Have I fired my alternator diodes?

Iain C

Iain C

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Oh the irony. Having borrowed a dymo label machine from work and even made a "do not go through off with the engine running" label last weekend, guess what I did?

Yep, I thought I was charging both batteries, of course I was charging no batteries. For about 5 seconds.

I'm really, really hoping that I have not fried my diodes. Especially as when fiddling around after the event charging an almost flat battery, the engine is clearly losing some revs as the load of the flat battery comes on the alternator, and going up again as I swap to the good battery.

Am I lucky or have I cooked them? Engine is a Lombardini M602 if that makes any difference...

Thanks!
 
Iain C said:
Oh the irony. Having borrowed a dymo label machine from work and even made a "do not go through off with the engine running" label last weekend, guess what I did?

Yep, I thought I was charging both batteries, of course I was charging no batteries. For about 5 seconds.

I'm really, really hoping that I have not fried my diodes. Especially as when fiddling around after the event charging an almost flat battery, the engine is clearly losing some revs as the load of the flat battery comes on the alternator, and going up again as I swap to the good battery.

Am I lucky or have I cooked them? Engine is a Lombardini M602 if that makes any difference...

Thanks!
Click to expand...

Think you've answered your own question really. No output= no load = no electricity. Output=load=electrickery,battery being charged.Easy to check voltage at battery while engine running.
 
It's NOT the engine you have, it is the alternator. Do you have an opportunity to get to a pontoon and use a shorepower charger instead of your alternator? Rather than trying to use the alternator o charge a depleted bank, recharge the bank first, then try the alternator.

I have investigated this in the past, and found this: see Reply #11: http://c34.org/bbs/index.php/topic,2977.0.html

Check the output of the alternator. With the engine running, preferably at more than 1500 rpm, measure the voltage at the battery bank. If it's well over 12.8 V you should be OK. If not, then maybe you're fried (rather than fired!;)).

Good luck, only you can be able to tell, since we're not there and can only suggest what to do "if it was my boat.".
 
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You may have been lucky especially if the load on the alternator was low when you switched the load off.

If you mean that you started and ran the engine with no battery connected to the alternator then there is no problem anyway because it is the voltage surge when you disconnect the load that causes the problem.

Some alternators are fitted with a surge protection diode.

If you did disconnect the load from it while running but it seems OK then it probably is OK but you could have blown only part of the rectifier. Keep an eye on the output. If it still delivers its full output (amps) when called upon to do so then it is OK
 
Iain C said:
I'm really, really hoping that I have not fried my diodes. Especially as when fiddling around after the event charging an almost flat battery, the engine is clearly losing some revs as the load of the flat battery comes on the alternator, and going up again as I swap to the good battery.
!
Click to expand...

If the revs drop, then you may well be ok, alternators were fitted with avalanche diodes in the late 1970's to avoid this problem.

As the your alternator generates watts, ( volts x amps ) , open circuit switch means no amps, so sky high volts. This voltage was blowing the diodes, by fitting the avalanche diodes, excssive voltage is avoided, and the rectifier diodes remain ok.

But check with a voltmeter / ammeter.

Brian
 
gasdave said:
Brian,

Was this all alternators? And if not necessarily, is it possible to tell if you have an alternator with avalanche diodes?
Click to expand...

It became a standard, wether it remained may depend on penny pinching at a later date by the manufacture.

In passing. years back there was a Westerly that motor sailed for three hours with both engine and service battery isolators off.
They were located on the chart table seat, the back of some ones legs accidently turned them off. The split charge relay was engaged, and the capacitance / load on the service battery allowed the alternator regulator to hold down the voltage. Only when they stopped the engine, did the boat get plunged into darkeness as they lost all electrical power.

So you can run alternators without damage, and may be another reason for relay split charging, but thats another thread.

Brian
 
Alternator

It does seem that if the alternator loaded the engine to the extent of reducing engine revs then it is working very well. An easy check is to measure the battery voltage when the alternator is charging it should go up above 13v. A far better check is to have an amp meter in the battery power wire. The actual current will depend on engine revs and battery condition. If you can get 10 to 20 amps into fairly flat batteries you are doing well.
The thing about alternators is that they use 3 phase rectifier ie 6 diodes. if one dies you will still get some output like about 1/3 of normal which may not be noticed by some people. ie only 3 to 6 amps of charge.
So an ampmeter can better confirm that it is really working properly. olewill
 
The trouble with this sort of question is that electronics are not always predictable in failure.
Even if the alternator works happily now, you may have shortened its life, changed its regulated voltage or some other non-total damage.

But the most likely outcome is that it will be fine imho.

Removing the battery from the system can also damage anything else that is in circuit at the time, but items intended for vehicle use should be reasonably resistant.
 
Some five years ago, I had a similar 'OFF' incident coming out of the Medway on an almost windless day.
Whilst mtoring across to the Essex shore, I asked my crew to change from '1' to 'BOTH'. Some ten minutes later, in the middle of the channel and passing well ahead of a ship, the engine died and the starter wouldn't work although depth and log displays were ok.
Turned out the crew had turned to 'OFF' but the log/depth kept working as they are on a separate master switch. The engine, a Ford XLD1600, has an electric fuel cut-off in the pump which had been kept energised by the alternator. A moments thought and returning to '1' again allowed the engine to start and heart rates subsided.
Neither alternator nor Merlin charge controller appear to have been damaged and continue working to this day.
 
Iain C said:
Oh the irony. Having borrowed a dymo label machine from work and even made a "do not go through off with the engine running" label last weekend, guess what I did?

Yep, I thought I was charging both batteries, of course I was charging no batteries. For about 5 seconds.

I'm really, really hoping that I have not fried my diodes. Especially as when fiddling around after the event charging an almost flat battery, the engine is clearly losing some revs as the load of the flat battery comes on the alternator, and going up again as I swap to the good battery.

Am I lucky or have I cooked them? Engine is a Lombardini M602 if that makes any difference...

Thanks!
Click to expand...

hello
no info on your alternator, so can only generalise.
The drop in engine revs when switching batteries is normal and suggests your alt. is working. I'm sure your voltage readings will confirm this. The question is how well is it working?
Listen & confirm a momentary drop in revs. If the engine doesn't come back up to speed within a few seconds (on the same battery) it could be that you have damage on one or more of the output phases.
(try on the near full battery also for comparison).

If not momentarily, personally, I would take the alt. off and bring it to an auto electric shop for testing. (explain that you want all phases tested). May be worthwhile getting your low battery tested also, unless you know how to do this already? It can be difficult sometimes to identify if a problem is with the Alt. or the battery its connected to.

don't know your selector switch type, but I have modified mine so that it can't be moved to the off position in error. doesn't take long & worthwhile considering.

hope this is of some help

rgds
c
 
halcyon said:
But then all you end up with are all the problems of a single battery bank, and the cost of a multiple battery banks.


Brian
Click to expand...

Huh? Can you expand on this?

We have been doing this for years in the US by running the alt directly to the house bank and then using a voltage sensed relay to charge the starting bank. Total cost about $80.00 US. The re-build of the alternator just once eclipses this. My neighbor blew his diodes twice in one summer before I convinced him to spend the $80.00 on the ACR (automatic charging relay)..

You still retain all the features of the 1/2/BOTH/OFF switch without the potential for frying the diodes. Most of the alts in the US are not protected against the OFF switch..
 
Thanks for all the replies (and sorry about the typo in the title!)

Hmm, well the engine does not go back to normal revs once the alternator load comes on, but then again how would it? Surely if a load is being put on the alternator, unless some very clever charging electrickery or throttle electricery is happening, then the revs are going to drop until more throttle is applied to compensate? If I hold the electric window switches up in my car with the windows already up, then the revs drop a little until I release, and I would bet that the chargins system and fly by wore throttle in an Audi is a bit more advanced than what is going on in what is essentially a cement mixer engine in the boat! (Lombardini M602, and quite modern, 10 yrs old or so). Then again, I'm such an electrics numpty anything's possible!

I'll have a fiddle with it at the weekend then and see what's going on. Thanks again!
 
Iain C said:
Hmm, well the engine does not go back to normal revs once the alternator load comes on, but then again how would it? Surely if a load is being put on the alternator, unless some very clever charging electrickery or throttle electricery is happening, then the revs are going to drop until more throttle is applied to compensate?
Click to expand...

I'm not sure I understand the continued reference to engine revs and load. If the alternator is working and the bastteries requrie a charge, then, sure, the load may, just may, be apparent. Sometimes I can't tell the difference. The only way I know is from my battery monitor showing that the bank is being charged.

If you don't have a battery monitor, keep it simple: use a DMM and simply measure the voltage at the bank.

Good luck.
 
Thought I would clarify a bit as my previous post isn't as clear as it could be on a second read.

My intention was to expand on the good advice posted by William_H.

All alt. phases will output at the same voltage, so a voltage reading won't tell you if all phases are working. An amp reading can help you if you know what readings to expect.

so , assuming no amp readings, that leaves engine rev.s as a troubleshooter.

On switching from light to relatively heavy loads, the engine revs. will drop momentarily and then increase once the alt. regulation has settled down. the extent to which the revs drop and rise will depend on the nature of the loads, the alt. rating/setup and the engine hp. You should be able to hear this clearly enough with a reasonably depleted battery and a relatively lightweight alt.

If I couldn't hear the rising revs I would suspect one of the following -
alt. - internal short or not outputing on all phases.
battery - internal short or severely depleted enough to demand continous full alt. output.

Rule out the severe delpetion by comparing engine revs with the cranking battery in line, (drain it down a bit first perhaps). failing that, I would advise verifying both battery and alternator independently.

Of course, alt. case temperature would also be an indicator, but only if you had a feel of what it was prior to the switching mishap.

hopfully some help
rgds
c
 
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Mmmm, all this sounds like an excellent case for an amp and volt meter to be included in each and every marine installation. Incidentally, clip on ammeters are not expensive, even in Great Britain.

Now, I do not want to sound “picky” boys but to me it would be the starting bank of batteries to be charged first then the house bank.

Or, perhaps, I have missed a finer point.

73s de
Johnth
 
Cimo

I think you have hit the nail on the head...the battery in question was depleted to the point that I only noticed my error when the car-style CD player stopped playing. So yep, pretty dead!

There was a big difference in revs between charging bat1 (in very good health) and bat 2 (very low) so I can live in hope perhaps!

I agree about monitoring instrumentation...at the moment I have nothing at all, and as the boat was very much a project, this is very, very near the top of "the list" as it stands now.

What do people recommend as the best easy, cheapish solution in terms of instrumentation? I see you can get a few ready made panels/instruments...
 
cimo said:
On switching from light to relatively heavy loads, the engine revs. will drop momentarily and then increase once the alt. regulation has settled down.
Click to expand...

No.

They will remain low until the load is reduced by the battery charging load reducing, from recharged battery, or the voltage coming up to regulation volts.

The regulator will only limit max volts, the current will be limited by alternator windings, or voltage available at battery,

Generating amps equals horse power, increased horse power equals more load on engine and less revs.

Brian
 
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