Can anyone tell me how to calculate how many amps an item is drawing in a a 12 volt DC circuit if it creates a voltage drop of 4.5 volts?
2006-08-23 06:52:31 · 11 answers · asked by Jonny B 5 in Science & Mathematics ➔ Engineering
I dont have the other values, what is in the circuit is a fan motor, and I am trying to figure out how many amperes it is drawing. The open circuit voltage is 12, and it drops to 7.5 volts when the fan is connected if you tell me how to calculate any of those values i need, I will supply them
2006-08-23 07:07:13 · update #1
Measuring the static resistance of the fan will not help, since when the motor is turning there is a back EMF which affects the current. If you do not have an ammeter, there is a way to get an answer. If you can get a power variable resistor or poteniometer and place it across your power supply (without the motor). Vary the resistor value (starting at high values) until the power supply voltage drops to 6 volts. (Careful, leave the resistor connected for only a short time, and don't touch it directly, it may be very hot.) Measure the value of the resistance, R. That is the source impedance of your power supply. The current being drawn by the motor is then (12-7.5)/R.
2006-08-23 15:22:03 · answer #1 · answered by gp4rts 7 · 0⤊ 1⤋
Do you have any resistor in your circuitry ? What is the voltage drop across that resistor ?
What other items you have in the circuitry and what are they ?
================ With the additional information you have gotten here. ========
Sounds like you are over drawing the capability of the 12V dc source.
If the 12V dc source is 12V and connect only to a device. The terminal should be 12 but it dropped down to 7.5V.
There is resistivity lost at the source resistance of the 12V source or the wiring to the fans.
You will need to put some current limiting resistance in series to not over-driving the power source.
2006-08-23 07:00:10 · answer #2 · answered by Anonymous · 0⤊ 1⤋
Hmm open circuit voltage of 12 volts. and then you connect the fan and you get a 4.5 volt drop accross the fan... Then you get 7.5 volts on the battery. Which makes a little sense because that is due to the internal resistance of the battery. But you didnt say it was a battery.
(+)----/\/\/\/\-----(-)
12v----7.5V-----0v
Where is the 7.5V drop coming from if it isnt a battery?
PROOMA answer is 1 amp.
2006-08-23 09:49:54 · answer #3 · answered by mrlong78 2 · 0⤊ 0⤋
You need more information. Either watts or resistance. Watts (Power) is equal to amps x volts. This means watts divided by volts will give the amps or watts divided by amps will give you volts. The formula is: P = I x E where P is power or watts, E is volts and I amps. Another way is E = I x R where R is resistance. This only works for DC current. For AC current you have to figure in the Cos of the angle...but that's another lesson
2006-08-23 07:36:48 · answer #4 · answered by blackec2000 1 · 0⤊ 0⤋
Ohm's law is E=IR I=E/R R=E/I Now you tell me how I can calculate voltage drop of 4.5 volts from the parameters you have given?... I would need to know either the resistance or the inpedance or the inductance to figure the voltage drop and you supplied none of those.
2006-08-23 06:58:53 · answer #5 · answered by Anonymous · 1⤊ 1⤋
There are three ways to solve your problem.
1) get the data sheet. It should tell you how much current it typically pulls.
2) measure the current in the system using a current measuring device.
3) determine the resistance of the fan then determine the resistance of the rest of the system.
2006-08-23 08:20:18 · answer #6 · answered by DoctaB01 2 · 0⤊ 0⤋
Why don't you take your multimeter and set it for resistance, measure the resistance of the fan circuit, then you can use the formula V=IR, or I=V/R.
2006-08-23 09:39:46 · answer #7 · answered by Jeffrey S 6 · 1⤊ 0⤋
Need resistance value.
2006-08-23 07:03:21 · answer #8 · answered by Handyman 4 · 1⤊ 1⤋
we need more information for that. give us the impedance of your circuit and we'll tell you.
2006-08-23 06:56:01 · answer #9 · answered by Anonymous · 0⤊ 0⤋
CANT ANSWER WITHOUT RESISTANCE or IMPEDENCE or RELUCTANCE VALUES !
2006-08-23 20:58:15 · answer #10 · answered by rockinghard 2 · 1⤊ 0⤋