Solar energy when battery disconnect is applied

[mockturtle]

My ignorance of solar energy and controllers is colossal. I'm planning to leave my RV for a few weeks with the house batteries disconnected to avoid dead batteries when I return. What will happen to the solar energy from my 2-100W panels during this time? If the battery controllers work off the battery how will the energy be controlled?

[DrewE]

mockturtle wrote:
Thank you all for your responses. Looks like I'll have to do some more research into my particular system. If I thought the sun would shine at least part of the three weeks, I'd definitely leave it. But in the Puget Sound area, as many of you know, there can be weeks and weeks sans sunshine.

Even very overcast days produce some power from the solar panels. Assuming you don't have any significant loads turned on, which stands to reason if you were planning to hit the battery disconnect, it should be easily able to keep up with the parasitic loads.

I mean, you can see outside without using flashlights most every day in the Puget Sound area, right?

[mockturtle]

Thank you all for your responses. Looks like I'll have to do some more research into my particular system. If I thought the sun would shine at least part of the three weeks, I'd definitely leave it. But in the Puget Sound area, as many of you know, there can be weeks and weeks sans sunshine.

[mockturtle]

2oldman wrote:
You have solar to avoid dead batteries. Why not just leave them to do their job?

Because I'll be parking it in the Pac NW where 'solar' can be a rare bird.

[BFL13]

How long is "a few weeks"? IMO when on a float you check the fluid level in the batts every so often. If you are away you can't do that.

[red31]

mockturtle wrote:
how will the energy be controlled?

open circuit (disconnected) panels do not make power.

Leave the panels connected to controller and controller connected to batts.

[naturist]

2oldman wrote:
You have solar to avoid dead batteries. Why not just leave them to do their job?

This.

Battery disconnects are there to prevent dead batteries due to small parasitic loads when the rig is being stored. As others have noted, many charge controllers MUST be connected to the battery at all times if connected to solar panels. Also, your system may be wired so that the solar is not run through the battery disconnect, but you need to find out for sure before you disconnect those batteries.

Regardless, the panels develops a charge if there is no battery or load, but they will not produce power because no current will flow. You can safely leave the panels out in the sun even if they aren’t connected to anything.

The solar charge controller’s job is to tame panel output and maintain full battery charge regardless of powers in or out. It will charge the battery full tilt until it is full, then cut back to only the power needed to overcome self-discharge.

Let the solar system do it’s job.

If the system was properly engineered and built, the solar does not pass through the disconnect. But there’s no guarantee of that. We all know of stuff designed by knuckleheads and/or built by idiots, don’t we? BTW, one day when you have to replace that battery, remember, you MUST disconnect the panels first.

[BFL13]

You could leave it all connected and let the solar look after the batteries, but there is a chance the float voltage will be wrong and cause the batteries to lose "water".

First disconnect the array from the controller by taking out the two wires in the controller's "array" terminals. Now you can disconnect the battery bank by removing the wires on the battery posts, including the ones linking the two batteries.

That will prevent the two from interacting while not being on a charger, and will make sure there is no draw on them. On return, hook up the batteries first, then put the two wires back into the controller's array terminals.

Put red tape on all the wires on the pos posts. Take a photo of the battery bank with the wires still on it, so you will put them back on the right posts.

When you get back, bring jumper cables in case the engine battery has run down too far to start the truck. Also, on that, disconnect the 7-pin too if any before leaving.

[2oldman]

You have solar to avoid dead batteries. Why not just leave them to do their job?

[wolfe10]

You need to VERIFY whether your solar is wired directly to batteries or is "down-stream" of the battery disconnect switch.

It could be wired either way.

[Ramblin__Ralph]

Some types of controllers (MPPT is one) warn against having solar connected to the unit w/o a battery connection. I installed a switch on my controller to disconnect the panel from the controller before disconnecting the battery.