PV Gap

Ramona Said:

so i have a solar power battery charging question...?

We Answered:

Hi Kris. As fate would have it, we have the exact boating arrangement you are talking about. There are several options, it all really comes down to how much performance you can afford. Our little boat has a 30 pound thrust motor and a 65 amp hour deep cycle marine battery. I am charging it with a 55 watt panel. First off, there is lots of misinformation about batteries. A deep cycle battery is designed to handle discharges and recharges, but that doesn't mean that they are good for them. If the sun is shining and you're trolling, by all means use the panel as well. The motor will probably use anywhere from 5 to 20 amps, the panel only puts out 3. Even if you stop running the motor for a bit, the 3 amps can feed back into the battery while you are stationary. The only battery type that developes a, "Memory," from cycling like this is the old Nickle Cadmium we used in cordless tools and toys for years. A lead acid does not have these issues. You can call the tech support guys at Trojan, Interstate or Exide and they will tell you the same thing. Better yet, stop at the library and check out, "The Complete Battery Book," by Richard Perez and read the chapters on lead acid batteries. Our entire home is powered by solar, wind and batteries, has been for almost 10 years, and we've already made all the mistakes.

As far as using a car battery, you can for a year or so, but it will fail after that. Car batteries have thin, light weight pourous plates designed only to give out heavy amperage for short bursts, enough to start the motor, then recharge all the time while you drive. To deeply discharge these types of batteries is to subject them to abuse for which they were not designed. Good deep cycle batteries have solid lead plates, and they are heavy.

A 55 watt panel like ours is about 18 inches wide and 40 inches long, and might cost about $200. At 3 amps maximum current, you can leave it hooked to a deep cycle lead acid battery all the time. The rule of thumb is if your panels maximum amperage is less than 2% of the battery's amp hour capacity, then no charge controller is needed, the panel can never overcharge the battery. All you need between the panel and battery is a diode, one with enough current capacity to handle the panels amp rating. Most panels come with them already installed in the junction box today, check to see if yours has one, or several inside already. The bad news is it will probably not keep up with daily use either. Ours doesn't, but it takes a good bite out of our charging needs. So now if we use our boat several hours a day, even if it's sunny, at least once a week, I take out the battery and hook it to a regular automotive charger overnight to bring it back up to full.

If you decide on a larger panel, and the panels amps exceed 2% of the battery's amp hour rating, then you will need a charge controller between the panel and battery in case the battery fills up on a sunny day and you're not using the boat. You can also use several panels together, as long as they are all about the same voltage. Look on the back of the panel, if they all have an, "Open Circuit Voltage," around 16 - 19 volts, you can wire them in parallel and into a 12 volt charge controller. As far as never having to charge the battery, you might be asking a lot from your panel. A 30 pound motor, the smallest I've seen, still uses 10 - 20 amps at full power. If you want to use solar only, you'll need something like 10 - 15 amps worth, or about 200 watts, a costly and fairly large array, maybe $800, and it might take up all your boat space. Another option is to charge the boat battery while you drive, if you tow your boat. You can run a line from your battery back to the trailer hitch, and use a separate trailer light harness, different from the one you have now that hooks your boat battery to the car battery. Just plug it in after you start the motor, and the boat will charge from the car alternator while you drive home.

If you want some real horsepower, skip the marine battery and opt for two Trojan T-105 batteries. They are made for golf carts. They are really heavy and well made, only 6 volts, that's why you'll need two, and they have a capacity of 220 amp hours. Two hooked in series will give you 12 volts at 220 amp hours. Now you can drive a 175 watt panel into them without a charge controller if you like, just make sure to water the cells at least once a month, they will go through distilled water pretty regularly. We plan on upgrading our little boat with T-105's this year just to carry additional loads, like lights, freshwater pump and fish finder so we can troll after dark too, but we'll probably stick with the one small panel for space, and just recharge a couple times a week at home.

There is a great periodical that covers the nuts and bolts of hardware like this, it's called Home Power Magazine, I'll include link below. Good luck trolling, and take care, Rudydo

Andrea Said:

When is the Big 3 Auto companies going to offer us a solar car?

We Answered:

Part of the reason behind the 'worse' fuel economy is that the Environmental Protection Agency (EPA) has reformulated how it calculates fuel mileage, thus making almost every car lower. My 2001 Escape went from 18/24 to 16/22. The new number is wholly unrealistic.

The problem with putting solar panels on cars is reliability. Solar panels aren't a proven source on highly abusive surfaces (vibration, weather, etc). Plus, the electricity transferred from solar panels is between 5% and 10%, thus making it rather ineffective compared to plugging it in. The photovolaic system puts added weight on the vehicle, also defeating the purpose, when it comes to mileage. Weather also defeats the purpose of having solar panels when you live in the northern states. Snow accumulates on the roof, covering the solar panels and blocking out all light.

I wouldn't expect to see solar panels on a car in the near future.

Donna Said:

Can you help make my motor run?

We Answered:

It's an impedience mismatch. When you load the solor cell down, it doesn't produce 3 volts. You might try using a small super capacitor and let the solar cells charge that up. The battery powered planes that run for short periods use that technique.

Charlotte Said:

Is Will Smith an idiot?

We Answered:

You forgot the sun screen....sheesh

Juan Said:

What are some other physics project I can do?Ideas?

We Answered:

There are many projects here classifid under different areas. Choose whatever interests you.
http://www.arvindguptatoys.com/toys/acti…