OK battery gurus....a little advice please.

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stealth6

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I'm dreaming up a new scratch build and I could use some guidance from those of you here on TRF that really know batteries.

Here's the situation - I might need to airstart as many as nine black powder motors at once. I would be using Q2G2 igniters. Avionics are still being considered but I have available either: a Perfectflite MiniTimer (which I've used on a few rockets already to airstart up to three motors at once), a MissileWorks RRC3, or a Featherweight Raven. I've been reading up on using dual 9v's (wired per specs from the altimeter manufacturers in question) and know that that is one possible option. And I've been reading quite a few threads that get into technical detail on battery outputs, voltage drops, amperage ratings, and such, and quite honestly I get most of it, but after a while my head starts to spin a bit.

So....those of you who DO really get it - what would you recommend? Which avionics/battery setup would you choose/recommend if you wanted to airstart 9 BP motors? Simple timer, or auxillary output from a full featured altimeter? Dual 9v's, or some specific LiPo? Do I even need more oomph than I could get from a plain old (but fresh) 9v? (and yes, "oomph" is plenty enough technical jargon for me).

thanks in advance, s6
 
I'm not sure about the avionics, but LiPo is absolutely the way to go. Take a look at this https://www.rocketmaterials.org/research/igniters.pdf which shows that the actual current draws from igniters is much higher than the all-fire current.

Also, from another Rocketry Forum post:
I got 48 of the long Q2G2 ignitors and measured all of them for resistance. All were close to 3 ohms. Lowest I saw was 2.1 ohms and highest was 3.9 ohms.

So an average of 3 ohms in parallel, V = IR, 9 = I * 3, I = 3A. You have 9 igniters, so 3*9 = 27 Amps! No 9V battery is going to be able to output 27 amps, let alone without dropping significant voltage. For this setup recommend a two or three cell (7.4 and 11.1V respectively) 30C battery at 1mAh or more, Such as this one from Hobby Lobby. It is capable of 1.5A * 30 = 45 Amps instantaneous current, and should be /reasonably/ light.
Power dissipation in parallel for each Q2G2 is going to be 11.1V * 3 = 33.3 watts, which is /lots/.
This means you'll need a circuit board capable of delivering 30-40 Amps at 7-11 volts.

HOWEVER! Since you're using Q2G2's, you can put them in series. Resistance in series is summed, so your equation would be 9 = I * (3*9), I = .33A. Voltage drop across each resistor is going to be 1V, and each will carry .33A of current, so you'll be dissipating P = IV = .33 Watts (1/100th of your parallel circuit) across each one. I'm not sure that's going to be enough to ignite them... You could possibly do three parallel batches of three series igniters, which would give you 1 amp per batch, power dissipation of 3 watts each. Even still, I personally would never recommend 9V batteries for any model rocketry anything. LiPo's are really the way to go.

TL;DR - Get a LiPo, put them in 3 batches of 3 and be able to drive at least 3 amps from the altimeter. This battery should work perfectly and weighs... virtually nothing: https://www.motionrc.com/admiral-250mah-3s-11-1v-30c-lipo-battery/?gclid=CPr4tofKrroCFYdQ7AodBB8Aaw WARNING: If you are going to have the altimeter on the pad for a long time, get a higher mAh battery, this one can only drive 250 milliamps for one hour.

EDIT: Oh, also, you'll need a smart charger such as this one from Tenergy to charge your LiPo.
 
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Personally, I'd be going with a 3S lipo, and I wouldnt be buying from Hobby Lobby (either massively overpriced, or older chemistries/heavier manufacturing)

I'd be looking at:
Turnigy nano-tech 1000mAh 3S 45~90C Lipo Pack (USA Warehouse) $10.20 - Can dump 90 amps for a few seconds - enough to jump start most petrol cars.
or
Turnigy nano-tech 1300mAh 3S 45~90C Lipo Pack (USA Warehouse) $12.93
Prices may be higher, as I was logged in when getting those, if you leave the page open for a minute or so the lower price might be offered.

Of course, if you don't have LiPo batteries, you'll need a good charger too - as they do have fairly specific charging requirements. Charging too fast or over-volting the cells when charging can/may/will burn your house down depending on how far you go.
Something such as: Turnigy Accucel-6 50W 6A Balancer/Charger w/ accessories (USA Warehouse) ~$23
Is a cheap, decent choice. I have one of these for the car and have recommended them to several people - they are nice and simple, but do the job well.
 
If you are doing airstarts you really need to read through this whole thread: https://www.rocketryforum.com/showthread.php?57823-best-place-to-get-e-matches. In it John Derimiggio, of MARSA4/54 fame, really explained the operation of e-matches and proper use and set up for airstarting. It seems counter intuitive, but the electrical properties of e-matches are designed such that serial wiring is the preferred method for operation negating the need for large, high current LiPo's (along with high current drive circuits for alts and timers) for the majority of these applications.
 
If you are using Q2G2's I would use them in parallel because it is unknown if they will be reliabile in series like commercial ematches are designed to be. If using ematches then a series-parallel combination will be needed because you do not have enough voltage for all 9 in a string. You should have about 3V per ematch. (Again see the above mentioned thread for Kevin's post on voltage requirements in a multi-igniter string).

I would recommend a 2S ~350ma 20C LiPo. It will source enough current. A 3S Lipo may be too much voltage for the regulators on some of the altimeters you are considering.
 
Q2G2s are a good choice for this, because they parallel well.

Start with a hypothetical setup:

If you put all 9 Q2G2s in parallel on 1 battery, the equivalent resistance is about 0.3 Ohms. If you use a small,single lipo battery, it has about 0.5 Ohms of internal resistance. So you would have about 0.8 Ohms total, maybe 1 Ohm with wiring. 4V into 1 Ohm will put out 4 Amps, and each igniter would get 4/9 Amp of current. This is a little close to the 0.3 Amp all-fire current of a Q2G2, so I would recommend bumping this up a bit.

If you use your Raven, you can split up these igniters between 2 or 3 channels. Let's say you use 3 of the Raven channels, and each channel has its own small (130 mAhr) lipo battery. Then each channel would have 1 Ohm equivalent resistance from the Q2G2s, and another 0.5 Ohm of battery and wiring resistance. Then you would have 4V into 1.5 Ohms, to give 2.6 Amps total per channel, or about 0.9 Amps per Q2G2. This represents plenty of margin (about 10x minimum power) for the Q2G2 ignition, and no danger of putting too much current through any output switch, even if all of the igniters short.

To wire this up, each group of 3 igniter would have one lead from each igniter tied together to the + side of a battery, and the other igniter leads tied together and connected to one Raven deployment channel. The - of each battery is connected to the Gnd terminal of the Raven. You could use a 4th battery to power the altimeter and the other deployment channel in the normal way.
 
If you are using Q2G2's I would use them in parallel because it is unknown if they will be reliabile in series like commercial ematches are designed to be. If using ematches then a series-parallel combination will be needed because you do not have enough voltage for all 9 in a string. You should have about 3V per ematch. (Again see the above mentioned thread for Kevin's post on voltage requirements in a multi-igniter string).

I believe Q2G2 igniters have a fail-over path like a Christmas tree bulb, they're virtually guaranteed to work in series.
 
I believe Q2G2 igniters have a fail-over path like a Christmas tree bulb, they're virtually guaranteed to work in series.

When a Q2G2 blows the charge, the electrical circuit opens up. I've seen this in the recorded electrical continuity data from dozens of flights using Q2G2s. For one example: https://www.rocketryforum.com/showt...e-design-and-build-thread&p=243544#post243544

If Q2G2s work in series (I haven't tried it), it's only because the ignition of all of them happens before the electrical circuit opens for any of them opens. That's not a race that I would want to bet my project on on without a lot of testing.
 
Excellent responses - thanks folks! Once again, I'm reminded about how great this place (TRF) is - fast friendly guidance and advice - such a great educational resource.

Adrian, I really like your approach using 3 channels from the Raven. I'm honestly a bit leery about using larger LiPos - your solution (using three smaller ones) sounds safer (for my rocket and my avionics), and I've already got 5 of them as well as charger. This also allows me another option of three separate, staggered airstarts (3 motors each time). I will likely use a separate altimeter to handle deployment (I would need more than one channel because of dual deployment) - either another Raven or the RRC3.

This project - like pretty much all of mine - will likely take place over a few months. Right now it's just in the idea/dreaming stage, but I'll give you a small teaser: twelve motors total, three 24mm and nine 18mm. The three 24mms are sort of a standard cluster in a 3" airframe, and can be either AP or BP. The nine 18mms will be BP and are canted, and sort of fire out the sides of the airframe. I could launch this with all motors igniting off the pad (all BP) - or the three 24mms (AP) would launch the rocket, with the other nine airstarting either all together or staggered in sets of three.

I'll start a thread dedicated to this rocket when the time comes. Till now, I've got some ground testing to do to see how well these ideas will work.

Til then, please continue to chime in with more advice/guidance/feedback on this particular component. It's much appreciated.

thanks, s6
 
Adrian, can you please have a look at this, and see if I've got the wiring right. I'm really not sure this is correct, in that am I not doubling up on power to each output channel this way? Would this setup damage my electronics? How would I go about powering the altimeter itself, independent of the power going to the igniter clusters, or is that not necessary?
I'd be using a PowerPerch, with the Raven mounted normally and a regular 130 mAhr Lipo attached. Each of the inline batteries (to the groups of 3-each Q2G2s) would also be 130mAhr Lipos. I'd set the Apo, Main, and 3rd channels as timer function, and not use the 4th channel. These MAY fire simultaneously, or the MAY be timed to fire in sequence (if I want to get really fancy).

I would be using a completely separate altimeter to handle chute deployment(s).

I believe launch sequence at the pad would be -
1. insert igniters into the main motors (which are fired by the regular launcher), and connect leads from launcher.
2. Power up the deployment altimeter - verify continuity to my deployment charges.
3. Insert all the igniters into the airstart motors, and connect leads to the Raven "timer array"
4. Power up the timer Raven (via the mag switch on the Power Perch) - verify continuity to the airstart motors.
5. Back at the launch button, verify continuity to the main motors.
6. Launch.
7. Either A) fist pump, whoop & holler, and beam proudly, or B) hang head in shame and walk away dejected, depending on outcome of flight.

Again, if you could second check me on this, I'd appreciate it.

Thanks for all your help, s6

9plus3 timer wiring.jpg
 
Adrian, can you please have a look at this, and see if I've got the wiring right. I'm really not sure this is correct, in that am I not doubling up on power to each output channel this way? Would this setup damage my electronics? How would I go about powering the altimeter itself, independent of the power going to the igniter clusters, or is that not necessary?
I'd be using a PowerPerch, with the Raven mounted normally and a regular 130 mAhr Lipo attached. Each of the inline batteries (to the groups of 3-each Q2G2s) would also be 130mAhr Lipos. I'd set the Apo, Main, and 3rd channels as timer function, and not use the 4th channel. These MAY fire simultaneously, or the MAY be timed to fire in sequence (if I want to get really fancy).

I would be using a completely separate altimeter to handle chute deployment(s).

I believe launch sequence at the pad would be -
1. insert igniters into the main motors (which are fired by the regular launcher), and connect leads from launcher.
2. Power up the deployment altimeter - verify continuity to my deployment charges.
3. Insert all the igniters into the airstart motors, and connect leads to the Raven "timer array"
4. Power up the timer Raven (via the mag switch on the Power Perch) - verify continuity to the airstart motors.
5. Back at the launch button, verify continuity to the main motors.
6. Launch.
7. Either A) fist pump, whoop & holler, and beam proudly, or B) hang head in shame and walk away dejected, depending on outcome of flight.

Again, if you could second check me on this, I'd appreciate it.

Thanks for all your help, s6

View attachment 153455

I don't have too much experience with the Power Perch, (I directly wire to the Raven) but I think you have all those batteries backward.
 
Adrian, can you please have a look at this, and see if I've got the wiring right. I'm really not sure this is correct, in that am I not doubling up on power to each output channel this way? Would this setup damage my electronics? How would I go about powering the altimeter itself, independent of the power going to the igniter clusters, or is that not necessary?
I'd be using a PowerPerch, with the Raven mounted normally and a regular 130 mAhr Lipo attached. Each of the inline batteries (to the groups of 3-each Q2G2s) would also be 130mAhr Lipos. I'd set the Apo, Main, and 3rd channels as timer function, and not use the 4th channel. These MAY fire simultaneously, or the MAY be timed to fire in sequence (if I want to get really fancy).

I would be using a completely separate altimeter to handle chute deployment(s).

I believe launch sequence at the pad would be -
1. insert igniters into the main motors (which are fired by the regular launcher), and connect leads from launcher.
2. Power up the deployment altimeter - verify continuity to my deployment charges.
3. Insert all the igniters into the airstart motors, and connect leads to the Raven "timer array"
4. Power up the timer Raven (via the mag switch on the Power Perch) - verify continuity to the airstart motors.
5. Back at the launch button, verify continuity to the main motors.
6. Launch.
7. Either A) fist pump, whoop & holler, and beam proudly, or B) hang head in shame and walk away dejected, depending on outcome of flight.

Again, if you could second check me on this, I'd appreciate it.

Thanks for all your help, s6

View attachment 153455

The Power Perch is designed to take care of all of the ematch connections for you, so for an application like this where you're doing something special it is getting in your way a bit. It can still be used, but you would only use one of the 2 connections per channel, the ones that go directly to each Raven deployment terminal. The other terminal on each channel is a Power Perch battery switched +, which you would need to leave open. The - side of each battery would need to be connected to the altimeter ground, which in the case of the Power Perch is not among the screw terminal choices. One of the mounting screw holes is connected to (-) though, so it's still possible. When I get back I'll figure out which screw hole and which of the terminals you should connect to. In that setup, the Power Perch isn't doing anything except switching power to turn on/off the Raven. You
 
The Power Perch is designed to take care of all of the ematch connections for you, so for an application like this where you're doing something special it is getting in your way a bit. It can still be used, but you would only use one of the 2 connections per channel, the ones that go directly to each Raven deployment terminal. The other terminal on each channel is a Power Perch battery switched +, which you would need to leave open. The - side of each battery would need to be connected to the altimeter ground, which in the case of the Power Perch is not among the screw terminal choices. One of the mounting screw holes is connected to (-) though, so it's still possible. When I get back I'll figure out which screw hole and which of the terminals you should connect to. In that setup, the Power Perch isn't doing anything except switching power to turn on/off the Raven. You

Please do get back to me in case I do decide to go forward with using the Perch.

That said, if I decide to just use the Raven without the Perch (as you advise), is THIS wiring setup correct:
9plus3 timer wiring sketch 2.jpg

thanks again for the guidance.
I love my Featherweight gear.

s6
 
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