Latching relay

Hello this is my first post so firstly greetings from me in UK. I have a Durite 0-728-02 latching relay to activate the ignition supply from a momentary switch built into my race car steering wheel. The wheel buttons have a 300ma max on wires song have a 300ma in line fuse. The pins are all wired up correctly I think by a thread I saw on here. 30- neg S- 12v signal for switch 56- per live 56b- to ignition supply 56a- not used The problem I have is that the relay latches but does not latch off when pressed the momentarty switch again. It worked at first one but now not? I have 2 other relays the same operating a rain light and fuel pumps from the momentary switches on the dash and they do the same. Please can anyone shed some light? Thanks in advance Dan

Oh no, not the bluddy 0 728 02 again! I looks as if your wiring is ok assuming you mean the same as at durite 0 728 02 relay wiring (page 5, top reply). As per that thread I still can't find any info on the coil current. Assuming you have clean switch S- GND connections, maybe overall resistance is limiting the required toggle-off current? Incidentally I'd be more inclined to use a 300mA current limiting circuit if switch current/protection is that critical since a 300mA fuse will allow 330mA for maybe hours and 1A for 30-50 seconds. Of course that depends on switch characteristics, and a current limiter will introduce a voltage drop (eg, 1.2V if using an LM317), but usually such low current interfaces are left unfused. If switches are that critical or expensive it's better using some buffer - eg, transistor or intermediate relay.

You will find that's a high low headlight switching relay. It would be cheaper to use a dual coil latching relay from RS Components or Maplin, then feed a regular relay from there, total cost about £7, also you'll need a kill switch for the ignition (goes to the second coil to "unlatch" the relay and turn the engine off. Go to the RS Components website and enter 12V. dual coil latching relays, any current from 200 milliamps will be sufficient. About £4, then a standard relay, RS, Maplin, Halfords £3-5.

Shoot we're doing it again Peter.

Ok I did not mention space is very limited hence why I have just one relay. It's all mounted behind the dash and its a single seater. Weirdly though it all worked fine for about a minute but then all relays went unresponsive?

A normal or new type "half cube" relay plus the latch would take up less space than the original.

Ok I will see if I can figure out why it's not un latching

Would the 300ma fuse be the issue by adding too much resistance?

No.

Well, unlikely... But yeah Howie, here we go again... safety & reliability, THAT relay, blah blah. I know I would not want a steering wheel switch to turn on ignition and pumps etc. Maybe to kill the ignition, and maybe the fuel pump even tho my fuel pumps are automated (unlike idiots that control them from IGN direct, or oil pressure switches...). But I have been finding more people that use relays for ignitions - either the >$600 types else cheap but usually non-redundant relays. Not that Ive searched but I haven't read yet that any have resulted in accidents or write offs or deaths tho I expect like oil-pressure switched fuel pumps they won't seek to publicise their embarrassment or liability. Of course IMO it's hilarious when such relays are installed for engine kill AND battery isolate systems. Not that such outcomes should be considered funny, but I'm sick of ongoing arguments and ignorance. With apols for my rant, but in case it causes some to rethink IMO hazardous implementations...