Wiring two 9V batteries to a PET2...

[marcusSRG]

I'm in the process of building a 4" timer and altimeter e-bay for doing airstarts in my LOC Ultimate. I'm almost done but I need a little help with wiring my batteries. I plan to run my PET2 timer on 2 9Vs to ensure I have enough current for multiple airstarts.

I think I heard somewhere that you were supposed to wire 2 9Vs from the terminals of the first battery to the terminals of the second battery and finally to the terminals of the timer, if that makes any sense. For example, the positive wire would start on the first battery's positive terminal, run to the second battery's positive terminal, and then run to the positive terminal on the timer. Same for the negative wire, of course. The switch would be in there somewhere but that's not what I'm worried about. Is that correct? It seems like it would be easier to just get 2 standard 9V batt connectors, hook each battery to a connector and then twist the two positive and two negative wires together and connect them to the timer's positive/negative terminals. Is this a no-no? Or would it work fine?

 

[dixontj93060]

Per the manual:

 

[new2hpr]

Are you asking about the older PET2 or the new PET2+ ?

For just increasing the available current to the igniters, either method would be fine.

-Ken

 

[dixontj93060]

Oh, sorry, if it is the PET2, not PET2+, Missileworks recommends using external relays with their own separate power circuits versus having a provision for two batteries feeding the system.

 

[xenon]

What igniters are you using and how many? I've fired 6 ematches off a PET2 (original) with a single 9V with no problem.

 

[MWC]

Marcus -

You could wire any PET (new or old) using the dual battery diagram posted by Tim... if you're using a low current matches, I've tried tests similar tests to xenon using 4 matches per event with a single battery. If you have any doubts, program up a breakwire timing test using a single 9V battery and connect up your required number of matches per event and simulate the loads on the ground.

 

[marcusSRG]

What igniters are you using and how many? I've fired 6 ematches off a PET2 (original) with a single 9V with no problem.

They will be the low current cluster igniters by Magnelite. Can't remember their designation off hand. I will start off airstarting two motors at a time (RMS 'G's) and I sort of figured a single 9V could handle 4 but I would like the added benefit of extra current and have future plans to air start many more motors utilizing this setup in future projects.

You could wire any PET (new or old) using the dual battery diagram posted by Tim... if you're using a low current matches, I've tried tests similar tests to xenon using 4 matches per event with a single battery. If you have any doubts, program up a breakwire timing test using a single 9V battery and connect up your required number of matches per event and simulate the loads on the ground.

Cool. Too bad I designed my ebay with the batteries mounted side by side. It would make that a little tricky the way I have it but I think I can do it with a little rewiring. I certainly plan to ground test once I order more igniter leads. I will try using a single 9V first too.

 

[marcusSRG]

View attachment 132110

I finally looked at this closer and I remember seeing it before... Interesting way to wire the batteries and I actually can do it with my setup. Took me a sec to figure it out since it only uses the negative input terminals on the timer. The pyro switch is a safety that's closed before powering up the unit, correct? I also have the safety interlock pull pin setup installed on my ebay.

 

[MWC]

I'd use this only if you need the extra current... if you're using augmented low-current matches for ignition, a single alkaline will work quite well.
I'd always arm the avionics first, then enable the pyro-power secondarily.

 

[marcusSRG]

I'd use this only if you need the extra current... if you're using augmented low-current matches for ignition, a single alkaline will work quite well.
I'd always arm the avionics first, then enable the pyro-power secondarily.

Okay, I'll start off with the single 9v and do ground tests. Probably will stick with that for a while. But curious, in the 2x9V wiring setup, how would the timer be able to read continuity on the event channels if the pyro switch wasn't closed before powering up the timer? ...I'm no electrician as you can see!

 

[MWC]

You are correct, the PET would not be able to sense continuity status until you enable the pyro power switch. If you do use the dual battery tandem, I suggest you enable the pyro switch shortly after applying logic power and validating the timer has booted up correctly by monitoring the piezo tone (ie. when it has deactivated).

 

[marcusSRG]

Ah, gotcha. Thanks for the help!