DC Drive Control Problem
DC Drive Control Problem
(OP)
We have a very old DC drive (Dodge-Mishawaka Ind. 300A circa. 1970)that has started eating up the external Speed pots.. They sometimes last months, others only a few weeks. 1K 2 Watt potentiometers.
There is a resister in series with the Speed pot. It's a ceramic 10 Ohm 1 Watt.
Could this ceramic resistor be going bad or a bad connection cause the Pot to burn out?
I read that it could also be attributed to a low resistance ground in the circuit but, I have no idea how I would find that.
Looking for ideas about this dinosaur.
There is a resister in series with the Speed pot. It's a ceramic 10 Ohm 1 Watt.
Could this ceramic resistor be going bad or a bad connection cause the Pot to burn out?
I read that it could also be attributed to a low resistance ground in the circuit but, I have no idea how I would find that.
Looking for ideas about this dinosaur.





RE: DC Drive Control Problem
Has anything changed to thermally insulate the pot? It needs to dump a whole lot of power and anything what-so-ever that reduces its ability to shed waste heat will cause it to fail quickly. Adding a knob to it, changing it's location, exposing it to external heat, a reduction in air flow such as a bad fan will all hasten its death.
Also a changed operating point can cause problems. As the pot is turned in one direction less and less of it's structure is available for heat distribution. If recently your process changed the setting that can be contributing.
I doubt the ceramic res is the problem but measure its resistance with the entire system depowered.
Keith Cress
kcress - http://www.flaminsystems.com
RE: DC Drive Control Problem
Maybe we are just wearing the darn thing out. Could it be they just don't make them like they used to?
this is a 2 watt pot, would getting one that might handle more wattage help?
RE: DC Drive Control Problem
RE: DC Drive Control Problem
Yes, that is certainly possible. I bought some cheap pots a couple of years ago. Several failed in a short time and I couldn't afford to test them all (customer upset). So I bought Bourns single turn cermet potentiometers, the blue ones, and they have worked ever since.
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 Drive Control Problem
I would love to replace this drive with a new one but before I spend the money, I want to figure out this issue.
1K, 2 Watt.
RE: DC Drive Control Problem
RE: DC Drive Control Problem
Ah ha moment. Thanks......
RE: DC Drive Control Problem
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: DC Drive Control Problem
I can't imagine the commutator being dirty enough to cause this.
There is a 10 Ohm ceramic resister in series with the wiper on this pot. I'm going to take a look at it this evening when the shift ends.
It may be time to just replace the drive and be done with it. The drive is so old there is nobody who can support it. Plus the company got bought a couple times since this was made. The Dodge name is no reflection of the Reliance Dodge products.