Perfectflite alt and ematches

[Skyhigh]

I have a question about my perfectflite altimeter and the usage of two ematches per channel. I've flown twice now on this perfectflite altimeter and the first flight I got no droque deployment and did get the main deployment. Today I got the exact opposite. I got droque deployment but no main deployment.

I've just completed some indoor testing with the altimeter in a glass canning jar with christmas light bulbs hooked up and when I suck air out of the jar and hold the air the droque channel fires and when I let air back in the main fires. The altimeter seems to be doing it's job time after time with this test.

I have three 3/16th holes drilled into the altimeter bay for venting which according to everyone at the launch should be more than sufficient.

OK< now my question..... Is it possible that by hooking 2 ematches to each channel that I might not be getting sufficient juice to either ematch. Would I be further ahead to try just one ematch per channel ???

 

[KenParker]

Have you tried two Christmas light bulbs per channel in your ground testing? Better yet.... try two e-matches per channel. I know the e-matches are expensive... but then how expensive is it to lose a rocket?

I don't know for sure, but I think the Perfectflite altimeter should have plenty of juice to fire two e-matches per channel - assuming that they are a low current type. Nothing like an actual test with the actual article, however.

Is the battery you are using putting out its full rated current? You probably know that to properly test a battery, you need more than just a voltmeter, you need a voltmeter that tests the battery in conjunction with placing a load on the circuit.

 

[Skyhigh]

Well with further discussion with the prefect, I'm gonna fly tomorrow on single deployment for the Cert 2 flight and at the same time the altimeter will be hooked up with 1 ematch per channel with no black powder loaded. If I get both ematches to fire then that's telling me that when it fired the first two ematches in the droque bay it drained the battery below sufficient current to fire the two ematches in the main bay on todays flight.

Only logical theory I can come up with at this point. Time will tell.

 

[shockwaveriderz]

skyhigh: you don't say what the diameter of this model is....the MAWD operation manual gives the following formula:

H= D * L * .006"
https://www.perfectflite.com/Downloads/MAWDManual.pdf

How far away from any joint is the 3 holes....?

PerfectFlite recommends 1 hole most smaller in size than 3/16" or 0.1875..thats a pretty big hole...

see page 11 of that manual...

 

[Skyhigh]

Figured it out guys and thanx for the replys. Today I flew single deployment but I hooked up two ematches for test purpose only to the altimeter. Both succesfully fired. Many at the launch agreed that because I used two ematches per channel yesterday, that was asking too much of the 9 volt battery and the perfectflite altimeter because of the resistance created in this configuration.

By the way, I certed for Level 2 successfully today!!!!

Ah, such a relief to get that out of the way. I must admit though, flying for a certification is a great feeling and alot of fun too !

 

[Juerg]

Weak batteries are a common reason for problems. Here some hints:
- Don't just use "new" batteries, test them before every flight.
- Use alkaline batteries only. NiCD my fry the output circuit of altimeters, zinc batteries are to weak.
- Don't test the voltage but the current! A good 9V Alkaline battery will supply 5-10A when shorted (just for a moment). Don't use it any more if it supplies less than 3 amps.

On igniters:
- If you use a pair of N28B igniters you should not connect them in parallel but seriell! Thrust me / try it! These are commercial igniters made for the demolition industry where igniters are allways connected in serial (3V/igniter to be on the safe side!). For other brands you will need to check the data sheet.
- Don't use the N28F for charge ignition, these draw high current that some altimeters may not be able to supply.
- It doesn't make big sense to put two commercial e-matches in parallel, these igniters are very very reliable. Check the resistance before connecting them to the electronics (typically 1-2 ohms). Continuity-checking by the altimeter is not good enough, there may be a short circuit that most altimeters will not detect.

Take care

Juerg

 

[RocketboyG80]

Not knowing that 28F's draw too much power, I used them for drogue and main in a recent flight with my MAWD. They both fired fine but I would prefer to use something a little lower. I may use 28B's but I wanted to know what people think about Quickburst HotShot E-matches. Are they a good sustitute for 28B's? They are cheaper. www.quickburst.net

 

[Juerg]

I have never used them but the product info states that the e-match takes 800mA to ignite what is still twice the current needed by a N28B...
So it is probably quite comparable to an N28F what is concerning the electrical power requirements.

Juerg

 

[Austin]

Under normal conditions, only one ematch should be hooked up per channel on most altimeters. Sure, they may be rated at a certain current, but it does not mean you should use the upper end of that number by using high current matches or dual matches. I am curious as to what you had two matches hooked to???...if it was for redundancy, you would be better off with dual altimeters to have a truely redudant system.

With over 30 dual deployment flights on just one L2 rocket in particular, each time my single altimeter performed flawlessly. Running redundancy in L1 or smaller L2 models (up to about 10 lbs) may be a bit overkill imho and many models that size are not big enough/practical to handle two alts.That doesn't mean you can't try...that's the beauty of this hobby...there is so much to do and try.

I did want to note that the Perfectflite Timers can easily handle two ematches or low current ignitors and with some small electronics added, they can consistently fire three matches at once for air starts...this has been tested.

Hope this helps and keep us up to date on your projects...they sound cool! Oh yea...pics...lots of pics.

Carl

 

[Skyhigh]

I sent a question to Perfectflite about using two Quickburst ematches on each firing channel and here is the response that I got. (explains why I had the trouble I had.)

> By the way, I'm using Quickburst ematches <

Therein lies your problem.

The miniAlt/WD will fire multiple daveyfire N28B or oxral ematches in
parallel for redundancy. These matches are very sensitive, requiring
under 20 millijoules of energy each to fire. The miniAlt/WD stores
190 mj of energy for firing, which is enough for about ten of the
davey/oxral matches at a time.

The Quickburst Hot Shots have a higher mass head and thicker bridge
element, and as such require considerably more energy to fire. Each
Hot Shot requires approx. 120 mj of energy, so a single match is fine
but two in parallel is too much of a load. Unfortunately if a
channel's firing energy is depleted before either of the parallel
connected matches fires, neither match will end up firing.

The solution is to use a single Hot Shot or to use oxrals or davey
N28Bs if you want to go with multiple matches.

 

[mshaner]

I have to ditto Carl on the part about the timers and in fact, I'm going to go out on a limb and say that he is referring to my timers from PF where I added a 1000 millifared (sp?) cap to accomodate the need for firing 3 matches. Incidentally, I don't use Oxral OR Daveyfire matches. I use the ones from Star Light and Magic

https://www.starmgc.com/pyrocont.html

As for redundancy, I would also have to ditto Carl. Are you trying to create a backup?

Shane Heilman