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DC Motor Starter Fried?

ChipChaff

Cast Iron
Joined
Dec 15, 2007
Location
Mid-Wisconsin
Hope this belongs here. I have machine that runs on a 5HP 250v DC motor. The person I bought it from was running it on 220 AC using a rectifier. I ran it off and on like that for maybe 100 hours max over a couple of years and didn't touch it for a couple of years after that. I needed to use it so I hooked it up. When I pushed the ON button I heard a mechanical chattering then the motor spun up as it normally did but I saw smoke coming from the starter housing. I shut it off. It's a very old machine and I wonder whether there are components which have deteriorated, like leaky capacitors or some such. The wiring in the box is packed tight and I have zero electrical experience.

The motor itself is a massive work of art and I would like to keep it if at all possible.

Can I just buy a starter for a 5 HP DC motor and hook it up? Is it a mistake to run a 250V motor on 220? Any other advice?

Thanks.
 
You have provided very little solid information....Some added info might be useful, such as pictures of the innards, data plates, etc.

However

Of course, smoke is a bad sign, but may be due to any number of causes of varying degree of "problem", including insects being roasted, moisture in the box, failures, overloads, dust, etc, etc.

A machine expecting 250V DC will, if loaded to maximum, draw more current at 220V than at 250V, simply because the same power at lower voltage means more current. But motors draw what they need, so at reduced load, the current may be fine.

Starting is a heavy load until the motor gets up to speed, so low voltage can be a factor, and at start, motors already draw excess current as they accelerate. With low voltage, the start may be extended, so excess current is drawn for a longer time.
 
Not my day - tried to edit my post and deleted it. Try again:

Thanks for the comment. I will pull out what I can and take images of anything interesting.

Bottom line though - if the starter is toast, can I buy a new one and plug it in or am I going to have to have the existing starter repaired? I ran searches and only found DC staryers up to 2 HP.

I suppose 3 can repower since it's connected to the machine by only a belt, but that seems to be an unnecessary expenses and I do so like the big retro beast it started with.
 
Its not the common practice to start a DC motor with only a relay, the inrush current would destroy everything including the comm and brushes of the DC motor. All DC motor should be feed low voltage on start up and the voltage slowly increased to the speed you need for a certain job...Phil
 
5 HP is on the borderline, maybe over it, depending. Smaller motors are less issue. Obviously this one has been started like that for quite a while, and the 220V is already a reduced voltage.

Maybe that caught up with it, maybe something else related to long term storage is going on.
 
Even a 1/2 hp would need a control (shunt wound), I have never seen a engineer build a cross the line start of a DC motor. Until the arm makes counter emf the arm is a dead short. Even in the old times (before ww2) The simple controls would be grids and a timing devise to control the ram up of the motor even if no speed control was involved...Phil
 
True.... there was generally a reason for that outside of the motor itself, however, so the option really was not there. The motor might be for traction, and a slow start was needed, it might drive something like a rolling mill, that was not going to start fast, so the motor might indeed be damaged, etc. Or there was a need for speed control, so the facility was going to be there and the slow start was a natural part of that.

In other cases, a whole set of motors had to start together, as with a printing press. Any speed change had to affect all at once, but each motor may have been specially timed and adjusted to keep in step with all the others at a particular operating speed..


It seems that whatever this thing did, it may have been dropped on the line to start, for many years..... But we really do not know if this one may have had a reduced voltage start, anyway. That has not come up.

It could explain smoke, though..... resistors get hot, and cook dust etc. Especially if the start resistance step does not get cut out.
 
I'm not able to upload to imgur so no pics but I have the data from the plate, some of which contradicts what the previous owner told me and had stuck on the starter box with those embossed letter plastic strips -

General Electric
Model 5B225A125 DC Motor
Type B
Frame 225
Winding: Shunt
Speed 1750
Amp: 11.4
Volts: 230
Enclosure: Open
Duty: Continuous
HP: 3
Hour: 40 degrees C Rise
Service Factor 1.15 at rated volts

Don't know if this sheds any light on the ultimate issue of what I need to do to get the motor running, but a 3HP motor swap seems more feasible than a 5 HP. Wonder why the previous owner thought it was 5 HP or why he felt the need to tell me it was.
 
I'm not able to upload to imgur so no pics but I have the data from the plate, some of which contradicts what the previous owner told me and had stuck on the starter box with those embossed letter plastic strips -

General Electric
Model 5B225A125 DC Motor
Type B
Frame 225
Winding: Shunt
Speed 1750
Amp: 11.4
Volts: 230
Enclosure: Open
Duty: Continuous
HP: 3
Hour: 40 degrees C Rise
Service Factor 1.15 at rated volts

Don't know if this sheds any light on the ultimate issue of what I need to do to get the motor running, but a 3HP motor swap seems more feasible than a 5 HP. Wonder why the previous owner thought it was 5 HP or why he felt the need to tell me it was.

It could be about the physical size of a 10 HP AC motor, weigh as much as a 20 HP, and have the low-end "pull" of a 5 HP. so.. easy error to make.

Be that as it may... a Monarch 10EE's 3 HP Reliance, "type T" not "B", is about 12-13 FLA @ 230 VDC in either of the "large frame" (slow..) or "small frame", (faster...), around 18-22 FLA @ 230 VDC in the various (3?) 5 HP versions.

So it isn't exactly alien technology to several of us.

But that is about ALL we know at this point.

And it is only enough to be able to say "Yes, this size CAN be started right across the line". IF .. you have the power for that. And yes, DC contactors to manage that level of current are not hard to find.

Both of which it must have had in fully working order... at one time, and for a long time.

That said?

If you want to go any FURTHER, you, or someone "local" better equipped to do it, will

EITHER:

- have to ID the specific equipment it was OEM'ed into ... and hope documentation exists and can be found,

ELSE:

- document the bugger from scratch - as-if reverse-engineering it.

Which isn't all that hard. If one knows how. Not a lot of mystery nor magic in it.

And the person doing it IS "local", hands-on, meter(s) on, etc.

Until one or the other of those enlightening circumstances is put into place?

There just ain't much as can be done by "guessing" from remote desktops.
 
Data plate info is not surprising. Current is about right for 230V DC motor, per NEC.

The motor being open may let you see the brushes. If so, you can see if there is any sign of distress, like heavy arcing, any smoke, etc at the brushes. If not, the problem if any, is in the controller, most likely. Looking for "ring fire", or arcs that seem to go around the commutator, is a good plan. They can indicate an open brush connection or open coil, which would probably make the motor start and run badly.

Old equipment often has things stuffed in much more closely than is allowed now. Not helpful in tracing wires, and can be an issue with old, brittle insulation.

If you can get pics of the box and maybe the brushes and commutator, that could be helpful. Imgur was working fine for me just a few minutes ago at time of this post.
 
OK, the link works for me.

Thanks for all the info so far. One drawback is I'm in the sticks of Wisconsin. Good to know the current/rectifier is an acceptable setup. I can take the inspection plates off later today.
 
Not familiar with that exact type*, but the "relay heater" seems to be rated at double the actual motor current....

If that is an "overload heater", it seems as if it offers no protection.

No obvious causes of smoke, but the amount of dust and crud seems to be enough to potentially explain it.

*Phil: I assume the device at the bottom is the time delay, and top right is main contact with arc chute. Can you identify and describe each of the parts as to function please? That old museum piece is not one I have dealt with before, although I have seen ones that are a bit similar.
 
Thanks, Phil.

I did pull the two inspection plates and did not see any evidence of arcing or thermal damage. More a layer of fuzz from disuse. No rodent nest either, which surprised me, as the bottom of the motor is open - or maybe that's why the little SOBs chose other, more secure locations.
 
You are right, the gear drove part controls the start up time, Could be used many ways. One way with a compound wound motor ( 2 fields, one shunt, one series) The motor would start with the series and shunt field in and switch out the series field after start up, but leave the shunt field in. The 2nd type would have a grid ( low ohm high current resistor) in series with the arm and switch it out after start up. The time delay also powered the fields before powering the arm so the motor would have full strength fields before start up. Where I saw a lot of them were on US Navy machines that came from DC powered ships in WW2. The overload had to be oversized to stay in on start up.Crude by today's standards but it worked...Phil
 
Thanks.

It looks as if the time delay may be an air vane slowed deal that is activated by a spring system from the main contact. I've seen maybe one of those ever, and I am no youngster. Presumably it resets when the main relay opens.
 
No, I think is was a centrifugal friction devise, I still have a few in the back room, I will look and see.I am not that old but in the 60s my dad sold a lot of navy surplus and I worked on the stuff.. The sawmills used a lot of DC motors in the day...Boy I sure miss the good old days...Phil
 
Although you do not specifically so state, I presume that the controls are run on DC. The relay probably has a resistor on the coil that is switched in when the relay closes. The reason is that it takes more current to pull the relay closed than it needs to hold it once closed. To avoid putting in a much larger coil, in the initial closure it is overloaded but only for the moment it takes for the relay to close. Once closed, the resistor maintains the holding current. If the contact shorting the resistor is stuck closed, you could be overloading the coil. Chattering implies a problem in the relay control circuit or poor voltage regulation in the DC supply making the relay close, then drop out because of low voltage.

DC contactors are different from AC ones because one currying AC current has the moments when the current is zero to extinguish the arc. DC contactors lack that opportunity so contactors over a low current have blowout coils next to the contacts which make a magnetic field that pushes the arc into an arc chute, making it so long that it breaks. AC and DC contactors are very different animals and must be chosen accordingly.

Lots of DC motors are used without current limiting on startup, other than the intrinsic voltage regulation of the supply which lets the voltage drop under high loads. The Monarch lathes often discussed on PM are an example. Neither the MG or thyratron versions have starting surge controls beyond the internal resistance of the supplies.

I have never seen a shunt wound motor control that shorted the series winding and cannot see a reason to do it since the series winding improves the motor's speed regulation.

Good luck finding a DC electrician in your area. Typical house electricians and even most plant electricians will be lost in DC systems.

Bill
 
The reason for switching in/out the series field was to have a strong field at startup to enhance the counter emf, and have the series field act as a voltage drop for the arm to control the inrush current. Also the series field was a full wound series field, left in the speed would be controled by load just as it a traction motor, IE no speed regulation, not your everyday compound wound motor, keep in mind in WW2 there were a lot of ships that were DC only, no AC, but the navy had lots of motors for pumps, hoists, ect ...Phil
 








 
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