OK, I feel dumb even asking this stuff... but then, I'm a complete noob when it comes to Alternator's as I've only ever had generators before.
😉
Anyway, it seems my new alternator has died. When first installed the system was all good:
- alt light would come on with the igntion, then go out once the engine was running
- 12.5 volts across the battery engine off
- about 13.5 volts across the battery at idle
Then, after first day of use:
- alternator light no longer comes on at all
- voltage across battery at idle was 12.4 volts and falling
- 20 minutes of running would drain the battery completely (I flattened two batteries doing just 6 runs at Warwick on Saturday)
- Light tested to be OK
- wiring tested OK (even ran a second charging circuit to be sure)
- belt, pulley etc. also all OK
So this morning I started double checking things:
- engine idling around 800 rpm gave 12.4 volts across the battery and falling to 12.2 within a few minutes
- Disconnect the V belt... now have 12.3 volts across the battery and falling, but idle now up at about 1400 rpm
- Engine also quieter - previously thought I had a tappet slightly out of adjustment, but now all can hear is exhaust and the straight cuts.
I'm thinking bearings gone maybe ??? It doesn't feel hard to spin... maybe slightly more resistance than my old generator, but not what I'd call stiff. Also not exactly noisy - just very slight scraping sound in the normal direction, which is more obvious if spun in reverse. Definitely quieter than the soft scrape-tick sound generators often make.
So here's my questions on alternators compared to generators:
- What should an alternator feel like when spun by hand...should it be about the same as a generator, or easier, or harder to spin ???
- Do alternators normally make any sort of noise when spun by hand ???
- Should they sound the same when spun in reverse ???
- Do they normally make any sort of noise when the engine is at idle ???
- Should disonnecting the V belt on an alternator affect the idle in any way ???
The alternator is definitely dead... at least electrically... so is going back today to be replaced. I'm just curious to know these things for future diagnosing efforts...
👍VWDCQ vice pres & web dude - vwdcqinc.org.au
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same-ish
no-ish
yes
no
no-ish
isn't the charge light meant to go on when the charging circuit fails though? (ie: alternator not working)
so ie: while its running, your charge light should be on full time if the alternator is dead.
(ô_!_/ô) (ô_!_/ô)
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I agree with Chris, if there is no output (which it seems there isn't as the voltages are def down), the charge/warning light 'should' come on, not at all means the excitation circuit isn't working, so either internal issue or your cars wiring is playing up. Put a test light in place of the warning light, at the engine so as to proove the cars wiring also.
The slight noise and drag you feel when spinning the rotor is the brushes. On a gen, the brushes run on a commutator which is segmented so makes a slight clicking noise, an alt has sliprings that are smooth.
If the bearings are shot, you will feel play or hear a grumble when spun. Def not after 6 x 1/8 mile passes.
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE
Cool - thanks Daimo !!!
🙂
Chris, yeah - I would've thought so too mate. Could depend tho on what the fault is in the alt. I have about 4.5 Ohms resistance between DF and ground when the alternator is stationary, which seems a lot to me... my old generator has less than 0.1 Ohms... so maybe the current can't flow along DF in EITHER direction, and the cicruit misses out on the exciting effect of the alt light ???
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I might add that not all Daimo's answers are correct 😀
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE
Thanks for the info Matt... tho not sure how your reply got in there before my reply to Daimo and Chris !!! I promise I wasn't ignoring you...
😉
I've checked all the wiring several times - done by connecting a test light directly at the alternator, and also measured voltage directly at the alt terminals both engine off and idling, and also checked resistance/continuity down the wires themselves both individually and connected as a loopback. All was as I'd expect, so I'm 100% certain it's not a fault in the wiring.
🤪
On some of Daimo's answers not being right... so it's OK for a slight shhh to come from the alt when spun by hand ???
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Sides wrote:On some of Daimo's answers not being right... so it's OK for a slight shhh to come from the alt when spun by hand ???
Correct
and
no probs Dave, sounds like the alt has a fault internally, you may want to remove the brush holder, depending on it's design, often the removeable brush holder has a questionable contact, and IIRC that's the circuit for the excitation, through the slip rings to the rotor to excite the magnetic feild......oooooo sounds exciting !!!!
Of course, removing the brush holder may void your warranty ...???
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE
OK, cool - thanks Matt.
👍
Yeah, I'd thought about pulling the brushes and the internal regulator out for a squiz... but decided sending the dead one back and getting a replacement was just the most pain free option.
Replacement should arrive tomorrow I'm told.
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Nope - not sure at all Craig. But then don't see how I could... everything new in the car is fused, and an alt charging circuit is very simple and effectively isolated from everything else. Wiring all checks out too - no breaks or shorts. Got any other suggestions ???
When I said drained in 20 minutes I don't mean dead flat... the engine wouldn't die of it's own accord, but if shut off then it would be touch and go whether could get running again off the starter without needing to jump it.
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yeah i wasn't talking about hearing aids turned to full volume re the noises (hi Matt 😀).........anything with contacting surfaces is gonna make "some" noise yes........i was assuming Dave was smart enough to differentiate between good noise and bad.....
it was a pretty well diguised bump tho hey and i've edited the first post now i'm not on a mobile 🙅
did you check the bulb in the warning dash light wasn't blown? seeing as it doesn't come on at all?
Heh heh - ish
Sometimes I just play dumb... other times I really am...
😂
Yup, checked the light with a direct connection to the battery... second thing I thought of out at the track, right behind "loose connection".
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yeah i know your being nice cause youre waiting on some goodies
Actually, i rekon your alternator is R.S and you should send it back
😂
Could be the reg, diodes in the rectifier or the wiring to the battery
71 notchback,
Past owner of, 70 NB, 73 SB and 72 FB TLE
if the tell tale dash lamp blows and doesn't work then Your alternator will NOT work
it needs a tell tale lamp connected the alternator for it to charge
sometimes its quicker to add one to the coil....lol
I've done that a few times until I get around to fixing the problem..
LEE
- Helping keep Air Cooled VWs on the road - location: SCONE in the Upper Hunter Valley - Northern NSW 320 kms NNW of SYDNEY---
what hell are you talking bout. lol
71 notchback,
Past owner of, 70 NB, 73 SB and 72 FB TLE
Well, the replacement alternator arrived yesterday. Hooked it up and wouldn't you know, the alt warning light now comes on with the ignition again.... YAY !!!
Only measurable difference between the dead one and the replacement (engine off) is the resistance from DF to ground... dead alt had 4.5 Ohms, replacement has 3.4 Ohms.
Resistance spinning by hand is about the same as my old gen... the only noise it makes is a slight 'shh' sound in the forwards direction, and a slightly lower pitch 'shh' when spun in reverse.
Hopefully get it fully installed and running over the weekend and confirm the Voltage across the battery.
😎
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