Some Electronics Help

[mark.f]

I finally got my plans for an ignition-coil-based igniter for spudcannons. Now, there are more immediate problems like powering the coil and switching it.

The main problem I've come up against is powering the coil. It takes some pretty heavy current to provide the same spark as on the ATV the coil came off of. The battery for the ATV is rated at 12 ampere*hours. Most standard consumable batteries are listed in terms of milliamp*hours. So this could be a problem. Switching the coil will be by way of a standard automotive relay.

My power solution is going to be simple 1.2 volt "Sub C" NiCd batteries. Lowes always has a recycle bin with old batteries like this in them. My friend says there's a way to test the batteries with a multi-meter, so I'll ask him about that unless anybody else can tell me how.

Each of these batteries provides 1.2 volts at around 1500 mAh, (milliampere*hours). So for a 12 volt power source, that would be 10 batteries, 12 volts at 15,000 mAh, or 15 ampere*hours, right?

That is my main question. My next question would be charging. How would I charge these batteries? Most of what I've read has suggested, to me at least, some sort of adjustable current charger with a timer. For the life of me, though, I can't find any of these. I would like to do the slowest charge possible, because the batteries are used and probably won't take many quick charges.

Any help here would be hot. Most of you know I'm not a terribly good electrician, although I can get by on simple circuits such as this. Thanks in advance for any advice.

[jrrdw]

Go with a garden tractor battery, cheep, easy to charge and carry and will be enough to power your ignition. The way your talking about doing it is going to be problem-matic. To test batteries, you need a load tester, much different then a multi tester. Useing old batteries is also going to be a pain in the ass. You can get a mower battery for 24 bucks, around 230 cca.

[dewey-1]

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[Fnord]

I believe Batteries like NiMH (the ones you're supposed to use for cameras and stuff) can put out far more amps than the standard NiCd ones.
They have lower internal resistance also, so they don't run out quicker than normal when under high load.

Or, you could just use a camera flash

[mark.f]

Jrrdw, if I get a lead-acid battery like that, it would make the thing as portable as a refrigerator, but I think that may be what I end up doing.

Dewey, I'm gonna research into your gel-cell batteries. I haven't heard of them before, so that might be an idea. I've already checked RC battery packs and couldn't find one with enough amperage.

Thanks for the ideas from all of you. Maybe when I'm forced to learn electronics as a prerequisite for fluid mechanics, I'll stop bugging you.

_Fnord, that'll be my last choice. I'm actually researching induction coils, (which you can pull out of a gag "shock lighter"), for driving an ignition coil to produce the spark voltage you need. Looks promising and cheap, as you can get them from the dollar store.

[jrrdw]

Jrrdw, if I get a lead-acid battery like that, it would make the thing as portable as a refrigerator, but I think that may be what I end up doing.

Dewey, I'm gonna research into your gel-cell batteries. I haven't heard of them before, so that might be an idea. I've already checked RC battery packs and couldn't find one with enough amperage.

Thanks for the ideas from all of you. Maybe when I'm forced to learn electronics as a prerequisite for fluid mechanics, I'll stop bugging you.

_Fnord, that'll be my last choice. I'm actually researching induction coils, (which you can pull out of a gag "shock lighter"), for driving an ignition coil to produce the spark voltage you need. Looks promising and cheap, as you can get them from the dollar store.

Not at all, the measure approx. 8"W X 6"H X 5"D. Only weight about 12lbs. Very portable.

Gel batteries are the size of car batteries and weight approx. 45/50lbs, they are normanly used in electric wheelchairs, or in very cold climents.

[ShowNoMercy]

The smallest lead acid or AGM battery you are gonna find is a size 24 which is similar to like a shoebox maybe. But look into lead acid batteries from jet skis, ski mobiles or atvs.

[jrrdw]

The smallest lead acid or AGM battery you are gonna find is a size 24 which is similar to like a shoebox maybe. But look into lead acid batteries from jet skis, ski mobiles or atvs.

Those type batteries cost twice as much as a garden tractor battery.

[ShowNoMercy]

I beg to differ, http://surpluscenter.com/item.asp?UID=2 ... e=electric

[jrrdw]

I beg to differ, http://surpluscenter.com/item.asp?UID=2 ... e=electric

Good find, but low amp hours. Heres what i was thinking of -- more shots.

Cost a little more, close to size, 1lbs less, that surprized me.

[dewey-1]

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[jimmy101]

The amp hour rating is really not relevant in this useage.

The "1200mAH" metal hydride batteries will put out ~10 amps for a short time. Since you won't be running your ignition circuit for more than a second or so for each firing, the amp/hour rating really isn't all that important. The important thing is the peak current for a short duration pulse.

10 amps might be enough, it is worth trying.

Most wall warts won't put out anywhere near 10 amps (usually more like 1 or 2 amps), so they probably won't work very well.

I would think your best bet would be a surplus sealed lead acid (gel cel) 12V battery. All Electronics has several types. This one should work well and will probably supply at least tens of amps in a pulse;

12 VOLT 5 AH GEL CEL BATTERY
Maintenance-free, rechargeable sealed lead-acid battery. Can be used in any position and trickle charged for long periods of time. Will not leak. 2.75" x 3.53" x 4" high. 0.1875" quick-connect connectors.
CAT# GC-125 $16.00 each

You can use a standard car battery charger to recharge the 12V gel cel batteries.

I've got a couple different batteries of this type, mostly salvaged from dead uninteruptable power supplies and home alarm systems. They'll put out a heck of a lot of current, not as much as a car battery but they are much smaller and cheaper than even the smallest car battery.

Another possibility is the "emergency batteries" you can usually pick up for $40 or so at car parts places, Kmart, Sears, etc. These'll supply at least a couple hundred amps for a short time. They are pretty small and usually come with their own wall wart for recharging. And, you can use it to start your car when the battery is dead.

Here is a $40 one from Sears that claims 750 peak amps. You can probably find simpler/cheaper ones elsewhere.

[dewey-1]

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[jrrdw]

How long the battery is going to last depends on the resistance load the coil and switch/s puts on the circuite???

[dewey-1]

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