Classic, ending absorb, firmware and lite issues

zoneblue

After some clarification from midnite i can now shed some light on some of the issues raised around our classic in my previous thread, Classic monitoring. As a guide, please read the below with the flavor of: The classic is a fantastic product, we just have to try to keep up with the relentlessly restless guys up at midnite.

So to kick off, if you are like me, you bought a classic, thought that its in a stable, factory programmed condition, you hence set it to its defaults, mostly, and then get on with building the system, house, farm, whatever.

However, its important to understand that the classic firmware is under rapid and continuous development. You might buy something thats been in the warehouse for a month or two, (in my case 4, small out of the way place that we are), and by the time you install it the firmware is 6 months old.

Well, I count not less than 24 firmware updates in the last 6 months. (I couldn't find the changelog online, but a copy is included in each firmware release.)

So make your (and our) life easier and get the latest firmware, and the latest local app, at the outset. I know there's a certain anxiety about messing with the software of the device, but if they are anything like modern computer gear they should be pretty hard to brick. Like any firmware, its good to work calmly, with an unplugged laptop with a full battery, be sure of the steps and allow them to complete fully. The instructions are clear enough.

Note, that their firmware numbering is both/alternately by number and by date. In most instances you want the latest stable.

Note also that, like many a good project, the manual is incomplete. Maybe they need a wiki where we can pool what we know, take some of the pressure off the midnite guys to do documentation, and let them get on with releasing their new products.

Anyway. The classic also gets more interesting with the lone lite scenario. Out here in NZ the classic will set you back between 1000 and 1100 dollars NZ. And thats the lite, the full version costs even more. So if your budget is tight, you might be tempted to choose the lite and rely on the local app software for configuration and logging.

You do need to understand that the configuration functionality present in the local app is only a subset of that found in the MNGP. Yes the important things are there, but many things are not. If you need "advanced features", get the full version, not the lite. Or be prepared to beg, borrow a MNGP from someone from time to time.

Heres an example of a lite quirk. The firmware readme says, after flashing, reset the controller to factory defaults. As this uses a certain key press combination on the MNGP, it cant be done on the lite. As a result you may not get the new firmware defaults set correctly. If this is the case watch it closely for a few days, to understand what its doing and see below for other work arounds.

The main issue that occurred for us here was we seem to have got caught up in the middle of the how-to-end-absorb method transition. There have been at least 3 different algorithms in the last year, (in pursuit of the holy grail of a perfect change termination), (i guess).

Our original firmware was 1070. In its view of the world, ending absorb was more governed by the min absorb time setting. After upgrading to 1370 the default had changed to one where max absorb time rules.

The lite, and in general the classic, now has only one setting, absorb time.

Prior to upgrading, our absorbs were exactly 30mins in length, as min/max absorb time was set to 30/120 in 1070. This is why we sometimes still had 15 amps no load, sometimes 20amps flowing in float. In 1070 the default EA is 0.1 which (effectively) means EA is disabled.

After upgrading, our absorbs were trying to get towards the old 1070 defaults of 2hrs, or 0.1A ending amps. Ie, quite long if the bank that starts the day at high SOC.

The current 1370 default formula works like this:

Absorb time has a single time setting, Absorb MAX Time. The absorb timer starts from Absorb MAX Time. While the battery is at or near the Absorb set point voltage, the absorb timer counts backwards towards zero. Should the battery voltage fall below the absorb set point voltage, (the controller falling back into Bulk MPPT), then the absorb timer will stop counting down until such time as the battery voltage comes back up to the absorb voltage set point.

This mode is therefore a fixed time method. Any absorb MIN time setting is ignored. Im not exactly sure which firmware this method became dominant, but according to the firmware changelog, sometime in august 2012.

Having discovered all of the above, i was able to force float, and reconfigure the lite.

EA initially changed to 0A, which is the new way of disabling EA. Absorb time set to 1 hour. That made our absorbs exactly one hour. The algorithm that took into account the relative length of the bulk stage is now gone. So with 1370, EA is quite important if you want to avoid overcharging your bank. I now have set 2hrs and EA=15amps. (Our daytime base loads are about 7 amps and C50 for my bank is 8 amps. We do need to be careful now not to have unusually heavy persistent loads on in the middle of the day. Like the wee heater ive been using by the desk.)

One of the other previous algorithms, varimax is still present in the controller as an option but cant be configured (easily) in the lite. Varimax uses the min absorb time as well as the max absorb time. Varimax is enabled by setting the varimax current to something below 101amps. Midnite recommend using the new default algorithm, as varimax can in some conditions create quite long absorb stages.

As you know, this whole EA business will radically radically improve once the battery shunt monitor is released. In the meantime there are tools available that allow the geekily inclined to configure the classic lite using modbus, see in particular rossw's newmodbus.

Of course not all of us feel the need to be so curious about whats going on inside their charge controller, right? But hopefully this helps others that might be scratching their heads, wondering what their CC is doing.