TheSamba.com :: View topic

Sun Apr 10, 2011 10:17 am

ashman40 wrote: If you're gonna test it, I'd like to hear the results.

I always thought there was a near linear multiplier involved between the primary and secondary voltages in the coil that only depended on the ratio of the windings in the primary vs secondary. This allowed higher voltages by having a better winding ratio. This was the difference between 20KV coils and 60KV coils... both running on 12-13v DC.

Correct...Direct ratios...minor losses due to transformer "hysteresis and eddy current".
12 vdc to 30,000
10 vdc to 25,000

For step up....Voltage increases linearly, current decreases linearly.

Though, I think the need for a relay in the engine bay is more related to voltage drops that could cause the coil or the carb cutoff solenoid to stop working.

Think the main goal of all auto mfg's adding a relay for most things was to reduce the load on Ignition switches and other switches. No need for bulky under dash wires for everything.

When I had my problem I was measuring only around 9v at the coil black wire.

A good test would be to add a variable resistor to the ignition coil wire before the coil and solenoid and dial down the voltage to see when the coil stops working. You'll need to test this with the engine running as well as when trying to start the engine. The starter will draw a LOT of current and cause voltage drops everywhere. So lower than normal voltages that allow the engine to continue running, may be too low to allow the engine to catch while starting.

A drop of 1 volt...12 to 11 would result in roughly a 10% drop in output of the coil...So 10% of 30,000 volt spark would be 27,000. Don't see that as a problem.
A drop of 2 volts 12 to 10 would be a 17% drop. Your spark would be down to about 25,000...

A resistor would work...but it would need to be a high wattage one...

A low wattage one would get HOT quick and burn up.

Example wattage is = to volts X amps...12X 5 (example)= 60watts

Maybe just turning on your lights on high beam may be enough to drop down into the 10's.

I have a couple of these for load testing auto and rv 12 vdc circuits

[/b]

Sun Apr 10, 2011 11:17 am

Your number not mine says
1volt 10% of 30,000 = 27,000
2volt 20% of 30,000 = 25,000
3volt 30% of 30,000 = 21,000
4 volt 40%of 30,000 = 18,000
So back to my question – is the lower voltage Ok for start ? and how often does someone get a 8 or 9 volt reading at the coil ?

Sun Apr 10, 2011 12:41 pm

I measured my 69's voltages..

I have a relay for the coil, located in the front dash area of the luggage compartment. Removed coil to rotor cap wire to prevent starting.
Pertronics electronic ignition.

All measurements taken at the coil + except for the first battery static reading and dash volt meter.

----------------Static------key on---------start------

Battery--------12.56

Dash volt-------------------12.2
meter

Coil +-----------------------11.0-----------9.8

Coil +
Lights on high--------------10.76

Coil +
Lights on high------------------------------9.69

Coil + lights on high--------10.3----------9.2
15 amp heater load
connected to the Alt hot lead.

After testing I left all the loads on and the engine starts just fine and runs the same. It does crank a little slower. hehe.

I know for a fact that without electronic ignition my battery could be so low that the engine would barely turn over and the engine would start. Same with my on fords and chevys...

50% reduction in voltage at the coil would make the secondary of a 30,000 volt coil be 15,000 volts to provide a spark across .035 gap.

I have seen VW's run when there was not enough voltage to barely make the headlights glow yellow.

Sorry I couldn't make my voltage drop below 9.2 but at least
We have some numbers.

Will a 12vdc non FI start and run on 6vdc?

Jim

Sun Apr 10, 2011 5:45 pm

9.2 is still a hell of a drop on a system that should be running over 12 volts.

JerryMCarter1 wrote:
Also 9 volts is one hell of a drop, you must have something going on to take up 3 or four volts .
Maybe I am all wet here but I have never heard of such a drop at coil. Usually one has 12 or one does not have 12.

That's just life with a 35+ year old electrical system.

I blame alot on the ignition switches but unless you go around clean every connector and ground, run an OEM quality ignition switch in perfect order and have a totally stock electrical system it's just the way it is unless you make changes like relays, heavier wiring etc.

I dont have a vw engine running an ignition coil anymore but when I did after adding a relay even with the engine at idle with my high beams on (130w) wipers on and hazards going I couldn't get voltage at the coil to drop below 12.4volts.
That was with my original 74 Bosch 50amp alternator.

Sun Apr 10, 2011 6:00 pm

Joel wrote: 9.2 is still a hell of a drop on a system that should be running over 12 volts.

JerryMCarter1 wrote:
Also 9 volts is one hell of a drop, you must have something going on to take up 3 or four volts .
Maybe I am all wet here but I have never heard of such a drop at coil. Usually one has 12 or one does not have 12.

That's just life with a 35+ year old electrical system.

I blame alot on the ignition switches but unless you go around clean every connector and ground, run an OEM quality ignition switch in perfect order and have a totally stock electrical system it's just the way it is unless you make changes like relays, heavier wiring etc.

I dont have a vw engine running an ignition coil anymore but when I did after adding a relay even with the engine at idle with my high beams on (130w) wipers on and hazards going I couldn't get voltage at the coil to drop below 12.4volts.
That was with my original 74 Bosch 50amp alternator.

Joel, the 9.2 volts is during cranking with lights and a 15 amp 12vdc . I am not allowing the engine to start.

Also my 69 is totally rewired.

My F250 460 engine loads the battery so it is around 8 vdc during cranking...

A battery can not present it's at rest voltage (12.6) when it has even a small load put on it.

Jim

Sun Apr 10, 2011 6:13 pm

Well curiosity killed the cat- It would be interesting to voltage down and see what exactly it took to start one of them thar VW's
yups !

Sun Apr 10, 2011 6:28 pm

JerryMCarter1 wrote: Well curiosity killed the cat- It would be interesting to voltage down and see what exactly it took to start one of them thar VW's
yups !

Come on Jerry do it for us...I am swamped for time for the next couple of weeks.

Any one want to bet on the voltage point where a Bosh Blue (stock) will not provide a spark across a .035 plug gap.

I'll guess 6.5 vdc.

Bet Glenn already knows.

Jim

Sun Apr 10, 2011 7:03 pm

Well a guess it would be !-- but I am certain it would be below 6 volts
Mostly because bugs used to be 6 volts

so the bet is on with BAHA - he says above 6 I say below 6 -- and my shadow McMillion mister -- well he is probably not interested -- he only looks for other poster errors and then get his jooly when he thinks he has found an error -- yaahhhooo yippie K ya aaa --- whooaaaa what fun !
-
how much money ar we a talkin sonny boy ! !!

Sun Apr 10, 2011 9:19 pm

I see you haven't been laying off the:

Sun Apr 10, 2011 9:31 pm

Way cool way down under

Nothing better than a bit of levity

Humor heals everything !

Mon Apr 11, 2011 12:12 am

Sense of humour... on the samba..... HA!

Mon Apr 18, 2011 4:02 pm

i-cortin wrote: Maybe someone here has actually done this "upgrade".

Really hard to imagine why VW never fused this circuit - seems necessary.

OK, I'm really embarassed. I had the day off today, opened my hood to take a look to install such an inline fuse on mine. I didn't remember that I had actually fused the wire to the coil quite a few years ago !!!

OK, so the fuse had never blown in all that time, good. I opened up the fuse holder to see what size the fuse was that I had been using - it was 5 amps !!! And I do have the reverse lights hooked up and working on this. The ignition is points, from a 1976 vintage 009 distributor. Anyway, after reading all these posts, I did upgrade to a 10 amp fuse; I put some spare fuses in the ashtray. So it sure hasn't hurt me all these years !!!

Tue Jun 28, 2011 8:57 pm

Cusser wrote: i-cortin wrote: Maybe someone here has actually done this "upgrade".

Really hard to imagine why VW never fused this circuit - seems necessary.

OK, I'm really embarassed. I had the day off today, opened my hood to take a look to install such an inline fuse on mine. I didn't remember that I had actually fused the wire to the coil quite a few years ago !!!

OK, so the fuse had never blown in all that time, good. I opened up the fuse holder to see what size the fuse was that I had been using - it was 5 amps !!! And I do have the reverse lights hooked up and working on this. The ignition is points, from a 1976 vintage 009 distributor. Anyway, after reading all these posts, I did upgrade to a 10 amp fuse; I put some spare fuses in the ashtray. So it sure hasn't hurt me all these years !!!

Bump. Good to know Cusser. I use a 10 amp with no problems either.