Converter (?) help needed

[Jericho]

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.

 

[Tony Wells]

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.

 

[Jericho]

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

 

[Tony Wells]

That's a 10 microHenry 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 milliHenries.

 

[Jericho]

That's a 10 microHenry 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 milliHenries.

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

 

[Tony Wells]

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.

 

[Jericho]

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.

 

[Jericho]

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.

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.

 

[R.G.]

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.

 

[Jericho]

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.

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...



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.

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.