RV setup is driving us crazy!

System · June 2006

We recently "went solar" on our RV, with the idea that we could run our 12V appliances - fans, lights, radio, an occasional shot of the water pump, and the led indicator lights for fridge, and occasionally fire up a 110V computer. We can ordinarily dry camp (12v only) for about 3 days on a fully charged battery, and figured the amount of charging the panel could provide should be adequate to keep us topped off. (the rv has a 110V power plug that can be plugged into a 110 power source, in our case into the inverter hooked to our 12V batteries. We don't ordinarily have the inverter hooked up at all.)

This hasn't been working very well. It seems as if the batteries are not properly charging - I admit, I may be sucking a bit too much juice with the computer, but we barely get an hour before everything goes gunny sack and the load disconnect light comes on the battery controller.

Our system is an 85W matrix panel, morningstar sunsaver-20 battery controller, and 2000W coleman inverter (we have 2 12V coach batteries). The batteries are about a year old, but they have been run down a few times. First question: which is the appropriate panel wiring to use? When we hook it up 12V we get 10V output. When we hook it up 24V we get 20V output (on a partially sunny day). When we actually hook the wire up to the controller, it drops to 13V. (this seems like a good idea but we're a little worried that in full sun this might cook the battery controller). Second: what is the load disconnect light all about? Does it mean we're not charging? Do we care about this light at all? Third: does anyone have an idea as to why our system isn't working? bad battery? Fault elsewhere?

I realize this is a lot of info to help us with, if nobody has the time for a pair of newbies we'd sure appreciate it if you could direct us to a learn-it-yourself source that really has user friendly comprehensive info. thanks much for any help!

niel · June 2006

Re: RV setup is driving us crazy!

karen and adam,
welcome aboard. please do excuse the occassional spam popping in here now and then as we are working on its solution.
as to your system, yes you are overtaxing it. just using the computer for 2hrs would require that single pv to charge your batteries for more than 3hrs. 3x85=255wx.9(for ptc w rating)=229.5w and derating for charge efficiency of about 80%=183.6w delivered for that 3hrs. with the other items running and some going 24/7, even if a small load, it's wiping it out of any reserve battery power. normally you shouldn't drain it below 50% depth of discharge. that 10v is indicating to me you killed the batteries. 10.5v is considered 100% drained. the lvd light or led is a way to power items (i believe up to 10amps for that model) that upon the voltage hitting a preset low point it will disconnect the load to protect the battery from discharging too far.
you need to add up all of the loads with the amount of runtime for each to get the watthours needed in a day. from that you know that the battery(s) need to be able to supply at least twice that in order to keep it at 50% or better capacity left. using too much capacity all of the time will take away the life span of your battery(s). now that you know the power needed to charge the battery(s) this is what has to be supplied by the pv(s) over how many hours of full sun you will average per day. if you asverage 4hrs then if your needs totaled in example 1000watthours then it is 1000/4=250watts per hour in pvs ptc. now multiply this by 1.2 due to charging efficiency and we get 300w of pvs ptc. now to put this into stc ratings (those are the ratings most sell pvs in) you must now multiply this by 1.1 to get 330watts of pvs needed to do this example.
this should be enough for you to figure what you need, but we are here to answer your questions if need be. crewzer is one of our guys that is up on solar in rving so he may wish to add to this or unconfuse you if i did that to you. in any case you will need new batteries, but i'd guess you need more pvs too.

crewzer · June 2006

Re: RV setup is driving us crazy!

k&a,

First question: which is the appropriate panel wiring to use? When we hook it up 12V we get 10V output. When we hook it up 24V we get 20V output (on a partially sunny day). When we actually hook the wire up to the controller, it drops to 13V. (this seems like a good idea but we're a little worried that in full sun this might cook the battery controller).

Your PV module’s key specs are 17.6 Vmp and 4.8 A Imp. For an RV, #10 THHN wire could be used for the connection between the module and the controller. Use red for the (+) connection and white for the (-) connection. This wire is readily available from Home Depot and Lowe’s.

Your combination of components (PV module, controller batteries and inverter) should only be wired for a 12 V configuration. Do not wire the batteries in series to make 24 V. The Matrix 85 is a nominal 12 V modules consisting of two 18-cell sections. I doubt that it can be wired for 24 V. Multiple batteries should be wired in parallel (plus to plus, minus to minus) to maintain 12 V nominal and add the Ah capacities. The wiring diagram on page 5 of the Morningstar SunSaver charge controller’s manual depicts the correct wiring.

Second: what is the load disconnect light all about? Does it mean we're not charging? Do we care about this light at all?

The load disconnect light is a low voltage disconnect (LVD) indication that the SunSaver controller has disconnected loads from its load terminals due to low battery voltage. See manual page 9, Section 5.3.4, Battery.

Third: does anyone have an idea as to why our system isn't working? bad battery? Fault elsewhere?

There are several possibilities. I’ll post additional comments tomorrow.

HTH,
Jim / crewzer

rplarry · June 2006

Re: RV setup is driving us crazy!

One problem maybe that you have an internal battery charger that comes on automatically when the coach is plugged into grid power. If you plug your external power cord into your inverter to power the coach then your batteries are trying to charge themselves. This will drain them pretty quickly. If this is the case, then check your circuit breaker panel and see if you can shut off the internal charger.
Hope this helps,
Larry

PhilS · June 2006

Re: RV setup is driving us crazy!

Larry's suggestion of making sure you aren't trying to "charge" your batteries from the inverter is a good one. Definately make sure the breaker is off for your installed charger/converter.

Another thing is your reference that you are powering the LED lights on your fridge. Make sure that the fridge isn't plugged into the 120V outlet located behind the fridge, accessable through the outside panel. If it is, and if it's set on "automatic" it could be seeing the AC voltage available and selecting that for the power. AC power for the RV fridges I have (both in an RV and in our home, as we are off-the-grid) uses 325 watts apiece. That is a significant load that could be using your battery reserve quickly.

When your fridges are operating on propane, there is a solenoid propane valve that is also a significant 12V load when it's energized (another poster may know the amp draw, I don't). There's not much you can do about that, just make sure you aren't trying to cool on inverter power.

Phil

crewzer · June 2006

Re: RV setup is driving us crazy!

Third: does anyone have an idea as to why our system isn't working? bad battery? Fault elsewhere?

There’s a broad range of possible explanations for why your system isn’t working as you’d expect. Based on your post, your system of various components may not be wired up correctly, so you’ll want to check on that possibility.

Assuming everything is hooked up correctly, I suspect that the performance problem is the result of too little net energy production, greater than expected / known / understoiod energy consumption and/or weak batteries.

The Matrix 85’s Imp spec is 4.8 hours. Assuming your module harvests the equivalent of six hours of “full” sun per day and that the batteries Ah recharging efficiency is 89%, the system’s net generation will be 4.8 Ah x 6 hours x 89% = 25.6 Ah. That assumes the module is correctly tilted and aimed, and is not shaded by trees or structures near your campsite.

If your loads consume more than 25.6 Ah per day, the batteries will never fully recharge. Specifically, if your 110 VAC computer and its monitor together consume 150 W and you run it for two hours through the inverter that’s 85% efficient, it’ll consume (150 W x 2 hrs) / (12 V x 85%) = 29.4 Ah. Energy used to power the fans, lights, LEDS, pump, radio, propane detector and any other loads will further deplete the batteries.

Weak batteries are generally the result of age, number of discharge/charge cycles, poor charging and maintenance and/or “phantom” loads. Batteries that are incorrectly charged or maintained generally suffer from sulfation. Batteries that are slowly discharged by small but long-term loads generally suffer a similar fate. Sulfated batteries loose much of their original capacity, and this may indeed be the cause for the symptoms you’re seeing.

The likely solutions are to increase energy production and/or reduce energy consumption, and to buy and correctly maintain new batteries. More on those topics later.

HTH,
Jim / crewzer

System2 · August 2006

Re: RV setup is driving us crazy!

crewzer wrote:

Third: does anyone have an idea as to why our system isn't working? bad battery? Fault elsewhere?

Weak batteries are generally the result of age, number of discharge/charge cycles, poor charging and maintenance and/or “phantom” loads. Batteries that are incorrectly charged or maintained generally suffer from sulfation. Batteries that are slowly discharged by small but long-term loads generally suffer a similar fate. Sulfated batteries loose much of their original capacity, and this may indeed be the cause for the symptoms you’re seeing.

The likely solutions are to increase energy production and/or reduce energy consumption, and to buy and correctly maintain new batteries. More on those topics later.

HTH,
Jim / crewzer

And I don't believe the average RV has a good charger on them..? It seems if I plug mine in during non use it reduces the life of the battery..slowely cooks em......The solar setup described would maintain the batteries during the non use months a lot better!

RV setup is driving us crazy!

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