safe max wire voltage drop between PV and CC?

myersfamilyhome · Dec 4, 2022

Is there a safe maximum % of voltage drop between PV and CC using the wire without long term degridation?

This is what I am wanting to do. I am wanting to connect the following together:

1 - Victron SmartSolar 150/35
12 - 4S3P PV's each rated max 41V/11A

This would give max output of 164V/33A

I was wondering if there was a way either using wire length between the PV and CC or another to safely reduce the voltage within the CC specs. I am leaning towards wire because I have that and on a tight budget.

Symbioquine · Dec 4, 2022

That won't work. Voltage drop is a function of amperage so there will be times when the panels are cold and not-yet really producing much power (or where the batteries are close to full), but may be close to full voltage. With the 150v max controller you should do 3S, not 4S. 4S with those panels and SCC would be a broken setup - regardless of the wire size/length.

time2roll · Dec 4, 2022

164v will damage the 150v rated controller. Need to go 3S4P. May need a second controller... what is the battery voltage?
Maybe go with a 600v controller all series 11 amps and standard #10 extension cable.

No, the cable resistance and related voltage drop cannot be used to drop voltage within the max controller input.

Symbioquine · Dec 4, 2022

Symbioquine said:
That won't work. Voltage drop is a function of amperage so may will be times when the panels are cold and not-yet really producing much power (or where the batteries are close to full), but may be close to full voltage. With the 150v max controller you should do 3S, not 4S. 4S with those panels and SCC would be a broken setup - regardless of the wire size/length.

Actually, correction; it doesn't even matter if the panels are cold. They could blow up your SCC any time your batteries get full.

myersfamilyhome · Dec 4, 2022

time2roll said:
164v will damage the 150v rated controller. Need to go 3S4P. May need a second controller... what is the battery voltage?
Maybe go with a 600v controller all series 11 amps and standard #10 extension cable.

Battery voltage is 48v. If I go 3S4P won't that exceed my current specs for the CC? Thats a max 123V/44A PV configuration

Symbioquine · Dec 4, 2022

myersfamilyhome said:
If I go 3S4P won't that exceed my current specs for the CC? Thats a max 123V/44A PV configuration

That's fine. It's called "overpanelling". The SCC manual probably states what amount of overpanelling is permissible - even though they may not use that word, they'll probably have a table showing the maximum wattage of panels that they recommend using with the SCC. The SCC should self-limit to a charging current that is safe for its internal electronics.

Symbioquine · Dec 4, 2022

Symbioquine said:
That's fine. It's called "overpanelling". The SCC manual probably states what amount of overpanelling is permissible - even though they may not use that word, they'll probably have a table showing the maximum wattage of panels that they recommend using with the SCC. The SCC should self-limit to a charging current that is safe for its internal electronics.

This ^ is the general answer, but always defer to your SCC manufacturers documentation.

The datasheet addresses this. https://www.victronenergy.com/uploa...charge-controller-MPPT-150-35-&-150-45-EN.pdf

Specifically, it says it will self-limit, but that you shouldn't overpanel by more than 5 amps for that model.

myersfamilyhome · Dec 4, 2022

Symbioquine said:
That's fine. It's called "overpanelling". The SCC manual probably states what amount of overpanelling is permissible - even though they may not use that word, they'll probably have a table showing the maximum wattage of panels that they recommend using with the SCC. The SCC should self-limit to a charging current that is safe for its internal electronics.

Nice! Missed that in the docs ?

Symbioquine · Dec 4, 2022

myersfamilyhome said:
Nice! Missed that in the docs ?

Make sure to check out footnote #2 of the datasheet though.

myersfamilyhome · Dec 4, 2022

I think I'm just at the tolerable margin to make this work as a 3S4P

MisterSandals · Dec 4, 2022

myersfamilyhome said:
Battery voltage is 48v. If I go 3S4P won't that exceed my current specs for the CC? Thats a max 123V/44A PV configuration

If you are worried about exceeding current limits of your equipment, with a 3S4P array you can point 2 strings east-ish and 2 strings west-ish. This will "mostly" double your charging hours and "mostly" halve the number of amps between your array and SCC.

myersfamilyhome · Dec 4, 2022

MisterSandals said:
If you are worried about exceeding current limits of your equipment, with a 3S4P array you can point 2 strings east-ish and 2 strings west-ish. This will "mostly" double your charging hours and "mostly" halve the number of amps between your array and SCC.

I absolutely appreciate "ish" options ?. Thinking outside the box and between the lines can be the only way to make it work lol

MisterSandals · Dec 4, 2022

myersfamilyhome said:
I absolutely appreciate "ish" options ?.

And the "ish" is proportional to the "mostly". In general.

timselectric · Dec 4, 2022

That would be approximately mostlyish.

myersfamilyhome · Dec 4, 2022

timselectric said:
That would be approximately mostlyish.

?

time2roll · Dec 4, 2022

myersfamilyhome said:
Battery voltage is 48v. If I go 3S4P won't that exceed my current specs for the CC? Thats a max 123V/44A PV configuration

35 is the amp rating? 35x48 = 1680 watts. Panels at 325w x12 = 3900 watts. I think you need 2 x 45 controllers. Or 2 x 35 will only be a little over paneled.

Checkthisout · Dec 4, 2022

Most controllers tolerate 150% over paneling.

Thats a lot of panel though. I would maybe sell your current controller and get one with a higher input voltage and charge amp rating.

This will allow you to avoid the larger wire and combiner box, if that's the objective.

time2roll · Dec 4, 2022

44 amps is over the single 35 amp Isc panel input rating of 40 amps.

Checkthisout · Dec 4, 2022

time2roll said:
44 amps is over the single 35 amp Isc panel input rating of 40 amps.

I absolutely abused a 40 amp Renogy I have with severe overpanelling (wattage, not voltage wise) and nothing happened to it. It just limited current to its rating and got a little less than hot.

At the end of the day, I like the suggestion that the OP should get a second controller.

OP, you have nice panels and a nice CC. If I was you, I would wire it up in 3 series and just go ahead and see what kind of Amps you get going into it. If it's too high, disconnect one string and wait until budget allows the addition of another controller.

It's not going to blow up right away if its input amps are exceeded.

timselectric · Dec 4, 2022

Over paneling, that's no big deal.
Panels don't push amps. It must be drawn from them.
I ran over 80a worth of panels on an 18a SCC, for several months. Until I got a second controller hooked up. Now running over 40a on each.
Just don't go over the voltage limits. The controller can't control voltage.

safe max wire voltage drop between PV and CC?

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