Power of a small 12v - Page 1
Forum section: electronics / beginners

author: MrZwing
author_rank: Regular Contributor
timestamp: October 25, 2014, 09:50:47 pm
content: I have a question about a really small 12v battery of this typeeBay auction: #http://www.ebay.com/itm/2-x-GP27A-27A-12V-Small-Car-Alarm-Door-Bell-Battery-/400787804490?pt=UK_In_Car_Technology&hash=item5d50d0914aI wonder is it enough to power a small Rocket igniter or will the battery give out before that?/MrZ

author: Simon
author_rank: Unknown
timestamp: October 25, 2014, 09:54:32 pm
content: The listing has been removed and you's have to tell us what power the rocket igniter requires

author: rexxar
author_rank: Frequent Contributor
timestamp: October 25, 2014, 09:59:37 pm
content: Quote from: MrZwing on October 25, 2014, 09:50:47 pmThose are generally a bunch of button cells in series. AFAIK, those can only provide tens of milliamps of current. The model rocket igniters I've seen use a few 1.5v alkaline cells in series, which can easily provide >2A in short bursts. According tothisPDF, igniters require several amps (I didn't read it very thoroughly).That 12V battery would probably not be able to deliver enough current to set off the igniter.

author: AG6QR
author_rank: Frequent Contributor
timestamp: October 26, 2014, 05:57:04 am
content: Don't know specifics about that battery, but if its internal resistance is too high to fire an igniter directly, it might be able to charge a capacitor that could do the job.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 26, 2014, 06:06:44 am
content: I concur with AG6QR. That battery by itself (approx the size of a single AA cell) would have the momentary power to heat a rocket igniter.It is possible that you might be able to cobble a circuit with a storage capacitor, but it would seem much easier to simply use a properly-rated battery.

author: IanB
author_rank: Super Contributor
timestamp: October 26, 2014, 06:10:35 am
content: According to a typical data sheet of an A27 battery, it has a capacity of 22 mAh and an expected continuous drain of 0.36 mA (360 µA). So no, it does not have the power to do anything other than run very low drain electronic devices.http://data.energizer.com/PDFs/a27.pdf

author: Simon
author_rank: Unknown
timestamp: October 26, 2014, 07:49:47 am
content: Just use a pack of AA's

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2014, 08:32:01 am
content: Those would not work, use either an alkaline 9V battery ( which can deliver 5A for a few seconds when new), or use 2 AA cels in series , as most ignitors need only 2V across them to fire. The 12V requirement is because of long thin cabling with high resistance. Short cable with a battery box ( with an arming switch that will both disconnect the battery and short out the output) and 2 or 3 AA cells next to the rocket, with a relay and a long cable to the remote fire switch will probably work best.

author: Psi
author_rank: Super Contributor
timestamp: October 26, 2014, 08:34:43 am
content: If you add a supercap to your pack of AA's with a series resistor it will increase the lifespan enormously.This way the AA doesnt have to provide huge currents, it only has to keep the supercap charged.

author: Tandy
author_rank: Frequent Contributor
timestamp: October 26, 2014, 09:56:15 am
content: Dry batteries typically have a high internal resistance preventing them from delivering a high current. For best results you are better off using a rechargeable such as a NiMH as they have much lower internal resistance.

author: MrZwing
author_rank: Regular Contributor
timestamp: October 26, 2014, 03:31:05 pm
content: Thank you for all the answers.i will build some igniters and experiment with diffrent batteries and diffrent gauge wire for the igniter and se what results i get./MrZ