PV Gap

Rick Said:

Using deep cycle batteries and solar charger........?

We Answered:

You can go to a solar shop and get some of what is required, either locally or off the web. You need a 36 cell (12V) solar panel, the bigger the better, a regulator (so it stops charging when the batteries are full), some cable rated to suit the current from the panel, and clamps for the battery. You can get clamps like a car battery has, with wing nuts. A bought regulator may be cheaper. Get a basic one if there are various types, current rated at least what your panel is.

If you go to the first link, there is a circuit for a satisfactory regulator up to 10A. CLick on it for a better image that you can print out. You can make it more current by paralleling the output FET with another. Note that Q3 the power switch is a P channel FET, not the more common N channel. The op amps are a CMOS rail to rail type, with no diode clamps on the inputs. They are +/- 8V rated (so 16V maximum). The panel can put out 22V when the battery is disconnected, so that is why they have a regulator. It is also the reference voltage. The transorb can be replaced by a 100nF capacitor. The thermistor can be replaced by a resistor of the same value. It is to adjust the charge voltage for temperature when using gel type (SLA) batteries. No need for a deep cycle or car battery (flooded electrolyte). It is a good idea to put a "gate stopper" resistor in series with PFET gates to make sure it cannot oscillate - 100 ohms. Q2 is a preregulator so the 7805 is safe with a 24V panel, not needed for 12V. S1B is not used (see parts list). The equalise switch is to give an overcharge, not really needed.

How it works.
It switches on until the battery voltage is the float voltage (13.85V or slightly higher), then off till the battery is about a volt lower, then back on. I have used a similar regulator on 12 different stations for about 20 years, so I can vouch for it as being satisfactory. No need to load panels down and so on, just disconnect them.

Other stuff
If you put a solar panel on the grass or ground, it will quickly get hot, over 60C, and stop charging. The output voltage has a negative temperature coefficient so the voltage is too low to charge. It needs air circulation.

D1 is a shottky diode for its lower voltage drop. A 36 cell panel has enough voltage to charge a 12V battery at 60C with one diode drop in series. Most panels have a diode in the terminal strip. If that is removed you could use an ordinary diode (20 or 30 amps), but the shottky type is better.

If the PFET is a TO220 pack it probably doesn't need a heatsink, or just a small one, say 6 Watts..

It is useful to have an ammeter in series with the battery. A ten amp one is fine. Helps line up the panel if nothing else.

The second link has a lot of good links, and is one example of a solar regulator.

The lines drawn heavier on the circuit should be 10A or 20A wire.

Where do you get the less common parts? Farnell, Radio Spares, Digikey.

Nora Said:

Can I power my laptop with only a solar charger and no battery?

We Answered:

Mark is correct. There is no way a solar panel can power on an laptop like that. Your best bet is to just use a charger. If you don't have one, you can look up one online.

I would personally suggest you visit Topmic for a new charger. Topmic is well known for their great services and their durable products. They include free shipping and free lifetime warranty. Yes, lifetime. This means if the charger ever stops working on its own for whatever reason, they would replace it as man times as needed at no additional cost, for life.

This is a great way to save money run but it also a good investment.

You should be able to find them online through google search.

Best of luck.

Daryl Said:

small fridge running off a 600ah battery for camping trips?

We Answered:

NOTE: Poster is in UK, AC is 220V
NOTE: Estimate total inefficiency at 0.75

Normalize: 0.8KW/H = 800W/Hr
Calc for day: 800 * 24 = 19200W/Day
Convert Amps: i=p/e, 19200W/220V=87.3Amps/Day
Inefficiency: pf=0.75, 87.3 / 0.75 = 116.4Amps/Day

Assuming a deep cycle 600A/Hr battery and no more than 75% depletion to avoid premature battery failure, you could run the fridge for 600 * .75 / 116.4 = 3.8 days without a solar charger. The 40W solar charger only provides 5% of the power required to run the fridge, and assuming 16 hours/day of full power output, would theoretically extend the operational time to about 4.1 days.

But 600A/Hr would be a honking-big battery. Standard automative starting batteries are not rated in Amps/Hr, but rather in CCA -- Cold Cranking Amps -- the amount of power that can be supplied in a short period to start a car. These batteries are not designed to provide long-term power supply, and their performance in such a situation will be very poor.

Better for the application would be a Deep Cycle battery. But standard size Deep Cycle batteries put out around 80-120AH, and following the 75% max discharge rule, neither would run the fridge as calculated above.

The next issue is whether the fridge really consumes 800W/Hr, or whether this is variable depending on how frequently the compressor cycles. I have no way to tell without access to your fridge and the conditions where you expect to camp.

How to overcome these obstacles:

* Extend runtime by connecting 2 or more batteries in parallel
* Recharge from car, generator or shore power
* Use a lower-power 12V/DC unit, such as from Engel, ARB, Coleman
* Use a 2-Way/3-Way RV fridge that can run off Propane, AC or DC

Tiffany Said:

How do I keep a thousand gallon water tank from freezing, cheaply?

We Answered:

I don't know how cold it gets in OR. so I don't know if this will work or not. First thing is paint the tank black. Build that simple structure you were talking about. Have the doors face south and leave them open in the day and close them at night.
Use the solar panel and battery with a timer to power a water fountain pump and circulate the water at night.