Relays for Pyro Ignition

[rharshberger]

I was wondering about using a relay and pyro battery inline between say a RRC3 and the e-match/q2g2 etc. I hear lots of concern about getting low amperage igniters, would it not be just as easy to rig a relay system to power a higher amperage igniter. Im not a electronics type person, but I have a basic knowledge (very basic but not design/integration/programming). I was just wondering about something like a LiPo connected to a relay triggered by the RRC3 it would add some weight but could be negligible in footprint. This is just me thinking out loud however input would be appreciated.

 

[Titan II]

See page 8 & 9 of the RRC3 user manual.

Dual Battery Wiring
The RRC3 is designed to fly using 9V alkaline batteries in tandem with low current ematches for the drogue and main
deployment charges. Should your application require higher current for output events, or your operating at lower battery
voltages you might consider using a dual battery wiring setup. This method isolates the RRC3 Logic Battery power from the
Drogue/Main Deployment charge power, thus eliminating any potential voltage brown‐out scenarios during event
activation. The logic battery must comply with the 3.5VDC to 10VDC rating as mentioned in the specs; however your pyro
battery may any voltage up to an absolute maximum of 30VDC.
It is also recommended when using this dual battery operation to first activate the RRC3 Logic Switch, and after verification
of a successful boot, then activate the Pyro Switch.

Wiring diagram in manual.

Also...check out the Egg Timer website.

 

[enderw88]

Relays that will operate in a rocket flight environment will be hard to find, and very expensive.

 

[rharshberger]

the RRC3 was just a hypothetical you could insert any other DD altimeter in there.

Enderw88..you probably have a point there. Ive looked at Eggtimer/Finders etc., they look like a great product, I haven't dug into their capabilities much. Im more interested in the Egg Finder for the 38mm Min Diameter I want to build. Our launch site has a cornfield a mile or so away with a propensity for eating high flying rockets.

 

[jcato]

Relays that will operate in a rocket flight environment will be hard to find, and very expensive.

Well, the smart thing then is to replace a mechanical component with a solid state one: i.e. a Power MOSFET.

I purchased some of these for a similar project - something over 200A rating at about 50c each:

https://tinyurl.com/lhl88pm

... and a similar product (in smaller quantities) for about 80c each (if you buy 5). Lists the rated current at 150A, but can surge to 600A --- far in excess of what any ignition circuit could ever generate:

https://tinyurl.com/irlb-8743

... and a good little tutorial on using MOSFETs as switches:

https://www.electronics-tutorials.ws/transistor/tran_7.html

-- john.

 

[enderw88]

Well, the smart thing then is to replace a mechanical component with a solid state one: i.e. a Power MOSFET.

I purchased some of these for a similar project - something over 200A rating at about 50c each:

https://tinyurl.com/lhl88pm

... and a similar product (in smaller quantities) for about 80c each (if you buy 5). Lists the rated current at 150A, but can surge to 600A --- far in excess of what any ignition circuit could ever generate:

https://tinyurl.com/irlb-8743

... and a good little tutorial on using MOSFETs as switches:

https://www.electronics-tutorials.ws/transistor/tran_7.html

-- john.

I completely agree. OP said he wasn't an electronics type so I didn't mention that.

 

[bobkrech]

A switch with no moving parts except electrons. Only issues are heat dissipation and inductive over-voltage and both can he handled by proper board layout and circuit design.

Bob

 

[cbrarick]

seems like you're just adding a potential failure point. Today's altimeters work well with today's ejection charge lighters. If you want to overcome any low amp issues, you can use 2 batteries in parallel

 

[ksaves2]

seems like you're just adding a potential failure point. Today's altimeters work well with today's ejection charge lighters. If you want to overcome any low amp issues, you can use 2 batteries in parallel

Ummmm, I think part of the deal was switching to a high amp requiring igniter for other uses. I agree, all the modern stuff works fine with low current ematches. Kurt

 

[bobkrech]

I think folks are discussing 2 different issues. It's a non-issue for e-match activation for deployment charges since the MOSFETs in the current altimeters will source sufficient current without self-destructing. It can become an issue for air-starts because many altimeter MOSFETs will only source 5-10 amps without damage.

For these altimeters it is easy to use a bigger MOSFET and higher capacity battery in series with the extant pyrocircuit to activate a bigger (current pig) motor igniter.

Bob

 

[ksaves2]

I think folks are discussing 2 different issues. It's a non-issue for e-match activation for deployment charges since the MOSFETs in the current altimeters will source sufficient current without self-destructing. It can become an issue for air-starts because many altimeter MOSFETs will only source 5-10 amps without damage.

For these altimeters it is easy to use a bigger MOSFET and higher capacity battery in series with the extant pyrocircuit to activate a bigger (current pig) motor igniter.

Bob

Yeah, that might be the only option for one not in a position to make a low current motor igniter out of some ematches and home made/commercial pyrogen
+/- thermite. Kurt

 

[cbrarick]

uhhh, airstart CTI motors with their inclosed low power igniters....

 

[rharshberger]

Ummmm, I think part of the deal was switching to a high amp requiring igniter for other uses. I agree, all the modern stuff works fine with low current ematches. Kurt

You hit part of it on the head there Kurt. Bob hit the other part of it, some of the posts I have read are that air starts are where the ematch is more likely to pull more amperage than the altimeter can handle because of plasma developing in the motor creating a connection (very briefly) between the legs of the igniter. Not that Im going to be attempting air starts anytime soon, at least not until next spring when I get my TLP Nike Hercules plan pack rocket built (no Im not building the darn tubes by hand rolling) and heavily modded.

 

[rharshberger]

uhhh, airstart CTI motors with their inclosed low power igniters....

From what I know of CTI motors the ignition nugget makes any ignition a breeze. I don't own any yet but am definitely looking to buy the 24mm sizes, and maybe a few others as well.