How warm should a 1/2hp 1725 rpm 115v motor get? (9 amps cont) - Page 1
Forum section: electronics / general

author: XOIIO
author_rank: Super Contributor
timestamp: August 21, 2014, 10:05:23 am
content: Hey all question for anyone who has worked with belt drive motors. (skip to the end for the question bit)Still working on that delta combination sander I got, called up the guy who had the three motors for $30, on my way there he called me and said he tried them out, and they run hot, and don't start every time, so he gave me them free. Not only that, but I actually got four!Two 1/2 hp, one might be a 1 hp based on the cap size, forgot to check the label, and one is a 1/3hp.Now, he was right, they didn't start every time, you had to turn it, and after a little bit it started vibrating around like it was going to explode, and the whole cord was getting quite warm, so much you would start to be worried it might melt the insulation. I also changed the cap to another one and it started to smoke a bit, very dry smoke, not what you would expect from a cap, anyways I unplugged it asap.Anyways, got a rubber mallet, and took it apart, and firstly some black, basically soot I guess, fell out the end, a decent bit, one of the other motors has a load of it in the capacitor compartment, and looked at the contacts on the rotor.Rust city baby. There was very little clean metal left on them. The contacts on the armature were not too bad, not worth cleaning, but man the rotor ones were, so I took some 100 grit sandpaper (which I got a roll of for 75 cents at a garage sale, best find I've had for a while lol) and cleaned them up, took a decent bit, and some cramped fingers, but got them much, much better. No before and after picture sadly, but I'll be making a video on the process using one of the other motors to show people how to do it.Purrs like a kitten now, runs a decent bit before the cord heats up at all, and that's just a couple inches near the plug, however, after leaving it run for 10-15 minutes, it's heated up a decent bit. It wasn't much at first but it does gradually build up heat, and it got to the point where the whole middle metal frame (basically not the end umm, cowels?) was quite warm, sort of like it had been sitting out in the sun on a +30 Celsius day.So, I'm wondering, how hot are these things supposed to run? It is thermally protected, and I probably won't be running them for long periods of time, but I was wondering what sort of temperature these get up to in normal operation conditions?Going to take my multimeter and thermocouple out later to see what the actual temp is, I am just wondering if it is fine that they get a tad warm. Original motor was blown so I have nothing to compare it to.

author: G7PSK
author_rank: Super Contributor
timestamp: August 21, 2014, 11:10:49 am
content: Many cheap induction motors run at 60 deg C or above as standard. The Chinese one are particularly bad also had similar with cheap Polish motors that are distributed by the likes of machine mart running too hot to put your hand on after half an hour or so.

author: bobcat
author_rank: Regular Contributor
timestamp: August 21, 2014, 11:13:28 am
content: Leeson Electric Corp Quote:Underwriters Laboratories sets maximum acceptable surface temperatures for a metal "surface subject to casual contact" at 70° C(158° F) after 30 minutes of operation in a 25° C(77° F) room.

author: N2IXK
author_rank: Frequent Contributor
timestamp: August 21, 2014, 11:40:44 am
content: Most motors will have a temperature rating right on the nameplate. Usually rated in terms of temperature RISE above ambient. Generally, the newer the motor, the hotter they run. Advances in insulation allow higher temperature operation, and constant cost-cutting drives manufacturers to use the absolute minimum of copper and steel that they can get away with for a given power output. This means that motors run hot, often too hot to comfortably touch.

author: XOIIO
author_rank: Super Contributor
timestamp: August 21, 2014, 12:26:18 pm
content: Alright, checked with my multimeter after 7 minutes of running, at it's around 50 degrees, so I guess that's not bad. Forgot to bring my phone out again but I'll get pictures of the labels on all of them, but I believe they are reputable companies.

author: German_EE
author_rank: Super Contributor
timestamp: August 21, 2014, 05:19:57 pm
content: 115V * 9A = 1035 Watts of electrical energy0.5 Hp (looking at my tables) = 373 Watts of mechanical energyYou therefore have 662 Watts looking for a home, some of this will be dissipated as sound but most of it will be as heat.

author: XOIIO
author_rank: Super Contributor
timestamp: August 21, 2014, 06:21:00 pm
content: Alright had it wired wrong, one wire had gotten knocked loose, could have been one of two contacts, anyways it works well. Took it to a small engine shop and the guy charged 10 bucks to grind the shaft from the old motor down so the pulley could be taken off, talk about a ripoff, damn Canadian tire taking forever to restock.Anyways, was miffed about the $10, then I hooked it up to the belt and held it in place...Jesus Christ this thing ROCKS! Even without a backing plate, the belt sander is ridiculously awesome! $10 totally worth it when I used it lol.Could use a new belt, though this one isn't bad, plenty o sparks fly from it. Now I need to drill the motor mount a few times to widen it for the bolts, and I also need to drill two holes for the back. The front matches with the pre existing ones, but the motor is longer, so I'll need to put a couple further down as well, then it's just a matter of mounting it and voila! I'll get the disc plate at some point probably but this is one nice bit of kit that I got for $10 (not counting the price of gas of course)

author: XOIIO
author_rank: Super Contributor
timestamp: August 21, 2014, 07:18:06 pm
content: PSA: Belt sanders areFRIGGING AMAZINGSeriously, this thing is just jaw dropping as someone who has never even really seem one before, it can eat material ridiculously fast, although it discolors it from the heat, and the flexibility is so freaking useful! I had a little old hammer that was pretty much coated 100% with rust excluding the metal handle, and now it practically looks brand new! I do need to get a belt for it if the stores around here have some this long, but holy crap! Being able to get around the bends in the hammer, and places normal sanders couldn't reach is just awesome.