float voltage for deep cycle marine battery

stevehull · 07-07-14, 05:21 PM

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

Daox · 07-07-14, 05:26 PM

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.

philb · 07-09-14, 10:18 PM

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.

OffGridKindaGuy · 07-10-14, 05:12 AM

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.

Xringer · 07-10-14, 07:09 AM

Just curious, are you using a charge controller?

stevehull · 07-10-14, 07:56 AM

Xringer,

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

Steve

Xringer · 07-10-14, 08:17 AM

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..

stevehull · 07-10-14, 08:31 AM

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

Steve

07-07-14, 05:21 PM	#1
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	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 __________________ consulting on geothermal heating/cooling & rational energy use since 1990

07-07-14, 05:26 PM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	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. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

07-10-14, 05:12 AM	#4
OffGridKindaGuy Hi-Tech Hillbilly Join Date: Mar 2010 Location: Ohio Posts: 97 Thanks: 1 Thanked 16 Times in 15 Posts	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. __________________ If it don't, I'll always think it shoulda..

07-10-14, 07:09 AM	#5
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Just curious, are you using a charge controller? __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less..

07-10-14, 07:56 AM	#6
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	Xringer, Yes, I am using one of those little 5 A Chinese battery charge controllers (e-bay for ~ $10). Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990

07-09-14, 10:18 PM	#3
philb Apprentice EcoRenovator Join Date: Nov 2010 Location: Oklahoma City Posts: 155 Thanks: 58 Thanked 17 Times in 14 Posts	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.

07-10-14, 08:17 AM	#7
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	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.. __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less..

07-10-14, 08:31 AM	#8
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	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 Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990