# Question on AMPS

• posted

Hi all,

I have a simple question I am sure for you guys, but I am merely an idiot when it comes to these things and most other things too. :) Anyway,

I am looking for a momentary key switch (just a lame project) that can handle at least. 2 AMPS in 12 volt DC. For example, I see switches that can do 4 amps at 120 volt and that very same switch the specs state 2 amps at 220 volt. etc. How is that possible? Aren't amps, amps?

Is it safe to assume if a switch is rated at 4 amps 120 volt AC, it will still handle or work well with say 12 volt power source in DC?

How exactly does amps work in DC? Thank you!

• posted

And a follow up. Lets say I have a switch rated at 120 volt AC, 1 AMP. Can I safely push 4 amps at 12 volt DC through it without the switch failing?

• posted

This topic has been discussed in this Usenet group many times before:

The big boys were recently kicking around a similar topic in a related Usenet group:

Don't ASSuME anything. Get a device that is RATED for the task for which you will use it.

• posted

If it were only the current-carrying capacity, yes. Unfortunately, you have to consider the dynamics of opening a closed switch and closing an open one. DC can strike an arc and keep it burning until your wire evaporates, while AC will extinguish an arc on the next zero-crossing (no more than 8 milliseconds from strike).

Closing an open switch, there's significant bounce, which (depending on the connected circuitry) can cause small sparking/ arcing that erodes the electrical contacts.

Usually, yes.

When the switch is closed, it doesn't matter WHAT the other circuitry has for voltage; the switch has zero volts. No, it isn't likely to pass 4A if it's rated at 1A.

• posted

No. Think of a switch as a valve. If the pressure is too high it'll burst. A switch will not be useful at all at a certain voltage.

Now stop thinking of it as a valve. ;-) A switch also has to break the arc cause by the contacts separating. The larger the voltage the longer the arc. The higher the current the stronger/heavier the arc. Also note that 120VAC has a peak voltage of ~170V.

Absolutely *not*. AC arcs tend to self extinguish as the voltage drops to zero. DC doesn't have this advantage. It's common to see a switch rated at perhaps 10A@120VAC and only 1A@12VDC.

The heat/work caused/done by 120VAC (RMS for the pickers of nits) and

120VDC is the same. How it gets there and how it has to be treated is very much different.
• posted

"ULB"

** As other have indicated - it is the ability of a switch to SWITCH a circuit on AND off that brings about its amp rating.

That amp rating will change DRAMATICALLY with the various things folk want switches to SWITCH !!

** In limited circumstances - yes.

The restricting conditions are that the LOAD being switched is NOT highly inductive or capacitive nor one that produces large surge currents.

** Switch ratings are highly dependant of the NATURE of the load being switched.

But YOU decided that such a trivial detail did not matter.

Like most PITA usenet trolls, you posted a waaaay too broad question that was irrelevant to your need for specific information.

Care get real ???

.... Phil

• posted

"krazy ratbag wanker"

** COMPLETE BOLLOCKS !!!

.... Phil

• posted

Once again, Phyllis has seen every specification on the planet.

• posted

"krazy ratbag wanker"

** COMPLETE BOLLOCKS !!!

FUCKWIT DAMN TROLL !!!!

.... Phil

• posted

I said, BACK ON YOUR MEDS, FREAK.

• posted

"krazy ratbag wanker"

** COMPLETE BOLLOCKS !!!

FUCKWIT DAMN TROLL !!!!

.... Phil

• posted

No it really isn't f****it.

As I said before, GET BACK ON YOUR MEDS, FREAK!

• posted

"krazy ratbag wanker"

** COMPLETE BOLLOCKS !!!

FUCK OFF & DIE you

FUCKWIT DAMN TROLL !!!!

.... Phil

• posted

Gee, DimWit (DimBulb's half brother), your "send" key is stuck.