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billybobrae
New Member
3 Posts |
 Posted - Sep 02 2007 : 09:21:54 AM
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I am looking for some kind of DC current sensing circuit. I have an
application whereby when the wiper motor on a car, 30 amp fused, is
activated by a switch or auto wiper control module that when the current is present in the postive feed wire to the wiper motor that a relay is closed. I would like to put the circuit inline just before the feed wire to the wiper motor. The reason for
this is that on a Buick LeSabre, the auto wiper system always powers
the headlights and dashlights. Thereby causing the instrument panel
lights to be on all the time and hence burning out. These lights are
expense to fix and I figured I could use this sensing circuit along
with a time delay relay to connect and disconnect the signal wire for headlights on from the wiper control switch on the steering
column to the Dash intregation module in the car. |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Sep 06 2007 : 10:11:41 AM
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| All you need is a low value high wattage resistor in series with the + line of the motor. Measure the voltage accross the resistor. It will rise based on how much current is being drawn. |
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billybobrae
New Member
3 Posts |
Posted - Sep 07 2007 : 9:04:45 PM
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Thank you for your response. It's been a long time since highschool electronics. So if I am to understand you, by putting a low value,
high wattage resistor inline of the postive feed to the wiper motor
I could then attach a wire to the side of the resistor farthest from the battery and then route this wire to my Dash module. Whereby when the wiper motor is off, no power would go to the Dash module and then when the motor draws current, the wire would then become + charged. What value of resistor would you suggest.
Sorry to re edit, but I would like to use the time delay module that you have on your website and change the S1 switch to a relay. If the
wiper motor goes into a slow pulse mode, if I ran a wire from the resistor to the Dash module without a time delay circuit, the headlights would pulse on and off. So I am wondering what size of a relay and resistor combination might work.
Thank you
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Edited by - billybobrae on Sep 07 2007 9:21:21 PM |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Sep 08 2007 : 10:41:27 AM
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| I'm not sure of the details regarding your dash module, but the voltage drop accross the resistor will be very low. So you need to take that signal and feed it to to a relay, likely through a transistor to amplify the current. Use a low value resistor (500 ohm or so) at the base of the transistor to limit current. |
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billybobrae
New Member
3 Posts |
Posted - Sep 08 2007 : 6:28:06 PM
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The + wire that comes from the wiper control switch is just 12 volts.
It is activated when the wiper switch is turned on to any postion and the auto wiper system is also activated. The + wire going to the Dash module is therefor only 12 volts on and the off. I am not sure what you mean in your last post about the transistor hook up
details. Sorry to be so unkowning.
Bob |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Sep 13 2007 : 09:35:14 AM
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The output from the series resistor will be a very low value. Less then 1V so it's not going to do much to power your switch.
Look up basic transistor circuits (on Google) for an idea of what you need to do. You'll probably need to use a "darlington" configuration to get enough output voltage and current to switch on the coil of a small relay.
Here's a good page that describes basic transistor circuits:
http://www.kpsec.freeuk.com/trancirc.htm
On that site I found this example of a simple transistor switch:
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DC current sensor circuit
