whats the difference between an AC Ignition coil and a DC one?

Im puttering around with the 1974 Honda XL 350...and the coil puts out a
weak spark...It may have something to do with the fact the lead wire to
the plug is only held on with the internal wire..the insulation is
broken around where its molded into the coil itself. I suppose I could
repair that with JB weld. The condenser is also molded as part of the
coil, and it may be bad, so I picked up a used condenser from a bike
yard and will splice it in.
I picked up a used generic 6vt coil for $10, and machined a mount to
adapt it to the bike. I tested the coil by grounding the hot lead by
scratching it to the frame and after 10 or 15 sparks, the coil split
around the circumference . It doesnt spark anymore...shrug. It had no
condenser attached to it. It "bumped" pretty good each time I sparked
it. Had a nice brite spark too.
Im testing the electrical with a 6vt battery charger hooked into place
of the battery
The wiring diagram I have and all references say that the Honda uses an
AC coil, fed by an ignition winding on the alternator. Honda wants $80
for a replacement coil, JC Whitney sells an aftermarket "can" coil for
$21, but doesnt indicate if its AC or DC.
Whats the difference between an AC and a DC coil????
Anyone got a surplus manual for a 1974-75 Honda XL 350?
Gunner
"They couldn't hit an elephant at this dist..."
Maj. Gen. John Sedgewick, killed by a sniper in 1864 at the battle of
Spotsylvania
Reply to
Gunner Asch
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Gunner , think about it for a minute - if that voltage input to the coil was AC , it'd be buzzin' all the time . There's gotta be a diode , or more likely a plate rectifier (My '74 CB750 has one of those on the 3 phase output from the alt coils) between that coil and the supply .
And a metal-filled epoxy on a high-voltage application ? The weak spark is more likely from a bad cap . Do ya get like a giant spark when ya break the circuit ? Sure sign of a bad cap .
Reply to
Terry Coombs
I've got a bit of info on the XL250 from an old Chilton, but nothing on the 350. Indeed, the wiring diagram shows a separate winding on the alternator for the ignition and an "AC ignition coil"-no rectifiers. You should be able to rewire so to use a regular 6V coil. I can try to scan the wiring diagram and send that to you if it's any help, but there's nothing in the Chilton about that alternator.
Reply to
Rick
I'd sure like to see details of that system ! How do they time the spark ? Kinda makes sense , AC will give a continuous spark , or rather arc ? Learn something new every day !
Reply to
Terry Coombs
Not sure of the difference but there surely is one. The old Ducati singles used both. Street bikes with batteries had the DC coil, the scramblers with magnetos had an AC coil. If you need an AC coil, try some motorcycle boneyards and look for dirt bikes, which generally all run mags. Also, I'll bet you could find a used coil on ebay for far less than the dealer wants.
Speaking of which, I remember Dirt Bike magazine running an article in I think the late 70's, touting how anyone could have their own $10,000 MX bike. Back then, those dollars meant works bikes. Well, all one had to do to own such an expensive bike was buy it one single part at a time. The markup is huge!
Jon
Reply to
Jon Anderson
Gunner Asch laid this down on his screen :
If the battery is used for the ignition, which I don't know that is or not, then you'll probably need a battery, not a battery charger.
You can see a listing of parts here
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Reply to
Wayne
Check your Email
Reply to
Steve W.
Do NOT use JB weld, it is metal filled and slightly conductive. Best is plasic bumper repair epoxy, or winsheild mounting urethane. Plain epoxy works pretty well too, but the bumper stuff stays flexible.
Reply to
clare
Depends 1 phase or 3 phase? remember stator rectifier/regulate
Reply to
John Scheldroup
It appears to be essentially a magneto winding..still uses points and a condenser.
Reply to
Rick
JB makes 'waterweld' epoxy putty. I repaired my case for my Fluke 12 with it. It is non-conductive.
Wes
Reply to
Wes
The Honda 350's will start and run just fine ( it will miss a little) without a battery, think lawn mower type of ignition, not automotive. They are self exciting, 3 ph AC output. Find a motorcycle junkyard, and get a coil from them, Honda made lots of the 350 twins, so it shouldn't be a problem. 350's will make it home, well the Prince of Darkness sits on the side of the road. gary
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Reply to
Gary Owens
Here is the wiring diagram...check it out for yourself
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Thanks guys for the heads up on JB Weld..Id not remembered that it was metal filled.
Gunner
Reply to
Gunner Asch
Battery charger puts out a nice DC voltage at 6.8 volts, think of it as a big wall wart...chuckle
$80 for the coil...
Ouch
Still no one can tell me the difference between an AC and a DC coil......
gunner
"They couldn't hit an elephant at this dist..." Maj. Gen. John Sedgewick, killed by a sniper in 1864 at the battle of Spotsylvania
Reply to
Gunner Asch
If I'd had my head in the light , I'd have realized that the ignition system is basically a magneto with the coils in separate units . Hey , embarassment can lead to learning too !
Reply to
Terry Coombs
Maybe waaaaaaay off course - could the AC refer to AC Delco rather than A.C. // D.C.
The AC / DC doesn't make much sense. AFAIK the primary difference with older (car) coils was if they had in internal or external ballast resistor.
Reply to
K Ludger
The markup on parts is usually more than the markup on the whole ;(
Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/
Reply to
nick hull
Electrical current through one coil will induce current in the other one. In the case of an ignition coil current flows through a coil with fewer turns and induces a higher voltage in a coil with many turns.
In order for a current to be induced the magnetic field around the powered coil must change, thus all transformers function through fluctuating/alternating current.
Now having said that the watts (Volts X Amps) that drive the transformer are reflected in the output coil (ignoring transformer losses) so if you have 1 amp at 6 volts flowing into the transformer you will have 6 watts of power flowing out. If the output voltage is, say 50 volts, then 6 watts / 50 volts = o.i2 amps.
Mext. The coil resistance and inductance (sort of alternating current resistance) controls the current through the primary coil so if it is designed for, say 6 volts and you try driving it with 12 volts you will have twice the current and just as with welding machines current = heat. Not good to try using too much voltage through the primary.
Finally, the current (heat) through the coil is also a factor of time. If you flow 6 VDC through a coil at one amp of current then you have 6 watts of power flowing through the coil. If you pulsed that 6 volts 60 times a second you would have approximately half the current (on a time basis) and thus heat flowing.
So, yes there is a difference in transformers designed for AC and DC but only in the sizing of the components.
Cheers,
Bruce (bruceinbangkokatgmaildotcom)
Reply to
Bruce in Bangkok
This is a guess rather than any semblance of expert opinion: in a DC coil excited by a battery, max primary current is limited by primary resistance or a ballast resistor. An AC coil would be driven by a winding in the alternator that is of the correct phase w.r.t. the engine (synchronized with engine rotation) so the alternating current in the primary would be about a max when the points open. Current is limited by primary reactance so primary resistance could be quite low. Possible advantage: the voltage produced by that winding increases with engine speed, as does the frequency. Coil impedance would increase with freq but since voltage does too the peak current remains about the same. A DC coil can have trouble getting up to current at high RPM's unless it's significantly overdriven at low RPM's.
Reply to
Don Foreman
Being the curious type, and having seen before the statement about JB weld being slightly conductive, I decided to see if it was true.
I have a number of pallets made of scrap circuit board material and JB Weld epoxy. The pallets carry circuit boards or panels of boards through our convection oven to solder the surface mount components to the boards. We use both leaded and lead free solder paste, so it gets very hot. JB Weld is the only common epoxy that will stand the heat over and over.
I checked the JB Weld on a pallet with a hand held DVM set to read 20 meg ohms. No matter how close I set the test leads, they showed a complete open circuit. If JB Weld is slightly conductive, it must be extremely slight!!! It should work just fine to repair electrical parts, including ignition coils.
Paul
Reply to
co_farmer

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