Classic 200 Aux 2 configuration

[Vanman]

Hello,

I installed a diversion load water heater on my existing PV system and have a couple of questions regarding programming the correct settings.

I have 4 Solarworld 285 panels in series, a Midnite Classic 200 charge controller, 4xL16 6v batteries in series.  Diversion load is a 500wdc water heater element running off of Aux 2 via a Crydom D1D60 SSR mounted on a substantial heat sink.

The system is functioning, however it won’t shut off when the battery voltage drops 1v below my float voltage.  I have also experimented with adding a load beyond the wattage that my panels are producing and it won’t shut off either.  For example, my system is currently producing 875w and I have an approximate load 950w.  My charge controller is saying the battery voltage is  25.5 v and my battery monitor is saying the battery voltage is 25.38v, battery SOC 95% and -21AH.

I have it set to the following:
Equalize voltage 30.9v absorb 29.2 float 26.3
Waste not Hi offset volts .5  width 1v
Tweaks Divert counter on

I can shut the diversion load off with the circuit breaker and the Aux2 function on the CC, so the relay has not been damaged. 

Lastly, if the Aux 2 waste not hi function is selected and the LCD shows Aux 2, does that mean it is sending current to the diversion load?  If it is not show Aux 2 does that mean it’s not sending current to the diversion load?

Based on the other posts regarding this matter I feel like I am missing something, but can’t figure out where I am going wrong.  Thanks for your insight.

[TimBandTech]

I reviewed your SSR selection and I think it looks good from first glance.
To verify your hardware I would recommend going through the Aux2 menu and simply turning on and off your heating element to verify that it works at 100% duty cycle through the charge controller. I believe these are labelled "manual on" and "manual off" in the menu. You should be witnessing your 500 Watt element from the bmk or even through heat at the element itself if need be. Ideally you're seeing a 20 amp change after dark coming out of your battery bank through the bmk.


Beyond this, the way that the PWM diversion works is to vary the duty cycle of its output, thus turning your 500 watt element into a continuously variable ( 0Watt to 500 Watt in some fine digital step) by timing. The beauty of Midnite Solar is that this is integrated into the configurable voltage so that as the charge controller walks through the stages of whatever program it is running; hit float and the heating element will get the max. You'd really like your heat element to match your array power to have a proper design. I've built a system with three elements driven by three SSRs all driven from one Aux2 port.

As I recall I came to disregard all information on the details of the two configuration parameters because the specs did not make sense. Nowhere in their language do they even discuss a duty cycle. It is as if tech pubs were required to translate into the language of the Aux1 system, and of course that translation loses everything that the PWM is capable of. As I recall the width parameter can be dropped way down to 0.2 or 0.1 Volt. These figures are claiming to be voltages yet the key in a tracking algorithm are more related to time. There is no reason that the diversion algorithm shouldn't simply track the target voltage exactly. The actual parameters will be causing overshoots or undershoots within an algorithm that really for a big battery bank won't matter much. If you were waiving your hands over the solar panels at just the right rate you might be able to make the thing swing hard and err, and this would be the same as turning on and off a large load off the inverter: the diversion load should drop when the inverter load comes on, then pick up again when the inverter load drops. Yet you see the timing of it is the challenge that the algorithm faces. It cannot just snap its fingers. If follows a control loop and those two parameters are likely PID parameters which tech pubs felt were too complicated to describe. The default values are bogus and the descriptions are as well. Shame on Midnite Solar for taking one of their best design features and marginalizing it. You won't get any decent tech information from them on this feature. It's "like a racecar" to them.

Really what is necessary to verify and monitor proper operation is a continuous meter that shows duty cycle. I can make you one or you can build your own. Feed a 10k resistor off the Aux2 out; feed it to a 0.1 uF cap to ground. Read this voltage with a meter; calibrate that voltage accross a  100k pot if you like.  This can then be fed to a continuous traditional needle movement meter or read digital but the traditional is far superior. Anything you do past the 10k resistor cannot affect the low impedance gate drive but of course we don't want to back feed anything big there. The point is that this work is small signal work; you can relax about fire safety here. I recommend you build a permanent one of these (with the 10k resistor link at the SSR gate) and witness the sensibility of it throughout the day.

Try dropping both config parameters down quite low, but you see your adjustments there require some feedback and you will only properly get that feedback with the monitor that I've described. Those parameters do matter quite a lot.

Hello,

I installed a diversion load water heater on my existing PV system and have a couple of questions regarding programming the correct settings.

I have 4 Solarworld 285 panels in series, a Midnite Classic 200 charge controller, 4xL16 6v batteries in series.  Diversion load is a 500wdc water heater element running off of Aux 2 via a Crydom D1D60 SSR mounted on a substantial heat sink.

The system is functioning, however it won’t shut off when the battery voltage drops 1v below my float voltage.  I have also experimented with adding a load beyond the wattage that my panels are producing and it won’t shut off either.  For example, my system is currently producing 875w and I have an approximate load 950w.  My charge controller is saying the battery voltage is  25.5 v and my battery monitor is saying the battery voltage is 25.38v, battery SOC 95% and -21AH.

I have it set to the following:
Equalize voltage 30.9v absorb 29.2 float 26.3
Waste not Hi offset volts .5  width 1v
Tweaks Divert counter on

I can shut the diversion load off with the circuit breaker and the Aux2 function on the CC, so the relay has not been damaged. 

Lastly, if the Aux 2 waste not hi function is selected and the LCD shows Aux 2, does that mean it is sending current to the diversion load?  If it is not show Aux 2 does that mean it’s not sending current to the diversion load?

Based on the other posts regarding this matter I feel like I am missing something, but can’t figure out where I am going wrong.  Thanks for your insight.

[ClassicCrazy]

Do you have the Aux2 set to Auto ? It almost sounds like you have it set to On which would keep it on all the time.

Larry

[Vanman]

Thanks for both of your responses. 
In the aux 2 menu, I have it set to the following parameters, waste not hi and .1 v offset and 1v width.  Right now, I am producing 118w and it is still drawing-21.2A on my BMK. 

[ClassicCrazy]

Thanks for both of your responses. 
In the aux 2 menu, I have it set to the following parameters, waste not hi and .1 v offset and 1v width.  Right now, I am producing 118w and it is still drawing-21.2A on my BMK.

What I was wondering is if you have the Aux2 set for Auto - there are three settings in addition to what you have above  - ON , OFF, Auto .

Larry

[Vanman]

Thanks again to everyone who contributed.  I am pretty sure I have it figured out. James at Midnite tech support was incredibly helpful, Midnite certainly owes him a pat on the back for his knowledge of their product and electrical engineering.

Here’s a document he wrote that helped me understand the PWN function and setting my voltage for both the charging stages and the AUX 2 Waste not Hi logic.  It can be found at

http://www.midniteftp.com/support/kb/faq.php?id=50

Ultimately, I raised my absorb voltage .3v to 29.5v and my float voltage.3v to 26.6v, to account for the  PWM at the respective stages.  The parameters I used for the Waste not Hi logic was voltage offset -.2v and a with of 1v. 

We’ve been experiencing cloudy weather here, but I have noticed a bit of hot water production.  I also used the Led 1 function the Miscellaneous menu as an indicator to when AUX 2 starts PWMing.  I’ve been pleased to see the yellow light flashing or steady when my battery voltage is at or above the set points for absorb and float. 

I’ll post an update after the next few days of sunny weather to report on the functionality of the system.