question on interpreting MPPT controller display

pianotuna wrote:
outboundwest,

It may depend on what is selected for set points. What controller do you have? Have you changed the stock settings?

the set points are per my batt manufacturer. I used some simple MPPT controllers made by BZ Products in the US. I don't have displays inside my camper. My Magnum 3012 display, because it has the batt monitor, gives me a net amp figure. This net figure is the gross on the controller, less the load (devices + phantom), which is fine for me. I wanted simplicity.

Someone answered my question I think. If I'm under good sun and if in BULK, harvesting 55 amps, but then in FLOAT, the controllers show only 25 amps, in the same sun, then that answers my question.

I thought the controller always showed the max potential harvest, when evidently, it is only displaying the usable amps based on the needs of the batteries.

The amps showing at the controller depends on the MPPT's output watts. You divide the output watts by the battery voltage to get the amps. So yes, the SOC of the battery affects the amps you see.

EG output watts 200:
Battery v 13, amps 200/13 = 15.38
Battery v 14, amps 200/14 = 14.29

Not all those amps go to the battery. Any load gets first crack at the amps, with any left over going to the battery. (Same as with any battery charger when the battery is connected to loads while also being charged--as with an RV converter)

To get the amps to the battery, you need a second ammeter just for that, downstream from the controller. EG, a Trimetric monitor with the controller's output going through the Tri's shunt.

Of course there remains the usual tapering of the amps to the battery when they get nearer to being full. The SOC when the amps start to taper depends on the charging rate. Higher rate, lower SOC when amps taper. Solar usually is at a low rate so amps would not taper from that until SOC in the 90s percent range.

You also have the IV curve for your panel, where as battery voltage goes up amps start to taper a bit until they fall right off at the knee of the IV curve, but this will be a higher voltage than what you would set the controller to get to, except with MPPT controllers using Vmp before they go to PWM after the Bulk stage.

outboundwest,

It may depend on what is selected for set points. What controller do you have? Have you changed the stock settings?

The controller can only report what is actually happening.

The potential amps cannot be known except in bulk mode as that is when all is running at max. You could briefly load the battery and watch the controller ramp up.

outwestbound wrote:
Does the controller always show what the max coming in can be, or does it show what the battery bank is capable of accepting, depending on the banks state of charge and thus, the mode the controller operates in (e.g., bulk, absorption or float)..

Any decent controller will show what's actually going to the batteries. Mine shows that, and what's coming in.