Midnite Kid input?

kaipo_boy · May 2015

A discrepancy I've noticed.... I have 2 trina 285w panels, and the Kid does note that input voltage is around 72v, so I'm on the money if each panel has Vmp of around 36v. However, the Kid is telling me on the first status screen that the output of my 2 panels is near 10A... but when I put the fluke on the panel input line going into the Kid, I read around 4A? The Imp of this panel is supposed to be around 8A... so 2 of them wired in series would still be 8A; today is high level overcast clouds, so I expected production to be around 50% or thereabouts... if I'm seeing near 4A that's about right. But why is the Kid telling me it is getting input of 10A from the panels?

Also, if I page through the status screens, I come to the last screen (it stops here, you can't go any farther) which says: Kwhr, then KID, then Ahr. For Kwh it is 1.4 and for Ahr it is 55... the instructions do not say what these values represent. Anyone know?

Vic · May 2015

Hi kaipo..,

Believe that the first screen on the KID shows input voltage, but the current shown is the OUTPUT current. So, on your 24 V system, this is believable (to me at least). IIRC, the KID has no input shunt to measure the input current, just an output Shunt.

The Kwh and AH values should be for the present day's production.

Am away from my KID, so cannot confirm ... also am not up to the newest FW revision on the KID here. FWIW, Vic

Mountain Don · May 2015

My Kid is 66 miles away right now... Going by memory I do believe on the first screen, the one where it tells us if it is in bulk, absorb, float or EQ mode, the amps is the amps going into the battery, after being processed through the MPPT circuitry. That screen also displays the battery voltage I think, as well as the instantaneous watts going into the battery. The last screen represents the days production (so far) in KwH and AH. I hardly look anymore as long as the green LED showing recent full charge is on. And at the end of the day the green "floated today" LED is on.

I don't recall there being any display of the amps from the PV array... and to my mind I don't really care about that. I still get things confused in my mind between my old FM60 and the Kid. It helps if I am looking at the display.

kaipo_boy · May 2015

Ah, daily production; of course. I knew what the kwh meant and guess the other was amp-hours but still not sure how to use that info. the kwh of 1.9 (in late afternoon after a day of high clouds) is useful info... between 2 screens and roughly 6 hours of useful light, that means each panel is producing avg of 150w at any given time. Interesting.

this morning I woke up and looked at the same status screen and confirmed both values have re-set to 0, so it is daily production.... obvious in hindsight. Thanks.

System is in bulkMPPT mode right now and battery voltage is still 25.5v, so I'll keep an eye on it... according to what you guys are saying, it should rise to around 28 -29v and transition to Absorb at that point.

There is a strange joy in seeing those 2 green LEDs on the left side of the KID (Received Full Charge and Float attained) at the end of the day.

edit: It is 9:15am and amps on 1st status panel is up to around 13.5A. I stuck the Fluke on the battery lines from the Kid and confirmed they also indicate current of 13.5A so the first status panel on the Kid is actually current INTO the batteries (the instructions says it is amps produced by your PV panels, which sounds like it should be panel amps to me). Thanks Mountain Don! It is morning sun (intermittent) and I'm seeing around 6A from the panels... rated at 8A... I'll know later today if the rating is a fairy tale or not. Voltage of the battery bank is climbing, 26.5v now.

edit: It is 10:30am and amps on the Kid are 17A... measured output from the panels and it is 8.1A baby! Hmmm some truth to advertising after all. Batt voltage around 27v and Cotek is green... all is well.

Vic · May 2015

Hi kaipo..,

Because the SG of your GC batteries is 1.285, your Absorb voltage should probably in the range of 29.5 - 30.0 volts. You are correct, that the US Battery site mentions 30.6 v for these batteries, but that is when a different type of charger is used -- Constant Current Bulk at a specified voltage, followed by the very high Absorb voltage.

Renewable Energy chargers often cannot operate this way, as the solar day is generally just not long enough.

If these batteries were mine, would try 29.5-ish volts (it is very important to use the Battery Temperature Sensor -- BTS -- to compensate all charge/EQ voltages). If this does not do the job of charging the batteries, on average, then try stepping up the Vabs a bit.

It is not uncommon to need to raise the Vabs a bit in the Winter, and decrease it a bit in the Summer, in order to try to use the lowest Vabs that gets the job done for the solar conditions at differing times of year, and to best match the weather conditions that are customary with certain times of the year, etc.

Opinions, Vic

kaipo_boy · May 2015

Great advice, Vic; thanks! I have it set at 28.8v for now, 180 minutes. Sometimes you git the bear and sometimes.... sigh. Its already 2:30pm and it didn't even get out of Bulk stage, today. Too cloudy

Will have to wait a bit before I can tweak some more. I did see it briefly go into Absorb, but then the clouds really came in and it went back into BulkMPPT.

I will add on the 3rd panel tonight (I work on the PV electrical only in the dark to minimize the chances of turning my skin a few shades darker) and see how that changes the mix.

Midnite Kid input?

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