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Old 05-09-2011, 11:06 AM   #1
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DC Speed Control Questions


Hi all,

I just purchased a machine from a buddy of mine, basically a conveyor belt that runs underneath a heating element - sort of an industrial-sized bagel toaster. The heater and the belt are wired independently, and the belt is driven by a 90v DC gearmotor (Dayton 1LPW1), hooked up to a Dayton DC speed control (for which I can't find the part number anywhere).

Anyway, it had been working in his shop up until the moment he unplugged it and brought it into my shop. I plugged it into what I thought was a 110v-20A circuit, switched it on, something in the speed control exploded after about a second, and the breaker tripped. Turned out that the socket I plugged into was running 220v - unlabeled, and through a regular-looking outlet. I re-plugged it into what I knew to be a 110v line, and the same thing happened.

I looked at the circuitry on the speed control, and found a blown 3A/250V fuse. I replaced the fuse, plugged it in, and, of course, the exact same thing happened, blowing the new fuse almost instantly.

I can now see that what I'm pretty sure is a ceramic disc capacitor has also blown (though unfortunately it blew off the side that was labeled with its specs), which looks like the only other damage to the circuit board. My questions are:

1) Should I go ahead and try to replace the capacitor? That would definitely be the cheapest fix.

2) If I need to replace the whole speed control, will any 110v AC-90v DC controller work (e.g. the KB controls that are available fairly cheaply on ebay), or would I need to get the exact Dayton controller that it's currently using (which is quite a bit of money)? I should say that it doesn't need to do anything precise (i.e. the speed doesn't have to be accurate, just variable), and the motor isn't doing a huge amount of work.

I should also say that I'm not an expert on this sort of stuff, but have done my share of rewiring in my shop and am very safety-conscious.

Thanks so much!

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Old 05-09-2011, 11:55 AM   #2
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DC Speed Control Questions


Now that you blew the speed control (or maybe the motor) from overvoltage, exactly what is wrong with it is unpredictable. Replacing the burnt capacitor is part of a trial and error process to getting it fixed. It is uncommon to use a more systematic approach to repairing devices such as speed controls because of the time needed to test individual components (like transistors).

If this is a DC motor, then the "speed control" has other functions in it too. Like converting AC to DC (rectifying). Fundamentally a DC motor speed control raises nd lowers the voltage. For a motor with two wires going into it you can substitute another brand of speed control that delivers the desired voltage with the needed number of amperes. Note that a motor draws more amperes as it starts up compared with running at normal speed.

I suggest that you immediately disconnect (at the panel or in the outlet box) that 120 volt receptacle that has 220 volts going to it.

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Last edited by AllanJ; 05-09-2011 at 12:03 PM.
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Old 05-09-2011, 12:10 PM   #3
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DC Speed Control Questions


It is unlikely that the capacitor is the only problem with the controller.
As far as a controller off ebay you also need to look at the current or HP rating not just the voltage rating.
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Old 05-09-2011, 12:29 PM   #4
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Thanks hugely for your help. Just want to double-check- the controller should have amperage and HP ratings that exceed the specs of the motor, right?

For instance, this motor draws 90V, .35 amps and 1/30 HP. Will a controller that supplies 6 amps max. DC and .5 max. HP work? I'm assuming I want something that puts out more than the motor's specs, rather than less. Or am I wrong?

Thanks again!
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Old 05-09-2011, 02:03 PM   #5
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You are correct.
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Old 05-09-2011, 02:11 PM   #6
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DC Speed Control Questions


Quote:
Originally Posted by korovyov View Post

I plugged it into what I thought was a 110v-20A circuit, switched it on, something in the speed control exploded after about a second, and the breaker tripped. Turned out that the socket I plugged into was running 220v - unlabeled, and through a regular-looking outlet. I re-plugged it into what I knew to be a 110v line, and the same thing happened.

!
a 240 volt receptacle, even if not labeled, is discernible from a 120 volt receptacle.. They are configured differently so you cannot accidentally plug the wrong plug into them.

If it looks like a 20 amp 120 volt recep and it is in fact a 240 volt circuit, I suggest you replace the incorrect receptacle with the correct receptacle.
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Old 05-09-2011, 04:48 PM   #7
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Quote:
Originally Posted by nap View Post
a 240 volt receptacle, even if not labeled, is discernible from a 120 volt receptacle.. They are configured differently so you cannot accidentally plug the wrong plug into them.

If it looks like a 20 amp 120 volt recep and it is in fact a 240 volt circuit, I suggest you replace the incorrect receptacle with the correct receptacle.
I had a similar situation in my house. In the closet in the master bath a water heater was wired with a plug and cord. It was a 20 amp receptacle and plug but was wired to a 240 volt circuit. Like many of the wiring issues I have found and corrected (but I did get the house cheap)

Imagine if someone had plugged a hair dryer into that baby. Would have gotten real hot- for a second!

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