solar charger effectiveness

I have 2 12v Batteries wired in parallel and have that 100watt panel that SMKETTNER linked to from Solar Blvd and it keeps my batteries charged up while the trailer is in the storage yard. I also have a battery disconnect switch so there are no phantom draws on the batteries. I hated taking out the batteries after a trip and bringing them home and hooking them up to my battery tender. it makes my life much easier.

Roy, with small solar chargers it gets even worse. There are people here that can explain battery chemistry better than me, but there will be undesirable side-effects if you try charging from 50% to 100% at 13.6V or lower. It's like trying to make a tea with a lukewarm water - you can infuse it all day long and it still won't be any good :)

But when it's already fully charged, this gizmo will keep it from self-discharging.

Progressive Dynamics describes the Battery Science rules for charging deep cycle batteries pretty good in this statement they include in most of their converter/charger manuals.

"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.

14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.

13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.

13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."

This becomes a more difficult task using SOLAR PANELs as a typical 120WATT PANEL will only produce around 5-6AMPS of usable DC CURRENT when in full HIGH SUN. This usually only lasts around 5-6 hours in a ONE SUN Day. It takes a good 15-18AMP DC current for each battery being re-charged to start out the charging process listed above in the Progressive Dynamics statement.

This is why a small 18WATT Device would take forever and maybe a few more days to re-charge a deep cycle battery from 50% SOC to even 90% SOC. It would however help maintain a battery that was already charged to 100% State of charge that you might have in storage...

Just my thoughts
Roy Ken

18W is good for ~250 or 300 AH battery bank in storage. So - yes, 2*6V batts. It probably doesn't have any current regulator, only a night-time diode. For a car battery you can go with a smaller 5W-10W charger.

There are few issues with these 1W-20W chargers:

1) Not weatherproof, can short or corrode in rain.
2) Not temperature-proof, plastic casing can melt in a hot sun if left under windshield.
3) Poor quality crocodile clamps, they corrode in a matter of weeks even when there is no rain - because of chemical reaction on battery contacts.

Hi,

Look at the price per watt. Panels are often under $2 per watt now and I have seen $0.74 cents per watt.

The unit you are looking at would be ok for a car battery.

18 Watts will just barely charge your iPad.

Charging current for 18watts would be approx. 1.3 amps into the battery bank, so as long as you are not drawing out more than you are putting in, you're good.

18 watts? No, that's nothing. Now, if you're just keeping them in storage.. maybe.

http://www.campingworld.com/shopping/item/nature-power-solar-battery-charger-kit-18-watt/56006

That is maintenance only for two batteries. I recommend fully charging and disconnecting a cable for best results in storage.

For $125 you could get a 100 watt panel then a low cost controller for a system that will actually do some charging.

http://www.solarblvd.com/Solar-Panels-&-Systems-12-Volt-Solar-Panels/c1_269/p2666/Solar-Cynergy-100-Watt-12-Volt-Solar-Panel/product_info.html