Identifying (the voltage of) a Pittman DC brushed motor that has lost its label. - Page 1
Forum section: electronics / beginners

author: cincin
author_rank: Regular Contributor
timestamp: April 08, 2025, 02:40:50 pm
content: I have an older Pittman brushed DC motor that has lost its model # label. It only has the generic Pittman label with no specs, numbers or anything.I've carefully looked over the body of the motor for engravings but there is nothing.I've also contacted Pittman about it, and they were less than helpful.How can I figure out its nominal voltage? The rest is less important... but if it's possible to ID the motor model number, that would be even better.Here's what I know about the motor:- Pittman brand, from before they switched to metric sizes.- 2" diameter- 3" stack length- 1/4" shaft diameter (geared) coming out the front only, 1/3" long- 1.7 Ohm lead resistanceAny idea?Thanks!

author: IanB
author_rank: Super Contributor
timestamp: April 08, 2025, 03:01:59 pm
content: Brushed DC motors will operate at any voltage that does not exceed any of their limits.Excessive speed: bearings will overheatExcessive voltage: brushes may have excessive arcingExcessive current/torque: windings may overheatAny one of these limits may occur at a different voltage, depending on the load and application. I think your best option is to figure out what you want to use the motor for, and then see if it is able to develop sufficient torque or speed with a reasonable supply voltage without signs of overload. (Overheating would be the most likely scenario, and this would be indicated by a bad smell during operation.)

author: Infraviolet
author_rank: Super Contributor
timestamp: April 08, 2025, 03:06:20 pm
content: There isn't really such a thing as a voltage for a DC motor, there is a "rated voltage" which was the voltage used when testing torque-vs-speed and torque-vs-current curves, but the motor can usually run below and above this level. There will be a much higher maximum voltage at which insulation might short, and a voltage rather higher than for normal use at which the brushes might spark badly enough to erode rather faster than usual. There will be a minimum voltage for th motor to run at all, that could be found be connecting to a variable supply and slowly raising the voltage until it moves.If you use a motor of known speed, or some setup involving and encoder to measure shaft speed, you could spin this motor's shaft and measure the DC level of the back-emf produced from it. That would give you a sense of the speeds it can achieve, in a no-load condition, for different supply voltages. If you've found datasheets for various models which this motor could be, then this info might let you work out which of those datasheets os the closest fit to your motor's measurements.You could also try it at some given voltage and put a litle pulley on the shaft with various weights hung off it, see what the stall torque is like (if it has an inbuilt gearbox rather than just a gear on the output shaft then be particularly careful here, some gearbox'd motors will generate enough stall torque to break their own gears), but that carries the risk of overheating the motor at stall. Some motors might be ok for several seconds at stall, long enough to run this test, but others might be damaged almost immediately, depending on how reliant the design is on the back-emf to reduce the current through the motor to less than the supply_voltage/winding_resistance which you get when the shaft is stalled. Such tests might be best done at lower voltages, as this would help limit the current possible during a stall.

author: cincin
author_rank: Regular Contributor
timestamp: April 08, 2025, 03:16:45 pm
content: Thank you!It won't run with any less than 6V, and that seems to be a struggle. Pittman's current selection of brushless DC motors that are that size are all 12V, so I'm guessing this one is 12V or 24V rated.I don't have a specific use for it, yet. I'm just trying to figure out what it can do.I was hoping there would be a tell-tale signs in the current consumption, or something.I'll give it 12V and 24V to see which seems most appropriate, I'll use my nose to make sure I'm not over doing it.I can figure out speed and load once I have an appropriate operating voltage.Chees!