[RE-wrenches] discharging Rolls batteries

Wed Jan 13 12:14:59 PST 2010

Hi Jamie,

How do these values correlate to the larger Rolls batteries? We have a
number of the 2-KS-33's out there along with other various sized large Rolls
battery banks.

Sincerely,

Chris Worcester

Solar Wind Works
NABCEP Certified PV Installer
Phone: 530-582-4503
Fax: 530-582-4603
www.solarwindworks.com <http://www.solarwindworks.com/> 
chris at solarwindworks.com
"Proven Energy Solutions"

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of James
Surrette
Sent: Wednesday, January 13, 2010 11:43 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] discharging Rolls batteries

Hi Hugh & Wrenches, 

Regarding the charge voltages you sited, you've got the gist. 

As battery temperature drops, you need to increase the charge voltage to
properly charge and, conversely, as temperatures rise, voltage needs to be
decreased to reduce the risk of overcharging. 

I believe the range we site to accommodate for temperature is (in C); 

0-16C: 2.5VPC 

17-27C: 2.4VPC 

28-40C: 2.36VPC 

These are your max bulk / absorb voltage settings. 

Regarding a low voltage disconnect, there is a significant difference
between on load and at rest voltages at 50% SOC. 

Below is a table of a cell being discharged at a known constant load (C/20)
over time at 25C; 

SOC        VPC 

100%       2.1 

75%         2.01 

50%         1.93 

25%        1.84 

0%          1.75 

Please note, this is for a cell(s) under constant load and at 25C.  If the
load increased, you would see lower voltages more quickly,  Moreover, once
the load is removed, resting voltages will increase dramatically, i.e.
1.75VPC on load will equal ~1.95VPC at rest.  If you were using 2.0VPC (on
load) as your cut off, you would only have been able to discharge ~25% -
which does not include capacity reduction due to temps <25C.......and I know
they are lower than that here! 

Hope this is of some assistance. 

Regards, 

Jamie 

James Surrette

Surrette Battery Co. Ltd
1 Station Rd.
Springhill, NS, CAN
B0M 1X0

Direct: 902.597.4027
Fax: 902.597.8447

>>> Hugh <hugh at scoraigwind.co.uk> 1/13/2010 2:26 PM >>> 

Hi wrenches, 

I have been selling and using a few sets of Rolls 4000 series S530 

batteries lately. 

I have downloaded the Solar Battery manual from
<http://www.rollsbattery.com> www.rollsbattery.com 

It's very interesting.  At 17 degrees C you need to charge at 14.4 

volts.  At 16 degrees it's 15 volts.  Hmm, Ok I get the idea.  I am 

certainly learning to compensate my temperatures this winter. 

I did a search in the document for the word 'discharge'.  I am 

cutting off at just below nominal voltage and starting my generator. 

I do not get much capacity.  A customer has suggested that a lot of 

the discharge capacity is to be had at 11.5 volts (he has a 12v 

system obviously).  Hmm.  Sounds a bit harsh.  But what voltage 

should I be considering to be 50% discharged, and time to start the 

genny?  And in a hard frost, the same voltage? 

No mention of discharge in the solar battery manual.  Any ideas anyone? 

Please don't tell me to buy an amphour meter (or worse still to sell 

them).  Those things are way too confusing to calibrate.   I can tell 

you that I am not getting many amphours out of my batteries in these 

low temperatures before the voltage per cell drops below 2. 

What do I tell my customers about the end-of-discharge voltage for 

sustainable cycling of their Rolls batteries?  And is it temp 

compensated? 

thanks 

-- 

Hugh Piggott 

Scoraig Wind Electric 

Scotland 

 <http://www.scoraigwind.co.uk> http://www.scoraigwind.co.uk 

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