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Totally not Unitronics related, but just a question for the community in general....

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Hey All,

I have a small piece of equipment that I am updating.

it has three small DC gearmotors,  two of which are variable speed using small 90VDC motor controllers.
and I am replacing these with 3-phase gearmotors and using AC VFD's.
the third is a small (1/17th hp) DC motor that is for a mechanical adjustment, and is run full voltage,
forward or reverse with a selector switch arrangement that switches polarity to the motor.

I plan on keeping this as-is, but the caveat is that it's power source comes from the Field supply on one of the DC motor controllers.

All that said, I'm looking for a simple 90VDC supply...

Warner makes some little 90VDC modules designed for brake/clutch operation, I thought about using something like that.

Or do I simply feed 120VAC (fused of course) into a bridge rectifier, which without a filter cap yields a little over 100VDC.

The motor is only run intermittently, so I don't feel the slight overvoltage will damage the motor (and the specs from the old DC controller say the Field supply is 100VDC anyway).

Anyone have thoughts or suggestions?  😵


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John, you know about my antique radio hobby.  When they made a battery eliminator or the +90V B+ line with exactly the circuit you describe you get 160 VDC out.  They used a high wattage ballast resistor sized to the load to knock the voltage down.  It's got to with the peak of the sine wave being about 167 volts.

You ought to take one of the old 90V controllers and re-purpose it as a 90V supply.  If you jump the center of the speed pot terminal to the pot supply you'll get your 90V.


Joe T.

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As for me  - you  must use two 48VDC standard AC/DC power supply.  On standard PS present voltage correction pot.

Then you can easly set 45VDC on both. Then (45VDC)+(45VDC)=90VDC.

But max current of PS must be sutable for used motor. 

Retrofitting with standard component - best solution.




Or you can use DIN rail mount PS.

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11 hours ago, Joe Tauser said:

You ought to take one of the old 90V controllers and re-purpose it as a 90V supply.

I'm with Joe on this, but also from the point of view that if the controller is any good, it will have inbuilt ramping which can be set quite short, but will greatly benefit motor/drive-train durability.

cheers, Aus

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Thanks all for the suggestions...

I'm still leaning for the little Warner clutch/brake power supply, it's compact and plugs into a 8-pin relay socket.

says its good for 1.25 amps at 90VDC, my little gear-motor says it draws 0.85 amps.....


I'm trying to get away from these little DC drive boards, I have a lot of moisture induced failures with these (the slightest dampness and they shut down, let them dry and they work again,  just a big nuisance...), and they also take up a little more "floor-space" in my limited panel.

Also, a common off the shelf item....



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2 hours ago, John_R said:

I'm still leaning for the little Warner clutch/brake power supply

You need small power supply. But


2 hours ago, John_R said:

moisture induced failures with these


2 hours ago, John_R said:

DC drive boards

CBC-801 is non isolated triac rectifire with fixed output voltage.

Then user must to use well isolated selector switch for motor or use isolation transformer (if moisture  present near system).


Is it isolation transformer present in original diagram for power DC motor?

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Yes, the CBC-801 is a non isolated, floating DC supply, so yes , care will have to be taken with the switch/wiring.

The original design has a step-down transformer (480-120) that feeds power to the DC drive boards (if you consider that isolation), and the DC boards are also non isolated...

Same situation would apply for powering whatever type of power supply I come up with.

Unless I roll my own, if I can find a transformer with about 65VAC secondary, with a full wave bridge and filter cap that should give me right around 90VDC.  But hat defeats the thought process of using off the shelf parts...

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