ballast resistor?

[fredvv44]

I am running an '85 Cal2 engine in a 3 wheel car. i made up my own electrical system and am running 12 volts to the coils and using a Dyna 2 electronic ignition.
the question is should I have a ballast resistor at the coils? The coils do get hot when running.
Thanks,
Fred V

[ccoli]

3ohm Dynas are green and AFAIK were meant for racing applications ie limited time usage.
5ohm are black and meant for more everyday applications.
I suppose you could run a ballast resistor with the greens.

[Chuck in Indiana]

FWIW, I tried a ballast resistor with the greens and Dyna S, and had a poor spark that eventually fouled plugs. Maybe I didn't use the correct resistor, but I took it off, and it's been fine ever since. What you *can't* do is leave the key on for extended periods without the engine running.

[fredvv44]

I have the black Dyna and just do street driving. Maybe it's OK then; I've put 12,000 miles on it with no problems.
Fred V

[wirespokes]

My 87 LM has the Dyna Green coils and hasn't had an issue for the last three years and 20K of my ownership. Coils do get hot in operation, but like Chuck said, do not leave the key on when the engine isn't running. Electronic ignitions often have a timer to cut current to the coils after ten or twenty seconds, but don't think the Dyna has that capability.

[fotoguzzi]

I am running an '85 Cal2 engine in a 3 wheel car.

pics, PLEASE!

[Muzz]

I am running an '85 Cal2 engine in a 3 wheel car. i made up my own electrical system and am running 12 volts to the coils and using a Dyna 2 electronic ignition.
the question is should I have a ballast resistor at the coils? The coils do get hot when running.
Thanks,
Fred V

If the coils are for automotive use (you don't actually say whether the actual coils are Dyna) they should have on the side their operating voltage. Most cars that were running points systems had an operating voltage of 8volts, cut down by the ballast resistor.  When the starter circuit was activated a lead put 12 volts direct to the coil, enabling it to give a nice fat spark in spite of the voltage drop that happened when the starter was engaged.  Went back to 8 volts once the ignition went back to "run".

If that is the case you will be over driving them.

[Antietam Classic Cycle]

If the coils are for automotive use (you don't actually say whether the actual coils are Dyna) they should have on the side their operating voltage. Most cars that were running points systems had an operating voltage of 8volts, cut down by the ballast resistor.  When the starter circuit was activated a lead put 12 volts direct to the coil, enabling it to give a nice fat spark in spite of the voltage drop that happened when the starter was engaged.  Went back to 8 volts once the ignition went back to "run".

If that is the case you will be over driving them.

I have the black Dyna and just do street driving. Maybe it's OK then; I've put 12,000 miles on it with no problems.
Fred V

[Rough Edge racing]

If the coils are for automotive use (you don't actually say whether the actual coils are Dyna) they should have on the side their operating voltage. Most cars that were running points systems had an operating voltage of 8volts, cut down by the ballast resistor.  When the starter circuit was activated a lead put 12 volts direct to the coil, enabling it to give a nice fat spark in spite of the voltage drop that happened when the starter was engaged.  Went back to 8 volts once the ignition went back to "run".

If that is the case you will be over driving them.

 What determines coil "voltage" is the primary resistance...In the USA, 6 volt cars had coils around 1.5-2.0 ohms...When they went to 12 volts around 1955,the coils were still the same ohms but with about a 1.2 ohm ballast resistor or wire to give 3.0 ohms when the engine was running. With points, 3.2-4 ohms primary Resistance is usually adequate for reasonable points life with a decent spark on most 2 cylinder engines..Coild tend to heat up when the dwell is longer time wise, like at lower RPM's

[fredvv44]

The coils are Guzzi but not sure what year or bike they are from. I could add a ballast resistor and tie it into the ign switch to cut it out during cranking.
Someone asked for photos.

[fotoguzzi]

Beautiful!

[Old Jock]

Coils don't look to me like Dynas, the Dynas I've seen are in an epoxy case whereas these are simply enclosed in the more common or garden "bean can"

The coil should have printed (or stamped) on it somewhere if it's a 6V or 12V coil. I doubt it's 6V as if you've run it for any time on a straight 12V supply, they would have burned out

It should be easy enough to determine the primary resistance.

First pull off the supply and ground connections on the low (12V) volts side, the spade connections.

Then get a meter and select resistance place the probes across the 2 connnections (not the HT Lead) and you'll find out what the primary resistance is. If it's 3 Ohm then a ballast may be an idea, if it's 5 Ohm or above then I would doubt it would need it. If it is 5 Ohm all a ballast resistor will do is lengthen the charge time which could then lead to it not fully charging during the dwell time and make your spark weaker.

As far as I understand all a ballast resistor does, is lower the primary voltage to the coil to prevent it burning out if it charges to quickly.

Low resistance means it charges fast and pulls more current in the process. It then sits fully charged until it's grounded via the Dyna, during that time it will heat up due to the current passinng through it.

Higher resistance means it charges slower, pulls less current and depending on the time between grounding (dwell time) will either be too slow and not fully saturate (leading to a weak spark), like for example a 4 cylinder engine only using 2 coils, or good enough as is the case with Guzzi lump

Just my understanding, if I've got any of that wrong I'll be put right soon enough on here     

That is a VERY nice 3 wheeler, it looks immaculate, betting you are very proud and rightly so

[Wayne Orwig]

As far as I understand all a ballast resistor does, is lower the primary voltage to the coil to prevent it burning out if it charges to quickly.

Low resistance means it charges fast and pulls more current in the process. It then sits fully charged until it's grounded via the Dyna, during that time it will heat up due to the current passinng through it.

Higher resistance means it charges slower, pulls less current and depending on the time between grounding (dwell time) will either be too slow and not fully saturate (leading to a weak spark), like for example a 4 cylinder engine only using 2 coils, or good enough as is the case with Guzzi lump

Looks good to me.
Except the Dyna/points open the circuit, not ground it, after the charge.

[Old Jock]

Looks good to me.
Except the Dyna/points open the circuit, not ground it, after the charge.

Of course they do Wayne, the coils are grounded during the charge and open when a spark is required, that creates a back EMF volts rise in the primary boosted further, by the turns ratio in the secondary

To set it straight on the previous post, instead of grounding, the Dyna leaves it grounded when ithe coil is charging then opens the circuit when a spark is required at the plug

Thanks for putting me & OP right

John

[fredvv44]

If I remember right my coils are 3 ohm so should I add a ballast resistor? If so, what size?
Thanks fro the info on what coil resistance does; I always wondered what the difference meant.
Fred
3 wheeler is the most fun car I've ever owned. I took it up to 95 once to see where the top end was. Exciting drive!!

[Moto]

I think I'm still on-topic here.

I have what I think are the OEM, stock coils in my T3, and have been running the Dyna ignition with them for thousands of miles. The instructions that came with the Dyna said it is for use with stock coils, so that's how I installed it.

So, am I headed for a problem? If so, why and how?

1) will the coils get too hot and die early?

2) will the Dyna control unit get too hot and die early?

I haven't had any problems at all, and am concerned that the coils that Dyna now touts for its system are a more of a revenue generating device than a real necessity.

Anyone know for sure what the situation is?

Moto

[Old Jock]

Well nobody is answering

fredvv44

I'd try a 1.5 Ohm or perhaps 2 Ohm ballast on the coils if 3 Ohm, although if it were me (I'm a bit spendy but a lot on here are more than they like to admit), I'd just change them out for 5 Ohm coils.

However nothing to be lost in trying it, resistors should be cheap. Thing to remember is the power rating, you'll need a resistor capable of handling, at least 3 amps (personally I'd up it to 4 to be safe). So power rating of 30-50W. The resistor will also get hot so mount it to a heat sink and make sure it gets some air around it.

Moto

First this is just my opinion, I don't run a Dyna and don't know about their latest offerings

What coil primary resistance, as far as I'm aware stock is 5 Ohm and it only takes a few minutes to confirm that. If they are 5 I'd go ride and forget all about it

If they are 3 as above, both coils and Dyna will be having to handle more current.

Most likely the Dyna would die first, but it may not die at all. The point is 3 Ohm means more current passing, means more heat and load on the systems associated with the ignition

Lots of posts about people fitting the 3 Ohm Dyna coils and Dyna ignition and then having a bad day.

That said, like all things some fail some don't, choice is yours at then end of it.

[Rough Edge racing]

If I remember right my coils are 3 ohm so should I add a ballast resistor? If so, what size?
Thanks fro the info on what coil resistance does; I always wondered what the difference meant.
Fred
3 wheeler is the most fun car I've ever owned. I took it up to 95 once to see where the top end was. Exciting drive!!

  I have measured several stock coils taken off circa 1980 points Guzzi's. The were 3.4 ohms each.....I replaced coils on a Cali 2 when the Dyna system and one Dyna coil failed...I bought generic auto 3.2 ohm coils and installed used points...I sold the bike to Petrus Rocks on this site..Thousands of miles later the engine still runs fine without ever touching the points...

[Muzz]

Just as an afterthought, have you checked the secondary output resistance?

Automotive ones at least, when the +ve terminal is linked to the secondary output, should read between 6k to 10k or more.  Some sources as as high as 15k.

If the resistance is too low excess current draw via leakage may be causing them to heat up.  However, this problem often shows up with the coil dying, motor stopping, but then coming back to life once it cools down.

[Chuck in Indiana]

FWIW, I've used 3 ohm coils with the Dyna S for years. And years. No resistor. Both with the stock Guzzi coils and Green Dyna coils.
Mouser also uses the 3 ohm coils with Dyna S for the secondary ignition. A magneto is primary.
2016-05-24_02-55-34 by Charles Stottlemyer, on Flickr
The only problem, as far as I know, is overheating a coil if the ignition (or master switch) is left on for an extended period without the engine running.

[Wayne Orwig]

You know, you could get a large light bulb (or officially a large PTC thermistor) in place of the ballast. Under normal operation the bulb/thermistor would be cooler and pass enough current to charge the coil easily. When the motor is stopped and the coil saturates, the bulb would just get hot, light up, and pass less current.

I measured a 35 watt bulb as of course about 4 ohms hot, and about 0.5 ohms cold. I'll bet that would charge the coil fast normally, and protect the coil when stopped. A PTC thermistor would be even better of course.

All meaningless in a way, since a low revving Guzzi motor really does not need low resistance coils.