Thread: Mars Lathe DC motor conversion.

Hi Ewan,

If it's only one winding, then I'd guess it's a choke, probably just for harmonic filtering.

Regards
Ray

I think they are in most Treadmills. I think it's an RF choke which helps reduce higher frequency noise on the line supply?


Simon

I imagine there would be a near riot at the gym if it interfered with an ipod!!!!

Makes sense i guess. There was no ferrite ring on the motor line with this one. It seems to be wired in on the DC side, but its hard to tell as a whole lot of stuff terminates into what looks to be a solid state relay. It also has no markings so it a bit hard to tell what it is doing and connecting to what. Plus its a double sided board so trying to trace things is a nightmare!

Originally Posted by Ueee

Thanks Andy,
I was amazed at the amount of high power resisters on ebay, so finding one is not a problem.
I had a rummage yesterday and today and found nearly everything i need, relays, switches, switched pot for the speed control, tranny for 12v DC supply etc. I just have to put it all together and make up a diode bridge to get 12v DC for the controls and Fan. I'm keeping as much as i can low voltage and using several relays to switch the AC and braking resistor.

Now for a quick game of "what is it", this tranny looking thing was in one of the treadmills. But, it only has 1 coil (only one pair of wires) It measures 1 ohm resistance, my guess is a big-### resistor? No markings anywhere. Its about a 4" cube.

My guess is that its an Inductor or Choke (same thing )

I ventured out today and picked up a few things from Jaycar and the KB power resistors for the controller. As soon as i got home i hooked the controller up to the motor and turned her on. Something seemed really wrong....the top speed was pitiful! After adjusting and fiddling i got the top speed up somewhat, but it still seemed a bit slow. I checked the out put voltage...220v what the? So i put the flywheel on the motor and set up the tacho to check.....well what a surprise i got! The motor was doing a touch over 6000 rpm.... Wow its smooth! So i re-adjusted the settings to bring the speed down and i am very happy.

I then set about making a switch box for all the electronics. .6 gal with ally trim. Tried my hand at welding the corners with the mig....its ok if you don't look too hard....i'm still not used to the mig.

I have OFF/FWD/REV, speed knob, emergency cut off, AC fuse, tacho and switches for the motor cooling fan and to turn the brake on/off. Yikes! no wonder i couldn't find a big enough box at Jaycar.

Looks good Ewan.

I'm on the last stretch with my conversion as well.

Heavily into wiring up the system.

One more day may just do it.

I just hope this all works as planned.

Cheers

Rob

Hi Ewan,

That's looking great! IRT motors and their smoothness, it never ceases to amaze me how smooth both the DC and 3 phase motors are compared to the regular single phase motor counterparts. I would love to have seen the look on your face when you read the optical RPM reading! 6000 RPM gives you a huge range and huge torque from wo to go!

The enclosure looks great. Not sure if you were going for the contemporary industrial look but I like it. Looks great!

Simon

I have my DC controller crammed into an old XT PC power supply case, with the tacho display mounted separately to suit with my Chinese lathe configuration, but seeing Ewan's metal box gave me an idea.

You could just buy one of those cheap rectangular $10 metal tool boxes Mitre 10 etc have and take off the handle and mount it vertically with the lid being the front. Hinges open nicely, add a few vent holes and presto great little controller box.

Save a lot of stuffing around making one.

Cheers

Rob

That toolbox idea is great Rob, would have saved me some time.
Although the motor revs rather happily to 6k i will stop it at about 3k. All the higher speed will do is wear it out quickly. I will already have to re-gear my lathe about 2-1 to make up for the extra motor speed.

I filled the box up with most of the wiring today, i am just waiting on the braking resister and then i can hook up its relay etc, and clean up the wiring. It all works as it should, the motor can be switched on/off with the speed pot or the main switch, and it runs just as well in reverse as it does forwards. Mind you the only reversing i can see it doing will be for threading.
I am using a 7812 reg for the 12v controls and fan and although i have it on a small heatsink it is getting pretty hot with the fan running. My rectified DC voltage is up near 19v so its a bit high for the fan unregulated. I'll just have to wait and see, the 7812 should be good to 1 amp and the fan is only .65a so its got me .

On a totally different train of thought i have been thinking of my "perfect" PWM controller, and have been wondering if a MOSFET could be used instead of a relay to control the braking, giving PWM adjustable braking speeds......

Hi Ewan,

The 7812 will run hot with 19V input, You can calulate the dissipation as follows, (19-12) - 7 volts drop, 7 * 0.65 = 4.5 watts, heatsink looks like about 10C/watt, so you'd expect something like 45C above ambient?

A good choice is to chuck the 78xx series, and use one the more modern 3 pin SMPS like this one, R-78C12-1.0 Recom Power Inc | 945-1392-5-ND | DigiKey

They run cool and don't need a heatsink.

Looking at your wiring, I don't see any strain relief anywhere, but full marks for heatshrinking all the terminations

Whenever I run wiring to a hinged door, I run it as an "L" shaped loom with the vertical part of the "L" close to ( and parallel to ) the hinge line, that way you aren't flexing the wires when the door opens/closes.

Regards
Ray

Good to see your conversion is going well Ewan.

I wired mine up today, and I've hit a snag.

I'm not sure what's going on.

The motor starts up,and blows either the AC or DC fuse almost straight away.

I've checked the connections and they look OK, so I'm not sure if it's a bad controller or what.

I will run the multimeter over the output tomorrow and see what's happening.

I have another motor I can try as well. Will check the output voltage first.

Cheers

Rob

Thanks Ray, i'll look into getting a few of those regs. 45deg sounds about right, although i didn't check it with anything but my fingers. Still need to anchor all of the wiring, i have plenty of length with most of it to do as you suggest. I have found in the past (the hard way) that the only way to makes sure a crimp fitting doesnt come loose is heatshrink, so thats why it is everywhere.....

Well I've tracked down my problem with the DC lathe conversion.

I sure can pick them, the donor DC motor is stuffed - arcing inside at anything over about 5 amp.

So it's back to square one, do not pass GO and collect $200 - go directly to Jail.

Wouldn't it just give you the ####s?

I have another motor that I know works (1.5 HP) but I now have to rework the entire motor mount and fans to fit it.

I am more than slightly peeved at this point in time.

Cheers

Rob

Originally Posted by nearnexus

Well I've tracked down my problem with the DC lathe conversion.

I sure can pick them, the donor DC motor is stuffed - arcing inside at anything over about 5 amp.

So it's back to square one, do not pass GO and collect $200 - go directly to Jail.

Wouldn't it just give you the ####s?

I have another motor that I know works (1.5 HP) but I now have to rework the entire motor mount and fans to fit it.

I am more than slightly peeved at this point in time.

Cheers

Rob

Sounds like that motor used to be owned by someone at BASTARDS INC.!

What a PITA. Sorry to hear that Rob.

Ewan, looking good. I love heat shrink, especially the stuff with the inbuilt glue!

Cheers,

Simon