ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

Topic Options
Rate This Topic
#127539 - 08/21/01 02:17 PM Amp Hours of Emerg. Lt. Battery
Frank Cinker Offline
Member
Registered: 07/29/01
Posts: 311
Loc: Pennsylvania
A particular emergency lighting unit (battery pack) is rated for 100 watts. Remote lighting heads will also be fed. The voltage is 6VDC. I'm trying to understand "amp hours" which I see listed on replacement batteries for emerg. lighting units. For this 100 watt unit, how many amp hours should the battery (batteries) be rated for?
Top
Tools for Electricians:
#127540 - 08/21/01 02:39 PM Re: Amp Hours of Emerg. Lt. Battery
Anonymous
Unregistered

100 watts @ 6 V for 1 hour is 16.67 A·hr.

If your actual wattage is 50, a 16.67 A·hr battery will last two hours.

What is your actual wattage and how long do you want them to remain fully lit?
Top
#127541 - 08/21/01 04:07 PM Re: Amp Hours of Emerg. Lt. Battery
Frank Cinker Offline
Member
Registered: 07/29/01
Posts: 311
Loc: Pennsylvania
eg. 75 watts for 90 minutes.
Top
#127542 - 08/21/01 05:11 PM Re: Amp Hours of Emerg. Lt. Battery
Anonymous
Unregistered

75 W <= 100 W

75 W @ 6 V = 12.5 A

12.5 A * 1.5 hr = 18.75 A·hr
Top
#127543 - 08/22/01 03:09 AM Re: Amp Hours of Emerg. Lt. Battery
Frank Cinker Offline
Member
Registered: 07/29/01
Posts: 311
Loc: Pennsylvania
Thank you. I now understand.
Top
#127544 - 08/22/01 06:31 PM Re: Amp Hours of Emerg. Lt. Battery
Redsy Offline
Member
Registered: 03/28/01
Posts: 2056
Loc: Bucks County PA
One other thought -- I remember reading that the amp-hour relationship is non-linear.
A 10 amp hour battery will deliver 1 amp for 10 hours, but will not be capable of delivering 10 amps for a full hour.
Top
#127545 - 08/22/01 06:58 PM Re: Amp Hours of Emerg. Lt. Battery
Anonymous
Unregistered

Correct. That's why it is important to note that his 75 W load is less than or equal to the 100 W rating of the battery. If he had a 200 W load, it would severely underperform. If he had a 10 W load, it would significantly overperform.
Top
#127546 - 08/24/01 03:16 AM Re: Amp Hours of Emerg. Lt. Battery
Frank Cinker Offline
Member
Registered: 07/29/01
Posts: 311
Loc: Pennsylvania
I'd like to give one more example. A 36 watt, 6VDC emergency lighting unit has it's battery missing for one reason or another. I would order a 9 amp hour battery based on the actual wattage (36) fully lit for 90 min. Am I correct?
Top

Member Spotlight
Member Since: 08/22/05
Posts: 44
New in the Gallery:
SE cable question
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box


Who's Online
0 registered (), 41 Guests and 9 Spiders online.
Key: Admin, Global Mod, Mod
 
New in the Gallery:
SE cable question
 
Top Posters (30 Days)
Admin 47
HotLine1 43
gfretwell 19
Ruben Rocha 12
Trumpy 9
 
Newest Members
Scotto, Freecrowder, clee512, Jdscott2005, FAIZAN

ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals