trouble sourcing a 7s bms

[Valman]

can anyone suggest where i can find a bms for a 7s9p pack consisting of these samsung cells INR21700-50E

if I understand correctly, that's 9.8A max discharge (continuous) per cell which means in my 9p configuration a bms that can handle a maximum discharge current of 88A continuous and 132A non-continuous.

voltage due to 7s will be 24v (25,2 nominal)

the 24v 7s bms I can find are generally all much lower amp rated than my 88A/132A figures above

could anyone point me towards a suitable bms please?

battery specs below - thanks

3.1 Standard discharge Capacity
Min 4,900mAh
- Charge : 0.5C(2,450mA), 4.2V, 0.02C(98mA) cutoff @ RT
- Discharge : 0.2C(980mA), 2.5V cutoff @ RT
* 1C = 4,900mA
3.2 Rated discharge Capacity
Min 4,753mAh
- Charge : 0.5C(2,450mA), 4.2V, 0.02C(98mA) cutoff @ RT
- Discharge : 1C(4,900mA), 2.5V cutoff @ RT
3.3 Charging Voltage
4.2V
3.4 Nominal Voltage
3.6V
3.5 Charging Method
CC-CV (constant voltage with limited current)
3.6 Charging Current
Standard charge: 2,450mA
3.7 Charging Time
Standard charge: 3hours
3.8 Max. Charge Current
4,900mA (not for cycle life)
3.9 Max. Discharge Current
9,800mA (for continuous discharge) 14,700mA (not for continuous discharge)
3.10 Discharge Cut-off Voltage
2.5V
3.11 Cycle life
Capacity ≥ 3,802mAh @ after 500cycles (80% of the Rated Discharge Capacity @ RT)
- Charge : 0.5C(2,450mA), 4.2V, CCCV 0.05C(245mA) cut-off @ RT
- Discharge: 1C(4,900mA), 2.5V cut-off @ RT
3.13 Recovery characteristics
Capacity recovery (after the storage) ≥ 4,278mAh (90% of the Rated Discharge Capacity @ RT)
- Charge : 0.5C(2,450mA), 4.2V, 0.02C(98mA) cutoff @ RT
- Storage : 30 days @ 60’C
- Discharge : 1.0C(4,900mA) 2.50V cut-off @ RT
3.14 Cell Weight
69g max
3.15 Cell Dimension
Cell height : Max.70.80mm Diameter : Φ Max.20.25mm

 

[Joachim]

How much Amps is going to take maximum from the battery ?

For example:as the consumer takes maximum 15A , then is a 7S Li-ion bms with a max peak disharge from 20/25Amp okey :thumb:

as the consumer realy takes the 80+Amps the search for a fitting bms become difficult for 7S .

 

[john61ct]

The only reason to run the whole load current through the BMS is because you want to use it for overcurrent protection.

Just use a fuse for that, and a lower-current rated BMS is just fine for the other functions.

 

[jonyjoe303]

chargery bms8t can do that. I got the one that came with a 100a shunt(86 dollars), but they also have larger shunts up to 300a. But this isn't some small circuit board bms like you regularly see. Also you have to supply your own contactors to stop the flow of current. I been using mine for the past month on a 4s lifepo4 220ah battery and has been working excellent, it also balances at 1.2 amps, something you don't see on most bms.
In the picture you see two parts, one goes by the battery , the other goes in a convenient place so you can read the lcd screen. They are connected by a wire. Not shown is the shunt which goes on the battery and measures amps in/out of battery. I been using a 30a automotive relay (4 dollars) as a contactor. I got it hooked to my 240 watt solar system, lots of room.

 

[Joachim]

bad advice wrong wrong

 

[Chalo]

When I search eBay with "7s BMS 150A", I get a bunch of results-- a couple under $50.

 

[hemo]

Have a look at this one to see if it will do the job for you.

https://www.aliexpress.com/item/Waterproof-7S-16A-25A-35A-45A-60A-24V-Lithium-Battery-Protection-Board-BMS-Electric-Charge-Li/32841326114.html?spm=a2g0s.9042311.0.0.27424c4dqBDFgq

 

[999zip999]

Bms"s that cheap scare me. How can I do it ?

 

[Valman]

How much Amps is going to take maximum from the battery ?

For example:as the consumer takes maximum 15A , then is a 7S Li-ion bms with a max peak disharge from 20/25Amp okey :thumb:

as the consumer realy takes the 80+Amps the search for a fitting bms become difficult for 7S .

2x 12v 60w motors which say 5.5a continuous each, = 24v 11A continuous, but I don't have a spec stating their stall current which could be significantly higher. The 24v motor controller they go via is rated at 22a continuous and up to 76A 10 second bursts. I don't expect the 2x motors are going near pushing the controller's max rating, but no way of knowing for sure other than perhaps comparing with other people's experience of similar wattage motors. Given that I'm spending a lot on batteries that are quite capable, I didn't want to 'cripple' the battery pack's ability unnecessarily, other than by choice via bms programming, should I ever want to use the pack on other applications, upgrade the motor/controller etc. So it seems I have 4 options, a) hunt down a rare high amp 7s bms or build one, (potentially bulky and expensive) b) find a bms that meets the motor controllers specced maxes c) guess what the max draw of the end consumer motors is likely to be and buy 'just enough' bms to cope with that and/or d) trust current overprotection to a fuse

 

[Valman]

Bms"s that cheap scare me. How can I do it ?

absolutely agree, I'm not totally comfortable that the majority of my bms choices seem to be via ebay or alibaba based vendors when I'm depending on this to protect >£500 worth of batteries and all associated fire risks. I'd like to know I'm buying a bms that's well tested and specs are proven to be genuine. I suspect the smarter folks on here have the ability to look at the circuit boards and get some confidence based off looking at the ICs and other electronics in the circuit board design of these bmcs.

 

[Valman]

bad advice wrong wrong

Can you tell a bit more please? Which bit of advice is bad? Thanks

 

[john61ct]

bad advice wrong wrong

That isn't very useful. Be more specific as to what is wrong, ideally state why, and counter it with good advice.

 

[john61ct]

Bms"s that cheap scare me. How can I do it ?

That mfg brand and seller are recommended here pretty regularly.

Yes of course more expensive **might** mean better.

Or it can just mean crazy profitable markups by the seller.

 

[john61ct]

Bms"s that cheap scare me. How can I do it ?

absolutely agree, I'm not totally comfortable that the majority of my bms choices seem to be via ebay or alibaba based vendors when I'm depending on this to protect >£500 worth of batteries and all associated fire risks. I'd like to know I'm buying a bms that's well tested and specs are proven to be genuine. I suspect the smarter folks on here have the ability to look at the circuit boards and get some confidence based off looking at the ICs and other electronics in the circuit board design of these bmcs.

Well there are first-world versions that usually cost hundreds of dollars.

Members here usually seem very shy about making specific Ali recommendations, and given the extreme variability of quality I guess best to be cautious.

eBay from a local-in-country to you seller will at least mean easier to return, cheaper than China anyway.

Try a few of the cheaper ones, test yourself and then you can be the one making recommendations!

 

[Chalo]

Your battery cells are most likely made in China. To the nearest approximation, all your electronic devices are made in China. But you're scared of a BMS made in China.

I can't help you with that.

I can observe that every so often, I replace a BMS that has expired (usually by flagrant user error). That's what you would have to do on the odd chance you got a bunk BMS. It's a hassle, but not a big deal.

If you're worried about it, get a Bluetooth BMS or cell monitor so you can easily keep an eye on voltages. If they stay the same, then there's no cause for concern.

 

[Valman]

Your battery cells are most likely made in China. To the nearest approximation, all your electronic devices are made in China. But you're scared of a BMS made in China.

I can't help you with that.

I can observe that every so often, I replace a BMS that has expired (usually by flagrant user error). That's what you would have to do on the odd chance you got a bunk BMS. It's a hassle, but not a big deal.

If you're worried about it, get a Bluetooth BMS or cell monitor so you can easily keep an eye on voltages. If they stay the same, then there's no cause for concern.

Thanks for the response. It's less the country of manufacture that concerns me but more the lack of any knowledge about the brands and reliability, fly-by-night sellers, In half the cases alibaba sellers are masking the names of manufacturers out of product images, and lack of good English language support.

Having said all the above, I'm going to try the Daly electronics 12v 60a 7s bms, and have managed to find a reasonable direct to factory channel to buy via (their official aliexpress store) so that gives me _some_ comfort, as does the fact others here are recommending it

Thanks again

 

[999zip999]

I have had trouble with signalab a quality company.