Am I losing amps?

Qfwfq · July 2017

I'm about to add more power to my solar array and it occurred to me that this might not work as intended.

I am upgrading from 1kw@24v to 2.8kw@48v.

My charge controller is a 60a mmpt that can do 12v/24v/48v both in and out and my battery bank is 600ah@24v.

So my question is this - if I am getting ~60a@48v input, my battery bank/system is wired at 24v, and my charge controller has a max of 60a output.... what is happening to the other amps? SImple ohms law states 60a@48 = 120a@24v - but I know the charge controller can't do more than 60a... so whats going to happen and do I need to redo my whole system electrical system?

Thank you

Estragon · July 2017

The charge controller limit means it will only draw ~30a at 48v from the array.

One option would be to add another controller to use more of the array capacity if you can use the extra power. This woukd also give some redundancy for when a controller fails.

Another might be to rewire the bank for 48v depending on what format the batteries are now (eg if you have 2 parallel strings at 24v now). You would likely have to replace your inverter though.

A third option would be to stay with the one controller. 60a into a 600ah bank isn't bad. Having extra pv would help get max power during light overcast days.

It really depends on your reasons for adding panels. If you have loads that can use the extra, but not high amp ones that justify 48v, adding a controller may be best. If you're running high draw loads like pumps, the second may be best. If you're just finding the smaller array isn't charging well on light cloud days, the third may be best.

Qfwfq · July 2017

uhhgg

I do have two parallel strings of batteries at 24v so I could tie them together at 48v - but then my inverter wont work and that was/is one of the more expensive components of my system and I really don't want to replace a perfectly good unit.

maybe I will look into purchasing a small cheap mmpt controller and split the load.

The reason for upgrading is that I need the extra watts - for some reason I never considered that 60a@48v != 60a@24v

Vic · July 2017

Charge Controllers (CCs) are usually rated for output current to the battery/inverter.

60 Amps IS 60 Amps. If you double the system voltage, the amount of POWER that the CC can deliver is doubled, if the CC has the capability to charge the higher voltage battery. (24 X 60 = 1440 Watts, 48 X 60 = 2880 W, as an example).

Of course, it is generally not a good idea to try to run power systems at their maximum capability continuously.

Vic

mike95490 · July 2017

Rewireing to 48V bank will give your controller full access to the larger PV array power. The amps for the controller is OUTPUT amps.

But you would need a new inverter.. There is no "small, cheap, MPPT" controller

Am I losing amps?

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