Dead Batteries, constant without charger

[captwoodyb]

For some time now I have been experiencing an electrical problem. If the battery charter is not left on, both battery banks 32volt will go dead. Usually starboard, then port. I have tried to search down the cause without success. Anyone out there ever have this problem? Looking for comments, advice, experience. Thanks Capt WoodyB. 1972 53FBMY. Batteries are new.

 

[Passages]

Yeah, been there. Two possibilities come to mind.

First, get out your voltmeter and check the output of your charger. Should be a few volts north of 32.

If that's OK, then you have a constant draw somewhere in the DC system. I don't know of an easy way to chase that down other that shutting down all DC units and systematically checking each lead.

Good luck.

 

[Genesis]

My Hatt had pilot lights on the DC panel. For obvious reasons if those are left on........

When I was docked somewhere without AC power (e.g. hurricane hole) I pulled 'em. My usual in that situation was to leave only the bilge pump circuits energized - everything else OFF. Never had a problem with battery drain doing this.....

 

[Nonchalant1]

Three possibilities. The charger's not charging to full capacity, they're being drawn down by electricity being consumed or there is one or more bad batteries in each bank. Treat each bank independently and find out which it is. You'll need an inexpensive (<$50) multimeter and a battery hygrometer (hydrometer) to measure specific gravity of the acid in each cell.

To see if the charger's doing its job, charge them up fully and turn off both banks at the big switch. Measure the voltage of each bank with your multi-meter. A fully charged 32V bank should have 35.5 to 37.0 volts right after charging, depending on your charger. After sitting for an hour,turned off, they should have something over 34.5 to 35 volts. If they do, the charger's doing its job.

Then find out how much draw there is on each bank when they're turned on. You can do this with your multi-meter via an ammeter reading parallel setup. See your multimeter's owners manual. Do this when they're turned off (should be zero amps) and turned on. The batteries in the bank will have a known amp-hour rating. If you have four 8 volt batteries to make 32V, the amp-hours for the bank is the same as the amp-hours for one battery. Compare the amps of draw and the number of hours to draw down to dead batteries to the battery bank's amp-hour rating. It should match within maybe 75% accuracy (it's not that accurate of a test).

If the charger and the amp-hour capacity utilization both seem to be OK, you just have too much draw. Find it and fix it, usually by isolating each consumer one by one (turn every other circuit breaker off) to find what's causing the excess draw.

If the charger is doing its job, but the bank is being depleted too soon, find the bad batteries. Get a hygrometer, the kind that measures specific gravity NUMBERS and check each individual cell in each battery (wear golves and glasses of course). If the batteries are charged, it'll probably be around 1250 or so. There should not be a cell out of range with the other cells by more than about 10 points in any one battery. If 3 cells are at 1245, 1250 and 1250, and one is at 1200, that's a dead cell. If you find a battery with one or more cells out of range, that can keep the whole bank from being charged because it'll give the charger a false reading which shuts off the charger early and then the battery and bank can go from charged to dead in just a few minutes. Check every battery and replace the bad ones.

Good luck,

Doug Shuman

 

[Pascal]

how long does it take for the first bank, then the second to discharge ?

if both banks are new, and both get drained, the only common element would be the charger. Charge them, then physically disconnect the charger from the batteies.

Coulnd't bad diodes in the alternators cause this ? but unlikely that both would do it...

 

[CapetaniosG]

As stated above, You may have a defective charger. Or one of your batteries is bad, eventhough you said are new.

What you should know about hydrometer readings is that for the specific gravity readings to correlate accurately to the battery state of charge the electrolyte should be at a homogeneous state and the readings are corrected for temperature.

If your batteries are new and you find that you battery charger is producing, as it should, then the next test I would do would be to test for earth leaks in the system. To do this test you must turn off all equipment. Do NOT turn off the battery isolation switch! Don't forget to turn off the battery charger.

Now disconnect the positive batery post from the battery. Take your multimeter set it to the proper DC voltage scale (say 50V) and connect it to the (+ ) battery post and the clam of the cable you just disconnected. The meter should read zero, which means no leaks. If it reads 32 (+ -) Volts then either a piece of equipment is still on, or there is a leak in the DC system somewere. To locate the leak is not an easy job but it can be done. This is a test that tells you, you have a ground leak but it does not tell you where or how large.

To determine how large the leak is connect the multimeter between the disconnected cable clamp terminal (NOT THE (+) BATTERY POST) and the negative battery post and switch the meter to the most sensative ohm scale. If you read:

0 to 10 ohms................Some piece of equipment is still on. Check it.

10 to 1000 ohms...........Major ground leak

1000 to 10,000 ohms.....Minor ground leak

Over 10,000 ohms.........Very minor leak

With the above you will determine if you have a leak and how bad it is, but still have to find it and correct it. Good luck.

CapetaniosG
Hatteras 53MY