Operating Dewalt 12v Li-Ion tool on car battery

[marcone]

I bought a Dewalt DCF813 impact wrench for a maintenance job on my motorcycle that requires an impact tool and because I won't be doing this so often, I did not buy battery and charger thinking that I will be able to get power from the bike battery.

I figured out the + and - wires (highlighted in the picture below) but when connecting the impact wrench to the bike battery that way I get the LEDs to light up for a short period of time with nothing else happening. I'm guessing the other 2 connectors are used for communication between tool and battery and in the absence of a particular signal on them, the tool will not work.

Would want to ask what are the signals on the other 2 connectors (marked with ?) in order to make it work on bike/car battery.

 

[bobcatdan]

I'm far from an expert, but I think all you are going to do fry your tool if you keep playing around with it. What is the true amps of a tool battery vs a car battery. Voltage is the push behind electricity, amps do the work. You put 300 amps to a tool designed for 3, I bet magic smoke comes out. Like I said, far, far from an expert, so if this something that works, I'll gladly eat crow on this.

 

[doan]

A car battery is only 12v (~14 with the car running). This is a great way to "save" tools with dead batteries.

A car battery has a lot of capability to deliver amps, but the tool will only draw what it needs.

Easiest way to do this is to disassemble a dead battery, put a wire where the battery leads were, then connect the leads to the car battery. For smaller tools a cigaret lighter adapter might work but will blow the fuse if you exceed 10 amps.

 

[unashamedlaborer]

I bought a Dewalt DCF813 impact wrench for a maintenance job on my motorcycle that requires an impact tool and because I won't be doing this so often, I did not buy battery and charger thinking that I will be able to get power from the bike battery.



I figured out the + and - wires (highlighted in the picture below) but when connecting the impact wrench to the bike battery that way I get the LEDs to light up for a short period of time with nothing else happening. I'm guessing the other 2 connectors are used for communication between tool and battery and in the absence of a particular signal on them, the tool will not work.







Would want to ask what are the signals on the other 2 connectors (marked with ?) in order to make it work on bike/car battery.

I'm a little rusty on batteries but when I was into rc hobbies li-ion and li-poly batteries have extra terminals for "balancing" I believe that is what those terminals are for.

 

[Kracin]

I'm far from an expert, but I think all you are going to do fry your tool if you keep playing around with it. What is the true amps of a tool battery vs a car battery. Voltage is the push behind electricity, amps do the work. You put 300 amps to a tool designed for 3, I bet magic smoke comes out. Like I said, far, far from an expert, so if this something that works, I'll gladly eat crow on this.

amperage is a measure of draw/flow, the tool likely draws less than an amp or something, haven't seen what they are rated at, but didnt think cordless tools had much draw to them.

12v dc from a small bat, and 12v dc from a large batt is the same voltage. it would probably work fine but no idea why you would want to do that.

on the other hand, for certain applications like a job site or someone who uses their truck as a mobile tool mobile or something, maybe someone can invent a cigarette lighter adapter that has a tool battery adapter to it, so you can plug your tool directly into your cig lighter.

 

[Kracin]

here you go, looks like some people have had the same idea.


http://www.instructables.com/id/Convert-a-perfectly-good-cordless-drill-to-a-corde/?ALLSTEPS

 

[firebox40dash5]

amperage is a measure of draw/flow, the tool likely draws less than an amp or something, haven't seen what they are rated at, but didnt think cordless tools had much draw to them.

Not to mention that you can't "push" current through something. I could put a group 31 truck battery in my motorcycle, and the only damage it would cause is extreme top-heaviness and sheet metal damage.

Where do people come up with these ideas? A 60w bulb is designed for 1/2 an amp (at 120v), better be careful powering it with that 15a circuit.

 

[Kracin]

Not to mention that you can't "push" current through something. I could put a group 31 truck battery in my motorcycle, and the only damage it would cause is extreme top-heaviness and sheet metal damage.

Where do people come up with these ideas? A 60w bulb is designed for 1/2 an amp (at 120v), better be careful powering it with that 15a circuit.

to some people electrical terms are a foreign language, we all aren't born with the knowledge and had no idea til we found out for ourselves what it meant. no use in trying to talk down to someone for not knowing (only do that if they continue to not want to know but still want to act like they know, we all hate those people)

 

[firebox40dash5]

to some people electrical terms are a foreign language, we all aren't born with the knowledge and had no idea til we found out for ourselves what it meant. no use in trying to talk down to someone for not knowing (only do that if they continue to not want to know but still want to act like they know, we all hate those people)

You don't see me on a sewing forum talking about things I have no clue about... if you don't have a clue what you're talking about, why talk about it? Or at least ask questions rather than make false statements.

Sorry, that one's a sore subject for me. I can't tell you how many times I read that on motorcycle forums... "Don't jump start your bike with your car! Your car has too many amps! You'll melt all your wires with all the amps!" It's like these people have never seen a small car get a jump start from a diesel with 2 batteries or something.

 

[bobcatdan]

My first post was my gut reaction to the post and I will dish up my crow. The more I think about it, yes on paper it should work, it is no different then hooking up any 12v accessory to a battery.

 

[marcone]

So, reading all your replies I went ahead and opened up the thing.
All the fancy electronics were in the trigger assembly, got rid of them, made a bypass solder, drilled a hole in the bottom for the wires to come out, hooked it up to the car battery and success, it works.
2 downsides: no more light from the LEDs (easily fixable, just need to play around with some resistors to get the right current through) and no more speed control through the trigger, it only goes flat out but I'll live with that. Procedure is fully reversable if get a new trigger assembly

I'll make a video of it working for the non believers, unfortunately it's already nighttime at my side.

 

[Danglerb]

Plenty of modern motor driven devices depend on the current limiting of the battery or power supply to protect the motor when it stalls. Lead acid could fry something in seconds as it has huge current capacity.

 

[broken1]

Plenty of modern motor driven devices depend on the current limiting of the battery or power supply to protect the motor when it stalls. Lead acid could fry something in seconds as it has huge current capacity.

So, that makes sense. If there are 10 cells in a 5ah, big Dewalt 20v pack connected in parallel, each with a 20amp draw, then that's 400 watts of power. So why does a cordless 1/2 impact have more torqe and breakaway power than a 12amp, 120v corded impact that is 2400 watts of power?

 

[mike93lx]

So, reading all your replies I went ahead and opened up the thing.
All the fancy electronics were in the trigger assembly, got rid of them, made a bypass solder, drilled a hole in the bottom for the wires to come out, hooked it up to the car battery and success, it works.
2 downsides: no more light from the LEDs (easily fixable, just need to play around with some resistors to get the right current through) and no more speed control through the trigger, it only goes flat out but I'll live with that. Procedure is fully reversable if get a new trigger assembly

I'll make a video of it working for the non believers, unfortunately it's already nighttime at my side.

Having an impact wrench that can only go full out is a success? I cant imagine wanting that.

I feel like you'll regret it at the first stripped or broken bolt.

 

[broken1]

Having an impact wrench that can only go full out is a success? I cant imagine wanting that.

I feel like you'll regret it at the first stripped or broken bolt.

Well spoken. I did some research on the 1/2 corded vs cordless impacts, and basically, the cordless ones are geared for low rpm, high torque, utilizing about 400 watts compared to a corded 900 watts. That's why we see the gearing and mechanics breaking on cordless models more often, where on the corded, we see the motors burning up because they are not geared low enough, stall out too many times.

 

[dcg9381]

So, that makes sense. If there are 10 cells in a 5ah, big Dewalt 20v pack connected in parallel, each with a 20amp draw, then that's 400 watts of power. So why does a cordless 1/2 impact have more torqe and breakaway power than a 12amp, 120v corded impact that is 2400 watts of power?

Gear reduction would be my guess.

I'm a little rusty on batteries but when I was into rc hobbies li-ion and li-poly batteries have extra terminals for "balancing" I believe that is what those terminals are for.

Your RC batteries had "per cell" balancing, so there was a ground wire and then a "cell balance" wire for each individual cell. These batteries do not have internal BMS, so you need to balance them.

I think those are either terminals to power the internal BMS balancer or "discharge" terminals. Not 100% sure. Not enough terminals to balance per cell unless the balancing is very basic.

If you look at one of the "Amazon adapters" for 20V to 12V converters, you can usually see what the "main" terminals are on all sorts of tool battery types.

As these have all sorts of protections (at least modern lithium), like low voltage, they have internal BMS (Makita, anyway).

More modern Dewalt batteries seem to have more terminals for balancing options.

 

[broken1]

I'm far from an expert, but I think all you are going to do fry your tool if you keep playing around with it. What is the true amps of a tool battery vs a car battery. Voltage is the push behind electricity, amps do the work. You put 300 amps to a tool designed for 3, I bet magic smoke comes out. Like I said, far, far from an expert, so if this something that works, I'll gladly eat crow on this.

It's good he said he's not an expert, because he is wrong. That's why this exists, to learn from others smarter. Bob voiced what many people were thinking. Thank you Bob!

 

[broken1]

I bought a Dewalt DCF813 impact wrench for a maintenance job on my motorcycle that requires an impact tool and because I won't be doing this so often, I did not buy battery and charger thinking that I will be able to get power from the bike battery.

I figured out the + and - wires (highlighted in the picture below) but when connecting the impact wrench to the bike battery that way I get the LEDs to light up for a short period of time with nothing else happening. I'm guessing the other 2 connectors are used for communication between tool and battery and in the absence of a particular signal on them, the tool will not work.



Would want to ask what are the signals on the other 2 connectors (marked with ?) in order to make it work on bike/car battery.

So thankful for you starting this. Through the replies from others, I gained exactly what I needed. Thank you SO MUCH for getting this thread started. I REALLY NEED IT!