Tethys
Member
Having read a number of threads on the subject of Volvo engine hour counters not working, it seems the pragmatic approach is to add a separate counter. However nobody seems to have mentioned the specifics of where to get the 12v from if you only have an ignition on/off switch and starter button rather than a key starter. Obviously, I could just take 12v from the ignition switch, but then I would have an ignition on hours counter rather than an engine run hours counter. (In the euphoria of a landfall, it's not unknown to leave the ignition on long after the engine has been stopped :-o, and I think in certain circumstances, it's good practice to leave the ignition on when sailing).
One idea is to take it from the alternator terminal that goes to the ignition light - this is at 0v with the engine not running and 12v with. This is the possibly the simplest solution, but there is a slight risk that this gives a return to earth for the ignition light, so it may not fully go out when the engine is running.
As far as I know, there is nothing else that has 12v on it only when the engine is running, so another slightly more complicated solution would be to use a relay, with the coil connected to the ignition switch and the oil pressure switch. In this way, with the ignition on and the engine not running (i.e. oil switch closed) the relay would be energised to hold power off the counter. With the engine running, the oil switch opens, the relay is no longer energised, and 12v from the ignition switch would go to the counter via the relay contacts. With the ignition switch off, there is no power to the relay coil or contacts, so no counting.
Any thoughts?
One idea is to take it from the alternator terminal that goes to the ignition light - this is at 0v with the engine not running and 12v with. This is the possibly the simplest solution, but there is a slight risk that this gives a return to earth for the ignition light, so it may not fully go out when the engine is running.
As far as I know, there is nothing else that has 12v on it only when the engine is running, so another slightly more complicated solution would be to use a relay, with the coil connected to the ignition switch and the oil pressure switch. In this way, with the ignition on and the engine not running (i.e. oil switch closed) the relay would be energised to hold power off the counter. With the engine running, the oil switch opens, the relay is no longer energised, and 12v from the ignition switch would go to the counter via the relay contacts. With the ignition switch off, there is no power to the relay coil or contacts, so no counting.
Any thoughts?