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Mon Aug 18, 2014 9:39 pm

Just checked my coil and it's a blue Bosch 12V "no resistance coil."

what is the difference between the 3-4 ohm Bosch 12V coil and the no resistance ones?

My car is running fine with this coil, but was wondering if there was a reason my car has a no resistance coil on it?

will I damage anything one day if I decide to get the 12V 4 ohm Bosch blue coil?

Thanks!

Mon Aug 18, 2014 9:42 pm

as I mentioned in another thread, I'm going to be running an IMDU off my coil. (intake manifold de-icer unit) if my coil is a "no resistance" one, will I be fine to use this coil for my IMDU?

All I have hooked to my coil is my dizzy, carb, and ignition wire. My car is a Mexican Beetle so it doesn't have the backup lights hooked to it, therefore I have an available terminal on my positive 15 side I plan to use for the IMDU.

Also, just hooked a 15A inline fuse to the ignition wire going to the coil in the engine bay just in case.

Mon Aug 18, 2014 9:49 pm

guessing that I have a cheapo coil. running the risk of frying things since it has no resistance. i will be better off getting the 4 ohm bosh blue coil like this one from Flat4? I live in Japan so this is where I shop.

https://www.flat4.co.jp/products/detail.php?product_id=2762

will having resistance affect my engine performance (spark, I use the long reach spark plugs for my mexi engine, NGK BP5ES) or my 34-PICT3 Carb and 009 dizzy? or does the higher resistance mean that it protects things from frying more?

the flat4 page says it can be used for street use all the way to high performance. guess I'm in the clear.

should I replace my coil with this one if I'm running that IMDU?

Mon Aug 18, 2014 11:10 pm

No resistance in the coil will have no effect on your IMDU. Basically your just using the coil as a convenient place to hook the IMDU to the 12 ignition wire, it doesn't actually use the coil.

I'm assuming that you're using points, no resistance coils will work with them (as you well know) but it's said that it will put greater stress on them and cause pitting and burnout faster. You can either get a new coil, like the one linked, or run an external ballast. Both will do the same job.

Tue Aug 19, 2014 9:03 am

The points are a switch. They open and close as the distributor rotates. When the points close, they build a field in the primary circuit of the ignition coil. When the points OPEN, this field collapses and induces a large voltage in the secondary windings of the coil. Read all about the Kettering ignition here:
http://www.ratwell.com/mirror/users.mrbean.net.au/~rover/ketterin.htm

The voltage in the primary circuit is multiplied based on the number of "turns" in the coil windings. A greater ratio of turns between the secondary and primary and you get higher voltages out of the secondary. Higher voltages allow sparks to jump a wider gap of the spark plug or provide a stronger spark.

Adding resistance in the primary winding lowers the current flowing through the coil to the points. The current will want to flow down other lower resistance paths. High amperage through the coil will cause points to pit and burn sooner. The contacts of the points are made from tungsten. They are very hard, but eventually the points will burn. Lower resistance through the primary circuit means the points will need to be replaced sooner. The ballast resistor in the primary circuit does not significantly change the voltage in the primary so does not significantly impact the secondary voltage.

You can just add a total of 3-ohm of resistance to your primary side of the coil. It is installed between the power wire (black #15) and the #15 (+) terminal of the ignition coil.

If your coil has close to 1-ohms of resistance between the +/- terminals you can just add the below 1.8-ohm ballast resistor to the positive side of the coil to get a total of near 3-ohms.

http://www.summitracing.com/int/parts/mor-72390/overview/

Or you can just find a 12v coil with 3-ohms already built in:
http://www.summitracing.com/int/search/part-type/i...nix%20coil

Tue Aug 19, 2014 12:36 pm

Most distributors, coils, etc, cannot handle more than 5 amps without burning up (some instantly, others over time). So if you have a 12V system, which means you have an alternator capable of putting out over 14V, and a normal 3ohm coil, then: 14V ÷ 3ohms = 4.7amps. Nothing burns up at 4.7amps. But if you have really low resistance (zero resistance coils still have some resistance) then 14V ÷ .1ohms = 140AMPS! At140 amps your coil, distributor and all your wiring will turn to toast!

That being said you may have a 3ohm ballast resistor hooked up somewhere on your ignition circuit. Or maybe your distributor is electronic and has a current limiter? Whatever it is that you have, just make sure it doesn't draw over 5amps through the coil and distributor.

Tue Aug 19, 2014 1:05 pm

Juanito84 wrote: Most distributors, coils, etc, cannot handle more than 5 amps without burning up (some instantly, others over time). So if you have a 12V system, which means you have an alternator capable of putting out over 14V, and a normal 3ohm coil, then: 14V ÷ 3ohms = 4.7amps. Nothing burns up at 4.7amps. But if you have really low resistance (zero resistance coils still have some resistance) then 14V ÷ .1ohms = 140AMPS! At140 amps your coil, distributor and all your wiring will turn to toast!

That being said you may have a 3ohm ballast resistor hooked up somewhere on your ignition circuit. Or maybe your distributor is electronic and has a current limiter? Whatever it is that you have, just make sure it doesn't draw over 5amps through the coil and distributor.

It doesn't pull 140amps constantly so it isnt as big a deal as you make it seem. It only draws 140amps for the time the points are closed which is a very short time period.

The reason high amperage ruins things is that wires intrinsically have a small amount of resistance. When current passes over something with resistance it produces heat, the formula is heat in joules of heat = current^2 x resistance. For low currents this heat is dissipated faster than it is produced, but for high currents the wire cannot dissipate the heat faster than it produces it so it eventually reaches its melting point and breaks.

However if the current is intermittent there is time allowed for the wire (or coil in this case) to dissipate the heat produced in between bursts. Therefore if the current is intermittent enough you wont burn anything out.

None of this is to say he shouldn't fix his coil, just taking an opportunity to explain what is happening...

Tue Aug 19, 2014 1:35 pm

Thanks! There is more to it than what I said. But there's more to it than what you said too. :wink:

First of all, the amount of time good old fashioned points are closed is actually a considerable amount of time. Our VW AC engines usually have a dwell of around 45º. As with any 4 cylinder, 45º dwell is exactly half the time (90º between sparks: 45º closed, 45º opened and fire!, 45º closed, 45º opened and fire!, etc.). So that turns 140A peak into 70A average. 70A will still fry things! It's still a whole lot more than the 2.5A average it's designed for!

You also forgot what happens if you turn on the ignition switch with engine stopped and points closed. You will be running maximum current until you start the engine. (Which is another reason to never leave the ignition on with the engine off.)

Also, the coil is an inductor. If you looked up what an inductor does you would see it resists changes in current. As a result, when the points open and current suddenly comes to a stop, the voltage spikes and tries to jump across the points or through the ignition module, whichever one you have. If the peak current is around 5A or less then the voltage spike will be only a few hundred volts. But if you are running 50A peak then you will have a voltage spike of a few thousand volts! 140A would make a several thousand volt spike at the points! That can't be good for the points or condensor, and it will kill any ingition module instantly.

If he has no resistance at the coil and hasn't fried anything yet I would suspect that either he has a ballast resistor or he has some sort of current limiter in his distributor. A zero resistance ignition system would melt down instantly!

Tue Aug 19, 2014 1:41 pm

This is all true, I wonder if he has a special distributor designed for a 0Ohm coil, or a special electronic ignition module.

Tue Aug 19, 2014 4:02 pm

thanks guys! very helpful.

I have an 009 with old fashioned Bosch ignition points. not sure if I have a ballast resistor somewhere or if my dizzy has a current limiter??? how to tell? I don't see anything extra hooked up to my dizzy in the engine bay. how to look for a ballast resistor?

If I have a ballast resistor somewhere and I switch my coil to the 4 ohm Bosch one will it be too much resistance then? mess something up?

Tue Aug 19, 2014 5:05 pm

Are your points hooked up directly to the coil? If so, you don't have a current limiter.

Can you unhook the battery and check resistance from possitive battery cable to the coil with the ignition switch left in the "on" possition? That will tell you if you have a ballast resistor or not.

Tue Aug 19, 2014 5:25 pm

As Relyt stated if you are just using the extra open tab on the positive side of the coil to draw power for your IMDU then it will have no effect on the coil itself.
As far as what resistance your current coil has or doesn't have don't sweat it if its working leave it be.
On the other hand how many amps does your IMDU draw? as the power supplied to your coil via the ignition switch is rated to run the coil, choke, and idle cut off. it may not be able to handle the load from the IMDU. Your best bet would be to install a relay to run the IMDU.
Then you can utilize the power from the extra tab on the coil to trigger the relay which will be minimal and the IMDU will be drawing its power from the battery as the relay will act as a switch and the IMDU will only work when the ignition is on.

Tue Aug 19, 2014 5:33 pm

thanks, I'll check that stuff today.

Looks like my points are hooked right up to my coil. The points are hooked up to the terminal inside my dizzy. If there was a current limited would it be somewhere on or in the dizzy, or between the dizzy and coil negative side? what would it look like if I had a current limiter?

So, I should unhook the battery, switch the ignition to "on," and then check resistance from that battery positive side all the way to the ignition wire on my coil? not sure if my multimeter cables will reach that far. might have to get some long leads. must be misunderstanding something as usual.

if I read 0 ohms that means no resistance, right? and if its about 2 ohms I have a ballast resistor somewhere on the circuit.

will I risk anything by running a resistor and my 4 ohm Bosch blue coil?

Tue Aug 19, 2014 7:24 pm

yes, I'm going to hook up a relay switch. decided. thanks again for the good advice, yellrhd! still don't know the amperage on the IMDU. still haven't written me back at air cooled vw uk. so slow!

I still need a good solution how to route wires through the rear engine firewall without destroying everything and tearing it all to hell and back. Need to get covers for my wires I plan to run, too.

I'll draw up a wiring diagram I plan to use and see what you guys think.

and just checked my dizzy. there is nothing special or strange looking about it. It has the old style Bosch points that are hooked up to the condenser terminal on the inside. nothing fancy.

I'll try and get a reading on the resistance of my ignition coil.

I swear I don't see any ballast resistor anywhere. Its not something that would be tucked away in the wiring loom somewhere i don't think. would it be in the front trunk area close to the fuse panel?

again I have a 2000 mexi beetle that has been converted to a carb. so the wiring is a little bit different at times.

thanks everyone!

Tue Aug 19, 2014 10:17 pm

Ok, so I came up with this wiring scheme for my IMDU.

To explain a little. I plan to mount the relay switch under my rear seat on the drivers side in a good, safe, secure spot.

I thought that the 15 positive lead on the coil would serve as a good switch for my IMDU, that way it comes on with the key all the time and I don't have to install a cheap, out-of-place looking switch on my dash. If I ever decide to not use my IMDU I can just unhook it in the engine bay, not that I plan to do so though.

For the time being I'm planning on using a 15A fuse holder coming from the battery. surely the IMDU won't draw any more amperage than that? If I don't hear anything from aircooled vw uk, guess I can just check to see what amp fuse the IMDU comes with. Also, plan on using 14 gauge wire (15A capacity wire) for the entire circuit.

Do you guys think I need a fuse between the 86 terminal on the relay and the 15 positive side on the coil? Shouldn't be pulling many amps through there.

Let me know if you see any issues with my diagram. Been a while since I did electrical work, lol. as you all can tell I'm sure.

Just have to figure out how in the f*** to get my wires back to the engine bay without it looking like my car was ransacked by the Creeper from Scooby Doo.

As I mentioned, the main wiring harness side is crammed full and I can see me having clearance issues, however the other side where the battery feeds the alternator has some space to work with...maybe...

and, here are some shots of my 009 dizzy, or at least I think it's a 009. I can see any numbers stamped on it and that little white tag on the front is faded.

Nothing special about this dizzy, right? sorry for the crappy shots. best ones I could get now while my son was taking a nap.

plus, its hard to get the cap off because, oh, just guess, that god damn AC compressor and bracket. Once my son grows up more and isn't little anymore, I'm chucking that thing into the deepest part of the ocean where it belongs. always in my damn way!

Sorry for my question heavy posts all the time. really I am. I'm just dying to know how all this works and hook it all up as safely and as informed as I can.

Wed Aug 20, 2014 3:55 am

so, I took my coil out of my car "Bosch Blue 12V Without Resistance" and tested the resistance. it measured precisely 4 ohms. I tried it at least 10 times and zeroed out at 4 - 4.1 ohms each time. how strange??

why in the hell would it say "without resistance?"

here is a picture of this mysterious coil from the twilight zone.

guess I don't have to worry about tracking down a ballast resistor since I clearly don't have one. also, answers my question about if my dizzy is special or has been modified. wha a relief? it's normal. :D

guess I don't need the new coil I just ordered, but hey I have a replacement now and this one looks pretty damn nice too I must say. should be getting it in the mail tonight or tomorrow morning.

Wed Aug 27, 2014 6:09 pm

just wanted to say thanks again to all the folks who helped me out last week. new bosch blue coil is on and working great. took a long road trip this past weekend and all went well.

was happy to see my car did fine at a steady 100-120 KM fpr 3-4 hours with no stumbles, overheating, or any issues. first time I took it on a trip and let it stretch its legs like that. gotta do that more often.

Thu Aug 28, 2014 8:35 am

type1vwjapan wrote: was happy to see my car did fine at a steady 100-120 KM fpr 3-4 hours with no stumbles, overheating, or any issues. first time I took it on a trip and let it stretch its legs like that. gotta do that more often.
Isn't the top speed on the "kosokudoro" (expressway) only 80kph (50mph)?! :shock: :o :lol:

I've never had the courage to push my car more than short spurts to 100kph (62mph). I think 110kph (68mph) is the most I've pushed it and that was "down hill with a tail wind"!

I think its great you got your car out on the road where it belongs!

Thu Aug 28, 2014 9:09 am

ashman40 wrote: type1vwjapan wrote: was happy to see my car did fine at a steady 100-120 KM fpr 3-4 hours with no stumbles, overheating, or any issues. first time I took it on a trip and let it stretch its legs like that. gotta do that more often.
Isn't the top speed on the "kosokudoro" (expressway) only 80kph (50mph)?! :shock: :o :lol:

I've never had the courage to push my car more than short spurts to 100kph (62mph). I think 110kph (68mph) is the most I've pushed it and that was "down hill with a tail wind"!

I think its great you got your car out on the road where it belongs!

How curvy are your roads that the top speed is only 80! Highways in Canada range from 100-120kph, and that is through mountains. 80 is dead slow.

Thu Aug 28, 2014 12:03 pm

1971 manual states 81mph (130kph) as top speed. 1979 states 80mph (128kph). 1995 owner's manuals recommend 127kph as max speed.

So yes, you can do 100kph to 120kph just fine. It's probably not a good idea to do much more than that without modifying the brakes and suspension and probably the engine too.