Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Short high current burst from 9v batt

Status
Not open for further replies.

vvanders

New Member
So I'm in the process of building a rocketry altimeter for fun. I used to do a bunch of high power rocketry stuff as a kid out in the Anza Borrego desert. Tons of fun and all that. One thing that I never really got around to playing with was altimeters.

Now that I've got a fair bit of electronics knowledge under my belt I thought I'd take a crack at designing my own. I've got the microcontroller, accelerometer and pressure sensors figured out. Data logging to a flash chip is straight forward enough. One thing I don't have a ton of experience with is blowing the ejection charge in a reliable manner.

Usually on the altimeters we'd use there's one charge blown at the top for a drogue chute and the one at 1,500-500ft for the main chute. Ideally I'd like to be able to pre-charge some high volume capacitors from a single 9v battery and provide enough amperage that I'm sure they'll fire. A common problem we'd encounter is that the drogue would fire fine but then the battery would be too weak to provide current for the main after a couple uses.

My current idea is to use a single boost step-up dc/dc converter to step 9V to 25V and store that in a pair of 470uF Aluminum-Elec caps and then use a transistor to control discharge. I simulated this in SPICE and I get about 500ma for ~100ms which should be enough, however I was wondering if anyone knew of a better way to provide a short high current burst. Usually when we fire igniters on the ground it's from a 12v car battery or similar.
 

MikeMl

Well-Known Member
Most Helpful Member
How about just paralleling the 9V battery with a supercapacitor? Since the voltage rating seems to be shy of 9V, you may have to put two in series.
 

vvanders

New Member
The problem with supercaps is they usually have a pretty high ESR which would be bad for a quick pulse.

I did a fair bit more googling online and it looks like most people go with lipo or e-match solution which is kind of a shame. I'd really like it to be a more off the shelf solution that can use 9v battery and standard igniter.

After doing a bit more digging it looks like the standard Estes igniter is 0.8 Ohms and requires about 4.5 amps for 1/10th of a second. I think that's going to be out of the range of charged caps without going really high voltage.
 

vvanders

New Member
Scratch my above post, I was doing some digging around digikey and came across this. 1.5F, 70mOhm ESR only 5V though.

Putting it through SPICE gives me a solid 5A with an 0.8Ohm load, looks like it might be closer to what I need.
 
Status
Not open for further replies.

EE World Online Articles

Loading
Top