Ignitor specs?

Is there a FAQ somewhere on the specs for all the various igniters on the market? I want to make my launcher universal if I can. Most people use the Estes because that's what's available local hobby stores, but I see there's a number of them out there.

Really the two important numbers are the maximum test current and minimum ignition current. I designed it for 12-volts. The continuity indicators are incandescent panel mount lamps and the ignition loop has 10-amp rated relay. It will do up to three at a time but each ignition loop has its own relay so the only parts that will take all the current are the battery and master on/off switch.

It actually looks like I'll have to bump up those relays. Apparently the estes igniter is about 790m ohms.

Estes igniters are 0.8 ohms. The typical igniter resistance is between 0.5 to 2 ohms. Ohm's law applies. I=V/R=12/0.5=24 amps for a single low resistance igniter.

You need a low impedence 12 volt battery. A 2 AH or larger sealed lead acid battery is a good choice.

https://www.allelectronics.com/make...atteries-Rechargeable/Sealed-Lead-Acid/1.html

A standard 10 A relay will not last long, and is likely to weld on. A better choice is an automotive power relay rated 20-40 A because they will handle 150 A inrush currents without welding. The automotive sockets work great for connecting them. Use wirenuts for connecting 14 gauge wire.

https://www.allelectronics.com/make-a-store/item/RLY-351/12V-SPDT-30-AMP-AUTOMOTIVE-RELAY//1.html

https://www.allelectronics.com/make-a-store/item/SRLY-2/SOCKET-FOR-AUTOMOTIVE-RELAY//1.html

Light bulbs for continuity use too much current for low current ingiter like the Quest Q2. Use an LED with a 1000 ohm resistor in series to limit the currrent to ~10 ma.

Do a TRF search on launchers for more information and circuits that work.

Bob

I was thinking I might add a 10a current limited power supply instead of bigger relays. They only cost about $20. That also avoids the problem with shorted leads. The only reason I used incandescent is they're easier to see in the daylight.

Speaking of this, are there any issues to be aware of using a high power MOSFET to fire an igniter?

JOTN said:

I was thinking I might add a 10a current limited power supply instead of bigger relays. They only cost about $20. That also avoids the problem with shorted leads. The only reason I used incandescent is they're easier to see in the daylight.

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The cost of the proper relay is only ~$2.50 on-line and ~$6.00 at your local autoparts store!

Bob

bobkrech said:

The cost of the proper relay is only ~$2.50 on-line and ~$6.00 at your local autoparts store!

Bob

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It has three relays so they can be fired in sequence and all at once. I would need to upgrade a couple other parts and fuses to cover a short.

I've been looking at the newer NiMH cells, and they might cut it. They can efficiently do 4A and will max out around 7 due to internal resistance. They're tested safe on a short until fully discharged. With that I could put the battery pack inside the project box instead instead of haul around an external battery.

I'm trying to find out the cold current on those bulbs. Unfortunately I don't have a scope and the spec sheet is a bit vague. I might just have to buy some ignitors and see what happens.

JOTN said:

It has three relays so they can be fired in sequence and all at once. I would need to upgrade a couple other parts and fuses to cover a short.

I've been looking at the newer NiMH cells, and they might cut it. They can efficiently do 4A and will max out around 7 due to internal resistance. They're tested safe on a short until fully discharged. With that I could put the battery pack inside the project box instead instead of haul around an external battery.

I'm trying to find out the cold current on those bulbs. Unfortunately I don't have a scope and the spec sheet is a bit vague. I might just have to buy some ignitors and see what happens.

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You will not have a problem seeing a superbrite led in sunlight. You can drop the resistor value to 500 ohms (20 ma) but not lower. This is the maximum safe continuity current you should use in any modern design launcher.

If you do not want to use the low priced sealed lead acid battery, the look at RC power packs. In any case, you will be flattening a 4 A capable battery quickly. All batteries can handle being shorted, that's not the issue. The issue is that the wires can burn.

Most folks simply use a battery pack that is easily disconnected, not a current regulated supply. Costs nothing.

Again I would again ask you to search TRF for launcher designs. There are many usable designs listed.

Bob

an R/C battery pack for cars/trucks (6 sub-c cells) 3300mah(and higher) are rated for 40 amp discharge rates(if they are shorted its more like 100+ amps...but the cells may be toast). a pair wired in series works nicely to power a launch controller.
rex

bobkrech said:

Again I would again ask you to search TRF for launcher designs. There are many usable designs listed.

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Well, this is a hobby not the job. Half the fun and learning is coming up with a design rather than using one.