The Classic manual does not explain the operation of this Aux 2 PWM method well, if at all. We will try to fix that real soon now based on your input too. In this case, the AC/DC mode and width etc. really needs more explanation.
For DC dump loads and Waste Not use, it should be set to AC (the default I believe) which is about 500 Hz. This should work for AC or DC Solid State Relay (SSRs). The only reason we have a DC mode and lower frequency operation is for our Clipper that uses the PV input voltage to run the PWM. Waste Not uses battery voltage. Power resistors can be very inductive and in the case of our Clipper, 500 Hz requires a large snubber.
Correct too, in that there is no extra power in Bulk MPPT. Have to wait until in Absorb or Float or EQ to use waste not in either Aux 1 or Aux 2.
If you have 3000 watts of dump load, you will not necessarily be able to use all of that. It can only use whatever is required to keep the absorb voltage from rising above the PWM threshold voltage relative to the voltage regulation set point. Relative to battery temperature compensated voltage actually.
The voltage regulation set-point for the battery bank is typically not an exact voltage requiring a 0.1 +/- 0.1 volt accuracy. If it were, then this mode would have a much less chance of being able to work. A 48V battery bank will work better than a 24V bank which will work better than a 12V bank due to that accuracy.
There will have to be some voltage buffer...
The actual set point voltages, Absorb, Float or EQ will have to be set slightly artificially high so that the Waste Not set point can operate before that set point voltage comes into play. The Classic's Absorb, Float and EQ voltage will then be the "fail safe" voltage in case the Waste Not dump load becomes dead or water becomes hot or whatever. When the charge stage comes out of Bulk and into Absorb (or Float MPPT into Float, etc) then the Waste Not or Diversion can be the method of voltage regulation for that battery voltage set point.
The Absorb timer is enabled by default in the TWEAKS menu so that when the dump load is operating via Aux2, the timer will run and it will finish the Absorb or EQ cycle when dump load has been regulating the voltage. This is necessary because the actual Absorb voltage is set higher and won't be met like normally when not using the extra energy... That higher voltage setting is not really desirable but shouldn't be so high as to hurt the batteries as long as the dump load and SSR doesn't die for too long a time. In a 24V or 48V system, it probably doesn't hurt to run the voltage higher for quite a long time. 12V is a bit tighter requirements.
The 1V width can start slightly above the voltage which it starts to go into voltage regulation mode as the battery starts its time in Absorb, Float or EQ.
If you have a 3000 watt dump load and you only have 300 watts extra to keep the voltage constant, then the PWM will be at some point just above the cut-in PWM voltage (the lower end of the width V). As the battery gets more full, it should take less power to keep that voltage at the set-point and there will hopefully be more power available for the dump load and the PWM should widen out a little bit.
The PWM regulation time should be fairly fast too. Too slow and the Absorb, Float or EQ set point voltages will reduce the power so fast that the dump load won't have time to react. For Aux 1, there is an adjustable Delay (attack) time if you want a slower response time. Aux 1 also has an adjustable Hold time (release). That is hysteresis time if you like. There is also a High and Low voltage setting but these 2 set points can be as close as 0.1 volts if wanted.
..........................
As for the 98% efficiency figure, we do not publish efficiency numbers for the Classic although some measurements were taken a long time ago. Not sure where the 98% came from ? It's not easy to measure accurate efficiencies either. There are hot and cold numbers. input voltages and output voltage and power, making measurable differences as well as unit to unit variations and instrumentation and shunt issues. i.e. those numbers can vary quite a bit. Some try to use the meters on the Classic for this. Not a good idea. Nice, and expensive Yokogawa power meters and automated measurements are a good way to go along with extremely well matched shunts.
Yes, the Classic gets hot when processing a lot of power throughput. But, even if it is operating at 98%, it could get hot. Say it is putting out 3000 watts and is 98% efficient. That would be around 60 watts dissipated in the Classic. That is a large amount of power for such a small unit. The XW MPPT-60 has a large-ish heat sink (and no fan), so heat is going to be distributed over a larger area as well as having a lower output current and input voltage rating. We could make it a bit more efficient but would take more space and cost more. We are working to improve efficiency or at least have larger heat sinks in future products. They will cost more, partly because of more expensive parts and partly from tariffs that some of the parts cost now.
boB