Changing the solar controller on a Renogy Suitcase

[Travelmonkey]

I have the Renogy 100W solar suitcase with the solar controller.  I want to switch out the Renogy controller with a small Victron 75/15 MPPT controller that I was going to use for a different project.  When I do this I also want to make it easy to add another panel connected in series.

Is there any issue connecting different sized panels in series?  When I’m done I’d like the option of adding a 160W panel that I already own to the the 2 x 50W panel (connected in parallel) from the suitcase for a total of 160W.

 

[DLTooley]

I’ve wondered about this too. I believe the answer is that you are fine so long as the total voltage and amps is less than the rated max of the controller.

I have the Victron 75/15 too, and my question is whether a mismatched series array will produce less than double the voltage.

I have NOT done this.

The simplest solution is to use both controllers, which is ok.

 

[highdesertranger]

The voltage of the panels must be close to the same. This is what I have always been told. the watts doesn't matter but the voltage does. Highdesertranger

 

[future_vandweller]

I have the Renogy 100W solar suitcase with the solar controller.  I want to switch out the Renogy controller with a small Victron 75/15 MPPT controller that I was going to use for a different project.  When I do this I also want to make it easy to add another panel connected in series.

Is there any issue connecting different sized panels in series?  When I’m done I’d like the option of adding a 160W panel that I already own to the the 2 x 50W panel (connected in parallel) from the suitcase for a total of 160W.

When panels of different ratings (voltage & current) are connected in series, the panels may not operate at their individual 'sweet spots' (Vmaxpower & Imaxpower).  The controller will push the panels to collective max power point.  The current will be limited by the panel with the lowest current.  Think of the panels as highway segments with different # of lanes.  The segment with the smallest # of lanes will determine the traffic flow (vehicles/hour).
As long as you're below 500 Watts overall, you're probably better off with a PWM, since PWM is more tolerant of voltage/current mismatches.  Beyond 500 Watts, MPPT's advantages get significant.

 

[DLTooley]

Although I suspect your conclusion may be close to correct, your reasons don’t make sense.  

Controllers do not effect the operation of a panel, they only broker the relationship with the battery in that circuit.  

Can you show the math for this?

It does seem quite feasible that the series voltage will only be double of the lower voltage panel, but that’s a bit more constrained conclusion.

 

[Freelander]

According to Renogy, you can't mix different panels, or use 2 controllers at the same time.

But that be because they want to sell more panels.

I think HDR is correct, if the panels are close to the same voltage it should make any difference.

 

[future_vandweller]

As to Renogy's response, it's not that can't mix different panels, but it's that you won't see the benefits you're expecting.  Before taking Renogy's words, remember that they're not an engineering company - they rebadge China sourced solar products.  On this forum & elsewhere, you can see several complaints about their tech support & the quality of their advice.

If the panels are of similar ratings, there's no issue at all.

 

[future_vandweller]

Although I suspect your conclusion may be close to correct, your reasons don’t make sense.  

Controllers do not effect the operation of a panel, they only broker the relationship with the battery in that circuit.  

Can you show the math for this?

It does seem quite feasible that the series voltage will only be double of the lower voltage panel, but that’s a bit more constrained conclusion.

Controllers do affect the operation of a panel.  MPPT controllers find the max power point of an array by adjusting the impedance the array sees and maximize the power harvested.  PWM controllers pull down the array's voltage to that of the battery bank and attempt to draw the short circuit current of the array.

If you're questioning my comment about the current being limited to that of the lowest producing panel in a series connection, consider a panel that is completely shaded (100% dark).  It'll produce zero electrons per second, completely shutting down the flow of current from other panels.

 

[Travelmonkey]

Thank you for all the input.

The back of the label on the 160W panel states 18.73V (@8.62A). The Renogy Eclipse datasheet states 17.6V (@5.68A). So around 1 volt difference...

The challenge I’m running into is when I camped in the fall. I ended up running my generator much more than I expected because my Renogy suitcase couldn’t keep the battery topped off. I was hoping the MPPT controller would be more efficient during the times of the day when there is full sun. Not sure if it would make enough of an impact over the the existing PWM which is why I thought I’d make provisions to add the additional panel. I have no issues during the summer.

 

[Travelmonkey]

When panels of different ratings (voltage & current) are connected in series, the panels may not operate at their individual 'sweet spots' (Vmaxpower & Imaxpower).  The controller will push the panels to collective max power point.  The current will be limited by the panel with the lowest current.  Think of the panels as highway segments with different # of lanes.  The segment with the smallest # of lanes will determine the traffic flow (vehicles/hour).
As long as you're below 500 Watts overall, you're probably better off with a PWM, since PWM is more tolerant of voltage/current mismatches.  Beyond 500 Watts, MPPT's advantages get significant.

The PWM controller on the Renogy Eclipse suitcase supports max 26V (@ 20A) so I’d have to connect panels in parallel. The cable to connect to my trailer is like 20-25 ft. I think it is 10 gauge.

 

[future_vandweller]

The PWM controller on the Renogy Eclipse suitcase supports max 26V (@ 20A) so I’d have to connect panels in parallel.  The cable to connect to my trailer is like 20-25 ft.  I think it is 10 gauge.

The Renogy PWM controller can tolerate input voltages of up to 26V.  This limit will be reached only when the panels are extremely cold and the batteries are in float (very little current draw).  As soon as you connect a 12 V battery & panels to the controller, the voltages on solar & battery terminals will be that of the battery.  This amounts to a near short of the panels terminals, causing the short circuit current (Isc) to flow.  In most panels, the Isc is about 10% more than the Imp.

 

[DLTooley]

Controllers do affect the operation of a panel.  MPPT controllers find the max power point of an array by adjusting the impedance the array sees and maximize the power harvested.  PWM controllers pull down the array's voltage to that of the battery bank and attempt to draw the short circuit current of the array.

If you're questioning my comment about the current being limited to that of the lowest producing panel in a series connection, consider a panel that is completely shaded (100% dark).  It'll produce zero electrons per second, completely shutting down the flow of current from other panels.

Thank you.

 

[Travelmonkey]

The Renogy PWM controller can tolerate input voltages of up to 26V.  This limit will be reached only when the panels are extremely cold and the batteries are in float (very little current draw).  As soon as you connect a 12 V battery & panels to the controller, the voltages on solar & battery terminals will be that of the battery.  This amounts to a near short of the panels terminals, causing the short circuit current (Isc) to flow.  In most panels, the Isc is about 10% more than the Imp.

Since the 2 panels I have will do 35V staying with my existing PWM controller doesn’t seem like it is an option. Not to mention the Victron MPPT is easier to monitor and make adjustments.

 

[maki2]

Maybe you can sell the suitcase panel and controller and invest in a larger panel then put that on your new, high quality controller. In the long run it will be a lot less of a hassle to have more power with less fussing around.

 

[future_vandweller]

Since the 2 panels I have will do 35V staying with my existing PWM controller doesn’t seem like it is an option.  Not to mention the Victron MPPT is easier to monitor and make adjustments.

Combing your 160W panels, in series with the 50W panels will only 2/3 of the 160W panels current.  Just use the two 160's in series with your MPPT controller, or the two in parallel with a PWM.  Don't include the 50's.  Happy to to explain the rationale behind this, if needed.