Here's a simple design I came up with (everyone needs another project![emoji3]) A coil AND spark plug tester you can make. The only thing you'll need to buy is a 12 volt SPDT relay, which you can order, ebay, US seller, 12v 40 amp! $2.99! Here's sellers listing. Ebay, search 12volt SPDT relay, sort price lowest, US only filter. QTY1 CAR RELAY BOSCH STYLE 5 PIN 12V VOLT DC 40A WEATHERPROOF & WATERPROOF SPDT $2.99 Free Shipping All you need is relay, spark plug, a ballast resistor (that's for safety to test both types of coils...internal/external, you'll need some wire (18 to 10 ga ok), and a plug wire (it tests them too!), clip leads (Harbor Freight if you need them). Three copies are the same diagram...which ever easiest to read. All you do is wire as shown. How to make is simple... Battery + clip lead goes to one side of relay coil as well as one side ballast resistor. Other side ballast clipped to coil +. The relay has 5 terminals...2 for relay coil, 3 for switch contacts. The switch common goes to ground (battery --), switch normally closed contact is wired to other side relay coil. Then switch normally open contact clip lead to ignition coil --. Coil center tower a plug wire to a spark plug. Of course, the spark plug threaded body to ground (battery --). Tip: when you get relay, ohm the 5 terminals , relay shows what's inside stamped on it. Coil will read some resistance (My guess about 100 ohms), the normally closed two will be zero, last terminal is the normally open contact. How it works... When connected to a 12v battery, the relay is energized, the switch "flips", relay disengages then cycle starts again. You'll hear the relay buzz as it quickly switched on and off. Now as this happens the coil -- terminal is grounded then not (on off on off) just like ignition points do. Tip: (I forgot to draw it in...but add a condenser coil -- to ground, across "points" just like in distributor. In closing, as a bonus, if you make it neatly you could carry it as an emergency ignition system. Just hook coil output to your distributor center (rotor ****on). With this you can test a coil, spark plug, ignition wire, condenser. Hope this helps! Sent from my SM-S320VL using Tapatalk
I made a similar circuit yesterday - not for ignition purposes, but using a relay oscillating this way. It's a cheap and simple circuit that can be quite useful - but be aware it might not work with any relay, as the relay stops pulling as soon as the circuit breaks the mechanism might not move far enough to let current through where the ignition coil is connected.
Thanks for doing this. Can you please make a drawing with a condenser coil for those of us who are challenged?
If you have a automotive battery charger handy you can probably use that instead of the battery. Just use a high charge or jump start setting. Sent from my SM-G950U using The H.A.M.B. mobile app
I want to reply...but if that's you in your avatar I sure don't want to make YOU mad!!!!![emoji16] You're correct, sort of...but battery chargers can output a lot of voltage, more than I would want to subject this to. Now 12v coil, a separate 12v battery would work like motorcycle, Li ion, etc. The higher the AH rating the longer it will run. Sent from my SM-S320VL using Tapatalk
Here it is. I left out a comma between condenser and coil --. Diagram has it added...just a condenser or use a capacitor...most condensers (another name for capacitor) are around 0.33 to 0.47ufd @ 600 volts. 400v probably ok. Very common. Sent from my SM-S320VL using Tapatalk
I can't take all the credit. Inspiration from a true automotive genius Mr. Henry Ford, over 100 years ago. That spark coil still works. Sent from my SM-S320VL using Tapatalk
Sorry, but I don't believe that is going to do anything at all. At least not as drawn. Maybe you've left something out?
How does an automotive (Kettering) coil ignition system work? Coil is an autotransformer with three terminals. + and -- on sides which go to turns of wire...then the high voltage tower, 1000s of turns of wire. Hook up battery + to coil +, hook up battery -- to coil ---. Magnetic field builds up, break the circuit, field collapses and that induces high voltage out tower. So 12 volts in multiplied by ratio of turns, 20-30kV out. What are ignition points? A switch to ground...opens and closes by distributor cam. This circuit is that. Please explain why it won't work? Sent from my SM-S320VL using Tapatalk
Maybe my quick drawing of the relay connections will make more sense to you. Hooked up this way the relay turns itself on and off continually. I tried this today but had no success with 2 different brand relays, Picker and Bosch. The picker would buzz but wouldn't fire the coil (I did check the coil first), the Bosch didn't buzz but seemed to test ok otherwise. Both these relays have the resistor on the coil though so I'm wondering if that makes a difference as I see the one shown on ebay doesn't. For $2.99 I may just have to buy one and find out.
Thank you, but you did his work for him (the external jumper wire connecting terminals 85 - 87A not shown in his drawing) .
I'm a retired electronic technician 43 years, the way I drew it is standard schematic nomenclature. I mean no offence at all, but I'm trying to explain in layman's terms how to make it. I keep it simple. Without getting into all the various kinds of relays, etc., I keep it simple and basic. Bear with me. A relay is composed of two parts, an electromagnet and switch. Electromagnet is wire wound around a form so that putting 12 volts across the coil it now is a magnet. The switch part has a metal lever that the magnet attracts so now that lever moves switch contacts. All you want and need is an SPDT (single pole double throw) relay that will have 5 contacts. You may like THIS relay drawing shown better... Pin 1 goes to battery +. Pin 2 you will wire connect to pin 4. Pin 3 goes to ignition coil --- negative. Pin 5 goes to ground, battery ---. That's all there is to it! If you keep it simple it's easy to understand. Connected this way power is applied, relay is energized by it's own switch. It clicks, therefore the relay coil no longer is getting power, so it clicks back...and the cycle continues. The whole time the ignition coil --- negative terminal is being grounded and not, so on off on off...exactly as the ignition points do inside the distributor. Now your turn to eviscerate me! [emoji3] Sent from my SM-S320VL using Tapatalk
Haha, sorry not trying to eviscerate anyone, just trying to make it clear to those that aren't so familiar with electronics.
I doubt the inexpensive relays will work for this. You'll probably have better luck using a ********, which is basically the same thing, only intended for just this sort of thing. A little more expensive though. https://www.tubesandmore.com/products/********-12-volt-3-pin-negative-ground
Here's an even simpler circuit shown in action I just threw together. A 12v car battery would be better, I just used two 6 volt flashlight batteries I had laying around. The relay I like because it's higher frequency. (A V8 engine at 6000 rpm points are opening and closing 400 times a second!). This one all you need is a two prong turn signal flasher. Open it up, you see the bi-metal strip that's wound with a few turns of wire. Bending the contact tab changes how fast it flashes. It's normally closed, the lamp load heats wire which causes bimetal strip to bend...it cools...cycle starts over...lights flash. So simple...battery + to coil +, battery--- to flasher, other flasher tab to coil ---. I put a neon inline spark tester series with spark plug. My high voltage automotive meter shows 26kV. Sent from my SM-S320VL using Tapatalk
Here's another option, using two relays - one to oscillate, the other to interrupt the current going through the ignition coil. Haven't tried it, there may be issues with relays that don't work at the same speed (it takes a while for the mechanism inside to work), but if you get it right it might work better than the single relay circuit. Even better would be a single relay with two poles, but as far as I know those aren't common in automotive electrics. Common in electronics though, if you want to go somewhere else to do the shopping.
I can barely make a sandwich, and you guys are coming up with this stuff. No wonder I push a broom for a living lol. Nice I’m gonna try to build one of these little ****ers. It’ll either work or shock the **** out of me or burn down my garage or maybe all three, will see. Thanks.
I can't see the purpose in that. When power is applied both relays oscillate. The relays shown may as well be spst. The coil -- is grounded and + is interrupted which is opposite how the ignition system works. I've always loved simplicity which is why I suggested using a flasher...2 prong cheap one. If you have a "bad" flasher laying around like one I removed cover, it was only bad because points weren't touching. I discovered by bending so they touch fixed it and also bend so it pulses fast. Picture shows an ignition coil and 1.5 ohm ballast on a bench power supply. At 13.1 volts it draws 3.9 amps (which is why never leave your key on engine not running as it will overheat/damage points and ballast). Second picture shows a tester, I made one as a kid like it, it's just a lamp socket, $1 6ft extension cord, two clip leads. Cut socket off cord, put on clips. Then a foot or so from plug end cut the "hot" side (narrow blade on plug side). Strip and wire across lamp socket. Install a 7w bulb. Touching clips together it's an easy continuity checker. (Careful! Shock hazard...I use a 60W sometimes but I'm used to fooling around electricity). I ordered some of those $2.99 eBay relays and will report back using those. Sent from my SM-S320VL using Tapatalk
The purpose is to, unlike the first suggested circuit, not require the relay to do a 100% switch to send current through the ignition coil. The original suggestion uses the normally closed (NC) contact to break the current to the relay, that means the relay may not engage fully and let the NO contact make contact, i.e. there is no guarantee the ignition coil would ever get any current with that circuit. My version uses two relays where only the NC contacts are used, one to oscillate and the other to control current to the coil. You are correct about me drawing the coil on the negative side while it usually is on the positive side of the breaker. Easily changed by putting the coil on the other side of the relay, if you want to, or just switch the + and - inputs and where you ground the spark plug. The testing function should be the same no matter what side it's installed on. Simplicity is always good. I also like the flasher relay idea.
Simplicity, build the flasher circuit. In auto parts store, cheaper is better as you want a simple basic $3 flasher...you do not want the newer solid state ones. When these relays get here in next few days I'll report back. With a standard points ignition the points do 100% of the work. A dual points distributor my understanding is just to increase dwell time supposed to give a more intense spark. Sent from my SM-S320VL using Tapatalk
The Jalopy Journal
