Harbor freight solar to keep battery charged

[hpcbmw]

I've got a 6 year old harbor freight 45w solar setup. I've also got a 80w solar panel. The 80w panel is on the roof of my Four Wheel pop up truck camper, with a charge controller. This keeps my single deep cell battery in the camper fully charged and in good condition. However, it weighs too much and makes it difficult to lift the pop top, even with gas struts installed.

I realize that I only really need the solar to keep the battery charged, not to really run any appliances. In 6 years, I've never used the camper without driving the truck every day (and using the alternator to charge the camper battery).

I'm wondering if I install one of the much smaller 15w HF solar panels on the roof, is that enough to keep the battery charged when the truck/camper sits unused for weeks at a time? The diesel truck also has 2 batteries. I think I could hook up the solar before the battery separator and keep all three batteries topped off, if the 15w panel is powerful enough.

I've read that the HF charge controller can often discharge the battery when the sun is down. Anyone hear of this, or have ideas for an inexpensive charge controller to control the one 15w panel?

[landyacht318]

The video link clearly shows a fully charged equalized flooded group 31 battery being brought up above 15 volts too, by 12 watts of solar.

Granted that is with a freshly equalized battery.

Whether these voltage would occur on the OPs bank in the OP's usage, is unknown.

One can get a cheapo PWM controller for under 10$. Is it worth the risk to a 100+ dollar battery to go without?

[time2roll]

5w per battery (like the OP) in my experience is marginal at best for FLA.

BTW my batteries were completely disconnected with a switch that I installed and wired. There were no loads.

Nothing wrong with a low cost controller. Most likely it will not control anything except night discharge. No need to get fancy.

I assume the OP will have some minor draw from the chassis computer.

[full_mosey]

smkettner wrote:

landyacht318 wrote:
12 watt solar overcharge

Does the OP have AGM batteries?
My experience is that 15 watts NEVER brought my 4x GC2 flooded batteries over 13.4 volts even during the longest sunniest days here in So Cal.

15+ volts? No possible way on its own.

Your FLAs likely have enough self discharge to keep the 15W panel at bay. There is likely parasitic loads involved as well.

Are you sure it is OK to leave a totally disconnected boat trolling battery connected directly to a 15W panel for an unlimited period of time?

HTH;
John

[time2roll]

landyacht318 wrote:
12 watt solar overcharge

Does the OP have AGM batteries?
My experience is that 15 watts NEVER brought my 4x GC2 flooded batteries over 13.4 volts even during the longest sunniest days here in So Cal.

15+ volts? No possible way on its own.

[hpcbmw]

I was a little concerned about the solar without a controller. Tom M - thanks for the link to the $120 flexi panel - that is very cool and very tempting! I could just glue it directly to the roof. Anybody have experience with a cheap controller that works well? Something less than $40?

Thanks!

[Tom_M1]

Solar Blvd. has a sale on a flexible 120 watt panel for $119. Very light weight. You would need a controller with this.

120 watt flexible panel at solarblvd.com

[mike-s]

landyacht318 wrote:
12 watt solar overcharge

Yep. These people who say you don't need a controller should keep to themselves and ruin their own batteries.

[landyacht318]

12 watt solar overcharge

[hpcbmw]

Thaks SMKettner, any idea how I tell if the panel has a blocking diode? I assume without a blocking diode, the panel will drain the battery when there is no sunlight. From what I've read, the HF controllers have a problem - they aren't supposed to allow discharge, but they do. Maybe I'll hook a panel and the charge controller to a spare battery for a few days and see if I can tell if it's discharging.

[time2roll]

15 watts on 3 batteries... no controller needed. If you do that make sure the panel has a blocking diode. Otherwise any controller is fine. Doubt the HF controller allows discharge. It is the other parasites that will get you. 15w is not much power.