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Daier 5s 50A BMS. I have doubts...
#1
Question 
I am building a 20v battery pack for my newly-to-build electrical outboard motor. I am using 3, 18V 208W motors, for a total of 624W @ 34.7A max.

The battery pack is a 5s, 20p pack made from recovered 18650. All-in-all pretty standard, although I am new to all this. :-)

So I purchased a 5s BMS from ebay: "
daier 5S 50A w/Balance 3.7V 18650 Lithium Battery Cell PCB BMS Protection Board". See images below for further reference.

As far as I can tell this should be the correct BMS, but when I received the item and seeing it was only the size of a credit card, I got concerned. How in the world can 30+ amps run through this tiny board??

Am I missing something? Or is this indeed not the correct board to use, or do I misunderstand something else? Before I do all the work to hook things up, I want to make sure I'm not screwing up  Big Grin

Thanks for the help




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#2
5s, 50a looks correct for the specs you listed

>Before I do all the work to hook things up, I want to make sure I'm not screwing up
Totally agree - excellent question - you are not crazy - you can't tell until you hook it up and test it  Smile        

For me?  I buy more more expensive ones that are programmable - but even those require test if you really want to know if its going to work.  The value in ones that are programmable is that one can change the settings (like min/max cell voltage or max amps) and observe it work rather than having to do it by putting a large load to exceed design amps etc. 
morningcoffee1 likes this post
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#3
Its often China amps Smile cut their Specs in half and it might be more suited Smile

Test is key for success here. Test all parameters
morningcoffee1 and Jim Jr. like this post
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#4
(07-15-2020, 08:29 PM)OffGridInTheCity Wrote: 5s, 50a looks correct for the specs you listed

>Before I do all the work to hook things up, I want to make sure I'm not screwing up
Totally agree - excellent question - you are not crazy - you can't tell until you hook it up and test it  Smile        

For me?  I buy more more expensive ones that are programmable - but even those require test if you really want to know if its going to work.  The value in ones that are programmable is that one can change the settings (like min/max cell voltage or max amps) and observe it work rather than having to do it by putting a large load to exceed design amps etc. 

Thanks for the response! Yeah this is a first test to see if I understand the concept of building battery packs before I dive into larger projects, where I will look at programmable BMS for sure. Can you send me a lin to an example of such BMS? Would like to plan ahead for the next build.

(07-15-2020, 08:45 PM)daromer Wrote: Its often China amps Smile cut their Specs in half and it might be more suited Smile

Test is key for success here. Test all parameters
Ha! Yes I had read about those concerns, and thats why I thought 50A would be "ok". I know I won't charge at that amperage for sure, so my concern is just when running the motors. 

However, those are Chinese too, and I doubt they will reach the advertised 208 Watts. Hmmm something else to test :-)
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#5
I've recently deployed a couple of the 16T vesions of Chargery.  You would use a 8T like this: https://www.ebay.com/itm/Balance-1-2A-Chargery-BMS8T-2S-8S-LiPo-lifepo4-LTO-Li-ion-Battery-BMS-Smart-Li/192843876497?hash=item2ce6640891:g:E~oAAOSw41dc93y    

It uses 12v to operate external relays - I'm using a couple of these  https://www.amazon.com/gp/product/B010L0...UTF8&psc=1   for 60a range.   The picture shows 80a DPDT but lately they've been shipping a 60a SPDT instead...  but still it's cheap and would work for you.

I like Chargery (above) because you can see/set everything without a phone - which works for me personally Smile

However, many folks use phone (bluetooth) accessible BMSs...  and that's a perfectly fine alternative.  I just don't have any advice/experience with a particular model to share with you.   Others may post some links to help you.
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#6
The pics of the OP's unit do show a row of MOSFETs so it should have a half decent current capability.
The thickness of the copper tracks & ability to get good connection to the board (hopefully soldered), etc will be important too.
Like daromer says, specs or often over-rated.
Sometimes the description will say you need extra heat-sinking.
Agree 50A would be stretch for it.....
Running off solar, DIY & electronics fan :-)
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