET types.
 
I have the Overkill Solar (aka JBD) BMS. It has been reliable for me and if you poke around on the forum, there aren't a lot of failures. The Daly has a lot of problem posts.

The problem with Overkill Solar at this time is their offering became too popular. They ran out of inventory and couldn't keep up with demand. So there are a few folks that couldn't get a BMS or when they had questions/issues, couldn't get an answer. A second vendor on the forum is now offering the same (JBD) BMS.

Victron sells the Battery Protect device that can be used to cut off loads. It's NOT designed to be used with an inverter (heavy loads). You would be more likely to put it in a circuit where there are lights and other low amp loads.
The other issue is aren't they limited to 100A so when I wanted a 250 and a 150 I went to Daly.
 
Go at least to a 48 V configuration, if you panel configuration and charger controller can have it even higher
I like 24v because I can hook up solar panels in parallel, so I think they are more tolerant to partial shade. Also I went with the Electrodacus BMS and that only works with up to 24v systems. (That and the cells are the only components I have ordered so far)
 
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