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Some advice on slightly over paneling a Victron Charge Controller

CantStopTommy

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Jan 22, 2022
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Hi all, some advice please. I've just sourced a monster 500w Risen panel for my camper trailer build and am looking to pair it with a charge controller.
I ran the sizing on the Victron MPPT calculator and was recommended a 150v/35a. See specs here: https://mppt.victronenergy.com#djE7...wLjA1LDEyLjUsNTAwLDQyLjQ1LC0wLjI5LDUxLDYsNA==
The panel's Voc tops out at only 51V and i'm only using 1, so would it be ok to spec a 100v/50a SmartSolar MPPT? Or even slightly over-panel the controller and go with a 100v/30a? Anyway smart people, let me know your thoughts! Cheers, Tom
 
It's OK to over panel the wattage, just not voltage. You will be fine with a 100/30. Doing the math, 500w / 14v = 35.7a, but if you mount it flat, you will never get the full rated wattage out of it any way so you're not giving up anything significant with the 100/30.

I'm running two 250w panels flat mounted with a 100/30 since this fall and I've yet to go over 12 charging amps, though that's a product of higher latitude winter more than anything. I don't expect to hit 30 amps much, if ever, unless I vacation farther south during the summer months.
 
I would choose the 100/30 for one panel.
Victron does not recommend over-paneling on their charge controllers.

I have 2S 215W, they have about the same spec as your one 500W - they're flat and I've never seen them go over 20A. Hopefully over summer they'll do a little better.

The chart showed a battery float voltage of 50-something - it should be 13.4 or thereabouts. Not sure if that would change the results in that chart or not.
 
Thanks guys, that was my suspicion but didn't want to risk it without asking. We're about 10deg south of the tropic of capricorn here in Sydney, so during summer I might get pretty close to full sun at noon, but still unlikely to get full power because it gets quite hot here too!

So that begs the question, do you know if the controller clips the controller's max output current to 30a at 12v?
This convention seems odd to me, but if so, my panel's max power output would be limited 360w (30*12)
This would probably be a deal breaker for the 100-30 for me.

or more realisticly, does the controller clip the max output current to 30a at 14.4v?
in which case my panel's max power output would be limited 432w (30*14.4)
I could probably handle this since I'm unlikely to get over this amount of power anyway!

OR does the controller have some sort of over current buffer built in? kind of like a factor of safety in engineering where the spec says one thing but the component can actually handle much more.

The chart showed a battery float voltage of 50-something - it should be 13.4 or thereabouts. Not sure if that would change the results in that chart or not.
Yeah I noticed that too, the little question icon next Float Voltage said this field is used only for RS Controllers. (whatever they are!) and it also wouldn't let me set it below 36v anyway, so i feel pretty safe ignoring it!
 
Your SCC and battery will only take what they can. So yeah, ‘clip’ is a reasonable term.
But you benefit from increased productivity early and late in the day.
 
Yeah I'm not too versed in electrical terminology, so I often find myself using the wrong words for things. apologies for that.

Regarding the actual mechanism of "clipping" the current, I assume that the charge controller does this by increasing the voltage the panel sees, which in theory will take the panel off its maximum power point and drop the current (and power) that the panel produces.
Can anyone confirm? or even better, have some insight into how this 'clipping' actually works?
 
I've just sourced a monster 500w Risen panel for my camper trailer build
Have you considered any bracing behind the panel?
One strengthening rib for 2m x1m of 2.5mm glass doesn't seem good enough for Australian roads.
 
I assume that the charge controller does this by increasing the voltage the panel sees, which in theory will take the panel off its maximum power point and drop the current (and power) that the panel produces.
If you consider that current/amps are pulled it makes it easier.

Your 100/30 can only charge 30A at ~14V max.
So, the SCC will only pull (assuming 100% efficiency) 30A x 14V = 420W

All the other “wattage” is clipped.
 
Have you considered any bracing behind the panel?
One strengthening rib for 2m x1m of 2.5mm glass doesn't seem good enough for Australian roads.
Good point Sunshine!

Bracing the backside of the panel is a very smart idea. I'm definitely going to be driving on corrugations quite a bit while crossing the outback.
Have you seen any good examples of how to do it?

My initial thoughts are to run a beam up the middle with foam pads mounted on 500mm centres. That would limit the panel's largest unsupported span to ~500mm which would probably help prevent the backside of the panel deflecting too much as i hit those bumps! Anyway I'm totally open to suggestions and I'll definitely implement one of them for sure, that panel would get wrecked otherwise!
 
If you consider that current/amps are pulled it makes it easier.

Your 100/30 can only charge 30A at ~14V max.
So, the SCC will only pull (assuming 100% efficiency) 30A x 14V = 420W

All the other “wattage” is clipped.

Thank you Sandals! that makes a lot of sense. Appreciate the response.
 
Victron and over panel: from user manual of 100/30, 100/50 page 54
1a) The solar charger will limit input power if more PV power is connected.
1b) The PV voltage must exceed Vbat + 5V for the controller to start. Thereafter the minimum PV voltage is Vbat + 1V.
2) A higher short circuit current may damage the solar charger in case of reverse polarity connection of the PV array.
3) Equalization is by default disabled.
4) For more information on data communication see the data communication paper in the Technical information section on our website.
 
Victron is solid stuff. Get the Smart one with the BT app. (y)

Solar energy pulled or absorbed is a better way to think of it for sure.

Besides, if you're flat mounting you never get full watts out of the panels.
 
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