Solar Charger and Panels - Page 4 - Fiberglass RV


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Old 05-01-2007, 11:49 PM   #43
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Adding solar power to our trailer is high on our list. I've bought a used 13"x48" Siemens/Shell 50w panel that I plan on permanently mounting to our roof, tucked between the centerline ridge in the roof and the awning housing where it'll be difficult to reach or see. These panels are known for providing good output even when the angle of the sun is far from ideal; hopefully it'll provide for all out dry-camping electrical needs, but if it turns out we need a little more juice for times we're parked under a tree or such I'll probably buy a set of Harbor Freight panels like yours, too.

--Peter
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Old 05-03-2007, 02:56 PM   #44
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Alas, I am the guy that Herb is talking about. The shorting of the wire did cause quite a bit of damage to the fridge in what seemed like a short time. From smelling the smoke to putting out the fire was probably 1 minute or so. In this time the fire grew and melted all the wires and even started to scorch the bottom of the drawer above the fridge.

As you can read from another post by Herb, these batteries, while low voltage have some serious amperage and with the right equipment, put out enough juice to weld steel.

Well the fridge is toast (ohh what a stink) so thats out and replaced and I've now added a fuse to the (+) lead of the battery to hopefully eliminate the chance of this in the future.

One question for those more electrically knowledgeable... What size fuse should i be putting on this wire? Presently i have a 15A fuse, but ive seen people recommend anywhere from 5A to 30A. As I'm only running lights and a water pump and perhaps the odd cellphone charger, am i in the right range? I turned everything on (including the fridge) and the fuse didn't pop so I think I'm okay.
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Old 05-03-2007, 05:59 PM   #45
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Quote:
One question for those more electrically knowledgeable... What size fuse should i be putting on this wire? Presently i have a 15A fuse, but ive seen people recommend anywhere from 5A to 30A.
The size of fuse is dictated by one of two things. The first is the size of the smallest wire on that circuit, the second is the maximum number of amps you think that circuit could be called on to provide.

In the case of the main charging circuit running from the battery to your fuse panel, the maximum load could (possibly) run is the maximum the wires can carry, so you fuse for the wires and skip all the adding and multiplying you might do for the other "device" circuits. My rule of thumb for 12v wiring is to use

20A fuses for 10g,
15A fuses for 12g,
10A fuses on 14g,
05Amp fuses for 16gauge wire.

Something to keep in mind is thinner-gauge wires (with higher numbers) experience a drop in voltage as the amps they are carrying go up. Basically the volts lost to the resistance of copper wire doubles with every 2g increase in diameter. I'm assuming it's a rare thing when you want to draw the full rated amperage of the wire, and that you'd rather loose energy from your battery than blow the fuse when that happens, so I'm suggesting fuses to protect the wiring, not transmit energy most efficiently or protect the appliances connected to those wires.

If, on the other hand, you have an appliance that regularly draws a set number of amps you'll probably want to use a heavier gauge of wire to reduce energy losses to that appliance and fuse that wire so the fuse blows if your appliance suddenly starts drawing way more power than it should. So, say you have a five amp appliance on its own circuit; you might want to use 14 gauge wire (instead of 16) to keep voltage and energy losses down but use a 5 amp fuse to protect the appliance and prevent the smaller-guage wiring within the appliance from catching fire if it shorts out.

--Peter
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Old 05-03-2007, 11:06 PM   #46
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I agree with, I think it was Gina, that this is not rocket science.

I've had my panel for 3 years now and I simply ran 2 wires from the battery to the solar controller. 1 negative and 1 positive with an inline fuse. Then from the solar controller I ran 2 wires to a jack on the outside of my trailer. 1 positive and 1 negative. I added a plug to the solar panel wires and simply plug my panel in to "charge the battery".

Nothing runs off this circuit, it simply charges the battery. All DC appliances run off the main DC circuit in the trailer as normal.
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Old 05-30-2007, 11:32 PM   #47
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Old 05-30-2007, 11:42 PM   #48
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How is the system working for you Fred?
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Old 05-31-2007, 08:10 AM   #49
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I agree with, I think it was Gina, that this is not rocket science.

I've had my panel for 3 years now and I simply ran 2 wires from the battery to the solar controller. 1 negative and 1 positive with an inline fuse. Then from the solar controller I ran 2 wires to a jack on the outside of my trailer. 1 positive and 1 negative. I added a plug to the solar panel wires and simply plug my panel in to "charge the battery".

Nothing runs off this circuit, it simply charges the battery. All DC appliances run off the main DC circuit in the trailer as normal.
The voltage coming from your solar panel is highly variable, depending on, of course, the sun. This is almost certainly unlikely to be anywhere near the voltage your battery wants to be charged at.. At worst, you will shorten the life of your battery (I measured 19V coming off my panel yesterday in the noonday sun) and at best, you won't be actually charging your battery... Just because your panel is plugged into your battery, doesn't mean it's doing anything.

A charge controller is much cheaper than a new battery.
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Old 05-31-2007, 10:10 AM   #50
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My panel came off a sailboat. 50W. I installed a charge controller (small yellow gizmo) from Camping World-$30.00. I didn't put a fuse in the line to the battery. Couldn't see why.
It's been cooking for three years- no overcharge and the green light stays lit. It's on the roof out of harms way. It's not real fussy about alignment to the sun.
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Old 05-31-2007, 02:49 PM   #51
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The open-circuit voltage from a solar panel can be quite high compared to the nominal 12V rating, but that doesn't mean a battery connected to it will ever see that high voltage. I've seen at least 19V, but as soon as the panel is connected to the battery, current flows, and the load pulls the panel voltage down to the battery voltage.

My "30 watt" panel will not produce more than a couple of amps under any condition under the sun (literally...), so there is no risk of excessive charge rate. There is a risk of over-charging eventually, so I use a simple on-off solar panel charge controller. With a small enough panel and large enough battery, indefinite charging would still be safe, which is why the panel suppliers make recommendations such as using a controller with panels of combined capacity of 15 watts or higher (they assume a typical RV/marine battery size).

The simple controllers like my under-$30 unit are the same circuit used in basic (not "smart") automatic battery chargers: it is a switch which turns on at some low battery voltage (eleven point something) and off at some higher voltage typical of a fully charged battery (maybe 14.2V). This type of controller does nothing to adjust the charging voltage or current flow, so it cannot optimize panel performance, limit charging current with large panels, or get useful charge voltage in low-light conditions.
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Old 05-31-2007, 03:04 PM   #52
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Sorry Brian. I mis-read Joy's message. I missed the part where a controller was in the circuit...

My excuse is that it was a pre-coffee posting.
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Old 05-31-2007, 08:41 PM   #53
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Quote:
How is the system working for you Fred?
I like it!

I have actually used it twice. At Applewhite, in the San Bernadino Forest, It maintained the battery where it did not fall below 12.4 volts at any time. Definitely kept up with my 12 volt usage, even the furnace blower motor. I did not skimp on light or pump usage. The battery left the campground with as full a charge as it had when I arrived.

At Lake San Antonio, while we were on plug-in power, I separated the panels and their charge controller from the trailer converter's wiring. I charged a group 27 battery (my separate auxillary battery) that had been run down below 11 volts. It was useable that afternoon.
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Old 06-02-2007, 03:23 PM   #54
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So, on this next trailer, I plan to add some fusible link between the batteries and the feed line. I imagine it should be available from auto dealers for relatively cheap..
Herb,

I would suggest staying away from a fusible link and install an inline fuse instead. I have had the misfortune of trying to replace a fusible link on the road, could not find one and had to splice a wire in its place. A fuse will be much easier to find.
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Old 06-02-2007, 03:34 PM   #55
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Liz,

A couple weeks ago when I camped on the two day weekend at Heartbar, then left the trailer for the 3 day..

I left the panels out all week while I was gone. I arrived back to a fully charged battery, and despite my stewpidity of leaving the heater on all nite Friday and running the battery down, I was back up with full power by mid day saturday.

Wanted for nothing power wise for 3 days, as usual.
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Old 06-04-2007, 07:35 AM   #56
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Herb,

I would suggest staying away from a fusible link and install an inline fuse instead. I have had the misfortune of trying to replace a fusible link on the road, could not find one and had to splice a wire in its place. A fuse will be much easier to find.
Carrying an extra $4.00 fusible link is fairly cheap insurance. I've had fuse holders that got corroded and had diminished current carrying capacity.. Hopefully it will stay 'dry' inside my trailer but I'm dubious. Anyway, it's an experiment and we'll see how it goes.
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