LCHIEN
this suggestion comes up every year or 6 months.
The answer is always the same, as someome mentioned its a current issue.
Batteries can put out low voltage and lots of amps.
AC is practically limited to 15 amps, 1800 w
if you have a cordless tool it has a low voltage motor, 9, 12, 18V typically
Corded tools have 120V AC motors.
A quick survey of corded drill on amazon shows 6, 7, and 8 amp drills.
So around 850 watts on average.
For a 12V cordless drill, it would take 70Amps to reach that power level for similar torque. Batteries can deliver that kind of current, and the wire losses are small due to the wire length being just a few inches.
Now your typical charger, even the fast ones, only put out about 1-2 amps. Its designed to charge continuoulsy for 1,3, or 15 hours to put a full charge in. You can deplete a full charge in a few minutes of high torque work. So a charger would not handle the running current of 70 Amps that might be requred. So a power supply of approximately 30-40 times as much current as the charger is required to meet the peak demands with a low voltage motor.
The power supply or AC/DC voltage converter would have to be 1) a big brick connected by a DC carrying wire to the drill or 2) be physically plugged into the drill battery connector and have an AC cord going to the wall.
if 1) the wire to the drill must carry up to 70 Amps. and be real big and heavy or risk losing a significant amount of power. A resistance loss of 1 V to AC motors is only 1% but the same loss of 1V to a 12V motor is almost 10%. So its a double hit on wire requirements- the lower voltage loss needed and higher current, we'll need a pair of 1/0 welding cable (1/0 is a gauge about 100 times more cross section than 16 ga, the conductor with no insulation is 3/8" dia) to power this thing for a distance of 6 feet from the brick to the drill. Of course from the brick to the wall can be 16 ga power cord.
If 2) then we need a 12V 70Amp power supply in the drill battery socket This would be heavy and inconvenient. Those bricks you have for many electronics devices, laptops, etc now run about 50-100 watts. So scale it up 10 times. It'll be much bigger and heavier than the battery pack it replaces.
For either solution, the cost would also be high, 12V 70A supplies are expensive. and for 1) the cord would be unweildy.
We could solve the problem by running the drill off of higher voltages, like 120VDC, then the currents would be reasonable and the wire sizes much smaller. The shock would then be the 120V battery pack for the cordless mode.
Finally, we could just make a wimpy AC/DC power supply, like 10A at 12V and sell it at a reasonable cost, people would plug it in and be happy it the drill turned. It would work for very light jobs. But when they really tried to drive heavy loads the thing would just hum and stall the motor and possibly burn it up, there's not enough current. Any one you can point to for sale is going to be this way. Not destined for much success.
So it won't work. I've listed the technical issues. If someone knew how to get around them, they'd be selling these things.
The only thing that might work is a hybrid system where a corded pack replacement would have a small battery to provide high current for momentary loads with an integral charger for charging the battery continuously (something like a hybrid car in principle) but I think it would futz out on you quickly if doing a bunch of high torque work... a 5% duty cycle would be unacceptable.
The answer is always the same, as someome mentioned its a current issue.
Batteries can put out low voltage and lots of amps.
AC is practically limited to 15 amps, 1800 w
if you have a cordless tool it has a low voltage motor, 9, 12, 18V typically
Corded tools have 120V AC motors.
A quick survey of corded drill on amazon shows 6, 7, and 8 amp drills.
So around 850 watts on average.
For a 12V cordless drill, it would take 70Amps to reach that power level for similar torque. Batteries can deliver that kind of current, and the wire losses are small due to the wire length being just a few inches.
Now your typical charger, even the fast ones, only put out about 1-2 amps. Its designed to charge continuoulsy for 1,3, or 15 hours to put a full charge in. You can deplete a full charge in a few minutes of high torque work. So a charger would not handle the running current of 70 Amps that might be requred. So a power supply of approximately 30-40 times as much current as the charger is required to meet the peak demands with a low voltage motor.
The power supply or AC/DC voltage converter would have to be 1) a big brick connected by a DC carrying wire to the drill or 2) be physically plugged into the drill battery connector and have an AC cord going to the wall.
if 1) the wire to the drill must carry up to 70 Amps. and be real big and heavy or risk losing a significant amount of power. A resistance loss of 1 V to AC motors is only 1% but the same loss of 1V to a 12V motor is almost 10%. So its a double hit on wire requirements- the lower voltage loss needed and higher current, we'll need a pair of 1/0 welding cable (1/0 is a gauge about 100 times more cross section than 16 ga, the conductor with no insulation is 3/8" dia) to power this thing for a distance of 6 feet from the brick to the drill. Of course from the brick to the wall can be 16 ga power cord.
If 2) then we need a 12V 70Amp power supply in the drill battery socket This would be heavy and inconvenient. Those bricks you have for many electronics devices, laptops, etc now run about 50-100 watts. So scale it up 10 times. It'll be much bigger and heavier than the battery pack it replaces.
For either solution, the cost would also be high, 12V 70A supplies are expensive. and for 1) the cord would be unweildy.
We could solve the problem by running the drill off of higher voltages, like 120VDC, then the currents would be reasonable and the wire sizes much smaller. The shock would then be the 120V battery pack for the cordless mode.
Finally, we could just make a wimpy AC/DC power supply, like 10A at 12V and sell it at a reasonable cost, people would plug it in and be happy it the drill turned. It would work for very light jobs. But when they really tried to drive heavy loads the thing would just hum and stall the motor and possibly burn it up, there's not enough current. Any one you can point to for sale is going to be this way. Not destined for much success.
So it won't work. I've listed the technical issues. If someone knew how to get around them, they'd be selling these things.
The only thing that might work is a hybrid system where a corded pack replacement would have a small battery to provide high current for momentary loads with an integral charger for charging the battery continuously (something like a hybrid car in principle) but I think it would futz out on you quickly if doing a bunch of high torque work... a 5% duty cycle would be unacceptable.
Loring in Katy, TX USA
so, he PM'ed me about this post...
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