Anyone familiar with using DC injection to anti-condenstate?

We have used dc injection on drives to keep shafts steady when not running. Has anyone ever used dc injection as a form of anti-condensation in a existing motor that does not have built in heater?

How much volts? How long? Things to watch out for motor wise?

Robert

Are you want to hold the motor shaft by dc injection.?
or If I underdtand the word condensation like you want to keep the motor dry?

This is done occasionally with good success. However, the DC amps will be much lower than for DC braking or even DC hold.

I would start very low, just a few amps, and measure motor temp after being idle for 4+ hours. Adjust upward from there until you get the standby temp you want. Remember, the outer shell of the motor will be a few degrees cooler than the windings.

This is a rather energy-wasteful technique these days. I would consider the next time this motor is repaired to have it epoxy or polyester VPI'd. That's Vacuum Pressure Impregnation. I've seen motors run UNDER WATER with this treatment! Be sure you use a motor shop skilled in doing this. There are plenty of wannabe experts out there.

Arik it is for anti-condensation. I used the "shaft still" with DC injection as a reference of my past experience.

Dick, thanks. Would there be a formula that I could use rather than "try and check temp in 4 hours"? Could I take known motor resistance and dc volts for an E(sq)/R? This is an existing app with about 50 motors which all have ASDs. Customer wants to explore this as quick remedy in moisture heavy area.

Here's another idea but one that may generate some safety issues which must be addressed.

If these motors are all on ASD's or VFD's, you could command zero speed instead of stopping. By adjusting the zero speed drive output voltage, you can control how warm you keep the motors.

I almost cring at this proposal, tho, because a motor at zero speed can easily be mistaken for a motor that is off. If a maintenance person should come into contact with the motor leads at zero speed, a nasty shock can result. You would have to be very careful to post warnings on the motors to cover this. Come to think of it, you probably should place the same warnings on a motor which has DC warming, as well.

Depending on the drive technology, commanding zero speed might cause the motors to resist turning. If the application requires motor freewheeling, this is not your best choice. The DC option will also build some resistance to rotation but not very much if done properly.

The other issue with using zero speed is that you may need a certain voltage level at very low speeds to get the torque you need to run. If you reduce this voltage by setting the zero speed voltage down, you will have running problems.

Much of this depends on the software available in the drives. Actually, some drives have DC injection capability and it may be that some even have a way to set continuous adjustable DC when stopped.

Not sure you can use this but it sure would be worth a look. You wouldn't have to spend anything except for the warning labels. Just imagine how much you would be appreciated for such a clever solution! I'm thinking that that just might be a joke!

Oh, almost forgot! Regarding calculating the input watts for warming, sure you can do that but it wouldn't get you anything unless you know the motor's thermal losses. I don't know of anywhere where you could get such info.

Trial and error isn't elegant but sometimes its your only option!

Used to do that in olden times...

Had some motors installed outdooors, in a place where the climate is not unlike Seattle's (in my previous life )

If you had not run'em for a couple of days, better hi-pot'em before you start... humidity was a killer.

So we just connected an autotransformer across any two leads and adjusted it so the current would not exceed the rated. Doesn't take that much when the motor is not spinning, about 10 - 20 V, that's it.

Of course, one should make sure that nobody can engage the motor contactor while it is being "dried" like that. Might be a spectacular view otherwise.