Rory's Dad Posted March 20, 2011 Share Posted March 20, 2011 I have an SPA digital gauge which measures oil pressure and temparature. It has a pin p***k of an LED on the gauage itself so last year I rigged up an independant LED warning light (one of these) but it's not really bright enough. The SPA book says that the sensor must have a max load of 100mA. Looking through some Googled answers the loads are different between different manufacturers of relay. If I arm myself with my multimeter, how can I discover how much load my relay draws? NB I hate electrics Thanks in advance. Rory's Dad Quote Link to comment Share on other sites More sharing options...
SparkyB Posted March 20, 2011 Share Posted March 20, 2011 100mA to drive a relay sounds tight, most in my experience draw at least 5 times that.... A transistor would work, but an easier option would be just to use an LED instead of the bulb you have fitted. RS have a range of sizes so you should be able to find one that will fit the hole you already have. Something like this would be a good bet: 12V LED Quote Link to comment Share on other sites More sharing options...
Welly Jen Posted March 20, 2011 Share Posted March 20, 2011 Hi Rory's Dad, I think we need a bit more information. Is the manual for your gauge this one? If so, are you using external channel 1 alarm, or external channel 2 alarm to drive the external LED? These have a 100mA limit each. If the current draw from the LED is less than 100mA, which it will probably be, then it can be driven direct from the Spa gauge without a relay. Make sure that the LED you pick is a 12V one. If you don't know the current, then connect it between 12V and ground with the multimeter in series and set on DC amps. This will give the current. 12V----LED-----meter-----Ground. If you do need/want to use a relay between the gauge and the LED, then measure the resistance across the coil with the multimeter set to ohms. If it is greater than 120 ohms, then it will draw less than 100mA at 12V. 150ohms would be safer, as this keeps the current under 100mA at 15V (current = voltage/resistance). The Spa manual says that the gauge sinks the current for external alarm 1 and 2, so the other pin on the LED will need to go to 12V, the best bet being the 12V supply to the gauge. Hope this helps, Jen Quote Link to comment Share on other sites More sharing options...
Dave Eastwood (Gadgetman) - Club Chairman Posted March 20, 2011 Share Posted March 20, 2011 As Sparky said, I'd just go for a nice bright LED. I did similar myself, big bright LED lamp from RS, it's not quite as bad as the fog light wannabes some of the racers use but you can't miss it either Quote Link to comment Share on other sites More sharing options...
Rory's Dad Posted March 20, 2011 Author Share Posted March 20, 2011 As Sparky said, I'd just go for a nice bright LED. I did similar myself, big bright LED lamp from RS, it's not quite as bad as the fog light wannabes some of the racers use but you can't miss it either I've found this one here - should do the job nicely... and it will fill the hole in my Mickmade dash. Sorry if this was not clear WellyJen - I'd taken the original LED out and was going to fit this one driven off the relay. Didn't like the colour of red much anyway Anyway problem solved - thanks everyone Rory's Dad Quote Link to comment Share on other sites More sharing options...
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