mppt and amperage

ws9876

Regarding the KID 30 amp controller...Midnite Solar says to only use 2 panels in a 12v set up. But if you put 3 in series and have about 105v
and 9 amps
to start...the KID isn't going to boost that to 30 amps..? or even to 25 amps..? Maybe 20-22...
so 3 in series wouldn't hurt a 12v set up...no?
What do you think?

Photowhit

You appear confused.

What says to only use 2 panels?

Did you run your panels through Midnites string sizing tool?

MidNite Solar - KID Sizing Tool.

littleharbor2

What is the Voc? voc x 3 in cold weather is likely to be too high.

ws9876

if VOC is too high then why does their manual show multiple 3 panel in series options? 

littleharbor2

Don't know what options you are looking at. It's all based on max open circuit voltage. Your panels are particularly high voltage. Also the colder the panels get the higher the voltage they produce.

littleharbor2

Another factor may be the allowable wattage in 12 volt vs. 24 or 48 volt systems. You can double the allowable wattage in a 24 volt system and quadruple wattage in a 48 volt system.

Dave Angelini

ws9876 said:

if VOC is too high then why does their manual show multiple 3 panel in series options? 

maybe this will help, I thought the previous responses hit the mark. You do not want to damage the electronics with high VOC !!!!

Some people live in places that do not get as cold, typically just before sunrise. It can be simpler for 3 in series also.

A 12v battery is going to get more solar power to it when you use 2 panels in series compared to 3 if the panel numbers were equal.

Maybe 3 in parallel will work if the panel model was listed. It would be best.

There is higher conversion loss as the voltage increases with 3 panels in series for a 12vdc battery bank.

There is more to this also, as always....

boB

It depends also on how many cells the panels in series have.  Is that 60 cells ?  72 cells ?   Less ?

Typically, these days, the PV module voltages are higher than they were say, 20 years ago.  Also, it is usually easier to buy the higher voltage modules used for grid tie now.  I find that 12V nominal PV costs more than these newer modules.  Been  while since I looked though.

That being said, 105 Voc at 25 degrees C ambient will only go up to 150 Voc at really cold temperatures.

For silicon, that is ~around~ 10 or 11% higher Voc at every drop of 25 degrees C or so as I remember.  It would have to get pretty cold, like, -50 degrees C ?   I may be a bit off on this but something like that.

Also, the higher the Vmp, (and Voc) the hotter the unit will get in general.  If you are charging a 12V battery, I would try more panels (even number)  in series-parallel if that works out which would take care of both problems.

I think the sizing chart/program may give a good idea what is going to happen ?

  I think I would just move somewhere sunny.   Solar works better where there is sun anyway.

boB

littleharbor2

boB said:

.That being said, 105 Voc at 25 degrees C ambient will only go up to 150 Voc at really cold temperatures.


boB

It's not clear whether were talking Voc or Vmp here. I was figuring the OP gave us Vmp. divided by 3 were talking 35 volts per panel. IF thats the case then Voc will be higher. I probably shouldn't be assuming anything here.

ws9876, can we get the specs from the back of the panel?

littleharbor2

105 volts x 9 amps is 945 watts, divided by 12 volts =78.75 amps. Clearly higher current than a 30 amp controller is capable of handling.

ws9876

your right....I will stick to 2 in parallel for now.I thought that was beating 2 in series but maybe not..its close..
Canadian Solar 315 watt/KID controller/SOK LiFePo 12v

Dave Angelini

I would say that Canadian solar has made over 1,000 models of panels. 
You need a model number!  It would have saved alot of the time on this thread.