Solar panel low output - I'm guessing they need replacement?

BurritoLover · December 2022

I recently picked up a 2018 Tab 400 and the solar system isn't charging the battery past about (11.8-12.2)V. The previous owner had it on shore power and the battery was above 12.8V. I'm only getting 0.6A to 1.5A out of the 2 rooftop panels in bright (but not direct) winter sun conditions. I think these Grape Solar panels are 100W each? I'm guessing the panels are done?

Also curious why my multimeter measures 21V from the wires on the roof, but 12V at the charge controller. Same amperes. Any insight?

Any tips how to deal with panel replacements if you can't weight the roof? I can't reach them from a ladder! I have no idea how I'll re-seal the roof vent too.

Thanks for any tips! As a first-time RV owner, catching up with all the maintenance the previous owner neglected is a bit overwhelming.

Image: https://us.v-cdn.net/5021717/uploads/editor/4s/49jzx5mkjuzp.jpg

pthomas745 · December 2022

You have to be careful in the winter on measuring the output of the panels. I live in Socal, at about 33 degrees north, and this time of year here we get the "earliest sunsets". My portable panel, located in the same spot it usually sits for most of the spring/summer/fall, is not "completely" recharging my battery from just basic day to day parasitic drains. When the sun is hitting the panel nicely...the charging input is still down a lot from the mid summer readings (only about 3 amps instead of 5-6 amps in the summer.)

So: not sure which direction your panels are pointing, but before you write them off get the trailer in full sun with the panels pointing south as close to noon as you can.

And: what device is telling you the battery voltage is 11.8 to 12.2? Are those readings from a "rested" battery? Battery switch off and no charge coming in?

Are you able to plug the camper into shore power....charge for a bit, and then take a rested battery reading?

The batteries in your trailer are 4 years old. If you don't know how they were treated from the previous owner, it could be the "aging" batteries are failing rather than the solar not charging for you.

MuttonChops · December 2022

BurritoLover said:
. . . 2018 Tab 400 and the solar system isn't charging the battery past about (11.8-12.2)V.
. . . only getting 0.6A to 1.5A out of the 2 rooftop panels.

Question:
How/where and under what trailer 12VDC loading conditions are you measuring the voltage?
Same question for solar panel amps - - - Current Clamp Meter ? or - - -

BurritoLover said:
The previous owner had it on shore power and the battery was above 12.8V.

Observation:
On Shore Power the WFCO Power Center charging function generally causes a Battery Voltage readings of 13.2 to 14.4 V with ~ 13.6 most typical. These voltages reflect which charging stage the Power Center is in. A shore power battery voltage of 12.8 may suggest the Power Center Charger/Convertor is not operating. Have you confirmed the "on shore power" trailer 12VDC value at your location?

BurritoLover said:
. . . curious why my multimeter measures 21V from the wires on the roof,
but 12V at the charge controller.

Questions:
       How/where are you measuring the 21Volts.
       Same question for the "12V at controller".

Observations:
       If your rig has Grape Solar 100W panels.
       The panel maximum Open Circuit Voltage is 21 VDC.
       Open Circuit meaning No Load, solar panel wires not connected to anything.
       If the Panel Voltage is measured connected to the controller I would expect a lower voltage.

       Next, if the 12V at the controller is on the controller output terminals to the battery.
       I would expect the voltage to be higher.
       The 12V suggests you are just reading the battery voltage.

       So, maybe your controller has failed; based on the input and output side voltages reported.

BurritoLover · December 2022

Thanks for the responses!

pthomas745

It's a tough time of year to troubleshoot the system! I realize the winter sun isn't great. I'm in the high desert, central CA and I would think that with no load the panels should slowly charge the battery. 0.5 to 1.5A from this setup seems low (even in indirect light) but I'm not sure of the efficiency of these flexible panels. I'll test in direct sun before I buy new ones.

The charge controller and plug-in socket battery monitor by the sink both tell me current battery is at about 11.9V for the last 2 weeks. The daily solar gain seems to do nothing other than minor daytime fluctuations.

I haven't tried charging with shore power yet. But when I picked up the trailer, the previous owner had it plugged in and the battery was strong (13+V) for a couple days of use. So an old battery may be contributing to the problem, but I'm surprised to only see 0.5 to 1.5A input from the panels. I'll try charging with shore power but suspect it will work fine and I'm really hoping to troubleshoot the solar system since I don't think I'll ever camp with hookups.

@MuttonChops

I disconnected the panel connections on the roof: 21V and 0.75A when I measured here with a multimeter today.

I re-connected the roof connections and the charge controller display read 12.5V and about 0.75A. At this time the battery was reading about 11.9V (both wall monitor and charge controller battery status). So, apparently, the battery is getting a very slight charge. I don't understand how the 21V (at panels) becomes 12.5V (at charge controller).

I also measured the 2 left bus screws on the charge controller (solar input connectors) and confirmed that charge controller display is correct: 12.5V and 0.75A. No load for all these conditions (other than tiny parasitic load for radio clock, smoke alarms, etc.).

So it looks like I'm getting proper open circuit voltage from my Grape Solar (200W?) panels but insufficient Amps? Maybe it's an indirect winter sun thing, but I'd expect more than 1.5A max from indirect sun in California (50deg F).

I haven't tried charging with shore power yet, but suspect it will fully charge the battery to 13+V.

Sorry for the long-winded post, but am I wrong thinking the panels are dead? Or maybe I shouldn't expect much from the flexible solar panels in indirect light? How would you diagnose the weak link? Thanks!

pthomas745 · December 2022

You have to try those battery voltage readouts again with the battery switch off for this test. Even a slight parasitic drain can have an effect on the voltage reading. No matter what device you are using for voltage: the voltage will always read low with the battery switch on, and read only the charging current going to the battery when charging with shore power or solar. And, you have a meter and know how to use it, so that is all very good.

Grumpy_G · December 2022

The panels are likely not dead, typically solar panels are designed for a 25 year lifespan. Unless damaged or really crappy quality they are fine.
Indirect sun light or partial shade reduce panel output significantly. The curved flexible panels aren't helping either.
What is the solar controller ? I'm guessing it's the PWM type as the current doesn't change from the panels to the battery. PWM "averages" the output voltage by switching the input voltage on and off rapidly.

MuttonChops · December 2022

@BurritoLover ; As @pthomas745 has noted you should have the Battery Cut-Off Switch in the off position . . . no power to trailer, no lights, etc. If your 400 also has an inverter [12VDC to 120VAC] turn if off.

The goal being to reduce the electrical load to just the solar controller. This will get you the most realistic 'displayed voltage' value.

Typical trailer wiring directly connects the Solar panels & controller to the battery bypassing the Cut-Off Switch:

Image: https://us.v-cdn.net/5021717/uploads/editor/ok/i4wiym7mtloy.png

BurritoLover said:
. . . don't understand how the 21V (at panels) becomes 12.5V (at charge controller).

Web-Article edited quote:
" The main function of a solar charge controller is to ensure the amount of power that is sent to the battery is enough to charge it, but not so much that it increases the battery voltage above a safe level.

Say you have a single 100-watt solar panel and a 12-volt battery. Remember a 12-volt battery is actually able to charge up to about 12.9 volts.

The 100-watt solar panel can put out a maximum of 21 volts, which is a little too high for the battery to accept safely. Leaving it connected to the battery too long could result in a dangerous situation . . . a charge (solar) controller in between the solar panel and the battery to limit the voltage available to the battery. "

Article: https://www.solarreviews.com/blog/what-is-a-solar-charge-controller

BurritoLover · December 2022

Thanks for all the info. I'm going to add an additional external panel (with charge controller) and see how the system works. At least I'll be able to point it towards direct sun. I plan to install a battery smart shunt also, so should be able to get some good data for comparison.

@MuttonChops The diagram is helpful, thanks.

I'm planning to connect the portable solar to the 7-pin connector for convenience. I know this works, but would it create a noticeable loss of efficiency (other than the voltage drop created by the longer wires)?

I don't know what goes on in the T@B power converter. When the tow vehicle provides current while driving does it go "uncontrolled" directly to the battery? Or is there some sort of basic charge controller built in the fuse box?

I guess I can use the shunt to monitor direct vs. 7-pin connections but would rather not buy a 7pin harness if it's a bad idea.

MuttonChops · December 2022

BurritoLover said:
. . . what goes on in the T@B power converter.
When the tow vehicle provides current while driving does it go "uncontrolled" directly to the battery?

Or is there some sort of basic charge controller built in the fuse box?

Yes and No to first question . . . . as the Tow Vehicle is controlling the Voltage Level. Plus the Tow Vehicle can only delivery 2-5 Amps (vehicle set-up dependent) or a real-world trickle charge.

No on second question. WFCO Power Center only monitors/controls the 12VDC level when Shore Power is used.

The WFCO Power Center has three functions:
++ 120VAC Distribution Panel, the circuit breakers
++ 120VAC-to-12VDC Convertor & battery charger
++ 12VDC Distribution Panel, the fuses

Here is another reference diagram:

Image: https://us.v-cdn.net/5021717/uploads/editor/kd/o60vmmh1j2ws.png

BurritoLover · December 2022

Thanks @MuttonChops

I'm still having issues getting set up. I guess I have a lot to learn!

I made a wiring harness to connect my portable solar to the 7-pin. My Renogy charge controller shows error code b01, which I believe means it dead/no battery. Sure enough, the multimeter only measures 0.8V at the trailer side of the 7-pin. But the battery has 12.8V charge. Any idea why the massive voltage drop between battery and 7-pin?

pthomas745 · December 2022

What did you use for a "wiring harness?"

MuttonChops · December 2022

BurritoLover said:
. . . made a wiring harness to connect my portable solar to the 7-pin
My Renogy charge controller shows error code b01, which I believe means it dead/no battery.
Sure enough, the multimeter only measures 0.8V at the trailer side of the 7-pin.

Am assuming:
++ The "My Renogy charge controller" means the Charge Controller included with the Portable
Solar Panel connected to the 7-Pin.

Normally a Renogy error code b01 means 'Battery Not Connected'.
Seems like your custom wiring harness has an issue; open, wire connection error.
And/Or the trailer Battery Cut-Off switch is in the OFF position.

A sketch of how you believe you have the system wired with Renogy model/part numbers might be helpful to understand your set-up and data points.

BrianZ · December 2022

Check for either the battery switch being off (turn it on), or maybe the trailer fuse at the battery (or that fuse's wiring integrity).

BurritoLover · December 2022

The Renogy suitcase panel has a built-in charge controller with mc4 connectors. I bought mc4 pigtails and a 7pin connector so I could plug the suitcase unit direct to the trailer when parked. Great video for making a wiring harness here :

https://youtu.be/LONcDJpJYdA

I confirmed continuity with my connections so I don't think that's the issue. The problem seems to be that I am only getting ~1V from the trailer 7-pin, which must be too low for the Renogy charge controller so it says b01 "Battery not Connected". The battery is reading 12.5V+ so I there's some major voltage drop between the trailer 7pin connection and the battery.

The battery switch is on and the 40A Gloso fuse (I've never seen one like that) next to the switch has continuity at the wired connections:

Image: https://us.v-cdn.net/5021717/uploads/editor/d1/benwa176nwv1.jpg

Anything else I should check?

MuttonChops · December 2022

@BurritoLover ; Thanks for the additional information.
And BTW - Nice Video Link.

It sure seems you have an Open Circuit.
If this were my rig, I'd triple check all the connections for Correct Placement and good electrical contact.

With the Solar Panel disconnected; What Voltage do you read at the 7-pin mc4 Connectors?

If the above is not ~ 12VDC; Next check the voltage at the trailer 7-Pin itself.

type-o on figure ~ 12 VDC not VDVC

If by chance the mc4 measurement is Bad and the Trailer 7-Pin is Good
then your adapter is not wired as you intended.

If both measurement locations are Bad; then cut-off switch, junction box, bad in-line fuse, broken wires are the most likely source of your Open Circuit.

BurritoLover · January 2023

Thanks for the diagrams and info @MuttonChops
It turns out that my RF brake controller was causing the open circuit. If I bypass the brake controller everything works great.

I’m still unimpressed with the output of my rooftop panels, but will need to investigate further when we have more sun!

Denny16 · January 2023

Glad you got it sorted. Another possible cause of a low voltage reading on the 7-pin, is dirty connector tabs on the 7-pin. A good cleaning with a small brash bottle brush and some conductive grease on the contacts will solve this issue.
Cheers

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Solar panel low output - I'm guessing they need replacement?

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