Need some electronics help

[im2smrt4u]

I want to have a reset switch for a project I'm doing. The device (a VFD) draws a maximum of 675 mAh @ 5VDC. This will be connected to my computer's power supply. I want a switch that will cut the power from the VFD in case there is an error so that the display will reset.

I have a pack of normally closed momentary buttons from Radio Shack (275-1548C) that are rated at 0.3A @ 50VDC. Doesn't the amperage go up as the voltage goes down? What amperage could it handle at 5VDC?

The bottom line is: will these switches work for me? Or do I need higher amperage switches? What would work that is available at a Radio Shack?

 

[blahblah99]

Yeah. And what's a VFD? If you can give us a little more details on what your doing... we might be able to come up with a better solution than a manual switch.

 

[im2smrt4u]

VFD = Vaccuum Florecent Display

I just want a switch that will cut the power to the display in case there is some bad input that garbles the display. Thenit will self-test again and be ready to start with a blank screen.

 

[im2smrt4u]

BUMP!

 

[blahblah99]

Im sure you can use that switch. Its rated at 0.3A @ 50V which corresponds to 50*0.3 = 15Watts. Your vfd uses 0.675@5 = 3W. It should be ok. At worse, your switch will just burn out and you have to replace it.

 

[im2smrt4u]

<< Im sure you can use that switch. Its rated at 0.3A @ 50V which corresponds to 50*0.3 = 15Watts. Your vfd uses 0.675@5 = 3W. It should be ok. At worse, your switch will just burn out and you have to replace it. >>



Well that is real confident!

J/K.

Can just one more person verify these equations? Thanks!

 

[CTho9305]

looks right to me (credentials: freshman ECE student

)

 

[ScottMac]

Personally, I wouldn't do it.

The current carrying capacity of the switch conductors is a function of the conductors size (diameter or w X h). If the conductors are spec'd for 0.3a, trying to run twice that may be a "Bad Thing."

If it were a voltage thing, then maybe; especially low voltage...but current, um, no.

The narrower conductor may be able to handle the current and not burn out, but you stand a good chance of having a higher resistance (with the associated voltage drop), which may adversely affect your system.

Do you really want to risk your hardware for the sake of a couple bucks worth of switch?

Just my two cents worth.....

Scott

 

[blahblah99]

To be on the safe side, hook up a multimeter in current mode, a motor, and your switch in series. Turn on your switch and measure the current draw. If its around 700mA and your switch is still working after 10 minutes (and it doesn't feel hot ) then its probably safe to use

 

[arcas]

I wouldn't exceed the recommended amperage by a factor of two. A momentary switch rated at an amp or two shouldn't cost more than a few
dollars at radio shack (which is a drop in the bucket compared to what you've already spent on the VFD).

Alternatively, you could use one of your 0.3A switches to control a relay capable of 1A or more and let the relay control the VFD power.

Either way, you're looking at about $3 worth of components (according to my DigiKey catalog).

 

[im2smrt4u]

Well, I went ahead and used it on my first attempt, and it seems to be working fine. It looks like ass compared to some projects I have seen, but it doesn't seem bad for a quick little job. When I make my second one, I guess I should pay a lot more attention to detail (like heatshrink, better cutouts, etc), but this one is really just a test to see if it would work.

You can see some pictures here and here.

EDIT: BTW, the wires are color coded.
Red = +5VDC
Black = Ground
Green = Signal

 

[MagnetStone]

as your "VFD" eats 0.675 A @ 5V = 3.375 Watt,
so,
if you get a reset switch with below rating ..... that will do better,
0.1A @ 50V = 5 Watt.
therefore "0.1A @ 50V" will trigger earlier than the "0.3A @ 50V", or you can say it will be more sensetive switch.