[Kobra000]

Hey guys whats up,im sorry for putting this here if this is the wrong forum for such a question...please tell me and i will correct asap

i was wondering if one of you gurus out there an help me out..lots of dudes here with invaluable amounts of knowledge.

i have selected a tread mill motor for a very simple lathe project and possibly the foundation of a simple mill.
i heard these types of motors are very well suited for this type of work as the torque is constant in all speeds
in case your curious or if it will help the motor is
P.M.D.C Motor
model c3364b4035 M
P/N M-314571
2.80HP TREADMILL DUTY @ 130VDC
2.60HP CONT. DUTY @ 110V/1940WATTS
OPEN CONST EXTERNAL FAN.)

i think its a great motor and iv seen lots of lathe build projects by others basically doing the same thing
.but..im having a heck of a time finding a ac to dc speed control in the following config for a perm mag motor
ac input 110v to 220v (regular wall plug juice)
output 110v-130v @ 1940watts...( though i only want a variable speed controller with a 1000-1500 watt max..a online voltage,wattage calc said @ 110v dc at 1000w ill be pulling 9 amps.give or take,@ 1500w =13.6 amps give or take.
i dont think anything more than 1000w-1500w would be needed,for the following reasons

1. at full load of 110v dc @ 1940 watts ill be pulling 17.5 amps
(again according to online voltage,wattage,,calculator found here Volts/Amps/Watts Converter)...

2..i dont need the full 5700rpm that the motor is rated at ..whats a good lathe speed 850 to 1000 rpm max?...

3.i dont need all the heat all this power would produce. (that would just end up killing all the components and be money down the drain..dont you agree?)


so my questions are these

does anyone know of a place that offers plans on building your own ac to dc motor speed control,or a reputable seller of such that doesnt want both my kidneys in exchange for one?
(i hate going ebay cause they have nothing but Chinese sellers selling this kinda stuff..though they are cheap, they take for ever and day for your item to get to you..plus no clue about quality of item..dont want it blowing up in the 3 hours cause of crap workmanship know what i mean Vern?)

is it bad to "under power" or under current a perm mag motor such as this by giving it only 5 to 13 amps when its saying it needs 18?
could under currenting damage the engine?
will i not have enough torque to do a proper latheing work?
must i use PWM on this motor? (heard that PWM is used on brushless motors only)


well thats about all i can think of...please feel free to give thoughts,suggestions and such..any and all information is greatly appreciated.

thanks very much

keith.

[CitizenOfDreams]

What made you choose a DC motor? A 3HP DC drive will be rare and expensive, I suspect. You may be better off changing your plans and going for a 3-phase motor and a VFD.

[Kobra000]

What made you choose a DC motor? A 3HP DC drive will be rare and expensive, I suspect. You may be better off changing your plans and going for a 3-phase motor and a VFD.

my fiances made me choose a dc motor....ac motors are $150,$250 and $300 ( at farm supply stores,poultry processing supply stores) and up here in south Mississippi.
.i purchased the 2.8 HP and a 3.0 HP tread mill motors for 20$ and $35 each..ac motors are just not in my budget...plus i figured dc motors would be easier to hook up...provided they make a 110vac to 110vdc converter /speed control out there somewhere.

[CitizenOfDreams]

Looks like the money you saved on the motor you will have to spend on the drive. DC drives of that power start at $200 used. 3HP VFD drives are $150 brand new.

Here are some Baldor 2HP DC drives on eBay:
Baldor BC154 Adjustable Speed Control DC Motor Drive 2HP 115 230V 69615 | eBay

Baldor BC154 Adjustable Speed Control DC Motor Drive 2HP 115 230V 74220 | eBay

[Kobra000]

Here are some Baldor 2HP DC drives on eBay:
Baldor BC154 Adjustable Speed Control DC Motor Drive 2HP 115 230V 69615 | eBay

Baldor BC154 Adjustable Speed Control DC Motor Drive 2HP 115 230V 74220 | eBay

those are really excellent..but sadly far out of my price range. .im limited to a 30 -50 dollar solution.
thank you for posting those i really appreciate it...

[Kobra000]

i did find this and its slightly in my budget range...just wish the wattage was higher. using the calculator a linked it says at 110v dc @ 600 watts thats only 5.45 amps..not exactly somethign to balk at but not exactly the best.

Input AC110V Output DC0 110V Motor Speed Controller 600W ZX6 611 | eBay

[CitizenOfDreams]

Input AC110V Output DC0 110V Motor Speed Controller 600W ZX6 611 | eBay

I would seriously advise against that one. I'm using a smaller version of it (rated at 300 "Chinese watts") for the spindle in my desktop CNC machine. Had all kinds of problems with it and finally had to bypass its current protection circuit. There is no way on Earth the "600W" one will handle your big motor without blowing up or tripping.

[CitizenOfDreams]

those are really excellent..but sadly far out of my price range. .im limited to a 30 -50 dollar solution.
thank you for posting those i really appreciate it...

Unfortunately, I don't see any way to do it in the $50 range, unless you find a very good deal for a used drive. Keep looking, you may run across one.

[Kobra000]

I would seriously advise against that one. I'm using a smaller version of it (rated at 300 "Chinese watts") for the spindle in my desktop CNC machine. Had all kinds of problems with it and finally had to bypass its current protection circuit. There is no way on Earth the "600W" one will handle your big motor without blowing up or tripping.

whoa! im glad you told me..ill steer clear of that one....there was something i read about a full wave rectifier with center tap on yahoo answers...fell wanted to power a battleship horn via 110vdc...do you know of any data bases that show plans and whatnot? perhaps i can get lucky there.

[Kobra000]

I would seriously advise against that one. I'm using a smaller version of it (rated at 300 "Chinese watts") for the spindle in my desktop CNC machine. Had all kinds of problems with it and finally had to bypass its current protection circuit. There is no way on Earth the "600W" one will handle your big motor without blowing up or tripping.

are they just a crappy built unit?

[CitizenOfDreams]

whoa! im glad you told me..ill steer clear of that one....there was something i read about a full wave rectifier with center tap on yahoo answers...fell wanted to power a battleship horn via 110vdc...do you know of any data bases that show plans and whatnot? perhaps i can get lucky there.

Well, if you have a large (10-20A) variac laying around you could add a rectifier bridge to it and get a crude DC motor drive. Just don't turn the variac past 50% or so.

[CitizenOfDreams]

are they just a crappy built unit?

It's well built, but not well designed. And the power rating is very optimistic to say the least. (And even if it wasn't, you would not want to use a 600W drive for a 2000W motor.)

[Kobra000]

so the current draw of this 2.8 hp motor is going to be so much that "under powering" it isnt even going to be an option right?...whatever i connect to it thats say like 5 or 10 amps is going to be overloaded because of the 18amp current draw of the motor correct? (so that means trip disconnects and possiably it going up in magic smoke)

[CitizenOfDreams]

so the current draw of this 2.8 hp motor is going to be so much that "under powering" it isnt even going to be an option right?...whatever i connect to it thats say like 5 or 10 amps is going to be overloaded because of the 18amp current draw of the motor correct? (so that means trip disconnects and possiably it going up in magic smoke)

Yes, you got the idea. Even if you load the motor lightly so it does not draw as much current when it's running, the startup or braking current may trip the protection, blow the fuse, or "let the magic smoke out".

Well, I'm off to bed. I'm sure other CNC experts will chime in in the morning. Best of luck with your project!

[neilw20]

If you have a small variac for the field and a big one for the armature power, each with a low cost rectifier block, you will be able to have lots of low down torque or slick high speed at the flick of a wrist. Reduce field voltage and max speed goes up. Increase field for slower operation.
Higher speeds are quite useful on a lathe. Wish mine would 2500 RPM, like the big one i had that did 3500.
Without speed control electronics, things like constant surface speed cutting are a thing to be wished for, but for general use two variacs and a double pole breaker/switch to turn it on/off will work just fine, or you just cut the AC power.

[Kobra000]

Yes, you got the idea. Even if you load the motor lightly so it does not draw as much current when it's running, the startup or braking current may trip the protection, blow the fuse, or "let the magic smoke out".

Well, I'm off to bed. I'm sure other CNC experts will chime in in the morning. Best of luck with your project!

so i have to go all out and find a 110vdc 18 amp power supply. or perhaps a ac to dc Variac @ 18 amps to control this thing. just might start looking on ebay for treadmill control boards and whatnot...best to go with what it orginally had i guess.

- - - Updated - - -

Yes, you got the idea. Even if you load the motor lightly so it does not draw as much current when it's running, the startup or braking current may trip the protection, blow the fuse, or "let the magic smoke out".

Well, I'm off to bed. I'm sure other CNC experts will chime in in the morning. Best of luck with your project!

thanks man..i appreciate it.

[Kobra000]

If you have a small variac for the field and a big one for the armature power, each with a low cost rectifier block, you will be able to have lots of low down torque or slick high speed at the flick of a wrist. Reduce field voltage and max speed goes up. Increase field for slower operation.
Higher speeds are quite useful on a lathe. Wish mine would 2500 RPM, like the big one i had that did 3500.
Without speed control electronics, things like constant surface speed cutting are a thing to be wished for, but for general use two variacs and a double pole breaker/switch to turn it on/off will work just fine, or you just cut the AC power.

yes i had seen some variacs on ebay..but dont really know enough about them...can they go ac to dc and supply lots of current? do you have a Variac in mind possibly?

[neilw20]

AC in, Variable AC out. 0 to about 110% of input.
You put a bridge rectifier on the output - AC ins converted to DC by the rectifier
NEW Diode Bridge Rectifier KBPC5010 50A 1000V F | eBay
and mount on a big heatsink.
Or buy one with a heatsink
QL100A Heatsink Bridge Rectifier Diode 1600V 100A Amp | eBay
It doesn't matter if you oversize the one for the field, but just a smaller variac for the field will do.

this one is too expensive. You will find cheaper ones around.
http://www.ebay.com.au/itm/Superior-...item2eb5066f1d

[Kobra000]

If you have a small variac for the field and a big one for the armature power, each with a low cost rectifier block, you will be able to have lots of low down torque or slick high speed at the flick of a wrist. Reduce field voltage and max speed goes up. Increase field for slower operation.
Higher speeds are quite useful on a lathe. Wish mine would 2500 RPM, like the big one i had that did 3500.
Without speed control electronics, things like constant surface speed cutting are a thing to be wished for, but for general use two variacs and a double pole breaker/switch to turn it on/off will work just fine, or you just cut the AC power.

cut the ac power?...can you elaborate please?

[neilw20]

Turn it off. Just a single on/off switch on the AC supply. Like turning off your vacuum cleaner.