Wander the West: What do I need to know about solar - Wander the West

pods8, on 30 September 2011 - 09:55 PM, said:

That's not hard to believe. The last time I did any real(ish) solar calculations it was for a buddies house many years ago to show him that it would never pay off. That system converted to AC and did a stepup to line voltage at the meter. So thanks for correction.

pods8, on 30 September 2011 - 09:55 PM, said:

Ah. Knowing this - use 14 gauge. The effect of the voltage drop at the controller is that it will have to dissipate less power as heat. So there is a ton of room to be lossy in transmission. (8.5 watts - (there is some required conversion cost))

And we know 2.22 amps. So, a 15 amp/day is 6.88 hours of charge time.
Don't have to guess the effeciency, it's dialed into the controller and it's linear. (Yuch) So, at 40 watts you lose 8.5 watts. Double the input current and lose double the power - 17 watts.

[edit]

I'm back. I thought I would back up the "use 14 gauge" argument a bit.

From "Amateur Radio Relay Handbook" 1985 I find resistance in 14 AWG is 2.575 ohms / 1000ft.

If we use a 100ft drop cord (that ought to be plenty, eh?) then we will be adding .2575 ohms resistance to each of the positive and negative leads for a total resistance of .515 ohms.

That drops our 18V input to (uhm calculator...) (6.35% loss) (uhm...) 16.86V.

Since we are constant current and assuming the 16.86V meets the cost requirements of the controller, we end up with the same 2.22 amps to the battery and need to shed only 5.9 watts as heat.

And since the controller is so ineffecient, I could even argue that 14 gauge is the right choice. It will let the controller run cooler.

Keep in mind that there are other losses in other places too. Hook everything together and test at the controller input. If it meets minimum voltage requirement for the controller then you are good-to-go.

I'm back. I thought I would back up the "use 14 gauge" argument a bit.

From "Amateur Radio Relay Handbook" 1985 I find resistance in 14 AWG is 2.575 ohms / 1000ft.

-snip-

That drops our 18V input to (uhm calculator...) (6.35% loss) (uhm...) 16.86V.

-snip-

And since the controller is so ineffecient, I could even argue that 14 gauge is the right choice. It will let the controller run cooler.

-snip-
[/quote]

Umm, most of that went over my head , but is not 14 AWG "thinner" than 10 AWG? I know this may sound dumb, I am so good at dumb, but would 10 AWG actually be not as good as it may possibly cook the converter because it delivers too much power?

And speaking of converters: I am thinking of mounting it above the battery in the battery storage area. Would this be a poor choice as there is not a lot of cooling? Another location would be under the couch so I could monitor it's little green light.
What AMP fuse would be good? I am thinking 10 amp between the controller and the battery, would that be sufficient? I noticed that FWC had 30 amp fuses on the pos and neg side of the battery.
Also what is the max distance I can mount the controller from the battery? I am thinking 2 feet would be the maximum before I had a lot of loss??
Thanks for all of your help.

Roger

I wouldn't worry about giving the controller too much as long as you're within it's rated parameters, it's designed to deal with it.

Maximum distance again is dependant on the gauge wire, however here your lines losses become more important since they drop the voltage going into the battery. But we're still talking low amps so you have lots of room to work with while still being in moderate gauge wire.

Roger, on 01 October 2011 - 01:36 PM, said:

Oh gosh, my bad. No, 10 AWG is perfectly fine. It's just overkill, like you said.

All of that stuff I wrote really just speaks to the really wide margins the designers put into the system.

Good evening!

I finally received the my other 30 foot cable today and I had the panel installed about an hour later.
I used a 10 amp fuse, but I probably should drop down to a 5 amp just to keep it under the 6 amp rating of the unit.(?)
I had some good clear sun and a battery that was a bit discharged.
When I plugged the unit in, even in the shade, the charge control LED glowed very dimly. When I put it in the full sun it glowed bright green and my battery charge indicator noted I had a "full" charge! SWEET!
Oh yeah, I didn't detect any voltage drop from the panel to the charge controller, but that could very well be a function of my cheap multimeter.

Some of the things I learned.
1. There is no "local" source of MC4 connectors.
2. It is cheaper to get one 100 foot MC4 cable then two 30 foot cables. You only need one cable for positive and one for negative. (duh moment) You just chop that 100 foot cable in half anyway.
3. Wander the west rocks.
4. If this panel is not enough I can add another panel on easily.

Again,
Thanks to everyone who responded to this tread.

Roger

Good to hear. Solar is on my short list.

If you use a multimeter to measure output at the panel, should you be reading amps, watts, volts ?

Den, on 21 November 2011 - 02:55 AM, said:

You're only going to be able to read volts with most cheap multimeters, most are only rated to measure up to .2amps. You'd need a rated amp meter of on sort or another if you want to find out how many amps or watts (watts = voltage X amps) you're getting.

Den, on 20 November 2011 - 06:55 PM, said:

I am using a "Watt's up" between my solar controller and the battery to "meter" my amps and amp hours.

My link

I'll check back in the new year, after my winter trip, to let you know how it works.

Roger

Roger, on 22 December 2011 - 10:00 PM, said:

This is the same meter that I've been using in my camper solar system for over a year, and I've been very happy with it!

From "My Post-Pork-Rally Eastern California Trip" report: