Series & Parallel on each module

[BMoore]

Why does Cobra not recommend series and parallel wiring circuits on the same module? I have a module I'm planning to fire two positions off of Left & right separated by about 50 feet on either side of the module. The last cue would fire 5 cakes. My plan was to use parallel wiring except for the last cue which I was going to wire in series. However, I read that cobra does not recommend that. I can certainly wire all the cues in series, but curious as to why parallel and series wiring should not be mixed.

[Rick_In_Tampa]

I don't want to speak for Cobra and I would always encourage someone to reach out to Scott Smith or a member of his team to get the official word on any Cobra related issues.

That said, I think this link from Cobra explains the differences between series and parallel wiring pretty well. https://help.cobrafiringsystems.com/support/solutions/articles/44001380462-continuity-clarified While they do mention that they do not recommend wiring in both series and parallel on the same module, they do not go into detail as to why. I could offer some guesses, but that's all they would be. So I won't. I would seriously reach out to Cobra and see what they say. If you do, please post their response here as I'm sure there are others that are curious too.

[Scotty Rockets]

Has to be a typo, the only problem I foresee would be if it was both parallel and series on the same cue.

[BMoore]

I received a response from Cobra but still not sure I totally understand. The response stated that the module itself is internally wired as a parallel circuit so adding series wiring creates a hybrid circuit. Mixing and matching wiring then makes it difficult to calculate the max fire numbers so their support documents indicating max cues are based on either all series or all parallel, but not a mix. I think I'll play it safe and just wire everything in series. It was more of a curiosity than anything. Sounds like it should work, but they simply haven't tested all the possible combinations.

[WithReport]

I don't know why creating a "hybrid" circuit would matter. It's all Ohms Law.

I suspect they just don't want to answer all the combinations of questions from everyone, and they shouldn't have to. They would likely get inundated with variations of the following: "What if I have two parallel paths on the same cue - each with three igniters in series?" One could do the math and figure it out. However we usually tend to oversimplify the calculations and leave out any resistance in cables, slats, connectors, etc. So, I would still suggest to have extra igniters for testing those odd situations first - regardless of the system.

I know on another system I have, I once tested three parallel runs of 100ft with two igniters in series at each end for a situation I wanted to use.

As for the OPs question, it shouldn't matter if you wire some cues in series and some in parallel. If concerned or wondering how much resistance your cables have, measure it or test it.

[Birdman]

I received a response from Cobra but still not sure I totally understand. The response stated that the module itself is internally wired as a parallel circuit so adding series wiring creates a hybrid circuit. Mixing and matching wiring then makes it difficult to calculate the max fire numbers so their support documents indicating max cues are based on either all series or all parallel, but not a mix. I think I'll play it safe and just wire everything in series. It was more of a curiosity than anything. Sounds like it should work, but they simply haven't tested all the possible combinations.

Makes sense. I work in IT and the software I support is highly configurable. There are "best practices" that should be followed to avoid creating unintended consequences. Cobra's response is pretty much what I would tell my customers. As I would say, it is not a supported configuration but that doesn't mean it will not work. It's just that we can't guarantee there will not be issues. If there are issues and you seek support you will be told you need to follow best practices (i.e. put the responsibility on them). Because I have years of experience I typically know how far out of the lines you can take things or with extra effort figure out a way to get the desired results (I've been forced to come up with some crazy unsupported solutions). However, if I provide unsupported guidance or help with an unsupported configuration, it could come back to bite me. Things can change, (e.g. software updates, and other changes to the system it's running on etc) that could create issues down the road and that could put everyone involved at that point in a bad situation. I know because I've been put in those situations before. Customer's typically don't want to be told that something that has been working can't be fixed. Software developers don't want to get involved because there is no problem with the software if used as intended etc etc...

Basically it would create a whole lot of extra work for Cobra if they were to support this. The matrx would probably result in numerous customer questions and just creating and testing that initial matrix would take a lot of work. It would need to be tested with every battery type and then retested with every software or hardware version released. I can totally see why they would want to avoid all of that.

If I were to mix series and parallel wiring I would start with using the the matrix for the max you can fire in parallel because this has the lower max. I would also test it to be sure all fire in the desired configuration. Even then I would anticipate, but not necessarily expect, an issue. Test environments may not be the same as your production environment when firing your show. When firing the show you could have more demands on the batteries then you did during testing or any number of other variables that weren't present during testing. If I needed certainty I would follow Cobra's " best practices".

[WithReport]

Well Birdman and Bmoore, I'm curious on why they have an issue, for example, with two igniters in parallel on cue 2 and 3 igniters in series on cue 3. At the end of the day, each cue has a voltage potential when fired that could be measured or know from the specs. Then you figure out how much resistance you have and if you can draw enough current through all the circuit.

I get they may have a reason, but I don't know why they say it is "imperative"

[Birdman]

I don't know if I ever heard the term imperative used. Honestly, I've mixed parallel and series on the same mod but on separate cues, fired separately. I'm speculating that one reason this is not recommend could be that it injects too many variables for Cobra to confirm what will and will not work. Say for example you're firing cues at the same time that are wired differently? Because it's a pro system Cobra needs to offer assurances on what will and won't work.

[BMoore]

Well Birdman and Bmoore, I'm curious on why they have an issue, for example, with two igniters in parallel on cue 2 and 3 igniters in series on cue 3. At the end of the day, each cue has a voltage potential when fired that could be measured or know from the specs. Then you figure out how much resistance you have and if you can draw enough current through all the circuit.

I get they may have a reason, but I don't know why they say it is "imperative"

What they say is that it is “imperative to know they do not recommend.” I don’t quite understand what the internal wiring being a parallel circuit and series creating a hybrid circuit has to do with it. Still seems to me like each cue is stand alone and as long as you stay within their parameters you should be fine. Seems like it all boils down to they won’t recommend anything they haven’t tested. Even though there is probably no reason it shouldn’t work they aren’t going to explicitly state that a situation will work if they haven’t tested it which I can respect.