# My 12v cluster launch controller build

### Help Support The Rocketry Forum:

#### Joshua F Thomas

##### Well-Known Member
TRF Supporter
I'm looking to get into clustered rockets. I knew from discussions with others, and The Handbook of Model Rocketry, that I was going to need a 12v launch controller capable of delivering large amperage quickly. Having some electronic skill, I decided to build my own.

I have to give appreciation to forum user Micromeister for sharing his own controller build in this thread, as I used it as a general starting point, and for various Radioshack parts numbers. Yes, you can still order them! The Igniter Continuity Tests by J. R. Brohm was also helpful for me to determine safe ranges of current for continuity tests. I ended up doing my own tests to find that limit, but having a source that agreed was quite helpful.

My build uses a power delivery box positioned close to the pad, drawing from a 12V sealed lead-acid battery of motorcycle size (any high-drain 12V source should work in theory), and a hand-held box with extension wires for launch activation. Power is delivered via a 12V relay. 14 AWG wire is used everywhere except for where LEDs are used, and there I used 22g just for ease of wiring. Wire from power delivery box to hand-held is 50 feet of 18g lamp cord. Microclips are used for the igniter leads. I'm building clip whips whips that can handle up to 4 igniters each, which should be enough for all my needs for quite a while.

The power delivery box has an on/off switch with indicator LED and continuity test switch with LED. I used a regular on-off and not a momentary for the continuity simply because I got multiple of the same switch when ordering, and it keeps the look clean. Having the continuity stay "on" even for prolonged periods is a low risk; total current draw is approx 10 mA via the LED. At that draw the igniters do not ever go off. I let several different ones run for hours, and they never even got warm. Brohm's testing also confirms this - you need closer to 100 mA for any of the igniter types in common use to go off. With both LEDs on the box draws about 20 mA, only 1/2 of that through the igniter.

#### Joshua F Thomas

##### Well-Known Member
TRF Supporter
I've upgraded my launch controller to use a more portable and less heavy power source: Lithium Iron Phosphate (LiFePO4) rechargeable batteries. I wanted a source that was going to be able to deliver close to 12 volts and high instant amperage.

The regular Lithium Ion batteries are 3.7 volts, which x4 is 14.8 volts. The LiFePO4s are 3.2 volts each which x4 provide 13.2 volts, much closer to the nominal 12 volts. In addition LiFePO4s are better for high-drain uses. I ended up using four of the 26650 size. They fit comfortably inside my case, along with the holder, and had no issues at all with those three Estees igniters.

Now I just need to work out a switch allowing me to choose between the internal batteries and an external source, and wire in a recharger lead. The project never ends....

#### jrap330

##### Retired Engineer, NAR # 76940
TRF Supporter
I've upgraded my launch controller to use a more portable and less heavy power source: Lithium Iron Phosphate (LiFePO4) rechargeable batteries. I wanted a source that was going to be able to deliver close to 12 volts and high instant amperage.

The regular Lithium Ion batteries are 3.7 volts, which x4 is 14.8 volts. The LiFePO4s are 3.2 volts each which x4 provide 13.2 volts, much closer to the nominal 12 volts. In addition LiFePO4s are better for high-drain uses. I ended up using four of the 26650 size. They fit comfortably inside my case, along with the holder, and had no issues at all with those three Estees igniters.

Now I just need to work out a switch allowing me to choose between the internal batteries and an external source, and wire in a recharge lead. The project never ends....
Josh...looks great..you did a lot of work since starting this thread.

#### hermanjc

##### Well-Known Member
I recently built a custom launch controller (inspired by a YouTube video) with the intent of firing Estes motor clusters. At first I just used a bank of 8AAs for 12v of power, but bench testing with 3 igniters proved that wouldn't work. So then I added external power jacks for my lawn mower battery, which worked great, except removing it from the mower and hauling it around was a pain. So most recently I modified an old Ryobi charger to provide 20v of power from my readily available power tool batteries (just needed to add some resistors to the LEDs) and today it worked great for 3 motors clusters. Far more convenient than the mower battery. I also use 50ft of 14awg speaker cable from the controller to the launch pad for clusters. I still have the AA battery bank inside, but I cut an access hole on the back to switch it off when using external power, the LEDs are a little dimmer now on the 12v, but still plenty bright in full sunlight.

#### Joshua F Thomas

##### Well-Known Member
TRF Supporter
Nice build! That looks like the same size project box I used, but you’ve added a coat of paint?

The voltmeter is also a nice touch and I wish I had added one.

Your voltage drop with 100 ft of wire (out and back at 50 ft) is probably mitigated by the 20 volt source. How rapidly did the igniters fire? I recall Stine saying in his book that over 18 volts the igniters burned so rapidly they might not be reliable.

#### arconhi

##### Well-Known Member
TRF Supporter
I'm looking to get into clustered rockets. I knew from discussions with others, and The Handbook of Model Rocketry, that I was going to need a 12v launch controller capable of delivering large amperage quickly. Having some electronic skill, I decided to build my own.

I have to give appreciation to forum user Micromeister for sharing his own controller build in this thread, as I used it as a general starting point, and for various Radioshack parts numbers. Yes, you can still order them! The Igniter Continuity Tests by J. R. Brohm was also helpful for me to determine safe ranges of current for continuity tests. I ended up doing my own tests to find that limit, but having a source that agreed was quite helpful.

My build uses a power delivery box positioned close to the pad, drawing from a 12V sealed lead-acid battery of motorcycle size (any high-drain 12V source should work in theory), and a hand-held box with extension wires for launch activation. Power is delivered via a 12V relay. 14 AWG wire is used everywhere except for where LEDs are used, and there I used 22g just for ease of wiring. Wire from power delivery box to hand-held is 50 feet of 18g lamp cord. Microclips are used for the igniter leads. I'm building clip whips whips that can handle up to 4 igniters each, which should be enough for all my needs for quite a while.

The power delivery box has an on/off switch with indicator LED and continuity test switch with LED. I used a regular on-off and not a momentary for the continuity simply because I got multiple of the same switch when ordering, and it keeps the look clean. Having the continuity stay "on" even for prolonged periods is a low risk; total current draw is approx 10 mA via the LED. At that draw the igniters do not ever go off. I let several different ones run for hours, and they never even got warm. Brohm's testing also confirms this - you need closer to 100 mA for any of the igniter types in common use to go off. With both LEDs on the box draws about 20 mA, only 1/2 of that through the igniter.

The hand-held box has a tube-key arming switch. I paid a bunch for this switch - almost \$15 - but I really like the way it looks and acts. It has a solid positive feel, and can not be removed in the armed position. It gives a highly authentic "I'm about to launch a rocket" feel. Another indicator LED is used to indicate the hand-held is receiving power and that the switch is in the armed position. Launch is a standard momentary pushbutton.

I have not had a chance to test this in the field yet; hoping for this tomorrow! About 3/4 of the way through this build I also realized that high-powered rechargeable batteries may also work and fit into the 7" x 4" x 2" power box. I would need close to or slightly better than 12 volts, and high-drain. After some research, it looks like 26650 sized Lithium Iron Phosphate (LFP) batteries will work. They are 3.3v each (x4 = 13.2v) and can handle large current delivery for short periods. Standard 3.7v lithium batteries don't add up well, you either get 11.1v or 14.8v. If I go this route I'm going to wire another switch to allow me to choose between external or internal batteries.

Photos below; any feedback or questions welcome. This was a fun build.

View attachment 421638

View attachment 421639

View attachment 421640

View attachment 421641

View attachment 421642
You can't get it any better than this. This is a nice system. Well done.

#### Joshua F Thomas

##### Well-Known Member
TRF Supporter
Well, after having built my system, I would do a few things differently:

1) Use 16g wire instead of 14g wire for the internal connections. It’s less stiff and the voltage drop isn’t significant for the short lengths.

2) Add a voltage indicator for the batteries.

3) Find a way to hold the relay stationary instead of it just being loose on the inside.

4) Use spade terminals for more of the connections.

They aren’t deal breakers and in total this setup works well.

#### hermanjc

##### Well-Known Member
Nice build! That looks like the same size project box I used, but you’ve added a coat of paint?

The voltmeter is also a nice touch and I wish I had added one.

Your voltage drop with 100 ft of wire (out and back at 50 ft) is probably mitigated by the 20 volt source. How rapidly did the igniters fire? I recall Stine saying in his book that over 18 volts the igniters burned so rapidly they might not be reliable.
Yup just added yellow paint to the black project box. I really like your idea of having the power box near the Launch tower with relays and the ignition switch be remote.

The igniters lit very fast (couldn't take my finger off the launch button fast enough to prevent total burnout of all 3). The video below is a slomo of my test.

I made a couple "triple whips" using alligator clips to attach to the main clip leads coming from the controller. I always make sure to do individual continuity checks for each igniter before connecting all 3.

#### Joshua F Thomas

##### Well-Known Member
TRF Supporter
Yup just added yellow paint to the black project box. I really like your idea of having the power box near the Launch tower with relays and the ignition switch be remote.
I can’t take credit for the idea, that was originally from Harry Stine’s Handbook of Model Rocketry, as well as other builds here on the site.

#### Joshua F Thomas

##### Well-Known Member
TRF Supporter
Update: Two months on and the LFP 26650 batteries have done very well. I have done about a dozen launches and they still read 13.4 volts. This is excellent performance - I have not charged them at all so far. Highly recommend these for portable launch controller use.

#### Greg Furtman

##### Well-Known Member
TRF Supporter
I recently built a custom launch controller (inspired by a YouTube video) with the intent of firing Estes motor clusters. At first I just used a bank of 8AAs for 12v of power, but bench testing with 3 igniters proved that wouldn't work. So then I added external power jacks for my lawn mower battery, which worked great, except removing it from the mower and hauling it around was a pain. So most recently I modified an old Ryobi charger to provide 20v of power from my readily available power tool batteries (just needed to add some resistors to the LEDs) and today it worked great for 3 motors clusters. Far more convenient than the mower battery. I also use 50ft of 14awg speaker cable from the controller to the launch pad for clusters. I still have the AA battery bank inside, but I cut an access hole on the back to switch it off when using external power, the LEDs are a little dimmer now on the 12v, but still plenty bright in full sunlight.

View attachment 426673
Nice voltmeter! Who makes or sells them?

#### hermanjc

##### Well-Known Member
Nice voltmeter! Who makes or sells them?
I got mine from Amazon (https://www.amazon.com/gp/product/B06Y3YS189/). They have lots of options if you search and you should find one to suit whatever your needs are.

Update: Two months on and the LFP 26650 batteries have done very well. I have done about a dozen launches and they still read 13.4 volts. This is excellent performance - I have not charged them at all so far. Highly recommend these for portable launch controller use.
That's excellent. Perhaps I will swap my AA battery pack out for those same batteries. Would certainly make it simpler to not need to bring a hobby battery or a drill battery with me.

#### jrap330

##### Retired Engineer, NAR # 76940
TRF Supporter
Update: Two months on and the LFP 26650 batteries have done very well. I have done about a dozen launches and they still read 13.4 volts. This is excellent performance - I have not charged them at all so far. Highly recommend these for portable launch controller use.
great, not surprise .