I've got a wireless ignition box (personal) that has been a real workhorse and has served me well, but it uses two "eBay special" wireless 315Mhz relays. I've got a microcontroller in the box to gate the logic, continuity check, safety switches, and key control on the launch side, but I've always been worried that someone else on the range bought the same cheap wireless RF relays. So, I've decided to rebuild a new one using higher power serial TTY radio/modems on each side (bi-directional). That way I can be absolutely certain the arm and fire messages are coming from me and I can see exactly what is going on with the remote controller. While I am at it, I've decided to upgrade some of the functionality to include an ohm check/report and additional safety controls. In the process a few questions have come up that I thought I'd pose to this group.
1. What is a "good" range I should use to test ignitor resistance? I did a sampling of everything in my garage and it seems that mine range from .5 ohm up to about 3 ohms, but I do not have a lot of variety.
2. My continuity test today is based on 3v and 10ma of power and so far I've never accidentally launched a rocket or burned an ignitor. I always test new ignitors on the box before inserting them, but what is generally a safe current limit for continuity check?
3. On the business end of the box I am using three 10A relays. One to "arm" and then I'm separately activating the other two on each side of the ignitor to complete the circuit across a 12V AGM battery. I've considered using Mosfets, instead of relays, but old school relays just seem safer to me (although contacts can fuse together). Pros/cons?
4. I've got a current limiting resistor in series on the firing circuit dialed in to about 5 Amps. I've also thought about adding an auto-reset breaker (10A), but I am just choosing these limits arbitrarily. My firing timer is usually set to 3 seconds and so far (80-100 launches) I have not fried anything with crossed leads. Thoughts on the limits?
I know this group has thought about these a lot more than I have, so I appreciate any advice or opinions.
-Mike
1. What is a "good" range I should use to test ignitor resistance? I did a sampling of everything in my garage and it seems that mine range from .5 ohm up to about 3 ohms, but I do not have a lot of variety.
2. My continuity test today is based on 3v and 10ma of power and so far I've never accidentally launched a rocket or burned an ignitor. I always test new ignitors on the box before inserting them, but what is generally a safe current limit for continuity check?
3. On the business end of the box I am using three 10A relays. One to "arm" and then I'm separately activating the other two on each side of the ignitor to complete the circuit across a 12V AGM battery. I've considered using Mosfets, instead of relays, but old school relays just seem safer to me (although contacts can fuse together). Pros/cons?
4. I've got a current limiting resistor in series on the firing circuit dialed in to about 5 Amps. I've also thought about adding an auto-reset breaker (10A), but I am just choosing these limits arbitrarily. My firing timer is usually set to 3 seconds and so far (80-100 launches) I have not fried anything with crossed leads. Thoughts on the limits?
I know this group has thought about these a lot more than I have, so I appreciate any advice or opinions.
-Mike