Whip it good! (multiple igniter newbie question)

[Marc_G]

MODS: Sorry, I posted in the wrong forum and can't seem to move or delete it. Can you please move it over to Propulsion? Thanks! -Marc

Hi folks,

In a week or so I start my first cluster build. It will be a Der Big Red Max outfitted for 3x18mm engines. Nothing too fancy.

To launch it, can I just customize an extra standard Estes (yellow) ignition system by hacking on some more aligator clip leads? I recognize the optimal way might be to set up a continuity circuit for each igniter, but I'm very lazy.

So, I guess the crux of my question is two fold:
1. Does the standard 4xAA battery set have enough juice to reliably ignite 3 igniters in sync?
2. If not, and if I add a lantern battery or whatever substituting for the AAs, will the extra current available now available at the continuity light stage be larger than before and thus ignite prematurely my igniters?

If the voltage is the same (4x 1.5V AA = 1 x 6V Lantern battery), and the resistance is the same (igniter resistance plus continuity resistor), the current flowing during continuity check stays the same, per Ohms law, right?

Sorry if this is a stupid newbie question!

Marc

 

[judo]

No, it's not a stupid question. The folks with tons of more knowledge than I have will tell you to go with a 12V system. We just had the same question come up last week, I think. An Estes contoller with FRESH AA batteries could PROBABLY launch a TWIN cluster with SOME reliablity. I'll let the EE's go into the Ohm's Law on why.

Stick around here and within 30 days, someone else will ask the same question again. We don't mind. It's why we're here.

 

[MarkII]

When a cluster comes along, you must whip it...

​

What Judo said. If you are using Estes igniters, you really should use a 12 volt power source to ignite a 3-motor cluster or larger. I haven't tried to ignite a cluster of Quest igniters with 4 AAs or a lantern battery, but that might be enough to fire a small group (2-3) of them. I prefer to use a healthy amount of power for even the quite modest clusters that I launch so that I can have some assurance that they will all fire simultaneously. I have been known to use my 12 volt AeroTech controller to fire clusters of 2 or 3 MicroMaxx motors. Granted, that's probably a slight overcompensation...

 

[Pantherjon]

I love clusters! Only thing is I don't use whips..What I do is use some thin gauge wire and make extensions for the ignitors..So far(knock on wood) I have had a 100% ignition success rate..Granted I only launch these at club launches were we have 12v power supplies to the pads..Here is a picture of the wiring to my 6 motor cluster rocket I call Trois Duex..

 

[bobkrech]

Marc

This is a fine place for this post. This forum is for support equipment and launchers and batteries are appropriate topics.

You need to know that as far as batteries are concerned, it the current sourcing capability of the batteries that is more important than the battery voltage. The all-fire of an Estes igniter is listed at 2 amps and the resistance is listed at 0.8 ohms. Using ohms law, V=RI=2*0.8=1.6 volts.

Three igniters in parallel require 3 * 2 amps minimum to ignite simultaneously. What ever battery you use, the battery must be able to supply at least 6 amps. It is difficult get 6 amps from alkaline AA batteries unless they are new. If you want to use the Estes launcher, you should purchase NiCad or NiMH rechargeable batteries. They have a lower internal resistance and will source much greater current.

A 6 volt lantern battery is expensive, and won't supply more current than AA alkaline batteries, it just has more capacity so it will last longer in lantern applications.

Bob

 

[Marc_G]

Bob and everyone,

Thanks for the fabulous info. I'll get some NiMHs and run a test with 3 igniters. Safety first!

 

[o1d_dude]

What about two 6v lantern batteries wired in series?

 

[luke strawwalker]

Doubling the voltage reduces the amp requirement by half to deliver the same wattage (heat). Volts times amps equals watts. So yeah, connecting two 6 V lantern batteries in series to get 12 V is a good solution.

That's why I've modded all my Estes controllers with external clips so that I can hook straight to an auto-battery jumper pack, which is a highly portable and very useful power source for launching, and serves dual purpose as a jumper battery if the truck battery gets low or something.

Another good recommendation for clustering is, use cluster-friendly Quest Q2G2 ignitors, which use only a small FRACTION of the power required by Estes ignitors and are far more reliable, IMHO. BUT, using them with Estes controllers requires modifications to the controller (LED indicator to prevent "fire at key insertion")

Later! OL JR

 

[o1d_dude]

Thought that might be the case with the series wired batts. Thanks, OL JR.

I opted to go with the Quest launch controller and the external jumper cable thinking I might one day be using the Quest igniters as well.

 

[luke strawwalker]

Thought that might be the case with the series wired batts. Thanks, OL JR.

I opted to go with the Quest launch controller and the external jumper cable thinking I might one day be using the Quest igniters as well.

Sounds like a plan... good call!

OL JR

 

[Evo666]

When a cluster comes along, you must whip it...

​

hahha i knew this was coming once i read the title. :clap:​

 

[bobkrech]

Folks

To correct a previous statement, if you double the battery voltage, the igniters will try to draw twice the current and 4 times the power.

V = RI and I = V/R so if you use 2 batteries and have 2V then 2V/R=2I.

P = V^2/R so if you use 2 batteries and have 2V the P = (2V)*2/R = 4V^2R.

Putting 2 bad 6 volt batteries in series is not a solution because the circuit wants to draw twice the current and develop 4 times the power. If a single battery can't supply the current, the 2 batteries in series won't supply twice the current or 4 times the power.

If you really want to use the expensive 6 volt lantern batteries and can't get enough current to fire the igniters, then you have to put the second one in parallel to double the current sourcing capability.

The better solution is simply to get batteries that will source more current such as NiMH, NiCad, or Pb-acid gell cells.

Bob

 

[Marc_G]

Thanks for all the discussion. This was exactly what I was hoping for!

 

[Micromeister]

Marc_G:

I try to remind folks new to clustering it's not the volts that are important, its the current (amps.)
As bob has already pointed out the rule of thumb is 2amps per igniter for successful "reliable" cluster ignition.

I recommend a Gel-Cell rechargable 12V battery as a minimum. I'm partical to the little Hobbico 7amp/hr gel-cells used by RC flyers for small cluster ignitions. I've used one of these with a rangebox relay system for years with a very high success rate for these smaller 2,3& 4 motor cluster applications.
Many folks have been using there cordless drill batteries with success on 2,3 & 4 motor BP clusters. I personally haven't tried this so I can't make a recommendation one way or another, I'd suggest static firing several clustered igniter groups to test any drill battery application before committing a model to it

All That said about the battery:

The single most important piece of Cluster ignition ground support equipment is the addition of a RELAY ignition system. This moves the battery from the controller side to or directly under the launcher greatly reducing power lose through those tiny little controller leads.
To be honest with the new Q2g2 Quest igniters 2motor clusters can be done for just about any standard ignition system. 3 and 4 motors ya really need to get into the relay mode

Attached is a drawing I recently reworked for my "rangebox relay" utilizing mostly Radio shack currently available parts. I've been using one of these little DPDT relays for almost 20 years now with simply GREAT success on 2 to 6 motor clusters.
If your really intending to get heavily into BP clustering I'd also suggest a visit to the www.narhams.org library section lookup and download tech-tip-006 clustering BP motors that should give you a lot in good solid info about the subject.
Hope this helps.

 

[qquake2k]

F

The better solution is simply to get batteries that will source more current such as NiMH, NiCad, or Pb-acid gell cells.

Bob

NiMH and NiCad batteries are only 1.2 volts, so four of them would only give you 4.8 volts (vs. 6 volts from alkalines). I know they have higher current capacity, but would the reduced voltage affect the simultaneous ignition of three igniters? If it were me, I'd go with a 12 volt gel cell for clusters.

 

[plano-doug]

NiMH and NiCad batteries are only 1.2 volts, so four of them would only give you 4.8 volts (vs. 6 volts from alkalines). I know they have higher current capacity, but would the reduced voltage affect the simultaneous ignition of three igniters? If it were me, I'd go with a 12 volt gel cell for clusters.

These types of batteries generally have much lower output resistance than comparably sized alkalines. So, while there may be less voltage at the source, with lower output resistance, there is less voltage loss along the way to the load, so you end up with more voltage at the load and hence more current in the ignitors.

Pretty much all my clustering has been with Estes ignitors. For those, I use a 12V lead acid gel cell, which also has a low output resistance. If I was using NiCads, I would feel pretty good with 9.6V, but if I had the choice, I'd use the 12V gel cell

Doug

.

 

[bobkrech]

NiMH and NiCad batteries are only 1.2 volts, so four of them would only give you 4.8 volts (vs. 6 volts from alkalines). I know they have higher current capacity, but would the reduced voltage affect the simultaneous ignition of three igniters? If it were me, I'd go with a 12 volt gel cell for clusters.

It's amps, not volts, that activate iginters. Estes igniters require 2 amps to activate, and have a resistance of 0.8 ohms. Using Ohm's law, we find that the voltage developed across the igniter at 2 amps is V=RI=0.8x2=1.6 volts. The reason you need more than 1.6 volts is to overcome the resistance of the wires.

Personally, I would build my own launcher if I did a lot of launching on my own, and I would use a 12 volt Pb-acid gel cell and charge it from my cars cigarette lighter. This type of launcher will light just about anything if you use a 7 AH hour battery.

Estes has several excellent free Tech Reports on launchers and igniters. All the equations are shown in these reports.

https://www.estesrockets.com/images/uploads/2811_Estes_Model_Rocket_Launch_Systems.pdf

https://www.estesrockets.com/images/uploads/Estes_Igniters_and_their_use.pdf

Bob

 

[Jclark]

I love clusters! Only thing is I don't use whips..What I do is use some thin gauge wire and make extensions for the ignitors..So far(knock on wood) I have had a 100% ignition success rate..Granted I only launch these at club launches were we have 12v power supplies to the pads..Here is a picture of the wiring to my 6 motor cluster rocket I call Trois Duex..

That's a cool rocket. Got anymore pictures of it, or videos of it flying?

Jeremy

 

[Marc_G]

OK, looks like it's time to buy a gel battery! But this may wait until winter as a project. For now I may just try some AA NIMHs I've got in a more-or-less stock Estes ignitor with an octopus whip at the end. Cat-O-8-tails (building for a 4-cluster though my rocket will be just three). Some static firing should give me an idea. I do plan to replace the long lead with a heavier gauge to minimize loss. What gauge do they use? I've seen pacemakers with thicker leads...

Over the winter I'll come up with a better solution that gives me individual continuity indicators and works off the relay principle. Thanks for the links guys!

I promise to take pics and video and post them when available. The rocket parts "arrived" today but nobody was around to sign for them (made mistake of insuring; caused "signature required-can't leave at door" problem. Won't get to the post office 'til mid week.

Then it will be Der Big Red Cluster Max time!

Marc