Help with RV solar

I’m thinking of installing a panel on my camper van. I’ve got two 90AH batteries that normally charge either directly from the van’s alternator, or via a converter and more sophisticated charger from shore power. My use is pretty minimal; the biggest draw is the fridge at about 2.6 amps, and that’s intermittent. I wanted to get a Uni Solar 64; the idea is to just help me get through a long weekend. It wouldn’t always replenish 3 days of use, but close enough. I also need to be able to remove the panel for use elsewhere when I’m home, and it’s more than enough juice for that application. And I like the fact the Uni Solar is relatively unbreakable, since the van gets abused on 4WD roads a lot.

So let me know if the following works. I’d mount the panel on aluminum rails I’d attach to my yakima rack, for easy removal. Run say 12 gauge wire (probably overkill, but if I add another panel someday I don’t wanna run new wire) with some kind of weather proof disconnect (suggestions?) down through the roof to a charge controller, say 10 amp. I’ve got a Link 10 meter, so from the controller I’d have to connect on the other side of that. I would think it would be a good idea to add a breaker/switch, but unsure where best to wire that. To use the Link10 to tell battery voltage I’d have to disconnect the panel circuit or I’d only see the charging voltage. And I’m wondering how RVs handle situations where the alternator is charging or the shore power is charging; do you disconnect the panel circuit? I’d also like to have a lead from the controller that doesn’t go to the house batteries, so that if necessary I could attach those leads to another battery (like the van’s starter battery), or something else.

Finally, recommendations about a buss for connections. As time has gone by, more and more stuff gets connected to the battery terminals. A mobile ham radio, etc. etc. What do RVs use to manage these connections neatly? as long as I’m doing this I should tidy up.



  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Help with RV solar

    Hi rob,
    This is now a 2nd attempt by me at answering to your post as i took to long in answering and thus i got automatically logged out. Typing was never my forte, but i'll see if my backing it up in this word processor will help matters and i hope that all points that i had thought of before will get addressed in this one. Probably not, but i'll try. Most of the others will notice it is capitalizing the beginning of my sentences that i normally don't do for time's sake.

    First of all, do know i am not an rv expert, but that there are many here that have solar experience with rvs and i'm sure they'll chime in as well. I see a few problems with your proposal to charge 2 90ah batteries. One such problem arises from alternator charging of the batteries. They do not get a full charge from the alternator from the voltages being held to around 14 volts or so and the use of isolators can cause a further reduction in that voltage by up to ¾ of a volt making it even worse. Now it may be possible to get most of the charge from the alternator and supplement with pvs for the rest of the bulk and final absorb charge stages. In any case i feel that 1 us 64 pv will not be enough to do the job even if you do aim it optimally at the sun. The pv is rated to 3.88amps, but don't hold your breath on getting it as it is not the norm to get the full rated pv current and is more a rarity. We recommend that the general range of charge be between 5 and 13% of the capacity. If you need to only supply the absorb stage with the bulk supplied by the alternator then this could be lowered a bit to the bottom end of say 5%, but without question shouldn't be below 3% and that's with no loads on during the charge that would take away from the pv's charge current. Now even if you got full current from the pv, 3.88/180=2.16% and that's far below what i'd recommend. Now mounting it flat on the rv roof and you'll find a significant current reduction, especially in winter, from the max rating.

    Also note that the us 64 pvs will break if stressed enough or hit hard enough, but they are indeed more durable than those with glass coverings. If you elect to use the us 64s then you'll notice they are inefficient compared to the non-amorphous types as you'll need nearly twice the room from the us 64s to come up with a similar current that the other types will deliver. In other words, 1 standard type pv like the kc130 will deliver nearly twice the power in about the same occupied area as the us 64. I also recommend the use of a controller with a battery temperature sensor to avoid some charging problems.

    As to your wiring that depends on the loads you will be using and my guess is you'll need better than #12. See the voltage drop calculator in the sticky and place the max current you will draw into it instead of the pv current in addition to the wire run x2 for the total length of wire used with different wire gauges. It is desirable to keep this below 3% and some even say below 2%, but should not go over 5% under any circumstances. The interconnecting wires for the batteries should be heavier to help circumvent any uneveness between them and should have loads and charging sources connected to them in a criss-cross manor. Example: The plus from the controller may go to the left battery's + post while the minus from the controller may go to the right battery's – post. It would also be a good idea to have the ability to disconnect those batteries from all loads or charge sources as well as have a fuse or circuit breaker rated slightly higher than that which it is expected to pass.

    Now as to a buss i am of the thinking you wish to make multiple connects to the 12v power, but in a remote location from the batteries, like near your radios. This can be done by you or you could buy one. If making one you will see the terminal blocks and terminal busses available from our sponsor and you could add fuses(recommended) and switches as well. Look towards the bottom of the page.
    You could buy something like that which mfj makes as seen here on this webpage:
    Some combination of the 2 may also suit you.

    I know i probably missed something, but i'm sure others will chime in that are more familiar with the operations in rvs and i know there were some threads concerning such in the past. If i've got you right you are a general class in bb's general area of california and using hf can draw up around 20amps. I have 2 us 64s and i have trouble keeping enough to supply long sessions using my ts2000x with the power cut back some.