Small solar charger system...

50% max discharge is for full timers. I would not worry about going down into the 60% to 80% discharged zone for the part time campers.

Hi Tim,

I applaud your use of LED lighting. Voltage is very sneaky. It can't really be relied upon.

The OP has 12 volt batteries. Going below 50% would not be advisable at all. 40% would be a better number (i.e. 60% remaining).

pianotuna wrote:
Hi,

Voltage is a poor way to check state of charge. It is only valid when the battery is at rest for 24 hours with neither loads nor charging going on.

If you had measured specific gravity that would be a valid indicator of state of charge.

I suspect the panels are amorphous in your 45 watt system. The do better in low light levels than many other types, which explains part of your results.

The other side of the coin is that you simply don't use much power on a daily basis.

Going lower than 50% state of charge is inadvisable with all lead acid battery types. It will shorten the life span, sometimes dramatically. Your batteries are some what forgiving--but even the die hard six volt crew avoid going below 50%.

timjcarter9 wrote:
At the end of the trip I took voltage measurements and was still at 70%.

You can safely discharge to 50% (or lower on six volt batteries) without damaging your batteries. They are made for that. You don't have to charge them to 90% each day.

The voltage reading is not as acurate as specific gravity but gives a good idea. I am not carrying one of those around but always have a volt meter.

I go by the chart on this page which is for batteries attached with no load. It is close enough.

Some people do discharge to 40 - 45% on 6 volt deep cycle batteries though I have never done it. With the led lights it would take a long time to get them down that low.

oakmandan wrote:
I am interested in using a basic solar panel with my camper to charge one or two 12V batteries. I would want to be able to run the water pump, a light or two and a 12V fan. Any suggestions of how to and what equipment I would need ?

Thanks, Dan

Actually after looking at this again you will not need any solar if that is all you are running. (for two or three days anyway)

Hi,

Voltage is a poor way to check state of charge. It is only valid when the battery is at rest for 24 hours with neither loads nor charging going on.

If you had measured specific gravity that would be a valid indicator of state of charge.

I suspect the panels are amorphous in your 45 watt system. The do better in low light levels than many other types, which explains part of your results.

The other side of the coin is that you simply don't use much power on a daily basis.

Going lower than 50% state of charge is inadvisable with all lead acid battery types. It will shorten the life span, sometimes dramatically. Your batteries are some what forgiving--but even the die hard six volt crew avoid going below 50%.

timjcarter9 wrote:
At the end of the trip I took voltage measurements and was still at 70%.

You can safely discharge to 50% (or lower on six volt batteries) without damaging your batteries. They are made for that. You don't have to charge them to 90% each day.

You don't need as much solar (or any) as most of these people are telling you.

For instance I just went dry camping for three days. I have converted to all led lights and have two six volt deep cycle batteries.

We camp in the mountains so not much direct sunlight. Lots of shade. I have a 45 watt portable solar bank. Got very little sun over the three days.

I was using lights unrestricted. I have the outside strip led lights with the remote control that were on for at least four hours per night. Also used the water pump as required for dishes and showers. Fridge on propane, ran DVD player (12 volt) and tv on an inverter for a total of about three hours per day. Charged cell phones and tablets daily from a 12 volt charger.

Furnace ran one night for an hour or two.

At the end of the trip I took voltage measurements and was still at 70%.

You can safely discharge to 50% (or lower on six volt batteries) without damaging your batteries. They are made for that. You don't have to charge them to 90% each day.

So you can calculate your solar needs to a 50% discharge level. You may find you don't need any. I probably don't but I always set it up anyway and have never come close to dead batteries in trips up to five days.

Hi,

If it is a decent charge controller there is no need for such a switch. In fact using the switch may be bad for the battery bank.

Imaroadrunnr wrote:
I also bought a surface mount switch that I use to turn off the flow from the panels to the batteries when I'm using shore power. Someone told me I needed this. I've been married 40 years so I do what I'm told but I'm not scared of anything:-)
Stan
2005 Ram Cummins
4W?D 6 speed Long Bed
2001 Cedar Creek 34 Ft.
Happy Camper

I bought 2 100 watt panels from Grape Solar through Costco and the charge controller from Fry's electronics and this keeps my two 6 volt batteries topped off. I also have a 700 watt inverter because I use a c-pap unit for sleeping soundlessly and never have had a problem when boondocking. I bought a small panel that I plug into my cig. lighter on my truck which keeps my truck battery up. My truck doesn't get used too often but when I start it, that Cummins really twirls. I also bought a surface mount switch that I use to turn off the flow from the panels to the batteries when I'm using shore power. Someone told me I needed this. I've been married 40 years so I do what I'm told but I'm not scared of anything:-)
Stan
2005 Ram Cummins
4W?D 6 speed Long Bed
2001 Cedar Creek 34 Ft.
Happy Camper

I have a "E-Meter" in my RV. It shows that with everything off, there is still a draw of 0.8 amps with the refrigerator off and 1.2 amps when it is running on gas. So this basically means that with the CO sensor, propane leak detector, and refrigerator on, it will consume about 35 AH daily.

THis is about what one of my 120 watt solar panels will put out on a sunny day.

I have two of the 120 watt panels, started out with a pair of 45 watt panels, and later installed a 75W. Back in 1994 - 1999, the panels cost well over $4 per rated watt. Now you can get them for under $2 per rated watt if you go to the right website, and get the correct panels.

For a low cost controller, a PWM (Pulse Width Modulation) controller will work with 12 volt nominal panels, or 19 - 21 volts open circuit. If you want a little more amperage (about a 5% boost) then a MPPT controller (Maximum power point tracking) controller will take in anything from 19 to 60 volts (or more on some models) and transform this to 12 volts, to charge the battery. So it can take in say 40 volts (from a 24 volt nominal panel) and put out 13.4 volts charge voltage, and put out 2.5 times the "Amperage" that it took in (because it is about 1/3 the voltage). You can save on wiring costs, and voltage drop through that wire.

Yet with the cost of panels being so much less than 6 years ago, it is not really cost effective to buy a MPPT controller. The PWM controller is only about $40 for a 10 amp controller, and you can get one for each panel or get a 30 amp model for less than $60.

Look at 12 volt panels here. SunElec.com

They also sell controllers.

Fred.

My kit from AM solar does great. 150w/mppt control/wire kit for $400 delivered. I run lights, pump, furnace a little and the batteries are fully charged every day. Craig