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dwightr

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Has anyone built a 20 volt launch controller?
My idea was to use a Dewalt 20V Battery as the power source
There are some adapters on ebay for about $20 that adapt a 20V battery into older style tools, I was thinking of getting one of those to use as the battery holder. I was thinking of epoxying the adapter to my controller box and then soldering wires to the contacts that would normally go into the tool.
I always have a couple of the Dewalt batteries in my truck on a charger.
Big question is how would the pyrogen on the igniters react with the higher voltage, ie would the bridgewire burn into violently enough to cause the pyrogen to break off and cause sporadic ignition problems
 

jsdemar

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I use an R/C 4-cell LiPo. 2200mA-hr. The battery and charger are cheaper than using the Dewalt battery and charger. And you don't have the voltage issue. You can also fit it inside a fairly small box with whatever form factor you want.
 

dwightr

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Price isn't so much of an issue. I use 20V Dewalt tools for work so I have a chargers installed in my truck and always have a couple of charged batteries laying around
 

jsdemar

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Try it through the same length of wire you plan on using. That will include the voltage drop across the leads. See how the different igniters burn. Then decide if you want to build up the full controller.
 

Brian H.

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Sounds like its time for an experiment!
Just make sure it is fused because a shorted lipo will put out more flames than the rocket motor it is supposed to ignite.
 

jsdemar

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I use a 10A auto-reset thermal breaker. The automotive style, inexpensive. It'll pass 30 amps for short bursts but kick out in a few seconds for a dead short. Saves on frying the wiring as well. I've put them inline with the igniter circuit on all the controllers I've built for 25+ years.
 

caveduck

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Test carefully with your preferred starters. Most are designed to work best with ~4-12V. On the ones with resistive bridgewires, the temp vs current curve goes up very quickly so there's a greater chance that the bridgewire can melt without lighting the pyrogen or propellant. This may be especially true with the new Estes igniters that basically have no useful pyrogen.
 

Scottoquinn

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Hey guys I fly giant scale r/c planes. I’ve been asked to do a gender reveal for my niece. My plan was to use 4 enola gay smoke bombs. I’m going to replace the fuses with the larger Estes igniters. My question is can I use a 4 cell lipo with the 10 amp auto trip fuse that was mentioned earlier on a micro switch. Don’t won’t to tick off the lipo. Will it work?
 

Wallace

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That's a marketing ploy. "20 Volt Max". What you'll commonly see with an 18 volt battery fresh off the charger.
 

Wallace

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Common 1/4" male spade terminals fit like they were made for it. No need to buy anything extra. Mythbusters regularly did it a LONG time ago..
 

DaveW6DPS

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I use 18 volt drill batteries, and they work fine.

If you look at the specs on ignitors, they are rated by current. Generally you will see the "no fire", "all fire" and a minimum recommended for firing somewhat above the "all fire" rating. Usually also a recommended firing current. There is no voltage rating.
Initiator ratings.JPG


The voltage is not critical, it just has to be more than enough to push the recommended minimum current through the ignitor resistance.

You might want to put a small value resistor in the lead to the battery, since shorting a LiPo battery is a very bad thing to do. A resistor that would limit short circuit current to 50% of the max current rating of the battery is a good idea.

Assuming the nominal 20 volt battery is actually 18:
With the example here, this resistor should be less than 23 ohms. [18 volts /(23 ohm resistor + 1 ohm initiator)= .75 amperes]
A 17 ohm resistance gives the recommended nominal current. [18 volts/(17 ohm resistor + 1 ohm initiator)= 1 ampere]


You should still take care not to short the battery at any time. It is unfortunately easy to short the leads to each other or to a metal blast deflector.
 

RocketRev

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Hello 20 Volters,

I know that this is going to sound strange to some, especially coming from me, but when it comes to voltage and igniters, I think that the real world is not the same place as the theoretical world.

Does anybody besides me remember when Kloudbusters rolled out their brand new $30K launch system back in, what was it, 1993 at LDRS? I was there and I remember it fairly well. And I remember being told that they had to boost the voltage up to 24 volts to get the system to work for that LDRS. I also remember that way too many igniters (that's what we called them back in those days) were failing to light their motors.

A good friend of mine, Robby Robinson one of the true originals in this whole hi-power rocketry hobby and one who is really missed by me, was selling a lot of igniters in those days. Robby got a few dozen "failed" igniters returned to him on the first day of that LDRS from customers. I know, because I was one of them. And he also got his hands on a bunch of other "failed" igniters during that same LDRS from rocketeers who used other manufacturers as well as some "home-made" igniters. Robby carefully cut them open to see if he could tell what was happening. In his words, "the bridge wire is burning thru without igniting the pyrogen."

According to the article in the Tripolitan, the Kloudbusters spent an additional $10K (total of $40K) to get their system working back at 12v as it had been designed. Oddly enough, that article was one of the reasons that Dan and I created Wilson F/X. There had to be a better way to build a launch system for a club at less than $454 per pad. (I know they had a pad #88, but I don't know if they had an 88 pad system or not. $40K/88=$454)

Now I'm not going to dispute the theoretical and even empirical musings of those who think that 20V will work just fine. All I'm saying is that those same high power rocketry igniters, I mean initiators today, which back then were designed to operate effectively at right around 12volts, are the same "motor lighter/initiator" things that are being manufactured today. And they are still designed to operate most efficiently at 12 volts which is the hobby standard. Raising the voltage of the launch system from 12 volts to 20 volts will increase the number/percentage of initiator failures in the real world.

So I am more than a bit skeptical of the value of a 20V launch system.

Brad
 

dwightr

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Brad that's exactly why I posted the question. I'm getting old enough that I don't have to make mistakes if someone has already made them. I just had the idea floating around as a way to repurpose batteries that I already have. Thanks from keeping me from going off on a tangent that has already been tried.
 

Glasspack

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To piggy back a bit on Brads response:

Remember the current for a specific device will decrease as the voltage to operate goes up. A 12 volt system will be almost twice the current doing the same thing in a 20 volt system.
The current is what heats up the nichrome wire. I may be wrong but I have watched Q2G2 igniters "POP" and fire instantaneously with my new 12vdc 20 amp capable relay system.
They popped so fast there was no ignition on the Aerotech E composite motors. Finally after several attempts with new Q2G2 igniters, I used a Copper head to ignite the motor.

Paul
 

Steve Shannon

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To piggy back a bit on Brads response:

Remember the current for a specific device will decrease as the voltage to operate goes up. A 12 volt system will be almost twice the current doing the same thing in a 20 volt system.
The current is what heats up the nichrome wire. I may be wrong but I have watched Q2G2 igniters "POP" and fire instantaneously with my new 12vdc 20 amp capable relay system.
They popped so fast there was no ignition on the Aerotech E composite motors. Finally after several attempts with new Q2G2 igniters, I used a Copper head to ignite the motor.

Paul
Your first statement is untrue. Current does not go down as voltage goes up unless the power is held to a constant value, which isn’t the case for a resistive circuit.
Ohm’s law: v = i * r. Rearranged, v/r = i. V is the available voltage. R is the resistance of a circuit. I is the current that flow as a result.
An igniter is simply a resistance. So, from the rearranged statement of Ohm’s law above you clearly can see the current that flows through an igniter increases in direct proportion to the increased voltage.
You’re not wrong about Q2G2s popping with increased voltage, but that’s because the current is increased and the bridgewire burns through too quickly to transfer much heat. Using a 12 volt launch system I’ve had terrible results getting Q2G2s to ignite composite motors. They’re much more like an electric match than a high current igniter.
 

Glasspack

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Thank you Steve ………

I was thinking about in general I guess. Like the aircraft I work on...… it uses 230V system instead of a 115v system. 230v versus 115v allows for less current motors, transformers etc.
... to perform the same function. Less current means less wire weight and so on.......

I think I tried to apply Ohms law the same way here.
 
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rharshberger

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Thank you Steve ………

I was thinking about in general I guess. Like the aircraft I work on...… it uses 230V system instead of a 115v system. 230v versus 115v allows for less current motors, transformers etc.
... to perform the same function. Less current means less wire weight and so on.......

I think I tried to apply Ohms law the same way here.
Aren't those motors also multi-phase? Some where I read that aircraft use a number of 3 or greater phase motors to gain more torque in a smaller package than a comparably sized 2-phase can produce, or did I totally misunderstand.
 

Steve Shannon

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Thank you Steve ………

I was thinking about in general I guess. Like the aircraft I work on...… it uses 230V system instead of a 115v system. 230v versus 115v allows for less current motors, transformers etc.
... to perform the same function. Less current means less wire weight and so on.......

I think I tried to apply Ohms law the same way here.
That’s true. Some motors may be wired to be connected to either 115 or 230 Volts AC (or in some cases 460 or 600). Those motors are rated for a specific power, which is volts * amps (reactive). When they are properly wired the relationship is exactly as you described: raising the voltage results in lower current which allows smaller wires. That’s also the basis of the electric transmission system. We step up voltages to half a million volts to send it thousands of of miles with the least resistive loss. Then we transform it to lower voltage when it’s close to the delivery point.
But those motors must typically be designed and wired correctly to use those higher voltages. If you plug a motor that’s designed for 115 v into a 230 v receptacle bad things happen.
 

Steve Shannon

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Aren't those motors also multi-phase? Some where I read that aircraft use a number of 3 or greater phase motors to gain more torque in a smaller package than a comparably sized 2-phase can produce, or did I totally misunderstand.
There are three phase machines also, which results in even better efficiency, but for household use most motors are just single phase 115 or 230.
 

Glasspack

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Of course …. I am not trying to imply plugging in a device to anything its not rated for....
Back to the original post …… I was thinking that Electric matches and igniters are basically the same thing.
Also
in your experiences..... are the Q2G2 igniters best left to the 6 volt systems ??
 

DaveW6DPS

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You need to look a bit beyond the battery voltage. All the discussion of battery voltage should really be focused on supplying the correct current range to a resistive device.

It is a generally bad practice to not have some resistance inline to prevent damage in the event of a short circuit. Alligator clips touching together is a fairly common occurrence.

You need to consider how much current is recommended to fire any of the ignitors you will be using, and how much current you can safely run through a short circuit. Then add a series resistor for a current between those two.

I use an 18 volt drill battery, and have 4 ohms of limiting resistor in the circuit. This limits current to 4.5 amps or less into a short circuit, but with another <2 ohms of ignitor resistance provides about 3 amps of firing current. Any of the ignitors I have looked up recommend a minimum firing current of around an amp.

I have used Estes, Quest, and Aerotech First Fire Jrs with this launcher with no issues.
 

UhClem

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I may be wrong but I have watched Q2G2 igniters "POP" and fire instantaneously with my new 12vdc 20 amp capable relay system.
When I did all fire/no fire testing on the Q2G2 one of the interesting details is that if they did anything at all, they popped. This was with current carefully controlled to be close to the threshold of firing.
 

Steve Shannon

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Of course …. I am not trying to imply plugging in a device to anything its not rated for....
Back to the original post …… I was thinking that Electric matches and igniters are basically the same thing.
Also
in your experiences..... are the Q2G2 igniters best left to the 6 volt systems ??
They work great for ejection charges and to ignite black powder motors. I’ve not used them with 6 volt systems. There are several threads here that describe augmenting Q2G2s or electric matches to work as igniters. You could test it on a 12 volt system by wiring one Q2G2 in series with a similar impedance resistor. The q2g2 and the resistor would each receive 6 volts.

Electric matches and Q2G2s do not transfer nearly as much heat to the inside of a motor as a true igniter.
 

DaveW6DPS

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When I did all fire/no fire testing on the Q2G2 one of the interesting details is that if they did anything at all, they popped. This was with current carefully controlled to be close to the threshold of firing.
That is what I would expect.

The only difference in lighting an ignitor or e-match with different current rates is how fast it gets to the ignition temperature.
Once it gets to ignition temperature it will basically burn at the same rate whether you ignite it with .6 amps, or 1.6 amps or 3 amps.
The few milliseconds difference will not be apparent to someone watching it.
 

Glasspack

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Thank you all......the only problems i have had wih my system so far was the "popped" Q2G2s not igniting the composite E motor.....
 

Glasspack

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Um none of them that i know of.....why ?
 

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