What kills alternators?

Do It Sidewayz Wrote:
-------------------------------------------------------
> what is in the car now is i suspect an OEM subaru
> alternator (mitsubishi) unit, but unknown
> history...likely off some JDM clip...
>
> I suspect picking up a NEW unit will be the best
> bet, along with checking everything mentioned.
>
> I am using the stock OEM pulley...well almost...i
> have used a fancy pants alloy replacement from a
> sponsor once or twice.
>
>
> The latest unit that was "dead" was spinning free
> no problem...but noticed when pulling into a
> control that the battery light in my SPA gauges
> would flash (set to 12V). This was with just the
> OEM headlights on.
>
> Chris

Chris, I think Gene, Robert, and Sean explained it best.

You're best off with a quality bigger alternator (Amp wise) than you need and underdriving it.

Cheers,

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Andrew M
Onterrible
30ish



Edited 1 time(s). Last edit at 02/18/2009 10:20PM by hudson.

Robert,

I just realized that I replied to your post.

I just meant to reply to the initial post, hence the confusion (I wasn't disagreeing with what you had said).

Cheers,

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Andrew M
Onterrible
30ish

No problem Andrew!

---

Robert.

"You are way too normal to be on Rally Anarchy." Eddie Fiorelli.

Do It Sidewayz Wrote:
-------------------------------------------------------
> what is in the car now is i suspect an OEM subaru
> alternator (mitsubishi) unit, but unknown
> history...likely off some JDM clip...
>
> I suspect picking up a NEW unit will be the best
> bet, along with checking everything mentioned.
>
> I am using the stock OEM pulley...well almost...i
> have used a fancy pants alloy replacement from a
> sponsor once or twice.
>
>
> The latest unit that was "dead" was spinning free
> no problem...but noticed when pulling into a
> control that the battery light in my SPA gauges
> would flash (set to 12V). This was with just the
> OEM headlights on.
>
> Chris


Chris I'll check my price on an STi 90 amp unit from the dealer if you want.

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Gone fishing

Rally vibration can sometimes cause the plates in the batteries to short when they come into contact and thus casue a large load spikes for the Alternator.

AGM type batteries prevent this as the plates are wrapped in a electrolyte infused fabric mat and thus can not come into contact with each other.

Not sure if this is killing yours but it is something to look at.

Derek

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In the long run reality always wins.

The Deka battery is an AGM battery..

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Chris

Chris,

I agree with Derek on the battery issue; sudden spike loads can blow out alternator diodes. Also, do you ever turn off the battery switch when things are running? That is a very bad thing for alterantors and can blow the regulators.

You said in your original post that the unit was SUPER hot when you took it off. Can you describe the conditions under which you removed it? At a rally service? After the car had set in the driveway for a week after not being run? This 'hot' info could be significant, but only can be used in context of the actual situation in which you found it thermally hot.

FYI, it is perfectly NORMAL for alternator's voltages to be lower when they are hot. The internal rectifier diode's forward voltage drop increases, as does the winding resitance, when hot, and these both reduce output voltage. If you finihsed a stage and the engine dropped to idle and the voltage reads lower than normal, that may be OK.

One thing I suspect as a problem for you is just killing the alternator thermally with heat. When transitor junctions (inside the rectifier diodes and transistors in the regulator) reach 115-120 deg C or higher with significnat ameprage through them, they will start to fail. And once one diode on the rectifer assembly goes, it puts more stress on the others. Is it possible that you have blocked off goo ariflow to the alternator? This is very easy to do when adding skidplates and splash guards. If you are finding the alternator 'super hot' during a rally, this is a very probable cause.

One very good thing to do for your rally car alternator on any car it to add an arihose from the front of grille area running directly to blow cool air on the alternator.

Regards,
Mark B.

Mark,

Super hot, meaning i count still touch it...but definately needed gloves!

This was in a Rally Service. We had completed a stage, transited about 3km, sat at the control for probably 3 minutes, pulled into the service, etc.

I have no tried putting the alt back in the car, and testing again, or even taking it to the local auto-parts store and testing also.

It's possible that airflow has been hampered slightly. I did add a front mount I/C right behind the grill. As you know on a Subaru the Alternator resides "front and center" at the top of the motor.

However...i did go through a couple alts before adding the I/C

thanks for your ideas/comments.

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Chris

Most new alternators or remans have a "tag" in the box requiring the battery be fully charged before installing. Usually it says something similar to "this device is not intended to be a battery charger". Sounds silly when you read it but the obscure message is they are used to maintain a battery not charge dead batteries. Running for very long at near capacity loads will kill them. They will actually melt the solder inside.

I like Mark's air duct idea. I haven't been paying attenion but I think most newer alternator designs don't have the cooling fan behind the pulley like in the old days either.

At some point back in the dinosaur days NASCAR teams were using Ford alternators as they resisted vibration better than the GM ones. I wired in a big old Ford unit, external regulator, on my 510 and with 8 100w lites never had a failure, except for the mounting brackets....

Maybe a marine unit like Balmar might be made to work. Most boats run near 4k rpm all day, real shitty air flow around the motor and routinely charge 2 or 3 low batteries.