Relays

[Munroast]

markings on a relay show 20A 14 VDC & 20A 125VAC
why such a big difference between direct and Alternating currant, does direct current tend to arc more ?

I take it 125vac means it is not suitable for mains 240v ? or is it close enough

 

[Why Not Indeed]

AC means it goes to 0 n times/second [usually 50] so much less arcing.
240V is nearly double 125V, can't see how that's going to "close" by any definition!

 

[Jurassicspark]

AC crosses zero volts twice every cycle, and if you average the voltage it gives you zero.

This limits the arcing potential when comparing it to DC. Therefore the AC rated voltage is much higher.

I take it 125vac means it is not suitable for mains 240v

Probably not.

 

[Munroast]

AC crosses zero volts twice every cycle, and if you average the voltage it gives you zero.

This limits the arcing potential when comparing it to DC. Therefore the AC rated voltage is much higher.

Probably not.

aye - probably not - I have got a 500v relay that works form 12v, can get one relay to work another, just seems a bit of an arse

I do like the argument that its average is zero, which I suppose it technically is, although it may tell a different story if you licked the terminals.

Is the effective aveargae 240v (RMS of its peak of 340) I always struggle to get my heed round this.

 

[Jurassicspark]

Is the effective aveargae 240v (RMS of its peak of 340).

240 x √2 = 339. Or 240 x 1.414 which also equals to 339. Without (cMIN)

Similar to AC getting converted to DC. It becomes approx 340 DC volts too.

 

[Jurassicspark]

I do like the argument that its average is zero, which I suppose it technically is, although it may tell a different story if you licked the terminals.

Have a think about this.
The average motion of a piston in a steam or other engine is also zero but it delivers torque and power.

 

[fixitflav]

I do like the argument that its average is zero, which I suppose it technically is, although it may tell a different story if you licked the terminals.

That's why quoted voltages are RMS, 230 volt for 1-phase domestic

 

[Harry Bloomfield]

AC means it goes to 0 n times/second [usually 50] so much less arcing.

100.