How long will it run?
10-02-14, 01:59 PM
#1
Full Member
Thread Starter
Join Date: Jan 2010
Location: West Sussex
Posts: 290
Bikes: Ridgeback Steel Tourer,Recumbent SWB,Steel Road,,Raleigh Twenty,Elephant Bike,Pashley Pronto TNT.
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 21 Post(s)
Likes: 0
Liked 5 Times
in
4 Posts
How long will it run?
How long will a 6volt 4AH battery,run a 3w Led light? thanks.
10-02-14, 02:12 PM
#3
Señior Member
Join Date: Sep 2005
Location: Michigan
Posts: 13,749
Bikes: Windsor Fens, Giant Seek 0 (2014, Alfine 8 + discs)
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 446 Post(s)
Likes: 0
Liked 8 Times
in
7 Posts
Teaching you how to fish:
P = I * E
watts = amps times volts
so amps = watts divided by volts
3 watts at 6 volts = 3/6 = 1/2 amp
an amp hour means it'll deliver an amp for an hour, or half an amp for two hours etc
1/2 amp from a 4 amp-hour battery = 8 hours.
Note that you have to derate batteries if you're trying to draw a ton of current from them because they have an internal impedance that will cause a lot of their energy to be converted to heat, but you're nowhere near that.
Also, never trust ratings. 8 amp hour batteries will give you that, maybe, after they've been cycled a few times, until they start to die.
P = I * E
watts = amps times volts
so amps = watts divided by volts
3 watts at 6 volts = 3/6 = 1/2 amp
an amp hour means it'll deliver an amp for an hour, or half an amp for two hours etc
1/2 amp from a 4 amp-hour battery = 8 hours.
Note that you have to derate batteries if you're trying to draw a ton of current from them because they have an internal impedance that will cause a lot of their energy to be converted to heat, but you're nowhere near that.
Also, never trust ratings. 8 amp hour batteries will give you that, maybe, after they've been cycled a few times, until they start to die.
__________________
Work: the 8 hours that separates bike rides.
Work: the 8 hours that separates bike rides.
10-02-14, 02:17 PM
#4
Senior Member
Join Date: Dec 2010
Posts: 8,951
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 14 Post(s)
Likes: 0
Liked 13 Times
in
12 Posts
Not enough info. Need to know the V/I characterstics of the LED and any associated circuitry. Based on LED voltage drop of 3.5 volts , I'd estimate worst case as something under 4.5 hours, and best case as much as 8 hr to battery exhaustion. It's never good to exhaust a battery so cut those down by at least 20%.
10-02-14, 02:25 PM
#5
Full Member
Thread Starter
Join Date: Jan 2010
Location: West Sussex
Posts: 290
Bikes: Ridgeback Steel Tourer,Recumbent SWB,Steel Road,,Raleigh Twenty,Elephant Bike,Pashley Pronto TNT.
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 21 Post(s)
Likes: 0
Liked 5 Times
in
4 Posts
Thanks everyone,I can now use my raleigh led dynamo light as a replacement for my old fishing headlight.I always take a spare,but its good to have an idea of the run time.
Thread
Thread Starter
Forum
Replies
Last Post
larryakoch
Electric Bikes
2
09-24-15 11:29 AM
