PDA

View Full Version : DC Motor Upgrade



Paul Alciatore
12-28-2007, 02:51 AM
I need some help finding a replacement DC motor. It is a blower motor in a RV heater. 12 Volt, 39 Watt, 3.25 Amps., 3" diameter with a 5/16" shaft on both ends. It mounts via a strap of steel around the 3" OD near one end.

I live in the RV most of the year and that includes winter in Iowa so it gets a lot of use for an RV. The OEM motor is made by Fasco and will last only one to two winters. At first I thought the bearings were giving out, but disassembly of the latest bad one revieled that the brushes were flat worn out. Mucho carbon powder inside the motor and one brush barely protrudes from the holder when at the extent of the springs range. I could replace the brushes, but I would still have to replace the motor every year or two and it is a miserable job, especially in the middle of winter when they usually fail.

I suspect a brushless motor, perhaps with ball bearings would last a lot longer and be worth several times ($150 to $250 or so) the price of the OEM replacements. I have looked in several catalogs and web sites but have not been able to find a replacement that matches the specs. The OD, and other dimensions are not subject to change as I do not want to modify the entire heater.

Can anyone suggest a source I can check for a possible upgrade replacement. It would need to be a source where I could buy in quantity of one (Christmas is just over).

Evan
12-28-2007, 03:45 AM
You don't need the same OD Paul as long as the new one is smaller. In that case just make a mounting sleeve to adapt it to the existing mount. Chances are that you can find a new motor that is much smaller with the same performance because the current crop of brushless DC motors are in a new class of power to weight ratio. Check into late model car heater motors at the auto salvage yard. Another possibility is electric radiator fan motors.

As for the brushes wearing out, there must be something wrong with the design. They should last for many years unless there is something wrong such as weak springs. The heater motor in my Land Rover is still going and it has been running for nearly 50 years of winter use.

macona
12-28-2007, 03:57 AM
Maybe switch the brushes to a harder composition. Maybe the sintered silver or copper they us in higher powered motors might last longer.

You could find a small AC motor and run it off one of those cheap little inverters. Nothing but bearings to wear out there. Put a transfer switch to run it off of 120v when your plugged in.

Your Old Dog
12-28-2007, 09:28 AM
Paul, Have you tried this place? I just browse through it till I see one that looks like mine.

http://www.grainger.com/Grainger/categories/motors-and-power-transmission/hvac-motors

If you have too much trouble finding one you might try getting an AC motor and letting the 12V act as triggor for a relay.

One last thought, ebay frequently has RV furnaces listed. I think you'll find they are pretty standard in sizing.

wirewrkr
12-28-2007, 05:02 PM
Keeping in mind what Evan said about different motors of smaller diameter, try these two sources if you haven't already
www.surpluscenter.com
or
www.youngssurplus.com
both have lots of motors.
I think we all have dealt with surpluscenter with good results,
and Youngs is a small family mom and pop place, real nice folks and good service to boot
HaveaHappy
Robert

Paul Alciatore
12-29-2007, 01:36 AM
Thanks guys.

Yea, it is a lousy design.

I thought about smaller and an AC motor, but I have a lot of other projects and want a drop in replacement. But I will do what I have to. I'm really more worried about the speed as air flow is critical. I guess with a bit of modifications I could even go a bit bigger. I have seen a lot of 3.5" motors out there.

I'll check the sources mentioned. Thanks again.

Mad Scientist
12-29-2007, 02:15 AM
As for the brushes wearing out, there must be something wrong with the design. They should last for many years unless there is something wrong such as weak springs. The heater motor in my Land Rover is still going and it has been running for nearly 50 years of winter use.

Correct. Most RV stuff is over priced and under designed. It just has to look pretty. By all means try to find an automotive heater motor. You will probably also what to grab it its voltage dropping resistors to control its speed.