Help w/ solar wiring

lvwilly

New member
I'm working on a solar setup for my Lance pickup camper. I thought I had it figured out but today I was ready to hook up and saw a voltage reading that didn't make sense to me.

Here's my parts list:

4 of these panels

2 of these panels

Controller

DC to DC charger

My issue is that I've wired the panels all together in series. Which seems to me that I should be getting 96 volts at a maximum. When I check the positive and negative leads from the panel array though it read 177.2v. I'm basing the 96 volts I should be getting on the fact that the larger panels are advertised as 12v-18v and the smaller panels are advertised as 12v. Can someone fill me in on what I'm missing and if necessary, a more optimal way to wire these?

Thanks.
 

NatersXJ6

Explorer
Not an expert, but IIRC, the open circuit voltage on the panels I installed was quite a bit higher than the nominal rating. I didn’t see an open circuit voltage in the specs for your rigid panels, but 100 Watt Renogy panels are 22 or 23 V each, so full sun, 4 panels is 88-90V in series, plus your little panels open voltages too.
 

Herbie

Rendezvous Conspirator
Yep, open-circuit voltages can be much higher than the nominal panel voltage. Sounds like it will easily exceed the safe input on your controller.

There are a lot of theories on Serial vs. Parallel panel wiring (including a very good long thread about it here on ExPo.) Given that you have two different panel groups, this might be a good opportunity to do a series/parallel arrangement with your big panels in one group and your smaller panels in a 2nd. This will also have the advantage of continuing a solid high-voltage source for the MPPT controller if there is shading on one group of panels but not the other (depending on how they're arranged on your rig.)
 

lvwilly

New member
Ah, thanks both. Is that 22 or 23v pretty standard for a 100w panel? I'll look into what works best with a hybrid arrangement.
 

john61ct

Adventurer
The voltage has nothing to do with wattage.

For cheap PWM controllers that throw away the power produced at higher voltages

mass-marketed direct to consumer panels are indeed around 19-24Voc

Nominal "12V", but with better MPPT controllers the **panel** voltage has little relation to nominal, just usually needs to be higher than the desired charge output.

Actually better quality larger panels designed for big stationary installs are usually 40+ Voc and that gives a better boost in overall output from MPPT.

The Victron MPPT first number is the max voltage, so 75/15 means stay (well) below 75V input, and will not output more than 15A.
 

lvwilly

New member
So how would one determine how many panels to hook up to a particular controller if nominal voltage differs from the actual panel voltage? My controller is 100/30 and if wired in series my panels would exceed this but not while calculating using nominal voltage ratings from the manufacturer. Do I just want to wire them in such a way that the voltage is high but not exceeding the 100v?

I'm thinking now that the best way would be to get a second controller just for the smaller panels. Does anyone know how the victron smartsolar controllers work together on the app?

Thanks.
 

john61ct

Adventurer
Forget that "12V nominal", just a general category for your overall system, as opposed to one at 24V or 48V.

The ideal would be to buy panels that maximise the SC specs, or v/v, so one SC per panel.

If you do connect multiple panels per SC, they should all be identical.

Serial connected panels' output are going to be drastically affected by **any** partial shading, even a stray leaf. Another strong reason to look for higher-voltage panels.

With a Victron rated for 100V, I would keep total Voc below 90-95V to be safe

But going all parallel, you can go a fair bit over that 30A, no fear of damage just lose a bit of wattage at rare peak moments, in exchange for higher average output per SC, at a charging voltage say 14.8V then 500W would be fine.

Anything below 440W would be wasting a bit of SC capacity.

With the Victron app, you can easily switch from one SC to the next to check their stats.
 

DiploStrat

Expedition Leader
Victron offers a handy/dandy calculator. Naturally, it shows their products, but the concepts are the same. You can input custom (i.e. non Victron) panels using as much data has you have. FWIW, the calculator is very conservative when it comes to voltages.

 

DaveInDenver

Middle Income Semi-Redneck
My controller is 100/30 and if wired in series my panels would exceed this but not while calculating using nominal voltage ratings from the manufacturer. Do I just want to wire them in such a way that the voltage is high but not exceeding the 100v?
The V-I curve typical of a solar panel.

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You have two characteristics, the short circuit current and open circuit voltage. This curve is what the controller will see this as input and match it to the battery on the output. The panel output could be anywhere along this curve depending on exposure and load, like @john61ct says.

So you have to match the controller's maximum input voltage to the Voc of the panels you're using, not what you expect to be the nominal voltage under load.

If your battery is fully topped and it's the middle of the day the controller will be trying to buck down a lightly loaded panel, so it could see close to Voc.

As an aside the very high open circuit voltage is why it's recommended that you connect the panel after the battery to a controller. You want the panel to be last connected and first disconnected. Asking a controller to regulate a panel without a battery (load) can damage them.
 

Herbie

Rendezvous Conspirator
FWIW, the calculator is very conservative when it comes to voltages.

Part of the reason for this is that the panel voltage is also a function of temperature (so much so that you can actually use panel voltage as a rudimentary temperature sensor). As the temperature drops, the panel will output a higher voltage. You want to factor for this when laying out your system, in order to prevent frying your charge controller the first time the sun rises on a frosty winter morning.
 

john61ct

Adventurer
Just to keep things simple, the panel(s) rated max VoC should just be kept well below the max voltage spec'd for the SC as I said.

So no possible problems, even in cold bright conditions with extra snow/cloud reflections.

And also, there is no **need** to get up near that max tolerated voltage, far below that is fine.

So say 40-50Voc panels with the 100V rated Victron, with a 14.8V charge output setpoint, there's plenty of leeway for the MPPT optimization functionality to work boosting extracted power.

If you're already stuck with say 20-24Voc panels, again not "a problem" as such, you just aren't getting **as much** an increase from the MPPT, but still a bit better than a cheap PWM SC.

If you are going for the optimal 1:1 ratio, then the other advantage of bigger higher-voltage panels, is reducing the wiring, complexity and total number of parts.

But ultimately, fitting the greatest **watts** per roof area is often the goal, and there may be fans or HVAC units to work around in your layout - becomes a bit of a jigsaw sometimes.
 

lvwilly

New member
Thanks all for the responses. I've settled on getting a second controller for the small panels so only similar panels will be grouped together.

I've wired two of the mighty max panels together in series and open circuit is 48-50v. As soon as I hook those panels to the controller the voltage on the wires drops to 0 and the victron controller isn't seeing any voltage and won't charge. I've checked polarity and it's correct. I've asked on the victron forum for help.

Thanks for the info, it's helping my understanding of solar but I still have a bit to go it seems. Cheers.
 

Alloy

Well-known member
Thanks all for the responses. I've settled on getting a second controller for the small panels so only similar panels will be grouped together.

I've wired two of the mighty max panels together in series and open circuit is 48-50v. As soon as I hook those panels to the controller the voltage on the wires drops to 0 and the victron controller isn't seeing any voltage and won't charge. I've checked polarity and it's correct. I've asked on the victron forum for help.

Thanks for the info, it's helping my understanding of solar but I still have a bit to go it seems. Cheers.

I'd find out if the Mighty Max panels are meant to be used with a controller.
 

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