Hello all,I have a unisolar 136 watt panel and a morningstar prostar 30 controller. IF I run the wires from the panel down the convenient place above the controller were there are already holes it will add about 5' from the panel to the controller. Then I could easily splice the pos from the controller to the battery cable near where it comes out of the floor to the converter. The neg could then be attached to the bus near the converter. This is probably 5' from the battery and 18" or so from the converter. The other option is try to run the wires down the front of the trailer to the controller and then to the battery. This will save some run to the battery but it will be a HUGE PITA and will require a lot of drilling into areas that I have no idea what is behind it and tearing some of the fabric off the bottom of the rv to find it near the water tank. So the question is this. I am willing to loose a little bit of voltage from the longer run, I only use the batts to run the lights and furnace blower and I am mostly just interested in keeping the batt charged when I'm not there but is there a problem with splicing the wires front the controller to the battery cables closer to the controller? This would be a very easy job and wouldn't require any drilling.Thanks

It's always best to make the controller to battery wire run with as large a wire and shortest distance as possible. However, for what you describe it will make very little difference for essentially a system being used primarily as a battery maintainer. Also with the ProStar you have ability to run battery sense wires which will make up the difference for slight voltage loss on the battery cables as the ProStar will controll voltage off those sense wires and raise charge voltage to compensate for the charge wires loss. I also use a ProStar controller

I have 4AWG cables going between my Converter/charger and batteries. I will mount a BLUE SEA BUS BAR TERMINAL STRIP where the SOLAR cables will hookup. I like all of my battery connections to use proper RING TERMINALS. Makes for easy removal for troublshooting or changing things...Roy Ken

You can connect any where you wantBut max voltage and max charge are archived when using the shortest wire run possibleI have a long wire run and I do not get as much charge as other members with the same amount of solar, in some cases members with less solar get more amp hrs than I doDo it your way, and be ready to change it if the batteries are not getting fully chargedI'm not condemning your actions, but I would (and did) run new wire all the way to the batteries, Mine was still a long run, but I ran #4 ga wire, which is very likely larger than what is connected to your converter, (you Will be lucky if it's 6 ga) and I should have used something larger

Hi,A long run can be compensated for by battery voltage sense wires.

Thanks again but I hosed myself. I got the controller installed and wired to the battery cables and was going to hook up the solar panel to make sure it worked before I stuck it on the roof and I got the wrong connectors on the extension. I noticed about 30 seconds after I cut in in half. Now I've got to order a new extension and try to sell the other one. Mostly I'm mad at myself because I brought the camper home mostly for this project and now I'll have to do the rest of it later.

Connect cables from solar closer to converter than batts?

16 Replies

Fixed_Sight_Tra
Explorer
Jun 03, 2014
I got everything installed. I ran the cables through the window instead of routing them correctly for now to make sure everything works. This weekend I have to go to the range. If it's good I'll probably finish the installation.

The one thing I wanted is an ammeter for the panel current. I know that when the light is on it's charging but that's it. I also don't know how much my batteries, a 5 YO group 31 and a 2 YO walmart group 29 are going to last. At some point I'll need a tri metric display because now I don't know how many amp hours I have to work with or how many I am harvesting during a day. I believe this is plenty of battery for my needs now but soon I'll have to figure out how much battery I need.
Fixed_Sight_Tra
Explorer
May 27, 2014
I ordered the Morningstar MPPT 15L. This project has cost more than I intended and is cutting into some of the budget for the other projects that I wanted to do to the rv but it should be done right. I'll probably have to get a meter at some point so I know what is going on with the solar input and batteries but that will have to wait. Some other projects are going to take priority.

I'm going to have to figure out how to scare up some more business so I can pay for all this. :)

Thanks again for all the help!

Chris
westend
Explorer
May 26, 2014
I use the Morningstar MPPT-15L that smkettner posted and linked. It is a good controller and is easy to use. It has a PC interface through the Morningstar software and can be programmed to tailor fit your battery bank and conditions. I bought mine on E Bay NIB for $200. It has temperature compensation with the added battery hookup wire so will keep your batteries charged correctly at various temperatures, also.
time2roll
Nomad
May 26, 2014
Fixed Sight Training wrote:
Okay, last question. Maybe. Does anyone know of an inexpensive charge controller that will handle the 24V panel?
Inexpensive is relative.
I recommend MorningStar SunSaver MPPT-15L about $240.
You can certainly spend more but this works.

http://www.solarblvd.com/Charge-Controllers-MPPT-Charge-Controllers-Morningstar/c6_46_228/p2000/MorningStar-SunSaver-SS-MPPT-15L-Charge-Controller/product_info.html

Gets cheaper if you feed it with two or three of those panels.
Fixed_Sight_Tra
Explorer
May 26, 2014
I think a few folks are using the eco-worthy. BFL13, perhaps?

I'm not sure that a cheap controller will provide the best results. For example there is one called BZ that is extremely poor at MPPT.

Thanks. I looked at both those and according to their specs neither will handle the uni solar 136 watt with it's 48 voc.

The bfl gives a max rating of 43 voc. Any idea how specific these numbers are? Do I have a little wiggle room?
pianotuna
Nomad III
May 26, 2014
Hi,

I think a few folks are using the eco-worthy. BFL13, perhaps?

I'm not sure that a cheap controller will provide the best results. For example there is one called BZ that is extremely poor at MPPT.

Fixed Sight Training wrote:
Okay, last question. Maybe. Does anyone know of an inexpensive charge controller that will handle the 24V panel?
Fixed_Sight_Tra
Explorer
May 25, 2014
Okay, last question. Maybe. Does anyone know of an inexpensive charge controller that will handle the 24V panel?
Fixed_Sight_Tra
Explorer
May 25, 2014
I found someone locally who helped me out and changed the connectors on the panel and tested the open circuit voltage. 47-48 volts at 1pm on a mostly clear day in denver.

Clearly I need to rethink this whole plan.
Fixed_Sight_Tra
Explorer
May 25, 2014
Thanks for the info. I will check the open circuit voltage.

The max voltage isn't listed anywhere in the specs or installation or operating manual for the prostar. As a matter of fact you have to put in "max panel voltage" in the search of the ws, "max input voltage" or "max solar input" won't do it. THEN you get the message

"Do not charge a 12 Volt battery with a 24 V solar panel."

Seems like that should at least be in the manual. Maybe on the front page in big letters.

It's been a while since high school electronics but it seems like if I put a resistor inline between the panel and the controller to reduce it from 33v down to 18v it should work. I'll loose some amps but so be it. As you said I need to measure the OCV before I know how much resistance to add.
time2roll
Nomad
May 25, 2014
Please verify the open circuit voltage before you go any further.

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Connect cables from solar closer to converter than batts?

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