On this video,
the person uses a drill battery to jump the car. I do have a jumper but several cars and can easily make this jumper for each car.
Do you see any problems with this idea???
Last edited:
Drill battery as a jumper
- Thread starter LazyDog
- Start date
- Status
On this video,
the person uses a drill battery to jump the car. I do have a jumper but several cars and can easily make this jumper for each car.
Do you see any problems with this idea???
JHZR2
Staff member
I didn’t watch the video, but starting out, 18V on a 12v system could create problems if it gets through to the electronics. Notionally the main battery, especially if degraded, would absorb it, but we don’t have data.
The conductors are too small, but overall this is like an uncontrolled jump pack. Those cells can probably source decent fault current.
Let’s assume 5s, so 3.7Vx5=18.5V. Let’s assume 0.008 Ohm per cell, so 0.008OhmX5=0.04Ohm for the pack.
Ohm’s law says for current (I), I=V/R, so I=18.5/0.04 and I=462.5A
So that battery can source 462.5A max, and let’s imagine that it won’t blow up (that is a real possibility when shorting Li-ion), then, using Vt=Vic-I*R, then, it will provide:
Vt=18.5-462.5*0.04=0V. Necessarily.
Let’s calculate what it takes to keep, say, 9V
9V=18.5-I*0.04Ohm
Solving for I, I=-(Vt-Voc)/R= 237.5A
So there’s some basis of the cranking amps is around 200A or less, with this approach.
I suspect that the cell design for the jump packs is deliberately designed for much lower resistance. A hand tool would probably burn up and/or hurt someone if the battery was putting out 237A at 9V (>2kW of power)!
The conductors are too small, but overall this is like an uncontrolled jump pack. Those cells can probably source decent fault current.
Let’s assume 5s, so 3.7Vx5=18.5V. Let’s assume 0.008 Ohm per cell, so 0.008OhmX5=0.04Ohm for the pack.
Ohm’s law says for current (I), I=V/R, so I=18.5/0.04 and I=462.5A
So that battery can source 462.5A max, and let’s imagine that it won’t blow up (that is a real possibility when shorting Li-ion), then, using Vt=Vic-I*R, then, it will provide:
Vt=18.5-462.5*0.04=0V. Necessarily.
Let’s calculate what it takes to keep, say, 9V
9V=18.5-I*0.04Ohm
Solving for I, I=-(Vt-Voc)/R= 237.5A
So there’s some basis of the cranking amps is around 200A or less, with this approach.
I suspect that the cell design for the jump packs is deliberately designed for much lower resistance. A hand tool would probably burn up and/or hurt someone if the battery was putting out 237A at 9V (>2kW of power)!
My cars are old and they do not have lost of fancy electronics.
Probably next time, I can disconnect the cars battery and connect a 12V or 18V from a drill and see it what it does to the charge on the battery.
Probably next time, I can disconnect the cars battery and connect a 12V or 18V from a drill and see it what it does to the charge on the battery.
This looks dangerous. The only situation I can see myself doing this is at 2am at a shady rest stop just to get the heck outta dodge.
Seems shady, but I have to wonder....how different is this from the "plug into your car lighter" jump packs? I think the only real difference would be 18V vs 12V, assuming thats an 18V battery they are using.
JHZR2
Staff member
Difference is that even the cheapo units probably have some level of control and protection that this doesnt necessarily have.
And the “lighter” jump packs are limited to 10amps or whatever the lighter fuse is. They can’t really jump the car so to speak, they give a small charge to the main battery over a few minutes in hopes that it can collect it and burst it back out to the starter. With a proper pulse-mode power supply, the drill battery could do that elegantly.
Only work if the car needed 1 or 2 more amps to start.
Why do people do idiotic things like this. Just get a jump pack and keep it in your car. Youre willing to ruin a car battery and/or a drill battery to save money? So lets see a noco battery pack is 75 -100 bucks. A car battery is about the same plus a drill battery is 60 to 70 bucks. Plus if either battery explodes you'll have chemical and thermal burns not to mention the issue of possible blowing out or damaging an ecu. Yeah makes perfect sense next thing you'll see is using Gorilla Glue as hair gel. Don't this get and use the right equipment for the job.
The car battery will easily absorb the 18V from the drill and bring the system voltage down to something friendly.
For this stunt, timing is everything-- you want the car battery to absorb enough to get a surface charge to get going but not wait too long and exhaust the dewalt one. Also, obviously, the contacts and thin wire from the dewalt battery aren't, alone, going to pop things over.
All this said, it's a known hack for the Prius when its 12V system isn't enough to close the main relay and boot the rest of the car up. That's a way lower current requirement than turning over an engine though.
For this stunt, timing is everything-- you want the car battery to absorb enough to get a surface charge to get going but not wait too long and exhaust the dewalt one. Also, obviously, the contacts and thin wire from the dewalt battery aren't, alone, going to pop things over.
All this said, it's a known hack for the Prius when its 12V system isn't enough to close the main relay and boot the rest of the car up. That's a way lower current requirement than turning over an engine though.
The cells used in those drill batteries are likely limited to 20, maybe 30 amps each, so they can give out 60 amps at best (for bigger battery packs with cells in parralel) before either damaging or dropping voltage. There's quite often a link inside the batteries that serves as a fuse aswell.
Maybe they can deliver a bit more in burst mode, who knows...
Maybe they can deliver a bit more in burst mode, who knows...
- Status
