dissimilar panels and common negative question

[towpro]

Sorry for 2 questions. My new RV system is GoPower PWM 30a with two 200w panels.
Since my new RV also has 12V only refrigerator I know from experience off grid camping this may not be enough. (300 was enough on last RV but that was without 12V only refreg)
I know I can add 1 more panel to current system and everything will support it but what if I wanted to go to a total of Four 200w panels?

The current solar panels are GoPower as supplied by Manufacture, but they cost 2x what Renogy does.
Here is the specs of the 2 panels

	GoPower	Renogy
Max power Vmp	19.11v	19.2v
Max power Imp	9.65a	10.42a
Open Circuit Voc	22.78v	23v
Short circuit Isc	9.32a	11.05a

I want to bypass the PMW controller mounted in the wall, and put a Victron 100/50 MPPT controller up near my Lithium battery (Inside RV front cabinet)
If I have 4 panels = 2 Gopower and 2 Renogy, it thought I would put one Gopower and 1 Renogy in series, than the 2 pair. Is this the best method?
I think anyway I look at doing this, the GoPower panels will pull the Renogy panels down to its level (which is only the loss of less 1a per Renogy panel).

Next problem. Currently the Solar panel output wires go to panel in wall, then the controller output Positive goes to battery and controller output Negative goes to to the RV chassis.
By me bypassing the current controller, this will cause the solar panel output negative wire to go to RV chassis.
since the RV chassis is Negative for everything, is this OK? Searching the internet you will find both answers yes and no.

But they make common negative mppt controllers

 

[HarryN]

I will just throw in some info to help you in your information gathering journey but not have a specific answer.

Many RVs come with a Furion or Zamp connector for the solar input. I seem to remember that it is rated for nominal 12 volt panels (like you have) and an absolute max current of 30 ish amps. When I look at connectors across a wide range of industries, most heat up significantly when pushed much beyond 50% of the rating, so I try to use connectors at that 50% point for current.

As far as using several panels in parallel with slightly different Vmp and a PWM controller - it is a non issue. The controller will just force them to all behave as one. Might be slightly non perfect but will work just fine.

I can't imagine buying anything from renogy but maybe look at rich, newpowa or solarland for panels in that RV size range.

I use a mixture of 2 each 12 volt panels wired in series and a 24 volt panel in parallel to power my off grid shop and it seems to work and it seems to work just fine - but I am not always a perfectionist about things for myself. More or less what you are considering - just a different panel voltage.

I didn't try the renogy pwm controllers but the rover mppt controller has surprisingly high standby power use.

If you want to stay with PWM, bogart has a setup for running dual 30 amp chargers wired in parallel with some kind of control that deals with controllers in parallel.

________

The thing to watch on RVs is to make sure that the grounding is all matching, and that a failure / frayed wire does not cause a fault if it is touching ground or not.

 

[Crowz]

Use the panel calculator in my signature anytime you want to know the answer to your question about mixing panels.

Here is the results of 2 of each of those panels used in different setups from that calculator I'm talking about :

All panels wired in SERIES:

• Max power output: 612.96W
• Max power voltage (Vmp): 76.62V
• Max power current (Imp): 8A
• Loss: 13.16%

All panels wired in PARALLEL:

• Max power output: 704.01W
• Max power voltage (Vmp): 19.11V
• Max power current (Imp): 36.84A
• Loss: 0.27%

All identical panels wired in SERIES, then all series strings wired in PARALLEL:

• Max power output: 704.01W
• Max power voltage (Vmp): 38.22V
• Max power current (Imp): 18.42A
• Loss: 0.27%

All identical panels wired in PARALLEL, then all parallel strings wired in SERIES:

• Max power output: 612.96W
• Max power voltage (Vmp): 38.31V
• Max power current (Imp): 16A
• Loss: 13.16%

 

[mikefitz]

is this OK?

The solar panel array feed wires connect to the positive and negative of the 100/50, idealy with a isolator in the feed path. Don't connect the solar negative to chassis. It's OK with your low cost PWM as battery negative, ( that for safety connects to chassis), internally is common to solar negative.
For your solar array connect the same make panels in series, then the two series pairs in parallel.

If you decide not to add panels, at least change the PWM to a MPPT, it's totally unsuitable for lithium.

 

[0truck0]

Agree...
You can charge batteries with multiple chargers (controllers) and be fine.
Double your same-as panels for 24 volts then charge battery. This give two sets of panels. Each set different as you say. This is no problem.

For fridge it depends how much it runs, and how well insulated it is etc. Mine is a fairly good size and will run fine on 200 watt panels.

Check these panels out that Will shared:
https://signaturesolar.com/grape-solar-100w-12v-solar-panel/?ref=cPwLcVc0SW-BjN

Agree, dont ground the panels. Have the pos and neg cables from panels to controller to batt both the same length and gauge. The batt is already grounded, so that is enough.

Tip:
Get a shunt. They are cheap and you will love knowing your levels. You simply wire it between the batt neg and the controller neg (and run a small 12v pos wire to it). So, if you ground anything then the shunt does not work right.

Better yet shunt and MT50 if you get better controller. The EP Ever work with it, so you can program your controller and view the status.

 

[towpro]

My RV came with a complete GoPower system PWM, and dealer threw in an extra 200w (GoPower) panel for a total of Two 200w panels.
I already have a Victron 500a shunt that is correctly installed on my 140Ah Lithium battery I monitor info using Bluetooth.
when I install the Victron (100/50) MPPT, which I will monitor with bluetooth.
I already have a Victron Energy 800VA 12-v 120V AC pure sign wave inverter. (to run TV/laptops when off grid)
I have been doing solar in RV's for over 12 years and displays were nice in the past, I just don't see the need anymore.

My problem is when I go to install the new controller, I will need to splice the 2 Panel wires in the wall to remove the old controller, and It will result in the negative wire from the panels using the RV frame as the conductor.
If I need that Negative wire from the Solar panels going direct to the controller, its a major wire job.

I don't want 2 controllers, one is enough and I only have 2 wires from the roof to inside the RV.
I am not looking to run new wires. current wiring is 8g, and my expansion will be using series/ parallel (thanks Crowz) I will well within the load capacity of my current wiring.


I also have a epever PMW dual battery system with MT50 on our pontoon boat. (charges trolling than starting battery).
The last 2 RV's I used Bogart SC-2030/TM-2030 RV and really liked the system but they were limited to 30a and its still PWM

 

[mikefitz]

problem is when I go to install the new controller, I will need to splice the 2 Panel wires in the wall to remove the old controller, and It will result in the negative wire from the panels using the RV frame as the conductor.

Perhaps I don't fully understand the problem . The additional new panels and the associated connections to the existing, will be outside on the roof. Two cables, solar positive and solar negative, will enter via a roof gland of some sort and connect to the new controller.
Are you saying the original install connected panel negative to the chassis and the controller picked up the negative from chassis.
If that's the case is a poor quality install.

 

[towpro]

no I am not saying that.
Current = panels -> (PWM controller) -> output positive is home run to battery, output negative goes to RV chassis which is used of negative battery everywhere.


Problem is the current PWM controller is mounted in a hole in an interior wall, and there is no space to put an MPPT on wall.
So I would need to remove the old controller, splice the wire that now to go the old controller, positive to positive, negative to negative, than put the controller back in the wall to fill the hole.

Future: = panels -> positive home run to controller, negative to common negative chassie -> (MPPT contoller) -> output to battery positive, and battery negative on Load side of shunt. (negative battery is also connected to chassies common negative (with shunt between battery and load)

but now the panel negative will also be connected to battery negative through chassis common negative.

BUT if I can find where the negative wire is connected to the chassis, and if there is space I could put the MPPT controller there, then send the output of the controller to common negative chassis and Positive home run to battery.
But MPPT controller would be in HVAC conditioned RV space with batteries in enclosed enclosed but unconditioned RV space (temp differences) with no way to run a separate temp monitor curcuit without Tearing the RV apart to run wires)

 

[RV8R]

Hi @towpro

Maybe you could post a schematic of your system & proposed changes ?

This would help reduce confusion.

I have a couple of Victron 100 | 50 MPPT chargers. I would wire those panels in series, but install big enough gauge wire for parallel. The reason being, in crappy sun areas, your array voltage will be about 40v @ 10a = 400W. As the Victron needs battery voltage plus 5 volts to start the charging process the 40V vs 20V will far exceed the 18V needed to start ( numbers rounded up ).

Then if Parallel is a better choice simply swap the connections ( by adding parallel connectors @ the panels ) as you have ran large enough wire for the “20” amps.

Series ,,, add up voltages of the panels

Parallel ,,, add up the amps of the panels

 

[mikefitz]

Current = panels -> (PWM controller) -> output positive is home run to battery, output negative goes to RV chassis which is used of negative battery everywhere.

That's no problem, wire the output of the Victron, positive to battery with a fuse/breaker at the battery end of the cable, and take Victron negative output to chassis, your wire splice will do this. The negative path will find its way to battery negative, also connected to chassis.
Provided the connections to metal in both cases are correctly made, there should be no problem. It's OK to assume the connections to chassis are valid and just in case there are unwanted volt drops, use a Victron smart shunt battery monitor, or Victron Battery Sence . Either of these report actual battery volts and temperature to the controller over Bluetooth, thus providing accurate charging regardless of possible volt drops in the path between battery and controller.

 

[HarryN]

Don't use the body of the RV for a return wire of the solar if that is your question.

It needs dedicated wires for the solar panels to the controller, and from the controller to the batteries.

You may need to add an additional power inlet to the RV for the additional solar setup. Maybe mount under the RV.

 

[0truck0]

Sorry. you going to have to do a little work. The RV dealer or manufacturer did not do you any favors. RV dealers/mans do not know what they are doing except how to trick you into thinking they do.
I would start over from scratch and do it right, not do it dealership method.
Don't use chassis for your negative connection!
You going to have to learn some very basic skills with wires. Get fish tape and run the neg wire down the wall.
I cant imagine not having room to mount a controller how big is your controller? Sounds like is way too big for your small amt of solar panels.
OK, so what, you have to do a little work to put a controller in the wall/??? Welcome to the club, is not easy like working on house stuff.