Batterypack advice 12V 7 Amp high current

[Walterk]

What battery-pack shall I take for a portable searchlight ?

Its a 12V 75W Halogeenbulb, and I want a runtime of 15 minutes.
(The 15 mins. is a backup, a plug to ships-battery is alternative power.)
Size and weight are less important as costs (no budget in mind yet ).

My first thoughts are Nimh-cells, or lead-acid baterys, the grey plastic boxes. I dont know what the limits for peak-currents are for different sorts of batterys.

Theoretically 75Watt at 12V makes 6,25 Amps.
For 15 minutes that means 1,6 Ah holding capacity, but it is probably not that simple .....

As I have little knowledge about batterys advice is welcomed!

 

[Mr Happy]

Here in the US many shops like Wal-Mart sell cheap and cheerful 12 V spotlights using 55 W, 75 W, 100 W or more halogen bulbs and a simple lead-acid battery with charger. You could quite cheaply buy one of those and cannibalize it for the battery and charger, or even use it as it comes. I don't know if they can manage 15 minutes run time though.

 

[Archie Cruz]

Any of the Tekkeon MP series. I like MP3450 and MP 345i
Welcome to Lithium Polymer :twothumbs

 

[Mr Happy]

Keep in mind that whatever battery choice you make you need to add charging into the equation. You can't just buy a battery, you have to buy a battery and charging system together.

 

[kramer5150]

cheapest solution would be this:
http://www.batteryspace.com/sealedleadacidbattery12v75ah20hrsforupsseascooterande-bikes.aspx

or this:
http://www.batteryspace.com/sealedleadacidbattery12v10ah120whs.aspx

Charge with this:
http://www.batteryspace.com/leadacidsmartcharger10afor12vleadacidbatteryworldwideuse-1.aspx

LiFePO4 would be killer:
http://www.batteryspace.com/lifepo4...with10timeslongerlifeand597lighterweight.aspx

 

[Nubo]

Here's a link to the spec sheet for a 12V 7AH SLA battery.

http://www.zbattery.com/GPL1272F2FR.pdf

You can see from the spec charts that this one will give about 30 minutes runtime at a 7 amp discharge (1C = 7amps for this battery). It may seem odd that's only about half of the rated amp-hours. But amp-hour ratings are usually tested at a low current draw (.05C). 7 amps is pretty high, but well within this battery's ability. 30 minutes is twice what you're looking for so there's a good margin. Though you can see that the voltage drops below 12 at 10 minutes, so the light will be not quite as bright, though probably acceptable out past 20 minutes. For a longer, flatter discharge curve, you could go with an even larger capacity battery, say 12 or 13AH.

Most decent 12V 7AH SLAs will probably be comparable to the example above.