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Truck not charging batteries, solar seems really slow


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Completely clueless about this but shouldn't my truck (with 7-point plug and 12V power) be charging my RV batteries when I'm driving?

I got down to 83% last night after watching a movie (17% seems a lot of power for a TV and PS3 for one movie but that's a different matter) and it was the same when I got to my campsite tonight after driving 4 hours.

Am I doing something wrong? Wiring checked on both RV and truck and is good. I was hoping to rely on this on gray driving days like today.

Also it seemed to take all day (mostly sunny, partly cloudy) yesterday to recover from 86% to 99%. I have 4 100W of Rengogy Eclipse panels and a 40A MPPT charge controller and 400AH AGM batteries with 4 or 6AWG wire. I have checked connections and everything seems okay and controller says it is charging. How can I even conceive of charging to 100% from 50% if it takes that long to charge 14%?


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Your truck may or may not actually be supplying a charge to the trailer while towing.  You need to put a meter on the 12 volt positive terminal in your trucks 7 pin connector at the bumper and see if it is energized with the truck running.  If it is not, there is a fuse somewhere that is either bad or was never installed.

Additionally, the charge coming through the 7 pin connector (when it is working) is minimal at best.  It is being pushed through a 12 gauge wire (most likely) from your alternator through a fuse block and all the to the back of your truck.  Then it goes through the 7 pin connector and into your trailer wiring (also probably 12 gauge) to wherever the batteries are located.  This is a long run on relatively small gauge wire for 12 volt which makes it very difficult to effectively recharge a depleted battery bank (especially a larger one like it appears you have).  You cannot expect a lot of charging from this set up.  It will help to maintain a fully charged battery bank while moving, but it won't do a lot to recharge a depleted bank that still has small loads on it.

As to your solar equipment, it is difficult to answer why it is not charging better than you describe.  It seems from the equipment that you are describing that it should.  Again, my first step would be to put a meter on the system and see what it is actually doing.  Measure the voltage/amperage coming from the solar panels to the controller and then the voltage/amperage going from the controller to the batteries and see what the readings are.  With that information, we can better determine how fast/well your system should recharge your batteries.

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Chad is spot on.

Alternator charging- Often requires re-wiring in order to get enough juice back to your house. It may also be, as he said, the "charging circuit" fuse and relays are not not installed. Newer trucks with tow packages "generally" come with them installed, but older trucks it's not "typically" likely (even with a tow package)... or it comes with the necessary fuse and relays in a little baggie in your glove box. Even if they are not... good news... you're talking $3-$5 relays and a buck or so for a fuse.

If you really want to wire for alternator charging, what many will do is to bypass the fuse/relay box and wire in a solenoid directly to the battery charging circuit. Less loss in transmission and MUCH easier to wire in a larger gauge. That's a completely different thread though.

Solar- You have to remember that pushing juice into that last 10%-15% of capacity is quite slow as your battery bank isn't accepting many amps. You can go from 50%-80% in a relatively short period of time and that last 20% can take even 3-4 times longer. That being said... it's highly likely some fine tuning can be done to improve performanace. I run a 440ah AGM bank with 540watts of panels, but you also have to remember that the watt rating of your panels isn't really the determining factor when considering actual production. Efficiency ratings can range from as low as 12% on up to 22% or a smidge higher.  Your renogy panels are rated at 15.47% efficiency. That falls within the "average" 15%-18% range. 

The first step is to check everything with a meter and see what it's "actually" doing during production hours. Check each panels output, controller output and receiving charge at your batteries.

You'll also want to check your array/s every hour or so to ensure you're not having any unexpected shading issue. If you've washed your rig recently then you also want to ensure you don't have "bird bombs" creating a shading condition. This generally only occurs within the first 48hrs of a wash so if you plan to rely much on solar you're better off to never wash your rig. :P:lol:

More information is required to help much though. Your wire gauge is only relevent if we know how long the run is. A run being both paths. Ie., a 5' wire is a 10' run.

How did you end up setting up your array/s? What solar region are you in?

If I remember correctly... your controller is the ROV-40-MPPT? If it IS the rover then the best charge profile for your AGM's would be (ironicly) the "flooded" setting, but they can handle more and you should consider going with a custom user setting to tweak your charge profile.

In addition... if you don't already have one installed, a temperature sensor will also improve your charge rates. I know you plan to rely on your solar at times so for $10 it should be a no-brainer to have one installed.

If all else fails, there is always the option to throw more panels at the problem.

Lastly, you have to have realistic expectations. Those kits are a great "foot in the door"... fairly low cost entry into solar, but may not produce the same results as a custom setup.

Edited by Yarome
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I have a few thoughts but hopefully one of the real solar experts will swing by:

1. I agree with Chad that you cannot expect much as far as the truck providing charge while driving.  I have heard of folks running a larger gauge wire from their alternator to actually make the truck charge worthwhile. I have never done this so I would get someone else's input as to whether is appropriate.

2. You need to factor in what your energy use is while you are on the road and subtract that from any potential gains. Your unit is going to have an electrical draw ( often referred to as phantom load) just when you are sitting.

3. You refer to your meter but people responding will want to know what kind of meter you are using. A really good meter will answer your questions. You need to be able to see both the amps used and gained. By far the most recommended meter is the Trimetric by Bogart Engineering.

4.  4 or 6 AWG for solar panels is acceptable but 4 would be better. Be careful of relying on any manufacturer prewiring as they are often inadequate. The gauge if wire needed also depends on the length of your run. Again the Trimetric will tell you how you panels are performing. If I read the specs correctly 4 Renogy 100 watt panels could theoretically provide 20 Ah per hour. However that is the theoretical high. Hopefully the real solar experts will swing by and give you estimates but I have heard to figure 5 good charging hours per day and certainly less than 20 AH per hour.  I see Yarome has responded as I write this. He could provide better guidance.

5. Finally, read Jack Mayer site over and over (I sure have). The best practical resource.  http://www.jackdanmayer.com/rv_electrical_and_solar.htm

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6 minutes ago, Daveh said:

3. You refer to your meter but people responding will want to know what kind of meter you are using. A really good meter will answer your questions. You need to be able to see both the amps used and gained. By far the most recommended meter is the Trimetric by Bogart Engineering.

Quite! Good catch, Dave.


One other word on the alternator, you'll also want to check your alternators output to ensure it is actually capable of outputing any meaningful charge in addition to your trucks demands. 

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46 minutes ago, DuneElliot said:

They charged 3% in serious cloud cover today, but they only charge when not moving

The solar is still charging when in transit. The low charge percentage is, it sounds like, just due to the cloud cover.

Even with nothing actively "on", if your batteries are connected you will still have a small "parasitic" draw (control boards, detectors, meters, radio memory, etc.) that can add up throught the day. Ie., if your rig has a .5amp parasitic draw.. that's 12ah's in a day. 1amp... 24ah's in a day with nothing actually "on".

A for example: With heavy cloud cover your panels may only be outputing... say... 6amps. Count 4 hours of production time... that would barely keep up with a 24ah parasitic draw.

That your solar kept up with whatever your parasitic draw is, kept your reefer running, and still pushed in 3%... that doesn't throw up any serious red flags.

Side note: Even on propane your reefer consumes 12v. It's required by the control board and for LP ignition.


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1 hour ago, DuneElliot said:

The only thing running or on when traveling is my propane fridge/freezer...no 12V involved

The controls for your refrigerator do use 12v power but it isn't a big load so doesn't usually deplete batteries. In most RV refrigerators, the 12v is fused for 3a and draws less. 

Edited by Kirk Wood
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Dune, like others, it comes as NO surprise to me that your trucks alternator doesn't provide much charge back to your RV batteries. The reasons are too much voltage drop and too much line resistance between the alternator and all the wiring and the RV plug and receptacle then finally to the RV batteries themselves. Sure that set up (and hey we use it)  can provide a few charging amps but nothing compared to a good charging system in the RV. If you were to over engineer and over kill the system with bigger wiring and perhaps relays etc that can help, but when driving  (subject to your system) your solar (if fixed, mounted and operating ???)  could still provide the bulk of necessary RV battery charging right????  

 Regarding achieving 100% SOC into your house batteries, that depends on the present loading and size, quality and charging algorithm of your charge controller.  When my so called "Smart" 4 Stage PD 9280 80 amp charger operates (serves 450 AH of lead acid) it takes x amount of time charging at the higher 14.4 or so volt BULK rate before it backs off to the lesser 13.6 volt ABSORPTION rate BUT THEN IT TAKES A LONGGGGGGGGGGG TIME TO ACHIEVE 100% before it begins to FLOAT at 13.2 volts. The reason it takes such a longgggggggggggg time to achieve the final 100% is because it's then charging at a lower rate and that's by design and algorithm.

 Similar with your solar charge controller, that final lower charge rate to 100% may take significant time as compared to an initial higher charge rate to begin with. As I already noted, this all depends on your load and solar capacity and solar charge controllers algorithm. I guess the only way to monitor all that is with accurate voltage and current monitoring of the controllers output to your batteries and then make a call to the controllers tech support as I cant say from here all what's going on. As noted (and I'm sure you're already aware)  the distance from controller to your house batteries and the size of the wire all makes a difference also. My 715 solar watts and 50 amp MPPT controller often (subject to sun and depletion) takes my 450 battery AH to 100% early in the day on bright days.      

 I guess what I'm saying in a nutshell is your system may be performing as designed and at its capacity and perhaps only requires some minor tweaking. Does your controller have settings and capacity to charge  AGM  ??????????????????????????????? 


 Let us know how things work out

John T

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All good info, thanks. 

I can change my controller's parameters if I knew what I was doing via the tracer meter it came with. Would like the Bulk charge to last longer and not shift so soon if it is safe to do so before it goes into the other two charging options.

I am definitely considering upping my solar panels to 600w especially going into winter...I have the room and better to do now while they are the same as what Renody has in stock.

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10 hours ago, DuneElliot said:

my manual says something about doubling voltage for a 24V system...does this mean batteries or PV array?

Dune, not being there or having read your manual, I assume your solar charge controller (subject to design and specs) typically accepts 24 or 48 and even higher DC input (PV array) voltage and converts it down to the appropriate charge levels/cycles for 12 volt systems. As long as its set for 12 volt AGM charging you ought to be good to go if all else is correct. I have no idea if your controller can charge a 24 volt (IE doubling 12 volt) system, but you don't have that anyway.  As I indicated earlier, it doesn't surprise me it takes a long time to achieve 100% SOC once you're charging in the lower rate Absorption cycle. My Bulk charge cycle goes fairly fast compared to the Absorption phase, but that's ONLY my particular charger NOT my MPPT solar charge controller which I'm sure uses its own likely different charging algorithm.

 Hopefully you're already in good shape???

John T  NOT any solar expert, so listen to your manual and solar experts over me............... 

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CJ, I just bought Book1, looking forward to reading it at the HDT rally. Can't say I ever knew anyone that even heard of  Brooks, much less read his books...I'm still waiting for the next one. Will read yours while I wait :)  

Safe Travels, Hope you get your solar issue solved.

Edited by Big5er
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 Hi again Dune, sure your 2000 watt Inverter (like any) "uses power" which of course depends on how much 120 VAC load its supplying (plus heat losses and other inefficiencies) and it takes something like 10+ battery amps for every 120 VAC single amp it supplies. The question is how much energy your panels and MPPT charge controller is supplying INTO your battery bank VERSUS how much the Inverter and other 12 VDC loads is going OUT of your battery bank.   Does your MPPT solar charge controller (or other monitors) have an indicator showing how many charging amps its pumping into your battery bank and battery voltage level ?? Of course, that changes depending on sunlight and angle and battery SOC and load, mine fluctuates quite a bit during the day. My MPPT controller also indicates the voltage and amperage flowing FROM the PV array INTO the controller. That type of data may help answer your questions. However remember even at bright sunlight at the max perfect angle your 400 watt solar array can only theoretically (and you dont get that) deliver around 30 amps max at 13 charging volts.  I would venture a pure "guess" not knowing and subject to the sun, its angle or your system, 22 amps might be the most you will ever harvest.  Obviously if your drawing more OUT of your batteries then the solar is pumping INTO them, its a net loss situation. Let me toss out a wild number of say when boondocking you consumed 75 amp hours of energy OUT of your battery bank (12 VDC plus 120 VAC Inverter use). How long would it take to replenish that amount of energy ???? Wellllllllllll if you were pumping say 25 charging amps into the batteries, in pure theory (but you dont get all that due to inefficiencies and heat and other losses) it would take three hours at 25 charging amps to restore 75 amp hours of energy BUT AGAIN with flat mounted panels and ever changing (sometimes very little) sun its NEVER gonna happen that you get 25 amps flowing for three + hours. If you were lucky with good bright sun direct overhead and you pumped perhaps a steady 20 amps into your batteries (and NO load during that time) it could take well over 4 to 5 hours  (inefficiencies and heat losses remember) to bring you up to 100% SOC and your charging algorithm may slow the rate down after some time WHICH MEANS IT MAY TAKE EVEN LONGER????


 I guess what I'm saying is 400 watts of solar and your controller may ??????????????? be working fine, its just that you may be using up more energy then your system can supply?????????????     Sorry I just cant say from here. I can say, when I initially just had 200 then even 400 solar watts and I was still only marginally keeping up when boondocking and felt like you SOOOOOOOOOOOOO I raised it up to 715 watts and now by golly I often (subject to sun and load) achieve 100% SOC (450 amp hours of lead acid) by mid or even early morning yayyyyyyyyyyyyyyyyyyyyyyyyyyy. I run a small dorm size auxiliary fridge 24/7 (via my 3000 watt PSW Inverter) plus the normal vent fans or furnace and LED lights and water pump and small electronics and with 715 flat solar watts I am pretty much fully self sustained as I'm a relative low energy user.

 Gather up some charging and load data (Killa Watt Hour meter) then call Renogy and let us know what you find. I'm curious. NOTE I'm NOT meaning to sound negative or discourage you (ANY SOLAR IS GOOD) congratulations on your system. I'm  just speaking from experience in hopes of providing some insight and assistance..........


 John T  NOT any solar expert so no warranty, ask them 

Edited by oldjohnt
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