Makita battery built in bms at 36v?

electricboard1 · May 22, 2020

I have a 36v electric scooter/board being powered with two 18v makita 6ah tool batteries. (Wired in series to make 36v)
I know these individual batteries have a built in bms safety feature which will cut the power from the tool if the battery is running low on power or getting flat.
But as I have wired these two batteries together in series I need to know if the bms in each battery pack would still work as it is now working at 36v ??

Would these batteries still cut out when the voltage gets too low?

Or by wiring both battery packs together does this somehow bypass the internal bms battery cutout feature when being used at 36v?

amberwolf · May 22, 2020

THe BMS's theoretically still do all the things they did on their own.

However, if their electronics (FETs specifically) are not rated to *at least* the fully-charged voltage of both packs in series, then if for any reason one of the packs turns off, it may (probably will) damage the FETs of that pack, as it now has across the FETs the full two-series-pack voltage (when it is only designed for one, itself).

You can look up BMS and Diode to find some threads about workarounds for this.

mark5 · May 22, 2020

BMS Protected Packs in Series by fechter
https://endless-sphere.com/forums/viewtopic.php?f=16&t=1312#p70490

electricboard1 · May 23, 2020

Thanks for the info
I was trying to avoid opening up the battery pack and tampering with it insides.
So to prevent one battery pack from switching off I was going to fit a battery voltmeter and monitor the voltage and recharge when it reads low. Would this be ok or is the diode really needed?
Could one pack switch off for other reasons other than just running flat?

electricboard1 · May 29, 2020

In the end I have fitted two diodes in between each battery pack as per the diagram. Also with a battery gauge meter to keep an eye on voltages.

After testing for continuity and testing with batteries all seems ok and it powers up correctly. However now when I plug just one battery onto one of the clips everything powers up and the volt gauge powers up too showing one battery connected
(before I fitted the diodes nothing powered up til both batteries were attached as it should)

Is this just because the diodes create a live circuit until I plug the other battery on?
Could this be a problem at all?

Crankin · May 10, 2021

Makita 18V batteries have no BMS, the BMS is in all the tools. Same with Dewalt I believe. Most other brands have BMS in battery.
How long have they lasted without a BMS?

JPALA · May 10, 2021

mark5 said:
BMS Protected Packs in Series by fechter
https://endless-sphere.com/forums/viewtopic.php?f=16&t=1312#p70490

But if i do this i will lose regen ? right?

The bms looks like this:

Each pack has 30 cells

I think the mosfet is this one ( NCEP85T25D )
http://ncepower.com/Upload/SGT/NCEP85T25Ddatasheet-14384485438.pdf

I have batteries with BMS they are 36v 9ah.
My question is can i connect 4 em series to make 144v nominal and then have 13 groups (117ah) of this 4 batteries in parallel (total of 52 batteries) ??

flippy · May 10, 2021

JPALA said:
I have batteries with BMS they are 36v 9ah.
My question is can i connect 4 em series to make 144v nominal and then have 13 groups (117ah) of this 4 batteries in parallel (total of 52 batteries) ??

no, it cant.

if you read the datasheet for the mosfet you can see that its only rated for 85V max so it would destroy itself (quite violently) if you were to switch 170V with it.

the voltage spikes and assorted crap that comes with a on-load mosfet tripping like that would certainly cause a quite the spectacle.

a spectacle best watched from afar, not when standing or sitting on them...

the parralel nature of this insane setup would only make it even worse.

i dont seem to see why you would even want to do something like this at this scale. the cost of these batteries is huge. the actual value of the cells is about 25~30 bucks or so if you cant find a deal.

JPALA · May 19, 2021

flippy said:
JPALA said:

I have batteries with BMS they are 36v 9ah.
My question is can i connect 4 em series to make 144v nominal and then have 13 groups (117ah) of this 4 batteries in parallel (total of 52 batteries) ??

Click to expand...

no, it cant.

if you read the datasheet for the mosfet you can see that its only rated for 85V max so it would destroy itself (quite violently) if you were to switch 170V with it.

the voltage spikes and assorted crap that comes with a on-load mosfet tripping like that would certainly cause a quite the spectacle.

a spectacle best watched from afar, not when standing or sitting on them...

the parralel nature of this insane setup would only make it even worse.

i dont seem to see why you would even want to do something like this at this scale. the cost of these batteries is huge. the actual value of the cells is about 25~30 bucks or so if you cant find a deal.

I want to change the batteries of my car, it uses old technology nickel cadmium battery = 300kg!! 120v 100ah i can push it to 170v 120ah.

I already have the 52 lithium batteries, do you thin i can replace the mosfets ? to something that can handle this level of voltages? any suggestion ?

This ones don't have bms? https://www.youtube.com/watch?v=6AawhFTYQRA ?

Makita battery built in bms at 36v?

electricboard1

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amberwolf

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mark5

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electricboard1

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JPALA

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