06-18-2012, 06:45 PM | #1 |
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HELP with horn
Does anyone know what values of resistors to use for converting a 6 volt to work on a 12 volt system. I bought a resistor from Speedway , but it wouldn't work. The horn works great on 6 volts. I need to know the watts and the ohms. I've used resistors before and they worked good, but can't remember what values that I used before. Thanks for any help. m.ralph
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06-18-2012, 07:12 PM | #2 |
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Re: HELP with horn
John Elliott, who posts to Ford Barn from time to time, was kind enough to provide a list of 6-volt to 12-volt conversion parts for our club newsletter. Although his list did not provide the resistance value, he did state that an Ohmite RKS2RO resistor was the item needed when using a 6-volt horn in a 12-volt system.
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06-18-2012, 07:31 PM | #3 |
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Re: HELP with horn
A quick Google revealed that the Ohmite RKS2RO is listed as a wire-wound 2-ohm, 100-Watt rheostst.
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06-18-2012, 07:48 PM | #4 |
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Re: HELP with horn
Bratton's sells a resistor kit especially for this (6v horn on 12 volt system) for about $20.
Goes inside of the horn cover and can't be seen. |
06-18-2012, 09:01 PM | #5 |
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Re: HELP with horn
I find a good working horn draws 5 amps, so 5 amps x 6 volts = 30 watts, but allow some extra for safety. A 35 or 40 watt resistor should be fine.
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06-18-2012, 10:11 PM | #6 |
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Re: HELP with horn
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06-19-2012, 10:25 AM | #7 |
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Re: HELP with horn
Something is wrong here.
If a good horn draws 5 amps, and the correct resistor is 2 ohms, then the battery has to have 16 volts output so that the horn gets 6 volts. 5X2 =10volts (ohms law). Marc |
06-19-2012, 10:47 AM | #8 |
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Re: HELP with horn
I have seen the Ohmite RKS2RO 6-volt-horn-in-a-12-volt-system resistor referenced in a couple of different places, the most recent being the "Standard bearing parts numbers?" thread posted yesterday. Perhaps someone who has successfully used a resistor from one of the Model A parts suppliers can measure the resistance and confirm or deny the adequacy (and wattage rating, inasmuch as this is a voltage-dropping application) of the 2-ohm resistor.
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06-19-2012, 01:16 PM | #9 | |
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Re: HELP with horn
Quote:
To take it up to 12 volts the formula would be 5A x ohms = 12volts. ohms would equal 2.4 ohms and then you need to subtract out the original 1.2 ohms giving you a 1.2 ohms resistor needed. But, since 6 volts is really more like 6.5 volts and 12 volts is not exactly 12 volts and 5 amps is just what this one horn pulls, a 2 ohm resistor is close enough as long as you get one rated for the high watts. Clear as mud? |
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06-19-2012, 01:49 PM | #10 |
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Re: HELP with horn
Sorry 30cabriolet , not clear.
If you are using an external 2 ohm resistor in the circuit, and the horn SHOULD draw 5 amps when it operates correctly, then the external resistor will have a voltage drop of 10 volts across it. So, if 10 is lost across the resistor and 6 across the horn, the supply needs 16 volts. Now, if the horn draws less than 5 amps, less is lost across the external resistor. So, I reduce sounding horn could be the result with a 12 volt (really 13.8V) battery. Marc |
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