Did I Damage the Alternator?

[Joeroc]

I don't know what I was thinking but the other day I inadvertently shut my yanmar 56 hp diesel off by turning the key before pulling out a the stop stick. Did I most definitely damage my Balmar alternator or is there a chance that its okay? I've literally NEVER done this before!! So stupid! Is there a chance that is okay?

[Jim Cate]

I think that you should be ok. What damages the diodes is disconnecting the load from the alternator whilst running. I'm not familiar with the switching set up on Yanmars, but I suspect that what you did merely shut off the field supply to the alternator which will not damage it.

Cheers,

Jim

[Stu Jackson]

I agree, all you did was turn the regulator off, which simply tells the alternator to stop producing current. You can check by turning things back on and checking the output voltage either at the alternator or at the house bank. Alo, don't ever interrupt the AO (alternator output) or you will fry the diodes. That's why many of us suggest moving the AO off the 1-2-B switch and directly to the house bank.

[Joeroc]

Okay. I hope you're right. And I'm sure you are. Just the same I just bought a beneteau 393 and sailed it 51 straight hours from Baltimore to Stonington CT so I was a little fatigued as you can well imagine. I was reading the manual and it says NEVER TURN OFF KEY OR BATTERIES BEFORE USING STOP STICK OR DAMAGE TO DIODES WILL OCCUR. I knew the very second I turned the key that I had screwed up but was holding out hope that maybe it's still okay. Sleep depravation is what I'll chalk it up to if it needs a rebuild.

[roverhi]

I've got a 3GM30f Yanmar and usually turn off the key before activating the fuel shut off. Have no cable to the shut off so have to go below to activate it on the engine. Don't want the 'low oil pressure' horn blasting when the engine shuts down.

AFAIK, you can switch off electrical power to the alternator at idle without blowing the diodes. Beiieve the alternator can't put out enough juice at that low rpm to do damage. Have done it a couple times over the years out of stupidity and didn't hurt the alternator. Do not try it at cruising rpm.

[Joeroc]

Thanks to all for your help. I feel better now.

[sailinglegend]

Definitely no damage to the alternator! Turning off the ignition switch cuts the activation voltage to the Balmar regulator which turns it off - see the manual.

Turning off the ignition switch has a very useful function if you want to kick the alternator back into absorption mode. Your regulator may be set to say three hours at absorption before it switches to float. Your batteries may not be anywhere near fully charged (The Charging Gotcha - FLOAT doesn't mean fully charged) so you can "force" the regulator back into a higher absorption voltage to get them charged quicker.

[Jim Cate]

Originally Posted by roverhi

AFAIK, you can switch off electrical power to the alternator at idle without blowing the diodes. Beiieve the alternator can't put out enough juice at that low rpm to do damage. Have done it a couple times over the years out of stupidity and didn't hurt the alternator. Do not try it at cruising rpm.

Rover, if the switch just cuts off power to the regulator (and thus the field coils of the alternator) the RPM at shutoff does not matter. Perfectly safe at cruising RPM.

Jim

[bill good]

I am charging LiFePo4 start batteries & shut off the alternator O/P at the B+ post as part of the charge control. (Trying not to modify standard alternator) No damage so far with standard alternator. But have added some extra capacitors to reduce any spikes. The "danger" is the extra voltage that is present, it is not high enough to damage diodes but could damage other electronic components still in circuit ie expect up to 17V with a battery disconnected. Will advise if the alternator is adversley effected over the next few months.

Regards Bill

[Ian R]

Originally Posted by bill good

I am charging LiFePo4 start batteries & shut off the alternator O/P at the B+ post as part of the charge control. (Trying not to modify standard alternator) No damage so far with standard alternator. But have added some extra capacitors to reduce any spikes. The "danger" is the extra voltage that is present, it is not high enough to damage diodes but could damage other electronic components still in circuit ie expect up to 17V with a battery disconnected. Will advise if the alternator is adversley effected over the next few months.

Regards Bill

Bill where did you buy your batteries, I'm in Maryborough at the moment.
Could you put a small load on the alternator side of your switch if it is too difficult to switch the field.
Regards Ian