What batteries...

[DexterLB]

... do you folks use in your launch controllers? Do I need a large car/UPS battery, or I can do with something smaller, to fire an igniter?

 

[sylvie369]

Are you talking about lighting Estes-type igniters for BP motors? Or are you lighting composite motors as well?

One motor at a time, or are you planning to launch clusters?

 

[spacecadet]

Four AAs will fire a single Estes igniter. If you use quick match for clusters that's all you need, but if you use multiple igniters you may need more.

 

[DexterLB]

I'm making a launch system for one rocket... some day I may use it to fire clusters as well.

I was thinking about a super-duper ultra-large hyper-heavy lead-acid UPS battery, but if you say so, I'll go to something smeller. Way smaller

how many amps do you think I'll need most? Do you think 8 A batteries will do it?

 

[bobkrech]

... do you folks use in your launch controllers? Do I need a large car/UPS battery, or I can do with something smaller, to fire an igniter?

Dexter

You do not need a car battery or anything that heavy, but you also don't want to us AA batteries because they are expensive. If you are going to do a lot of launches, the 12 volt sealed lead acid gell cells found in emergency lighting units and computer UPS supplies are the least expensive way to go.

You should check out the following threads.

http://www.rocketryforum.com/showthread.php?t=2465

http://www.rocketryforum.com/showthread.php?t=727

12 volts sealed lead acid gell cells in the 7 AH to 12 AH range work fine for launcher applications where your doing hundreds of launches. In the US they are inexpensive and readily available, and 5 AH units are fine individual launches. These batteries have low internal resistance so they will source a lot of current for clusters.

Bob

 

[sandman]

Two old Ni-Cad batteries from a couple of no longer used R/C cars work fine.

With a total of +14volts they'll fire darn near anything.

 

[DexterLB]

Nah, I don't think AA batteries are expensive.

I won't spend more than $10 for 8 batteries ---> 12V ----> many launches
Anyway, I'll make a plug on my launching thing, and I can put whatever batteries i like
I think I won't need to make a charger etc

 

[spacecadet]

I've had well over 100 launches out of my current set of 4 AAs in an Estes firing box. They're Kodak and have lasted at least five years. If you don't launch very often, the shelf life of expendables is helpful. You can't really leave rechargeables for a year.

 

[BsSmith]

You could use one of those batteries typically found in the model airplane field boxes, they're powerful and they can be recharged! Ni-cad and Li-poly model airplane batteries could even work too.

 

[Handeman]

I have a car battery charger so I bought the smallest motorcycle battery I could when it was on sale at the auto parts store for $20. It is rated at 70 CCA (cold cranking amps). I charge it in the spring and routinely launch 3 and 4 motor clusters with estes ignitors all summer.

 

[TheAviator]

You could use one of those batteries typically found in the model airplane field boxes, they're powerful and they can be recharged! Ni-cad and Li-poly model airplane batteries could even work too.

Ni-Cads could work, but Li-Polys are a big danger. With gel cells and car batteries, you can have a short at the pad while holding the launch button and nothing too bad will happen unless you hold it there all day. With Li-Polys will fail catastrophically when subjected to this kind of torture for more than a fraction of a second, (and we know what happens when you get a misfire: "Oops, didn't work. Let's hold the launch button in for 10 seconds, then see what's wrong.") A melting/venting/burning Li-Poly is the last thing you want a couple inches from your hand.

 

[bobkrech]

Ni-Cads could work, but Li-Polys are a big danger. With gel cells and car batteries, you can have a short at the pad while holding the launch button and nothing too bad will happen unless you hold it there all day. With Li-Polys will fail catastrophically when subjected to this kind of torture for more than a fraction of a second, (and we know what happens when you get a misfire: "Oops, didn't work. Let's hold the launch button in for 10 seconds, then see what's wrong.") A melting/venting/burning Li-Poly is the last thing you want a couple inches from your hand.

That's not correct. Lithium-ion and lithium polymer batteries are quite safe as long as they are not overcharged, physically damaged to the point of developing internal shorts, and are properly packaged.

Lithium-ion batteries (the ones in your computer) and Lithium Polymer batteries (the ones in your cell phone) are a bit more robust, and less hazardous, than you portray. If they weren't, you couldn't have them in your computer or your cell phone.

The big danger with lithium batteries is due to overcharging. Most lithium batteries will be damaged if they are charged to more than 4.2 volts per cell. This will overheat the batteries and in the case of Li-ion batteries, the casing can rupture, and because the electrolyte used in a Li-ion battery is flammable, it can catch fire. Li-poly batteries do not use a flammable electrolyte, however the plastic casings can overheat, rupture and burn if they are overcharged.

Lithium-ion and lithium polymer batteries themselves get warm and even hot when they are discharged at a high rate, however the hazard is a heat burn, and not a flame. The flaming laptops that you saw on youtube were due to a manufacturing flaw inside one of the lithium ion batteries that created an internal short inside an individual cell which caused the electrolyte to catch fire, and then set off the rest of the batteries and the laptop. This will not happen with lithium polymer batteries since the electrolyte is not flammable, but it is possible to get a severe skin burn from an internally shorted lithium polymer battery.

If a wire accidentally shorts a high capacity Lithium-ion, lithium-polymer, and even a NiMH, NiCad or Pb-acid battery, the wire can become very hot and ignite the surrounding container. (After all, this is how igniters work.) This is a very real hazard and is the reason why you are not allowed to carry loose, unpackaged batteries of any type on an airplane.

Bob

 

[TheAviator]

Ooops, sorry about that! I was under the impression that it was over-current, not over-charge that caused the fatal damage. I have not used them yet for fear of my mishandling them and causing a fire. Good to know it only happens when charging.

I do know that the electrolyte in NiMH's is flammable from experience, but that was a very high-gee crash on a DBF competition aircraft (thankfully not ours). The batteries (very high cell count, 20-30V range) broke from their mounts and hit something more solid than them inside the airframe. There was nothing left but ash and small bits of metal within about 3 or 4 minutes.

Anyways, sorry for the misinformation.

 

[bobkrech]

Ooops, sorry about that! I was under the impression that it was over-current, not over-charge that caused the fatal damage. I have not used them yet for fear of my mishandling them and causing a fire. Good to know it only happens when charging.

I do know that the electrolyte in NiMH's is flammable from experience, but that was a very high-gee crash on a DBF competition aircraft (thankfully not ours). The batteries (very high cell count, 20-30V range) broke from their mounts and hit something more solid than them inside the airframe. There was nothing left but ash and small bits of metal within about 3 or 4 minutes.

Anyways, sorry for the misinformation.

Probably wasn't clear about the other batteries. The electrolyte in NiMH is not flammable. AFAIK only the electrolyte in Li-ion batteries is flammable.

The fire hazard in a crash involving any high capacity rechargable battery pack regardless of type is the accidental shorting of the battery either internally by breakage or externally by a wire. The short generates a lot of heat which in turn causes some other part of the rocket or the grass to catch fire.

Bob

 

[DexterLB]

Well, I don't think that I am going to short my batteries for such a long time... My hypothetical (probably misspelled that word) launch controller will have a fuse and an AVR-based controller, which will stop the current, for example, 4 seconds after the launch button is pressed. Anyway, I decided to make a connector for the power supply and put the battery in a seperate box. I could make a box for 8 AAs, with clamps on the sides and a connector, to clamp it to the launch controller

Now I'm ready with the AVR firmware, and I'm working on the PCB design

 

[RimfireJim]

I normally use a small sealed lead-acid 12V battery, like Bob suggests, for my relay launcher. The number of launches I do in one day (30?) doesn't come close to draining it. I recharge it with an inexpensive 1 amp charger. The charger is not regulated, but lead-acid batteries are pretty tolerant.

Recently I've used the battery from my 12V cordless driver/drill. It's lighter and a little more compact than the lead-acid battery. I made a socket that has contacts for the battery terminals and studs for my battery clips from the launcher, into which I can put the battery just as if I was putting it into the drill, except I didn't worry about having it clip into place.

 

[MikeCr]

however the hazard is a heat burn, and not a flame.

This will not happen with lithium polymer batteries since the electrolyte is not flammable, but it is possible to get a severe skin burn from an internally shorted lithium polymer battery.

The Lithium Polymer batteries as used in electric powered RC airplanes most definitely WILL ignite if severely mistreated. All you have to do sometimes is puncture the package (very easy to do on them) and get them wet as the lithium reacts very violently with water!

I fly E-Power RC and although I have never had a problem personally there are plenty of examples online of people burning their vehicles or houses down through carelessness. There's actually a paranoia with some about using LiPo's. I feel the dangers are way blown out of proportion, but there are definitely dangers with using them, most of which are the result of user error.

If you overcharge, overdischarge or short a LiPo, it can "puff", or expand like a balloon because of the increased pressure. If this ever occurs you must quarantine it in a non flammable area immediately! Often what happens is some time later it will ignite with an extremely high temperature flame! You never, ever charge these batteries unattended and always in some type of flameproof container! I use a LiPosack, a nomex bag with a velcro closure at the top to charge mine.

Now metallic cased Lithium Ion cells are a different matter. The big thing these days are A123 cells which are a Li Ion cell, very high charge and discharge rate and very tough case. One of the big problems with using LiPo in an aircraft is crash damage. They're not very tough and will be damaged in a bad crash and may ignite destroying your model in the process!

So if you use LiPo batteries you need to be careful not to mishandle them or you won't like the result. I do sometimes use a LiPo battery for my launches when I want to be as portable as I can. I use either a 6 cell NiMH or a 2 cell LiPo with my Apogee launcher when I'm only launching Estes rockets at home. If I'm launching a bunch of rockets or especially when launching Aerotech stuff, I use my main launch control panel with a 12V sealed leada acid.




Mike