Trying to understand how multiple strings are connected to an inverter.

[Alaska Man]

If you have an inverter that has two string inputs but you have 3 or 4 strings, I understand that you need to do something called "series fusing" with a combiner box. What I don't understand is how does this work?

If the inverter you are using has a maximum input watts of 5250 per string, why does it work to have 2 strings (of say 21 x 250w panels) through a combiner box?

Looking at this diagram, it looks like a combiner box just takes each string and combines them all? Doesn't that then add up all the watts?

I'm new hear, but just went through something similar.

When you combine the "Series" wired Panels Volts mutiply. At the Combiner Box the connection is a "Parallel" one. So the Amps increase not Volts. If each Array String is 5KW at the combiner box what comes out the other end is 5KW, but your Amps are now 3 times higher.

[bcroe]

Thank for the reply Mike. I think I was trying to find something else out.

This inverter I'm looking at from SolarEdge has two inputs for the solar panels, so you could feed two strings into it. Each string though can only be up to 5,250W even though the inverter can handle up to 12,400W (or 14,250 for the next size up inverter). I was told by SolarEdge that if you want to fed more power into the inverter, say the maximum 12,400, then you need to three strings and combine the strings using a combiner box. You can either combine two strings together and feed to one of the input and then the third string on it's own into the other input or combine all 3 strings through the combiner box and then input just one of the inputs (leaving the other input unused).

I'm trying to understand how that works. Why is it that going through a combiner box allows you to connect 3 strings to 1 input whereas if you didn't use a combiner box, you could only connect 1 string to 1 input.

My combiner box has 2 separate output circuits. Bruce Roecombiner.jpg

[Mike90250]

Possibly some sort of power sharing arrangement, where it can handle more power with both inputs supplying power, than it can with only 1 input. Something with it's internal topography. Like my 6KW inverter can only handle 70% un-balanced load on its output, or full power with loads more equally split.

[HX_Guy]

Thank for the reply Mike. I think I was trying to find something else out.

This inverter I'm looking at from SolarEdge has two inputs for the solar panels, so you could feed two strings into it. Each string though can only be up to 5,250W even though the inverter can handle up to 12,400W (or 14,250 for the next size up inverter). I was told by SolarEdge that if you want to fed more power into the inverter, say the maximum 12,400, then you need to three strings and combine the strings using a combiner box. You can either combine two strings together and feed to one of the input and then the third string on it's own into the other input or combine all 3 strings through the combiner box and then input just one of the inputs (leaving the other input unused).

I'm trying to understand how that works. Why is it that going through a combiner box allows you to connect 3 strings to 1 input whereas if you didn't use a combiner box, you could only connect 1 string to 1 input.

[Mike90250]

OK, so that array is about 5Kw, if it's well aimed.

The voltages (340 - 450 VDC) are for a grid tie system, no batteries.

I'm a bit wobbly on the 3 fuses, they are nearly 2x the panel amps of a single string, and may not reliably blow if there is a fault on one of the 3 strings.

The fuses protect a bad string from the other live strings. The combiner fuses are not protecting the inverter or controller.

If one of the 3 strings goes bad somehow, and the other 2 feed power into it, 1 fuse is supposed to blow, and isolate the bad string from further damage. The inverter will limp along with only 3,000w and you will not have a fire on your roof.

Hope this helps

[Mike90250]

Anyone? Inetdog?

Sheese, give us a bit of time to digest this. I've got a life, and maybe someone else does too.

Of course, there is always "Pay for Promptness", I take paypal.

[HX_Guy]

Anyone? Inetdog?

[HX_Guy]

If you have an inverter that has two string inputs but you have 3 or 4 strings, I understand that you need to do something called "series fusing" with a combiner box. What I don't understand is how does this work?

If the inverter you are using has a maximum input watts of 5250 per string, why does it work to have 2 strings (of say 21 x 250w panels) through a combiner box?

Looking at this diagram, it looks like a combiner box just takes each string and combines them all? Doesn't that then add up all the watts?