Running battery charger and engine

[callistov42]

I am often guilty of having my battery charger running via the generator and cranking up the main engine (and therefore the alternator). Is that a diode killer? This question is related to my question about rebuilding my old Balmar. Also, when your alternator stops putting out, how do you determine if the problem is the alternator or the regulator?

[wingssail]

Originally Posted by callistov42

I am often guilty of having my battery charger running via the generator and cranking up the main engine (and therefore the alternator). Is that a diode killer? This question is related to my question about rebuilding my old Balmar. Also, when your alternator stops putting out, how do you determine if the problem is the alternator or the regulator?

Question 1. I don't think that is going to hurt anything, but let the experts on this forum give their opinion.

Question 2. I take a cord with alligator clip on one end, (clip it to a 12v source) and a probe on the other end. With the engine running touch the probe to the field wire either on the plug for the regulator (unplugged please) or on the field connector on the back of the alternator.

If the alt starts putting out current then it is the regulator. If not it is probably the alternator.

[rslifkin]

Running an engine with a battery charger also online won't hurt anything. I do it any time I'm doing a test run for engine maintenance at the dock. And if it's early or late in the season (colder weather), I'll sometimes start my engines before unplugging from shore power to give them the extra minute of warmup time.

[smac999]

Nothing wrong. Will charge faster with both on.

Most Alts have the reg inside so either way the alt is going to a shop.

If reg is external there are ways to test both. Check for field voltage from reg. Check ohms of feild input of alt. Put 12v direct to alt field post to bypass reg. All of those done with feild wire disconnected .

[rslifkin]

One way to diagnose an alternator problem is to start the engine, confirm the alternator isn't putting out power. Then hit the alternator fairly hard with something. If it suddenly puts out power, the brushes are worn or sticking. If not, then it's something else that's wrong.

[Scubaseas]

Originally Posted by callistov42

I am often guilty of having my battery charger running via the generator and cranking up the main engine (and therefore the alternator). Is that a diode killer? This question is related to my question about rebuilding my old Balmar. Also, when your alternator stops putting out, how do you determine if the problem is the alternator or the regulator?

Usually not a problem but putting the running alternator to open circuit like when switching a 1-2 all-off selector switch can fry diodes.

Apply battery voltage to the field wire terminal at the alternator and the alternator should go to full output. If you have voltage at B+(the heavy gauge wire , 12V at field terminal and the alternator is grounded it should work. If it doesn't work the brushes may be stuck or there is some other issue. If it charges with the regulator bypassed (i.e you powered the field wire) then your problem is in the regulator or power supply/wiring there to.

Or look at https://shop.pkys.com/Troubleshootin...tor-_b_79.html

If it were three weeks later you could buy me a beer and I could come over and tell you. I'll be doing a refit in Seabrook Shipyard.

[donradcliffe]

One time I put full battery voltage across the field on a Balmar 612 regulated alternator that wasn't charging. The alternator started charging, but the Balmar went flatline after that. I was offshore, and had to spend the next week putting various incandescent 12v bulbs in the field circuit to limit charging current.

I'm not sure that that regulator wasn't already the problem, but next time I will disconnect it before I flash the field.

[skwanderer]

Originally Posted by Scubaseas

Usually not a problem but putting the running alternator to open circuit like when switching a 1-2 all-off selector switch can fry diodes.

Would you expand on that and explain further please? Which selector switch position(s) can fry diodes?

[Scubaseas]

Originally Posted by donradcliffe

One time I put full battery voltage across the field on a Balmar 612 regulated alternator that wasn't charging. The alternator started charging, but the Balmar went flatline after that. I was offshore, and had to spend the next week putting various incandescent 12v bulbs in the field circuit to limit charging current.

I'm not sure that that regulator wasn't already the problem, but next time I will disconnect it before I flash the field.

Excellent point. I actually know what I am doing being a ASE and other master mechanic of over 50+ years but writing about how to do it is not my forte. You should disconnect the field wire. Using a test light with a bulb in it is also a good way to apply power to the field wire. So use a test light with a 20w bulb, one end on the B+ or heavy wire or starter wire to battery for you power and the use the probe end on the field terminal on the alternator.

[Scubaseas]

Originally Posted by skwanderer

Would you expand on that and explain further please? Which selector switch position(s) can fry diodes?

In the good old days one could remove the battery cable while the engine was running to tell if the generator was charging. Doing so now on your car may fry literally thousands of $ in ECUs. If you open circuit an alternator the resultant voltage spike may damage the isolation diodes in the alternator and or anything that's on when you do it. Fix I can do, explain why/how not so much. So have a look at a most excellent website and store you should be buying stuff from to help support:

From https://marinehowto.com/1-2-both-bat...onsiderations/

..."Blown Alternator Diodes & Voltage Transients:
This big blunder happens when you, or a crew mate, tries to switch to another bank and pass the battery switch through the *OFF position, even momentarily. With the engine running and the alternator charging this creates an open-circuit between the alternator and the load (load = battery bank) it’s charging. Momentarily passing through OFF, or disconnecting the load from the alternator, can cause a massive voltage spike as the load/ battery bank is disconnected from an alternator. This quite often results in damaging the alternators rectifier diodes & rendering it non-operational near instantly. it can also damage sensitive electronics that are connected to the “C” post of the switch.

*Most quality 1/2/B battery switches, from reputable manufacturers like Blue Sea Systems, BEP/Marinco, Guest & Perko, are designed to be make-before-break. Make-before-break means that as you turn the switch from position 1, to BOTH or 2, the previous position does not open-circuit or disconnect until the next position can carry the current.

As some battery switches age they can wear and become break-before-make. For this reason it is not a good idea to move the switch while the engine is running unless you perform an occasional make-before-break test. The best way to test your switch is to turn on the cabin lighting (incandescent bulbs work best not LED’s) then slowly rotate the switch from 1 to BOTH to 2. If the incandescent light/s flicker at all during this rotation, replace the switch. Even a fraction of a second disconnect is enough to cause an alternator load-dump...."

Marinehowto also sells This nifty problem solver: https://shop.marinehowto.com/product...tection-device

[Cheechako]

One charging source may read what the other source is putting out, sensing it needs to back off.

[skwanderer]

Originally Posted by Scubaseas

In the good old days one could remove the battery cable while the engine was running to tell if the generator was charging. Doing so now on your car may fry literally thousands of $ in ECUs. If you open circuit an alternator the resultant voltage spike may damage the isolation diodes in the alternator and or anything that's on when you do it. Fix I can do, explain why/how not so much. So have a look at a most excellent website and store you should be buying stuff from to help support:

From https://marinehowto.com/1-2-both-bat...onsiderations/

..."Blown Alternator Diodes & Voltage Transients:
This big blunder happens when you, or a crew mate, tries to switch to another bank and pass the battery switch through the *OFF position, even momentarily. With the engine running and the alternator charging this creates an open-circuit between the alternator and the load (load = battery bank) it’s charging. Momentarily passing through OFF, or disconnecting the load from the alternator, can cause a massive voltage spike as the load/ battery bank is disconnected from an alternator. This quite often results in damaging the alternators rectifier diodes & rendering it non-operational near instantly. it can also damage sensitive electronics that are connected to the “C” post of the switch.

*Most quality 1/2/B battery switches, from reputable manufacturers like Blue Sea Systems, BEP/Marinco, Guest & Perko, are designed to be make-before-break. Make-before-break means that as you turn the switch from position 1, to BOTH or 2, the previous position does not open-circuit or disconnect until the next position can carry the current.

As some battery switches age they can wear and become break-before-make. For this reason it is not a good idea to move the switch while the engine is running unless you perform an occasional make-before-break test. The best way to test your switch is to turn on the cabin lighting (incandescent bulbs work best not LED’s) then slowly rotate the switch from 1 to BOTH to 2. If the incandescent light/s flicker at all during this rotation, replace the switch. Even a fraction of a second disconnect is enough to cause an alternator load-dump...."

Marinehowto also sells This nifty problem solver: https://shop.marinehowto.com/product...tection-device

THANK YOU!! AWESOME RESPONSE!!

[seabreez]

Originally Posted by rslifkin

One way to diagnose an alternator problem is to start the engine, confirm the alternator isn't putting out power. Then hit the alternator fairly hard with something. If it suddenly puts out power, the brushes are worn or sticking. If not, then it's something else that's wrong.

..
OUFFF I would never hit an alternator with something fairly hard... I casn only hit with the probes of my dvom...

[seabreez]

Originally Posted by skwanderer

Would you expand on that and explain further please? Which selector switch position(s) can fry diodes?

When a known good charging alternator is running it charges up to 14.7 volts. When disconnected it drops to 0 volts and when reconnecting goes back up to 14.7 volts. When a battery is dead and needs a boost you start the engine and you observe the voltage start charging and gradually comes up. No problem. The spike when switching from 0 to 14.7 is the killer for the diodes.

[Stu Jackson]

Originally Posted by skwanderer

Would you expand on that and explain further please? Which selector switch position(s) can fry diodes?

The alternator output.


Some of them go to the battery selector switch, the big RED thing.