HELP! Midnite KID with an AGM battery bank: settings?

[kateonmars]

Hi there,

I have some confusion over our settings on our Midnite Sun Kid inverter that I'm hoping you fine folks can help resolve!

We've got a system that consists of:
-2 x 250 W panels
-4 x Surrette 460AGM 6V 415Ah batteries, set up for 12V
-MMS-1012 Pure Sine Wave Inverter
-Midnite Sun Kid charge controller

Our installer initially installed our system and the Midnight Sun Kid with a certain set of settings (float to 13.5, absorption to 14.4, absorption time to 3 hours). He said these were "conservative" numbers because he had to look up the exact settings for our AGM battery bank. Then he emailed us a few weeks later requesting that we change them to the following: float charge to 13.6, absorption setting to 14.7, and absorption time at 10 hours (600 minutes).

However, ever since implementing these setting changes, we haven't seen our batteries reach the "float" stage despite plenty of sunshine and very minimal draws on power in our cabin. Today, worried about the state of charge of the bank, we ran our generator (50A) for 9 hours, and even though the starting voltage of the battery bank was 12.5, the batteries *still* weren't fully charged after 9 hours.

This all seems totally perplexing to us, but we can't seem to get any clarification from our installer. More than a month ago he promised us a MERC-50 Remote Meter that he still hasn't delivered, which is frustrating to say the least.

Can anyone here shed some light on the issue? Namely, why does it take so long to bring a barely depleted battery bank up to a fully charged state? Are these settings correct? Is there any risk to the AGM batteries if these settings are not correct?

Many thanks for your insights.

[dgd]

What were the battery charge settings before the installer asked you to change them?
Are the batteries new and were they fully charged when installed?
What loads are in use?
The KID controller can only MAX output 30amps so on a 12v battery system that is about 400 watts maximum, so your 500watt solar panels make 400w at most in good bright conditions.
400w is not a lot of pv power for a 12v 830Ah battery bank.

You may have more success by using just two of those batteries in series for a 12v 415Ah bank then the pvs would have a more realistic chance of charging them
10 hours absorb time is not realistic, default it to 2 hours, but thats not your problem, just getting the voltage up to abs voltage.

If you needed that much battery capacity then why configure it to just 12volts?
24 volts would have been a better option then the KID could have managed 800 watts of PV power (or four of those 250 watt solar panels)
24v means that inverter would need upgraded to a 24vDC type.

dgd

ps its called Midnite KID    not   Midnite Sun Kid

[SolarMusher]

Without ME-RC or ME-ARC, this magnum can only charge to its defaut settings which are a bit low (defaut Vabs 14.6, time 2hrs, 400Ah battery capacity). As DVD said, 9hrs absorb time is too long, 3hr-3hr1/2 should be enough. A better design for this cabin would be to add a Midnite Whizbang jr batt monitor with shunt and to set your endamps to 7A max (end current for these AGM batteries is 3A). It would at least allow you to slowly charge this bank at 100% SOC when you're not there (no loads). If you need this battery capacity and want to keep it at 12V, you'd be better to add x2 more 250W panels and another kid or to change it for a Classic 150/Whizbang 96A.
I agree with DGD, a 24V inverter system with 1kw PV would have been a better choice for a kid controller.
Erik

[Halfcrazy]

Rolls Surrette batteries like a VERY long absorb time. if you doubt the values given by the installer I would give Rolls a call and get the values from them.

The reason you do not see it go to float is you have absorb time at 10hrs so the sun does not stay out long enough to get the timer satisfied.

Ryan

[kateonmars]

Thanks so much for your thoughts! To answer your questions...

>What were the battery charge settings before the installer asked you to change them?

He set the absorption voltage to 14.4 initially, and absorption charge at 3 hours -- said these were conservative values because he wasn't sure what the numbers should be for the Surrette AGMs. He set the float at 13.5. With these numbers, the system seemed to work great, and the batteries were fully topped up each day by the sun, according to the KID.

>Are the batteries new and were they fully charged when installed?

Yes, new batteries, fully charged when installed (we used the generator to charge them up completely).

>What loads are in use?

We charge two MacBook Pro laptops daily, use the internet a few hours a day (<10W), and use a 10W LED light in the morning and evening.

>The KID controller can only MAX output 30amps so on a 12v battery system that is about 400 watts maximum, so your 500watt solar panels make 400w at most in good bright conditions.
400w is not a lot of pv power for a 12v 830Ah battery bank.
You may have more success by using just two of those batteries in series for a 12v 415Ah bank then the pvs would have a more realistic chance of charging them
10 hours absorb time is not realistic, default it to 2 hours, but thats not your problem, just getting the voltage up to abs voltage.

I am very confused; I don't know why he had us use the Midnite KID when it can't even handle 500W?!

>If you needed that much battery capacity then why configure it to just 12volts?

I don't know why he thought this would be best. I'll ask...

>24 volts would have been a better option then the KID could have managed 800 watts of PV power (or four of those 250 watt solar panels). 24v means that inverter would need upgraded to a 24vDC type.

Hmmm...I will try to get answers out of him.

Much thanks for your insights!
Any further insights you can offer would be welcomed!

[dgd]

>What loads are in use?

We charge two MacBook Pro laptops daily, use the internet a few hours a day (<10W), and use a 10W LED light in the morning and evening.

These are negligible. So why is the battery bank getting so discharged?
Do you have some background loads such as a fridge or freezer?
Even allowing for the inverter to have a tare load of 25w thats only 600watts a day.
All up maybe 1 - 1.5 Kwhr per day usage with the loads you mentioned
Thats not going to have a lot of impact on a 12v/830Ah or 10Kw battery bank that is being charged with 400watts pv input for several hours a day.

Why was a 10Kw battery bank used for your system? Was it designed to cope with a week of more of no sunshine (hence little/no pv charging)?

>The KID controller can only MAX output 30amps so on a 12v battery system that is about 400 watts maximum,
...


I am very confused; I don't know why he had us use the Midnite KID when it can't even handle 500W?!

Its not the KID thats the problem. If you are only using 1.5Kwhr a day then the 500watts pv and KID combination looks pretty good.

>If you needed that much battery capacity then why configure it to just 12volts?

I don't know why he thought this would be best. I'll ask...

In meantime I'd go with the 3.5 hours absorb time Erik (SolarMusher) recommended.

dgd

[Vic]

Hi kateonmars,

Some/many AGM batteries need a very,  very long Absorb stage 8 - 12 hours,  at least on occasion to make certain that they are fully charged.   This probably does not need to be done every day.

And,  given the nature of the sun,  this usually cannot be accomplished using PVs.

Others on this Forum use AGMs,  although each manufacturer's design and requirements for charging are probably at least somewhat different from others.

Surrette Battery has excellent telephone and e-mail customer Support,  so agree that you should ask Surrette for guidance on your system charging parameters.

FWIW,  Good Luck,   Vic

[zoneblue]

800Ah for two laptops. Daily 10hr absorbs. Crikey. Sorry but this system is not well setup. Its an old school design, small pv, big storage.

But if we take the Kid and the solar, at 12v, here is what we get:

500Wp pv, means 500W/13V*0.77 derating= 30A. So fine, bang on there.
Optimum AGM battery for 30A at 12V, 0.2C -0.1C which is 150Ah- 300Ah. Round this to the nearest you have 415Ah ( remove half the bank as dgd said)  thats a 0.07C, bit low but doable. Agms like a decent charge rate.

Expected daily deliverable load is say 2.0 Wh/day per Wp. Call it 1000Wh/d. At 415Ah, daily DOD is 1000Wh/5200Wh which is about 20%, which is as expected suitable, giving you 2-3 days reserve storage.

Whereas: at two strings of 415Ah. Your charge rate is 0.03C, thats well under the recomended charge rate for even a flooded bank. Daily DOD, is 10%. Which means the bank is not even cycling hardly at all, and you should definately not be absorbing this every day. Its spending its entire existance in absorb, which is very inefficient, and hard on the bank in terms of grid erosion, and catylyst wear.

Now lets look at a better setup: Assuming for now that the batterys are the least exchangeable part of your gear.

Midnite kid, 30A. Keep the 4 batterys but put them all in series. for 24V. Buy some more PV to get somethign more like this:

1000W PV. Charge rate 0.07C. Deliv load: 2000Wh/day. Bank 415Ah. Daily DOD 20%. Get him to swap the inverter for a 24V model.

Now if you dont actually need 2000Wh per day. Then well, lets for the heck of start from scratch....

Midnight Kid (great controller). Existing 500W PV, daily load (insert what you need), lets say:

- 1000Wh/day, because thats what the pv can support, ideal battery is 25% DOD daily (2d storage) , which is  100/25*1000, or 4000Wh, at 24v is 160Ah. Charge rate is about 0.18C.

- 500Wh/day, gives you 12hrs of two laptops runtime. or 4hours of runtime plus 30Ws of LED lighting for 5 hours. Ideal battery a mere 80Ah. Charge rate, 0.36C. Too high, but pack will be charged by mid morning so thats mitigated. Use the current limiting feature if need be.

-250Wh/day. "We charge two MacBook Pro laptops daily, use the internet a few hours a day (<10W), and use a 10W LED light in the morning and evening." =3*(20+20+10)+10*7 =220Wh/d, plus a bit for luck. Battery for this: 40Ah. Now you really need to reduce the array, or output limit radically, otherwise the battery will fry.

Looks like your battery is as much as 10 times too big for your application.  And you dont even need an inverter at all. You can run all that gear off the battery, and car laptop adapters.

[kateonmars]

Thanks for your input DGD, Vic, and Zoneblue! Much appreciated.

A few more details that might be clarifying: we truly aren't running any other powered devices or appliances other than those I mentioned, to answer your question, DGD, so I'm baffled as to why the battery bank seems so drawn down. Our installer says the inverter meter should clarify things, but I don't really see how... I'm baffled here.

To boot, we live in the Canadian north, near Whitehorse, Yukon, which as you know means a surplus of sunlight in the summer months and a deficit in the winter. To this end, I believe the system was designed to cope with long stretches without sunlight.

Do these facts might change your view of the system? I'd be very curious to hear your (further) thoughts. We're quite anxious about the whole thing.

[ClassicCrazy]

It could be that they designed the battery bank larger for the long dark days. But with batteries the important thing is that you don't draw them down too deeply often .  The battery life is determined not just by age but by how many deep cycles. More shallow cycles  than deep cycles means longer battery life.

So the main thing is when the batteries get to a certain discharge , charge them back up and if solar can't do it then use the generator. The Midnite Whizbang which was mentioned once properly set up will tell you how much you have taken out of the battery and also let you know how much has been put back in . So if you used 30 percent of the capacity it would say 70%     and then if solar  charged up 10 percent more during the day you would know you were at 80 % .  Best way to really know where your batteries are at . The Whizbang also tells how much is really going in and out of your battery . The Kid without the Whizbang would only tell you how much the panels are putting out.

[zoneblue]

What i said above is that you dont have enough pv to properly maintain that battery. I suggest that in the interim, for the sake of the battery that you every two weeks do a full charge cycle with the genset. That might take some time, but if you dont do it and the SOC remains low you will kill the battery.

If your loads are not going to grow and what you have now is it, then you need a smaller battery. Short days long days, none of that changes the maths of charge rates. Days and days and days of low sun wont charge a battery any better just because its bigger. In fact the reverse applies.

The "right size" battery for your setup is 160-300Ah.

[dgd]

I would recommend you immediately disconnect two of the batteries so your bank is 12v at 450Ah.
Connect up a few more led lights and lcd tv/radio and maybe occasionally use a small microwave - one that fits with the power the inverter can make.
Change absorb to 2.5 hours then every couple of months do a 10 hour absorb using your generator.

Then in medium term.
Get the installer to change the inverter for a 24volt model
connect all four batteries in series to make a 24volt 430aH bank
Spend some $ and get another two of those solar panels so you have 1000watts pv.

dgd