Beginners Guide to Processing 18650 Cells | Cell Database


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Batrium BMS Questions
#1
Hi all,

Not sure if there is a thread dedicated to thiis already but I have some questions around the Batrium system.

I think I'm going to go with their BMS for my Calb Lifepo4 cells as I like the user interface and programmability

First question I have is.. I have 16 x 60 ah cells and 16 x 100 ah cells which I plan to run in seperate strings for a 48 volt system

Are there boards I can mount to each cell for balancing until I can get the funds together for the rest of the gear needed for over / under voltage etc?
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#2
You would need 1x watchmon.
Then you either go with 16 or 32 *mons. In this case most likely the Longmons. (You can save some by paralelling the 60 and 100ah cells even though it may not be recomended)

You do not need to buy the expansion board as a start but i do recomend to get the shunt directly.


I run 3*120ah for each Longmon to save some mons. I would have needed 198 of em otherwise Big Grin
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#3
(05-02-2017, 07:42 AM)daromer Wrote: You would need 1x watchmon.
Then you either go with 16 or 32 *mons. In this case most likely the Longmons. (You can save some by paralelling the 60 and 100ah cells even though it may not be recomended)
Havi
You do not need to buy the expansion board as a start but i do recomend to get the shunt directly.


I run 3*120ah for each Longmon to save some mons. I would have needed 198 of em otherwise Big Grin

Thanks.

Having 60 ah and 100 ah cells in parallel, I would imagine the 60 ah cells would charge and discharge first, is that right?

If that was the case wuld you need to set the disconnect for when the 60 ah cells are discharged? Just trying to get my head around this
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#4
Its the same as when we parallell 2Ah and 2.1Ah or 2.5Ah 18650 cells in parallell. They will even out. But the cell/battery that have lower resistance will of course deliver some more than the others but it will in the end even itself out again.

As long as the 60Ah and the 100Ah is of the same chemistry and all its fine. Just make sure to cross connect the batteries so you have negative for instance on the 60Ah string and then the positive on the 100Ah string.

Edit: With that said its always better not to paralell if you know that the 60Ah differ alot in usage compare to the 100Ah packs...
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#5
(05-03-2017, 08:35 AM)daromer Wrote: Its the same as when we parallell 2Ah and 2.1Ah or 2.5Ah 18650 cells in parallell. They will even out. But the cell/battery that have lower resistance will of course deliver some more than the others but it will in the end even itself out again.

As long as the 60Ah and the 100Ah is of the same chemistry and all its fine. Just make sure to cross connect the batteries so you have negative for instance on the 60Ah string and then the positive on the 100Ah string.

Edit: With that said its always better not to paralell if you know that the 60Ah differ alot in usage compare to the 100Ah packs...

Thanks for your advice Daromer, I appreciate it!

Yes I partially understand. I get the part of mixing capacities like we do in 18650 packs.
I'm not sure exactly how to physically connect them but will think about that one a bit more.

I have connected all of the cells in parallel.  ie. 60 ah and 100 ah cells in seperate 12 volt packs as recommended on Calb document I found trawling the net. They seem to be staying fairly well balanced after being cycled for a couple of weeks.

I have now connected the 60 ah cells in a 16s for 48 volt, will do the same for the 100 ah cells but need a 48 volt inverter now Angry

In relation to the bms, if the 60 and 100 ah cells are paralleled will one longmon be able to balance each pair of cells?
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#6
1 longmong per cell yes.


So if you run 16s you would then need 16 longmons in total.
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#7
You can't balance/charge 2 separate packs that are in parallel directly. The only way to do it is to temporarily disconnect the one being charged. The can be a physical connection that you unplug during charging, or if you want to automate it with switching using relays/mosfets/diodes/etc for when the charger kicks on it disconnects the pack.

The problem is when you charge in parallel, the current going in is spread out over all the packs connected. Kinda like dumping a bucket of water on concrete, it spreads out somewhat evenly. In series, however, you can control specifically which pack is being charged; like the water example but now with pipes and "T" fittings flowing water between and two "T" connections will only allow water movement between those "T"s and nowhere else.
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#8
Korishan: Im not sure i follow what would not work?

If you paralell 2 cells they will both have the equal state of charge in best of worlds (If we just make sure the resistance between them are close to nil and also try to have the connection crossed)

This is how Im running my system and have for quite some time.
[Image: w5ukJz.jpg]

I have connection between each pack to make sure there is balancing done on both strings. This would reflect the same scenario as TS talked about. Even though this is not optimal and so forth... it works in long term as long as the balancing current do not exceed what the connection can handle in between the packs.
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#9
What I was referring to is, when you have 2 string of parallel cells, you can't charge 1 string w/o charging the other one as well. Both strings get charged at the same time. I may have misunderstood what what Wattsup was asking, but that's what I was thinking he was asking. Could you balance pack-1 and not touch pack-2 that is in parallel. Essentially, no you can't because the two packs +/- are connected directly.

However, if you have series connections within the pack, you could possibly charge "those" cells separate from the rest and work your way down the line till all the "series" sets of cells are charged.

I could be missing something here, but that's my understanding at least. Maybe I'm not explaining my thinking totally correctly and understandably. Hrmmm
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#10
Hi guys

Thanks for the input.

Korishan, sorry for the confusion there mate. I was asking what Daromer has responded to. I would want to charge all cells at the same time.

Yes I  get the picture now Daromer, thanks for that makes more sense.

One last thing and I'm not sure why I'm thinking this as we mix capacities with 18650 all the time. I guess these cells are worth a bit more so want to try to look after them.

Would there be any additional stress on the 60 ah  cells being smaller capacity? If they are paralleled that is.
As I'm asking the question I'm thinking probably not as the chemistry is the same.

If you don't ask you don't learn.  Smile
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