Almost Instant Battery Drain?

[Stray-Cat]

Originally Posted by NCountry

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?

To answer your question on a bad alternator

If there is a bad diode and it is running the battery bank down the power drain has to go somewhere,the alternator will feel warm/hot to the touch after the engine is shut down and cold
Easy to check

[Paul Elliott]

Could you have a poor connection to the batteries? Perhaps when the connections heat up they become high-impedance. I would measure the battery voltage at the battery terminals.

It's a long-shot, but an easy thing to check.

[NCountry]

Pulled both alternators and had them checked. One was bad. Took care of that problem and put it all back together. Also fully charged and load tested ALL the batteries. Start, House Bank and Windless. They all test good. House bank still appears to be discharging at a higher than normal rate. Was able to start the motor and run it for a while without the complete discharge. Interestingly, the guy that tested and rebuilt the alternator says there's no way an alternator can do what I was describing. He swears I've got a bad cell in one of the house batteries (6 6 volts). Can this be possible if they all charge then load test good?
My plan at the point is to take my time and check as much of the wiring as I can for a ground. Initial inspections make me believe I'm not going to find anything but it's an 81 model. It can't hurt to go over everything anyway. I'm beginning to think I've just got a bunch of weak house batteries and I'm about to dump about $800 or more in to replacing the house bank.

[sartorst]

Well I can tell you for sure that bad diodes will draw the battery,s down and depending on how many diodes are bad how fast!!
If you have an ammeter use it at the house battery cable and check for a draw if you are using an inductive type be careful to zero properly most are not sensitive enough to test lower than an amp are 2
If you dont have an ammeter disconnect the battery cable and connect a test light between the cable and battery with all the breakers off and all loads turned off if it lights, there is a draw now there may be things that are not wired through the breakers such as bilge pumps alternators etc that have to be disconnected by other methods this will tell if you have an abnormal draw
Oh!! be sure all chargers are off this will give you a false reading also the negative cable can be easier to isolate, all this is assuming the batterys are good !!!

[Stray-Cat]

Originally Posted by NCountry

Also fully charged and load tested ALL the batteries. Start, House Bank and Windless. They all test good. House bank still appears to be discharging at a higher than normal rate. .

Then the batterys are OK, you have tested them properly

Originally Posted by NCountry

He swears I've got a bad cell in one of the house batteries (6 6 volts). Can this be possible if they all charge then load test good?.

No bad cell in my opinion, you have checked them out and they are fine

Originally Posted by NCountry

I'm beginning to think I've just got a bunch of weak house batteries and I'm about to dump about $800 or more in to replacing the house bank.

You have checked them so they are not weak
At a battery replacement cost of $800 its time to either purchase a clamp-on dc ammeter ,mine cost $125 to confirm there is a draw, and to measure the rate of draw
Or have an electrician come down and diagnose the problem

Originally Posted by sartorst

Well I can tell you for sure that bad diodes will draw the battery,s down and depending on how many diodes are bad how fast!!

Agree ,I have seen this before when the diode shorts across,another draw could be a faulty voltage regulator , hopefully no need to worry now that that alternator is repaired

Originally Posted by sartorst

If you have an ammeter use it at the house battery cable and check for a draw if you are using an inductive type be careful to zero properly most are not sensitive enough to test lower than an amp are 2
If you dont have an ammeter disconnect the battery cable and connect a test light between the cable and battery with all the breakers off and all loads turned off if it lights, there is a draw now there may be things that are not wired through the breakers such as bilge pumps alternators etc that have to be disconnected by other methods this will tell if you have an abnormal draw
Oh!! be sure all chargers are off this will give you a false reading also the negative cable can be easier to isolate, all this is assuming the batterys are good !!!

Agree , he must see if there is a draw

[Redcoat]

Hope it didn't eat your zincs or prop.