Not solar again ?

Put a disconnect between the panels and controller but keep it with the truck. That way you can connect up to any battery bank you care to.

May not be quick but you could even charge the truck starting battery in a pinch.

Thanks for the reply's ,

Gdetrailer wrote:
Actually, the panels when not connected to anything WILL "produce" a VOLTAGE at the panel terminals when sun is shining on them.

But when no LOAD is connected (battery, controller or light bulb) there just will not be any CURRENT flowing.

This can be easily proved by connecting a volt meter to any solar panel with sunlight on it and nothing else connected..

Practically I agree, but this isn't proof. As soon as you connect a voltmeter there is a load and hence amps flowing even if it's extremely small.

Not sure how to "prove" it, any ideas?

Gdetrailer wrote:
This can be easily proved by connecting a volt meter to any solar panel with sunlight on it and nothing else connected.. If panel is good, you should see a voltage reading up to the rated voltage listed on the panel.

Actually 2 checks are commonly used in full (or close) sun: Voltmeter and compare to Voc (open circuit) spec and ammeter and compare to Isc (short circuit) spec.

Z-Peller wrote:
If you mount the controller with the truck, then the truck is just a "solar suitcase' basically. My solar suitcase with controller connects to my batteries when I want it, and when I disconnect no harm comes to the controller. If you are going to be switching between 3 different trailers then using your truck like a solar suitcase would make more sense to me. Some solar suitcases are using 20' of cable from controller to batteries.

Never said it "would harm" anything if connections are made in different order.

However, some controllers are designed to detect if battery voltage is present before it will pass the solar panel voltage to the battery terminals of the controller.

In those cases, no battery voltage detected=no solar panel voltage passed to the controller terminals..

Real cheap controllers without adjustable parameters or without wide panel and battery voltage most likely won't care, more expensive controllers with adjustable parameters and wide panel and battery voltages may care.

Suitcase solar is generally small, etc. The OP suggested 300-400W which could warranty more efficient wiring etc. for other users. But the OP is not going to do this and sometimes his truck is not near the trailer.

400W of solar suggests 30A. Parallel 12V panels would require large wire to the controller vs serial panels at about 8A. For the OPs application 10 ga wire at 8A would be ideal, maybe even 12 ga. There are tradeoff factors for any installation.

CA Traveler wrote:
Practically I agree, but this isn't proof. As soon as you connect a voltmeter there is a load and hence amps flowing even if it's extremely small.

Not sure how to "prove" it, any ideas?


Actually 2 checks are commonly used in full (or close) sun: Voltmeter and compare to Voc (open circuit) spec and ammeter and compare to Isc (short circuit) spec.

Typical DVMs will have input impedance of 1-10 megohm if not much greater, comparable to the olden days of VTVM (vacuum Tube volt meters) then the FTVM (FET transistor voltmeter) that replaced the VTVMs.

DVM will present a nearly immeasurable load than the lower impedance of the solar panels unless you have some access to laboratory quality picoamp meters.

Lets just say that the average cheap DVM isn't going to drop the open circuit voltage enough to be measured by even the best Fluke meter..

I mean if you really wish to get crazy you can buy lab quality meters which have GigaOhm impedances.. Like THIS which is rated 70 GigaOhm input impedance..

But reality is a DVM does not present enough "load" to alter your reading of a 18V panel so why make such a fuss?

A DVM simply PROVES that the panel is generating a output voltage (panel has no internal circuit damage).

And as you mentioned, the OTHER test is to use a short circuit test which is done by placing a ammeter across the terminals (standard ammeter looks like a short but also has a resistance). So one would have to use a very large ga wire to create the short then read with an indirect ammeter if you wanted to nitpick things this far.

CA Traveler wrote:
400W of solar suggests 30A. Parallel 12V panels would require large wire to the controller

Agreed - Attempting to run 12-16 volts at 30 amps for any significant distance is going to require thick, expensive wire.

Connecting all 4 panels in series would give you 48-64 volts at only 6-8 amps - which could be done with much thinner, cheaper wire.

Naturally, you'll end up spending some of that wire savings on a more expensive charge controller that can charge your 12 volt batteries from 48-64 volt power.

Solar on the truck and move some of the batteries from whichever trailer is in use to the truck during the day to get recharged somewhat. Put the batts back in the evening. Move the other batts to the truck next day for their turn at some solar.

BFL13 wrote:
Solar on the truck and move some of the batteries from whichever trailer is in use to the truck during the day to get recharged somewhat. Put the batts back in the evening. Move the other batts to the truck next day for their turn at some solar.

Sounds like fun - :S

I'd opt for a very small gen. :)

CA Traveler wrote:

BFL13 wrote:
Solar on the truck and move some of the batteries from whichever trailer is in use to the truck during the day to get recharged somewhat. Put the batts back in the evening. Move the other batts to the truck next day for their turn at some solar.

Sounds like fun - :S

I'd opt for a very small gen. :)

Or just stay home?

My hats off to folks that want to camp/live/work without commercial power and be willing to go to all of this backbreaking work shuffling panels, wires, controllers and yes hundreds of pounds of batteries.. You guys put way to much work into camping, I would rather put that energy into sitting back in my camp chair sipping on my favorite beverage enjoying watching other folks labor..

If I was in this situation with three different trailers all needing some means of charging I would personally dump the single one panel array idea on the back of a truck.

Instead put the (invest) money into enough panels to populate each RV reasonably well enough to to help assist with charging. Then fill in any additional charging with a portable gen. Solar is reasonably inexpensive now days, 100W 12V panels often can be had for $80 each new.. So, you invest $320 in 4 100W panels for each trailer, install on the trailer off and be done with it.

Expensive up front? You bet.

Much easier to deal with? You bet.

Less backbreaking work?, You bet.

Less chance of something stupid happening like connecting things backwards or forgetting to disconnect wiring before moving the truck or someone snagging your wire damaging your panels and wiring with a bicycle, motorcycle, quad or just walking through your site? You bet.