Alternator blown?

[marginal]

Hi all,
Hoping the electrical Jedis here can shed a little light on my recent issues.

I have a pretty stock late model A4, but the charging system uses a Blue Sea SI-ACR (auto charging relay) with a Blue Sea Dual Circuit plus battery switch.

When all my instruments stopped working, I realized my house battery has discharged down to ~9V.

On further investigation, the ACR is not combining the batteries, and since the alternator is connected to the start battery, no charge is delivered to the house battery when the engine is running.

So the next step is to figure out why the ACR has not been combining the batteries. I installed the LED indicator, and it is Off, indeed indicating the batteries are not combined.

This was a bit of a surprise, I expected the LED to flash, indicating that the start battery was being charged, but the house battery was locked out, due to the under voltage condition. The ACR was never trying to combine the batteries.

A little reading later, and the threshold for the ACR to combine is >13.5V on the start battery (from the alternator) for 2 minutes.

With the engine running at moderate revs, voltage at the start battery is about 13.3V, with only 13.0 on the other side of the fuse that connects to the ACR. At least I think that big square thing is a fuse....

So, now chasing the alternator voltage:
Output terminal of alternator with engine at moderate revs = 13.5V
Stopped the engine, disconnected the load from the alternator, started up again, and can see up to 15V at the alt output.
Stopped, reconnected load, restarted, 13.5V again.

Chasing the alt voltage around the boat:
alt output 13.5
Positive terminal of ammeter 13.5
Negative terminal of ammeter 13.5 (after tightening the nuts...)
Positive terminal of solenoid 13.3 (other side of fuse)
Both sides of battery switch, and battery post 13.3
Lead to ACR 13.0

Is my alternator simply pooched, and should be putting out >13.5 with the load connected?
Could it be anything else?
I'm surprised I'm losing 0.2 on the connection to the solenoid through the fuse.
Side note, if the fuse to the solenoid ever blows, is that not the same as suddenly disconnecting the alternator load, and risking the diodes?

I think my next step is a trip to an alternator shop, but I'm wondering if the wisdom of the board can point me in any different directions.

Thanks in advance for the help. This place is awesome. I've learnt so much already but this one is outside my knowledge.

Thanks
Simon

[ndutton]

13.5V alternator output is far too low, should be a minimum of 13.8V but modern charging systems are more like 14.0 ~ 14.2V. The lower numbers you're reading downstream are a result a voltage drop caused by wire size, wire length, poor connections or any combination of the three. You might look for another voltage drop through the ACR when it starts behaving.

One caution: if you have or are considering electronic ignition, resolving this low voltage issue can wreak havoc with critical ignition system maximum amperage. Be sure to read any of the electronic ignition threads and you'll be good.

And I agree with you, it sounds like the fuse could cause alternator diode damage when it blows. Some protection, huh?

[hanleyclifford]

If you are charging into a dead battery or one that may no longer be able to take a charge it is possible the 13.5 is OK because the alternator is putting out a lot of amperage or charging into a shorted cell, which you can read on your digital ammeter. If you get 15 volts at alternator +, the unit is good. If you show only 13.5 volts with connected load you better be putting out beaucoup amps.

[marginal]

Thanks Neil and Hanley.
I did try completely disconnecting the ACR from the start battery, so that the alternator is only connected to the start battery, and the dead house battery (and ACR) is completely out of the system. There was no change, still 13.5 max.

I guess it's time to take the alternator off and get it checked.

Thanks
Simon

[marginal]

Another thought... I think I have an exciter wire going to coil + (the one with the gold paint on it that goes to the connector)

https://www.dropbox.com/s/z5fygezfl3u4pao/2013-11-09%2012.53.22.jpg?dl=0

Is that simply a connector, or is it a fuse as well? Would a lack of 'excitation' cause what I'm seeing? Anything I should check?

Thanks
Simon

[BunnyPlanet169]

In the stock Motorola alternators I've seen, that plastic piece is just a cover for a spade lug male/female connection. I don't think you'll get anything from the alternator without the field excitation.... Maybe a volt or two (?) from residual magnetism.

[joe_db]

FYI: The A4 alternator is small enough, and the pulley ratio is low enough, that it is entirely possible that a large dead-ish battery can keep the system voltage quite low for quite a long time.

[ndutton]

After disconnecting everything except the engine start battery, if it had enough juice to start the engine I wouldn't consider it dead enough to be overly taxing on the alternator. Time for a trip to a real alternator shop (NOT Auto Zone!!) for a dyno test.

What battery chemistry are we talking about?

As it's a holiday weekend I'll spare you the agony of a sermon on my low opinion of ACR's in general.

[marginal]

Yep, that's where I ended up too, and I pulled the alternator last night.

I think there.s something weird going on with the house bank too, but with only the start battery connected, and only getting 13.1V from the alternator I decided to figure that part out first.

Not sure on the battery technology. Here's photos of them:

Start

https://www.dropbox.com/s/5b14c5rx4n92jrf/2014-08-31%2015.24.50.jpg?dl=0

House:

https://www.dropbox.com/s/gzmo89lvo66r809/2014-08-31%2015.24.56.jpg?dl=0

I'll let you know what the conclusion is on the alternator.

Thanks
Simon

[BunnyPlanet169]

Looking at your pictures, you may wish to consider some rewiring. You may indeed have a failing alternator, but you could also have significant losses in the wiring.

The battery terminals all have exposed copper stranding, and moisture will wick into the cables like you wouldn't believe. Also, I'd be curious what gauge the orange wire in your alternator picture was... From your description, that's a longish run through the ammeter and back to the solenoid. Some people here remove the ammeter completely and run directly to the solenoid. Others (including me) run a fat wire to minimize (but not completely eliminate) voltage drop. It the terminations are like the batteries, you will probably have significant losses here too.

[hanleyclifford]

IIRC Shawn posted that battery combiners cost about .9 volt in a system. Anybody else noted that?

[BunnyPlanet169]

Old diode combiners lost at least 0.7v, newer Shottky diode combiners less, but still at least 0.15v. I can't find a good number for a MOSFET SSR, it really depends on the manufacturer.... I was expecting < 0.1, but now I'm curious.

[ndutton]

Now guys, you're drawing me in

Guess how much voltage my old school manual battery switches lose.
Guess how much easier it is to troubleshoot the system without automated devices to out-guess.

K.I.S.S.

Simon, those appear to be conventional wet cell lead-acid batteries. Had they been something other like AGM's the charging voltages would have been higher. Looking forward to your debriefing after the alternator shop sortie.

[marginal]

Back from the alternator shop, $100 lighter but with an alternator that now puts out 14.8V and 40A

The in-boat fault of not being able to get >13.5V was confirmed on the big alternator machine. The diodes were OK, so the conclusion was that the regulator was bad.

New regulator fitted as I waited, and now things look good.

Thanks for the help and advice - I'll get to those battery cables and other wiring projects over the long winter. For now the priority is get it on, and get out there!

Simon (in Ottawa)

[joe_db]

Mine has essentially 0 voltage drop. Depends on how they are made. Mine uses a relay to make the connection.

IIRC Shawn posted that battery combiners cost about .9 volt in a system. Anybody else noted that?