Solar trickle with a battery switch.

[carbonman]

I have asolar battery maintainer . Is there a switch I can use to disconnect the battery from the travel trailer and would connect it to the solar charger? Also is this maintainer large enough and do I need any controller for this charger?

[Fire Instructor]

IMHO, 1.8 watts is too small to do anything effectively for you. You're better off just charging the battery to full, then disconnecting.

[Triguy]

I had a nice post going but then the forum zonked out on me. I'll try to be short this time.

As for your questions on the disconnect, I would say you would want to disconnect the batteries or install a disconnect switch if your don't have one to avoid the parasitic draws in the trailer. I know nothing about controllers.

First, I'm not a solar expert but decided to do some of the math for my situation recently and this might help you decide if that 1.8W is enough for you.

Start by reviewing this article or Google others like it. Its basic but it gives a start.

Here's my math. I have two Trojan batteries with 260Ah. I live in Wisconsin and its winter so assume I should lose about 8% of my battery capacity each month or 0.69Ah per day (260 * 8% / 30 days).

I can expect between 3.5 - 4.5 of sun hours per day. You can look up solar maps for your area and the month here.

If I divide the total capacity loss per day (.69) by the total number of full-sun hours per day (4) I get 0.17A or 170 mA as the desired minimum current of the panel.

I don't know this, but I am sure the manufacturers are optimistic with their figures so I would plan to double that to 0.35A needed from the panel. It seems that a charger up to 5W would be sufficient for me.

[herk7769]

Originally Posted by Triguy

It seems that a charger up to 5W would be sufficient for me.

This seems reasonable to me if you just want to keep your fully charged, disconnected battery; fully charged.

There are many types of battery disconnects around from ones that mount on your battery post to ones that wire right into the hot or ground side of your battery cables.

If you plan on wiring your solar trickle charger up permanently, a double pole,double throw switch will totally isolate your solar charger and camper converter from each other and yet still give what ever charging source you are using full access to the battery.

[carbonman]

Thanks every one. I will look for a bigger panel because I was also thinking of adding a second battery. Herk: that switch was originally made for 2 batteries and one load, so I am assuming that the "make before brake" feature is ok for switching the solar panel to the travel trailer? I don't see what it would hurt, it's all 12v anyway.

[herk7769]

Originally Posted by carbonman

Herk: that switch was originally made for 2 batteries and one load, so I am assuming that the "make before brake" feature is OK for switching the solar panel to the travel trailer? I don't see what it would hurt, it's all 12v anyway.

You misunderstood. I was showing my dual battery kill switch setup. I have two batteries and that switch can select battery 1, 2, none (off), or both at the same time (it's normal position) to power the camper. The grounds of both batteries are tied to the frame (through a shunt used by my battery monitoring computer).

This same switch could be wired differently to accomplish your goal. Put the Solar charger's positive output to battery 1 and the camper's red lead to battery two and the battery bank to the common of the switch. YOU MUST NEVER use "both"

All grounds must be tied at the frame.

The reason I recommend a dual pole dual throw switch (switchin both hots and grounds) is to totally isolate your solar trickle charger from the camper's converter. I would hate to burn out those cells with a mistake.