I've bought a second hand motorhome with two 100W solar panels fitted. It has two Bluesolar 75/15 controllers fitted and I want to upgrade to Smartsolar. I don't understand why the previous installer fitted two as one should handle 220W of solar panels according to the datasheet. Is there any good reason why I cannot just combined the panels and use one 15A controller? If I can't then presumably one 20A controller would be perfect in preference to gain two controllers.
Hi
You should be fine to use one MPPT as long as you keep within it's design limits. With many manufacturers it is better to stay clear of those limits by some margin as to prolong the life of the equipment. With Victron MPPTs you don't need to have such large margins.
As long as you never go over the max PV voltage (75V in this case) you should be fine. Just remember that panels can give very high voltages under cold conditions, so check you panel datasheet for that.
For the current it will be limited by the MPPT, so if you go over the design limit the MPPT will just keep to the current limit. (within reason as these smaller models do not come with a hardware current clamp). Something to remember is that the current limit is on the battery side. So if your PV panel give you 100W at 35V (2.85A) that will give you a current of 8.3A for a 12V battery. Two parallel PV panels will give you 16.6A, so you will loose 1.6A and the MPPT will run only up to 15A. For a 24V system it will give you 8.3A which will be fine.
Also note that each MPPT only has one tracker. That is fine if both panels face the same direction. If they are facing different directions them having each it's own tracker will be more effecient.
