Thread: Mars Lathe DC motor conversion.

Hi Ewan,

You need one of these

Digital Thermometer Temperature LCD Module Gauge °C/°F | eBay

I couldn't resist, mines on the way.

Here's a mock up of how it should look.

Cheers

Rob

More bad news.......The 1hp motor's bearings are shot, they are pretty quiet when the motor is cold but noisy as once it warms up. Need to find another motor....I'm still sold on the DC, but the small collection of 3hp 3phase motors i have is making me think long and hard about a VFD.....I'll have to put the old 240v motor back on for now, luckily i havn't stripped the old wiring out yet.

That's bad luck Ewan. Maybe you could swap over the bearings from the dud 1.5 HP unit.

You're going to have withdrawal symptoms going back to fixed speed.

There's nothing quite like variable speed once you've experienced it.

It would be good to get a proper industrial grade Baldor DC motor, but they are mega bucks.

Temperature rise on the DC treadmill motors can be pretty severe when you really push them, and that little temperature readout I have ordered will be very handy - just put the probe in the air stream between the two piggy back fans.

Be great to just glance at the gauge and see how things are going.

Cheers

Rob

Yeah, i'll be in a corner in the fetal position shaking by weeks end.......

I have put the old 1/2 horse motor back on, using the same belt ratio's, so i get 140/280/410/560/820/1640. Parting off certainly was not so good at a fixed speed.
The one thing i must say is the ac motor has more power than the 1hp DC, but certainly not as much as the 1 1/2hp....like they say, there is hp and then there is hp.....
The ac motor is about a million years old, a GE with babbitt bearings (hey, the spell check don't know what babbitt is ), It is about the same size as the 3hp motor on my air compressor.

Oh deary me.

Somethings a cookin in the shed, and I think it's my motor.

I seem to have Ewan's syndrome - my DC motor just went "ffffffizzzz, and smoke rose ignominiously towards the roof. Very impressive, DOH.

Seems like while these treadmill motors are OK for general light turning, if you ask them to really do the hard stuff they can't cut it.

I was milling on the lathe all morning with small HSS and no problem.

Switched across to my big 20 mm carbide slot cutter and on the second pass - flash bang thank you mam, that's all for now. Pass the motor please.

Hmm, this is a bit less than I anticipated.

Heavy milling does hammer the guts out of lathes, but the AC unit could take it - just.

Oh well that's life.

Cheers all (having a beer and a think right now)

Rob

Hi Rob & Ewan,

Sorry to hear about your motors. There is nothing more heart breaking than going to all that effort and have something go kaput. This thread has been so so entertaining and I have really enjoyed watching your work in progress and the pics. I hope you guys can both source new motors and that these motors were just on their way out anyway.

Maybe it's just a matter of more DC horses? Perhaps you should consider 2.5HP and above only?

Cheers,

Simon

Hi Simon,

The issue appears to be the severe and fast thermal rise (heat build up) of these motors under heavy load (ie anything greater than 2/3 of the potentiometer range).

I'm not greatly upset, it's par for the course with experimentation/modification.

I was actually looking at using a 12V in line boat bilge blower to push a lot more air through the motor. Not sure what I will do next, as VFD does not come cheap.

Variable speed is awesome and I will certainly keep heading in that direction.

I suppose in treadmill use the motors never get the continuous heavy torque loadings that machinery applies.

Keeps life interesting.

Please sir.......... could I have another free motor ?

Cheers

Rob

Put the old motor back on the lathe and jury rigged the electrics so she goes.

Will finish the big milling job tomorrow.

Found this web page which gives some insight into the problem faced regarding temperature rise.

SCR-Rated DC Motors

So either an SCR rated motor or some seriously heavy duty air flow is required.

How some of the web write ups on treadmill conversion to mills and lathes get by with no fan at all is beyond comprehension.

Poms and yanks

Cheers all

Rob

Not good Rob....

The biggest problem with cooling IMO is the huge restriction of the air flow caused by the armature and magnets. The total cross section of free space would be tiny. I'm wondering if sticking some fins on the outside of the case and putting a cowling over the lot and forcing air through that may be better.

The other option is a larger motor, 2hp and maybe one even of higher voltage may be better at putting up with the heat. I noticed Blu Rock said he had a 2hp 220v motor from a york machine, so they are out there!

Good link on the motors too, thermal runaway can be a problem with any motor, but it just seems to be worse with the DC ones.

Hi Ewan,

I wondered about external cooling fins, but the problem is really the armature and the only way to cool that is a good strong air blast.

Maybe something like this:

4 inch in line vent exhaust blower boat bilge SC 12V dc Seachoice 41841 | eBay

Yes, the air flow is restricted by the armature - but air can flow easily through relatively small gaps.

I haven't given up on this and when I get another motor I am going to try the above fan.

An SCR rated motor would be best, but that may be a bit expensive.

The armature sure was cooked a nice light blue colour


Cheers

Rob

I would think a squirrel cage type blower would be better, and actually force are into the motor rather than suck air through it. If the case and magnets can be cooled surely that will help to cool the armature? Your lucky you can see the damage on yours, mine looks perfect...

As i have several 3hp 3phase motors i am very seriously thinking of getting a huanyang VFD eBay Australia: Buy new & used fashion, electronics & home d and trying it out. I can always put it on the mill if i decide i like the DC better. Not having variable speed is not good once you have a taste of it......

That inverter looks like excellent value and even the shipping is cheap.

Do they reverse?

Can you use that one for a smaller motor?

I know nothing about this type of controller.

Rob

You can get smaller ones Rob, but as long as the motor is smaller than the VFD rating it will work. I have no experience with them but they offer reversing, braking V/F curve adjustment and a handfull of other things. The downside is they only offer about 4-1 speed with decent torque. That why i'm thinking the overkill 3hp, just to get a bit more speed range.
Mind you, i could still have say 50-200, 100-400, 250-1000, 500-2000. Pretty neat range with 4 speed, but it lacks the slow speed....i do have the advantage of a back gear though

I had a look at their web shop and it's weird regarding the postage.

This 3 HP one is $19 US but the others are all about $50 US or more

This one sounds good though for the money.

Rob