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Antique Gas Engine Discussion

How much wire?

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Old 08-04-2005, 06:21:34 PM
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Default How much wire?

I'm making a low tention coil. Total core length is 7 1/2 in. 6 in. to be covered by 18 Ga. magnet wire. Core is 3/4 in. diameter and made of multi strands of mechanics wire, varnish coated. How much 18 Ga. wire should I wind for a good strong spark? Would 6v or 12v make any difference in the length of the wire? Sure hope this works better than the puny spark of the auto coil and the AC clutch coil. Thanks for all advise.
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Old 08-04-2005, 11:50:21 PM
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Dick Graybill Dick Graybill is offline
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Default Re: How much wire?

I don't have the answer to your question,but I took a coil from an old briggs and it made a strong sparking low tension coil, also one from a lawnboy. Works great. Dick in central PA.
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Old 08-05-2005, 12:29:34 AM
RHudson RHudson is offline
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Default Re: How much wire?

i've made two coils so far. made both on 7018 welding rod cores. i was shooting for 6 ohms resistance (ballpark) to keep 12 volt amp draw to around 2 amps. i used a basic electrical text book to figure length of wire for 6 ohms. (sorry for lack of detail, all my information is back at office) i wound this using a lathe. electrical tape insulating about every other wind. i found it impossable to keep pretty uniform windings and depended on the tape to even out the winding lavers. anyway result is i got a strong spark but with a higher amp draw than expected. maybe from inductive impedance? on the next coil i wound the balance of wire i had on the bulk spool. which amounted to about about 1/3 more wire on the core than the first.. the spark, it may have been a little stronger....but by much. ....Maybe magnetic saturation? amp draw slightly lower, but again not much..

I can only go to local shows with my schedule...but noticed an engine running with a little puney coil that looked original...i bet it didnot have more than three layers of wire,,,,,maybe a hundred feet of wire. it ran fine...

i have found a few cores from a trap metal seperator in a local junk yard....too bad they had already removed the copper wire...else i feel i would have a source for hundreds of low tension coils ready made. day late...anyway i look forward to using these cores to make my third low tension coil on.
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Old 08-05-2005, 09:46:29 AM
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Elden DuRand Elden DuRand is offline
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Exclamation Re: How much wire?

A little surfing found this:

Copper Wire Resistance Charts: American Wire Gauge (AWG)


18 ga=6.385 Ohms/1,000 ft.
16 ga=4.016
14 ga=2.525
12 ga=1.588
10 ga=0.999
8 ga=0.628
6 ga=0.395
4 ga=0.249
2 ga=0.156

Figure for around 1/2 to 2 Amp current at whatever voltage battery you plan to use. The more core, the better!

In other words, for 12 Volts and 1 Amp, use about 1,800 feet of 18 ga wire. for 12 Volts and 2 Amp, use about 900 feet of 18 gauge wire.

FYI, for direct durrent coils, inductive reactance is not a factor except for the very short time the magnetic field is building up. After a few thousandths of a second, resistance is the only factor that determines the current that is drawn by the coil.

Hope it helps.

Take care - Elden
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