12v Drill hacked to powerfeed for Mini Mill

[rodw]

Don't forget that a motor will only draw maximum power at maximum load (torque). So if you are going to use the ratchet on a drill motor to protect from over travel, you will not be anywhere near a full load situation so power draw (amps) won't be anywhere near the rated capacity.

MCRIPPPer, if you had a surplus laptop power supply rated at 3.5 to 5 amps, I would give it a go. Worst case is it won't work as they usually have overload protection. Remember that typically in a circuit you would have at least 20% headroom in any specs so your 12 amp drill will probably only pull 10 maximum and on a SX2, probably a lot less than that. The only way you would know is if you put an amp meter on it while it was running.

I had an electric motor tested recently, it was rated at 12 amps on the plate and it was only drawing 6 under load which the repairer said was about normal. Work that out!

I would not get too worried about how much current it draws, my experience with cordless drills is that you know when they are working hard cos you can smell the battery and they don't last very long at that power level. The power feed is never going to tax it at that level and I expect it will be close to idle.

 

[MCRIPPPer]

it is true it will draw less as the rpm increases. at start up it will pull large amps if it is suddenly flipped on. i am having issues making a power system for my power feed because it wants so much power. it was a dewalt 18v drill. i measured the resistance of the motor and got 1.5 ohm, so when i connect the 18v to the motor, it is no wonder why it sparks and the wires even heat up (same size wires as the motor came with.) with the low resistance, the motor runs on very low voltage. it will happily move the table running only on a single AA cell. so maybe i will try to find a lower voltage source so it doesn't draw so much power.

 

[ZipSnipe]

Ok I am confused, when I read the beginning of this post, the NC momentary switch is on the ground of the speed pot according to Troyo in post #14.
But in his diagram on post #33 he mentions shorting the wiper and the load , which to me means you would need a NO momentary switch, am I right?

 

[rodw]

Ok I am confused, when I read the beginning of this post, the NC momentary switch is on the ground of the speed pot according to Troyo in post #14.
But in his diagram on post #33 he mentions shorting the wiper and the load , which to me means you would need a NO momentary switch, am I right?

I think you got it right. Somewhere, Troyco says his original drawing was wrong. I have not had time to play but in my mind, it makes sense to be able to short out the resistance by closing a NO switch between the central wiper and one end of the pot which is equivalent to turning the knob to full scale.

 

[TroyO]

I'm not sure that's what I did in the end. I may be able to get a chance to open it up to be sure this weekend but I suspect that the "best method" for the GoBabyGo switch is to disconnect the GND from the pot, which should let the wiper be pulled high through the potentiometer no matter it's position.

LOL, I just went back and re-read my own posts.... Post #14 of this thread is exactly what I ended up doing, I'm pretty-much-almost-sure. ;-)

I updated the Schematic from earlier, sorry I forgot about how I did it! LOL, I had the best intentions of documenting everything but there didn't seem to be all that much interets at the time so I dropped it.

 

[ZipSnipe]

Thanx again Troy for your help and great contribution to the DIY spirit !! I have copied almost all that you have done with the exception that my drill motor was 14 volt and my controller is a 5 amp even though I ordered a 10 amp but ended up with a 5 amp. So we will see what happens, just waiting on the power supply to arrive.

 

[ZipSnipe]

Power supply came in and go it hooked up and am happy to say, works almost perfect !!!! The only things wrong were, the lighted power switch I bought is 125 volts and not 12 volts so the light doesn't work. And the momentary switch is not hooked up. But other than that the speeds are right on and I like it. I will replace the power switch tomorrow and give the momentary switch two more test tries tomorrow.

 

[Davo J]

I think if you end up with a 5 amp one you would have grounds to raise an eBay dispute if the supplier won't send you a new one.

That's a big power draw you are looking at. What power supply are you going to use?

I agree, just start a paypal dispute and get you full money back as what you got is not what you paid for.
I have had 100% success with getting back what I wanted with the few problems I have had over the years.

Dave

 

[canadianhorsepower]

Thanx again Troy for your help and great contribution to the DIY spirit !! I have copied almost all that you have done with the exception that my drill motor was 14 volt and my controller is a 5 amp even though I ordered a 10 amp but ended up with a 5 amp. So we will see what happens, just waiting on the power supply to arrive.

If you really want a 10 amp you only have to replace both transistor mounted on the heat sink to a higher rating
as for your lighted switch use it as on and off on your power supply source
and you'll be fine
if you need clarifying please ask

 

[ZipSnipe]

Well had everything hooked up and it looks like 5 amps is not enough to move my table if the controller really is 5 amps. It will move it some but then fades out and doesn't want to turn the motor. So I am assuming the controller is not pulling the amps that the motor needs.

So Luc, all I need to do is change out the transistor?

I have two , one says this

P75NF75 &
CZ010 T
MAR 237
ST 3 (ST is slanted and the 3 is in a circle with a small symbol next to it)

The other transistor says this

L7812CV
G401X V6
CHN 249
ST 3 (same as above)

 

[Hopper]

You might hook a 12volt car or large motorbike battery up to it just to make sure the power supply is the problem. If it runs ok on the battery, you know the motor and mechanism are all good.

 

[John Rudd]

Well had everything hooked up and it looks like 5 amps is not enough to move my table if the controller really is 5 amps. It will move it some but then fades out and doesn't want to turn the motor. So I am assuming the controller is not pulling the amps that the motor needs.

So Luc, all I need to do is change out the transistor?

I have two , one says this

P75NF75 &
CZ010 T
MAR 237
ST 3 (ST is slanted and the 3 is in a circle with a small symbol next to it)

The other transistor says this

L7812CV
G401X V6
CHN 249
ST 3 (same as above)

ZS,
Those two devices you list, one is a mosfet ( first one) the other device is just a plain old 12 v regulator..

If the speed controller is rated for 5 amps then changing the mosfet device isnt going to help, the speedo is probably designed for 5 amps and is done with selective components...

You got a link to the speedo you bought?

I looked at the link for your speedo....Doesnt look like there's anything exciting about it in terms of current limiting...

RodW, Can you see anything on your board that looks like it could limit current to the mosfet?

Might be easier to buy or trade up your speedo for one of a suitable rating that meets your needs.....

 

[ZipSnipe]

You are correct John, upon further research I found the data sheet for the power regulator chip, it is rated at 1.5 amp. So wouldn't this mean the board is actually a 12v 1.5 amp speed controller rather than the 12 v 5 amp that the seller claimed?

 

[purpleknif]

Got a readout on my power supply and running in the low gear range on the drill I haven't pulled 4 amps yet

 

[ZipSnipe]

Purpleknif is yours connected to the table yet? Mine ran fine until I connected it to the table.


I decided to remake my coupling, it was tapped out of whack so it might be causing some binding, I will also remake my mounting plate as my hole for the x axis screw was also off.

 

[phansen39]

The 7812 only powers the circuit not the motor. If you look at the 8 pin ic it is probably a ne555. The P75NF75 is rated at 80 amps. This powers the motor. With the small heatsink and small circuit traces it cannot source enough current. If it is a ne555 looks like it drives the gate of the P75NF75 through a resistor. Might not have enough current output pulsed to fully turn on the gate.

 

[ZipSnipe]

Thanx for the info Phansen, I will be concentrating on fixing my screw ups with the table /powerfeed alignment.

My biggest mistake was when I went to make the mounting plate, I forgot to do my deduction for my edgefinder, I also tried to use a measurement for the leadscrew hole by just measuring it while it hung in place instead of measuring the supplied handle mount.

Luckily I discovered I don't have to remake the plate but will instead tap out the lead screw hole and plug it with a threaded insert with some Threadlock. Mill it flat and re drill for the leadscrew hole.

I won't to eliminate all mechanical binding before I go blaming the electronics again. It works fine when not connected to the table , so once the binding is worked out, it should hopefully work smooth.

 

[purpleknif]

Yes mine is connected.. I have a Real Bull mill and it has an extra handwheel on the left end so I just took the handle off, made a bushing and couple it wit a socket and a square tapped to go in the drill

 

[ZipSnipe]

Hey Phansen, I want to correct my earlier statement, it does not do a dead crawl. In fact its pretty iffy at its slowest speed. I am trying to determine the ground lead coming off the speed pot. I tried reading cont. between the pots contacts and ground but no luck. I assume that maybe one of the chips opens the ground to the pot when its not powered up. I want to try adding a resistor to the ground like Troyo mentions earlier in the thread.

I also corrected the alignment issue with the much better new coupling and lowered the motor mount so it sits more in line with the lead screw, this was a big improvement. However with little effort I can hold the table and the clutch starts to kick in. I am going to adjust the clutch setting one more time see if that helps, it looks like I have it set mid way but its possible I have the clutch cover on in the wrong spot which would mean looks are deceiving.

 

[John Rudd]

The 7812 only powers the circuit not the motor. If you look at the 8 pin ic it is probably a ne555. The P75NF75 is rated at 80 amps. This powers the motor. With the small heatsink and small circuit traces it cannot source enough current. If it is a ne555 looks like it drives the gate of the P75NF75 through a resistor. Might not have enough current output pulsed to fully turn on the gate.

Mosfets are voltage driven devices not current like a transistor that has Hfe...

Like I said before, if the current is limted to 5 amps as the seller claims, then there must be a way in which it does this via a sensing network...Else if the mosfet is driven from the 555 then there isnt really a limit only the mosftet's Rds....and the power supply's current capability