DC motor drive ideas desired.
DC motor drive ideas desired.
(OP)
Today's railcar puzzle:
We have a 1hp 120V 8A two-ended DC motor on a car that was ENTIRELY 120VDC. The car has to be converted to AC and - with the exception of the aforementioned motor. Replacing this motor with an AC equivalent would be a nightmare of epic proportions. It's the size of a 25hp 3ph motor and has non-standard mounting bosses.
When 120VAC is fed to this motor it turns about 10% its rated 1750RPM in the correct direction while making lots of noise.
So. What do you guys suggest to get this motor running correctly with 120VAC?
We have a 1hp 120V 8A two-ended DC motor on a car that was ENTIRELY 120VDC. The car has to be converted to AC and - with the exception of the aforementioned motor. Replacing this motor with an AC equivalent would be a nightmare of epic proportions. It's the size of a 25hp 3ph motor and has non-standard mounting bosses.
When 120VAC is fed to this motor it turns about 10% its rated 1750RPM in the correct direction while making lots of noise.
So. What do you guys suggest to get this motor running correctly with 120VAC?
Keith Cress
kcress - http://www.flaminsystems.com





RE: DC motor drive ideas desired.
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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RE: DC motor drive ideas desired.
RE: DC motor drive ideas desired.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: DC motor drive ideas desired.
Thanks Wayne. Essentially you're describing a transformer/rectifier filter scheme, as a charger would probably freak at not seeing any batteries as a load.
Just rectifying 120Vac would get us ~160V which would be too much. I can't think of a transformer that's readily available that would give us ~80V that we could rectify.
Gunnar: Pulling legs? That swished over my head. No clue what you're referring to.
Commutation? It has no less than four brushes and not more than eight. We can only see it thru a small access hole.
Do repulsion-induction motors run on pure DC?
Keith Cress
kcress - http://www.flaminsystems.com
RE: DC motor drive ideas desired.
RE: DC motor drive ideas desired.
Surely you were not connecting AC directly to a DC motor were you?
And I know, DON'T call you Shirley...
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: DC motor drive ideas desired.
Jeff; Yes, certainly, someone, did try that. Universal motors have brushes too! (Can't say I've ever heard of a 1kW universal motor.) Hopefully the ancient insulation didn't stroke-out. I'd probably have heard about funny smells and blown fuses when they did it, if it didn't like it.
Keith Cress
kcress - http://www.flaminsystems.com
RE: DC motor drive ideas desired.
Keith Cress
kcress - http://www.flaminsystems.com
RE: DC motor drive ideas desired.
RE: DC motor drive ideas desired.
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If we learn from our mistakes I'm getting a great education!
RE: DC motor drive ideas desired.
RE: DC motor drive ideas desired.
Starting will be a greater problem than ripple. This will be almost a dead short if started DOL. With some design ingenuity you may be able to use the transformer impedance to limit starting current. A series reactor on the AC side may help.
A 120:48 Volt transformer as an auto transformer will give about 85.7V.
(120V + 48V = 168V... 120V / 168V = .7143.... 120V x .7143 = 85.7V)
If you use a series reactor you may be able to size it to drop the voltage closer to the 80 volts that you want.
How heavily loaded is this motor? Can you accept a little extra heat? External fan?
You may consider two rectifiers and a slightly higher voltage to the field. You may then use field strengthening to slow the motor down a little to shed some load if possible. A separate field supply will also allow you to add capacitors to the field circuit alone. The value may be an order of magnitude less than that required to filter both field and armature current.
I would be investigating the possibility of having a good motor shop clean, dip and bake the rotor and field.
Yours
Bill
Bill
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"Why not the best?"
Jimmy Carter
RE: DC motor drive ideas desired.
Looking like a lotta hassle here.
How's this for odd: The two end-shafts are both over two feet long!
Now I find out the car has a Gen-a-motor on it. An axle driven over-riding clutch started spinning the generator at speeds over 28MPH. It charged a bank of batteries that could carry the car for quite a while. When pulled into a station the car was plugged into shore power which would run the same generator with a 240Vac motor.
A recent "upgrade" was to remove the batteries and install Head End Power which is a 460Vac ~5kA buss that runs the length of the train. They installed transformers to run the Gen-a-motor. Now they want to add new refrigeration (240V 3ph) and they've be running a 120Vdc Amplidyne to AC power the lights and outlets. The transformers are not cutting it as they're TOO SMALL and they're certainly not going to support new refrigeration. Their proposed solution was to ACize the aforementioned fan motor and switch everything to AC and dump the Amplidye and the Gen-a-motor.
I'm suggesting they just upgrade the transformers to correctly sized ones - which will avoid the need for creating DC for the fan motor.
Keith Cress
kcress - http://www.flaminsystems.com
RE: DC motor drive ideas desired.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: DC motor drive ideas desired.
Bill
--------------------
"Why not the best?"
Jimmy Carter