Midnite Kid Minutes Setting on Absorb?

kaipo_boy · May 2015

OK, stumbling through the setup on my Kid...
When in the BATTERY menu, it allows me to set the ABSORB voltage... which is great, but it does NOT ask for a BULK setting first, it goes straight and only to ABSORB and that's it.... so, since the bulk is usually a short timeframe of the charging routine, I decided probably better to use just the absorb setting for both? is this right? I have Interstate GC 6v batteries in series (4 of them) and according to their website, the BULK setting is supposed to be 28.8v and the ABSORB setting, 30.6v (the 6v setting times 4)... since the Kid only allows one selection here, should I use the 28.8v or the 30.6v setting? 2nd question, after setting the ABSORB voltage, next to it is a time setting, default was 120 minutes.... I'm guessing it will just use the absorb setting for 2 hours then say job accomplished and go to FLOAT? The instructions don't say anything about it looking at the voltage to figure out if it should go to float... is this purely a time function on the ABSORB stage of charging? That wouldn't make sense as we can't predict if clouds will come later that day and reduce the panel output. Any help on these settings would be appreciated.

Mountain Don · May 2015

There is no setting for bulk voltage, at least nothing labeled as such. The charge cycle starts in bulk and starts at whatever voltage and amps the MPPT controller figures to be the best use of what is coming in from the PV. It changes with the voltage rising through the bulk stage. The bulk stage lasts until the voltage reaches the absorb voltage that is set. Depending on the SOC of the battery bulk could be long or short.

Absorb is usually a timed event. How long depends on the battery type / capacity. 2 hours is a start point. Two hours on ours works well most of the year. Absorb duration can also be determined by using "end amps" which is best done when the Whiz Bang Jr. is used. At the end of the absorb time, or at end amps it then goes to float. You can use your hydrometer to check if the battery is fully charged at the end of 2 hours. You can also monitor the amps going into the battery in absorb and when that stops dropping it should be full. That is what "end amps" is doing. You could then adjust the absorb time up or down. End amps is often set to be approx. between 1 and 2% of the 20 hr AH rating for FLA batteries.

kaipo_boy wrote: »

the BULK setting is supposed to be 28.8v and the ABSORB setting, 30.6v

The 28.8 you mentioned would be the absorb set point, the point it changes from bulk to absorb.

The 30.6 seems high for float. I would have expected the float on a 24 VDC battery bank to be more like 27.2 or so; lower than the absorb. EQ would usually be in the 30 - 31 VDC range. Check those specs from Interstate again.maybe point to a link for that battery info if you can.

I hope that helps.

Vic · May 2015

Hi kaipo..,

As Don says, there is NO Bulk voltage setting for many off-grid charging situations. You only need to set Absorb voltage and Time, or use End-Amps instead of time. The WBjr and a Shunt is the best EA method, as it is measuring the actual battery charge current.

The required time for Absorb is directly dependent on the Depth Of Discharge that the battery experienced in the previous discharge. This is the reason that an Absorb time is not noted in docs.

Also, the need to vary the Absorb time is one of the main reasons that EA is such a good approach, as the current doing into the battery tapers to a value of approximately 1 - 2 % of 20 Hour Capacity. We only use EA for the batteries here, and for these banks, the proper Shunt EA setting is about 0.9 % of C. But, this will depend on the battery SG, and other factors regarding your exact batteries.

If you must use time, then 2 hours is a good starting point, and if your batteries are Flooded, as Don mentioned, measuring the SG of the batteries when the CC has just gone to Float, will help you determine what is the approximate, average time required for Absorb.

Believe that you mentioned two values that USB noted for Vbulk, and Vabs. There will be no need to set Vbulk. Vabs of about 29.5 is probably a good place to start.
Agree with Don, that 27.2 is a good place to set Vfloat to start.

In the event of clouds reducing the available power from the PVs, the KID will simply bo back to Bulk, and do its best to charge the batts with the available PV power. When the cloud cover is reduced and there is more PV power, the KID will resume the Absorb stage, no problem.

FWIW, Good Luck, Vic

kaipo_boy · May 2015

My thanks, guys! That's a lot to digest.
Interstate says the FLOAT value should be 26.8v and the EQ 31.2v. I haven't set the EQ yet, I've only just connected everything together (not yet in final trim, this is only testing).
When the Kid goes from ABSORB into the FLOAT mode, what specific gravity am I aiming for? Argh, another thing to order (whizbang jr and a shunt)... will wait until I figure out the Iota vs Meanwell mess, then move onto using the End Amps method. My DOD so far has only been near 75% or so, but I'm only in data gathering stage so may drop it to 50% on purpose in a few days to try and see if a full day of sun will get me that coveted green LED on the Kid (RFC: Received Full Charge). I am only running on 2 panels now, 285w each; I have 3 panels, but have not hooked up the 3rd panel. Want to do some experiments first with 2 panels and see if they will get me the full charge on a 50% DOD in one day of sun.

Vic · May 2015

kaipo..,

It appears that the target SG for Interstate GC-2s is about 1.285, according to this:
http://www.interstatedealers.com/pdf/201535.pdf

Good Luck, Vic

kaipo_boy · May 2015

My thanks, all.
Vic, 1.285 SG is supposed to be for a 100% charge... when the battery comes off absorb and goes into float mode, is the target 95% or 100%? or does the SG change that much in those 5%? I'm assuming DOD does not have an affect on your target SG?

Vic · May 2015

Hi kaipo..,

Different people have different approaches to charging Flooded batteries. In years gone-by, we all (or almost all of us) tried to fully charge FLA every day -- sometimes we could not get that done. In those days, we were shooting for full target SGs every day.

Now, I do a full recharge every 4 to 5 days (depends upon the system). But these banks with Skip Day charging approaches are moderately large banks. Believe that banks that are not large, and those cycled below 90% SOC each day would probably want to be fully charged daily or perhaps every other day. Depends on the amount of PV or other charging sources, etc.

There are some that note that a complete full charge is not required when recharging batteries. But, for me, on the days that we charge the banks, am shooting for the 100% Target (1.265 SG on these banks).

Some have said that the battery bank needs some rest time before target SG is reached -- I've never seen this on the banks here. AND, on fully off-grid systems it would be difficult to run the test, as the batteries are always running inverters, and so on.

FWIW, opinions do differ, and change over time. Vic

kaipo_boy · May 2015

My thanks, Vic. Sounds like something with a bit of philosophical approach than a pure hardware discipline?

I'm kidding... experience always tempers your hardware approach as hands on training will always show you the true machine. Form follows function and a wise man is never so set in his ways that he can't see the signals when his machine tells him he's screwing up. Hopefully I'll be able to see something just before the catastrophic failure....
Interesting that Interstate's values seem a tad higher than a generally accepted norm here... just slightly. Higher charging voltages and higher SGs. A lot to digest in a short time. My learning curve better be steep (my pocketbook tolerance certainly isn't).

kaipo_boy · May 2015

The Kid JUST went off from Absorb to Float... so I quickly grabbed the SG tester and it seems to show around 1.260 ish... hmmm. I know its calibrated at 80 deg F and it's probably 85ish today, close. Do you guys rinse out the tester when done? or just put it away?
Also, the Cotek inverter doesn't seem to like the higher (28.8v while on Absorb) voltages while the batteries are charging, the "input" LED was orange. Soon as the Kid went into Float and dropped the voltage to near 27v, the orange LED on the Cotek went green.

Mountain Don · May 2015

kaipo_boy wrote: »

Do you guys rinse out the tester when done?

...with distilled water. I keep a jug of distilled water in the battery compartment.

What operating voltage range does the Cotek inverter spec? It is possible that it will totally rebel if/when the Kid goes into an EQ.

Vic · May 2015

kaipo_boy,

Believe that your Absorb is terminated by time. So seems that you need a longer Absorb time, at least until you get the batteries fully charged.

The SG measurements should be Temp Compensated, but the SG difference between 80 F and 85 F is very small, essentially you can ignore this small difference.

You might try setting the Absorb time to about four hours (240 mins), and see if you can get the SGs up to Target in a day or two, if you have enough sun.

YES you should rinse the Hydrometer about three times, with Distilled Water when you are done measuring SGs. This is very important. Otherwise, a sticky residue will cause air bubbles to adhere to the float, and the outer tube (or case), and cause erroneous readings.

Many 12 V and 24 V inverters do not like high-ish battery voltages, and may complain. This is probably what the Cotek is doing. Sometimes, cool/cold batteries can cause some inverters to shut-down when charging, due to high-ish voltages. This is an issue with the inverter, not the CC, in this case.

Opinions. Good questions, nice that you are paying close attention to your new system. FWIW, Vic

kaipo_boy · May 2015

Mountain Don, now that's a thought... checked the literature that came with it and it says over voltage is defined as 30.0v.... since my EQ voltage is just over 31v, it means the inverter will fault out? sounds like i have to turn it off prior to doing any EQ.

verdigo · May 2015

I use Interstate's GC2 batteries and also sell them at my garage. The local distributer will leave them unchecked and uncharged for months before exchanging them only to recharge them and eventually sell them somewhere else. So I wouldn't be afraid to use their high voltage charging recommendations and a good EQ to boot. My distributor didn't stock the GC2XHD 232ah version and had to order them in so I feel pretty confident about them as they haven't set around too long sulfating at a retailer somewhere.

kaipo_boy · May 2015

Vic, my thanks again! You have a lot of experience and I appreciate the primer and handholding. Yes, I was set on 120 min Absorb... with only 2 panels @285w per panel. I have just upped the Absorb time to 180 min (3 hours, taking it slow to gather data as this is not really a working system yet, with only 1 chest freezer to keep happy... the reason I'm running the chest freezer is that even if the inverter has to shut down for a couple days, I'll catch it quick and switch the power back to grid without damage to the contents in that time). We have another day of high overcast cloud cover though

Wouldn't you know it?! Everyday sun sun sun all year long and then when I plug the panels in first time, its nothing but clouds.

Mountain Don · May 2015

If you are still wondering if the batteries have reached a true full charge you might want to disconnect the loads altogether for a day or even two. And use the third panel. Then reconnect the load and see if two panels can keep up. Just a thought. It can also take several cycles before the new batteries gain their true capacity.

kaipo_boy · May 2015

My thanks, Mountain Don. I'll wait till its dark and hook up the 3rd panel tonight, and hope that does it! Only problem is, I'll be at work if/when it transitions from Absorb to Float so won't be able to do an SG reading just then... Will have to wait till next weekend to get that info and hope its sunny! Interestingly, in the late morning when the panels were actually putting out near Imp (around 8 amps), the Kid said it was putting around 17A into the batteries... this is with 2 panels. So 3 panels should get me a max of around 26A and the Kid is only rated for 30A... so 4 panels of around 285w each will be too much and will be over 30A and power will be wasted.

kaipo_boy · May 2015

OK, first day after hooking up the 3rd panel... and it was mostly sunny!
But, before I get into that, I was watching the system last night and stepped out (barefeet) next to it and heard a distinctly ugly POP and stopped my foot immediately. It is super windy and the hydrometer was not where I had left it... didn't see it in the dark. Sigh. Good thing I stopped downward pressure immediately as the glass was stuck to my foot but not yet cutting into it. So now, I am temporarily hydrometer-less.

So today after a pretty full day of sun, the production screen reads 1.8 kwh and 64 ahr.... hmmm? I thought with 2 screens producing 1.9 kwh, 3 screens should have gotten me over 3 kwh on a nice day. Or is the Kid dumping what it can't use because the batteries were fully charged?

I also had to come home during middle of the day today and saw that voltage for the 3 panels was up to about 115v.... so each panel is near 37-38v.

Tonight when I got home the Kid was in float, (I've dialed in 3 hours at 29.1v)... I turned off input from the panels and shut down the inverter so no draws... and after over an hour of silence, the batteries were rock steady at 26.0v... Interstate says it should be 25.92v for 100% charge and I have no better way of checking without a hydrometer.

ouch?

I left the 3 hour charge time on the Kid but backed the Absorption voltage down from 29.1v to 28.8v... the batteries when I came home tonight and when I popped in during lunch were cool to the touch; not even the least bit warm. Completely ambient temp. Is that a sign they are not being stressed at all? What about the 26.0v? I flipped on the inverter and the freezer started up (only the freezer is connected to the inverter right now) and the voltage immediately sagged to 25.6v... after 5 minutes I shut the inverter down again and waited a few minutes and voltage was up again to 25.9v so I'm pretty sure I overshot whatever I was aiming at. However, yesterday it was cloudy all day so the Kid didn't go into float when I got home... so today it probably just finished off the charge quickly in the bright sun and went into float pretty quick.

Midnite Kid Minutes Setting on Absorb?

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