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NiCd to Li-ion battery pack conversion successful but has one strange issue

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MesabiRangeMike

Nov 6, 2023
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Converted two DeWalt 18V NiCd battery packs to Li-ion. Each pack has a 5S 15A BMS boards (BW-6022-5S), five Samsung 30Q 18650 3000mAh 15A batteries, and a 10K NTC thermistor. Both packs exhibit the same problem, when used in various tools, in that a quick mashing of the power trigger causes the tool to work for a microsecond then fail as if the pack was near complete discharge. If the trigger is slowly pressed all the way down the tool will behave as expected and will run at full speed for longer than I can hold the trigger without cramping/tiring.

The batteries were spot welded together rather than soldered and were purchased new from the 18650batterystore. After the first rebuilt pack exhibited this problem I tested the remaining 5 batteries using the Discharge-Charge-Test feature on a Opus BT-C3100 charger with no indication that they were anything but fresh and not reclaimed. The DeWalt battery charger will charge the packs, but errors out (rapid blinking) near the end of the charge cycle.

Any tips as to what to check would be greatly appreciated
 

kellys_eye

Jun 25, 2010
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The BMS you are using has a maximum instantaneous current protection value of 35A which is clearly being exceeded by the power tool at startup hence the protection circuitry is being brought into action.

Getting a board (BMS) that allows a higher instant amperage would fix it.

A more practical method would be a decent series inductor (suitably rated) for the motor. Search for power inductors.

A 'bodge' fix would be a series resistor (with the motor) of a low value but this resistor would require to be shorted almost immediately after start-up to allow full power to the motor.
 

MesabiRangeMike

Nov 6, 2023
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Thank you for your reply and the information you provided. I now have a course of action which is a relief
 

Bluejets

Oct 5, 2014
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Any tips as to what to check would be greatly appreciated
Learn from what problems you have caused yourself by trying to save a few bucks.
Your description fails to mention the quality of the replacements using specs.
A quick Google will show just how many of these cells are from the dodgy brothers store.
I'd like to say it seems you have learned something but I fear not.
Guaranteed all we will get is an argument on the fairies benefits.

In short, buy a new one from Dewalt.
Even a clone from China would possibly have been superior.
 

MesabiRangeMike

Nov 6, 2023
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Learn from what problems you have caused yourself by trying to save a few bucks.
Your description fails to mention the quality of the replacements using specs.
A quick Google will show just how many of these cells are from the dodgy brothers store.
I'd like to say it seems you have learned something but I fear not.
Guaranteed all we will get is an argument on the fairies benefits.

In short, buy a new one from Dewalt.
Even a clone from China would possibly have been superior.
Thannnnnks Dad. I'm retired and this is just a hobby to piss away time & money. Sorry it stressed you out
 

davenn

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Sep 5, 2009
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OK thread is done

thanks to those that tried to help
 
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