Altimeters in parallel ?

[johnloveshiking]

Can you connect two "Easy Mini" dual deployment altimeters in parallel?
For instance, the apogee connections for both to just one igniter?
I would think not but it would be cool if I could.
How about other brands?
The discharge for one would fry the other?
Any thoughts on this rocketeer?

 

[Titan II]

Why? The idea makes no sense whatsoever.

 

[cerving]

Don't do that. If you don't have enough room for two separate charge wells (which would be the only reason to do what you're suggesting), use one that's slightly larger and use a separate ematch from each altimeter into that charge well. I have never seen BP not ignite... but I HAVE seen ematches fail, although it's fairly rare.

 

[johnloveshiking]

Thanks Cerving for your reply. I have a large enough charge well for multiple igniters.
I was just curious.

 

[Zeus-cat]

Look at the potential failure modes in a typical fully redundant ejection system versus the one you proposed:
Fully redundant system:
Altimeter 1
Battery 1
Ematch 1
Charge 1

Altimeter 2
Battery 2
Ematch 2
Charge 2

A failure of one or more components in system 1 has no effect on system 2 and vice versa. The probability of a failure of any component is low, but not zero. For the rocket to have no deployment requires BOTH systems have to fail. If either system works you will have a deployment if your charge is sufficient to deploy the recovery system.

Your proposed system:
Altimeter 1
Battery 1
Altimeter 2
Battery 2
Ematch
Charge

Let's assume there are no electrical issues with your proposed system.* If battery 1 or altimeter 1 fails, the system will still work if altimeter 2 and battery 2 work. The same is true if battery 2 or altimeter 2 fail, the system will still work if altimeter1 and battery 1 work. However, the entire system fails if the ematch or the charge fail. So, you have the extra weight of a second altimeter and battery and little of the benefits of a redundant system. A second charge and ematch add little weight and make the system fully redundant.

*In general you want to avoid sending a large current from one electronic device into another one. If you were to use a system like this, you would want to electrically isolate the two systems from each other.

 

[johnloveshiking]

Thanks Zeus-Cat.
I'm going to use the fully redundant system.
Too much T&M invested not to.
Was just curious to get input to see if there were any reasonable options.
Thanks for taking time to drop me a line.
John

 

[atestani]

I'm going to use the fully redundant system.

Building on what @Zeus-cat said, I would add redundant switches and make sure wiring is all "home-runs" and not daisy-chain any of the wires.

Here is an example of you are interested:
https://www.rocketryforum.com/threads/dual-deploy-poll-backup-altimeter.184392/post-2539212

In this system, I have both 7.4V and 11.1v LiPo batteries, where the 11.1V is for the pyro channels as well as the beeper. Both of those will work fine on 7.4V, if necessary, which is why the third battery is 7.4V and is automatically switched in if either (or both) of the main batteries has an issue. BTW, I set the Proton to fire a charge 1 second after nose-over and the Quantum to fire at 3 seconds after nose over.

One note... In another thread there was a discussion of using 2 JL Chute Releases as I do where some people were negative on the idea. Think about it, if everything is redundant and you always have separation and then the one JLCR you have fails to open, the recovery system has failed and your rocket crashes. Without 2 JLCR you do not have a fully redundant system.

 

[johnloveshiking]

Thanks for your angle Al:
I checked your thread link.
I like your using dual JLCR.
I never thought to use two in series.
I will keep this in mind.
Thanks
John

 

[lr64]

I don't know the specs of the devices involved, but presumably diodes could protect one output from the other. Might cost you a volt. This doesn't mean using a single ematch is a good idea.

 

[johnloveshiking]

I don't know the specs of the devices involved, but presumably diodes could protect one output from the other. Might cost you a volt. This doesn't mean using a single ematch is a good idea.

Thanks Ir64:
I was thinking about diodes when I first started thinking about this.
I'm actually not going this route but 2 altimeters and the associated e-matches for these.
Was just thinking.
Thanks again.
John

 

[cerving]

I don't know the specs of the devices involved, but presumably diodes could protect one output from the other. Might cost you a volt. This doesn't mean using a single ematch is a good idea.

Paralleling the output of two altimeters to a single ematch could potentially fry some electronics. Don't do it. Ever.

 

[lr64]

Even WITH good diodes?

 

[cerving]

Most altimeters use some kind of trickle current for continuity, you may or may not know which way the current is flowing. Plus, when one fires it may be dead-shorting the other's output. Nope, don't do it. Diodes or not. Just put an ematch on each system and be done with it.

 

[FredA]

Paralleling the output of two altimeters to a single ematch could potentially fry some electronics. Don't do it. Ever.

Bad plan from the get-go - you're clearly not a EE and shouldn't attempt anything you're considering.

 

[Voyager1]

Thanks Cerving for your reply. I have a large enough charge well for multiple igniters.
I was just curious.

Using 1 charge well with two igniters is not true redundancy. If the primary igniter does ignite the charge but doesn't successfully deploy the chute, then you have no secondary charge to complete the job. Use separate wells for true redundancy.