Electric motor question

[stephenc]

I had to replace the squirrel cage blower on the wood stove in my shop yesterday .

Unfortunately I wasn't able to easily find one that was appropriately sized for the stove or my heating requirements and had to go with a direct drive blower intended for a whole house and it blows way to much air .

Actually it isn't the volume of air it moves that's the problem it's the noise level that's the problem ... it sounds like a darn jet engine running twelve feet away .

I came up with a solution that leads to my question .

In an effort to reduce the noise level I got a bright idea ... I plugged the motor into my veriac variable transformer .
It worked like a champ , the motor starts and runs smoothly , speeds up and slows down just like a 3 phase motor on a vfd

The good news is that I don't have to reduce the voltage all that much to reduce the noise level to an acceptable volume @ 90-95 volts things are just about perfect .

So here's my question. .. will running a single phase motor at reduced voltage harm it in the long run ?

[Bob D.]

Here is a really easy way to determine if any harm is in the works. Run the blower for an hour at full voltage. Put your hand on the motor and note the temperature. Now bring the variac into play and set for what you want to run at. Run for an hour and check the temperature. If you can keep your hand on it your ok. Low tech at it's best!

Bob D.

[stephenc]

That was a rather good suggestion .... I just ran the blower for about 4 hours on the lowest voltage that would reliably start the motor , which also happened to be the lowest voltage that the motor didn't sound like it was straining to run ... 60 volts .

Everything stayed cool to the touch and didn't let any of the magic smoke out .

[spro]

Everything including the Variac. This is timely information because failure could be catastrophic when you least suspect. Right. Nanny again.
I like, in my simple way, how things are designed. For instance with a fired furnace and circulator motor pump. There have actually been instances where the circulator was piped at the boiler's exit instead of the return. This, of course burns out the pump's motor(with the newer) but the older were separate motors and would run the pump at the wrong end of things.
To where this applies, there is a heat factor to these motors and to how they are rated. The burning of one small connection within the case is not going to raise the case temperature. It is what happens after the motor fails-if. there is always "if" factor. Taking a broad view across disasters centering about stoves and furnaces, there are insurance policies. You know where I'm going here and I stop there.

[ChipMaker4130]

Nah... you can 'what if' yourself into never doing anything. You checked it out, it works, enjoy it. The 'one small connection' failure mentioned above would likely be worse at full voltage/power because of the increased tendency to arc. Some motors draw excessive current at lower than specified voltages. Yours apparently does not.

[stephenc]

I tend to not be a "what if " type of person. , chipmaker is right you can what if yourself into never doing anything .

But when working with furnaces and wood stoves a person does need to practice a bit of caution so as to not burn our houses or shops down .

If the stove was in my house I'd never even consider using a variac to control the blower speed . I would have just bought a brand new blower .. or motor if I hadn't been able to find a correct used replacement .

But in this case it happens to be in my shop .. where I am perfectly fine with taking a very small calculated risk .
And it isn't much of a risk at that , my shop is a concrete block building and there are no combustible materials near the stove . Plus the blower is only used when I am in the shop .
Worst case scenerio ... one of those wires arcs and possibly burns up a bit of wire insulation and I have to live with the stink of a burnt motor for a week or two .

My biggest concern was with a failure on a cold winter day and not having any heat while I tried to scavenge up another squirrel cage .

Funny how over the summer I must have seen 10 or more of them kicking around ... but when I needed one they instantly became an endangered species.

[pete]

Shop = machining capabilitys. You could always build yourself a large enough stirling engine to run a fan and just use the heat off the wood stove to run the engine.

[John Hasler]

stephenc
> So here's my question. .. will running a single phase motor at reduced voltage harm it in the long run ?

It'll work fine with that type of motor in that application.