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10A Controller too small for 150w panels?


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I’m upgrading the solar system. My current mppt controller is 10amp and rated to 130w. Will an extra 20w be too much for it? The panels SCC is 8.5amp. I don’t want to cook anything so if there is any doubt I will get the 20amp controller.

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Multiply your panels wattage by 1.5, that's the minimum size your controller needs to be in NZ. Technically 1.25 will do it by 1.5 give you a little wiggle room.

 

If you were in the top half of Sweden that 'multiply by 1.5' would be 'multiply by 0.6' to size the controller. A panel rated 100W can run at 125W in NZ but only 60W in northern Sweden. It's all to do with the amount of sun the location gets and NZ gets 25% more than the 'standard measurement' of solar panels. In Sweden they only got about 60%.

 

I'm changing my 250W controller out as I have 2 x 100W panels so on a good solar day my controller is maxing out.

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Thanks guys. 20A is rated for up to 260w so not a huge amount spare if we work on the 1.5 x numbers? Should I just go for the 30A and be done with it? Not much different in price. Is there any issues/inefficiencies from being over spec?

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No prob being over spec... I run 2 x 120w panels on a 20A controller. No problems...

That's interesting, we've seen 18.5 amps coming in with both 100W panels in good sun. That's after the system sucks what it needs to run, around 0.6 amp. I have wondered how 'calibrated' my fuel gauge is. It does tend to read around what the controller also does. That would suggest your 2 x 120W could exceed 20 amps in peak sun.

 

Do you know if there is any way to calibrate this gear or benchmark it to a known 'something' ?

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Yep, check the measurements with a decent meter, like a fluke.

Most panels produce a little more than rated output when new in NZ. Usually drops to about rated after 6-8 months, or after a summer.

Most decent controllers have a thermal cut out - if over current, they get too hot and cut out, no problem. Cheap ones can burn wires if not fused. Fuses should be correctly sized. Read the manual for your unit!

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A fluke, I shall suss the lads to see if they have one of those.

 

My controller getting warm was what I fast noticed. I ran the system down to 30% on purpose then plugged in a mains feed 10Amp charger set up for lithium's higher voltage. After about 60 minutes that got so hot you couldn't touch it so I thought it was busted or there was a system issue but on sussing it was due to the charger running at 100% (showing 10.5amps going in) as battery will take all you throw at it. Since then I've been sussing for heat during my fly-by type checks and that's when I noticed the warmer than expected controller.

A quick check says it has thermal cut out so that's nice to know.

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All good to know. I think the 30A is only about $20 more than the 20A so will just get that to be super safe.

Check the space for install though. The 30A will be bigger, and probably require more clearance for heat dissipation etc. In theory, the 30A will produce 50% more heat than the 20A (when compared to the 20A output).

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