Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Help please. need .10 amps

Status
Not open for further replies.

adamalden

New Member
I don't have much knowledge when it comes to electricity but I have learned a bit here and there...

My project right now is to make a 12 volt power source and then drop the amps to .10

I know the store carries 12 volt batteries but these are to strong for my device. I know this from my past mistakes. How do I turn this into a .10 battery?
 
Well you'd need a 120R resistor to get 0.1A from a 12V battery but I suspect that's not what you're asking.

Sorry but your question doesn't make any sense.

As long as the appliance is designed to run off 12V it will be fine, 0.1A is the amount of current it will draw from the battery.
 
Well you'd need a 120R resistor to get 0.1A from a 12V battery but I suspect that's not what you're asking.

Sorry but your question doesn't make any sense.

As long as the appliance is designed to run off 12V it will be fine, 0.1A is the amount of current it will draw from the battery.
That's exactly what I was looking for thank you... All I need to do is make the battery run through a 120R resistor and it will drop the current from what it was to 0.1 and this will prevent the appliance from shorting out. Is this correct? I think that the battery hooked up to it without this 120R resistor would result in to powerful a current resulting in a wire burning out disabling the device is this correct?
 
Without some idea of what your "device" is we cannot give proper advice.

Some components will require current limiting (such as diodes, most notably LEDs). Others do not and will only draw the current that they require.

What is your device?
 
No, that's not what I said.

That's exactly what I was looking for thank you... All I need to do is make the battery run through a 120R resistor and it will drop the current from what it was to 0.1 and this will prevent the appliance from shorting out. Is this correct? I think that the battery hooked up to it without this 120R resistor would result in to powerful a current resulting in a wire burning out disabling the device is this correct?


You don't need a 120R resistor, as I said, the appliance doesn't need anything to limit the current, 0.1A is the amount of current it uses.

This is a very silly question, for example the mains in your house can supply hundreds of Amps and you don't need to connect a resistor to power any of your household appliances do you? So why on earth would you even think about doing it with a battery?

There might be a fuse but that's just to stop the cable from melting if a short circuit occurs and is not required for when it is working properly.

Do you know that those little AA batteries you put in a torch (flash light) can supply 10A? But you don't need to add a resistor to power a little bulb which uses less than 0.5A.

I was giving an example of Ohm's law, 12/120 = 0.1A, if you've not heard of it, you should look it up.

If you want to protect the battery and wire, then I'd recommend you add a 1A fuse in series but you don't need anything to protect the device.
 
Last edited:
Well I know what you mean about the appliances but they have all that stuff built in. I'm trying to hook up a small laptop computer fan that I have floating around. It has no protection such as fuses or resistors... The back reads 12 volts 0.10 amps... So your saying the 12 volt batter will power the small fan without burning it out even though the amps are higher than the fan needs?
 
Well I know what you mean about the appliances but they have all that stuff built in. I'm trying to hook up a small laptop computer fan that I have floating around. It has no protection such as fuses or resistors... The back reads 12 volts 0.10 amps... So your saying the 12 volt batter will power the small fan without burning it out even though the amps are higher than the fan needs?

Suppose you took the 12V battery out of your car. That starting battery is capable of delivering up to 1500A for short duration. Now connect your 0.1A fan to your car battery. How much current will actually flow into the fan?

answer: 100mA
 
Last edited:
As I said before, look up Ohm's law and all will become clear.

The resistance of the fan at full speed will be about 120R so the current will be 0.1A, the same goes for any other appliance.

R = V/I

I = 12/0.1 = 120Ω

Of course you won't measure 120Ω if you measure the fan with a meter, this is because its resistance is dependant on its speed.
 
As much as the wires will supply. All that current will try to go into the fan over loading the little wire that wraps around making the coil then a section of wire will burn out disabling the fan.
 
You're not listening.

As much as the wires will supply. All that current will try to go into the fan over loading the little wire that wraps around making the coil then a section of wire will burn out disabling the fan.

I suggest you look at your computer's power supply and note how much current the 12V wire can supply?

I can assure you that it'll be more than 0.1A.

Now, the fan is designed to be directly connected to the PC power supply without an additional resistor so there's no need to add one when powering it from a battery.
 
Last edited:
A fuse, say 1 Amp, in series is a good idea.

As others said, the fan will take 0.1 A if it is working.

However, if there is a short-circuit, there will be a huge current. A 1 Amp fuse will then blow and save you from burnt wiring.
 
Yes you're right about the 1A fuse, it is a good idea, an automotive blade fuse will do.

I just wanted to impress upon him about the fact that the fan not blowing up. I'll give it one last try before giving up.

I've edited my previous post.
 
Last edited:
Ok so what I am getting from you guys is that the fan will take as much amps as it needs as long as the volts are right. Resistors and fuses are not needs but a fuse is a good idea.

The fuse will blow when there is an excess of volts right? if not what is the point of the fuse if my fan just takes what it wants?

Thank you guys for helping. I are not very smawt.
 
adameldon, you seem to have the same problem understanding device and power supply power requirements and availability as many people do. If a power supply is rated for 12 volts, then it will power ANY 12 volt device you hook up to it, as long as it can supply at least as much current as the device needs. The amperage capacity of a power supply is how much it CAN supply not how much it WILL supply. The voltage/current rating on a device are the voltage it's designed to run at, and the current it will draw under normal operating conditions.
 
adameldon, you seem to have the same problem understanding device and power supply power requirements and availability as many people do. If a power supply is rated for 12 volts, then it will power ANY 12 volt device you hook up to it, as long as it can supply at least as much current as the device needs. The amperage capacity of a power supply is how much it CAN supply not how much it WILL supply. The voltage/current rating on a device are the voltage it's designed to run at, and the current it will draw under normal operating conditions.

Awesome! I think I get it! ! ! XD I will tell you if it works!
 
A single 12 volt battery (if it's a lead acid) will probably power one of those fans for at least a day if not more, or a LOT of them for a shorter period of time.
 
The fuse will blow when there is an excess of volts right? if not what is the point of the fuse if my fan just takes what it wants?
A fuse doesn't protect against an over-voltage.

A fuse protects the cable and the battery if the fan malfunctions and tries to draw more current than the cable and battery are able to safely supply.

I suggested a 1A fuse because a fairly thin piece of cable should be able to supply 1A for a short amount of time before overheating.
 
The fuse will blow when there is an excess of volts right? if not what is the point of the fuse if my fan just takes what it wants?

No.

The fuse will blow if there is an excess of current. The fan will only take 0.1A if it is working, but if it goes wrong, the current would be very large. That is when the fuse blows and saves your battery and wires from damage.
 
The fan will only take the power is needs. Like when you drink with a straw, you can only sip your soda so fast :)

It sips the power it needs, and that's it. Maybe you can think of it like a funnel:

No matter how much you pour into it, only a certain amount comes out at a time.

The fuse is there so if something bad happens with the fan, the fuse will sacrifice itself and stop the power flow, to save more components from breaking.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top