# Recommended wire gauge for Level 2 launch controller

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#### Nilo

##### Well-Known Member
TRF Supporter
Members:

Would 12 gauge be better than 14 gauge wire for the wire from the control box to the rocket?

I need 300 feet for a Level 2.

There's a big price difference between the 14 gauge wire versus the 12 gauge wire, as well as weight difference.

Nilo

#### Nytrunner

##### Pop lugs, not drugs
TRF Supporter
A common suggestion will be to use have a small wire from the controller carrying the signal to a relay at the pad with the launch battery and high current leads.

The next question will likely be where are you getting your FAA COA for the L2 rocket, and can folks come join you?

#### UhClem

##### Well-Known Member
At 300' you are going to be hard pressed to activate anything but the most sensitive igniter which is why the usual thing to do is build a relayer.

Even with 12 AWG wire the resistance will be ~1 Ohm (Not by any stretch the only source of resistance in that circuit) which means that with a 12V battery, current into a 1 Ohm igniter will be at most 6A.

Oh, 300'? You are planning on a level 2 certification flight using an L motor?

#### Nilo

##### Well-Known Member
TRF Supporter
At 300' you are going to be hard pressed to activate anything but the most sensitive igniter which is why the usual thing to do is build a relayer.

Even with 12 AWG wire the resistance will be ~1 Ohm (Not by any stretch the only source of resistance in that circuit) which means that with a 12V battery, current into a 1 Ohm igniter will be at most 6A.

Oh, 300'? You are planning on a level 2 certification flight using an L motor?

I want to give myself the required wire distance for up to an L motor, but after your input I'm reconsidering.

So, a simple built launch controller with 12 gauge will ignite a sensitive igniter. If I use only 200' for a K engine- will I'll be OK? I looked at the link for a relayer, but is a device I don't want to try to build.

If I want to fly a rocket with a L engine I'll go to a sponsored club launch that has the equipment to launch it.

#### Nilo

##### Well-Known Member
TRF Supporter
A common suggestion will be to use have a small wire from the controller carrying the signal to a relay at the pad with the launch battery and high current leads.

The next question will likely be where are you getting your FAA COA for the L2 rocket, and can folks come join you?

Now I'm leaning on building a system that could launch up to an K engine.

I live in Southern California and we have the Friends of Amateur Rocketry (FAR) launch site. They take care of the FAA clearance.

#### Bowman

##### Well-Known Member
I want to give myself the required wire distance for up to an L motor, but after your input I'm reconsidering.

So, a simple built launch controller with 12 gauge will ignite a sensitive igniter. If I use only 200' for a K engine- will I'll be OK? I looked at the link for a relayer, but is a device I don't want to try to build.

If I want to fly a rocket with a L engine I'll go to a sponsored club launch that has the equipment to launch it.

You could always increase the voltage to overcome drop over that length.
But launching with a club that has the gear already seems like a better approach.

#### Nilo

##### Well-Known Member
TRF Supporter
You could always increase the voltage to overcome drop over that length.
But launching with a club that has the gear already seems like a better approach.
I'll be using a 12volt car battery, 500 CCAmps. Will this suffice for a 200' distance?

#### Bowman

##### Well-Known Member
I'll be using a 12volt car battery, 500 CCAmps. Will this suffice for a 200' distance?
Voltage drop is the issue, not current. If you can't overcome the resistance you can't get any current to flow.
Again, it seems like you are relatively new to this so I recommend working with an established club.

#### prfesser

An automotive relay is quite inexpensive, and with a relay system one can use 14 ga, even 16 ga extension cords from launch system to pad. A car battery will have too much voltage drop at 100 ft, no matter how many cold-cranking amps it has.

Nice things about extension cords: they tell you the distance (two 100 ft cords mean a 200 ft distance); and if more distance is needed, just buy another cord.

One of those small 12v gel-cells at the pad (much lighter than a car battery), with a relay, works nicely for 100 ft distance. There's less than 10 ft from battery to motor starter. I've done it.

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#### Nilo

##### Well-Known Member
TRF Supporter
Voltage drop is the issue, not current. If you can't overcome the resistance you can't get any current to flow.
Again, it seems like you are relatively new to this so I recommend working with an established club.

Thanks for your input. Right now I have a system for 50' length for launching my rocket with G engines. If I could make the system work up to 100' I could launch up to J engines.

The reason I'm requesting advice is because, as you stated, this is my entrance into high power rocketry.

Nilo

#### Voyager1

##### Well-Known Member
TRF Supporter
I have often used 13 AWG twin flex speaker cable over 200' powered by a 12V / 7Ah SLA battery with no problems. However, this represents ~1 Ohm resistance for the return length, plus ~1.5 Ohm for the igniter. You are dropping ~5V over the cable and limiting your ignition current to ~4.5A. While this is still sufficient to fire your igniter, it is very inefficient. As others have suggested, a relay based system it the logical choice for high power launches where your standoff distances are from 100' (200' for complex) and upwards.

To directly answer your questions though, 12 AWG @ 300' is ~1 Ohm return, and 14 AWG @ 300' is ~1.5 Ohm return. So, yes, 12 AWG is better, but that's still a heavy pile of cable to carry around and probably expensive. As suggested above, using 3-core extension cords is an economical idea, as you can parallel two of the conductors to halve the resistance of one of the lines to the pad.

As this is your entry to high power, the suggestion to achieve this through an established club is good advice.

#### JimByrne

##### Active Member
Thanks for your input. Right now I have a system for 50' length for launching my rocket with G engines. If I could make the system work up to 100' I could launch up to J engines.

The reason I'm requesting advice is because, as you stated, this is my entrance into high power rocketry.

Nilo
I use 12 ga. extension cords with no problem powered by my 12v truck battery---30' from battery to the controller, 100' to launch stand and 8' of 16 ga. from the end of the extension to the igniter. 138' total.

#### sghioto

##### Well-Known Member
If I could make the system work up to 100' I could launch up to J engines.
I think the least expensive way is using a relay. You don't have to build anything. 12 volt relay modules are available and this system would only require a separate battery at the pad and the wire to complete.
This module uses a low voltage input to activate the relay. You can use 22 ga alarm type wire to over 500 ft if you want.

Relay Module One Way 30A Optocoupler Isolation Relay Module High Power Relay High/Low Level Trigger YYG-2(12VDC)
Available at Amazon: $11.19 #### Attachments • 262.4 KB Views: 46 Last edited: #### Japheth ##### Member Are wireless controlled relays worth anything for those distances or further? #### sghioto ##### Well-Known Member They can be but require additional safety features to comply. #### Voyager1 ##### Well-Known Member TRF Supporter Are wireless controlled relays worth anything for those distances or further? Yes and no! If your referring to garage door type remote relays or similar, then they might not have sufficient power or security features to reliably operate over 300’ and over, particularly if there are other similar units at the launch site. Additionally, many of these wireless relay modules only use 10A rated relay contacts - you really want at least a 20-30A rating @ 12V. You also want something with a suitable transmission protocol and an electronic or mechanical lockout for operating safely, as alluded to above. Last edited: #### Greg Furtman ##### Well-Known Member TRF Supporter I built a launch controller last year that is 2 piece. The battery (12v gel cell for a UPS) and electronics sit close by the launch pad. I used automotive relays that are electronically tripped. I used Cat5e to run from the battery box to the hand controller. I can check continuity at both the battery box & the hand controller. With a system like this you don't need long lengths of heavy wire. I have maybe 10' of heavy wire running from the battery box to the ignitor clips. I used this thread to build it. And I highly recommend using wire with a silicone jacket. It is much more flexible that other wire (helps with the tight wiring inside the battery/electronics box) and it stays flexible in the cold. Last edited: #### Philip Tiberius D. ##### Old Fashioned 2.5oz Rye/H2O 8 drops Orange Bitters #### pbahorich ##### Active Member Now I'm leaning on building a system that could launch up to an K engine. I live in Southern California and we have the Friends of Amateur Rocketry (FAR) launch site. They take care of the FAA clearance. Thanks for your reply. FAR has launch controllers you can use so there is no need to build your own. If you still want to build your own, use a relay as described in posts above and a battery like this: Amazon.com: ML8-12 - 12 Volt 8 AH SLA Battery - Mighty Max Battery Brand Product: Electronics It's only 5 lbs and can launch a ton of rockets on one charge. I use a similar one in my system (which I used for launching G motor rockets on my own but never use any more). #### RocketRev ##### Lifetime Supporter TRF Lifetime Supporter pbahorich is correct........... FAR has a launch control system that they use for anybody flying with them. I......uh....know the vendor they bought it from and it has both hardwired and wireless capabilities. One could say that I know the "ins and outs" of their launch control system very intimately. It will be more than adequate for flying any high power rocket motors you might want to fly. Now, I'm not saying don't build your own. It can be fun as well as educational. But if you're going to build a system for 300 feet, you need to go with a relay system. If you don't feel up to building your own relay system, Pratt Hobbies website says that they sell what looks to me to be an interesting 40-amp Relay Module for$25. They say it can be activated by any 12v launch system. I've not seen one and I don't know the specifications, but it might be exactly what you're looking for to add at the end of your 300 feet of home-grown launch system in order to add the relay capability that you will need out at 300 feet.

However, I would not bring your home-made launch system with you expecting to use it at a FAR launch. As far as I know, they are not a club doing a "Miss-Fire Alley" launch set-up where everybody brings their "own" launch control equipment.

#### prfesser

I cribbed together this circuit diagram for a simple relay launch system. Please excuse my lack of artistry. (And someone please let me know if there's something incorrect in what I've done.) BTW safety interlock and continuity check will require some more work.

The same battery is used to activate the electromagnet in the relay and to provide launch current.

When the launch button is pushed, electrons go from the negative (top) pole of the battery to pin 85, thru the electromagnet, pin 86, back to the switch, and up to the positive pole of the battery. Relay closes.

The electrons have been waiting anxiously for this event, because now they can flow from (-) pole to 85 to 30, from there to 87a, through the clips and motor starter, and back to the (+) pole. Ignition!

Best -- Terry
PS: two simple safety interlocks. (A) Add a second pushbutton in series with the launch button, so that both must be pressed to launch. (B) Get an ordinary $1 duplex socket and a plug (cut from old appliance or whatever) with a couple inches of wire attached. Wire the socket in series with the launch button. Strip the ends of the wires to the plug, and twist & solder together, or use a wire nut. The shorted plug must be inserted in the socket to launch. Oh, and a "handy box" or a plain plastic electrical box, with cover, makes a simple enclosure for either end of the system. #### Attachments • 45.8 KB Views: 23 #### Nilo ##### Well-Known Member TRF Supporter pbahorich is correct........... FAR has a launch control system that they use for anybody flying with them. I......uh....know the vendor they bought it from and it has both hardwired and wireless capabilities. One could say that I know the "ins and outs" of their launch control system very intimately. It will be more than adequate for flying any high power rocket motors you might want to fly. Now, I'm not saying don't build your own. It can be fun as well as educational. But if you're going to build a system for 300 feet, you need to go with a relay system. If you don't feel up to building your own relay system, Pratt Hobbies website says that they sell what looks to me to be an interesting 40-amp Relay Module for$25. They say it can be activated by any 12v launch system. I've not seen one and I don't know the specifications, but it might be exactly what you're looking for to add at the end of your 300 feet of home-grown launch system in order to add the relay capability that you will need out at 300 feet.

However, I would not bring your home-made launch system with you expecting to use it at a FAR launch. As far as I know, they are not a club doing a "Miss-Fire Alley" launch set-up where everybody brings their "own" launch control equipment.

Your suggestion for the Pratt relay module might be my solution. My only question is how do I integrate this module to my regular launch controller? Do I connect my igniter cables to this module, and then my control box could check continuity?

#### RocketRev

Hello Nilo,

I'm sorry, but the only info that I've got on Pratt's relay module is what's up on the Pratt Hobbies website. It uses a battery at the pad for ignition but all the website says is that the relay is activated by any 12v launch system.

I can only guess looking at the one picture that they have up, that your leads from your own 12v system plug into the central part of the relay module. You will need to have the polarity correct in your own 12v launch system, but correct polarity's necessary for activating any relay. But that's as far as I can go on mere speculation.

I have no idea how many volts/amps are required to activate the relay module. The website does not include that information.

Has anybody on this thread actually used one of Pratt Hobbies "Relay Modules" or better yet, have one in hand with instructions so that we can hear from an actual owner/user of this module? Or better yet, anybody heard from Pratt Hobbies directly? I'd ask, but it might seem a bit weird as the question would be coming from the ......uh.......competition. You know.... the whole Wilson F/X thing........

#### Nilo

##### Well-Known Member
TRF Supporter
Hello Nilo,

I'm sorry, but the only info that I've got on Pratt's relay module is what's up on the Pratt Hobbies website. It uses a battery at the pad for ignition but all the website says is that the relay is activated by any 12v launch system.

I can only guess looking at the one picture that they have up, that your leads from your own 12v system plug into the central part of the relay module. You will need to have the polarity correct in your own 12v launch system, but correct polarity's necessary for activating any relay. But that's as far as I can go on mere speculation.

I have no idea how many volts/amps are required to activate the relay module. The website does not include that information.

Has anybody on this thread actually used one of Pratt Hobbies "Relay Modules" or better yet, have one in hand with instructions so that we can hear from an actual owner/user of this module? Or better yet, anybody heard from Pratt Hobbies directly? I'd ask, but it might seem a bit weird as the question would be coming from the ......uh.......competition. You know.... the whole Wilson F/X thing........

Called Pratt and left a message for them to call me. I too noticed the central connection on the module.Just like you I'm guessing that's how you connect to the base control box, and then be able to check the continuity.

Are you the owner of Wilson F/X?

Nilo

#### pbahorich

##### Active Member
I was at FAR last month and I saw people using their own launch systems. This surprised me a bit so I asked an officer. I was told that you can use theirs but sometimes you can wait until it is available so there are advantages to having your own.

#### jrap330

##### Retired Engineer, NAR # 76940
TRF Supporter
I'll be using a 12volt car battery, 500 CCAmps. Will this suffice for a 200' distance?
You have not thought this completely. Besides voltage drop, who knows what 300 feet of 12 gauge or 14 gauge cable weights ..not to mention the painstaking issue of bundling it back up. My 100 foot outdoor extensions is heavy and every time I have to roll it up to put in my garage...I cringed. Tons of post on building a relay launcher but be smart launch with a club. And consider this...would you launch level II rockets/engines on your own..

#### jrap330

##### Retired Engineer, NAR # 76940
TRF Supporter
Thanks for your input. Right now I have a system for 50' length for launching my rocket with G engines. If I could make the system work up to 100' I could launch up to J engines.

The reason I'm requesting advice is because, as you stated, this is my entrance into high power rocketry.

Nilo
And therefore..High Power launch with a club....

#### Voyager1

##### Well-Known Member
TRF Supporter
On the subject of using modified extension cords (e.g., removing a connector from one end), be sure to clearly label it as such, just in case someone else who doesn’t realise, tries to plug it into the mains!

#### Nilo

##### Well-Known Member
TRF Supporter
Hello Nilo,

I'm sorry, but the only info that I've got on Pratt's relay module is what's up on the Pratt Hobbies website. It uses a battery at the pad for ignition but all the website says is that the relay is activated by any 12v launch system.

I can only guess looking at the one picture that they have up, that your leads from your own 12v system plug into the central part of the relay module. You will need to have the polarity correct in your own 12v launch system, but correct polarity's necessary for activating any relay. But that's as far as I can go on mere speculation.

I have no idea how many volts/amps are required to activate the relay module. The website does not include that information.

Has anybody on this thread actually used one of Pratt Hobbies "Relay Modules" or better yet, have one in hand with instructions so that we can hear from an actual owner/user of this module? Or better yet, anybody heard from Pratt Hobbies directly? I'd ask, but it might seem a bit weird as the question would be coming from the ......uh.......competition. You know.... the whole Wilson F/X thing........

Yes, you are the owner of Wilson FX.

Will your unit PBU-1w satisfy my need, including wireless?