# Converter (?) help needed



## Pacer (Jul 31, 2011)

Bill,

Think "treadmill" ---

Get on ebay and search "treadmill motor controller" theres always dozens and with some patience can be bought cheaply.
Like this one for example:
http://cgi.ebay.com/ICON-MC-70-DC-M...=US_Cardio_Treadmills&amp;hash=item2c5e2fb3a0


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## Tony Wells (Jul 31, 2011)

Would benefit from some filtering also, so if you can find some (2) large electrolytic capacitors, add them to the circuit. Google will turn up millions of hits on a basic bridge rectifier circuit.


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## Jericho (Dec 26, 2011)

mechanicalmagic said:


> Bill,
> If you don't need rpm adjust-ability, go to Radio Shack and get a full wave bridge. ($1.39-$2.69) It will convert AC to DC. Be sure to get one rated for more current then your motor. Connect the AC to "AC" and your motor to "DC" on the bridge.
> 
> Knowing full well that there is going to be a debate over my answer, I'll start with these comments. There will be a short time when the voltage output of the bridge will be in excess of 115V. There will also be a time when it's less. It happens so fast, the motor won't care. The average will be 115V. The LOAD will control the current draw, which determines the heat generated. If you are nervous, keep checking the motor for excess heat for a while.
> ...





Tony Wells said:


> Would benefit from some filtering also, so if you can find some (2) large electrolytic capacitors, add them to the circuit. Google will turn up millions of hits on a basic bridge rectifier circuit.



Similar situation for me. Got a treadmill motor 1 HP 6950 rpm@ 120 VDC and I think (since I'm away from it right now) continuous duty 9 amps at 75 VDC. I think it has 5 leads and though I wish now I'd noticed it was DC when I got it at the scrap yard, I didn't get the controller since I assumed( everyone knows what that means)it was AC and the controller was only for speed control. I liked the 6950 RPM and hoped to make a tool post grinder with it.A bridge rectifier is one thing to look at and another to know how to wire it and then there is the 5 motor leads and possibly throwing in some capacitors. Since I am unfamiliar with the component parts, how about a wiring clue or diagram for "Dummies". I was planning on speed control with pulleys at the grinding wheel.


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## cjsamples (Dec 27, 2011)

Jericho said:


> Similar situation for me. Got a treadmill motor 1 HP 6950 rpm@ 120 VDC and I think ...


I really don't want to try that treadmill out!! Sure it isn't some much slower RPM? Of course it might be a CNC Treadmill.

Chris


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## Tony Wells (Dec 27, 2011)

Just guessing a little here, but I'm thinking 4 leads from the motor. Should have a red and a black for the power and a couple of smaller wires from a sensor inside that you can ignore.

Gotta head to work, but if nobody else does before I get back in, I'll either sketch a drawing or find one. You might google 120 volt dc powere supply. Most of those will probably be overkill for running a tm motor though, and can be simplified a bit.


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## Jericho (Dec 27, 2011)

cjsamples said:


> I really don't want to try that treadmill out!! Sure it isn't some much slower RPM? Of course it might be a CNC Treadmill.
> 
> Chris



LOL Chris. it has a toothed pulley on the end and I'm sure wasn't a direct drive.Most had been destroyed , the frame etc by the scrap yard.As I recall, the red and black leads go to the perimeter of the motor and the other leads go amongst the winding areas.I thought they might be used for a lower voltage (i.e. as transformer taps) or sensors to feedback info to the controller.Sure do wish now I'd had a screwdriver with me to remove that high dollar controller.
Another electrical question for me is:   Can bridge rectifiers be wired in parallel to increase ampacity?That would seem to be the easiest way to wire it as long as I don't load it heavily all the time. also would 60 mfd 480 V be large enough for the capacitor and a 10,000 ohm 2 watt bleed resistor suffice for smoothing the voltage as I have to get those anyway for a solid state 3 phaser?


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## Jericho (Dec 27, 2011)

Tony Wells said:


> Just guessing a little here, but I'm thinking 4 leads from the motor. Should have a red and a black for the power and a couple of smaller wires from a sensor inside that you can ignore.
> 
> Gotta head to work, but if nobody else does before I get back in, I'll either sketch a drawing or find one. You might google 120 volt dc powere supply. Most of those will probably be overkill for running a tm motor though, and can be simplified a bit.



Tony:I did a google for DC power supplies and for 1 hp I'm thinking $400 and up. Too much for me and the treadmill controllers on Ebay start at $50 and up with no instructions or external dial speed controls, etc.. I don't 100% know the motor works but it looks and smells good.No apparently baked windings.The size is what was appealing to me and the price for bridge rectifiers seems to be a great start. Please respond to question in my other remarks concerning wiring bridge rectifier, capacitor and bleed resistor.Thanks.Jasper


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## Tony Wells (Dec 27, 2011)

I didn't mean to buy one, I meant to build one. Should be pretty cheap, actually. I wouldn't try to parallel bridges. Large enough bridges are available. And don't use a resistor, use a choke as in the diagram below. If you can confirm that the motor is a permanent magnet motor, with no field coil windings, then we can get specific with the components. Treadmill power circuits use a choke. Too bad you didn't snag that too. There is a catch to this, but until I hear back from you on the specifics, we won't discuss it. One thing at a time.







If you choose to build such a filter circuit, be sure to use an  iron-core inductor for maximum inductance, and one with thick enough  wire to safely handle the full rated current of power supply.  Inductors  used for the purpose of filtering are sometimes referred to as _chokes_,  because they "choke" AC ripple voltage from getting to the load.  If a  suitable choke cannot be obtained, the secondary winding of a step-down  power transformer like the type used to step 120 volts AC down to 12 or 6  volts AC in the low-voltage power supply may be used.  Leave the  primary (120 volt) winding open


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## Jericho (Dec 27, 2011)

Thanks for the responses Tony. As soon as I return home from the holidays with family, I'll get all the info I can feed you off the motor and we can proceed.Appreciate the help.
Jasper


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## Jericho (Jan 5, 2012)

Tony Wells said:


> I didn't mean to buy one, I meant to build one. Should be pretty cheap, actually. I wouldn't try to parallel bridges. Large enough bridges are available. And don't use a resistor, use a choke as in the diagram below. If you can confirm that the motor is a permanent magnet motor, with no field coil windings, then we can get specific with the components. Treadmill power circuits use a choke. Too bad you didn't snag that too. There is a catch to this, but until I hear back from you on the specifics, we won't discuss it. One thing at a time.
> 
> 
> 
> ...


......

http://s1206.photobucket.com/albums/bb457/Methuselah3/?action=view&current=100_0697-Copy.jpg

http://s1206.photobucket.com/albums/bb457/Methuselah3/?action=view&current=081.jpg

http://s1206.photobucket.com/albums/bb457/Methuselah3/?action=view&current=082.jpg

Tony,
 Hopefully the above links will show the faceplate picture of the motor and a transformer. I went back to the scrapyard but couldn't find any electronic parts for the build. The 120 V DC permanent magnet motor has 4 leads. Two (red/black) go to the perimeter of the motor for the brushes and 2 leads ( blue) attach to what I presume is a heat detector circuit as they connect close to the end plate to a small common device on the housing. While at the scrapyard I picked up a transformer for possible usage.I have several oil filled capacitors mostly 60 µfd and at least 1 30 µfd that I've gathered for my phaser project but that's another story. Will start a new thread for that.On your diagram, I conclude the following. Left most symbol is 120 v AC.Rectangular with diodes is the bridge. Transformer is to be used if chokes not available???? and the cross connections are chokes??????. I tried to look for chokes and bridges on the internet but couldn't find any big enough as I thought you had described so you may have to rub my nose on the location for me to see them and give me numbers for amps/volt ratings required.I saw some small "torroidal" chokes on the computer boards at the scrapyard and wouldn't have known what they were except for my attempt at research on the web. Thanks for your help.
Jasper


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## Jericho (Jan 5, 2012)

EdK said:


> Jasper,
> 
> Make sure that motor turns in the correct direction for your needs. It's only a clockwise turning motor and can't be reversed because of the brushes in it.
> 
> Ed



Thanks for the tip Ed. I see that the motor needs to turn clockwise (looking at the pulley end away from the brushes) from the ways the impeller on the fan works but heretofore would have thought it was only a matter of changing wires . First DC motor for me and I got it because of size to make a tool post mounted grinder .Can I hook it to a 12 V battery to confirm rotational direction with no load?

I've seen all the warning about grit on my lathe especially the ways. I'm trying to make some homemade bullet swaging dies that require precision fits of piston to cylinder configurations and grinding is the only way I see to do it. Next obstacle seems to be wheel size. Most wheel sizes start at 6 ". Lot of wheel to be slinging on a 10L tool post.I'm gonna browse the grinding forums some more for clues.


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## Tony Wells (Jan 5, 2012)

Jerico, the "cross connects" are the electrolytic filter capacitors. They are polarized and should match polarity with the markings on the bridge. If you can find a large choke, fine, but a 120/12 stepdown transformer will sub as a choke. Just be sure you use the primary (120 side). Ignore, but make safe from shorts on the secondary. Wire nuts, etc.


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## Jericho (Jan 6, 2012)

Tony Wells said:


> Jerico, the "cross connects" are the electrolytic filter capacitors. They are polarized and should match polarity with the markings on the bridge. If you can find a large choke, fine, but a 120/12 stepdown transformer will sub as a choke. Just be sure you use the primary (120 side). Ignore, but make safe from shorts on the secondary. Wire nuts, etc.



Will this work as a choke
http://search.digikey.com/us/en/pro...ND/1144863?wt.z_cat_cid=Dxn_US_US2011_Catlink


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## Tony Wells (Jan 6, 2012)

That's a 10 _micro_Henry Choke. You'd probably do ok with it, as this is not a demanding circuit as far as the purity of the DC is, but if you can, get one on the order of  few hundred _milli_Henries.


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## Jericho (Jan 6, 2012)

Tony Wells said:


> That's a 10 _micro_Henry Choke. You'd probably do ok with it, as this is not a demanding circuit as far as the purity of the DC is, but if you can, get one on the order of  few hundred _milli_Henries.



OK , so now I've searched Digi-key and Allied Electronics and find nothing on the order of a few hundred milliHenries. This is one from Digikey is 1 mH and has apparently two sets of windings on a common core. How are 4 wires hooked up as a choke. I can't find anything on the order of hundreds of mH and the ones I find have low ampacity. What am I missing here? Large µf capacitors( beer can looking) are mostly low voltage for car amplifiers.

http://search.digikey.com/us/en/products/744824101/732-1449-ND/1638854


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## Tony Wells (Jan 7, 2012)

Skip the choke if you want to. Use 100 mfd electrolytic capacitors rated at least 200 volts. You should be fine. If it doesn't act like you want, we can revisit the choke. Or if you have an old, dead UPS (battery backup), take the transformer and wire in the primary where the choke should be. It's just there to add a little inductance that will smooth the ripple a bit.


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## Jericho (Jan 28, 2012)

Back at the drawing board on my DC treadmill motor. Finally got my bridge rectifier and capacitors in on the slow boat from China and built the DC output  circuit as suggested without the choke. Get a good output @110V dc. That was the easy part. I'm getting about a 3/4 " "flame" from the brushes that heats the end of the motor housing etc  too hot to touch in less than a minute. Motor runs smooth and fast like I wanted but the excessive arc from the brushes can't work. Armature has wear grooves on it from former usage(seen also as lines in the brushes) and I am wondering if that sort of lack of smoothness is causing the arc.Any thoughts before I take it to a motor shop. Minimal investment so far and really would like to keep it that way.
P.S. I don't have an oscilloscope so my observation of good DC is by reading 110V on and electric meter.


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## Jericho (Mar 21, 2012)

Tony , I finally got the dc converter built similar to your specs. Going to have to get a variable speed control on it as it runs about 150% of rated speed unloaded.Found some large waveform ( so they were described that only have a primary side winding) and some 1100 mfd capacitors about the size of an oil filter . It stopped the flame throwing from the brushes but I need to get it hooked to a load and some speed control. Am going to see if a light dimmer can handle the amps. If not than a variable speed controller for a router.












Tony Wells said:


> Skip the choke if you want to. Use 100 mfd electrolytic capacitors rated at least 200 volts. You should be fine. If it doesn't act like you want, we can revisit the choke. Or if you have an old, dead UPS (battery backup), take the transformer and wire in the primary where the choke should be. It's just there to add a little inductance that will smooth the ripple a bit.


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## R.G. (Mar 23, 2012)

Bill Gruby said:


> I found an old set of prints to machine a Shaper to use in the lathe. It uses a Bodine Reduction Motor. I have one here that reduces 1725 RPM to 96 RPM. Problem is it is for 115 VDC. Is there a converter from 115 VAC to 115 VDC ?



It's amazing how this dovetails with some other stuff I'm doing.

Get yourself a KBLC-19PM DC motor controller from ebay for $25-$50. It's a pro DC motor speed controller that takes in 115VAC, makes DC out of it, and controls the amount the motor gets to give you variable speed. YOu may or may not want variable speed, but electronically, full wave rectifiying 115Vac gives you peaks of 170Vdc. 

This is what mechanicalmagic meant. However, the average of a 170V peak sine wave (i.e. what you get from the wall) when full wave rectified is 103-105V average. This is fine for the motor if it wants 115Vdc. 

However, putting filter caps on it converts this to 170Vdc by charging the caps up at the peaks and them holding the peaks through the valleys. This will be something your motor probably won't like. 


> If a  suitable choke cannot be obtained, the secondary winding of a  step-down  power transformer like the type used to step 120 volts AC  down to 12 or 6  volts AC in the low-voltage power supply may be used.   Leave the  primary (120 volt) winding open


This is a bad idea. Transformers are designed for no DC current flow through them. Chokes are designed for DC to flow. Using a transformer secondary for a choke will saturate the core, and you'll get nearly no effective filtering from it unless you take the trannie apart and rewind/restack it with a gap. I used to design transformers and chokes for a living. 

A choke is OK, but not great for a DC motor; the treadmills use them (I think!) for suppressing electronic noise emissions. The motor winding itself is a big choke electronically. An additional choke can make things worse by making the commutator and brushes arc badly...



> I'm getting about a 3/4 " "flame" from the brushes that heats the end  of the motor housing etc  too hot to touch in less than a minute. Motor  runs smooth and fast like I wanted but the excessive arc from the  brushes can't work. Armature has wear grooves on it from former  usage(seen also as lines in the brushes) and I am wondering if that sort  of lack of smoothness is causing the arc.



It may be that the motor is being run the wrong direction. DC motors run both ways, but motors design for specific direction have the brushes cheated one direction to minimize wear and arcing in that direction. It's better than the purely balanced position for brushes in a reversable, but it makes arcing worse in the non-preferred direction. 

What happens to the arcing when you reverse the DC polarity to the motor? Is it much less? If so, your motor is intended for the least-arcing direction rotation.


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## Jericho (Apr 19, 2012)

R.G. said:


> It's amazing how this dovetails with some other stuff I'm doing.
> 
> Get yourself a KBLC-19PM DC motor controller from ebay for $25-$50. It's a pro DC motor speed controller that takes in 115VAC, makes DC out of it, and controls the amount the motor gets to give you variable speed. YOu may or may not want variable speed, but electronically, full wave rectifiying 115Vac gives you peaks of 170Vdc.
> 
> ...



Been away for couple weeks .   R.G.:::my latest setup is made from some parts scavenged from some DC panels out of some larger device found at the scrapyard(my favorite shopping center)I got two 10 amp .5 mH waveform (?) devices which look like transformers to me except they only have one set of windings( two wires to use). Also got some 1100 µfd capacitors that look like oil filter size. The smaller electrolytic capacitors that I used popped like a party favor on use.I wired the two 5mH waveforms in parallel and the capacitor in the circuit and got rid of the extreme arcing on the brushes but I still have more than it had when used on the power supply at the local motor repair shop. The motor revved so fast I didn't check it for RPM as it sounded( not a good measuring stick I know) faster than it had before when I'd clocked the 6950 rpm motor at over 9000.Next I need to control speed by varying the AC voltage into the rectifier and again I'm clueless as to how and do that. Suggestions? Seems like the router speed controls that are available most likely reduce frequency rather than voltage for AC motors.Don't KNOW that but suspect. Really don't want to buy one without knowing and what's the likely hood of a store salesman knowing. To them like me, it's sort of magic and electronics is a whole different ball of wax than electricity.


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## mrbreezeet1 (Dec 29, 2014)

Tony Wells said:


> Jerico, the "cross connects" are the electrolytic filter capacitors. They are polarized and should match polarity with the markings on the bridge. If you can find a large choke, fine, but a 120/12 stepdown transformer will sub as a choke. Just be sure you use the primary (120 side). Ignore, but make safe from shorts on the secondary. Wire nuts, etc.



OK, I'm going to butt in here and ask a question, just for my knowledge, 
So you would was the primary side of the t-former?
I thought I had read somewhere someone said to use the secondary side. 
Thanks
Tony,


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## cathead (Jan 4, 2015)

If you want to vary the DC voltage, a good way would be to use a
variac on the AC side of the circuit.  It is basically a variable
transformer.  I use one a lot in the shop mostly for my 4.5 inch
angle grinder.  It is very simple to vary AC voltages and not so with DC.  
The AC voltage can be varied from 0 to 100% of line voltage or more and will transfer
these relative voltages through your power supply circuit and you will have
infinitely variable direct current.


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