HELP! The alternator is HOT when not in use???

[ao.frog]

Hi.

We're in the process of checking all the elec stuff (avionic, lights etc etc) on my RV-7 before the first start.
Therefore the power (both batt switch and alternator switch) has been on for an hour or so at the time lately.

Yesterday I noticed that the Plane Power 60 A alternator was too hot to touch...! The hottest part was the "wheel" in front of it where the alternator belt goes into.
The wheel was too hot to keep the hand on for more than a few seconds.
The other parts of the alternator was warm (not hot) and the hand could be kept there.

The alternator may have been hot earlier too, but I don't know this for sure since I haven't checked.


After this experience, I turned off the alternator switch but left the battery switch on. Then the alternator gradually cooled off...

Is this normal??? Seems very strange to me....??

 

[jsharkey]

Alf

I assume that the field current is enough to heat it up, especially when it's not turning and driving the integral cooling fan. I haven't got that far yet but in the future I'll remember not to leave the "Alt Field" switch on when the engine is not running - even in my flying club C172s.

Jim Sharkey
RV6 - Wiring

 

[L.Adamson]

I haven't felt the alternator for heat build up; but since I wired my amp meter with the Van's method instead of the alternative; I can see that it consumes a noticeable load from the battery, when the alt field is turned on along with the master switch.

L.Adamson

 

[Mitch757]

Hot Alternator

Hi Alf,

I forgot and left the battery and alternator switches on for about 20 minutes and the same thing happened to my Plane Power alternator. I sent the alternator to Plane Power and they checked it out, gave me a call and shipped it back to me at no charge!

They said that it would "try" to make voltage even if not turning. In my case the alternator was not damaged and I learned a lesson.

Plane Power is first class!

Mitch Garner
RV-4 flying

 

[airguy]

If the alt breaker is on, the regulator will feed the field coil up to it's maximum rating (about 6-8 amps for most alternators) trying to bring the voltage up. With no airflow from the fan, this will definitely get warm.

Don't run the alt. breaker for ground checks unless the engine is running, you'll just pull your battery down and warm the alternator. The ammeter will show you a definite discharge if you turn on the alt. breaker, this is the regulator feeding current to the field windings.

 

[ao.frog]

My mind is at ease now....

Hi again!

Thanks for the responses folks! That was REALLY a relief to know!
I was starting to think we'd wired something wrong.... yuk!
Now I know why I've had to charge the battery so often during wiring and testing!

For the rest of the testing, I'll make sure the battery switch is on and the alt switch is off!

By the way; for grund testing we're using an external battery, 120 Amps capacity, sitting on floor, and hooked up to the a/c + and - leads.
That way I don't have to use my 680 for electric testing.
I hope this is a good idea??
(I'm not so good with electrics and wires.... it's more fun with rivets...)

Thanks again guys! You put a big smile on my face today!
(It's both time consuming and expensive to ship stuff from Norway to the US for repair...)