Hello Guys,

I need help to make a battery adapter for Dewalt circular saw.

Planning to use Milwaukee m18 batteries and charger and would like to use them as well for the Dewalt circular saw which works on 18v XR series battery.

Tried connecting the m18 battery +ve to Dewalt saw +ve and battery -ve to saw -ve terminals as well using jumper wires to test. However, not working.

I have attached some readings from the battery.

There are only four contact pins on the tool. They are B+, TH, C3 and B- in their left to right order. And their readings are on the 3rd image.
Thinking,.. missing some resistors/connections in between the tool/battery terminals? ie; linking battery TH or ID terminals?

Any help would be much appreciated.

 

Did you look for one on Ebay? They have adapters for many different brand tools to use different batteries. Don't think you could make a DIY version for what they sell them for.

 

Did you look for one on Ebay? They have adapters for many different brand tools to use different batteries. Don't think you could make a DIY version for what they sell them for.

Readymade adaptors I tried were; 1. Not enough gauge for terminals/contacts and inner wiring to carry enough amps/power from battery to tool. And ended up doing again.

Also I do have some 3D printed M18 adaptors and a dud dewalt battery for parts.
Would love to make one by myself and learn in the process. Thanks.

 

The ID terminal is almost certainly required. I have read some speculation that it is resistive, and requires 800Ω to read as a 20V pack.

The DeWalt packs do not include overvoltage or undervoltage protection and rely entirely on the tool for that. The B+/B- are wired directly to the cells. I would imagine that something on the PCB assists in determining SoC and has to communicate with the tool.

If you have a DeWalt battery you might want to try using plain jumpers from the +/- terminals to see if it operates. Then you can try adding terminals if it doesn't. Unfortunately it is very possible that there is some magic going on since the ID terminal seems to be shared with the thermal sensor.

 

The ID terminal is almost certainly required. I have read some speculation that it is resistive, and requires 800Ω to read as a 20V pack.

The DeWalt packs do not include overvoltage or undervoltage protection and rely entirely on the tool for that. The B+/B- are wired directly to the cells. I would imagine that something on the PCB assists in determining SoC and has to communicate with the tool.

If you have a DeWalt battery you might want to try using plain jumpers from the +/- terminals to see if it operates. Then you can try adding terminals if it doesn't. Unfortunately it is very possible that there is some magic going on since the ID terminal seems to be shared with the thermal sensor.

Thanks Ya,
This is what I did exactly.

There are total 4 terminals on the tool. (no terminal for 'ID' on tool) Their order is B+, TH, C3, B- (from left to right order, as you could see in the 3rd image I have posted earlier)

1. I have insulation taped both the middle terminals on the tool and inserted battery - not working.

2. Took insulation off the 'TH' terminal (now three terminals connected) - not working

3. Insulated 'TH' again and took insulation off the 'C3' terminal (now three terminals connected) - not working

4. Took insulation off the 'TH' terminal (now all four terminals connected) - working!

More info and readings ( resistance and voltage) between these four terminals of the battery are on the third image drawing in the post.

Any input would be appreciated.

 

Is your saw a Dewalt XR saw or just a regular one?

 

Thanks Ya,
This is what I did exactly.

There are total 4 terminals on the tool. (no terminal for 'ID' on tool) Their order is B+, TH, C3, B- (from left to right order, as you could see in the 3rd image I have posted earlier)

1. I have insulation taped both the middle terminals on the tool and inserted battery - not working.

2. Took insulation off the 'TH' terminal (now three terminals connected) - not working

3. Insulated 'TH' again and took insulation off the 'C3' terminal (now three terminals connected) - not working

4. Took insulation off the 'TH' terminal (now all four terminals connected) - working!

More info and readings ( resistance and voltage) between these four terminals of the battery are on the third image drawing in the post.

Any input would be appreciated.

I didn't realize there are two contacts on stacked so that TH and ID are separate but aligned. Base on that I think it is probably like this: the ID is a 1K resistance, and the C terminals are the balancer connections for the charger, but the drill is somehow using C3 (about 12V) to determine S0C to prevent over-discharge. I believe the pack is in a 5S2P configuration so each C pin is on the Nth cell in the series (maybe only on one set?)

It's approximately the center point of the battery, so it could be using the full output from B+/- and C3 (Cell 3?) to watch for over-discharge. If this is the case, you need to emulate this voltage which you might be able to managed with a voltage divider since I suspect the current on that pin is very low.

 

Is your saw a Dewalt XR saw or just a regular one?

It's a XR circular saw pls.

 

I didn't realize there are two contacts on stacked so that TH and ID are separate but aligned. Base on that I think it is probably like this: the ID is a 1K resistance, and the C terminals are the balancer connections for the charger, but the drill is somehow using C3 (about 12V) to determine S0C to prevent over-discharge. I believe the pack is in a 5S2P configuration so each C pin is on the Nth cell in the series (maybe only on one set?)

It's approximately the center point of the battery, so it could be using the full output from B+/- and C3 (Cell 3?) to watch for over-discharge. If this is the case, you need to emulate this voltage which you might be able to managed with a voltage divider since I suspect the current on that pin is very low.

Thanks for the reply.

From where we need to start counting the cell number order just to make sure not over volting the tool controller.

If you could download and look at the second long image, each cells volt reading is there.

And how do we work out a simple voltage divider (any diagram/sketch) for this pls? Will any resistor in series will do (won't it heat up)?

 

You don’t have to worry about over voltage so long as you are using 18V batteries like the M18.

​

The voltage divider needs to supply what C3 would presumably do on the native pack from the a ~18V input. The “20V”batteries are just the nominal full charge of 4.2V per cell with a 5S configuration (actually 21V). It is a marketing name.

The voltage divider would look like this. These values are as close as I could easily get with common resistor values. The B+ goes in at the top, and the output to the C3 pin comes from between the pair and the 10K resistor. I have been distracted all day but I think I have gotten this right.

​

 

You don’t have to worry about over voltage so long as you are using 18V batteries like the M18.

​

The voltage divider needs to supply what C3 would presumably do on the native pack from the a ~18V input. The “20V”batteries are just the nominal full charge of 4.2V per cell with a 5S configuration (actually 21V). It is a marketing name.

The voltage divider would look like this. These values are as close as I could easily get with common resistor values. The B+ goes in at the top, and the output to the C3 pin comes from between the pair and the 10K resistor. I have been distracted all day but I think I have gotten this right.

View attachment 270882​

Thanks a lot Ya,

I'm more confident now that we can do it!!

Btw;

1. Why would we need to use separate R1 & R2 in parallel, can't we use one resistor pls? (also R1 &R2 comes from B+?)

2. Where would the R3 connect ends (to the B-) ?

3. What about "TH" pls?

 

Thanks a lot Ya,

I'm more confident now that we can do it!!

Btw;


1. Why would we need to use separate R1 & R2 in parallel, can't we use one resistor pls? (also R1 &R2 comes from B+?)

The upper resistor needs to be about 3.13KΩ that's not a standard value. By using two standard values, 4.7KΩ and 10KΩ we can come close to that. I don't know how much precision it needs to behave well but this is very close resulting in .1V difference at the output.

2. Where would the R3 connect ends (to the B-) ?

Yes, the down pointing arrow is the signal ground symbol. In this case it is just "the low side", the negative terminal of the battery.

3. What about "TH" pls?

That's a good question. The M18 pack doesn't have discrete pin for a thermal sensor. I believe the one on the DeWalt is a simple thermistor. But, it school be as simple as putting a 47KΩ resistor between TH and B+.

NOTE: The drill will not protect the battery from overheating with this arrangement, but that should not be a problem since the battery will have on-board protection. Nonetheless, keep an eye out for heating.

 

The upper resistor needs to be about 3.13KΩ that's not a standard value. By using two standard values, 4.7KΩ and 10KΩ we can come close to that. I don't know how much precision it needs to behave well but this is very close resulting in .1V difference at the output.


Yes, the down pointing arrow is the signal ground symbol. In this case it is just "the low side", the negative terminal of the battery.


That's a good question. The M18 pack doesn't have discrete pin for a thermal sensor. I believe the one on the DeWalt is a simple thermistor. But, it school be as simple as putting a 47KΩ resistor between TH and B+.

NOTE: The drill will not protect the battery from overheating with this arrangement, but that should not be a problem since the battery will have on-board protection. Nonetheless, keep an eye out for heating.

Thanks Ya,

I have got all the setup ready just before connecting them and to double check;..

C3 is 12v right? Because as in secind image of the post,
if we start measuring the cell volts, beginning from B+ side it's around 8v. Or if we start measuring the cell volts beginning from B- side it's around 12v. Which makes the B+ 5th cell group (C5).

In this post article says that, in Dewalt batteries they seems to count the cells backward?
https://www.sevarg.net/2017/04/22/dewalt-20v-max-60ah-pack-teardown/

 

Thanks Ya,

I have got all the setup ready just before connecting them and to double check;..

C3 is 12v right? Because as in secind image of the post,
if we start measuring the cell volts, beginning from B+ side it's around 8v. Or if we start measuring the cell volts beginning from B- side it's around 12v. Which makes the B+ 5th cell group (C5).

In this post article says that, in Dewalt batteries they seems to count the cells backward?
https://www.sevarg.net/2017/04/22/dewalt-20v-max-60ah-pack-teardown/

You should measure ~12V on what we will be connecting to C3, you should check that before connecting it. You measured he signal from the battery on C3 to be about that. Since there are 5 cells, C3 will be in the middle and have the output of 3 cells no matter which way you count them.

I am juggling a lot of plates just now so unfortunately I have limited bandwidth to spare. If you think this arrangement is wrong, you should exercise caution. It seems correct to me with everything I have in front of me, but it's your tool. I don't expect there is much danger to the tool even if it is wrong, but I am unable to guarantee anything.

I can say that I would do it but YMMV, this is not an offer, may contain shell fragments, etc.

 

You should measure ~12V on what we will be connecting to C3, you should check that before connecting it. You measured he signal from the battery on C3 to be about that. Since there are 5 cells, C3 will be in the middle and have the output of 3 cells no matter which way you count them.

I am juggling a lot of plates just now so unfortunately I have limited bandwidth to spare. If you think this arrangement is wrong, you should exercise caution. It seems correct to me with everything I have in front of me, but it's your tool. I don't expect there is much danger to the tool even if it is wrong, but I am unable to guarantee anything.

I can say that I would do it but YMMV, this is not an offer, may contain shell fragments, etc.

Thank you Ya,

I have tried,..

And works like a charm

I have attached the images of connector that connects to the Dewalt XR tools.

I have soldered the resistors as you mentioned in the sketch. It works as if I'm using Dewalt battery

Wondering;
1. Why the resistors are not getting hot/burn out!!! being exposed to so high amps.

2. Also shorting the terminals using resistors, not damaging/tripping the fuse in the M18 battery!!!

Pls correct me.

 

Can I ask a dumb question about this? It seems like you are going about doing the opposite of what people/contractors in this area are doing. My middle son is a carpenter and works for a couple of contractors. All of the carpenters he works with are doing just the opposite, they are adapting Dewalt batteries to Milwaukee tools. This is due to the new Dewalt batteries having a much longer run time compared to the Milwaukee batteries. It was different with the older Dewalt stuff, Milwaukee ran longer so every one changed to Milwaukee tools as their Dewalt stuff died, but Dewalt made many leaps and bounds to get better and regain the market.

 

Thank you Ya,

I have tried,..

And works like a charm

I have attached the images of connector that connects to the Dewalt XR tools.

I have soldered the resistors as you mentioned in the sketch. It works as if I'm using Dewalt battery

That's great to hear, the remaining question I have is what the drill will do as the pack gets to a low voltage. The battery might go into overhdischarge protection before that, though.

Wondering;
1. Why the resistors are not getting hot/burn out!!! being exposed to so high amps.

You've answered your question. The current through the voltage divider i very small. I assume the input to the ADC (Analog to Digital Converter) the is reading the voltage is probably high impedance and so we can ignore that for our purpose here.

How much current is going through the resistors? Ohm's Law says E = I/R where E is voltage, I is current in amps, and R is resistance in ohms.

We have a peak voltage of about 21V, so that is our worst case for high current, The resistors add up to ~3.2KΩ so:

I = 21 / 3200

We gat a current of 7mA., which is just .147W! So the current is very small and the heating will be very little.

2. Also shorting the terminals using resistors, not damaging/tripping the fuse in the M18 battery!!!

Same answer as above, the current in all cases is very low because the resistance is very high.

Pls correct me.

No correction. You had an observation and asked a question because it seemed at odds with some other thing you know. You never asserted there would be a problem, you asked what there wasn't, I don't need to correct that.

[EDIT: fixed a malformed quote tag]

 

Can I ask a dumb question about this? It seems like you are going about doing the opposite of what people/contractors in this area are doing. My middle son is a carpenter and works for a couple of contractors. All of the carpenters he works with are doing just the opposite, they are adapting Dewalt batteries to Milwaukee tools. This is due to the new Dewalt batteries having a much longer run time compared to the Milwaukee batteries. It was different with the older Dewalt stuff, Milwaukee ran longer so every one changed to Milwaukee tools as their Dewalt stuff died, but Dewalt made many leaps and bounds to get better and regain the market.

Hi,

The main reasons are;

1. Majority of my power tools are Milwaukee M18s'

2. Do have a few M18 batteries of various Ah and spare chargers. So would prefer develop/convert all the power tools around this ecosystem.
(Which I assume would help me save time and money in the long run.)

3. M18 batteries generally tend to have more energy density options for different demands. (they come in various flavours like; CP, XC, HD etc.)

4. They started and continues to improve their strategy for battery protection long since than many other brands. Which is handy in these kind of scenarios to prevent total battery drain. (Where we are trying to adapt different make tools to different make batteries.)

5. The learning curve is saved if we have only one kind of decent battery system which is repairable and withstands abuse/errors. Because "most frequently damaged or money wasted area" of power tool ecosystem is battery department.

My thoughts may be different to others though...

 

My thoughts may be different to others

I don't use either of the brands, I'm retired and have a lot of extension cords. According to my son, when I asked him, your Milwaukee batteries must be better than his.

 

That's great to hear, the remaining question I have is what the drill will do as the pack gets to a low voltage. The battery might go into overhdischarge protection before that, though.



You've answered your question. The current through the voltage divider i very small. I assume the input to the ADC (Analog to Digital Converter) the is reading the voltage is probably high impedance and so we can ignore that for our purpose here.

How much current is going through the resistors? Ohm's Law says E = I/R where E is voltage, I is current in amps, and R is resistance in ohms.

We have a peak voltage of about 21V, so that is our worst case for high current, The resistors add up to ~3.2KΩ so:

I = 21 / 3200

We gat a current of 7mA., which is just .147W! So the current is very small and the heating will be very little.



Same answer as above, the current in all cases is very low because the resistance is very high.



No correction. You had an observation and asked a question because it seemed at odds with some other thing you know. You never asserted there would be a problem, you asked what there wasn't, I don't need to correct that.

[EDIT: fixed a malformed quote tag]

Dear Ya,

You are so wonderful. Selfless people like you make "this place" thriving and vibrant.

My attempts or doubts could be simple for others. However, you took some time out of your busy schedule and patiently walked me through to finish. Couldn't thank you enough

God bless.