Will an A4 run without a working Alternator

[Bryanphaas]

Forgive the newbie question; but I cant seem to come up with a reasonable answer to this: Will an A4 run without a working alternator.

I pulled my Alternator this spring to have it bench-tested; simply as a precaution and for peace of mind. Last season as I winterized the boat, the engine was running mostly fine.

I've never noticed any real "charge" on the circuit from the alternator; regardless of engine RPM.

When the Alternator was removed and tested today, my Alternator guy told me its completely shot, with no voltage reading whatsoever. He figures the regulator is shot. 89$ to get it fixed...

My understanding of engine mechanics tells me that the batteries provide the initial starting crank via the starter. Once the engine is running, the alternator/battery circuit provides electricity to the coil and spark plugs to ignite the fuel.

Therefore, Id assume, without a working alternator, the engine would be "running" off battery alone. I would also assume that this is a rather significant load, and probably would wear down the batteries rather quickly. (To winterize the boat I have a 10 trip upriver, motor only. I'd be surprised that the batteries could handle that requirement).

While it is possible that the alternator died in the final few minutes of running last season, Im curious to know your thoughts!

[romantic comedy]

The engine should run for hours on a good battery.

[Mo]

Forgive the newbie question; but I cant seem to come up with a reasonable answer to this: Will an A4 run without a working alternator.

I pulled my Alternator this spring to have it bench-tested; simply as a precaution and for peace of mind. Last season as I winterized the boat, the engine was running mostly fine.

I've never noticed any real "charge" on the circuit from the alternator; regardless of engine RPM.

When the Alternator was removed and tested today, my Alternator guy told me its completely shot, with no voltage reading whatsoever. He figures the regulator is shot. 89$ to get it fixed...

My understanding of engine mechanics tells me that the batteries provide the initial starting crank via the starter. Once the engine is running, the alternator/battery circuit provides electricity to the coil and spark plugs to ignite the fuel.

Therefore, Id assume, without a working alternator, the engine would be "running" off battery alone. I would also assume that this is a rather significant load, and probably would wear down the batteries rather quickly. (To winterize the boat I have a 10 trip upriver, motor only. I'd be surprised that the batteries could handle that requirement).

While it is possible that the alternator died in the final few minutes of running last season, Im curious to know your thoughts!

As stated by RC, batteries will last a while. You should have an alternator working as well. As for the trip, 10 minutes or 10 nautical miles...a battery in good condition, well charged, no other electrical draw...should make it. Battery won't last long going up and down, so you need to order up an alternator.

[Bryanphaas]

So it's quite possible that I've been running without a working Alternator for quite some time?

I've got a robust solar charging system (I'm on a can); which keeps my starting and house batteries topped off. And other than the quick weekly motor in and out, the engine doesnt see much use.....

[Mo]

Certainly possible if you don't have a gauge to monitor your charging.

[ndutton]

My understanding of engine mechanics tells me that the batteries provide the initial starting crank via the starter. Once the engine is running, the alternator/battery circuit provides electricity to the coil and spark plugs to ignite the fuel.

One way to look at it - and all other electrical on the boat - is it ALL runs off the batteries. All the alternator does (and/or solar and/or shore power) is replenish the batteries.

[joe_db]

Your running load is likely about 5 amps for the engine. Assume you can use 50% of the AH ratings of your battery. My house battery is 190 AH, so I could safely motor 16 hours and stretch it to near twice that if nothing else is on. A voltmeter will help here, once you drop below 12.0 volts you need to think abut being tied up and recharging.

[Dromo]

If it were me I'd hook the alternator back up start the engine and remove the + post on the battery , if the engine dies it the alternator .
if it keeps running , the alt. charging
P.S if the engine doesn't quit running reconnect the + post as soon as possible

[ndutton]

If it were me I'd hook the alternator back up start the engine and remove the + post on the battery , if the engine dies it the alternator .
if it keeps running , the alt. charging
P.S if the engine doesn't quit running reconnect the + post as soon as possible

Oh-oh.

How is this test any different than turning the battery switch to 'Off' while running and risking the very real possibility of a transient spike blowing the alternator's diodes? The test could be destructive.

[Dromo]

Your Right, a battery switch would do the same thing, my line of thinking was , if he was told the alternator was already shot . why not take a risk, if it meant keeping $89. in pocket

.

[ndutton]

On the other hand if the problem is the regulator as they suspect and not the diodes, the test risks destruction of good parts. It won't be $89 any more.

I dunno, if Bryan trusts this alternator shop and they'll guaranty their work . . . . y'know??

[Dromo]

Good point $.
I just have the basic of how these things work .Not my line of expertise
that's where you guys come in
I have done this test on older cars and my A-4 without anything blowing
guess I got lucky

[ndutton]

It's not guaranteed to damage the diodes every time but the risk is great enough that most if not all battery switch manufacturers include dire warnings about 'switching through Off' and tout their 'Make Before Break' contact feature.

It's good we chat about it though. Good info for those unaware, good reminder to those who are aware.

[Dromo]

Alternator field disconnect ?
Is this a mod. , or something to do with the make of alternator you have ?
I'm lost .
do you think this topic would warrant a new thread ?

[ndutton]

The field disconnect is another tier of alternator protection for those who can't remember not to turn the switch off while the engine is running. Not all alternators can be protected that way though. The popular internally regulated single wire alts can't, no field wire to interrupt. My Delco is that way.

Also, I've never had a field disconnect battery switch. Good thing I've never had an engine running - switch off incident in over 40 years of boat ownership. This is a similar argument the Automatic Charging Relay guys make, impossible to damage the alternator when the relay does all the thinking for you. I argue back, "So what's it do for me? I've never damaged an alternator despite never having an ACR."