Electric fan motor runs briefly stops. Will run but slower speeds - Page 1
Forum section: electronics / repair

author: electronics-whiz
author_rank: Regular Contributor
timestamp: July 03, 2016, 04:56:45 pm
content: I am trying to fix a large garage fan for a relative. The last time we had a similar issue and I suspected the run capacitor, that one looked to be bulged out so seemed like could be bad. We found a new cap Dayton brand ordered from Grainger. Now it's acting somewhat similarly. This cap shows no signs of bulging, etc. And I measured it on my meter and it read 4UF which is what it should be. I also put 60V DC in both directions since this an AC cap and it seemed to hold the charge. Looking online they say it may be a start switch of governor failure too, but I can't imagine this motor having a governor.Thinking it's worth a shot replacing the cap anyways as seems old one still acted normally in my tests, but had some other issue. Thinking this time go with a CDE cap. If there is something better then I'd consider it. I think it's an oil filled cap, needs to handle 120V AC and be 4UF and it is the oval type metal casing.Curious if anyone has other ideas to look at or would you think the cap is bad too? any good caps like this besides CDE?

author: wraper
author_rank: Unknown
timestamp: July 03, 2016, 05:12:14 pm
content: This sounds like could be a bad bearing as well.

author: electronics-whiz
author_rank: Regular Contributor
timestamp: July 03, 2016, 05:49:05 pm
content: Perhaps that too, but i would have expected that to fail with heat. From what I was told it was only ran for like 15 maybe 30 minutes before it started acting up.I want to measure some things too with my multimeter check it's not an open or shorted winding, etc. I'll try and give the blade a spin too and see how that feels.In my tests on the cap when I applied 60V DC both directions with no load except my digital meter the voltage dropped to like 40V within a couple seconds, go to like 25 V was still slower and it took like 30 sec to drop from like 25V to like 20V which is seems more like what i usually see on caps (at least electrolytic oil, AC caps may differ though).

author: TheMG
author_rank: Frequent Contributor
timestamp: July 03, 2016, 11:03:54 pm
content: Those caps can sometimes read the proper capacitance but have a high ESR which causes them to malfunction. I would replace it anyways as they are cheap enough and if it turns out it's not the capacitor, well, you've got a spare.Give the fan a spin by hand (with power off of course). If it spins relatively freely and doesn't make noise when running, the bearings are probably fine.Determining if there is a shorted winding can be done quite easily. Disconnect the motor from the fan so there is no mechanical load on it, and measure the current it is drawing. Compare it to the manufacturer's rating for no-load current. If this data is not available, then a rule of thumb is that it should be no more than 1/3 of the full-load current, which is normally indicated on the motor nameplate. If there is a shorted winding, then the current is going to be quite excessive. In fact, visual inspection of the windings in a shorted turn condition will often reveal a noticeably overheated section.

author: SeanB
author_rank: Super Contributor
timestamp: July 04, 2016, 04:49:36 am
content: With fans that do that I would suspect the bushings as well. Only way is to strip the fan apart ( mark the position of the end housings and the stator, as you need to put it back together exactly the same way) and clean out the old oil from the bearings and polish the shaft with some cloth, then relubricate with engine oil. Check the tolerance in the bush when out, you will find one end is going to be worn and tight, and as well look at float on the shaft forward and rear, as there are shims used to take up this float and they also either break or wear out.I have had to resort to scrapping cheap motors to get the bushes and spacers to fix others, the bushes used to be made out of sintered bronze, but the newer ones are powder steel parts and are not as good at holding oil. Check as well the little felting ring outside the bush is not rotted, as it holds the oil reservoir that slowly seeps into the bush to lube it. Those as well you can grab from a scrapped cheap fan, as often there is no oil applied to them at all in manufacture aside from a single drop.

author: BMack
author_rank: Regular Contributor
timestamp: July 05, 2016, 05:56:26 am
content: If the current going into the fan is correct for the unit, it's the bearing. That's my experience, though limited with large fans(only the occasional AC unit). Does it make any noise when spinning? How does it feel when you spin it by hand? Should be smooth, if there feels like gritty or it doesn't continue to spin (without voltage of course) after you release it, it's the bearing.

author: electronics-whiz
author_rank: Regular Contributor
timestamp: July 09, 2016, 05:31:16 pm
content: Sorry for the late response.I did give the blade a spin. Seemed to spin fine I gave it about a 1/2 turn push by hand and let it spin it probably spun for a good 15 seconds or so before it stopped. Even if power up and run at slow speed because the issue it still took a good 30sec-1 minute to come to a stop.I ohm tested all the wires I found and to the chasis no dead shorts to anything, most the windings seemed to read like 600-1000 ohms. I saw somewhere said maybe the governor is bad, but usually those motors are kind of big and I can't imagine that being justified for a fan. Another said maybe brushes, but I can't imagine that this has brushes as usually they have their own screw covers and I've never seen a brushed motor use a capacitor for anything. Usually fans use a shaded pole or induction motor setup.Be nice there was a way to know if it had brushes. I looked up the motor online, but all I can find is a GE motor that has no real casing or mounting setup like maybe would go inside the case this fan has. To me the motor looked like a motor you'd see in a box fan or ceiling fan. The only way I can think to check brushes is to measure the resistance on the windings slowly spin the motor see if the value changes as the windings change or spin it backwards and see if it feels like it spins harder or it is rubbing something that is worn the other direction.