# Batteries in parallel

Discussion in 'The Projects Forum' started by cgama, Mar 26, 2012.

1. ### cgama Thread Starter New Member

Dec 23, 2011
19
0
Hi!
I am so sorry!! this post has nothing to do with this tread but i cant make a new thread, don't know what happened!! once again, sorry!!

I have a circuit powered by 2 12V lead acid batteries in parallel. The circuit draws 94.7 mA and after the batteries fall below 9V it stops working (it stops doing what i want it to do).
I have been reading about battery life calculations in this website, but I'm still a bit confused: the batteries that I'm using are Yuasa NP 1.2 - 12, which have a capacity of 1.2 Ah. Of course if I do a simple division it gives an absurd result... Well, in the datasheet it shows a graph about "discharge characteristic curves". Should I go through this? And was it the CA??
Here is the datasheet:

http://www.yuasabatteries.com/pdfs/NP_1.2_12_DataSheet.pdf

Another question: I have tried to measure the battery life by running it and measuring the voltages on Labview. (it lasted 6h) When measuring with the multimeter I measure one side of battery against the other to give the voltage out. But in this experiment I have measured the positive rail and the negative rail against the circuit ground, and this gave me about +14V for the positive rail and -13/14V to the negative rail. I don't even know what to make of this

Sorry about the long post. And thank you for the time and help!!!

2. ### MrChips Moderator

Oct 2, 2009
12,449
3,368
How do you fit two 12V 1.2Ah lead acid batteries into a hearing aid? That would make it somewhat heavy I should think.

3. ### cgama Thread Starter New Member

Dec 23, 2011
19
0
you dont!! like i said yesterday and today i have been trying to post a new thread and i can't
sorry for the confusion

4. ### Wendy Moderator

Mar 24, 2008
20,766
2,536
Welcome to AAC!

A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits. I have therefore given you a thread of your very own.

This was split from Hearing Aid Design

I know you are having problems, the site is experiencing difficulties, but you should have contacted a moderator, who would have helped you set up a thread

5. ### Felo Member

Feb 20, 2012
91
13
Hi, first of all, VRLA's should not ever, ever, be discharged below 10V or 1.7 VPC, as it will impact on the overall battery life expectancy.

This information comes from me working 6 years in a subsidiary of emerson power, (UPS related tech service) and all the battery manufacturers I've dealt with are very clear on this, "Do not, set EOD's below 1.7 VPC never".

The battery discharge curve, will give the best idea of how much a battery will last against a know load, but instead of amp, you must translate to Watt, it is a bit tricky as battries lower the voltage as they discharge, then again, refer to the curve.

As a side note I would recomend recharging with a constant voltage (13,7-8V) and limited current of 10% de AH capacity of the battery.

Good luck

6. ### wayneh Expert

Sep 9, 2010
12,154
3,061
By "absurd" do you mean the calculation of 12.7hrs run time, versus your observation of only about 6?

So what you're really asking is why are your batteries giving you only about half their nominal capacity?

Could be lot of reasons, including inadequate starting charge and/or a few excursions below 9V have degraded you battery's capacity.

I suggest you charge each battery properly - with a description of how you did that, for the experts here - and test each battery individually. Measure the time to to decay from full charge to no lower than 10V. I'd suggest using a defined, DC load. (I'm not convinced your load is a steady 95mA load.)