battery pack for Makita 8434D drill

tonyfenoll

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Joined
Oct 16, 2018
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11
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 andbms4s 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 thestartcurrent 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 ido not use the appropriate terms but my knowledge of this matter is almost zero.
I know that a possiblesolution would be to buy a new original battery, but the price is so high that it's not worth itwhile I can make a battery pack.

Thanks in advance for your help.

Kind regards, Tony
 
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
 
jdeadman said:
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
 
wim said:
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
 
Hi guys,

as promised, a report of my results.

As say, i received my batteriesBMZ 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 60C again. And again 1 battery that had that temperature while the other 3 batteries were remarkably colder (around 35C)
After thistest the voltage of the 4 batteries was 3.99v.

In the meantime, I also ordered another BMS to test.https://www.benl.ebay.be/sch/sis.ht...nce Battery PCB 12V 3 7V&_itemId=253653851404
I have performed my test again with the same result,the batteries become very hot.
After thistestthe voltage of the 4 batteries was3.97v.

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.
 
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.
 
Sounds like too much draw for the batteries to Handle. So they get hot
 
Thanks Geek & jdeadman for your reply.

I use 4S 1P bms.

Then I think it's a hopeless case. I do not get 8 batteries in the housing.Or I have to play Mcgyver and design a bigger pack so that 8 batteries get in.

Are there other types of batteries that can handle it so much draw?

Have a nice day.

Kind regards, Tony
 
I've ran into this with a DeWalt drill that was designed for nicd. I had to cut out the bottom of the pack to extend it for the length of the 18650 cells. For drills you really need the highest amp cells. My 20v maximum is 2ah 30A cells that are off brand (factory). But something in that range may be nessessary. Also wonder if current limiting might be an option? Not sure the best way exactly.

Just a quick question,. You said one battery gets hotter than the rest,. Which position is it in? So for example the one most positive would be battery #1 and the one on the negative side would be battery #4?


My last comment would be did you test the new cells? When using for power applications you need to have really close cells and one being off or less capacity could also allow one to heat up more
 
jdeadman said:
I've ran into this with a DeWalt drill that was designed for nicd. I had to cut out the bottom of the pack to extend it for the length of the 18650 cells. For drills you really need the highest amp cells. My 20v maximum is 2ah 30A cells that are off brand (factory). But something in that range may be nessessary. Also wonder if current limiting might be an option? Not sure the best way exactly.

Just a quick question,. You said one battery gets hotter than the rest,. Which position is it in? So for example the one most positive would be battery #1 and the one on the negative side would be battery #4?


My last comment would be did you test the new cells? When using for power applications you need to have really close cells and one being off or less capacity could also allow one to heat up more




Hi jdeadman,
Original batteries are 3.0Ah Ni-MH. I will do son bricolage an find a way to get a battery pack with 8 cells. :huh: The question I have: do i have to use a different bms for "4S2P"? (Again forgive my ignorance:dodgy: )


image_wntczc.jpg


The battery who got hot is on my test always the same: battery 2.
I have tested this with 2 different kind of batteries: first "pack"with the NCR18650B an the second test with "pack"BMZ NCA18650. This should have a discharge current 30A


image_rzqaxl.jpg


I'm not sure how to test the new cells. The only thing i check is the voltage when i received themfrom the store: all cells has a voltage 3,58 Volt. After fully charge them with iMax charger3cells had 4,1 volt and the 1 cell had 4,08 volt.

Thanks for your comments. Much appreciated.

Kind regards.
 
Hi all,

latest update :D

i have assembled 4S2P pack and indeed the same stress test as before and batteries doesn't heat. Temperature around 30Celsius.

For assembling the pack itself, i cut off the bottom. I have asked someone with a 3D printer make the bottom with walls at the height I need and it has been pretty good.

My adventure to make a battery pack has reach his end: I have learn a lot about 18650 and BMS....

Thanks for the support you give me.

Kind regards.
 
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