Switching the Ignition off while Engine running

[britinusa]

I read about an issue of potentially blowing the Alternator Diodes and Regulator if the engine ignition switch is turned off while the engine is running.

In our case, the Alternator is wired to the batteries, ie. not via the Off-1-2-both switch.

Is this a real issue or sales hype for a device to prevent the damage?

Paul

[KWKloeber]

Hi Paul

The effect that the key switch has on the Alt, is simply to excite the field so that (at low rpm) the alt starts moving electrons. 
If the (purple) field wire is cut, or was never energized, or the switch is turned to off, it has no negative effect.  And the alt will still charge if the RPMs are up and the Alt is already "excited" and happy about the job it's doing. 

The replacement regulators that RC sells, converts the Alt into a self-exciting (so does away with the wire from the key switch to the Alt.)

Now, turning the battery switch through "off" (not in your case) is a completely different story and will likely result in blown diodes.

-ken

[scgunner]

   Paul,

      Weather it's a real issue or not why take the chance since there's no advantage(at least that I know of)to doing it.

[britinusa]

Here's where I saw the issue:

https://www.electriccarpartscompany.com/12V-24V-Alternator-Open-Circuit-Protection-Device

Paul

[Stu Jackson]

>>>>>>>>>>>>>>>>>>>>

Now, turning the battery switch through "off" (not in your case) is a completely different story and will likely result in blown diodes.

Simply not true in Paul's case because he clearly said: "In our case, the Alternator is wired to the batteries, ie. not via the Off-1-2-both switch."

He could turn the 1-2-B switch off with the engine running and do no harm.

[KWKloeber]

Paul,

Nowhere in that advertisement do I see it mentioned re: disconnecting the field excite circuit.  If you look at where the lifesaver is installed, it's on the AO, or Batt, or Pos Output terminal of the Alt, and prevents "spikes" (huh?? lightning maybe?  ) on that end of the circuit.
I take the "turning off the engine's electrical power" as a broad statement that doesn't mean anything.

A terrible advertisement that doesn't exactly describe what it's protecting against.  They'd never get away with that in the UK

Stu,
Yep, thanks for agreeing with me! [emphasis added below]

Now, turning the battery switch through "off" (not in your case) is a completely different story and will likely result in blown diodes.

Simply not true in Paul's case because he clearly said: "In our case, the Alternator is wired to the batteries, ie. not via the Off-1-2-both switch."

He could turn the 1-2-B switch off with the engine running and do no harm.

[KWKloeber]

Paul

Here's another thing on that page I forgot to mention...

Failure of a fuse if fitted in the alternator's circuit

That could affect you -- I presume you have a fuse w/in 7" of the battery terminal at that end of your charge cable?
If the Alt charges thru the starter solenoid "B" terminal post, then there should no fuse on the alt output cable.

-k

[Stu Jackson]

I apologize.  I was wrong.  Still failing Reading Comprehension 101...  :D:D

[mark_53]

I read about an issue of potentially blowing the Alternator Diodes and Regulator if the engine ignition switch is turned off while the engine is running.

In our case, the Alternator is wired to the batteries, ie. not via the Off-1-2-both switch.

Is this a real issue or sales hype for a device to prevent the damage?

Paul

I believe I have turned off the ignition switch while the engine is running and my alternator is still working.  Sounds like sales hype or missing information.

[mainesail]

I read about an issue of potentially blowing the Alternator Diodes and Regulator if the engine ignition switch is turned off while the engine is running.

Myth..

Here's where I saw the issue:

[urlhttps://www.electriccarpartscompany.com/12V-24V-Alternator-Open-Circuit-Protection-Device[/url]

That device is for when the alternator B+ (not the excite wire) is inadvertently disconnected from the battery bank when the alt is running. This can certainly blow the diodes, and beyond that, can result in a very damaging voltage spike on your DC bus. The Sterling Power Alternator Protection Device is very good insurance policy for that application.

The reason you see it on EV web sites is because folks design LiFePO4 systems incorrectly or use "drop-in" LFP batteries that have an internal sealed BMS that can open the battery circuit without warning. It can do so based on battery temp, high voltage, low voltage or too much current draw for the wimpy FET based BMS switches to handle....

The Sterling Power Alternator Protection Device can also be use on your DC system to prevent damaging voltage transients, not just from an open circuited alternator.
https://marinehowto.com/voltage-transients-in-marine-electrical-systems/

The Sterling Power Alternator Protection Device can also be purchased for a lot less $$: https://shop.marinehowto.com/products/sterling-power-12v-transient-voltage-protection-device

[mainesail]

Paul

Here's another thing on that page I forgot to mention...

Failure of a fuse if fitted in the alternator's circuit

That could affect you -- I presume you have a fuse w/in 7" of the battery terminal at that end of your charge cable?
If the Alt charges thru the starter solenoid "B" terminal post, then there should no fuse on the alt output cable.

-k

This is why any fuse, for an alternator connected directly to the bank, should be sized at at least 150% of the alternators rated output. If a fuse sized correctly fails, it needed to.

[scgunner]

     Lots of interesting information on this topic(as usual)but it just seems like a problem that solves itself.

[Bobg]

never know whats going to happen on your boat with guests aboard, the music was too loud in the cockpit and I asked my brother to go below and turn the radio down, told him to turn the big knob on the radio, (volume control) which was located above the nav station, he came back up and the music was still loud and because we were on a boat he didn't understand and turned the 1-2-both switch, he is not a stupid person, just confused on a boat.  didn't hurt anything but I wired my alt output to the battery right away.  Always get ready for the helpful new guy.  :)