Power for dc motor

[mikey553]

Just for information my 120 VAC motor started to move at around 5 VDC. So if you want just to check if the motor is dead or alive you can use a 12 V battery from your car. It is free, how can you beat that. The motor will not make any decent power or RPM at this voltage, but you can check the functionality.

[BCRider]

You can run it on 12v or 24v if you wanted

But only at low speed and somewhat lower peak torque. VERY low speed in the case of the 12v into a 100vdc motor. So certainly not suitable for the grinding he wants to do.

Why not just try something like this ...

https://www.ebay.com/itm/15476171700...4AAOSwHXphxr21

That isn't a full supply. It's just the speed control. It would then still need a power supply. And it would need a properly filtered supply. Not just the bridge rectifier by itself.

Those low cost 24V supplies might work if the motor doesn't need more than 5 amps. Mind you I've used the 12v version of those little black bricks to run LED strip lighting. They aren't as durable as they are rated. If run at all close to their limit they seem to die pretty fast.

Also if it's off a treadmill then it's a pretty sure thing that if loaded hard it'll need more than 5 amps. And that would push towards something more like 2 of THESE 48V 10A supplies in series... and around $100.

Scrounging for old computer supplies might be an option. But you'd need 8 of them using the high current 12V lines to reach 96 volts.

[mikey553]

That isn't a full supply. It's just the speed control. It would then still need a power supply. And it would need a properly filtered supply. Not just the bridge rectifier by itself.

It is a full power supply with 110 VAC input and 0-90 VDC output. But it is rated only 400 W, which may not be sufficient for the motor in question.

Why do we even continue this discussion? I spent an hour today for testing and concluded that nothing more than a bridge rectifier is required, but it looks like the OP is not listening.

[Stu]

It is a full power supply with 110 VAC input and 0-90 VDC output. But it is rated only 400 W, which may not be sufficient for the motor in question.

Why do we even continue this discussion? I spent an hour today for testing and concluded that nothing more than a bridge rectifier is required, but it looks like the OP is not listening.

Go back a half dozen posts, I ordered a bridge rectifier and will post after I try it, Thanks again to all who replied.

[mikey553]

Go back a half dozen posts, I ordered a bridge rectifier and will post after I try it, Thanks again to all who replied.

You said "Will be ordering a 10a diode, to be continued." That is why I made my comment.

[Stu]

You said "Will be ordering a 10a diode, to be continued." That is why I made my comment.

Fair enough.

[BCRider]

It is a full power supply with 110 VAC input and 0-90 VDC output. But it is rated only 400 W, which may not be sufficient for the motor in question.

Why do we even continue this discussion? I spent an hour today for testing and concluded that nothing more than a bridge rectifier is required, but it looks like the OP is not listening.

I saw the size of it and figured that it was only the speed control. The box is only the size of a wall switch box after all. But hey, my favorite exercise is leaping to wrong conclusions...

The specs appear to be misleading too. On one line it says "Scope of application: suitable for DC motors less than 400W". Then a couple of lines lower it says "When the output voltage : DC0～90V the power is ≤120W" Or maybe that's the input power? Hard to say from such a vague translation.

[darryl]

What is the probable application? I might have missed that- but if you're going to spin a grinding wheel for example, you would want a power supply that can regulate rpm. There are several applications that would benefit from control of rpm. In some applications you would not want to have rpm dependent on loading.

What happens if you feed the ac input voltage through a single rectifier- you probably get a lot of rpm until you load it down- then you start to get half wave humming and of course less power than you could be getting from the same input voltage. If you use a full wave bridge you'll have more rpm, but not double, and more power- and also the noise of the pulsating dc. If you add a filter cap you reduce the noise, raise the rpm a little more, and get the greatest amount of power from the motor- while also drawing the most current from the input source. The no-load rpm would be the highest in this case, probably running the motor up to around 10,000 rpm. This is not likely to hurt it, but it could if the armature windings are not tied, epoxied, etc. In normal use, I'd suggest that the motor is probably used in the 3k to 5k rpm range, giving it an estimated capacity of 300 to 500 watts, something like that.