Ground testing altimeter, e-matches and ejection charges - need advice

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I'm beginning a new thread so as to not hijack the e-match thread I started this on.

Gearing up for my very first pyro dual-deploy flight and ground testing has begun. I've done tests on the altimeter and e-matches but I'm still waiting for the reload shop near me to get 4F BP in stock so I can test the ejection charges.

I'll be using a StratoLoggerCF for my alt. Powering this is a Turnigy 2S 300mah Lipo. (discharge 35C-70C).

E-matches purchased off ebay are these ones: https://www.fireworksigniter.com/eproducts/90.html

Specs are as follows:

1. 21°C(70°F)resistance: 1.3±0.15Ω — 1.7±0.15Ω
2. Fire current: 0.40A /0.37A
3. Safety current: 0.25A 5S/0.18A 5S
4. Testing current: 0.5MA


This is my first time using e-matches and I wanted to see how they fired, so I just shorted one across a battery. Pop. Check.

Next I bench tested my altimeter. I snipped off two christmas tree lights from an old strand, tinned the ends and attached one each to the drogue and main pyro circuits. To pull a vacuum, I put everything inside one of the canisters that hooks up to my FoodSaver vacu-bagger. Worked like a charm. Drogue lit up after it sucked all the air out, then the main lit when I pressed the "unseal" button on the lid.

Next I did the same thing, but with e-matches attached instead of the lights. I used 2 matches per channel as I'm going to to be putting two matches in each charge for redundancy. This was a little tricky since the match heads were outside the canister, meaning the four wires bending over the lip of the jar prevented a perfect seal. I eventually got it to pull enough of a vacuum to set off the drogue, and the main popped almost immediately after. All four matches lit. I forgot to note the battery voltage before and after, but there was only a slight drop in voltage after firing the matches as I recall.

Next up I'll be testing everything inside the actual rocket, but until then, my questions so far:

1. Is this an acceptable battery for my altimeter? Power range for the StratoLogger is 4-16V and I'm at 7.6 with my 2S lipo.
2. Am I using the right e-matches? So far in testing they seem to be ok, but I just want to double check as I'm EE challenged. I would love it if someone could explain how the above e-match specs translate to real-world rocketry.
3. The StratoLogger specs says not to exceed 5 amps for the output current. If I understand this correctly, my battery of choice can provide more than that, but the matches only require .4A to fire each. That would only be 1.6A total? Am I ok here? I don't want to blow up my altimeter. Everything tested ok on the ground.
4. E-match question: do people take those little plastic caps off or leave them on? I'm going to be holding my charges in glove tips taped to the bulkhead.
5. Am I missing anything?

Next up I will do as follows:

- Test the whole set up again (sans black powder) inside the AV bay using a shop vac to pull a vacuum.
- Test my ejection charges (no altimeter - just some long wire and a battery) to see if they are sized properly. I'll be using 2x 2-56 shear pins on the nose cone. Booster will be friction fit.
- Finally test the entire setup with full ejection charges using a shop vac.

Now the big question: would it be considered acceptable to not have a second altimeter for redundancy? I have an Adept22 I can use as a backup, but my preference would be to keep this first flight as simple as possible. I am intending this to be my L2 cert flight, so I need a J motor. Unfortunately none have a delay long enough.



 
I feel like you're not testing enough /s

I just use 9V's, so I can't speak to the battery. I think the one you are using is pretty popular though.

I use the exact same e-matches and they have never failed me on a 9V. I take the little red bit off the end before installation.

For testing ejection charge size (black powder ground testing), I would run a switch to the circuit (I used an Estes hobby launch controller because its on a 9V). Don't rely on pulling a vacuum with a shop vac. If you already know your hardware is working, no sense in adding more variables / unknowns to your next test. Here was one of my tests: [video=youtube;nMNDSLDVoxs]https://www.youtube.com/watch?v=nMNDSLDVoxs[/video]

Good luck =)

Brian
 
1. Yes, probably. I still use 9V with my SLCF.
2. Yes. They look like the usual Chinese cheap ematches that work just fine.
3. Maybe. Put your redundant matches in series, not parallel. It is a V=IR thing.
4. Off

These little baro altimeters are super-reliable, so there is no need to keep testing with your home made vacuum chamber. Do it once to please yourself that it works, then just use the test functions in the software. After you confirm that the altimeter can fire the 4 ematches, then just use light bulbs. Test your BP amounts without the altimeter at all.

Yes, totally acceptable to have just one altimeter in my book. I am in the distinct minority of this forum who thinks redundant altimeters are a waste of time, money, and add more errors than they prevent.
 
I don’t know enough about LiPos to help with those (I use 9 volt Duracells on my Stratologgers) but I can answer your other questions.

Those e-matches work very well. I remove the little plastic caps before use to get them out of the way.

I do similar initial tests on my new altimeters using Xmas light bulbs. I would skip the step where you test the altimeters in the av bay sans black powder with a shop vac. Just make sure you have your vent holes size and number correct and you can be confident the altimeter will sample the air correctly.

I would skip to the ground testing with BP charges to confirm sizing. And I would just do one TYPE of test, either with the wires to a battery or the shop vac. Test one deployment at a time. Test the drogue alone, then set it up again and test the main alone. Test multiple times with different size charges until you’re dialed-in, then do one more test to confirm. The shop vac can work but will be inconsistent (it's tough to get a trace the altimeter likes enough to fire a charge). I only use it if the av bay is all buttoned up and I don't want to open it again. Running the wires outside the rocket to a battery is much more consistent and reliable.

Test your charges with your laundry all packed as if you were doing the launch.
Remember to plug the MMT hole when testing the drogue.
I’m a believer in redundant back-up if you can fit it in the rocket. If it makes you more comfortable by all means, go for redundancy. If you do, make sure you’re offsetting the redundant charges so they don’t both fire at once (apogee/apogee +1 second. Main at 700 ft/500 ft. And wrap the charges in foil so one doesn’t ignite the redundant charge next to it.

Once you get consistent deployments during testing you’ll launch your first DD flight with confidence. It’s fun watching the rocket take care of itself.
 
I use 2s 180 mAh lipos in all my Perfect Flite altimeters/timers and Peter of Perfect Flite says that’s all he uses for testing of same.
 
Thanks to all. Great advice here.

I did want to get some clarification from you Buckeye on this point however:


3. Maybe. Put your redundant matches in series, not parallel. It is a V=IR thing.

Wouldn't wiring in series defeat the purpose of having two matches since there would be only one path to the power source? So if the first match fails, the second one won't light. The instructions for the altimeter suggest using two matches in parallel but to make sure your battery has enough current to fire them.
 
Wouldn't wiring in series defeat the purpose of having two matches since there would be only one path to the power source? So if the first match fails, the second one won't light. The instructions for the altimeter suggest using two matches in parallel but to make sure your battery has enough current to fire them.

This is a catch-22 situation. Even a parallel connection can come undone if one of the e-matches goes short circuit. In this case the ‘redundant’ e-match is not able to fire due to a short-circuited parallel e-match. This is a good argument for true redundancy.
 
Thanks to all. Great advice here.

I did want to get some clarification from you Buckeye on this point however:




Wouldn't wiring in series defeat the purpose of having two matches since there would be only one path to the power source? So if the first match fails, the second one won't light. The instructions for the altimeter suggest using two matches in parallel but to make sure your battery has enough current to fire them.

There is a thread on this topic in the forum somewhere. I think cerving, jdermiggio, and bobkrech chimed in on it, if you want to search. A guy fried his altimeter with a LiPo because resistance was too low and Ohm's law prevailed. 9V power sources don't have this problem. Your SLCF setup is probably fine, as confirmed by the manufacturer's instructions. I know, it is hard to get your head around why serial matches work, but they do. I do it all the time now, regardless of the brand of altimeter and type of batteries I am using.
 
FYI to the OP, I use 2S 280mah LIPOS and after flight day I recharge and never put more then 40 mah back into them - even after sitting on pad for 30 minutes and in the field for another hour.
Sometimes I forget to disconnect and leave them connected in the rocket but OFF for months - still never put more than 50 mah back in. So use them with a clear mind. You can certainly use 9v but a LIPO is nice as when you charge you know exactly how much of that battery was used

I use them for GPS Trackers too but those will drain much more but still very useable.

Just an opinion here, after you tested your alts in a vacuum there is no need to test in your rocket with the vacuum- that is an unneeded test. At that point you are testing amount of charge to separate halves. You have already proven the alts work so when you put them in your AV bay , power up and they beep continuity that portion is complete. So your separation test you can wire to output terminal and simplify it - just my opinion.
 
True redundancy would use a secondary altimeter, not two matches per channel on a single altimeter. There is probably no real gain in using this form of pseudo-redundancy.

The gain is due to the fact that the e-match probably has the lowest statistical reliability of all the components in the dual deploy system. However, even the cheapo Chi-com matches have made great strides in recent years. I have yet to see one fail.
 
I think cerving, jdermiggio, and bobkrech chimed in on it, if you want to search. A guy fried his altimeter with a LiPo because resistance was too low and Ohm's law prevailed. 9V power sources don't have this problem. Your SLCF setup is probably fine, as confirmed by the manufacturer's instructions. I know, it is hard to get your head around why serial matches work, but they do. I do it all the time now, regardless of the brand of altimeter and type of batteries I am using.

Ematches are designed to be wired in series. That's how the pro pyro display guys wire them and they have alot more at stake ($$$). An ematch may fail to ignite (common failure mode) but usually will still conduct current. If one is open your altimeter continuity check will detect that. Plus series wiring requires 1/4 the current than parallel wirin. Its easier on the altimeter outputs and will have 1/4 the momentary battery voltage drop when the pyro fires which is better for the altimeter electronics.
 
So I'm clear on the setup for wiring matches in series, it would basically look like an M? The leg on either end in the output terminal block (+/-) and the middle two wires twisted together?

As suggested I'll forgo the unnecessary testing I've considered apart from sizing my ejection charges.

Thanks again all y'all.
 
So I'm clear on the setup for wiring matches in series, it would basically look like an M? The leg on either end in the output terminal block (+/-) and the middle two wires twisted together?

As suggested I'll forgo the unnecessary testing I've considered apart from sizing my ejection charges.

Thanks again all y'all.

Yes, series simply means the two matches are connected the way you describe, end to end. The current runs through one ematch into the other. When devices are connected in series the same level of current runs through both. Ematches are just resistors, so you simply add the resistance of the two ematches together to find the total resistance. Divide the voltage of the battery by that resistance and you’ll know the maximum current that will run through both matches. As long as that exceeds your all-fire rating your matches should light.
 
Yes, series simply means the two matches are connected the way you describe, end to end. The current runs through one ematch into the other. When devices are connected in series the same level of current runs through both. Ematches are just resistors, so you simply add the resistance of the two ematches together to find the total resistance. Divide the voltage of the battery by that resistance and you’ll know the maximum current that will run through both matches. As long as that exceeds your all-fire rating your matches should light.

Thank you Steve - this is precisely what I wanted to learn. So to use my setup as an example (and to check my math): 2x ematches with a resistance of 1.3 ohms = 2.6 total resistance / 7.4 volts = 2.8 amps? Well under the stated 5 amp output limit of the StratoLogger and well over the .4 amp fire current.

How would this change if the matches were wired in parallel? Asking out of curiosity and because this is how the manufacturer says to do it.

Adding to my confusion, in a recent email list discussion for my club, the topic of Lipo discharge rates was brought up. at 35c constant, 70c burst, are the ones I have too high? Will this be a factor? As I said, this setup tested fine with four matches (two in each channel), but I want to make extra sure I'm using the right battery. I still have time to get some of the 2C 180mah ones suggested above- they have a discharge of 25/40C. I got the 300mah batteries primarily to run my eggfinder, so would be fine getting others for the alt. FYI, I'm not entirely opposed to simply using 9v batteries, but I don't like the idea of having to replace them after every flight or two and I already have lipos and a good balance charger...
 
When deployment altimeters like the StratoLogger speak of maximum output current, they are referring to maximum current for each deployment channel (or output), not the system in total, so when you consider your power requirements you should think in terms of what each output has to handle in terms of firing current.

So, let's consider the case of the main channel firing two ematches in series. According to spec we shouldn't exceed 5 amps of current on this channel when firing, but how do we determine how much current is being generated? For simplicity's sake, when the altimeter fires an output channel, it essentially closes a switch in a simple circuit such that the battery is now directly connected to the igniters, the simplest possible circuit. So if we want to know the total current in that circuit, it's a simple application of Ohm's law:

V = I * R, or to solve for current:

I = V / R

You want to use a Turnigy 2S 300mah Lipo (discharge 35C-70C)which is capable of a 70C momentary discharge rate, which means it can supply 70 * .300A = 21 amps of current at 7.6 volts nominal. We know that the resistance of 2 ematches in series is somewhere in the neighborhood of 1.5 + 1.5 = 3.0 ohms. Plugging those values in to the current equation: I = 7.6 volts / 3.0 ohms = 2.53 amps. This level of current is easily delivered by the battery, and is well under the 5 amp maximum.

What if we wanted to just fire one ematch? In this case the total resistance of the circuit is cut in half to just 1.5 ohms. I = 7.6 volts / 1.5 ohms = 5.06 amps. The battery can easily supply that much current, but now we're knocking on the door of the 5 amp limit.

It's important to note that in both cases above the output current is determined by the resistance only. The discharge rating of the LIPO battery has absolutely nothing to do with the circuit calculation.

So, why would a LIPO battery not be as good a choice as say a standard 9 volt battery?

Consider the firing current of both scenarios above when the source voltage is 9 volts:

Two ematches in series: I = 9.0 volts / 3.0 ohms = 3 amps
One ematch only: I = 9.0 volts / 1.5 ohms = 6 amps

Uh oh! The 9 volt battery is delivering 6 amps, which is over the maximum! How can it be a good choice?

The answer is that a standard 9 volt battery has much higher internal resistance, and cannot really deliver 6 amps no matter how low the resistance of the circuit is because it has to combat its own high internal resistance. Lipo batteries don't have this limitation and will happily deliver huge amounts of current. If you were to connect a voltmeter to a 9 volt battery while it was firing in the 6 amp case, you would see that the voltage of the battery would sag (drop) to a much lower voltage and the actual current delivered would be somewhere in the 2-3 amp range.

This is why some people prefer nine volt batteries for this purpose. It's capable of delivering a decent fire current up to a couple of amps, but has a natural limiting factor that keeps you from blowing out your output circuit with too much current.

----------------
-Robert
 
Also, you asked about what would happen if you wired two ematches in parallel...

The equivalent resistance of two resistances in series is simply the sum of the two resistances.

The equivalent resistance of two resistance in parallel is the inverse of the sum of the inverse resistances: 1 / ( [1/R1] + [1/R2] ) If R1 = R2, then the equation simplifies to R / 2. In other words the equivalent resistance of two resistances that have the same value is half the value of one of the resistances.

Using the example I gave above for 7.6 volts:

Two ematches in parallel: I = 7.6 volts / .75 ohms = 10.13 amps

That's way over the maximum current, and your battery would easily deliver it.


---------------
-Robert
 
Just to chime in, you can have true redundancy with two altimeters/batteries, and also use two e-matches with each (in series). Some e-matches will test positive for continuity; but if there is a defect in the chip beneath the pyrogen, it can fail to fire. As stated above, it will still pass voltage to the second match, but fail to fire itself. There is always a chance that your main e-match on the primary alt and main e-match on the back-up alt could both be bad. Rare, but possible. With two alts, and two matches for each charge, you are really narrowing down your possibility of a failure.
 
Thank you Steve - this is precisely what I wanted to learn. So to use my setup as an example (and to check my math): 2x ematches with a resistance of 1.3 ohms = 2.6 total resistance / 7.4 volts = 2.8 amps? Well under the stated 5 amp output limit of the StratoLogger and well over the .4 amp fire current.

How would this change if the matches were wired in parallel? Asking out of curiosity and because this is how the manufacturer says to do it.

Your underlined math above is upside down. Current (i) = voltage (v or e) divided by resistance (r), so
i = v/r
Using your numbers:
7.4 volts/ 2.6 ohms = 2.8 amps. That’s the same answer you got so apparently you did the math right but wrote it incorrectly.
If two identical resistors are wired in parallel the total resistance is half of each resistor. So, instead of 1.3 ohms, it’s 0.65 ohm.
Using Ohm’s law again:
7.4 volts/0.65 ohm = 11.4 ohms max current.
It’s important to understand that’s theoretical. Resistance within a battery or introduced by the circuit and wiring affects it also.
Edit: I see Robert gave a much more complete answer than I did. I should have read his before I quoted your reply and answered. And I agree with Bat-Mite.
 
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Just to chime in, you can have true redundancy with two altimeters/batteries, and also use two e-matches with each (in series). Some e-matches will test positive for continuity; but if there is a defect in the chip beneath the pyrogen, it can fail to fire. As stated above, it will still pass voltage to the second match, but fail to fire itself. There is always a chance that your main e-match on the primary alt and main e-match on the back-up alt could both be bad. Rare, but possible. With two alts, and two matches for each charge, you are really narrowing down your possibility of a failure.

Geez. Two alts, two batteries, two battery restraints, two switches, four terminal blocks, four charge canisters, and eight ematches. Do you guys actually launch these rockets or just spend all day prepping the electronics bay? :rolleyes:
 
Geez. Two alts, two batteries, two battery restraints, two switches, four terminal blocks, four charge canisters, and eight ematches. Do you guys actually launch these rockets or just spend all day prepping the electronics bay? :rolleyes:

I don’t use two ematches per output. But I do use redundant altimeters on my larger rockets. It takes a lot less time to prep than to replace the rocket and all its parts.
 
You need to figure out a level of redundancy that works for you. Too complicated and your likely to mess it up, too simple and a single failure can cause loss of rocket. It will also vary depending on the situation, big expensive rocket should have a good level of redundancy, smaller rocket with limited space may not have room. Also don’t forget that motor ejection as a backup may also be an option.

Personally i I think that 2 battery, 2 switch, 2 Altimiter, 4 ematch & 4bp, is a good level of redundancy that I normally aim for. If I’m forced to a single Altimiter then I look for other ways to create redundancy, such as use an Altimiter that can also fire a backup charge, motor eject backup or double up the ematches.

As your level of redundancy decreases your level of caution should increase. Do for instance check your ematch resistance on a multimeter, if it’s not within spec then discard it, this will help prevent 2 types of failure. Also check your battery voltage, if it’s looking a bit low don’t fly it.
 
Okay one last question: In my effort to keep things as reasonably simple as possible, I'd like to direct-wire my e-matches to the altimeter. I'll be using glove tips for the ejection charges. My current setup uses a pull-pin switch to arm, but I'm realizing that without terminal blocks on the bulkheads or some kind of connector, there's really no easy way to connect the charges unless the sled is outside the coupler. Meaning I will have to pull the pin and arm the altimeter for the minute or two it takes me to button everything up and re-insert the arming pin. That doesn't seem ideal or safe. It seems like my best (and only?) option is to eliminate the switch and just use twist and tape to arm. I'm fine with this (basically copying CrazyJim's Darkstar build stickied in this sub-forum) but wanted to see if anyone had other ideas I may be missing.
 
You could also use a screw switch, but agreed that continuing with the pull pin isn't the best way forward.
 
I usually prep my electronics at home, and I almost never fly a rocket more than once in a day. That said, I direct wire my matches directly to the altimeter. I seal the holes in the bulk head with silicone rtv. I also tape my charges to the bulkhead to keep wires from getting snagged. I also tape them to the eBay sled to provide some strain relief and to keep them in place during assembly and flight.

On redundancy. I fly dual altimeters on larger rockets. My Wildman Extreme is dual altimeters, but it was also my L3 cert rocket. I am building a 3” Wildman Dual Deploy and I will likely set it up for dual as well. Anything smaller I probably would go with single altimeter.

Considering my interest is tending towards smaller rockets I am doing more single altimeter. The thing is to be careful in your design and prep. Test it all before putting powder in the charges. Last thing to do before putting it in the rocket is to put powder in the charges.

Pull pin switches are a bad idea. I used to use the Schurter switches until I was helping a friend prep his rocket and one literally came apart in his hand. Since then, I have switched to either the Missileworks or Featherweight screw switches.
 
Geez. Two alts, two batteries, two battery restraints, two switches, four terminal blocks, four charge canisters, and eight ematches. Do you guys actually launch these rockets or just spend all day prepping the electronics bay? :rolleyes:

When you're putting a $2000 beast in the air, the time spent is worth it.
 
Okay one last question: In my effort to keep things as reasonably simple as possible, I'd like to direct-wire my e-matches to the altimeter. I'll be using glove tips for the ejection charges. My current setup uses a pull-pin switch to arm, but I'm realizing that without terminal blocks on the bulkheads or some kind of connector, there's really no easy way to connect the charges unless the sled is outside the coupler. Meaning I will have to pull the pin and arm the altimeter for the minute or two it takes me to button everything up and re-insert the arming pin. That doesn't seem ideal or safe. It seems like my best (and only?) option is to eliminate the switch and just use twist and tape to arm. I'm fine with this (basically copying CrazyJim's Darkstar build stickied in this sub-forum) but wanted to see if anyone had other ideas I may be missing.

Whatever kind of switch you use, NFPA 1127 is clear. You must be able to safely arm after it’s standing up and disarm your rocket before taking it down.
A pull pin switch can certainly do that if you put it somewhere it can be used while assembling the rocket, but if you’ve used a hole that’s blocked when sliding the rocket together, requiring you to turn on the altimeter while assembling, then you have an unsafe design that’s not permitted by our safety code (I appreciate that you already recognized that!). I don’t understand how you could replace that with twist and tape because a wire hanging out would also block assembly of the rocket, or would you be bringing the wire out through a different location that’s not blocked during assembly?
Twist and tape is allowed, but twist and tuck is not unless you design in some way to retrieve the wires so they can be disconnected.
 
I don’t understand how you could replace that with twist and tape because a wire hanging out would also block assembly of the rocket, or would you be bringing the wire out through a different location that’s not blocked during assembly?
Twist and tape is allowed, but twist and tuck is not unless you design in some way to retrieve the wires so they can be disconnected.

My plan was to use the same technique CJ does in this build thread: https://www.rocketryforum.com/showt...x-quot-build-starts-now!!&p=457167#post457167

Going through each step in my mind it seems to work with my rocket - I'll test for certain when I do my ejection tests this weekend. After charges are wired, I'll fish the switch wires (trimmed so no actual wire is exposed) through a static port in the switch band, then button everything up. Both ends of my av bay are removable, so I should be able to set everything up outside the coupler, then install the sled and bolt everything back together. On the pad I'd strip the wires, then twist and tape to arm. Does that seem right?

I've read every book and every post I can on dual deploy but I'm finding there are still aspects that aren't fully explained. The theory and best practice yes, but because there isn't just one way to do it, it creates a lot more variables for a noob to consider. I'm sure I'll have this down soon enough, but in the meantime I'm extremely grateful for the help and suggestions.
 
Also: Regarding the series vs. parallel discussion above. I'm posting the following advice I got from Peter Lawall at PerfectFlite. This is not to continue the debate (I think you have very well outlined the pros and cons each way) but for the sake of anyone searching the forums in the future that might have similar questions. Please keep in mind this is specific to his StratoLoggerCF.

Peter says:

The bridgewires in the ematches are extremely fine, and if you wire two (or more) in series then if one of the bridgewires burns through without igniting the pyrogen, it will instantly kill power to the other one. If the other one hadn't ignited yet, it never will, and both matches will fail. Considering how high volume/cheap/potentially inconsistent the Chinese matches are, this seems like a more legitimate concern than that of a shorted ematch (see below), which is easy to check for on the ground.


Many of the fireworks people do wire their matches in series, as it is more convenient for what they are doing. The difference is, if they get a failure their shells don't fire (and they can reuse them later), but if your ejection charge doesn't fire you have a safety issue and likely damage to your rocket, property, or people.


If you wire them in parallel and one burns through without igniting, the other will still get power and should ignite properly (unless you have two defective matches...). The downside of parallel connection is that if you short the leads on one match, both will end up shorted and neither will fire.


If you have a DMM and check the resistance of each match (should be 1 to 2 ohms, shorted would be 0.2 ohm or less), and then check your wiring carefully to make sure you don't have a wiring short, then parallel is the better choice in my opinion. I have never used anything other than parallel and have never had a failure.


Also bear in mind that even if you wire the matches in series, if you accidently short the wires going into the altimeter you will still get a failure. So the only real difference would be if the match itself were shorted at the tip, and the DMM resistance check will determine that.


Parallel. Parallel. Parallel.


As far as connection goes, yes you can twist one wire from each drogue match together and clamp in one drogue block terminal, and twist the remaining wire from each drogue match together and clamp in the other drogue terminal. Repeat for the main. Don't mix them up -- if you accidentally connect a main match to the drogue terminal everything will open at apogee and you'll have a long walk! Also make sure that you strip enough wire so that you are clamping copper and not insulation, but don't leave enough copper exposed that it could short to an adjacent wire. Its easiest to strip and twist a bit longer and then trim the twisted wires to the right length. After clamping give a little tug on the wires to make sure they don't come loose.

Regarding my battery choice for the StratoLoggerCF, Peter suggests a smaller 125-150mah lipo instead. The smallest 2C I can find is 180mah, also mentioned earlier in the thread, so I'll be going with those. (FYI, I had to order in a pack of 5 and only really need 2 or 3. If you're going to LDRS I'll be happy to sell my extras)

 
Also: Regarding the series vs. parallel discussion above. I'm posting the following advice I got from Peter Lawall at PerfectFlite. This is not to continue the debate (I think you have very well outlined the pros and cons each way) but for the sake of anyone searching the forums in the future that might have similar questions. Please keep in mind this is specific to his StratoLoggerCF.

Peter says:

The bridgewires in the ematches are extremely fine, and if you wire two (or more) in series then if one of the bridgewires burns through without igniting the pyrogen, it will instantly kill power to the other one. If the other one hadn't ignited yet, it never will, and both matches will fail. Considering how high volume/cheap/potentially inconsistent the Chinese matches are, this seems like a more legitimate concern than that of a shorted ematch (see below), which is easy to check for on the ground.


Many of the fireworks people do wire their matches in series, as it is more convenient for what they are doing. The difference is, if they get a failure their shells don't fire (and they can reuse them later), but if your ejection charge doesn't fire you have a safety issue and likely damage to your rocket, property, or people.


If you wire them in parallel and one burns through without igniting, the other will still get power and should ignite properly (unless you have two defective matches...). The downside of parallel connection is that if you short the leads on one match, both will end up shorted and neither will fire.


If you have a DMM and check the resistance of each match (should be 1 to 2 ohms, shorted would be 0.2 ohm or less), and then check your wiring carefully to make sure you don't have a wiring short, then parallel is the better choice in my opinion. I have never used anything other than parallel and have never had a failure.


Also bear in mind that even if you wire the matches in series, if you accidently short the wires going into the altimeter you will still get a failure. So the only real difference would be if the match itself were shorted at the tip, and the DMM resistance check will determine that.


Parallel. Parallel. Parallel.


As far as connection goes, yes you can twist one wire from each drogue match together and clamp in one drogue block terminal, and twist the remaining wire from each drogue match together and clamp in the other drogue terminal. Repeat for the main. Don't mix them up -- if you accidentally connect a main match to the drogue terminal everything will open at apogee and you'll have a long walk! Also make sure that you strip enough wire so that you are clamping copper and not insulation, but don't leave enough copper exposed that it could short to an adjacent wire. Its easiest to strip and twist a bit longer and then trim the twisted wires to the right length. After clamping give a little tug on the wires to make sure they don't come loose.

Regarding my battery choice for the StratoLoggerCF, Peter suggests a smaller 125-150mah lipo instead. The smallest 2C I can find is 180mah, also mentioned earlier in the thread, so I'll be going with those. (FYI, I had to order in a pack of 5 and only really need 2 or 3. If you're going to LDRS I'll be happy to sell my extras)


I have used 2 e-matches in parallel on both the SL100 and SLCF, but using a 1S 350mAh 25C LiPo. I did this to both the SLCF and SL100 roughly 8 times on each altimeter, between actual flights and bench testing. I still use those altimeters and I never experienced a failure due to the choices of LiPo or parallel. According to the logs in the altimeters the current draw was typically somewhere around 5 amps when using dual e-matches in parallel.

Having said that at this stage I use single e-matches but dual altimeters. I also switched from a 1S to a 2S just to give me a bit more margin on the voltage. Two other changes I made to my battery choice were to lower the mAh from 350 to 250 and the C rating from 25 to 20. This gives me a better margin of protection for max current draw which works out to roughly 5 Amps, give or take.

To calculate your max current divide your mAh by 1000 and multiply by the C rating. So a 250 mAh is 250/1000 = .25x20=5Amps
 
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