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  #1   IP: 99.127.160.180
Old 04-08-2014, 05:30 PM
Bryanphaas Bryanphaas is offline
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Will an A4 run without a working Alternator

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!
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Old 04-08-2014, 05:32 PM
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The engine should run for hours on a good battery.
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Old 04-08-2014, 05:41 PM
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Quote:
Originally Posted by Bryanphaas View Post
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.
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Old 04-08-2014, 05:42 PM
Bryanphaas Bryanphaas is offline
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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.....
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Old 04-08-2014, 05:44 PM
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Certainly possible if you don't have a gauge to monitor your charging.
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Last edited by Mo; 04-08-2014 at 09:28 PM.
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Old 04-08-2014, 05:59 PM
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Quote:
Originally Posted by Bryanphaas View Post
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.
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Old 04-08-2014, 06:07 PM
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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.
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Old 04-08-2014, 06:41 PM
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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

Last edited by Dromo; 04-08-2014 at 06:51 PM.
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Old 04-08-2014, 07:21 PM
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Quote:
Originally Posted by Dromo View Post
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.
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Old 04-08-2014, 08:47 PM
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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

.

Last edited by Dromo; 04-08-2014 at 08:58 PM.
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Old 04-08-2014, 09:06 PM
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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??
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Old 04-08-2014, 09:31 PM
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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
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Old 04-08-2014, 09:41 PM
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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.
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Old 04-08-2014, 10:26 PM
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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 ?
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Old 04-08-2014, 11:01 PM
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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."
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Old 04-08-2014, 11:15 PM
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Lightbulb Fwiw

I once ran for 6+ hours when the belt snapped as I was entering the fairway in Emerald Bay. We spent the weekend and I did not get into the "ditty box" for a belt. When it was time to leave I just started and figured in less than an hour the wind would be up and I could change the belt then. Well no wind and I motored all the way back on my house which also ran the stereo, autopilot, radio and the blower. I did only run the blower about 2+ hours.

This was done on 2 #2356V golfcart batteries (235 ah). I did not use the start battery at all even starting. We sat for 2 nights and 3 days plus the 6 hours of running. I was a bit curious and just tried it to see for myself. Once I arrived back in Long Beach I did a normal shut down and in the morning the house bank would not start the engine, it did barely turn over though.

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Old 04-09-2014, 12:52 AM
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similar to my experience with a chevy years ago. belt went in the middle of nowhere and just kept driving. it wasn't 6 hours but likely more then 100 miles. pulled over the crest of a hill, the engine called it quits when the battery could no longer support ignition....rolled into a gas station.


i think there's a bob dylan song in there....somewhere

why not just install an amp gauge or if you have one test it
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Old 04-09-2014, 01:24 AM
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Quote:
Originally Posted by nyvoyager View Post
similar to my experience with a chevy years ago. belt went in the middle of nowhere and just kept driving. it wasn't 6 hours but likely more then 100 miles. pulled over the crest of a hill, the engine called it quits when the battery could no longer support ignition....rolled into a gas station.


i think there's a bob dylan song in there....somewhere

why not just install an amp gauge or if you have one test it
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Last edited by lat 64; 04-09-2014 at 01:33 AM.
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Old 04-09-2014, 08:32 AM
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That is a great way to make SURE the alternator isn't working

Quote:
Originally Posted by Dromo View Post
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
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Old 04-09-2014, 08:36 AM
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http://www.amazon.com/Digital-VOLT-M...ital+voltmeter


Spend the $7.99 and do some non-destructive testing

Quote:
Originally Posted by Dromo View Post
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

.
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Old 04-09-2014, 02:34 PM
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Thumbs up

Even with the stock Motorola alternator, you should see 13.8 volts at the battery when the engine is running. If you see 12.6 or less, the alt. is not working. This can be easily checked with the meter above.

As already stated, the A-4 will run for hours on just batteries. I did a 45 minute motor up the creek, after deliberately pulling my alt. belt when I thought it was overcharging..The volt meter on the DC panel barely moved and the engine ran fine. Once I realized my $7.99 volt meter was no good, I hooked the alternator back up.
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