Bit of simple electrical help needed!
Discussion
Simple when you know how...!
Working on a little project and need a bit of a refresher of my electronics!
How do I use my multimeter to measure the current across a little 12V pump?
Then, how can I work out what resistor I need to reduce the voltage into the pump, what's the formula (a worked example might be useful!)?
Many thanks,
Chris
Working on a little project and need a bit of a refresher of my electronics!
How do I use my multimeter to measure the current across a little 12V pump?
Then, how can I work out what resistor I need to reduce the voltage into the pump, what's the formula (a worked example might be useful!)?
Many thanks,
Chris
If you want to measure current through the pump, set the multimeter to DC Current and connect the multimeter in series with the pump ... i.e. positive terminal of the battery to the +ve terminal of the multimeter, then -ve terminal of the multimeter to the +ve terminal of the pump, then -ve terminal of the pump to the -ve terminal of the battery.
If you connect 2 resistors in series, then apply a voltage across the pair, the voltage drops across them in proportion to their resistance. So, in the dig below you're applying +V volts across the two resistors R1 and R2:
+V o----[R1]----o------[R2]------o Gnd
The voltage across R2 is V * R2 / (R1 + R2)
You might need to be a bit careful choosing the resistor to put in series with the pump because the resistance of a DC motor varies from depending on whether it is spining or not. Also you must calculate the power that the resistor must be able to dissapate. If for example your motor is designed to run at 1 amp at 6 volts, then, assuming you've used the right resistor, it will have 1 amp running through it and perhaps 9V dropped acorss it (assuming the car's alternator is producing 15 volts). You'd then need a 9W resistor (or 9 1W resistors or whatever). It'll get hot.
>> Edited by ATG on Monday 29th November 10:20
If you connect 2 resistors in series, then apply a voltage across the pair, the voltage drops across them in proportion to their resistance. So, in the dig below you're applying +V volts across the two resistors R1 and R2:
+V o----[R1]----o------[R2]------o Gnd
The voltage across R2 is V * R2 / (R1 + R2)
You might need to be a bit careful choosing the resistor to put in series with the pump because the resistance of a DC motor varies from depending on whether it is spining or not. Also you must calculate the power that the resistor must be able to dissapate. If for example your motor is designed to run at 1 amp at 6 volts, then, assuming you've used the right resistor, it will have 1 amp running through it and perhaps 9V dropped acorss it (assuming the car's alternator is producing 15 volts). You'd then need a 9W resistor (or 9 1W resistors or whatever). It'll get hot.
>> Edited by ATG on Monday 29th November 10:20
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