Thread: Mars Lathe DC motor conversion.

Oh dear.....I must be getting better, my mind is starting to come up with all sorts of ideas. Firstly, thanks to the switching suggestions earlier in the thread. Unlike most of you I do not need or want to keep the current switches as they are fully independent of the lathe. My thoughts are that I might set the lathe up as planned with the kbic controller, and work on a pic or atmega(I know arduino's are toys, but I like them.....) Based pwm controller with a full set of mosfets for forwards and reverse, sensor feedback for speed regulation, etc etc. The programming is probably all out there already, it may just need some cutting and pasting to get it right. (ok so it may not be that easy....)I can then use the kbic controller on a drillpress or something where reversing is not needed.

Just to prove there is much I dont know, I recall a factory half wave rectifier that was made with 8 parallel diodes. Though I think that were 80amp diodes with a total rating of 200amps, not sure about the short circuit amps.

Cant explain that.

Stuart

Originally Posted by Stustoys

Just to prove there is much I dont know, I recall a factory half wave rectifier that was made with 8 parallel diodes. Though I think that were 80amp diodes with a total rating of 200amps, not sure about the short circuit amps.

Cant explain that.

Stuart

I think the theory goes that if you have enough semiconductors in parallel vs the required current it statistically evens out, in that case 640A of devices vs 200A required. I seem to remember a car battery tester with hundreds of 1A diodes in series/parallel for load testing, although I was never sure why they tried that approach when a dummy load resistor would have worked. As a kid I saved up for a 240V MIG welder that had two pairs of parallel diodes and a centre tapped transformer: it used to blow the diodes like popcorn at the high setting so I fitted two diodes of the required current and it worked fine ever after.

Hi all,

Not wanting to hijack Ewan's thread, but I have been given the OK to put up some photo's and info on my CQ9325 lathe conversion to DC motor - to kick along the thread a bit.

I'm using a 2 HP 180 v DC motor and a KBI-240 controller.

The attached photo's tell the story so far.

On top of the headstock is a little metal box to house the tacho and forward reverse switch - that used to be the gearbox for the treadmill incline motor until I milled it's guts out and got it to where it is now

The motor pulley is all new and made by me. New belt sized and fitted.

The DC motor is in a welded up/fabricated cradle fitted onto the existing pivot adjuster plate so I can use some of the original belt ratios as required.

The controller inverter housing is that XT power supply case hanging off of the large angle aluminum heat sink. The case has external fuses for AC and DC and will have a rocker power switch.

All the wiring will run across to the existing terminal block on the belt drive enclosure and will be connected through the original AC magnetic actuator switch for safety - this has to be reset after power failure.

Just waiting for some thermal compound to mount the controller and I will wire it all up.

Also there is a photo of a Hall effect sensor I got off Ebay for about $6 - now $5

Seems to work OK and has pretty little LEDs to brighten up your day.

Just what Ewan needs - get well soon.

Hall Sensor Module M44 Switch for Magnetic Field Detecting 16mA DC 0-15V | eBay

Left LED is power on/active and right LED indicates switch status.

FYI the bodgy looking rear chip guard on my poor hard working Chinese lathe is actually a Brownbuilt steel shelf I tacked on as a temporary measure. Still there years later - it works OK.

Cheers

Rob

Hi Rob,

I had a grin from ear to ear looking at your lathe! I'm excited for you! Looks great and I bet you can't wait ti fire it up.
With the motor and pulley combination, what speed range do you anticipate?

Good work.

Simon

Hi Simon,

It's certainly taken a while to get this far.

I don't have a millimetre to spare on some stuff, but waiting for components to arrive from Ebay isn't all bad as it certainly gives you time to rethink stuff.

If my calculations are right the maximum spindle speed should be around the 2100 RPM mark.

This will vary slightly depending on the difference in belt ride height of the various V pulleys.

I had to go for a larger motor pulley after realising that the motor would have it's best power at 60% of RPM (limited motor speed level) and that the pulley I had already machined up was therefore too small.

Going to a larger motor pulley will also give much better grip, so it's a good thing. Just have to watch I don't stress out the toolpost too much.

In addition to the 2100 maximum speed (which I need as I mill on my lathe - with carbide) I will have other lower pulley ratios available which together with the bottom end torque of the DC motor, should provide stump pulling power if needed.

Fingers crossed it all works out.

Cheers

Rob

Hi Rob,

Taking into account the ride height difference on the pulleys? Wow you are getting technical! 2100 RPM crickey! my lathe only goes to 1400 rpm but like you said, you use your lathe for milling too.

Have you noticed that some of the stuff coming out of HongKong (especially with free postage) seems to take forever? I am wondering if they send stuff to countries in batches and that they weight until they get enough orders before sending or something. Whenever I have ordered stuff from US or UK it comes within 2 weeks but HK can take up to 5 - 6 weeks. I ordered something and paid for it on 10 August and I'm still waiting. The seller gives some crap story about it should arrive anytime....

I don't mind waiting if I know it's going to take that long, I factor the time in so I'm not waiting for the part to complete the next part of the project. I'm slowly wising up to this now. If I need anything from HK then I try to look 2 months ahead!

Simon

Hi Simon,

The original lathe speed was 1800 RPM and getting a bit more speed out of this will help a bit with carbide, which needs a high cutting speed for a good finish.

1800 is OK, but faster will be better.

Yes, UK and USA are fast on delivery, but Asia is pretty variable. Some are good but most are slooooow.

They mark the stuff as posted almost immediately, but then it comes by row boat I think.

Sometimes I wonder if I did the right thing buying small value items from overseas - just to save $1.

Difference in belt/pulley ride hight can have a bigger effect than you realise - can vary speeds by 50 RPM or so.

Cheers

Rob

Hi Rob,
Looks good! I see what you mean about pulling clean air in from the pulley end of the motor. Are you going to make a cover for the motor? I would be worried about chip sticking to it. As my lathe has a countershaft my motor is behind the chip tray so i have all the space in the world. I think a foot break/switch is a good idea too and i might make sure i can implement one into the wiring with a latching relay easily.

Here is the link for the braking resister size Dynamic Braking Resistors Calculations - Engineers Edge this site is actually handing for all sorts of calculations. By my math for my 1.5hp motor i need a 1.2w resister at 118k max. The bigger the resister in rated current the smaller it needs to be in ohms, presumably as a bigger resister can cope with more current (dah) and dissipate more heat? The current running through the resister at 100k is tiny, like .3w.KBIC240 braking.jpg

Attached is the pic of the breaking circuit from the KBIC manual. It is pretty fuzzy on any details.....

Originally Posted by nearnexus

Difference in belt/pulley ride hight can have a bigger effect than you realise - can vary speeds by 50 RPM or so.

Hi Rob,

I was only having fun about the rpm calcs! Hey when it comes to RPM, it's like horse power, more the merrier! Even if you don't use it. And before everyone points out that the spindle bearings, chuck etc may not be designed for it etc etc.... I'm not talking 3,000 or 4,000 rpm but a little more than it came as standard can only be an added bonus for a home modification.

PS I'm stuck in the shed servicing the Misses car! Now, if only I could then invoice her for services rendered! Alas, she would probably do the same to me!

Simon

Originally Posted by Ueee

Hi Rob,
Looks good! I see what you mean about pulling clean air in from the pulley end of the motor. Are you going to make a cover for the motor?

..

Hi Ewan,

I trust you are improving. I have the other two hall sensors put aside for when I do the linisher - so they will be used.

Yes, I have a metal cover I glued over the fans (see photo), for the reason you suggested. The other AC motor also got sprayed with hot chips and grindings, but the plastic fan in the end didn't seem to suffer too greatly.

Maybe one day I will finish off the rear chip guard properly and include a motor cover

Dynamic braking is something I will tackle later if necessary. Thanks for that link. It will be interesting to see how quickly the DC drive system comes to a halt. With the AC motor it was almost instantaneous. Would DC be any different in the same circumstances ?

Cheers

Rob

I'm not sure how fast it would be Rob. I was going to have a play with my smaller motor and maybe the electric drill just to see what it is like. Mind you i don't want my machine to stop too quick as i have a threaded spindle nose!

I'm getting there, but 1/2 hour in front of the puter is about all i can cope with for now.

Ewan, are you sure of those figures? 1.5hp is a bit over 1Kw, but you only need a 1.2W resistor to disipate the rotational power?
I'm not electrically minded but I would have thought that a power in = power out rule of thumb would apply here - that is, the braking resistor would need to be about the same rating as the motor if you intend slowing things down in roughly the same time as you speed them up.
Have you lost a multiplier (eg kW instead of W)?
Perhaps for power disipation you need to look at a heating element of some sort like a bank of light bulbs or an old style electric jug.
Find an old electric urn of some sort - at least after a day's shed activity you can get a cup of tea from it...

Michael

Michael I totally agree with you.......but thats what the maths says from that engineers site i linked. The only ? may be that the motor power is not mentioned as to what it should be in- Amps watts etc. However i worked it out in amps then converted the resister to watts. I figure the resister has to be sized to get hot......otherwise there would be no loss of energy other than from friction. When i am feeling up to it i will do some tests. Probably next week at this rate.