[RE-wrenches] discharging Rolls batteries

[James Surrette]

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 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 
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