Heatsink on a DC motor?

[Jamie Buxton]

I've got a cyclone with a Leeson motor whose nameplate says it will work on 208-230 volts. I'm now in a 3-phase building, so it gets 208 or more on a good day. On a not-so-good day like today (when the temperature is very high, and electric usage is very high), the line voltage drops down to 200 or so. The cyclone draws more current at the lower voltage, and eventually gets hot enough to trip the over-temperature protection. Short of fixing the electric company, what can I do? Can I bolt radiating fins to the motor? Mount an external fan to it?

[Steve Strickler]

Most folks do not realize how serious of a problem this is... is your computer on a voltage regulator?

My computer's UPS's have given-up...it just sits and beeps while trying to keep up with voltage demand. I have a neighbor that pulled out an AC cord the other day that was charred on the end, the cord was hot, it was pulling too much current for too long.

A good web site that talks about this (and solutions) is here http://www.elect-spec.com/faqbrwn.htm

A 220 regulator to support that kind of usage is $$$. Have you made sure that the pipeline (wiring) to the motor is large enough. Breaker, wiring to the outlet, plug, wire from plug to motor?

I have a Leeson motors too, I hope I do not run into this. Good luck!

[Rick Christopherson]

Because your motor is rated for either 208 or 240 volt 3-phase, you could use a boost transformer to bring the voltage up to 240 volts. These are pretty common. However, because a single-phase 208 to 240 transformer is more common, you may find it cheaper to use three of them instead of finding a single, 3-phase transformer.

[Jamie Buxton]

Rick, boost transformer looks like a good solution. I'll look for one Monday.

[Jamie Buxton]

Rick -- further thinking about boost transformers....

They carry VA ratings based, I think, on normal operating conditions. Electrical motors have a start-up current which is substantially larger than the normal operating current. Do I size the transformer for the start-up current or for the normal current? My first instinct is to size it for the larger current, but I know these transformers are often used for powering 230-volt airconditioner compressor motors in 3-phase buildings where they'd only get 208. That is, the manufacturer expects the transformer to be doing exactly what I'm going to be doing with it -- driving a motor, complete with start-up surges. So maybe I can select the transformer on the basis of the normal operating current?

[Jim O'Dell]

I guess I look at things a little differenty, but have you called your electric service? Could be a transformer problem. I would think that they should be providing you the standard current, and if something is wrong, then THEY should fix it. Is there something about 3 phase I don't understand? (that is likely :rolleyes: ) If this is a standard 220 volt single phase motor, I would not want to have to buy something else to make it work. If it is a 3 phase motor and this voltage is normal for 3 phase, I would think that the motor would be built to work properly with it. I'd call the electric service. Jim.

[Jamie Buxton]

Jim, it is a single-phase motor. The nameplate says that it will work from 208 volts to 230. My guess is that the cyclone designer wanted to get as much work out of the motor as he could (more CFM results in more sales), so his impeller design loads the motor nearly to its full rated power at 230 volts, which is the usual voltage seen in most home shops. He may have allowed a little wiggle room for lower supply voltages, too. However, I'll bet he didn't design for (or maybe it is "test at") a 208 volt supply. Or maybe he allowed no wiggle room for a supply voltage even a little bit below 208.

The electric company does have some allowance on the voltage it provides. A nominally 208-volt line may be a few volts low, and still be within their spec. As I see it, the problem is that I'm using the cyclone in a way which it should tolerate, but it doesn't. The manufacturer (Woodsucker) seems to be out of business, so my only course seems to be to fix the problem myself. As I read up on boost transformers, one does seem like it should fix the problem.

[Rick Christopherson]

I didn't realize this was a single-phase motor. You wouldn't need a 3-phase transformer, nor would you need more than one single-phase transformer. like I suggested above. Even though it is rated for 208-volt operation, this is down at the lower limit of the motor, whereas a 3-phase motor would be more attune to this. This is why it is overheating.

This reaffirms the original assertion of getting a boost transformer.

You should not need to oversize the transformer to account for the startup current, because the motor windings are experiencing the same spike. The only time you would need to derate the transformer like this is if the motor had a rapid duty cycle with frequent restarts over a short period of time. This is not an issue for a DC.

However, you may wish to use a larger transformer and install it so that the output goes to a new load center for other 240-volt tools. If you choose this route, please let me know so that I can tell you how to handle the grounding of the panel. It is late at night, but I think this is treated as a main load center (separately derived system) where the ground and neutral are bonded, which is not the same as a sub-panel.

(After a couple of minutes of thought, I am 95% confident in this assertion. However, this is a completely moot point if the new panel is strictly 240-volt loads without a neutral. There is no reason why you would want 120 volts on this "boost panel"; hence, no need for a neutral.)

[Tom Jones III]

FYI, you mentioned that the power company has some wriggle room in the voltage they produce. A thread a long time ago stated that +/- 10% of the voltage is considered within normal operating range. This means that 240V service can be from 216V through 264V and be considered within normal parameters! I noticed when I put 240V in my shop that it usually runs 254V.

[Don Baer]

The bost tranformers are a good solution for this. Size em for the Full load amps. If you need a 5 volt boost and the motor FLA is 15 amps then you would use a 75 VA transformer.