what size charge controller?

[ronsmith]

I am going to add two 90w pv panels to my other panels which are both 90w. I will have a total of about 360 watts at 12v. What size charge controller will I need to carry the load. I am using a 10watt sun-setter now. Also will I need to install a diode between each panel?

[Volvo farmer]

360W / 12V = 30A

A Xantrex C35 or C40 would do and the C35s are only running about $100. If you plan on adding more panels in the future, you might want to look at a C60, or if you're really serious and want MPPT, an Outback MX60. The Outback is about $500 though.

Commercial panels will have the diodes built in. If you're making homebrew panels, I'm pretty sure the charge controller prevents the batteries from backfeeding the panels at night.

[Nando]

Think in the future !! What do you plan to do in the near future ( 1 to 3 years).

360. watts if you use a controller like the C60 from Xantrex.
     
420. to 460 watts if you use a MPPY charge controller like the MX60.
     
     

In both cases the you will be able to charge up to 60 amps.

MX60 is more expensive than the C60, though you get additional wattage from your panels.

Nando

[Clifford]

Do you have any idea of the max amps you are able to see with the current arangement? Are you getting 5 amps?  10 amps?  

The max your panels are rated for would be 360 watts or 30 amps.

However, you may or may not see the max current, especially if you have sub-optimal conditions in the winter.  

Anyway, knowing the emperical data of what you are getting currently should help with the decision.

MPPT controllers usually are only rated to provide benefits at over 100 watts (8 amps or so).  However, if you have enough power, they may give you significant benefit, and thus cost savings.

--- CK ---