Wonder if a 60's Chrysler ballast resistor in the line would work?
using a 6 volt horn on 12 volt system
- Thread starter stangguy
- Start date
We already shot that down!
CleanSump
Site Donor 2022
Why not a simple voltage splitter by putting a resister in parallel to the horn?
CleanSump
Site Donor 2022
You missed the point. Sorry, I didn't state it accurately.
This will 'splain it Lucy.
https://en.wikipedia.org/wiki/Voltage_divider
This will 'splain it Lucy.
https://en.wikipedia.org/wiki/Voltage_divider
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eBay has knockoff road runner horns.
I’m adding one to my zero turn when it comes in.
You'd need some pretty hefty resistors to handle the power dissipation. 100W or more. Those resistors aren't common and they aren't cheap.
seems least hassle, and of course horn ohmic value or current draw from 6v must be known to pick right bulb.
They're not exactly uncommon and expensive either. Suppose 5A running current, BUT is the driver going to lay on the horn all day? Probably not, so the resistor doesn't need a continuous operation/heat (wattage) rating for only a few seconds operation. 50W should be plenty.
12V/5A = 2.4 ohms resistor which is about $6 plus S/H:
https://www.digikey.com/en/products/detail/te-connectivity-passive-product/HSA502R4J/2366308
Then the question becomes how long the horn is realistically going to be activated, since this determines how much heatsinking the resistor needs. I might just hook it up with no heatsinking yet, lay on the horn the longest you think it'd ever be used (10 seconds? Even that seems a long time) and feel the temp of the resistor.
I figured that the horn will use as much as 20 amps.
Therefore the resistor will need to drop 6V and pass up to 20 amps, which means it will dissipate up to 120W.
Such resistors are about $15 or so.
You can get a 12V to 6V DC-DC converter rated at 20 amps for not much more. And then you don't have to figure out the resistance you need.
No, I didn't miss the point...and what you posted is the same as what I posted...a voltage divider circuit. In this case, the horn itself is the 'resistor' load...although, not knowing the internals of the horn in question, it could be resistive, capacitive, or inductive or a combination of the three. But being DC current, assuming a pure resistive load should be good enough. So, think of the horn as 1 'resistor' so, you need a second resistor in SERIES to divide the voltage. You can put the second resistor before or after the horn. There will be a voltage drop across the second resistor (depending on the current) which will reduce the voltage across the horn.
The reason you don't want a resistor in parallel with horn is the current will be 'split' between that resistor and the horn...although depending on the resistor values, current will take path of least resistance which could throw your voltage divider calculation out the window.
So, let's say you create a voltage divider with two resistors, R1 and R2. Let's say you use a resistance value of 6 ohms for both R1 and R2 and they are connected in series from +12V to GND. Total resistance is 12 ohms (R1+R2), so the current through both resistors is 1 amp (V=IR)...so, the voltage across R1 is 6V and R2 is 6V (one end of R2 is to GND).
Now, put the horn in parallel with R2...think you are still getting 6V across R2/horn? If the horn was a high (ideal) impedance device, then probably yes, but if not, then R2 in parallel with the resistance value of the horn will effectively (two resistors in parallel) reduce the resistance in that part of the circuit which will change the current value in this circuit thereby changing the voltage.
But the horn already works with 12V, so it's not critical, just use a powerful bulb.
Current takes all paths, in an amount inversely proportional to their resistance.
For DC current, yes you are correct...but for AC and high frequency...things start to 'act funny'...
We have proverb, fire shows the path. (On circuit board) lol
That's known as "letting all the magic smoke out".
