Will This Switch Work????

[airbusdrvr]

If a switch is rated at 250VAC and 5A, could the switch be used in an application for 6A at 1.5VDC? I know that P=Volts X Amps so it would seem the switch is capable of 1250watts. So the 1.5V times the 6A max is 9 watts. Here is a link to the type switch I am asking about:
http://www.radioshack.com/product/index.jsp?productId=2049718

[Miami Mike]

No. The current rating applies when the switch is closed and conducting, while the voltage rating applies when the switch is open and the voltage appears across the contacts. Watts have nothing to do with it.

This is not to say that the switch definitely won't work, but your application does exceed the rating.

[rick.benjamin]

Look closer and read 5A125,250VAC. This is the rated peak or momentary load.

Derate the switch by 125% 5/1.25= 4A is the rated working load.

4 x 120 = 480 watts maximum working load at 125VAC.
It's a little switch.
Will it work for your application? Buy 2, test one.
Harbor Freight is selling a digital thermometer for $10 this week.
Under your load, a perceptible temperature rise is not good.

[Miami Mike]

4 x 120 = 480 watts maximum working load at 125VAC.As I said before, watts have nothing to do with it. That calculation is absolutely meaningless.

airbusdrvr, if you tell us what you're building we might have some suggestions for you.

[airbusdrvr]

I'm looking for a switch that can be actuated by a servo to connect a 1.5V battery to a glow plug. Here is a link to my question a day or two ago that only got responses to use an electronic type circuit, http://www.rcgroups.com/forums/showthread.php?t=1059940. I feel certain there is a reaonably priced source to buy a lever type switch(or other type switch easily operated by servo power) that would be acceptable in a 1.5 volt circuit drawing approx 6A.

[Miami Mike]

There's no reason you couldn't use two of those switches wired in parallel. Just fasten them next to each other and solder a connecting bar across the metal levers.

[pmackenzie]

FWIW, DC switch rating is usually lower than AC rating.
Putting a capacitor across the switch can help to avoid welding of the contacts in a DC application.

Keep it simple. Just use the single switch. Give it a bunch of test cycles on the bench. If it does fail it will fail closed due to welding.
Glow plugs only draw a couple of amps so you should not have much of a problem.

Pat MacKenzie

[dmccormick001]

Miami Mike is right about the voltage rating of a switch, however, in my experience it does make a difference in an application like this because the very low voltage at which you will be operating the switch, 1.5 V DC, will cause almost no arcing of the switch as it is closed. The higher the voltage across the switch, the more the current will try to "jump" across the terminals as they begin to get close to one another. That arc is what welds the contacts together, or sometimes makes the switch impossible to move either direction again. But at 1.5 V DC, there won't be much of that happening, and the 5A rating, in my opinion, will be fine for the current your glow plug will draw. Much more than that will burn it out anyway.

That's the exact kind of switch a lot of modelers have used successfully to do what you want to do.

[Miami Mike]

I don't think arcing is the issue here, I think it's heat from excessive current, which might soften and deform the plastic housing of the switch, causing it to fail.

Still, I agree that the switch will probably work okay in that application. All I said was that 6 amps would exceed the manufacturer's rating.

[dmccormick001]

I wasn't really disagreeing with what you said at all, Mike. You were exactly right. I was just offering my opinion about the use of that switch in that situation. I've exceeded the current rating of a lot of switches in low voltage apps with no problems, in some cases by quite a bit, and I just always figured that was probably the reason.

[Miami Mike]

I understand. In that case, think of my comment as being directed to Pat's post #7, where he says:If it does fail it will fail closed due to welding.Switches like the one airbusdrvr is looking at are made of plastic that can melt and deform easily, and that's what will happen with too much current flow. (And of course a capacitor won't help.) The only question is whether it will actually happen at 5 amps or at some higher current.

http://rsk.imageg.net/graphics/product_images/pRS1C-2110709w345.jpg

[ghoti]

A primary difference between AC and DC switch ratings is from the zero crossings in AC which allows the arc to quickly drop out when contacts open. This is probably not an issue at this low voltage. bill

[coriolan]

A good circuit for that purpose:http://www.uoguelph.ca/~antoon/gadgets/rc-sw.htm
Built a few to power various loads, the only limit is the Mosfet rating and it can be adjusted at any point of the trottle range. Servo and switch where Ok 20 years ago and a big problem to adjust and keep working reliably

[Miami Mike]

That's exactly what airbusdrvr isn't interested in, according to his post #5 (http://www.rcgroups.com/forums/showpost.php?p=12400538&postcount=5).

[airbusdrvr]

That's exactly what airbusdrvr isn't interested in, according to his post #5 (http://www.rcgroups.com/forums/showpost.php?p=12400538&postcount=5).

You are partially correct. I was trying to stay with a simple system. I didn't realize that even discussing a switch could be so involved. There are several on-board-glow systems for sale that are of the pulsed type. They pulse the power from a 4.8vdc to 55vdc(depending on the manufacturer) source and the glow plug operates as if it is receiving 1.5vdc.

Now to another question. Today at the RC field, one of the helicopter guys mentioned this website and product; http://www.dimensionengineering.com/BattleSwitch.htm . Would you with greater electrical understanding give an opinion if this type "electronic" switch could be used to control a 1.5vdc source going to two glow plugs that might require upward of 6amp each? Thanks

[Miami Mike]

There you go! That'll do the job for you as long as you're okay with the price.

[dmccormick001]

I didn't realize that even discussing a switch could be so involved.
LOL :D :D

Sounds like you might be new to this forum. These cats can turn the simplest of questions into a discussion worthy of a doctoral thesis. That's why I check it several times a day! I've learned more from these guys than I could tell you, especially from the ones with whom I may have disagreed occasionally.