RV Solar set up

Retired747

Greetings,

I have just installed a total of 3 x 12v solar panels on my RV (2 x 120w and 1 x 100w) I have also bought a 30A MPPT controller.
I have a couple of questions, so here goes:

1) Is it possible or worth connecting the 2 x 120w panels in parallel then wire them in series with the 100w panel (total 24v) feed it into the 12-24v MPPT that in turn is connected to a 12v deep cycle battery (yes 12v)?
2) Is the MPPT capable of recognizing that there is a 12v battery connected even though I am feeding the MPPT with 24v?

OR should I just wire all 3 panels in parallel and be done with it!?

Looking forward to all suggestions

Thanks

BB.

Re: RV Solar set up

Need to know the Vmp/Imp (voltage max power/current max power) for the panels...

You want to match panel voltages to ~10% or better for parallel connections. And 10% or better for Imp with series connections.

You cannot, for example, put two 8 amp panels in parallel for 16 amps total, then put that in series with another 8 amp panel... That will be very inefficient or could damage a panel.

Also, what MPPT charge controller are you thinking about? Their input requirements can be a bit confusing. Solar panel output voltage Voc (open circuit voltage) rises as the temperature falls below freezing--So temperature (min/max) is also important too.

-Bill

Cariboocoot

Re: RV Solar set up

Retired747 wrote: »

Greetings,

I have just installed a total of 3 x 12v solar panels on my RV (2 x 120w and 1 x 100w) I have also bought a 30A MPPT controller.
I have a couple of questions, so here goes:

1) Is it possible or worth connecting the 2 x 120w panels in parallel then wire them in series with the 100w panel (total 24v) feed it into the 12-24v MPPT that in turn is connected to a 12v deep cycle battery (yes 12v)?

This is a no-go: most likely the 120W panels have Vmp 17.5 and Imp 6.8, making the Imp of two in parallel 13.6. The 100 Watt panel would likely be Vmp 17.5 and Imp 5.7. Put it in series with the other two and it will limit the Imp to 5.7, effectively making your 340 Watts of panel operate as about 200 Watts; worse than leaving the 100 Watt panel out altogether.

2) Is the MPPT capable of recognizing that there is a 12v battery connected even though I am feeding the MPPT with 24v?

Yes, with a few exceptions such as certain Blue Sky controllers which require the in/out nominal Voltage to be the same (or else there are current limitations). Almost all MPPT controllers can take whatever their maximum V-in rating is and convert it to any standard system Voltage with varying degrees of efficiency.

OR should I just wire all 3 panels in parallel and be done with it!?

For the panels you mention and on a 12 Volt system this is your best choice. It will be most efficient, unless you have very long wire runs between the panels and controller.

Retired747

Re: RV Solar set up

Thank you gentlemen for the info..

Some more thoughts...

As the panels voltage output is 'temperature sensitive', does this mean the controller would need an external sensor to detect ambient temperature and compensate for the panel voltage changes? or does the MPPT detect voltage changes from the panels and compensates accordingly?

My MPPT was purchased on EBAY from the far east, and has a 30A 12-24V rating (no brand as such).

Thanks
Eric

BB.

Re: RV Solar set up

Retired747 wrote: »

As the panels voltage output is 'temperature sensitive', does this mean the controller would need an external sensor to detect ambient temperature and compensate for the panel voltage changes? or does the MPPT detect voltage changes from the panels and compensates accordingly?

The MPPT controller esensally "sweeps" the solar array... Starting from Zero Amps to Maximum amps it can draw. Then figures out P=I*V.... So it finds Vmp*Imp and holds "Vmp" for the next few minutes until it does the next sweep.

Where a temperature sensor can help is with is the battery bank. A remote battery temperature sensor monitors that actual battery bank temperature and "adjusts" the charge controller voltage setpoints based on the reported temperature (otherwise the controller uses an internal air temperature sensor--which is not as accurate).

If you want your batteries charged quickly and "safely", then you should have a remote battery temp sensor (if your controller supports it).

My MPPT was purchased on EBAY from the far east, and has a 30A 12-24V rating (no brand as such).

Many of the no-name MPPT charge controllers are just PWM controllers with MPPT slapped on the case and firmware updated to print MPPT Mode on the LCD display.

Unless the unit has a fairly big inductor internally--There is a good chance it is not MPPT.

-Bill

redwire

Re: RV Solar set up

Is this going to charge when parked for long periods?

My concern is you not being there and the battery over charging if the controller goes bad. Makes a mess.

Is it a deep cycle battery or a normal car battery? How many?

You might want to parallel them all and just live with it, but put a switch on the larger panels to take them out when parked so only the 100W panel is in circuit and probably wouldn't over charge the battery too badly if something went wrong. Or buy a smaller 25W panel for when it's parked just to keep the batteries charged.

If you want to know if it's really a MPPT controller, watch the panel voltage side and see if it changes a volt or 3 back and forth somewhat quickly in the mornings. Let us know!