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Date Posted: - Thursday - 12/28/06 - 5:07pm
Author: Randall, Murre, M31
Subject: Electrical Question

I use Battery 2 as the house battery. It's deep cycle, 12v, and about 3 years old. The issue is that w/one or two cabin lights on, it drains w/in an hour or two, and even at full charge, has less "gusto" than Battery 1 (same type, same age), which I only use for starting.

My history w/batteries suggests that over time, the house battery always seems the weakest. I don't know why, but suspect it has to do w/the type of low/slow usage compared to the quick/deep draw of the starting battery.

But this recent problem--that number 2 drains so completely I can't read by the lights--is new, and I don’t understand. One thing I have noticed is that the light sockets get hotter to the touch than the light bulbs, which are 12v/25w. I THINK only a couple do this, not all, but haven't tested this out thoroughly yet. I've taken one of the sockets in question off the bulkhead and had a look inside--all looks good. The lights are original, so maybe the switch itself is just wore out?

I need to but have not yet measured the charge level right after charging. It's likely the battery is not charging fully, but that only begs the question.

The battery to main switch connections are clean. The switch is less than a year old.

So, a few questions:

1. Should I expect the house battery to wear out faster than the starting battery?
2. What would cause the hot sockets?
3. Do I have a short in the line? If so, shouldn’t that blow the fuse?

RR

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Replies:

[> Battery issues -- Steve M-32 Pyxis, - Thursday - 12/28/06 - 5:28pm

To answer question #1: Probably. It is most likely that you aren't ever getting the battery up to full charge and that is degrading it over time because you are drawing from deep in the plates as opposed to surface pull on the starting battery. For a better understanding of this I would suggest you get Nigel Calders "Boatowners electrical and mechanical manual". He has a very thorough description of batteries, their loads, and what happens. I think I have several of the original bulbs on Pyxis (at least they have Kanji characters on them) and they are all 20w. That could be causing your hot sockets. As far as a short goes the answer is: "You might" and "not necessarily". You need to get an ampmeter on the battery and find out what the pull is when the lights are on. With two cabin lights at 25W each it should be just a little over 4A. Anything more would indicate an electrical leak somewhere which is not quite the same thing as a short. Shoot me a PM if you want to discuss it further.


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[> [> Here's a web site on 12V electronics -- John Bye, - Thursday - 12/28/06 - 9:32pm

It's for RV's (my new adventure) but the same principals apply.
http://www.ccis.com/home/mnemeth/12volt/12volt.htm


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[> How is your charging system set up? -- Capt'n Mike "Gypsy Mariner" TM 36, - Friday - 12/29/06 - 11:29am

Randall,
What type of charging system(s) do you use for your batteries? Also, what type of batteries (gell, wet cell, etc.)? Do you use an alternator when under way and battery charger when on shore power? If so, how are the charging systems set up, what is the output, and what type are they? I know from my own experience that a cheap battery charger (or one charging at too high a voltage) will ruin your battery within a year.
A lot goes into diagnosis of electrical and battery charging problems. But, as Steve pointed out, it all starts with a good quality digital voltmeter. You really can't go any further without getting a good handle on your battery bank set up and charging systems. Does your alternator only charge both batteries when the selector is in the "Both" position? Also, does your shore battery charger charge both batteries at the same time, and if so, how is your charger regulated? One of my past boats had the same problem because the house bank was getting overcharged ("fried")by the cheap shore power charger.


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[> Thanks Gents... -- Randall, - Friday - 12/29/06 - 3:55pm

I know I've not done all appropriate testing yet, but thanks for the feedback. Was kind of hoping for that easy answer, like “replace the light sockets” or “rub lanoline on the battery terminals and boil the fuses in hot water for 10 minutes”. No such luck.

I do have an amp meter and was all set to do the various gauging you suggest last week, but found I had left the meter ON during some previous adventure and its own 9v battery was dead. Batteries. Damn. After much searching, no spare on the boat. Windy and rainy day--would rather read. No lights--hmm. Would rather nap.

Comments based on yours:
-Wow! Light bulbs w/the old Kanji. And they work over thirty years later? Interesting re 20w. This problem I have became super noticeable when I tried 12v/50w. Nice bright light, just don't crack open too big a book.
-For several years now, I've charged the batteries only by running the engine. An hour or so almost every week at high revs. I cooked my first set by plugging in to shore power and leaving the charger on all the time. Didn't know any better at that point. Charging via engine-only seems to work fine (at least for the starting bat) and helps to avoid the electrolysis in my marina. It also is good for the old Perkins I suspect.
-Thanks for the Calder lead. I have that book and use it frequently, but not for this yet.
-After starting the engine, I switch to ALL on the assumption that that's what it takes to charge all. Never thought to check that both bats may charge regardless of switch position.
-Wouldn't be surprised if there's a leak...all the wiring is original and somewhat ratty aft of the aft cabin bulkhead.
-The batteries are wet cell, deep cycle.


I'll do the other testing you all suggest and get back.

Thanks again.

RR


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[> [> Check my logic, please -- Randall, - Tuesday - 01/ 2/07 - 2:30pm

Based on your suggestions (and a little bit of reading in Calder), did the following tests and reach the following conclusions. See if you agree...

After an engine running episode last week and a week at rest in the cold,
Batt 1 (starter) = 12.46 volts
Batt 2 (house) = 11.51 volts (ouch!)

Started engine and ran for 3 hours, 1 hour at moderate high idle (no tachometer at moment) and 2 hours motoring around Angel Island at about 5 - 6 knots.

Immediately after engine shut off:
Batt 1 = 12.58 volts
Batt 2 = 12.05 volts

Over the next two hours and with the master switch OFF, Battery 1 gained in voltage reaching a resting rate of 12.62 (normal); Battery 2 lost voltage, reaching a resting rate 11.96.

Tested for ground fault on Batt 2; none exists.

While engine running, tested for alternator charge rates. At idle, no significant change to charge rates on either battery; at moderate high idle charge rates on both batteries were plus 1 volt...i.e. normal.

Charging both batteries can only be done on the ALL switch (bummer).

Tested the light socket. Voltage sent from the battery and received a the light socket were identical at the moment of test.

Conclusions:
1. Batt 2 is toast. Inability to make maximum charge and loss of charge directly after 3 hours of charging indicates sulfation, or poor charge maintenance by yours truly over its three years (so says Calder).
2. Contrary to my previous belief, my regime of running the engine every week or so is NOT sufficient to maintain the HOUSE battery, especially since it is often drained somewhat by lights, etc AFTER we return to the Marina and shut off the engine (while we clean up, etc.).
3. The “hot sockets” issue is not proved one way or the other, but it appears there is no leak in the line.

One question: shouldn’t the alternator kick a good charge when the engine is at idle rpms? It does when the engine is at high rpms, but not otherwise. (Lose belt or other issue?)

RR


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[> [> [> I get 13.9 Volts - Check you bilge pump too! -- Capt'n Mike - Gypsy Mariner, - Friday - 01/ 5/07 - 9:22am


When you ran your engine at "idle", what was the engine RPM? I have a Balmar 150 Amp alternator that charges each battery bank independently. It will does not put out it's maximum charge amps until it is rev'd a good bit above idle. I will check this weekend, but it seems like the max. charging voltage of 13.9 kicks in around 1000 rpm and the maximum amps are not reached until somewhere between 1250 and 1500 rpm, but I haven't checked the exact rpm so it may be a little higher or lower. My alternator's charging voltage is 13.9 volts, which seems to be about a half volt or so higher than what you are getting.

If the belts are slipping you should hear it happening and get a lot of black belt dust around the pulleys. My alternator belt wakes the dead when it slips! What is the amp rating for your alternator? You may what to pull it and bring it to an auto electrical shop for bench testing.

When you are ready, you may want to look at replacing your batteries with AGM or Gell cells. When they are not in use, they hold there charge much better than wet cells, but they are expensive. After Hurricane Katrina, my slip did not have electrical power (it still doesn't a year and a half later), so I ran a generator and the engine to charge the batteries. I only used the lights and the radio on the weekends in the slip so I did not have a huge demand on the house bank, but the house bank still would get depleted rather quickly. What I wasn't thinking about is that the bilge pump was tied into the house bank and was an automatic that would turn on sometimes and draw quite a bit of power for a short time. This made it almost impossible to stay ahead of the game only charing the batteries for an hour or so ever week or two. Finally I bit the bullet and bought a large 120 watt solar panel with a great "smart" solar charge regulator. I bought the stuff on e-bay and it seems like it cost about $700 total. It can put over 6 amps an hour back into the house bank at high noon. It was the second best purchase I've ever made for a boat (an autopilot being #1). Now I don't need shore power and can leave the Gypsy Mariner alone for months if I wanted to and the house batteries will be fully charged when I go aboard.


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