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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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#6
I am having trouble understanding one aspect of the BMS

I totally understand the thin wires

It is the solder points that are confusing me because unlike say an eBike or Skateboard on a drill you remove the battery from the drill where it is discharging and plug it in using the same connectors to a charger.

On my BMS there are three connectors and on the battery there are two, so do I join these and will they still work or do I create some elaborate switch that move it from discharge mode to charge mode.  if so why was this not required on the lawn mower I took the battery pack from?

Here is my BMS with a crude drawing of the battery



So which wires go to B- P- and C-

Here are a collection of suggested ways to wire the BMS, what is confusing me is that on a Drill battery Charge and Discharge are the same wire, but I am concerned that it would not perform as expected if these were not separated somehow..

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#7
The battery pack Positive connector goes directly to load. This is also the connected to the charger Positive as well. So, common Positive

C- connects to the Charger's Negative
P- connects to the Load Negative
B- connects to the Battery Negative


This is the closest of the above that I think is the most accurate and understandable:
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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#8
Hi & thanks for your reply

I think I must be a bit blonde because I am stil confused.

As far as I can see the positive side is pretty easy, according to that diagram they both go to what is described as "Main Terminal B+" or the positive end of the battery.

B- is also easy because it connects to what is described as "Main Terminal B-" or the Negative end of the battery

The issue is

C- connects to the Charger's Negative
P- connects to the Load Negative

Because if you look at my crude drawing of the battery and connector for the drill there are only two wires, negative and positive, because the connector

Does that mean that C- connects to P- because if it did I can't imagine that the BMS would work or maybe it would?

If you look at how most of these batteries work it is the same

The battery comes out of the tool and plugs into a charger as shown in this image



So there is never anything taking the load when plugged into the charger except the charger negative itself, so maybe they DO connect together?
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#9
It is quite possible the C- and P- are combined externally from the BMS. They have some pretty beefy FETs on the circuitry which keep current flowing the wrong way through the gate. So charging while connected to the P- won't be forced in through the P- but will be readily accepted through the C- connection.

But before connecting anything like that, pop that cover off and look at the traces. Could even be surprised that the traces are connected together internally.
If you pop the cover off, please post a few pics of the circuitry so we can better see what's going on.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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#10
I've done something like this... here is my project link in case you wanted to check it out.
https://secondlifestorage.com/showthread.php?tid=4670

Personally I would build the packs, but use a RC / balance charger to charge / maintain the batteries. I don't use a BMS because the currently handling and performance (or lack of it) , just a cell monitor that will alarm.

I do agree with the comment about not using laptop packs. For projects like these, high drain cells all the way. I bought new, but things like those used hoverboard packs would be ideal.
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