Question on Absorb Time and Voltage Classic 200

Robert_W · August 2014

Hi folks, forgive any noob stupidity but I figure if I don't ask I don't learn.

Just added a Midnite Classic 200 and 4 Trojan 6 volt T-125's in series...245 Amp hours @ 24V to supplement power to an out building on an existing 570 watt panel system that is powering a well pump. The pump only runs rarely to fill a 1500 gallon tank so I it was time to put the panels to use. Well and batteries are on separate manually switched circuits. This system is primarily for small lighting, small propane heater fan, and emergency back up. Also to keep misc odd batteries charged. At the moment it probably needs to be powering more cause it won't get much use and I realize that the batteries need to be used for best performance down the road. I plan on a chest freezer / fridge convert at some point and I'm sure I'll find more along the way but for now it's what it is.

Put a Samlex 1500 watt inverter on the same terminals as the Classic 200. Guess it could have gone to opposite -+ but assuming this doesn't matter cause it works. Right?

So......all is hooked up and working. (First time through which is always a positive.)

The Trojans list their charge rate for a 24 volt system @ 29.6 Daily Charge (Absorb) 26.4 Float and 31.0 EQ. http://www.trojanbattery.com/BatteryMaintenance/Charging.aspx
This seems high when compared to others. Is this OK? Are others having good luck with this high of a voltage setting?

On the Classic 200 there is supposed to be ...according to the manual...http://www.midnitesolar.com/pdfs/Classic_Just_the_facts_RevD.pdf ....an Absorb Minimum AND Maximum time. But on mine all I have is the Maximum available. There is no Minimum in the settings. Assuming maybe it needs a firmware update. But really don't want to hassle with that unless truly needed. I've read here that a general rule of thumb is 30 minutes for each 100 amp hours of capacity. So should I just go with say 1:30 minutes on the Maximum Absorb setting?

Also wondering about Ending Amps and Rebulk settings. How low should these be set on a 24 volt system?

I noticed tonight that as the sun went down the Classic 200 would struggle and switch on and off at very low wattage like 5 watts and .2 amps or some such and go into Bulk MPPT mode. I'm thinking this can't be good. Or maybe it's normal. Don't know. Maybe the above setting keep that from happening?

Can someone recommend a basic configuration and I can tweak from there? What is the lowest voltage I should see on a 24 volt system before it goes into Bulk MPPT mode? For that matter what is the lowest safe battery voltage period. There must be some voltage point I don't want to get them below.

And it came with the Whizband Jr. Should I add a shunt to this system and use this or is there an easier more generic general way to check battery usage and or capacity? Just how do I tell how much power is left in the batteries?

Thank you.

BB. · August 2014

Re: Question on Absorb Time and Voltage Classic 200

How does your specific gravity look? And water usage?

-Bill

Cariboocoot · August 2014

Re: Question on Absorb Time and Voltage Classic 200

Start with Trojan's recommendations. Yes, they are higher than most batteries. It is not a mistake in the specs. Be sure you have the RTS in place.

Vic · August 2014

Re: Question on Absorb Time and Voltage Classic 200

Hi Robert,

The Min Absorb time setting has been removed from the Classic. The Max Absorb time setting remains.

You should try using End Amps, in the Advanced menu. You should install the WBjr. You will need a Deltec 50 mV 500 A Shunt, as you know. This will allow precision termination of Absorb, based on the actual charge current into the batteries. Although, if you have light/predictable loads on the batteries, End Amps from the Classic itself will probably suffice in the interim.

Deltec Shunt:
http://www.solar-electric.com/batteries-meters-accessories/metersmonitors/mkb-500-50.html

Rebulk setting is very system specific, and can probably remain at its default.

The exact Absorb time required to fully recharge the batteries depends on the Depth Of Discharge (DOD) that the batteries experienced in the previous discharge. This can vary from day to day.

For Flooded batteries, the correct EA setting is usually between 2% and 1% of 20-hour Capacity of batteries. If you have two strings in parallel, this EA would be twice that percentage. You will need to experiment to find the correct EA setting.
Rebulk setting is very system specific, and can probably remain at its default.

More later. Have Fun, Vic

Robert_W · August 2014

Re: Question on Absorb Time and Voltage Classic 200

RTS in place? Acronym for?

Bill, just hooked this up in the last 2 days. So no water loss yet. Hydrometer was on back order. Still waiting for it.

So 1:30 minutes is a good rough estimate starting point for the Max Absorb time?

And what is the lowest voltage I should ever see?

Thanks

Oops..wrote this while Vic was replying.

So the end of day low light constant switching into Bulk MPPT...will that ever stop?

Thanks Vic.

BB. · August 2014

Re: Question on Absorb Time and Voltage Classic 200

Remote Battery Temperature Sensor.

If the batteries are discharged daily--Relatively moderate discharge levels--2 hours minimum (75% state of charge or less)

If heavy discharge, 4 hours (50% state of charge)

That is what I would suggest starting with.

-Bill

Robert_W · August 2014

Re: Question on Absorb Time and Voltage Classic 200

Thank you Bill. Much appreciated.

SolarMusher · August 2014

Re: Question on Absorb Time and Voltage Classic 200

BB. wrote: »

Remote Battery Temperature Sensor.

If the batteries are discharged daily--Relatively moderate discharge levels--2 hours minimum (75% state of charge or less)

If heavy discharge, 4 hours (50% state of charge)

That is what I would suggest starting with.

-Bill

Forget time and listen to what Vic said. Buy a shunt and install your WBjr, don't forget to update your Classic to the last firmware first. See Midnite website. End amps between 1-2% and time for 3 to 4 hours. Check your real end current on the WBjr display and adjust EA value.
Erik

Vic · August 2014

Re: Question on Absorb Time and Voltage Classic 200

Hi Robert,

1. You can buy an inexpensive Glass Hydrometer at an Auto Parts store, the next time that you are in town (perhaps a NAPA store?). This will tide you over until the one on BO comes.-- I might buy two of them at the parts store, so you might be able to "vote" them.

2. If you leave the ReBulk set at 8 V (or whatever the default is), then as the sun starts to wane, the Classic should go from "Float", to "Float MPPT". This just means that there is not enough sun to maintain the Float voltage, but the Classic is still producing power for the batteries/loads.

3. ReBulk, when set a bit below your Float voltage setting in the Classic, will cause the Classic to attempt a new Bulk charge cycle on a given day. You may want this to happen, if there has been some cloudy weather, and you want the Classic to try to get the batteries more fully charged before evening. But, generally, the fewer full-charge cycles that your batteries endure, the better - IMO. The ReBulk strategy depends on how much PV capability and battery capacity your system has, and just what your night demands will be/are on your system. Believe that ReBulk is one of the last things that you might try to play with, when you know much more about how your system has been performing.

End Amps is a very good general way to end Absorb, because it looks at the current that is going into the batteries (with the WBjr installed and FW updated), or at least the current that the Classic is delivering toward the batteries (without the WB, this is the battery charge current PLUS any current into the inverter and/or loads).

A timed Absorb is better than nothing, and generally, a bit of battery overcharge is much better than general undercharging. However a timed Absorb may be a bit off from the ideal on many days ... a bit of a crap-shoot.

FWIW, my opinions, Vic

Robert_W · August 2014

Re: Question on Absorb Time and Voltage Classic 200

Thank you gentlemen. I'll make the adjustments. Shunt is ordered.

Question on Absorb Time and Voltage Classic 200

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