ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
dsk 13
Admin 4
Recent Posts
electircal ageing test on IPC
by SIAME. 08/15/17 02:43 AM
electrical aging test on IPC
by gfretwell. 08/15/17 12:27 AM
Bathroom electrical
by gfretwell. 08/14/17 02:05 AM
"Line level" audio on Cat 5?
by gfretwell. 08/08/17 10:39 PM
Fire alarm phone lines and color coding
by gfretwell. 08/08/17 10:26 PM
New in the Gallery:
Housebilding DIY wiring
Popular Topics(Views)
239,891 Are you busy
175,467 Re: Forum
167,743 Need opinion
Who's Online Now
0 registered members (), 27 guests, and 9 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#215746 - 07/12/15 08:48 PM Batteries connected in series  
twh  Offline
Member
Joined: Mar 2004
Posts: 916
Regina, Sask.
I had a battery go bad in a fire alarm system. It has two 12 batteries in series to make 24 volts.

Because it was at night on a weekend, I took one battery out of a emergency light and installed it. The combined voltage was 24 volts but when connected and being charged the voltages were 14 volts across the charged battery and 10 volts across the discharged battery. So, I had to rob a second battery out of another emergency light.

It made me wonder:

If I install two new batteries and they do not have equal charge, like one being fully charged and the other discharged, will the charged battery prevent the discharged battery from charging?

Before I install the new batteries, would it make a difference if it let them sit in a parallel connection for a couple hours so the charges balance out?


Work Gear for Electricians and the Trades

#215749 - 07/13/15 01:16 AM Re: Batteries connected in series [Re: twh]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,103
Estero,Fl,usa
Batteries connected is series have to be the same type and same state of charge. Virtually all batteries are cells wired in series but they were the same when it was new and theoretically they stay relatively the same. When one cell gets weak, the battery is toast. You are just seeing that effect with separate batteries.
There are troubling problems with batteries in parallel too although GM tried it with some of the Diesel cars. You pretty much had to replace them in matched pairs too.


Greg Fretwell

#215750 - 07/14/15 12:31 AM Re: Batteries connected in series [Re: twh]  
JoeTestingEngr  Offline
Member
Joined: Nov 2005
Posts: 785
Chicago, Il.
http://www.mpja.com/2-Ohm-120W-Power-Resistor/productinfo/17786%20RS
I have one of these with test leads attached, to test my inverter batteries at work. I clamp my Fluke 187 leads onto the lugs. A charged battery should still be above 12V with the 6 Amp load imposed. I'm referring to 7.5AHr & up batteries. It's not good to discharge your VRLA batteries below 1.75 Volts Per Cell(VPC). It's normal to see 14 or more volts across bad batteries on charge, and 10V or less when you disable the charger. With your FACP, it's supposed to run for 24 hours on standby and then 5 minutes in alarm. You should definitely swap them out together or you won't likely make the requirement. Remember that brand new batteries will self-discharge and die on the shelf, so you should float charge them or top them off at least every 6 months.
Joe



Member Spotlight
mersadrad
mersadrad
Montreal, Quebec, Canada
Posts: 28
Joined: March 2011
Show All Member Profiles 
Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.014s Queries: 15 (0.002s) Memory: 0.7533 MB (Peak: 0.8767 MB) Zlib enabled. Server Time: 2017-08-18 07:03:24 UTC