Need electronics help to slow a drill

[peteski]

You mean R11 (is it 1501 or 1051?) not R1 right? R1 is on the hi voltage side (Far right in closeup) and reads 823

Yes, R11 - sorry!  Didn't proof read my post carefully.  The value is unclear in the photo.  Usually there is some clue as to which way is up on those numbers.  in this example I didn't  see anything identifiable.  Maybe the shape of "5" givers a clue?  I was going by the orientation of the nearby resistors of the same physical size.

1501 is 1500 ohms (a standard resistor value).
1051 is 1050 ohms (a non standard value, but often resistors that have 4-digit values are precision resistors with odd values, so it might be feasible for it to be 1050 ohms).

With it being either value, replacing it with a 750 ohm resistor (or piggybacking a 1500 ohm resistor) should shift the low voltage limit without blowing anything up).  If you are going the piggyback route, and don't have a 1500 ohm resistor handy, you could try using a 1000 ohm resistor.  Again, should not blow up anything.  All we want to verify is that the drill runs slower than it did unmodified.

[u18b]

Just out of curiosity.....

Would a sewing machine pedal work to do what you want?

It's a house voltage side rheostat (I think).   Voltage goes from the wall to the machine.   As you press the pedal, more voltage goes to the machine.

[eja]

Beat me to it . ...

It works well. I have used a sewing machine pedal for my Dremal tool for years.  Easy, instant speed control.

[Lemosteam]

The resistor piggyback worked.  I can't measure the RPM difference but it feels slower than when I first turned it on.  No heat from the motor or smoke anywhere.  I was not able to find a 1501 in my stash of resistors but I did find a 1621 so the value went to 780 ohms instead of 750.  What would be the next step in resistors to lower the speed more?

@Iain see this thread for the drill motor: https://www.therailwire.net/forum/index.php?topic=49127.0

[peteski]

Just out of curiosity.....

Would a sewing machine pedal work to do what you want?

It's a house voltage side rheostat (I think).   Voltage goes from the wall to the machine.   As you press the pedal, more voltage goes to the machine.

That type of a device (that lowers 120V line voltage can work with motors which are 120V motors, running directly from the wall outlet (Dremell, sewing machine, and similar).

What John has is a power tool with a low-voltage DC motor.  This is no Dremel or a sewing machine. It has a fairly complex universal-voltage switching power supply which  accepts 100-240VAC voltage and produces a variable low-voltage DC output.  feeding AC voltage to this power supply through a speed pedal (which simply reduces line voltage) would likely just cause the power supply to go into shutdown (insufficient AC input voltage).

[peteski]

The resistor piggyback worked.  I can't measure the RPM difference but it feels slower than when I first turned it on.  No heat from the motor or smoke anywhere.  I was not able to find a 1501 in my stash of resistors but I did find a 1621 so the value went to 780 ohms instead of 750.  What would be the next step in resistors to lower the speed more?

@Iain see this thread for the drill motor: https://www.therailwire.net/forum/index.php?topic=49127.0

Excellent!  As far as smoking goes, I don't thing there is a chance of the motor smoking. If anything, the power supply will fry!  Just kidding John. 

Since the experiment worked as expected, lets go low. Remove the resistor you piggybacked, then replace it with any resistor in the range of 680-1000 ohms.

[Iain]

Tried a Google search, wasn't very successful in sourcing one of these here drills.

[Point353]

Tried a Google search, wasn't very successful in sourcing one of these here drills.

Try a Google search for Walfront Micro Electric Drill Kit.

[mmagliaro]

My reference to "smoking" with this drill was meant to imply that as you get that drill running slower and slower, it is probably going to be pretty low on torque, and will be easy to stall.  I'm dubious of how robust that motor will be if you stall it for any length of time.  Now that you have it running more slowly, do you have any feel for how powerful it is (or if it has less oomph?)  You would probably have to cut or drill some metal, but maybe just drilling small holes in a 2x4 at low vs higher speed would show the difference.

[Lemosteam]

I was able to drill two 1/8" holes in steel and oak with it. Stalled in the metal like any other drill upon breakthrough, when the burrs catch. No issue in the oak.

My 18v ryobi drill does the same thing, except it has a clutch.

 Nice nice thing it has is a moto brake. It stops intantly when switched off. It also has a slide switch with fwd, off rev.

I didn't feel any negative vibes from it that would make me concerned.

[peteski]

What were the results of the latest modification? Did it get the speed low enough for you?

[Lemosteam]

Actually, I left it with my last resistor. I guess I was happy with that. I would say that it is 2/3 the speed it was before the change. I mean 8500 rpm is fairly slow for a drill and 2/3 of that is 5600 rpm, so that is substantially slower to me.

I realize you really want to experiment, and I still might.. Maybe this weekend. I'm still not sure about your latest piggyback resistor value of 608-1000 since I already plunked a 1620 ohm resistor on there, or maybe I don't understand what piggybacking is actually doing.

I'm so confused.

[peteski]

Actually, I left it with my last resistor. I guess I was happy with that. I would say that it is 2/3 the speed it was before the change. I mean 8500 rpm is fairly slow for a drill and 2/3 of that is 5600 rpm, so that is substantially slower to me.

John, if you are happy with the speed, just leave it alone.

I realize you really want to experiment, and I still might.. Maybe this weekend. I'm still not sure about your latest piggyback resistor value of 608-1000 since I already plunked a 1620 ohm resistor on there, or maybe I don't understand what piggybacking is actually doing.

I'm so confused.

I guess my original statement "Remove the resistor you piggybacked, then replace it with any resistor in the range of 680-1000 ohms." was not clear enough.
I meant to remove the original resistor you piggybacked onto the one on the circuit board, and and piggyback a new resistor of lower value.  Not to add a 3rd resistor to that piggybacked "pile". 

But adding a 3rd resistor would also work to lower the total resistance.  But again, if you are happy with the low speed as it is now, leave it alone.