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Dyna coil sizes #255459
05/25/09 5:50 pm
05/25/09 5:50 pm
Joined: Sep 2006
Posts: 731
Melbourne Fl
T
Terry_tr6 Offline OP
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Terry_tr6  Offline OP
BritBike Forum member
T
Joined: Sep 2006
Posts: 731
Melbourne Fl
I see a lot of raves for the dyna coils. does anyone have the size difference between the 3 ohm green twinlead coil and the miniature black twin lead coil? Any preference? The dyna web site doesn't seem to give much info on sizes

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Re: Dyna coil sizes [Re: Terry_tr6] #255540
05/26/09 5:47 am
05/26/09 5:47 am
Joined: Apr 2006
Posts: 255
Vancouver Island
waspfarmer Offline
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waspfarmer  Offline
BritBike Forum member
Joined: Apr 2006
Posts: 255
Vancouver Island
Sorry about this Terry, but a search of Dyna and coil may toss this up for others. May I add "Boyer, ignition, and resistance" for search purposes? This dosn't answer your question, but is a good wee read. Boyer's appearently like 3->4.5 Ohms accross the primary windings. This includes a great number of 12V coils.
Generally, you want to get the biggest physical size coil of comperable spec you can jam in there as it will likely use larger guage wire for coil winding, and/or thicker wire insulation.

I found this while researching coils. It's written by the Bransden part of Boyer/Bransden:
http://piled-arms.com/tech53.html :as follows,



""I think the ignition coil is one of the least understood things on Brit bikes following electrics in general. But what is the coil and how does it work in an ignition system? Which coils for a Boyer on twins? Iíll try to keep the technical part of it all down to layman terms.

COILS AND BOYERS:

The coil is simply an Alternating Current (AC) transformer. It has N1 number of turns in the primary winding and N2 number of turns in the secondary winding. If an AC voltage is put into the primary it comes out the secondary multiplied by the turns ratio of N2/N1. In our case the voltage comes in as a switched 12 volts (switched by the points or by the Boyers output transistor; switched DC acts like AC under some circumstances, like in an ignition system) and goes out at thousands of volts to the spark plug. There is more to it than a simple transformer, but more on that later.

The primary winding wire has resistance and that resistance limits the current flow through the primary winding. Typical Brit 12 volt coils end up with about 4 ohms. So instantaneously, when the switched 12 volts is applied, about 3 amps flows through the primary windings. Typical Brit 6 volt coils end up at about 2 ohms, hence the same 3 amps flows through their primary.

The Boyer Electronic ignition was designed to operate one 12 volt Brit coil of about 4 ohms. That limits the current out of the Boyer to about 3 amps. In a points system the primary resistance is not all that important as the points can handle many more times the current of 3 amps. But a Boyer uses a transistor to switch the voltage onto the coil and transistors have voltage and more importantly current limits. Too little current (too high of a resistance) and the coil may not generate enough energy to reliably spark the plug. Too much current (too low of a resistance) and the transistor melts from the heat and the Boyer is toast.

Many combinations of coils have been tried for twins but it has come down to only a couple of choices: two 6 volt, 2 ohm coils or one dual spark plug output 12 volt, 4 ohm coil. Whatever the combination, the resistance the Boyer sees can not fall out of the 3 to 4.5 ohm range. Ballast resistors have been suggested but the energy the Boyer
instantaneously delivers is fixed at about 36 watts (3 amps times 12 volts). If you turn part of that energy into heat in the ballast resistor, then the coil(s) get robbed of energy they need to jump a spark gap in the secondary circuit.

How about two 12 volt coils connected in series? The resistance in series circuits is additive and the resistance the Boyer sees would be 8 ohms. That limits the current flow through the coils to 1.5 amps and the voltage across each coil to 6 volts. They were designed for 3 amps at 12 volts or 36 watts and they get 1.5 amps at 6 volts or 9 watts, 1/4 the energy for which they were designed. Power in is power out for the coil so the spark plugs get starved for energy. The bike may run fine at low RPMS but may miss in high RPM running or under heavy loads.

How about two 12 volt coils connected in parallel? The resistance in parallel circuits is not additive and the resistance the Boyer sees would be 2 ohms. That results in the Boyer having to supply 6 amps amps which exceeds the current specification of the Boyer and the Boyer is burned up toast. The bike may run fine, for a while, but eventually the output transistor of the Boyer will overheat and melt, resulting in a potentially long walk home.

So for a Boyer installation choose some combination of coils connected in series or parallel that limit the Boyers output current to 3 amps (the resistance the Boyer sees must be in the 3 to 4.5 ohms range) and puts the rated voltage to each coil (that is, 12 volts to 12 volt coils and 6 volts to 6 volt coils). It matters not how you get to that situation but the above two combinations of two series connected 6 volt, 2 ohm coils or one 12 volt, 4 ohm dual output coil flat work.

HOW COILS WORK IN AN IGNITION CIRCUIT:

Ignition circuits include a condenser (capacitor in modern terms), even inside a Boyer. It is connected so that it is placed across the coil(s). This makes the coil circuit into an oscillator. That is, when the circuit is instantaneously supplied with a voltage, over time it oscillates from positive to negative building with each transitions through zero volts until it reaches a peak voltage dependent on the values the circuit components. In the case of the ignition circuit, that primary coil terminal to terminal voltage reaches about 300 volts peak to peak. Given the turns ratio, the output of the coil has the potential of 30, 000 volts. But long before that the spark gap is jumped (dependent on cylinder conditions, compression ratio, spark plug gap), at about 15,000 volts. So we end up with about a two to one safety factor to accommodate worn plugs with wide gaps, excessive engine loads and compression ratios enhanced by carbon buildup in the cylinder head. Bad condenser? Then maybe youíll get no spark or at least a very weak spark. The Boyerís condenser is internal but modern condensers (now called capacitors) by nature are very reliable and donít wear out. Old automotive condensers and Lucas condensers are not modern capacitors. Hence they probably should at least be tested if not regularly replaced. ""


"This is not work you want to do after a couple of beers."
(RF Whatley)
"have a fire extinquisher handy or be careful"
(rmaffeo)
1968 Atlas
1998 Daytona 955i
1987 exMoD 110 Landy
Packet of crisps and a gob stopper
Re: Dyna coil sizes [Re: Terry_tr6] #255552
05/26/09 8:43 am
05/26/09 8:43 am
Joined: Aug 2001
Posts: 1,081
Cheshire UK
Phatt Bob Offline
BritBike Forum member
Phatt Bob  Offline
BritBike Forum member
Joined: Aug 2001
Posts: 1,081
Cheshire UK
The Dyna coils are a bit bigger, I run both types in my bikes and can measure them later in the week unless someone beats me to it.

From memory dynas are about 3 1/2 inches long and 2 1/2 in diameter, mini coils are about 3 inches long and 2 in diameter not including the iron core/mounting stubs. Dynas are also a lot heavier.

When I had my Dyna fitted Daytona 12 featured in "Streetfighters", the journo claimed that dyna coils would "happily set fire to a bucket of p1ss". Nice turn of phrase, but on reflection I think the ordinary black ones are cheaper, smaller and do an adequate job.

Cheers

Bob

Last edited by Phatt Bob; 05/26/09 8:49 am.

Phatt Bob
'95 Daytona 1200
'98 Daytona 1200 dragbike
ex-850 T140 Caff Racer, 850 Triton, Morgo T120, Starfire and Pretend Daytona 500 owner
Re: Dyna coil sizes [Re: Phatt Bob] #255561
05/26/09 10:01 am
05/26/09 10:01 am
Joined: Oct 2006
Posts: 343
southern N.H.
GREEN MONSTER Offline
BritBike Forum member
GREEN MONSTER  Offline
BritBike Forum member
Joined: Oct 2006
Posts: 343
southern N.H.
Terry tr6 make sure that if you are using an older ANALOG or POINTS based ignition system do NOT use the modern miniture size coils.

If memory serves me correctly the dwell angle is allot longer on older sytems, hence the need for a physicly larger coil or coils becouse of the heat generated by the coil's saturation time.

I tried a couple years ago to play the size game and used a modern MINI coil MELTED the coil and people wonder why I always carry spare stuff!!! .

Anywho you get the picture unlees you're willing to pony up for the latest technology ign. system use the old big coils with the correct primary resistance.

Good Night and Good Luck Signed GreenMonster


Good Night and Good Luck Signed GreenMonster
Re: Dyna coil sizes [Re: GREEN MONSTER] #257351
06/04/09 3:30 pm
06/04/09 3:30 pm
Joined: Aug 2001
Posts: 1,081
Cheshire UK
Phatt Bob Offline
BritBike Forum member
Phatt Bob  Offline
BritBike Forum member
Joined: Aug 2001
Posts: 1,081
Cheshire UK
DYNA blue 0.7 Ohm coils are 117 x 72mm overall and weigh just under a pound.

The mini equivalent I have is 60 x 70mm and weighs 5 ounces.

These are for the Hinckley Triumph and Boyer Micropower systems.

Cheers

Bob


Phatt Bob
'95 Daytona 1200
'98 Daytona 1200 dragbike
ex-850 T140 Caff Racer, 850 Triton, Morgo T120, Starfire and Pretend Daytona 500 owner
Re: Dyna coil sizes [Re: Phatt Bob] #257614
06/05/09 11:17 pm
06/05/09 11:17 pm
Joined: Aug 2001
Posts: 4,470
Owego, NY, USA
Mark Z Offline
BritBike Forum member
Mark Z  Offline
BritBike Forum member
Joined: Aug 2001
Posts: 4,470
Owego, NY, USA
Just a heads up for those who have an eye on cost: An HD-Sportster dual-lead 12V coil (of the correct resistance, there are two varieties) provides an adequate output voltage, significantly greater than the 6V coils typically used with Boyer systems. The knock-off brand can be had for about $60.

Also, they're black (personal preference).


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Dyna coil sizes [Re: Mark Z] #257623
06/06/09 12:44 am
06/06/09 12:44 am
Joined: Sep 2006
Posts: 731
Melbourne Fl
T
Terry_tr6 Offline OP
BritBike Forum member
Terry_tr6  Offline OP
BritBike Forum member
T
Joined: Sep 2006
Posts: 731
Melbourne Fl
i think i'll just stick with my pair of 6V german coils. They work fine and fit in the stock coil holder. It ain't broke, why fix it. especially when i saw the price of the dynacoils....

Re: Dyna coil sizes [Re: Terry_tr6] #257628
06/06/09 1:24 am
06/06/09 1:24 am
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Tiger Offline
BritBike Forum member
Tiger  Offline
BritBike Forum member
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Twin lead 12V Jappa coils work fine with EI and most measure around 3.5 ohms primary resistance, the later stuff [since the mid '80s] also have replacable HT leads.

Almost free on fleabay, mine gives a noticieably better spark than the previously fitted Lucas copies.


1969 TR6R
7.62 x 51 is not a maths puzzle.

Moderated by  Alan_nc 


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