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Post by ernie wrenn on Jan 11, 2012 10:45:12 GMT -5
I need to drop from 24 vdc to approx 6 vdc .... What resistor valve do i need.
This is to drop the voltage to the fuel sending unit so not real amp draw.
ernie
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Jan 11, 2012 17:10:59 GMT -5
Ernie, if this is just for signal power, not working power than all you need is a simple voltage divider www.raltron.com/cust/tools/voltage_divider.aspFor Vin=24 and R1=20k0 (20000) and R2=6k8 (6800) your resultant output voltage is 6.09 What is the current draw (I) for the signal? If it is only a few milliamps then you won't have to adjust for the load making the voltage sag. Just remember that V=I*R and the wattage rating for the resistors will need to be (R1+R2)*(I^2) so that they can physically handle the drop since you are dropping the total voltage across both resistors. |
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Post by ernie wrenn on Jan 11, 2012 18:21:56 GMT -5
amp load is milliamp. Power to gauge>senders only.
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Post by enginewhisperer on Jan 11, 2012 22:41:51 GMT -5
fuel senders are a voltage divider already, and sometimes draw a fair bit of current. You may have to experiment a bit with the dropping resistors to get the right value (or measure the resistance of the sender unit, and make it the 6v side of your voltage divider - then you just need one series resistor)
Otherwise, get a 7805 regulator. They're cheap and will handle more current. You can add diodes to the ground pin to bring the output voltage up .6v at a time - or can use a resistor there to adjust it.
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Post by ernie wrenn on Jan 12, 2012 9:19:02 GMT -5
Thanks..
ernie
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Jan 12, 2012 16:32:18 GMT -5
instead of adding resistors to adjust a 7805 (fixed 5 volt output) simply because this is bad practice... just use one of these... $0.76 for a fixed 6 volt regulator... search.digikey.com/us/en/products/NJM7806FA/NJM7806FA-ND/805764follow the datasheet recommendations for the input and output capacitor that are shown in test circuits on page 5, they keep the regulator happy |
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Post by turbochris on Jan 15, 2012 8:30:56 GMT -5
2 things- I got Ernie a 7806 -ernie needs to post a picture of the original regulator, ..... doctor strangelove shit.
I asked ernie about an electric fuel pump for my pocket bike for some afterburner effects. The first pump he shows me was as big as the bike and weighed more. Huge fire! We got it figured out.....
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