How to calculate the value of the mains fuse?
- Thread starter syn
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Help Support GroupDIY Audio Forum:
Well, the mains transformer data only tells you the maximum current (or power) that the transformer can provide.
It is possible that your circuit is drawing a lot less than what your transformer is able to provide....
You could calculate using maths what maximum current your circuit is likely to draw, or you could try and run it at max (whatever that involves) and measure using a multimeter.
Are these circuits you are using standard designs? Some people here may know what fuses to use....
Roddy
It is possible that your circuit is drawing a lot less than what your transformer is able to provide....
You could calculate using maths what maximum current your circuit is likely to draw, or you could try and run it at max (whatever that involves) and measure using a multimeter.
Are these circuits you are using standard designs? Some people here may know what fuses to use....
Roddy
rodabod thanks again
shall i go to data sheets, add up max power consumption for active components, and that would be it?any hidden points? sorry if i'm p.i.a. but i also racked some of the less common ch. strips and will continue with that practice so don't want to bother community every few weeks with "what is the fuse for this whats the fuse for that".
or it is not simple like i written above?
cheers
m
shall i go to data sheets, add up max power consumption for active components, and that would be it?any hidden points? sorry if i'm p.i.a. but i also racked some of the less common ch. strips and will continue with that practice so don't want to bother community every few weeks with "what is the fuse for this whats the fuse for that".
or it is not simple like i written above?
cheers
m
Yes, you could add up the max current drawn for the active components...
The only hidden point might be the current used by the active components while driving signals - ie. more current will be drawn when the circuit is working harder, but this depends on the circuit and also might not make a huge difference.
There are general guidelines for chips like the NE5534 - eg. just count how many you are running and multiply by a certain amount, but I don't know if this will apply here...
Remember that your mains fuse is current at 240V (or 120V... whatever you are using in Belgrade!) and therefore the current at mains Voltage is less than the current at say, 15V.
Calculate the Power drawn in the circuit, and then divide by your mains Voltage to get the Current.
Someone else with more experience in this field can maybe chip-in here...
The only hidden point might be the current used by the active components while driving signals - ie. more current will be drawn when the circuit is working harder, but this depends on the circuit and also might not make a huge difference.
There are general guidelines for chips like the NE5534 - eg. just count how many you are running and multiply by a certain amount, but I don't know if this will apply here...
Remember that your mains fuse is current at 240V (or 120V... whatever you are using in Belgrade!) and therefore the current at mains Voltage is less than the current at say, 15V.
Calculate the Power drawn in the circuit, and then divide by your mains Voltage to get the Current.
Someone else with more experience in this field can maybe chip-in here...
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radiance
Well-known member
Someone over here (I think it was CJ..) said the following about this:
Short the secondaries of your power trannie and meassure the current draw (don't take too much time for this :wink: ). Choose a fuse with a lower A rating than the current draw you just meassured....
Short the secondaries of your power trannie and meassure the current draw (don't take too much time for this :wink: ). Choose a fuse with a lower A rating than the current draw you just meassured....
NewYorkDave
Well-known member
I don't know if this is the "right" way to do it, but what I do usually is to measure the current drawn by the device under normal operation. Then I use a fuse rated for about twice that value.
bcarso
Well-known member
The advice of radiance is good, supplemented by that from NYD. Be sure to use a time-delay ("slo-blo") fuse to handle the inrush current. Otherwise the fuse will fatigue ("work-harden") and fail prematurely.
Safety agencies test to make sure a fault condition upstream will not cause a fire. If the transformer has an internal thermal fuse then you will be protected by that. But it doesn't hurt to have an additional level of protection.
Safety agencies test to make sure a fault condition upstream will not cause a fire. If the transformer has an internal thermal fuse then you will be protected by that. But it doesn't hurt to have an additional level of protection.
G
Guest
Guest
Seems like there are a lot of ways to select fuses. Here is a simple rule of thumb I use.
Add all the secondary VA ratings up. Divide the total by your mains voltage to get current draw. Multiply by 1.25 and use the next largest slow-blow fuse.
So, if I had a transformer with two 6VA secondaries, I would have a total 12VA. Since I have 120V system at my house, I divide 12VA by 120V and get 0.1A. Multiply 0.1x1.25 and I get 0.125. So I use a 1/8A slow-blow fuse.
Add all the secondary VA ratings up. Divide the total by your mains voltage to get current draw. Multiply by 1.25 and use the next largest slow-blow fuse.
So, if I had a transformer with two 6VA secondaries, I would have a total 12VA. Since I have 120V system at my house, I divide 12VA by 120V and get 0.1A. Multiply 0.1x1.25 and I get 0.125. So I use a 1/8A slow-blow fuse.
radiance
Well-known member
[quote author="syn"]......Now, this should be more than enough info for anyone tackling similar task........
[/quote]
Yeah, this thread should go to the Meta's...
[/quote]
Yeah, this thread should go to the Meta's...
NewYorkDave
Well-known member
The maximum current the fuse can interrupt safely, without flashing over.
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