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battery pack for Makita 8434D drill
#1
Hi all,

i would to explain my problem:
I have an old Makita 8434D that still works perfectly butt not the battery.

I have seen some videos on YouTube and i ordered li-on batteries and bms  4s 30A
battery: NCR16850B  (4 pcs)
BMS: BMS

I have 2 problems with this setup:
1. If i push the switch to the end, the  drill starts a few turns and stops. ( i suppose the startcurrent if to high and bms shuts down. There are videos on YouTube that show the same problem that I have)

2. If i use the battery without "discharging control from bms" the drill acts normal, but the battery get very very hot.  I measured yesterday 80 C° .  The result 1 cell is dead. 

Is my combination BMS/BATTERY wrong ?

Which batteries/BMS are the most appropriate?

Sorry if i do not use the appropriate terms but my knowledge of this matter is almost zero.
I know that a possible solution would be to buy a new original battery, but the price is so high that it's not worth it while I can make a battery pack.

Thanks in advance for your help.

Kind regards, Tony
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#2
The BMS is cutting off from Voltage sag. Which means it is doing it's job. What is probabally happening is once cell is dropping voltage before the others and then setting off the BMS cutoff. With any Pack they need to be really balanced in capacity and voltage sag as you use the power. What I do for my drill packs is to bench test them first.

By that I mean build the pack and charge it with an external charger. this could be a RC charger or Bench power supply. to full and watch the differences in the voltages and as it gets near full (or just before the bms cuts it off) check each cell voltage.

this will tell you how the pack is in terms of balance. if they are all within .01V then your good If not you got balance issues.

Then discharge till the BMS cuts it off and as it gets close to cutoff again check the voltages. you are looking for all the cells to be the same or as close to the same voltage as possible. If not the lowest cell has issues.

What the BMS is looking at is each cell voltage first then the entire pack. it has upper and lower limits for each cell and a upper and lower limit for the pack as a whole.

the reason one cell hot really hot (therefore transferred that heat to the other cells) is that it was discharged below 3V and well below the others. Any battery under high load will get warm. and if you push them much past there current rating they could get quite hot.

Since they are only 10A cells watch your current draw from the drill as it might take more than that
tonyfenoll likes this post
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#3
(10-17-2018, 12:26 PM)jdeadman Wrote: The BMS is cutting off from Voltage sag.   Which means it is doing it's job.  What is probabally happening is once cell is dropping voltage before the others and then setting off the BMS cutoff.   With any Pack they need to be really balanced in capacity and voltage sag as you use the power.   What I do for my drill packs is to bench test them first.

By that I mean build the pack and charge it with an external charger.  this could be a RC charger or Bench power supply.   to full and watch the differences in the voltages and as it gets near full (or just before the bms cuts it off) check each cell voltage.

this will tell you how the pack is in terms of balance.  if they are all within .01V then your good  If not you got balance issues.

Then discharge till the BMS cuts it off and as it gets close to cutoff again check the voltages.  you are looking for all the cells to be the same or as close to the same voltage as possible.   If not the lowest cell has issues.

What the BMS is looking at is each cell voltage first then the entire pack.   it has upper and lower limits for each cell and a upper and lower limit for the pack as a whole.  

the reason one cell hot really hot (therefore transferred that heat to the other cells) is that it was discharged below 3V and well below the others.    Any battery under high load will get warm.    and if you push them much past there current rating they could get quite hot.

Since they are only 10A cells watch your current draw from the drill as it might take more than that

Thanks for your reply.

I will do what you propose.  I bought just in amazon a RCSKY balanced charger. I hope this will help a bit.

Because 1 cell is dead, which cells do you recomend? (i have to buy)
I think that my makita drill gets to 22A when drilling o screwing large screws.

Kind Regards, Tony
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#4
The 10A would be fine if you had a 4s2p setup so 8 cells total otherwise you'd need to get 25A cells something like https://www.alibaba.com/showroom/18650-2...harge.html
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#5
(10-17-2018, 02:59 PM)jdeadman Wrote: The 10A would be fine if you had a 4s2p setup so 8 cells total  otherwise you'd need to get 25A cells something like https://www.alibaba.com/showroom/18650-2...harge.html

Thank you very much. 

I keep posted my results.  


Regards, Tony
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#6
If you want to buy new cells, take a look at nkon.nl  they  have good prices and fast delivery ...
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___________________________________
18x 300Wp solar off grid and 10x 180Wp solar tracker grid-tie
10KW 3phase hybrid inverter. 40Kwh 18650 storage (for now)
My setup: https://secondlifestorage.com/t-Instant-powerwall
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#7
(10-17-2018, 06:42 PM)wim Wrote: If you want to buy new cells, take a look at nkon.nl  they  have good prices and fast delivery ...

Thanks Wim for the link.

I ordered  BMZ NCA18650 31PM - 3120mAH 30A.

Have a nice day.

Regards, Tony
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#8
Hi guys,

as promised, a report of my results.

As say, i received my batteries BMZ NCA18650 31PM - 3120mAH 30A that i ordered in NKON. I receive them in 4 days. (Fortunately I did not have to wait 6 weeks had I ordered them at banggood or aliexpress)

I have assembled the battery pack (with the same BMS as before: CF-4S30A-A).

Before I started using it I loaded the pack.  I measured the voltage of each battery: 3 batteries 4.1v and the 4th battery 4.08v.
Then I started doing tests with the drill. After having screwed 10 screws into a block of wood and drilled a hole in the wall of 8 mm, the batteries were again much too hot. I measured about 60ºC again. And again 1 battery that had that temperature while the other 3 batteries were remarkably colder (around 35ºC)
After this test the voltage of the 4 batteries was 3.99v.

In the meantime, I also ordered another BMS to test. https://rover.ebay.com/rover/1/1553-5347...olid=20008
I have performed my test again with the same result, the batteries become very hot.
After this test the voltage of the 4 batteries was 3.97v.

My knowledge in this matter does not go further. 
Is there a solution for my "problem"?  (different BMS , other batteries ......Or do I connect the BMS incorrectly?) 

All advice is welcome and much appreciated. 

Thanks in advance.
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#9
Did you use 4s2p? If you only have 4 batteries you are still asking too much of them. You would do well to go with 8. By halving the load on the batteries they should not get hot.

Be careful with a high current BMS. Too much current may burn the windings in the drill.
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#10
Sounds like too much draw for the batteries to Handle. So they get hot
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