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Have I killed it?
ste - 10/1/19 at 04:36 PM

So, I funked up a bit. I forgot to fit an earth between engine and chassis on the Dax I'm building. I am in the middle of wiring the thing up and was doing a bit of testing. Engine turned over just fine. Took the exhaust off to fit the lambda sensor and soon noticed the charge light lit when ignition was off and then it went off with ignition on, tried to turn the engine over and nothing!
Turns out, the engine was earthing through the exhaust.

After a bit of head scratching, figured out it wasn't earthed and made a lead.

Connected everything back up and all seemed fine.

But after about half an hour, i touched the alternator and it was hot.

Tested the current draw and it was pulling 36mA from the battery.

Disconnected the plug on the alternator and it cooled down.

Have i killed it?

I think it is a small Daihatsu/Nippon Denso Alternator

ste - 10/1/19 at 04:42 PM

Click for pic

theconrodkid - 10/1/19 at 05:02 PM

if it was hot then yes it is toasted, electrickery will try to find a way back home, no earth lead and it will follow throttle cable or anything else where live meets earth...ie inside the alternator.

gremlin1234 - 10/1/19 at 05:06 PM

36mA at 12V is 0.036x12 = 0.43W, which I wouldn't expect to noticeably warm (certainly not hot) an alternator

ste - 10/1/19 at 05:15 PM

quote:
Originally posted by gremlin1234
36mA at 12V is 0.036x12 = 0.43W, which I wouldn't expect to noticeably warm (certainly not hot) an alternator


It wasn't hot in the normal sense of the word, but compared to everything else in my garage at about 5 degrees it was quite warm at 40 degrees C

gremlin1234 - 10/1/19 at 05:39 PM

quote:
Originally posted by ste
quote:
Originally posted by gremlin1234
36mA at 12V is 0.036x12 = 0.43W, which I wouldn't expect to noticeably warm (certainly not hot) an alternator


It wasn't hot in the normal sense of the word, but compared to everything else in my garage at about 5 degrees it was quite warm at 40 degrees C

how did you measure the 36mA? because that is only about a quarter of what the panel light itself would normally take. I would believe it feeling warm if it were 10 times that, (4W )
also from the picture the alternator earth path looks like its trying to earth though a loosely fitted, powder-coated bracket.
bolt it all together, and measure current again. (it might just sort itself out)

Mr Whippy - 11/1/19 at 12:55 PM

ditto you can't heat up an alternator on 36mA!

adithorp - 11/1/19 at 01:28 PM

Was this after 1/2hr running or stopped. If the latter (which I read it as) then it's knackered. If its the first then you might be ok. What's the voltage when running like?

MikeRJ - 11/1/19 at 02:46 PM

quote:
Originally posted by gremlin1234
36mA at 12V is 0.036x12 = 0.43W, which I wouldn't expect to noticeably warm (certainly not hot) an alternator


Agreed. 36mA leakage is too much for a healthy alternator, but nowhere near enough to noticeably warm it up. Perhaps the OP misread 3.6 Amps, which would get it hot.

ste - 11/1/19 at 02:46 PM

quote:
Originally posted by adithorp
Was this after 1/2hr running or stopped. If the latter (which I read it as) then it's knackered. If its the first then you might be ok. What's the voltage when running like?


It doesn't run yet, this was just trying to crank the engine over.

It's coming off and going to a local alternator specialist to be tested and repaired. Lesson learned!!