Fried alternator...

[mcframe]

... or yet another electrical thread...

After ~3hrs all ahead flank to windward in a swelly F6, I fried my alternator.

<spends 45 mins reading previous PBO threads>

It was the original 35 amp Hitachi on a 1GM10 (so 21 years old).

I've no reason to suspect any other part of the system (batteries, Sterling booster, VSR, BM-1, etc), and I've got a replacement from my local auto-electrician.

I did briefly see 30 amps going in a couple of days before (low batteries, dropped to 15A after ~5 mins; 5A after 15 mins as expected), but we had been on shorepower the night before it failed.

Can anyone think of anything I should check before/after fitting the replacement?
(oh, and a new belt - very /slightly/ wider than the REMF-1295 previously fitted, and derided as "too thin" by auto-electrician)

The wear on the belt was obviously why I was down on power, but is it likely that alternator failure was the *cause*?

I'm considering fitting a manual cut-out switch to the field wire for occasions where I might want more motive than electrical power.

 

[VicMallows]

I'm considering fitting a manual cut-out switch to the field wire for occasions where I might want more motive than electrical power.

Nothing wrong with doing that.

Based on your description, can't see anything wrong which might have caused the failure. Have you analysed the old alternator to try to establish the cause? Do your really mean 'fried' (as in something burned out; definite diode failure etc) or do you just mean it has stopped working?

Vic

 

[mcframe]

Have you analysed the old alternator to try to establish the cause? Do your really mean 'fried' (as in something burned out; definite diode failure etc) or do you just mean it has stopped working?

"Fried" as in burned out (and dropping little bits of metal when I removed it) - part of the coil, internal wiring near the brushes and one brush more than the other. Hang on! What happens if a brush fails when you're not paying close attention to what's going on?

 

[Billjratt]

Sounds like you're looking at an electrical failure when it could possibly have been mechanical.
If the bearings fail and the rotor and stator come together for a while you will have mayhem both physical and electrical... and with a typical boat installation you won't hear it happening.
Strip the old one and have a look, it's not unreasonable for an old unit to have bearing failure - especially if the belt has been too tight.

 

[mcframe]

Thanks Billj - the bearings /seemed/ OK, but the rotor was badly scored, so I think it was mechanical failure.

I'll check everything for normal readings when I put it back together.

BTW: Vic - I might mount a switch for the field wire *upside down*, next to the engine controls so I can label it "Turbo Boost" ;->

 

[duncanmack]

I might mount a switch for the field wire *upside down*, next to the engine controls so I can label it "Turbo Boost" ;->

Fine, possibly, if you start the engine with the field wire switch in the off position, however many alternators will self excite when the revs are high enough - though not all.

Almost all will continue to produce charge when running and the field wire is interrupted - until the engine stops.

A trick we can sometimes make use of in the vehicle breakdown world...

 

[mjf107]

Field cut switch

Fine, possibly, if you start the engine with the field wire switch in the off position, however many alternators will self excite when the revs are high enough - though not all.

Almost all will continue to produce charge when running and the field wire is interrupted - until the engine stops.

A trick we can sometimes make use of in the vehicle breakdown world...

Agreed but if you want to open up the alternator and fit your switch in series with the field
coil it will cut the output even with the engine running

 

[VicMallows]

Agreed but if you want to open up the alternator and fit your switch in series with the field
coil it will cut the output even with the engine running

I for one assumed that was what the OP was proposing
(not just interrupt the warning-light circuit).

Vic

 

[mjf107]

I for one assumed that was what the OP was proposing
(not just interrupt the warning-light circuit).

Vic

Yes I think your right, I was just pointing out that there is a way round the self excitation phenomenon

 

[mcframe]

That's quite enough self excitation for tonight!

Vic was right - by upside-down I meant that the switch would *break* the connection between the field coil and the boost charger thus providing the mighty Yanmar with extra "boost" 'cos it's only being asked to provide normal (non-Sterling) alternator charge. (i.e not much if batteries are above ~70%)

Thanks all.

 

[VicMallows]

I meant that the switch would *break* the connection between the field coil and the boost charger thus providing the mighty Yanmar with extra "boost" 'cos it's only being asked to provide normal (non-Sterling) alternator charge. /QUOTE]

You can also switch the Sterling off by breaking the connection which is normally taken to the switched side of the 'ignition' switch. This has the advantage that when you switch it back on you still get the gradual ramp-up to avoid belt slip.

 

[mcframe]

Update - lots of yummy amps (up to 26 after running house bank down) with slightly wider belt, *after* much head-scratching and replacement of charge-warning-light bulb on engine panel.

I initially got no charge from the recon alt, so after discussing with crew*, and RTFM, I noted that the only untested item in the circuit was the charge bulb (normally lit for no charge, unlit when charging).

A bulb is just a bit of wire with resistance such that it emits light, right?
It was blown and hence open cicruit - as the engine panel is indoors under the bridgedeck, I rarely pay attention to it - the trip on the VSR (start full) and BM-1 (house charging) are generally more interesting.

To test that, I shorted it out, and it worked - obviously, the little warning-light clip connector to the alt relies on continuity, but it seems like a rather strange way to fail-safe. A temporary swap out with the water-temp** bulb got us sorted - 9 days around the Solent, fridge on all the time, heating occasional, groundings at Newport & Ryde (not Bramble!), and good tide-runs to/from Yarmouth for start of the gaffers.

I tried disconnecting the field-sense wire, but didn't see a noticeable difference in motive power - maybe I'm under-propped and it's time to think^W come up with an excuse for a folder....

*AKA the "cardboard manager" tactic - Imagine you're explaining the problem to your manager - or a cardboard cut-out; makes no difference - by the time you've reduced the problem to simple enough terms for him to understand, you've worked out the answer ;->
Cabin Boy (age 6) /tried/ to help with "But Daddy, you said the alternator spins to generate electricity, so why can't you just turn it with your hand?"...

** Not even sure I've got a water temp sensor...

 

[VicS]

Update - lots of yummy amps (up to 26 after running house bank down) with slightly wider belt, *after* much head-scratching and replacement of charge-warning-light bulb on engine panel.

I initially got no charge from the recon alt, so after discussing with crew*, and RTFM, I noted that the only untested item in the circuit was the charge bulb (normally lit for no charge, unlit when charging).

A bulb is just a bit of wire with resistance such that it emits light, right?
It was blown and hence open cicruit - as the engine panel is indoors under the bridgedeck, I rarely pay attention to it - the trip on the VSR (start full) and BM-1 (house charging) are generally more interesting.

To test that, I shorted it out, and it worked - obviously, the little warning-light clip connector to the alt relies on continuity, but it seems like a rather strange way to fail-safe. A temporary swap out with the water-temp** bulb got us sorted - 9 days around the Solent, fridge on all the time, heating occasional, groundings at Newport & Ryde (not Bramble!), and good tide-runs to/from Yarmouth for start of the gaffers.

I tried disconnecting the field-sense wire, but didn't see a noticeable difference in motive power - maybe I'm under-propped and it's time to think^W come up with an excuse for a folder....

*AKA the "cardboard manager" tactic - Imagine you're explaining the problem to your manager - or a cardboard cut-out; makes no difference - by the time you've reduced the problem to simple enough terms for him to understand, you've worked out the answer ;->
Cabin Boy (age 6) /tried/ to help with "But Daddy, you said the alternator spins to generate electricity, so why can't you just turn it with your hand?"...

** Not even sure I've got a water temp sensor...

It varies a bit with alternator but the small current that flows through the warning light sometimes/often/usually gives the alternator rotor its initial excitation. Once the thing is generating it supplies its own field current but because the rotor retains no magnetism it needs this little bit to get it started.

The original Hitachi alternator may have been one with a parallel circuit that excited the alternator despite a failed/non operating warning light

 

[onenyala]

On a vaguely connected subject. I have a Beta BZ 482 engine with a 40 amp alternator charging two 85 amh batteries in paralell. In addition I have an 18 watt solar panel hooked up directly to the batteries.
In the manual Beta suggest a battery amh of 35AH to 50 AH. My 2 x 85AH batteries are wet batteries and thanks to the solar panel are always well charged.
What is the potential problem with the 2 x 85 AH batteries against the recommended 35AH - 50 AH batteries

 

[VicMallows]

What is the potential problem with the 2 x 85 AH batteries against the recommended 35AH - 50 AH batteries

There is none. You can use any capacity battery. You will actually replace a given number of AHr discharge faster into the larger battery bank.

I think that Beta meant that as far as their engine was concerned a 35-50 AH battery was adequate for starting duties ... though it would have been better if they had quoted a CCA (cold cranking amps) figure.

Vic