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Old 07-07-14, 05:21 PM   #1
stevehull
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Default float voltage for deep cycle marine battery

Recently installed a "deep cycle" marine battery (type 24M) for one of my automated pasture gates (to open/close gate with automatic opener). The battery label says it has a capacity of 1000 cold cranking amps (CCA) at 32F.

Use a 25 watt PV panel (17 V open voltage; 1.25 A) and have been looking at battery voltage every day. Assuming 5 hours of full PV panel output, then I get about 100 watt hours of charge each day.

This battery has not risen above 13.1 V and I have had it on the PV panel for almost two weeks (very sunny days). Have I gotten to the float voltage?

This voltage measurement is done with the PV panel disconnected and the measurement is onto the actual battery terminals.

The battery is a sealed type (NAPA) so I don't know if it is a gel or what inside there. Yes, it is a Pb-acid 6 cell, but I can't find V-I charging curves on the web.

Only open the gate 1-2 times a day. At basal (not opening the gate) the control box system constantly draws about 40 mA (16 watt-hours/day). During the 12 second open cycle, the current draw is about 2.3 A; same for close cycle.

A remote opening gate is a very necessary thing so you can scoot out of the pasture (through gate) while keeping livestock in timing the gate opening with a remote "clicker" as you drive in and out.

Steers may look dumb, but they know that if you are out of the car opening the gate, that this is the moment to dash out on the road!

May look funny with me driving about pasture honking horn, then a dash out the gate, but it SURE beats "running of the bulls" out on the main road.

Thanks for the information on float voltage. 13.1 seems low, but I am rather ignorant on this stuff and know there are people here with lots more experience/knowledge than I have.

Steve

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Old 07-07-14, 05:26 PM   #2
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Its low for a float voltage, but it is fine for your setup. 12.7 is considered fully charged at rest. Below 12.5V or something like that sulfation starts to occur which kills your battery capacity. IMO your setup sounds fine.
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Old 07-09-14, 10:18 PM   #3
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I agree with Doax.

If you want to be sure, take it out and charge it with a good battery charger. Wait 3-4 hours and check the voltage.

My golf cart batteries float at 13.85 volts while the large traction batteries float at 12.75 volts. The same batteries manufactured within a few days of each other can be off by 1 or more volts. So it depends on what's normal for the battery or battery bank.

I recharge the batteries immediately when they at or below 80% of the battery capacity. That's when I see sulfation and battery capacity dwindling.
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Old 07-10-14, 05:12 AM   #4
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You should check the voltage during sunny conditions connected to the panel around 1-2 in the afternoon. The voltage shouldn't go above 13.4 - 13.6 volts maximum.
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Old 07-10-14, 07:09 AM   #5
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Just curious, are you using a charge controller?
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Old 07-10-14, 07:56 AM   #6
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Xringer,

Yes, I am using one of those little 5 A Chinese battery charge controllers (e-bay for ~ $10).


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Old 07-10-14, 08:17 AM   #7
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I've got 3 of those..

One (sealed Fios) on the tracking mount and two indoors, on old SUV batteries, also sealed.

Using 5W PVs, they keep batteries at 13 to 13.4 volts. Even when there is no usage.
When the green CHARGED LED comes on, they might stop charging..
I supect some models might have an over-charge preventer built in..
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Old 07-10-14, 08:31 AM   #8
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Xringer,

I have a similar unit. They prevent overcharging, prevent backloss of battery current to PV at night, cut out and prevent load operation when battery voltage gets too low.

Three LEDs show state of battery charge (two of the three are on), another LED lights up when PV panel is charging battery and a third LED indicates when a load is present.

Here is the link to the e-bay site describing this controller. You can get them in 5, 10, 20 and 30A configurations. I got the 5 A model.

Solar Panel Battery Charge Controller 30A Amp 12V 24V Solar PV System Black | eBay



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