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Old 09-29-2009, 06:48 AM   #1
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Question Batteries losing charge

I have two 6V golf cart batteries that will usually last a few days with lights heat/fan and fridg/gas.

This past weekend they were drained by about 4am when we woke without heat.

So I hooked up to a friends gen and recharged in about 20-30 min.

Next night same thing.

Checked the batt connections and water all was good.

How can I find out what is drawing down the juice.
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Old 09-29-2009, 07:11 AM   #2
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This little gadget has been a big help finding circuit drain...

Got mine from Snap-on guy.
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Old 09-29-2009, 07:23 AM   #3
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I doubt that a 20-30 minute charge is going to put much back into the batteries. You may not have been fully charged to start with.
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Old 09-29-2009, 07:54 AM   #4
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I doubt that a 20-30 minute charge is going to put much back into the batteries. You may not have been fully charged to start with.
I agree with the Flycaster. If the battery is drained it will take quite a few hours to recharge the batteries with a genny.

Based on the description I suspect the furnace fan was running but the furnace stopped heating.
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Old 09-29-2009, 07:21 PM   #5
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I tested the power after 30 min, it showed 12.8.

The furnace was running all evening and cut out early am, I turned a light on it was barely lit.
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Old 09-29-2009, 07:50 PM   #6
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The battery will show a higher level when you charge them. If you let them sit for 15 minutes after you stop charging, they will probably be lower.

The difference between 100% and 50% is only about 1/2 of a volt.
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Old 09-29-2009, 07:57 PM   #7
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Quote:
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I tested the power after 30 min, it showed 12.8.

The furnace was running all evening and cut out early am, I turned a light on it was barely lit.
If you charged the battery sufficiently and it quickly looses charge suspect a bad battery. Did you wait after shutting off the converter before testing the voltage? I would test the battery voltage several times over a couple of hours with the battery disconnected. It would be normal to have a higher volt reading immediately after charging followed by a slight drop in voltage. If you test the voltage after several hours with the battery disconnected it should be just about the same. I would also take the battery, with or without the trailer, to a garage or autoparts store to do a load test. Also test the specific battery on all the battery cells. They should be close to the same voltage. One cell with a significantly lower voltage means the battery is bad.

Flycaster posted while I was writing mine. Looks like he is reading my mind again.
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Old 09-29-2009, 08:14 PM   #8
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How old are the batteries? (or did I miss that! lol)

When my battery goes, I'm going to set up three 21ah SLA's in parallel to increase my amp hours. I take care of equipment for the high school band and set their power supply (to run inverter) up that way and it works great. I like the longevity
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Old 09-29-2009, 08:41 PM   #9
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Almost 3 years old
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Old 09-29-2009, 08:42 PM   #10
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LI pets, as you have found out, you CANNOT use VOLTAGE as a good gauge of your battery bank's state of charge!

If you want to equate the battery bank's voltage to it's state of charge, you'll have to let them rest at least 24 hours (without any use) for the charge on the outer surface of the plates to 'soak' into the interior of the plates...

The only easy way to tell your battery bank's state of charge while the charger is running, is to dip a hydrometer into individual cells...it's not really convenient do do this when the batteries are tucked away in a remote location...

I always tell my battery sales customers that there's no 'free lunch' when it come to recharging batteries - whatever energy you use from your batteries has to be replaced, and when you've used em' for hours and hours, it sometimes takes hours and hours to bring them back up to a full charge...

1. For example - two 6 volt GC batteries in series for 12 volts, will give you about 225 amp hours of service - that's the 'size' of your battery engery 'tank'...

2. if the fan in your forced air heater is drawing 4 amps, that will be 4 amp hours drawn from the batteries in ONE HOUR...thats about 50 hours running time from fully charged batteries in good shape...

3. if your fan quit early in the morning, we have to assume your 225 AH batteries are fully discharged...

4. Now let's assume your converter charger is in the 50 Amp range, for sake of our example...and it probably charges the batteries at about a 40 amp rating while running (the 'advertised rating is seldom what it really charges at!)

5. if we divide the 225 AH by 40 amps, we'll see that it will take about 5.6 hours in a 'perfect' world...unfortunately, as lead acid batteries get to about 80% of their charging capacity, the internal resistance within the batteries change to the effect that they won't accept as high a rate of charge, and the in effect 'tapers' off the amp charging rate...

6. Due to this 'tapering' of the charge rate, I usually advise to use a factor of 150% when trying to predict the REAL amount of time it takes to bring batteries back up to full charge, when in a discharged condition...

7. So that 5.6 hours x 150% will actually bring you closer to 8 hours TOTAL charging time...!!!

8....er', sorry to say your 20-30 mins running your charger didn't even come close to recharging your batteries fully...don't feel bad, I run into this all the time, where the 'voltage' looks OK, but the battery then runs down quickly - you didn't get it charged back up, it's just that simple!

9. the larger the amp hour 'size' of you battery bank makes recharging worse, if you let your batteries run all the way down - it just takes hours and hours and hours to bring em' back up...

10. when boondocking, it's very important to run your generator to recharge your batteries EVERY day after use so you avoid that 'black hole' of a completely discharged battery!

11. these are 'approximate' ratings and examples, but you'll get the main idea...

As I said above, there's no free lunch - what goes 'out' has to be put back 'in'...
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Old 09-29-2009, 08:51 PM   #11
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thanks that explains a lot.

I'm leaving Thursday 5 AM for a 4 day trip.
I'll plug in tomorrow evening that should give it almost 10 hours to charge, I have a 55 watt charger.

Let you know!
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Old 09-29-2009, 09:17 PM   #12
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Bob,
That should get you going again...

BTW, if you still have the original Univolt converter/charger, it will eventually 'overcharge' your batteries if you leave it plugged in all the time...

be sure to check the water level in the cells - 6 volt GC batt's have a large fluid reserve area above the plates, but don't let the level fall below about 1/4 inch of fluid above the plates - that's minimum...! Use distilled water whenever possible...

I replaced the original Univolt charger in our 78 with a modern three-stage unit from bestconverter.com - these new units quickly recharge, have a finishing charge, and then go into 'float' mode, so I can leave the AS plugged in for long periods and not have to worry about overcharging our batteries...

Have fun on your trip...

Ray
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Old 09-29-2009, 09:24 PM   #13
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Quote:
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I tested the power after 30 min, it showed 12.8.

The furnace was running all evening and cut out early am, I turned a light on it was barely lit.
Let them sit for a while before checking after charging. They will "settle down". You may only have 12.6 or less. If batteries went completely flat, they may be toast. The plates and chemistry are changed.
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Old 09-29-2009, 09:42 PM   #14
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Yes, Mexray is right, a quick charge may show a high voltage, but that is just a "surface" charge. You need to "hammer" the batts for quite a long time, to get the "charge" deep into the plates.
Run into this all the time in marine systems.
A good 3-stage charger will initally charge at ~14.2 > 14.4, untill the batts are around 75>80%, then drop to ~13.6>13.8, until they are ~85>95%, then go to a float mode of ~13.2,,. That last 5>10%, usually takes a long time, because the cell resitence is high, and the input voltage must be low, to control heat build-up.
Lead-acid batts like to float at around 13.1>13.2, every tenth of a volt over the optimum float voltage doubles the currant, this leads to corrosion of the positive plates, and rapid loss of water.
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