F-R Best way to drop Volts for a 6v choke?

[jbjennings]

F-R,
I suspect you have a good way to drop voltage from 12 to 6 to keep those old chokes from burning out. I noticed a voltage regulator diagram at ask-a-member on another guy's thread related to this subject, but didn't fully understand it. I figure you have already come up with a clever scheme for doing it cheaply and was hoping you might let me in on it.
I was thinking about using a resistor from radio shack but I'm worried they won't have one that will take the current produced by a big battery.
Later,
JBJ​

 

[Texasmark]

Re: F-R Best way to drop Volts for a 6v choke?

I assume you are referring to an electrically activated (via remote) solenoid controlled choke.

If you know the amperage, which for that may be on the order of 1 amp, give or take 0.5 amps, applying Ohm's law yields: R= V/I. For 1 amp it yields 6/1 = 6 ohms. For 500 milliamperes it doubles (current halved) to 12 ohms, and for 1.5 amperes it drops to 4 ohms.

Power dissipation (unit of measure: Watt) for the device is again Ohm's law at IxIxR, or (VxV)/R. Also it is a good practice to specify the resistor rating at twice the expected load to keep the component temperature down. Therefore for 12 ohms, the dissipation would be 3 Watts, 6 = 6 Watts and 4 = 9 Watts. Applying a suitable safety factor you would be looking for:

1ea 12 ohm 6 Watt, or 1 ea 6 ohm 12 Watt, or 1 ea 4 ohm 18 Watt. Radio shack may stock wirewound resistors in this area, or you can go online to Allied Electronics or other retailers.
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Since the choke is a dc solenoid, made of many turns of wire around an iron core, the dc resistance of the choke (measured with your DMM/DVM/Ohmmeter, whatever) is a good indication as to the size of the resistive element you will need. Equaling that resistance and applying the power formula x2 should easily give you the resistance value and wattage that you are seeking.

The higher the wattage the hotter the device can get (radiate more heat) so when mounting keep that in mind especially around plastic insulated wiring.

HTH

Mark

 

[Silvertip]

Re: F-R Best way to drop Volts for a 6v choke?

If you are old enough to remember the clamp under dash variable heater motor controls like this one, be aware that they are still available at any auto store but the best bet would be to try NAPA first. Since this thing is variable, connect it, attach a voltmeter to the choke lead, set the control to the highest resistance and then gradually turn it back (decreasing resistance) until you achieve the 6 volts (or close to it) that you are looking for. Someone will obviously need to hold the choke switch (or ignition key) in during the measurement and adjustment.

 

[MudLake]

Re: F-R Best way to drop Volts for a 6v choke?

I would use a 6 volt zener diode that way you would drop 6 volts across the zener and 6 volts across the 6 volt choke solenoid.
I would think that a 10 watt zener or a minimum of 1 AMP 6 volt zener diode should work.

the zener gets placed in series with the battery source and the solenoid.

I use this for current source solutions.

cheers

 

[F_R]

Re: F-R Best way to drop Volts for a 6v choke?

JB, you have a PM

 

[Fl_Richard]

Re: F-R Best way to drop Volts for a 6v choke?

Ditto the zener diode. What a great component. Too often forgotten.

 

[Chris1956]

Re: F-R Best way to drop Volts for a 6v choke?

Zener Diodes are great, however, in this case since the choke coil is of a known wattage, a wire wound resister is fine.

You should put an ammeter on the choke coil (use a six volt supply) and see what she draws. Then use Ohms law to determine the resister needed. Hopefully it will not be a large watt resister.