Boost converter 1.5V (or 3V) -> (12V, 40V] - Page 1
Forum section: electronics / beginners

author: roblkc3
author_rank: Contributor
timestamp: May 07, 2017, 03:36:51 pm
content: 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

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 07, 2017, 03:47:21 pm
content: 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.

author: roblkc3
author_rank: Contributor
timestamp: May 07, 2017, 04:21:33 pm
content: 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...

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 07, 2017, 05:44:05 pm
content: 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

author: Gyro
author_rank: Super Contributor
timestamp: May 07, 2017, 05:49:11 pm
content: 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 = 200WNow 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!

author: Gyro
author_rank: Super Contributor
timestamp: May 07, 2017, 06:02:23 pm
content: Quote from: jeroen79 on May 07, 2017, 05:44:05 pmI 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.

author: capt bullshot
author_rank: Super Contributor
timestamp: May 07, 2017, 06:16:49 pm
content: Take a look here for a starting point:http://electronics.howstuffworks.com/camera-flash3.htmBuild 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).

author: roblkc3
author_rank: Contributor
timestamp: May 07, 2017, 06:50:43 pm
content: 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...)

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 07, 2017, 07:11:34 pm
content: 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.