First, I ~try~ to avoid confusion between all the Bob's and myself by spelling
my name backwards. boB as opposed to Bob. Now, you're name appears to
be spelled bob, which is even different. We still have room for a bOb here
too, which is sort of spelled inside-out.
You are right that you won't get 98% efficiency with a 12 Volt battery system.
that 98% number for the MX60 was measured at 3000 Watts output on a 48 Volt
battery and a 48 volt PV input (about 64 volts input). It can actually be
better than that. Now, one thing you cannot do with a typical PWM controller
is to connect a 48 volt PV array to charge a 12V or 24 volt battery. Or,
a 60v or 72 volt array to charge a 48 volt battery. There are pretty much
2 basic advantages to doing this. 1 is when there is a long PV wire connection
to the controller, say, 75 feet or more. 2 is when there is a partially
shaded array when the max power point voltage can be below the battery voltage.
Another is when the panels are hot and the MPP voltage is at or below the
battery voltage. It's better to wire it for a higher voltage usually.
Not always the highest voltage, but one or 2 nominal voltages higher.
So, bob, how many Watts of PV do you have hooked up ?? The use of an MPPT
controller might be questionable with say, 250 Watts of PV or less.
On the 0.5 Amps out when the battery was disconnected... What that is, is
an offset in the current sense circuit because it got warm. It would come
back down to around 0 after a while I think.
This is one reason why the MX "opens up" once in a while to reset that offset.
The newer units should be better than the real old ones, like over serial number
6000 or so as I seem to remember.
boB
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