On/Off Switch

[Bill Fitzpatrick]

I am almost positive that MicroSwitch makes what you want. I assume that you have called switch distributors?

Also, there are some machine tool switches that will do it but they tend to be large.

And, yes, a 3 position toggle with one position momentary would do but you still need one pair of n.o. relay contacts.

[roger-k]

Yes, I have called some switch distributors.
It is possible to use a relay with two coils (set and reset) and a chip manufactured by Nais, VS5-24.
But this chip require 4-30VDC and I don't want any voltage on the transformer or on the electronics when I shut down the amplifier.
Some distributors also had swithes which can handle this, but the switches is very big because they were designed to use with industrial equipment.

[em2006]

A very interesting, clever design, from an old book on relay circuit design, a toggle flip-flop, using two relays only , is shown in attached file:
toggle2relays.png

[dnsey]

Sounds like you want something on the same lines as the failsafe switches fitted to machine tools etc. These (at least the older type) usually involve a contactor, which is really just a heavy-duty relay with mechanical override, which could be arranged just as easily with a smaller relay. You would still need a seperate 'off' button though, unless you could arrange a pair of break contacts on the mechanical actuator.

I have in my junkbox a switch made by Airpax which does just what you want - press the toggle down for on, up for off, and it reverts to the off position under no-voltage conditions. I don't know if it's a 'special', but it might be worth investigating.

[AndrewT]

Hi Em or anyone else awake enough to see the solution,

How are the contacts in the 1.1 & 1.2 connected to latch in the switch?

Does a second press unlatch the relays?

Does loss of power unlatch the relays?

[em2006]

The schematic I posted does the same thing as the first
schematic on this thread, posted by roger-k.
I redrawen my schematic for the analogy with roger-k's
schematic to be more evidently. (attached file toggle2relais_2.png).

[em2006]

Originally posted by AndrewT
Hi Em...
How are the contacts in the 1.1 & 1.2 connected to latch in the switch?

d1.1 and d1.2 are NO contacts (Normal Open)
They are connected like as shown in the schematics.

Originally posted by AndrewT

...Does a second press unlatch the relays?

Yes.

Originally posted by AndrewT

...Does loss of power unlatch the relays?

Yes.

The new schematic toggle2relays_3.png, attached
contains a table wich will clarify the functioning of the circuit.

[roger-k]

Great!!!
But....hmm... in step 2 the relay coils will get half voltage?
Because they are ine series?

[roger-k]

Will half voltage pull the relay?

[em2006]

Yes.
The relays are either both energized or both de-energized,
NOT ALERNATE!

For this circuit you have to choose relays having nominal
voltage = around half of the supply voltage.

The choice of the relays is based on HOLD current and
PULL-in current.