The Stovebolt Site Forums The Shop Area The Electrical Bay Heater keeps blowing fuses!

After screwing up the original heater fan motor in my '63 I purchased a new one, but one listed for '64 and up. This was because it was some $50 cheaper and looked, externally, the same. Can't be all that different right?
Problem is when I turn the fan on high it almost instantly blows the fuse. Medium and low is fine. Increasing the size of fuse simply lets the fan run a little longer. Tested on the bench with no problem spins like a bugger. Checked the resister block thingy (techical term) that controls the voltage. No problem. 6v at slow 10v at medium and 12v at high, before the fuse blew. So any ideas? If I run an ammeter on the line to the fan will that give me an idea why it blew a 20a fuse?
Thanks in advance.

Check to see if the fan cage is the same size. Sounds like the 63 had a smaller dia. cage. The larger fan will draw more amps.

Replace the fuse with a circuit breaker. It will trip at the same time, only it will reset itself. This won't solve your problem but will save on fuses till you find the problem. That fan shouldn't pull that many amps. Our school busses run two motors off one 20amp circuit with about 25 feet of wire or more. You could have a bad motor, two small of wire, or a bad switch. I believe you are right about the amp gauge. It should show what it is pulling. Joe

Freedo;
Sounds to me like Joe is on the right track check the gauge of the wire you're using if the wire isn't heavy enough you will blow fuses all day long.

No you won't! Small wire acts just like a resistor. It will reduce the voltage to the fan motor and make it slower, until it heats up and melts.

Thanks for the responses. I haven't had a chance to hook up the ammeter yet. The motor, I don't beleive came with a squirel cage. Just the motor by itself. It doesn't make any scraping noises, just picks up speed in the high mode and then blows the fuse.
I may try and run it straight off the battery when I do get the meter hooked up, then use the fan switch just to see if there is any difference. High should be a 12v feed. I wonder if it may have something to do with the actual switch on the dash. Just grasping at straws.

Hence the term FUSE

Hey,, is it grounded properly?

Make sure you are using a slo-blo fuse in the circuit. Sounds like you may be using a quick blow fuse. A DC motor looks much like a short circuit at startup until the motor spins up. After that is settles out and all is well. What the fuse will "see" however is the intital short circuit current spike followed by the normal operating current. The slo blo will allow the fuse to hang in there until the spike is past while the quick blow will not.

dc motors all operate on the same principal of M F C [motion,flux,current] you need any 2 to get the third,you have flux [perm magnet in motor]so you add current until motor gets to its full rpm. If you have wrong blower cage you might have too much load and never get to full rpm without drawing excessive current.The reason it wont pop a fuse on low/med is you have a resistor [that coil of wire thingy] that limits current.

Hi Freedo,
I knew a guy that had the same problem with his '64. I think it was a bad ground that kept blowing the fuses.
David