Change over relay + momentary button

Thread Starter

tal mann

Joined Apr 23, 2015
6
A question about a change over relay with a momentary button, do these flip and latch each time the button is pushed or do they flip back when the button is released?
 

Thread Starter

tal mann

Joined Apr 23, 2015
6
@MaxHeadRoom Thanks Max.

I am not sure about whether I should start a new topic as this may be drifting away the original topic.

I have drawn up a circuit for an battery isolator with three relays, a TE high current relay (TE V23132A2001B200), a change over relay and a make and break relay and using momentary push switches. For the change over and a make and break relays, I am contemplating using:

* Song Chuan 301-1A-S-D1-12VDC and
* Song Chuan 301-1C-C-D1-U05-12VDC.

These are diode type relays. The data sheet for these is located at: https://au.mouser.com/datasheet/2/378/301-2555.pdf

Does this circuit work as I intended?
 

vu2nan

Joined Sep 11, 2014
95
1. Your circuit would not work since the relay contacts would stay actuated only as long as the push buttons remained pressed.

2. Your objective could be realised with a single relay.

2.1 By using a standard relay with 3 normally-open contacts, a 'master' push button switch with a normally-open contact and two 'kill' push button switches with normally-closed contacts. However the relay coil would be required to be kept continuously energised in the 'battery not isolated' condition.

2.2 By using a latched relay with 2 normally-open contacts and a 'master' and 2 'kill' push button switches with normally open contacts. The latched relay would avoid the problem of keeping the relay coil/coils continuously energised.

3. In the probable event of only standard automotive relays being available (not latched), there would be no getting away from the standard lever-operated isolator switch!

Regards,

Nandu.
 
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Thread Starter

tal mann

Joined Apr 23, 2015
6
Thank you Nandu. I'm still learning about how relays work. :) My preference is to use an ISO 280 style relay but I haven't found one that latches. I have found a couple other types such as 0-728-2 (Link) which are quite expensive.
 

vu2nan

Joined Sep 11, 2014
95
That's good, tal mann!

My comments are as follows:

1. S2 & S3 are to be 'NO' and wired in parallel. By the way, why two 'Kill' buttons?

2. I suppose the cable from the isolator relay 'B' terminal is terminated in a junction box where the cables from the fuse box, starter/alternator and relay R3 coil are also terminated.

3. What is the purpose of relay R3? Doesn't the isolator relay by itself isolate the ignition circuit also? Is the existing ignition wiring required to be altered?

Regards,

Nandu.
 
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djsfantasi

Joined Apr 11, 2010
5,929
That's good, tal mann!

My comments are as follows:

1. S2 & S3 are to be 'NO' and wired in parallel. By the way, why two 'Kill' buttons?

2. I suppose the cable from the isolator relay 'B' terminal is terminated in a junction box where the cables from the fuse box, starter/alternator and relay R3 coil are also terminated.

3. What is the purpose of relay R3? Doesn't the isolator relay by itself isolate the ignition circuit also? Is the existing ignition wiring required to be altered?

Regards,

Nandu.
Regarding two kill buttons, by the naming of the switches, it appears that this allows killing the circuit from two separate locations. Which could be desirable.
 

vu2nan

Joined Sep 11, 2014
95
Hi djsfantasi,

It certainly does, but I needed to know 'where ?'. :)

Many thanks.

Regards,

Nandu.
 
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djsfantasi

Joined Apr 11, 2010
5,929
Hi djsfantasi,

It certainly does, but I needed to know 'where ?'. :)

Many thanks.

Regards,

Nandu.
You don’t need two NC switches, unless you want to reset the circuit from different locations. For example, in the engine compartment and the drivers seat. If you only need one location, use one switch. If you need multiple locations, add another NC switch in series with the others.
 

vu2nan

Joined Sep 11, 2014
95
No, I mean NC, as they appear in the schematic. I missed that you kep referring them, incorrectly, as NO.
Please understand it's a latching relay and the coil is to be energised to reset. That those contacts should be 'NO', and wired in parallel, is obvious.
 
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Thread Starter

tal mann

Joined Apr 23, 2015
6
Thanks for the comments. Two kill switches are required by the relevant motorsport regulations. One switch mounted inside the cabin to be operated by the driver and one mounted externally for the crash rescue teams, with either switch to disconnect the battery and stop the engine.

Thanks vu2nan. I think I can now see a possible problem with the NC switches. They are constantly grounded. I am not sure what the NC switches running constantly to ground would do for this relay and whether opening either would activate the relay like I had hoped. With this insight, I think changing to NO switches in series won't help in this case as they'd require the two being pushed at the same time to operate. Not useful if the driver is in anyway incapacitated. NO in parallel would be required as you said.

R3 relay is supposed to kill the ignition stopping the engine, otherwise the alternator will keep the engine running. However I now see a flaw. As it is is wired, the alternator will still supply power to the coil circuit of R3. A rethink is necessary if I plan to use the BDS relay.

I might not use this option. Instead the original circuit using conventional toggle switches rather than the momentary ones. This probably the simplest approach as per vu2nan's original point 3 above.

It's been useful for me to work through this. I'd look at a circuit and as long as the lines complete a 'loop', I'd this "yes, OK" but I need to focus on the logic underpinning it.
 
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