How to set absorb time?

Donut roller

I have a midnite classic 250 and I don't want to overcharge the 16 battery 6v bank. Will the controller fry the battery's if it is set to absorb for to long? Or does it sense their getting full and go into float? I have looked for hours and the setup disk doesn't work w macs?

Vic

Re: How to set absorb time?

Hi D r, Welcome to the Forum,

The setup disk is basically the manual, and a number of other files. All/almost all of these are available on the MidNite Solar site:
http://www.midnitesolar.com/doc_prod_list.php?menuItem=products&productCat_ID=21&productCatName=Charge Controllers for Solar, Wind, Hydro

The following link details all of the current documents on the MidNite site:
http://www.midnitesolar.com/documentIndex.php

The Absorption time required is based on the Depth Of Discharge that the battery has experienced, so the ideal Abs time will vary, often being a bit or very different from day to day. This is probably why you have not found any exact data on it.

Using Ending Amps on these Charge Controllers can be an almost ideal choice to end Absorb. The only issue there is that any loads on the inverters looks to the CC as battery charge current. Midnite will be introducing, very soon, a Battery Monitor (WhizBang) that will use a Shunt to measure the current actually going into the battery as net charge current, and tell the Classic when your EA setting has been reached. So you are lucky to have a Classic IMHO.

For now, you can probably find a good enough EA setting to do the job, especially if your batteries are Flooded (with removable caps). This way, you can measure the actual State Of Charge of EACH cell with a Hydrometer or Refractometer.

I DO hope that all of those batteries are on a 48 volt, two battery string system -- fewer strings of batteries are generally better. ONE string is best, in my opinion.

Please tell us more about your system. Doing a Signature line now, will save a lot of typing for you, and allow any questions to be answered more quickly (without asking you to detail this and that), and allow less guessing on the part of responders. Thanks, Vic

Donut roller

Re: How to set absorb time?

Thanks for the awesome reply! Will the classic fry my battery's if I set it to absorb to long? Lets say i set it for 5 hrs and I'm in jail for 5 days are my battery's toast? Since no load was used and I'm slamming in 1.4 kw into bank ? With the gc2 Costco golf cart battery's 2 48 v banks tied in parallel what would be a the swag number for ending amps? With no load? Does the classic have fail safes for dummies ?

Vic

Re: How to set absorb time?

Hi D r,

Forgot about that question. Great that your batteries are Flooded, and that your system is 48V.

Nominally, GC-2 are considered to be about 225 Ah per string. So, on your two string 48 V bank, this is about 450 Ah total. Normally, at reasonable Absorb voltages, end of absorption is between 1 - 2% of this total Capacity, or between 9 and 4.5-ish Amps of charge current into the batteries. For the DIFFERENT Flooded batteries here, we use 1% of C. However, this is assuming that there are NO loads on the batteries. A constant load can be compensated for, as can short-term ntermittent loads. Long term loads like pumping water for hours can cause the Absorption stage to be elongated, as the CC may never see the EA value, as this load does not switch off at a time around the time when the correct EA value is reached.

The Abs voltage has an effect on the required EA finishing current. If your GC-2s are 1.265 SG nominal electrolyte, then your Abs voltage would be in the range of 58.5 or perhaps 59 V from my very limited experience with older Trojan GCs. You might try about 6 - 7 Amps as an initial EA setting on the Classic, and MONITOR THE SGs with YOUR HYDROMETER, daily, or even during the day to see how this is working.

It is ESSENTIAL that you use some SG measuring device, either a good Hydrometer or a calibrated Refractometer.

Be certain to use the Battery Temperature Sensor that came with the Classic. Place it in the center of the battery bank, between the two individual strings, midway down the case on one battery.

There is a Maximum charge time setting in the Classic 'Charge' Menu. This will cause the Classic to end charging for that charge cycle, regardless of the EA setting.

Just keep an eye on the SGs, and be prepared to change the EA value, Max Time or, perhaps the Absorb voltage.
Others here will have a better idea of the correct Absorption voltage setting required for your Costco GC-2s, and quite possibly the EA value for your batteries.

Good Luck, Vic

mike95490

Re: How to set absorb time?

Donut roller wrote: »

..fry my battery's if I set it to absorb to long? Lets say i set it for 5 hrs and I'm in jail for 5 days are my battery's toast? ....

It will likely get the bank pretty warm, shortening the battery life from heat. Somewhat ameliorated by having a temperature sensor attached to an inner battery in the bank.

And you will consume a lot of water, by dissociation into O2 and H2. Not too bad, unless levels drop enough to expose plates and they dry.