Boost converter 1.5V (or 3V) -> (12V, 40V]

[roblkc3]

Hi,

I would like to build a light-weight circuit that, from 1 or 2 1.5V AA batteries is capable of generating a 2-3 seconds impulse in the 12-40V range (the higher, the better). Is there a very easy way of doing that? I saw many boost converters on the net, but they either output a lower voltage, or they are very complex.
Ideally, the impulse has to be driven by a switch and should not empty the batteries in a single shot (I would like, let's say, a dozen of these impulses at least)...
Thanks a lot in advance!!
Rob

[jeroen79]

It would be useful to know the purpose of these impulses.

When you say 12V-40V range, does that mean that the exact voltage doesn't matter?
The pulses would last 3s, how long can the off time be?
What current will be drawn during the pulse?

My first suggestion would be some cheap Chinese boost dc-dc converter.

[roblkc3]

No exact voltage required, the higher the better (and can vary between over time).
Ideally between 1 and 5A (again, the higher the better and no precision/stability over time required).
No precision for the time either, roughly 3s.
I would like to use it to "burn" a resistor for fireworks ignition... 

[jeroen79]

Will this be professional fireworks?

Why do you need to boost it to 12-40V?
If you choose a smaller resistor/heater you can power it directly from the battery at a higher current.

You could make a simple boost circuit to charge up a large capacitor and then dump it's charge into the igniter.
https://en.wikipedia.org/wiki/Boost_converter

[Gyro]

You need to step back a bit and look what you're asking...

At the bottom end of your range, 12V @ 1A = 12W,  12V @ 5A =60W. At the top end of the range, 40V @ 1A = 40W, 40V @5A = 200W 

Now you might just squeeze 12W out of a pair of AA cells into a direct load (3V @4A) but given that you are starting at a low input voltage, efficiency of a simple boost converter probably wouldn't be that good. If you assume 50% efficiency as a starting point (maybe pessimistic) then you're looking at 24W input, probably not achievable.

Your best bet would be to simply buy 8-10 AA cells and put them in a holder. Probably more reliable too given what you are trying to do. Lighting fireworks with resistors doesn't sound like a very safe hobby!

[Gyro]

Will this be professional fireworks?

Why do you need to boost it to 12-40V?
If you choose a smaller resistor/heater you can power it directly from the battery at a higher current.

You could make a simple boost circuit to charge up a large capacitor and then dump it's charge into the igniter.
https://en.wikipedia.org/wiki/Boost_converter

I can understand the wish to use a higher voltage. 3V would mean very high losses in the wiring - I certainly wouldn't want to be that close.

I suspect that the capacitor would need to be pretty heavy to supply enough current to get a resistor up to ignition temperature - a proper ignitor, maybe.

[capt bullshot]

Take a look here for a starting point:

http://electronics.howstuffworks.com/camera-flash3.htm

Build a simple converter circuit that way, but use less secondary windings on the transformer. A circuit like this will suck relative constant power off the battery and push it into the load (more current at lower voltages, less at higher voltager). The maximum power that one can draw from a AA primary cell is quite limited, maybe 2 or 3 Amps if the battery is fresh, the voltage will heavily drop under this load. You may want to consider to use beefy rechargeable cells ("good old" NiCd perform quite well here).

[roblkc3]

Thanks for all the replies! I'll explore a bit what capt bullshot suggested and see what I can get...
Anyway, no professional work here, just playing around (and no real risk, we are talking about freely available fireworks, no stuff requiring a license...)

[Red Squirrel]

If you get to pick the type of battery (ex: you're doing this from scratch) I would go with 18650's, as they are not that much bigger than AA and are 3.7v each and overall have more energy capacity and current capability.  4 of them in series would give you 13.8v nominal, but probably more like 16v when they're fully charged.

You do want to watch out shorting those things though or you'll be setting off a fire works display a bit more local than you want.. 

Another option is just a 12v gel cell. They are readily available.  That might be bigger than what you want though, I'm guessing the reason for wanting to use AA's is the size.  But thought I'd throw those ideas out there anyway.