Not solar again ?

[wanderingbob]

I ain't gonna do it , but I am Curious . In the course of a year I pull 3 different trailers and I was wondering : My pickup has a metal topper like the phone companies had in the past , if I put 3 or four hundred watts of panels on top of the topper to charge the 4 golf car batteries on the front of my trailer , where would I put the controller , close to the batteries or close to the panels . A portable suitcase panel would not work as we may leave the trailer all by its lonesome and I am to lazy to tote the suitcase . We work craft shows and sometimes the trailer and truck can not be near each other . Also would it hurt the panels when I unplug from the trailer for a day ? Where does all that electric that I ain't catchin , where do it go ?

[CA_Traveler]

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.

[Gdetrailer]

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.

[CA_Traveler]

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.

[wanderingbob]

Thanks for the reply's ,

[valhalla360]

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.

[Z-Peller]

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.

[Gdetrailer]

3 tons wrote:
OP says, “Where does all that electric that I ain't catchin , where do it go ? ”

The panels will merely have the ‘potential’ to produce, but won’t produce unless the power has somewhere to go.

3 tons

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.. If panel is good, you should see a voltage reading up to the rated voltage listed on the panel.

Same idea as a battery whether it is a dry cell (D, C, AA, AAA), lead acid battery, AGM, Lithium.. They all will have a voltage at the terminals if they are good and/or charged.

With that said, some controllers will have a specific hookup requirement which may need batteries connected first and then the solar panel.

Best to read and understand the controller manual before making connections.

[time2roll]

Put the controller close to the battery and you will have no issues. A quick connect between the panels and controller would work fine.

Where does the electricity go? Same as a battery with nothing on the terminals or a wall outlet with nothing plugged in. The electricity does not move unless you attach a conductor.

[KD4UPL]

There are several charge controllers that will be damaged if the battery is disconnected with live PV still connected. I don't remember which models but I have run across them over the years. Whatever charge controller you get you will need to read the instructions to see if this is the case.
I would put the controller with the batteries. Are the batteries on all 3 trailers the same or are they different sizes, types, brands, etc.?
You may need to program the charge controller differently for each battery bank to get optimum charging. Yes, generic settings will work well enough but specific settings will be better.

[3_tons]

OP says, “Where does all that electric that I ain't catchin , where do it go ? ”

The panels will merely have the ‘potential’ to produce, but won’t produce unless the power has somewhere to go.

3 tons

[naturist]

wanderingbob wrote:
Where does all that electric that I ain't catchin , where do it go ?

Same place all that horsepower from your truck engine goes when you turn it off. I.E., it isn't being created, so goes nowhere.

[Skibane]

wanderingbob wrote:
where would I put the controller , close to the batteries or close to the panels.

Close to the batteries usually works best, so that the controller is actually measuring the voltage at the batteries (instead of the voltage at some point along the wiring that may be different due to losses in the wiring itself.)

Some controllers have a separate battery voltage "sense" connection that allows you to run a second wire to the batteries just to measure their voltage without the effects of losses in the main current-carrying wires - in which case you can mount the controller just about anywhere.

[CA_Traveler]

Wire the panels in series and use a MPPT controller next to batteries to reduce wiring loss.

[Boon_Docker]

If you are using 3 different trailers then I would leave the controller with the panels instead of having a controller with each trailer.
There is no "electric" produced if the panels are not connected to a controller and battery.
It does not hurt the panels if they are not connected to the trailer. They just sit there idle and do nothing.

[pianotuna]

Hi,

If you disconnect the panels from the charge controller no damage occurs.

If you disconnect the battery bank from the controller there is a good chance of letting the magic blue smoke out of the controller.