My New system comments.....

Re: My New system comments.....

I figure the high demand of electricity should keep the MX-60's in constant "absorbing", but will the varying loads cause the sweeping mmpt of the MX-60 screw things up, ie: if the sweep is done at high loads and then the loads go down to "0" will the mx compensate to "no need to charge now". Or if a sweep happens when "0" watts are used and then a 4k load comes on will the mx-60 kick in?

Frank,

Any charge controller will start the day in its bulk (MPPT) mode. Depending on the battery bank’s state of charge, the array size, the weather, and loads, it may reach its absorb target voltage during the day and then switch to absorb mode. Once the absorb mode is complete, it’ll switch to float mode. The charge current (and therefore charge power) won’t drop to zero until the Sun sets.

If the battery load is switched from essentially zero to, say, 4 kW, the battery voltage will drop and the controller will respond accordingly by selecting the correct charging mode for that voltage. Similarly, if the battery load is dropped from 4 k to zero, the battery voltage will rise, and, again the controller will respond accordingly by selecting the correct charging mode for that voltage.

In short, the controller will “do the right thing” in dynamic conditions, be they environmental or loads.

HTH,
Jim / crewzer

Re: My New system comments.....

John,

The “sweep and sleep” description is something of a misnomer, as the controller doesn’t really “go to sleep” during normal daytime operating conditions.

Rather than “sweep and sleep”, a more accurate description of the MX60’s MPPT function might be “periodic sweep”. The “sleep” term was somewhat derisively chosen because the MX60 is not operating in active MPPT mode between the end of a sweep and the start of the next period. The only time the controller truly “goes to sleep” is when its output current falls below a user selectable value of between 0.2 and 1.0 A.

In short, while operating in Bulk / MPPT mode, the MX periodically sweeps the array looking for the combination of array voltage and current that produces the highest output charge current to the batteries. It basically holds the array voltage setting for the duration of the period. The sweep interval can be user set from between 0 and 15 minutes. Dynamic environmental conditions may result in less than optimal performance until the next sweep occurs.

While operating in absorb or in float modes, the MX60 does not operate in MPPT mode at all. Instead, it operates in PWM mode to maintain target battery voltage by limiting charge current. This is not an operational limitation of the MX60. The TS-45, TS-60, Xantrex XW, OutBack FLEXmax80, and Apollo T-80 all operate in essentially the same way.

The MX60 also does not operate in an active MPPT mode when the controller output current is < 5 A. Instead, it sets the array voltage at the “U-Pick %”of array Voc. Although not really at all active, it’s still a useful form of MPPT, and the result is usually higher output current than what would be available from a PWM controller.

Finally, since the controller isn’t ever “asleep” from the perspective of this discussion, it doesn’t really ever have to “wakeup” when conditions change. If the battery load increases dramatically, the battery voltage will drop and the controller will respond accordingly by selecting the correct charging mode for that voltage. For example, if might switch from absorb mode back to bulk/MPPT mode.

I hope this additional information is useful to. See the following old posts for additional reading:

http://forum.solar-electric.com/showthread.php?t=1470
http://www.outbackpower.com/forum/viewtopic.php?f=9&t=2333

HTH,
Jim / crewzer