balancing output from multiple controllers [RE-wrenches]

[Jeff Yago]

Although I try to design/install systems at the highest voltage to reduce
components and wire sizes,  I sometimes am forced by a client who needs lots
of solar pv but insists on a low battery voltage to match existing DC loads.
I have also repaired many systems by others who had  older MPPT controllers
to match higher array voltages to lower battery voltages, but many had
"fried" controllers so I am holding back on MPPT until Outback comes on
line.

Whenever this happens, I usually end up with two to four Trace C-40's or
C-60's and at least one is always "stepping" on the others causing them to
think the battery is full and stop charging.  Yes, I always use a quality
meter to set the pots the same settings, and make sure the temperature
sensors are located together at the same point on the battery bank.

I know this only will happen when the battery is reaching a fully charged
level, but you would have thought all of the controllers would back off
together and each start lowering their output instead of one or two staying
at full output and the others going to zero.  I assume the output of the one
or two at full is providing the same charging as would happen if all were
operating at half output, but there is always the client who thinks part of
his array is dead.  What's the deal?

Jeff Yago

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