Adding a solar panel

[Jeepster360]

So our new 24RKS has 2 factory pannels on the roof feeding 4 6v agm. I want to add a third pannel to the system. I have been reading alot about parallel and series wirering. Can I series 2 of the pannels and leave the other single? Or just use the 3rd factory plug in and leave it at that? I don't want to replace the zamp controller at this time. Also can the new pannel be more or less rated to the other 2 already up there?

John

[MechEngrSGH]

Originally Posted by Jeepster360

So our new 24RKS has 2 factory pannels on the roof feeding 4 6v agm. I want to add a third pannel to the system. I have been reading alot about parallel and series wirering. Can I series 2 of the pannels and leave the other single? Or just use the 3rd factory plug in and leave it at that? I don't want to replace the zamp controller at this time. Also can the new pannel be more or less rated to the other 2 already up there?

John

The rules for combining dissimilar panels on a single charger controller are;
1) Panels in parallel must have substantially the same voltage
2) Panels in series must have substantially the same current.

These rules are practically inviolable. Meaning, if you violate them, the resulting array of 3 panels will possibly have less capacity than the original 2.

If the existing panels are in parallel and you change them to series, the same rules apply to adding the third panel.

An instance where this is likely (though not guaranteed) to work is to have 2-100W/12V panels, put them in series (making a 24V pair) and parallel them with a single 200W/24V panel....that could work.

You have not mentioned enough about the charge controller capacity (voltage and current) but despite the fact you 'don't want' to replace it, says nothing about whether it will deliver the needed capacity. If you invest in the correct 3rd panel to get a larger capacity array, if the controller cannot handle more power, you will have gained less. Arrays having more power than the controller is not a problem that will result in failure, just a loss of capacity. All that happens is the excess array power will deliver more, earlier, then hit the ceiling sometime before peak sun through sometime after peak sun goes to waste. 'Peak clipping' is something that is not a terrible idea (more panel than charge controller capacity) because theoretical panel capacities are rarely reached. There are many days when the panels may not overload the control and you will experience an energy advantage.


Look at the rating label of the current panels (assuming they are the same) and go shopping with that information and these two rules.

[Jeepster360]

Thank you for that info. The controller can handle 30 amps of charging l believe and from the factory can support 3 panels. I can't remember for sure but 190w panels comes to mind, could be 170w. The controller and the panels are Zamp brand. The controller is PWM type. Sounds like I should probably just add a third zamp panel and plug into the 3rd socket on the roof. Thanks again for the help.

John

[MechEngrSGH]

A 12V PWM charge control can operate with a high(er) voltage input such as provided by 2-12V panels in series but will be very inefficient. With 2 in series, it will produce little more than a single panel.

An MPPT controller uses DC-DC voltage conversion to very efficiently use all the power by converting it to the proper charge voltage. This voltage reduction is called 'bucking'.

A 30A charge controller is capable of providing 30A of charge to your batteries at up to 14.4V. This has a maximum power capacity of 30A x 14.4V = 432W. The efficiency of PWM controllers is ~85% (or less) so to get this 432W OUT, you need to put 432/.85 = 508W IN. If you are running two 190W panels on it now, at midday, it will still not be near maximum capacity (if you have perfect solar conditions). In general, solar conditions are far less than perfect.

If your solar panels are mounted flat and you are in the south, assume 10% reduction in the summertime. If you are in the north, assume a 20% reduction in the summertime. If you are in the north, things get worse. If you are in the winter, things get worse, etc.

Adding a total panel array of 570W to a 432W charger is not as bad an idea as it may sound. With an assumption that the panels are not ideally oriented to the sun, they are likely only able to produce 70-80% power at the peak. 508/570 = .89 so the charger can absorb 89% of the maximum array output....since they are already 'hobbled' by these shortcomings, you are losing a lot more power by poor panel arrangement than you will be by having an 'undersized' charger controller.

Adding a 3rd panel in parallel is likely to work fine AS LONG AS the panel current panels are '12V' and the new one is '12v'. A '12V' panel is one designed to charge a 12V battery. A '12V' panel will put out ~22V when not connected to a charger and about 17V when it is. When dissimilar panels are connected in parallel, they will operate at the VOLTAGE of the lowest voltage panel.

[Vintage465]

Originally Posted by Jeepster360

So our new 24RKS has 2 factory pannels on the roof feeding 4 6v agm. I want to add a third pannel to the system. I have been reading alot about parallel and series wirering. Can I series 2 of the pannels and leave the other single? Or just use the 3rd factory plug in and leave it at that? I don't want to replace the zamp controller at this time. Also can the new pannel be more or less rated to the other 2 already up there?

John

My set up is similar to yours. I have three 150's running thru a 30amp PWM controller to four 6v batteries. The big difference is I moved my controller down into the pass thru to get it closer to the batteries.....and I ran #4 welding cable from a new combiner on the roof to the pass thru. I think this is more important than adding a third panel. There is at least a half volt of charge voltage lost with your current set up. Don't get me wrong, a third panel is great, but it will be choaked with the current #8 wire and the controller in the cabinet over the bed. Also, there is some discussion about the polarity of the Zamp set up that I don't 100% understand. I thinks I saw on a Zamp site that it's not polarity that is reversed but the Acme connection is mirrored or 90 degrees out from what is normally positive vs. negetive.....but again, I have no Zamp equipment so I'm not certain what the complete story is on this. I would get that understanding prior pulling the trigger on any new equipment for your set up. All in all, with three panels wired with solid wiring and the controller in the pass thru, you will charge your 4 sixers with ease.

[TimtheToolGy]

Originally Posted by Vintage465

My set up is similar to yours. I have three 150's running thru a 30amp PWM controller to four 6v batteries. .... I thinks I saw on a Zamp site that it's not polarity that is reversed but the Acme connection is mirrored or 90 degrees out from what is normally positive vs. negetive.....but again, I have no Zamp equipment so I'm not certain what the complete story is on this. I would get that understanding prior pulling the trigger on any new equipment for your set up. ...

You are correct that the Acme (or SAE?) connector is reversed in comparison to most equipment. When I added two 170W generic solar panels (2019 21RBS Anniversary) to the existing single 170W I purchased adaptors (SAE reverse and MC4 to SAE). https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 Then added MC4 connectors to new panels.

[Cumminsfan]

Don't ORV's come with a 3 port combiner box on the roof? Can't you just plug the 3rd panel into one of the ports?

[Dave Pelletier]

Originally Posted by Cumminsfan

Don't ORV's come with a 3 port combiner box on the roof? Can't you just plug the 3rd panel into one of the ports?

Yes,

By far the simplest plan would be to simply get one more 170W Zamp panel and plug it into the factory combiner box on the roof and call it done.

I have the exact same system as the OP and am considering exactly that (currently have the two 170W Zamp panels and 4 - GC-6's)

Dave

[Passin Thru2]

We have 3 Zamp 170 watt panels, in parallel, plugged into the stock Zamp roof plug with 3 Battelborn 100 amp batteries controlled by a Victron 100|30 controller. We have not replaced the stock 8 gauge wire. The controller is in the overhead cabinet above the bed as was the stock Zamp PWM. We did not move it to be closer to the batteries.

We could not be happier. Even though we have a 12v only refrig and have been off-grid for 48 days in 2023 we have not ran our genset for charging yet. Even when we run the furnace at night (fan is a big amp user) and are 50 to 60 amps in the hole in the morning we are usually back to 100% by noon. Of course clouds slow it down a bit, but have never been below 100% by the time the sun sets.

Now if you are a big inverter user, then your needs will change. We use our inverter only when my wife wants to use her sewing machine or mixer.

Real world results trump theories.

Priorities.

[TimtheToolGy]

Originally Posted by Dave Pelletier

Yes,

By far the simplest plan would be to simply get one more 170W Zamp panel and plug it into the factory combiner box on the roof and call it done.

I have the exact same system as the OP and am considering exactly that (currently have the two 170W Zamp panels and 4 - GC-6's)

Dave

Agree with you two. I went with two additional high rated generic panels in addition to the factory Zamp three years ago, which if I remember correctly, were about $500 less each, but this took more time to plan, shop and install, and added two additional electrical connections (not ideal).

In hindsight, if it made sense, it would have been nice to add two higher capacity panels (instead of two 170W). I use two 6V AGM CG batteries and no inverter so really am fine 95% (heavy clouds or tree shade issues) of time with what I have installed even though I dry camp in the middle of winter for a number of weeks at a time and have never owned a generator.

[judithw]

Originally Posted by MechEngrSGH

The rules for combining dissimilar panels on a single charger controller are;
1) Panels in parallel must have substantially the same voltage
2) Panels in series must have substantially the same current.

These rules are practically inviolable. Meaning, if you violate them, the resulting array of 3 panels will possibly have less capacity than the original 2.

If the existing panels are in parallel and you change them to series, the same rules apply to adding the third panel.

An instance where this is likely (though not guaranteed) to work is to have 2-100W/12V panels, put them in series (making a 24V pair) and parallel them with a single 200W/24V panel....that could work.

You have not mentioned enough about the charge controller capacity (voltage and current) but despite the fact you 'don't want' to replace it, says nothing about whether it will deliver the needed capacity. If you invest in the correct 3rd panel to get a larger capacity array, if the controller cannot handle more power, you will have gained less. Arrays having more power than the controller is not a problem that will result in failure, just a loss of capacity. All that happens is the excess array power will deliver more, earlier, then hit the ceiling sometime before peak sun through sometime after peak sun goes to waste. 'Peak clipping' is something that is not a terrible idea (more panel than charge controller capacity) because theoretical panel capacities are rarely reached. There are many days when the panels may not overload the control and you will experience an energy advantage.


Look at the rating label of the current panels (assuming they are the same) and go shopping with that information and these two rules.

thanks for sharing

[Jeepster360]

Thanks for everyone responding with the help and suggestions. I will most likely install a third pannel and use the 3rd port with no other upgrades. Zamp panels are more money but it would be plug and play so there is that. Thanks again all.

John

[Passin Thru2]

Check for a Zamp panel direct from Zamp. Occasionally they have panels with minor cosmetic flaws that they sell for a large discount. Same full warranty. I think I saved $150 +/- on my last 170 watt panel.