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36v Drill Project
#1
Hi All

I am trying to do one of those drill conversions after all the nickel batteries died on my 36v Drill.

I know that strictly speaking I should get some high stength 18650's but to begin with I want to prove I can make it work.

I plan to use 18 or 20 18650's for the project. (9x3.7=33.3 or 10x will be 37v but not sure if this will damage the drill)

I have bought a few bits and pieces off ebay for the project but I think my biggest problem is going to be finding a charger that is practical to use and that can charge 36v. 

The battery housing in the Drill is removable and plugs into a custom charger that came with the drill.

It will not be practical to remove the batteries from the Drill Housing for charging.

My first thought was to cut hole in the battery housing and charge it via the IMAX but the IMAX can't do 36v

I have collected all the 18650's I need from old and newer Laptop batteries for the trial, if it all works

I also bought a 36v BMS board on eBay so that the batteries are charged properly


My problem is the charger, then I saw this video and thought how it would be good if I could do a conversion of the old charger to make it support 18650's



Currently it does provide 36v but I gather it does this for NM batteries that were previously fitted.

Can someone tell me if this type of conversion is practical and what components I would need, it would be ideal if I could get that to work.
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#2
If it provides the correct input voltage to the BMS you are all set.

A lot of people use printer power supplies

You can search ebay for such having the required input voltage for BMS
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#3
So are you saying that I can use the existing power supply which does produce 36v but I imagine has a different charging profile?

I was thinking to put the BMS in the battery pack,

I am using one that people seen to use for electric bikes, 36v seems to be popular for that too.

I like the simplicity of using the same power supply but I need to know it is safe, I have heard all sorts of comments saying you must not use a power supply for NMH or Ni-Cad for L-Ion project,

The video seems to suggest that one can rip out the parts and replace them with cheap components BUT he does not put a BMS on all the time,
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#4
DC powered motors can handle a wide range of voltages. The drill may be "rated" at 36V, but it can safely run up to 40V, maybe even 48V without issue. The higher the voltage, the lower the amp draw. But also increases heat generation. But for a drill that's used intermittently this shouldn't be an issue.

You use nominal voltage to calculate wattage/power of the packs. But for voltage ranges, you need to use top/bottom voltages.

So, with standard 18650's, we'll use 4.1V - 3.2V
10s:
4.1V = 41V top end
3.2V = 32V bottom end

9s:
4.1V = 36.9V top end
3.2V = 28.8V bottom end

You should go with 10s in this case. Otherwise, you'll have a "weak" drill all the time.

Going with 11s would yield:
45.1V - 35.2V
This will make the drill more powerful. It'll have more torque and faster drill speeds

You "can" use the same charger. The problem is there is a difference in the charge profile, as you mentioned. Also, the 36V "NMH/Ni-Cad" charger will not charge to the full voltage of lithium ions. It'll only charge up to about 38V. I'm assuming 25s on the current battery pack. But your packs might have multiple cells in series in a mini-pack so that you may only have like 5s (5s * 5 = 25s)

Getting a charger that can actually charge lithiums at 36V would be better as it'll give not only range, but also the charge curve. Or, you could use a buck converter to drop a 48V-ish supply down to 38V and charge at full current. Then drop the current down by 50% for the final charge to make sure the packs are full.
Proceed with caution. Knowledge is Power! Literally! Cool 
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#5
For any 36-Volt tool, you need to use 10 cells in series (20 in total for 2 pairs).
The reference for high power cells is 3.6 not 3.7.

Overpowering it with an additional pair may cause over-drain of cells and I don't know of any 11S BMS.

Laptop cells will NOT work for a powerful drill because they cannot provide sufficient sustained current. You need to use cells recovered from power tool li-ion batteries.

A measured 36V for a charger is not sufficient.
In theory, you charge cells up to 4.2V and that would mean 42V++ charger (45, 48 or even 50+ measured while not connected).
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