[RE-wrenches] Info On 2 V batteries Please

Wed Nov 28 12:08:03 PST 2012

I didn't want to originally load you guys down with minutiae, but we have been having problems keeping the battery bank fully charged. We would put it on the charger and after a while it settled down to about 17A, which is about 3.1-3.3% of the rated capacity. The total series voltage was 57.9 V. 

We have had a couple of service calls from "Tower of Power". First guy came out Monday and determined that two of the batteries had been installed backwards! The second guy came out yesterday and replaced the reversed cells. He said that the replacement cells were fully charged but they weren't (rested they were at 2.079 V/cell). They recommended that we put it back on the charger for four hours -- I am concerned about this approach, does it work to charge a 24 cell bank, with two weak cells in the series? Well, we did for about 30 minutes and got the following readings, while charging:

V=57.9 V, 17 amps. Original cells varied around 2.38 V to 2.41 V under charge, with the two replacement cells at 2.13 V to 2.14 V. I stopped the charge last night, to get more information on how to proceed. 

This morning, the readings were: original cells at 2.128 V to 2.169 V and replacement cells at 2.045 V and 2.063 V.

Under the circumstances, how should we bring these two replacement cells up to snuff, so that we can operate the system going forward?

- Peter

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Larry Crutcher, Starlight Solar Power Systems
Sent: Wednesday, November 28, 2012 9:06 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Info On 2 V batteries Please

Peter,

To your first question: fully recharging any lead acid battery as soon as possible will give you longer cycle life. Waiting to charge and/or deep discharges lead to shorter life. If you have the proper 3-stage charger, leave it on the battery until you needed to use the forklift.

100% SoC voltage after appropriate rest varies among batteries. I have worked with a few forklift batteries in off grid homes. Flooded rest at 2.117 VPC. For AGM about 2.183 VPC. (77°F)

As I have posted in the past, most AGM battery can easily withstand up to 5C initial charge rate. Proper voltage and time is the more important factor when charging AGM's. 

Larry Crutcher
Starlight Solar Power Systems

On Nov 27, 2012, at 2:31 PM, Parrish, Peter wrote:

We recently purchased a battery powered forklift, with 24 ea. 2V batteries. Approximate dimensions: W=5", L=6-3/16", H=~21" (hard to tell). Enersys is stamped on the top.

The battery supplier claims the batteries are "24-85-13" but this refers to a 24V battery as far as I can tell. He also claims that the batteries are rated at 510-550 A-hr. I am assuming that the lower number is for 6 hours discharge.

I would like to know more about the batteries. Also, how to discharge / charge them. Should they be run down to 20% SOC and then fully charged? What if we don't use the forklift for a week at a time?

Based on my experience of using AGM batteries, it would seem that the Bulk charging rate should be some percentage (e.g. 20%) of the 6-hour ampacity, then there is a constant voltage absorption charge (e.g. Vabs=2.385 V), and a switch to Float when the charging current drops to some low percentage (e.g. 0.5% of capacity), and the Float voltage being 2.125 V. Again everything at 25 deg C. It seems like the forklift guys like to refer everything to a 6 hour capacity, which may be related to the maximum typical daily usage.

What is the relationship between Voc and SOC after resting the battery for 6 hours at 25 deg C?

Thanks in advance for your help, guys.

- Peter Parrish

Alternative Energy Department
College of the Canyons
peter.parrish at canyons.edu
O: (661) 362-3888 C: (323) 839-6108
_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org