Author Topic: Aux 2 Waste Not Temp Compensated?  (Read 303 times)

Iboondock

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Aux 2 Waste Not Temp Compensated?
« on: November 12, 2017, 09:29:44 PM »

I've been using the Local App to monitor a new system that has an opportunity load. As the sun goes down, I can see that in float, AUX2 is pulsing high well below the target compensated voltage(28.5v) minus the offset(-0.9). It appears to be offsetting from the set voltage(27v). I've seen the AUX2 light come on all the way down to 26.5v, at that point a safety contactor opens cutting off the opportunity load.

While researching how to set up an opportunity load with Waste Not Hi, I came across several posts that indicated that Waste Not was temperature compensated. Possibly that changed in later firmware? Can anyone confirm that it is, or isn't?

Thanks

boB

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Re: Aux 2 Waste Not Temp Compensated?
« Reply #1 on: November 15, 2017, 01:23:06 PM »

Yes, it does follow the temperature of the battery.

Maybe unplug the temp sensor and try ?

boB
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Iboondock

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Re: Aux 2 Waste Not Temp Compensated?
« Reply #2 on: November 19, 2017, 03:39:22 PM »

Yes, it does follow the temperature of the battery.

Maybe unplug the temp sensor and try ?

boB

I'll try that the next time I get out there. But I don't think it's a temp sensor issue, because it's correctly compensating the charge voltages.

wesolows

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Re: Aux 2 Waste Not Temp Compensated?
« Reply #3 on: November 28, 2017, 01:30:35 PM »
I'm seeing something similar on a 48V system with a Classic 250 and version 2079.  AUX2 offset is -0.9V and width 1.0V; the setpoint is 58.8, and with temperature compensation I see in the T-Comp menu that it's correctly calculating the setpoint as 59.9.  AUX2 starts PWMing at around 57.6 or 57.7.  I also sat and watched how much current the diversion load drew as I changed the AUX2 offset once the controller kicked into Absorb at the correct setpoint of 59.9 (with lots of extra power available from the PV system so that we'd stay in Absorb regardless of how much or little current was diverted).  The load was fully on or very nearly so at -0.9V offset, but was PWMed at smaller negative offsets (e.g., -0.5V).  As one would expect, the diversion load current draw rose seemingly linearly as I moved the offset voltage farther from 0 until the load was fully on.  I didn't try raising it above 0 to see where the load cut off completely; I guess I can try that the next time I see the sun, which if this year is like most will not be any time soon.  It's not clear how well this works in Float, either.  The load stays fully on as we kick out of Absorb into Float, at the float setpoint, as it should be.  But I have rebulk set to only 0.3V below the float setpoint, so if AUX2 is working properly, we'd switch to Bulk again long before AUX2 would hit the cutoff for Float.  That part seems to be working ok for me.  But if we don't make it to Float before sunset, I see what you described -- the load remains PWMed as the voltage sags far below the Bulk/Absorb setpoint.

So I'm not quite sure what to make of this.  It seems like the offset works as specified once we're in Absorb and voltage is at or very near the absorb setpoint, and perhaps in Float too.  But AUX2 starts PWMing at voltages much lower than it should given the settings.  Whether that's because T-comp is not happening where it should or there's some other problem with how the adjusted AUX setpoint is computed (maybe when we're in Bulk?) I don't know.

I'm sure there's some reason this mode can't just do what we really want, which is to employ feedback to slew the pulse width continuously in such a way as to hold the battery voltage at its setpoint (which it seems must be very similar to how current is drawn from the source to hold the setpoint).  This might be approximated by an offset of -0.1V and a width of 0.1V, but width can be set only in 1V increments.  Regardless, it does not seem to be working as expected even given its limitations.