sma overvoltage

[Gavin A]

yes it is a 3600tl-20 not a 21 which i gather would stop this problem

That's well outside the spec then, no way it should have been installed in this way, but I suspect it was a genuine error in terms of confusion over whether it should have been a 21 or 20 model.

The installer should swap this to dual string at their expense, or replace the inverter with a 21 model - either option would be acceptable IMO, though I'd want the varistors testing to see if they've been damaged.

 

[jimbo1]

will installer check varisistors or sma service engineer what are the parameters for the varisistors sma3600tl-20

 

[ExtremePV]

the varistors are like fuses - they either work or don't... so not sure how your going to test them?
They are there to blow in over (more extreme) voltage situations.
Get the installer to split it into 2 strings - don't have them poking around inside the inverter - they are more likely to break it than do anything useful!
(I've only had to change them once in the past 6yrs..and that was a wind inverter with significant over voltage!)
Once in 2 strings you won't have over voltage, so the varistors won't be being 'worked'

 

[jimbo1]

thanks again ,i will keep you posted

 

[yorkshiremike]

The varistors aren't fuses as such, they're there to attempt to 'clamp' the input voltage to a safe level. The name comes about because they're 'variable resistors' that have a very high resistance at low voltages and a low resistance at high voltages. They are usually put across the DC inputs and if the input voltage rises too high they start to conduct, disipating some energy and keeping the voltage down. Conducting current and disipating energy degrades them, so if running at high voltages they will eventually fail and then the rest of the inverter input may be exposed to the high voltage (some have a mechanism to test if the varistors are operational).

 

[jimbo1]

UPDATE!!

I have had a long discussion with sma technical and resolved issue , the overvoltage is due to excellent dc input from mono panels inverter is getting replaced with a higher dc input, no overvoltage will show as panels should not produce more than their 650-700v.

 

[SolarCity]

So it looks like you had the 20 model rather than the 21 model?

Easy mistake to make, in my opinion. I would imagine fairly common too.