Running a igntion coil off 12volt 1millamp / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Running a igntion coil off 12volt 1millamp

1 2 next

Move Thread

LAN_403

Andy

Mon Apr 30 2012, 04:18AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi, I'm trying to run a ignition coil from a weak battery. I was wondering if there's any way to get 1000volts from the coil ever half second.
I've thought about a 2.5volt 50F cap and a zener diode and trigger it with a 555 timer. Would it work?

Dr. Slack

Mon Apr 30 2012, 07:00AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

What might be better is to use your 12mW in a boost circuit to charge a small value capacitor, 0.1uF ish say, to 100v, then use a thyristor to dump it into the coil. That's the "capacitor discharge" method of using an ignition coil.

<edit_for_Pinky's_benefit>

What I mean is

a) charge a small value capacitor, 100nF say, to 100v

b) dump it into an ignition coil using a thyristor

"Dump" sort of implies just throw it there, without caring much what happens afterwards (as in dump CO2 in the atmosphere). Suggesting a thyristor, which doesn't turn off until the current has stopped flowing, confirms this flavour of the word dump.

c) I don't think I can see any references to zener diodes in there.

d) Naming it the "capacitor discharge" method gives something to google on, though you'd probably want to put ignition coil in the search string as well. There's plenty of information out there. Just because a low coupling transformer is good for flyback service doesn't mean it won't produce many kV if you suddenly make the primary terminals go to 100v. Put it this way, I wouldn't put my tongue on the sharp end of capacitor discharge fed iggy coil, even if Pinky would.

</edit_for_Pinky's_benefit>

Pinky's Brain

Mon Apr 30 2012, 11:56AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Just to be clear, you mean to do this :
- charge the cap
- put voltage on the primary for x amount of time
- shut off voltage on the primary and use flyback to generate the high voltage on the secondary, limiting the secondary to ~1000 volt by putting a zener on the primary?

I doubt putting a zener on the primary will effectively limit the secondary voltage during flyback, also I'd use a TVS so you are sure it can take the energy of the pulse. Ignition coils just aren't made for that kind of thing, you would need something with high coupling, low parasitics and low impedance. Maybe one of those coilcraft battery charger flyback transformers.

Flybacks in general aren't really meant to generate pulses at X volt, peak output voltage is dependent on load impedance (unless you put a zener or TVS on the primary to limit it, but that's inefficient) and has exponential decay.

PS. don't make people guess at what you want to do, be a little more explicit.

Patrick

Mon Apr 30 2012, 04:32PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Andy wrote ...

Hi, I'm trying to run a ignition coil from a weak battery. I was wondering if there's any way to get 1000volts from the coil ever half second.
I've thought about a 2.5volt 50F cap and a zener diode and trigger it with a 555 timer. Would it work?

givin that iggies are usually the "I" type core, and the metal isnt often mu metal, your 12mW may dissappear in the magnetic circuit as heat, long before it ever generates any useful electrons, givin the poor magnitising coupling of I cores. and i dont think 50 Farads will do much but heat the copper.

I think what you are wanting to attempt will not work.

a camera flash or strobe trigger transformer would be ideal for such a purpose though. (The trigger transformers can produce 3-6 even 10kV)

Andy

Mon Apr 30 2012, 07:17PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

What might be better is to use your 12mW in a boost circuit to charge a small value capacitor, 0.1uF ish say, to 100v, then use a thyristor to dump it into the coil. That's the "capacitor discharge" method of using an ignition coil.

Could I use 75V 1N4761 ZENER DIODE to trigger C106D1 400V 4A SCR with only 12mW. If it charges the cap upto 75volt and then discharges the cap, rinse repeat.
Would that SCR work.

Just to be clear, you mean to do this :
- charge the cap
- put voltage on the primary for x amount of time
- shut off voltage on the primary and use flyback to generate the high voltage on the secondary, limiting the secondary to ~1000 volt by putting a zener on the primary?

charge the cap and use then diode to stop the cap frying. I thought it would charge fast with high volts. Then discharge it throught the coil.

@Patruck will look into the trigger transfomer.

Ben Solon

Mon Apr 30 2012, 08:39PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Can you give a bit more detail on your power source and what you intend to do with this so we can give you some real help? Iâ€™m sure we all could think of an easier and more efficient method if we had more details.

Andy

Mon Apr 30 2012, 09:10PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

I;ve made a copper/zine battery, and i;m trying to charge a cap to high voltage with the battery, and use the same battery to power the switching. I can make more volts than 12 , but the amps are small and drop to zero when connected to a load. I;ve already got the ingtion coil and 20kv would be enough,but if there's a different way i'm open to suggestions.
I don't think there will be enough power to run a 555 circuit that's were the zener and scr idea.

Ben Solon

Tue May 01 2012, 02:37AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Have you measured the current it can supply? You might be able to charge a small cap to supply power to a buck converter. Though the losses and voltage drops may kill you... It depends on the current. Maybe 24v to 5v and then feed that 5v to a trigger transformer and drive circuit. Note that with the batteries you use, you won't be able to supply power in general, let alone pulse power. Your best bet is to let these voltages slowly charge small caps, then pulse from these caps

Your intent is to just charge your sypercap to just under 2.5 volts though right? All these methods are really lossy. I personally think you should make a bank of your batteries in series and parallel to achieve the right voltage and enough current.

Little Phisics here: as the capacitor voltage approaches the supply voltage, it gets harder to charge- so you are right with the high voltage idea. But 12v is more than enough.

Edit: I think I may have misunderstood you. If your final goal is not to simply charge a supercap, then disregard the last two paragraphs.

Pinky's Brain

Tue May 01 2012, 07:31PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Okay, so you don't really care about the voltage ... in that case the 1000 volt was needlessly specific. Here is an electric fence pulser built with a CD4001 (much lower quiescent current than a 555) to create some multivibrators to drive a MOSFET for an ignition coil flyback. AFAICS pulse repetition should be around twice a second and he says it consumes around 85 uA, so that should work. You just need a capacitor to supply the peak current, although 50F is probably overkill.

To use it to charge a high voltage capacitor you need to put a diode string on the output obviously.

Andy

Tue May 01 2012, 07:40PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Thank you, thats what I was after.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob