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NCountry · 24-10-2012, 14:40

I've got a house bank that is 6 deep cycle 6 volt batteries. They're wired together to produce a 12 volt house bank.
I've got 2 alternators on my Perkins 4-154 diesel.
The other day we spent the night on the hook and everything looked good on the house battery bank in the morning. Barely touched. The start battery and the windless battery fully charged. Motored about 30 minutes to where we anchored for the day for a regatta. (Committee boat so we didn't get to put up the sails)
I get ready to start the diesel to leave where we were anchored and my house bank was almost dead. Got the motor started but opted to motor all the way back.
At the slip I top off the fluid levels just to be sure and turn on the charger (xantrex true charge 2) It took about 36 hours to get the house bank back to fully charged. On friday I turned off the 120 and left the boat on the house bank for about 3 hours. There was no noticable drop in the charge level of the batteries. The next day I start the motor and hear a loud whining coming from the alternators. I shut the motor down and while checking the alternators check my house bank. Almost dead!
What the heck? I've pulled the alternators and will have them tested but my question is.... Is it possible for a bad alternator to drain such a large house bank in such a short time? OR am I going to discover my alternators are good and are whining because of a load placed on them? Weird huh?
I'll report back in a day or two once the alternators are tested but it was such a weird occurance that I just had to post it here. There's no sign of anything overheating. I'm not seeing anything that is shorting out and the house bank recharges when I turn the charger bank on. So, what am I looking for?

Cheechako · 24-10-2012, 15:02

possible you have a dead short in one battery? After charging for a few hours, feel the temp of each battery, one with a dead short will be very hot. Maybe the alternators were whining in "high output mode" due to the short...?

Factor · 24-10-2012, 15:06

You are looking for new batteries. Failure to hold a charge like that is a reasonably sure sign of a rooted battery.

S/V Illusion · 24-10-2012, 15:29

Can you say "dead cell"?

sartorst · 24-10-2012, 15:43

A whining alternator is sometimes evidence of bad diodes which will allow
voltage to back flow and drain battery's

motion30 · 24-10-2012, 15:58

fully charge them then unhook the cables then you will know or check sg

Sailor Doug · 24-10-2012, 16:37

I had a true Charge 2 that only went to a low float voltage so it never charged the batteries.

NCountry · 25-10-2012, 06:41

With the batteries showning fully charged (I have two other meters besides the control panel for the charger) we load tested all the batteries. They all show good and they continue to hold a charge as long as the motor is not started. I also looked for obvious shorts or anywhere the wiring became hot from such a sudden discharge. Nothing showing. Have also felt the temp of the batteries after charging and nothing is hot there either. Having trouble finding somewhere to test the alternators. One is a Wilson 55 amp and one a Wilson 65 amp. We did put a meter to the diodes on the back and they appear to be working correctly.... Dang, electrical stuff is frustrating....

DeepFrz · 25-10-2012, 08:38

Get a clamp on Ammeter and check the current flow on the cable from the + battery terminal when you add a load. Then start the motor and see what happens. That will give you an idea of current flow. If your batteries are good and they are fully charged then there must be a large current flowing somewhere when you start the engine. Perhaps the starter stays energized.

Kenomac · 25-10-2012, 09:07

Have your batteries checked out. Probably one or more bad batteries. Most likely time to replace all of them.

belizesailor · 25-10-2012, 09:18

If it is not an internally shorted battery cell, then it sounds like a short to ground somewhere. As suggested, test current flow at battery cables to see if you have a big flow exiting in certain conditions.

delcrest · 25-10-2012, 09:20

Quote:

Originally Posted by S/V Illusion

Can you say "dead cell"?

have to agree almost certainly a dead cell on one the batteries

sailorboy1 · 25-10-2012, 09:26

Quote:

Originally Posted by NCountry

With the batteries showning fully charged (I have two other meters besides the control panel for the charger) we load tested all the batteries. They all show good and they continue to hold a charge as long as the motor is not started. I also looked for obvious shorts or anywhere the wiring became hot from such a sudden discharge. Nothing showing. Have also felt the temp of the batteries after charging and nothing is hot there either. Having trouble finding somewhere to test the alternators. One is a Wilson 55 amp and one a Wilson 65 amp. We did put a meter to the diodes on the back and they appear to be working correctly.... Dang, electrical stuff is frustrating....

Are you saying that the batteries only drain when the engine is running???

Is the start circuit staying energized (I would think the starter would burn out before draining the batteries)?

If the alternator was shorting wouldn't the batteries drain back even with the engine off?

Sounds like you are getting close to a fire, which of course becomes a strong clue.

donradcliffe · 25-10-2012, 09:44

While a clamp-on DC ammeter is less than $50 at Sears, you can do quite a bit of testing with a cheap digital multimeter.

Test the voltage across each individual battery, both under load and under charge conditions. If the batteries are the same age and type, any differences of more than 0.1 volts will likely be due to a failing battery.

Loosen the main cable from the battery bank, and touch it to the battery terminal a few times. You can guess the current draw by the size of the spark. If the spark is significant and repeated when you have the panel loads/bilge pumps/windlass breaker turned off, you have a phantom load problem (sometimes you get a good spark on the first touch which does not reoccur, due to something like charging a capacitor in an inverter).

If you get a phantom load, try disconnecting the output wires of the alternators one at a time to see if it goes away. Then disconnect the power wire to the engine control panel, then the starter, and any other wires which bypass the DC panel (here is where the clamp-on meter saves a lot of time, because you can simply clamp it on each wire).

How are you determining whether the house bank is full or empty?? Voltage, battery monitor, or specific gravity reading? Did the voltage come up when you started the engine??