Stupid Electricity Question aka self electrocution

[eddie]

Ok, I understand about zero when it comes to electricity, and I know we have guys here that know it inside and out, and this is kind of aviation related...

I have built a model rocket. It's nothing special, just cardboard and balsa: kid stuff like Estes, for those who are familiar. Thing is, I've built it as a three-engine cluster and need to ignite all three engines at once, and must upgrade my power source. From what I have been able to glean from various kit manuals/guides and the internet, I know I need 5 amps per engine to get successful ignition. So, I need a battery that generates at least 15 amps (more=better) over a very short period of time. What can I get that can do that?

Should I just go out and buy a car or motor cycle battery (I plan to increase size and power as I get better at building these things...)? I have some 6 Volt lantern batteries, are they any good?

All help is greatly appreciated. Thanks.

 

[NavyLonghorn]

I think even reading this post may make girls not want to date me.....

 

[HueyCobra8151]

Are your 3 engines in series or parallel? What is their resistance drop?

Figure out their resistance, then use Ohms Law (E = I * R) to determine the power source.

Actually, your BEST bet might be to use a capacitor. Charge it and set it to discharge when you connect the circuit (easiest way would be through a double pole double throw (DPDT) switch. That would give you a lightweight, short, powerful (depending on the size of course) burst that MIGHT be what you need.

I don't know that much about your situation, so a cap. might not be feasible; disregard if so.

Alternatively, put on a brown cranial (or deck jersey), go through preflight, then call out a (g)Avi troubleshooter. Down the plane, cann and swap the power source into another bird, do a DNT on the new bird, determine that it is down too, and cann and swap the power source back into the original bird. Curse at maintenance control. Go back into the flightline shack until (g)Avi gets it fixed and drink coffee...

 

[eddie]

I cannot remember if they are going to be wired series or parallel... which ever one doesn't suck... I think. Uh, I'm pretty sure it's in series.

Huey, I think I understand what you are saying.

Ok, I think I lose.

 

[HueyCobra8151]

Do you have a schematic for this thing?

Edit: If it is in series, look on the schematic, find the total resistance of the system, then use Ohms Law. Easy.

 

[eddie]

No, this thing is scratchbuilt, and I can't find the specs for those engines, except the whole 5 amps thing. I don't even know what an amp is.

 

[Texan]

hehe... try this bad boy... if you cant light 15 engines at the same time with a 50 farad capacitor, it's not going to work... just dont stand too close to the capacitor itself when you set it off... arcing one of these is about as close a civilian can get to setting of a grenade.

PS... DONT ACTUALLY TRY THIS >> YOU WILL PROBABLY KILL YOURSELF AND ANY LOCAL FURRY ANIMALS THAT MAY BE WATCHING.

---------------------------------------

12V = 5amps * R

R= 2.4ohms

Just figure out how to get your 3 ignitors to 2.4 ohms on a car batery and you've got it made. just remember to use fairly thick wire with 5 amps.


Lets assume a 1/5 ohm resistance on the ignitor (check this with an ohmmeter and substitute the value)

if you have three ignitors at .5ohms, in parallel they would be 1/5+1/5+1/5= 0.6 ohm so you would need to add a 1.8 ohm resistor in series with the circuit.

OR

set the ignitors in series and you get .5 + .5 + .5 = 1.5 and all you need is a 0.9 ohm resistor.

or just try things out - that's half the fun of this experimenting / rocketry thing anyway. for more resistance, try using a tarnished spoon or something (use the ohmmeter to find out what the resistance is before hand to make sure it's close to what you need.

Also note that a small battery may not last long enough at these amperage levels - a decent car battery is usually rated at a couple hundred cold crank amps so that should be MORE than enough (just dont drop the spoon across the terminals... remember the GRENADE thing).

hope this send you in the right direction.

Texan

Disclaimer - I am a MATERIALS engineer - not an ELECTRICAL Engineer - take this at face value and double check everything before losing a finger or an eye.

 

[eddie]

I think, I'm just going to dig a small pit in the back of my yard, wire three engines and touch the two ends to this one battery i think will work. If they all fire at the same time, I'm gold. If not, I'll just buy a motorcycle battery: the internet told me it would work.

I'll try the "grenade" when I can find a wide open space to set if off.

 

[HueyCobra8151]

Oh, the battery isn't going up in the air w/ it? I thought you wanted the smallest battery possible w/ the given resistance...I'm an idiot.

Here is a thought: If you got a variable resistor, you would be able to control the amperage without having to solder/resolder as you are fooling around w/ different numbers.

 

[eddie]

Oh, the battery isn't going up in the air w/ it? I thought you wanted the smallest battery possible w/ the given resistance...I'm an idiot.

Here is a thought: If you got a variable resistor, you would be able to control the amperage without having to solder/resolder as you are fooling around w/ different numbers.

I was trying to be cheap with a power source. I'm going to need to upgrade to a large scale battery anyways eventually, so I'll just buy it now. That way, it's overkill no matter how you look at it. A car battery will supply more than enough power to fire all of these things off at once.

Thanks everyone.

 

[Brett327]

Ok, I understand about zero when it comes to electricity, and I know we have guys here that know it inside and out, and this is kind of aviation related...

I have built a model rocket. It's nothing special, just cardboard and balsa: kid stuff like Estes, for those who are familiar. Thing is, I've built it as a three-engine cluster and need to ignite all three engines at once, and must upgrade my power source. From what I have been able to glean from various kit manuals/guides and the internet, I know I need 5 amps per engine to get successful ignition. So, I need a battery that generates at least 15 amps (more=better) over a very short period of time. What can I get that can do that?

Should I just go out and buy a car or motor cycle battery (I plan to increase size and power as I get better at building these things...)? I have some 6 Volt lantern batteries, are they any good?

All help is greatly appreciated. Thanks.

I guarantee that no Estes rocket motor igniter is developing 5 amps of current, considering that my childhood model rocket system ran off of 2 AA batteries back in the day. All you poindexters can work the magic @sshole and ohms law until you're blue in the face, but I'm here to tell you that you don't need a car battery, or even a lantern battery to light off a few igniters. As for your synchronization problem, I'm sure you're not the first guy to deal with this issue - don't try to reinvent the wheel.

Brett

 

[Banjo33]

1.21 Gigawatts!!?? You need a bolt of lightening!!

 

[eddie]

Brett: I wouldn't have thought so either, but I have been given the impressiong that I do.

UI: I thought about that, but I need to trigger everything simultaneously. If I wired 12 AA's together, would that produce the power of 1 AA for 12 AA lives, or would it give the power of 12 AA's for 1 AA life. A happy medium?

Jboomer: hahaha, Doc.

 

[Crowbar]

Am I the only one thinking that 5 amps (especially X3) is a helluva lot of juice to be screwing around with in the backyard?

Why not just shut off the breaker to your house, then splice an ignition wire in there. You should get about 200+ amps when you turn it back on. More is better, right? It's AC, though, so be careful. (I'm not serious, don't try this unless you just hate this cold, cruel world...)

 

[JIMC5499]

Stupid Electricity Question

According to Estes you need 1/2 amp at 6 volts to fire their igniters. I think that he might have missed the decimal point on his instruction sheet. A 12 volt lantern battery should be what he needs. To make sure that they all fire at the same time I'd just use 3 sets of wires and have them terminate at the switch and then one set to the battery. Tape the wires together to make it easier to connect them to the motors.

Estes Igniters