henk Posted May 22, 2020 Share Posted May 22, 2020 (edited) So I have the second alternator installed but can I use a led light as control light to check the working of the alternator or do I need to use a normal bulb? Solved: it's not a good idea Edited May 22, 2020 by henk Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted May 22, 2020 Share Posted May 22, 2020 Normal bulb or an led with parallel resistor equivalent to a normal bulb. Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted May 23, 2020 Share Posted May 23, 2020 I'm not great on electrickery, but what about an LED bulb and a resistance (normal bulb) in series? Mike Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted May 23, 2020 Share Posted May 23, 2020 In parallel, yes, that would work, in series, no. 1 Quote Link to comment Share on other sites More sharing options...
western Posted May 23, 2020 Share Posted May 23, 2020 Led charge light works OK using a td5 instrument pack in a older 90 or 110 with the existing charge light resistor remaining in place, so a similar set up for the 2nd alternator should work. Quote Link to comment Share on other sites More sharing options...
cackshifter Posted May 23, 2020 Share Posted May 23, 2020 To enlarge a bit they often have a resistor in parallel with the bulb in case the bulb blows; if you didn't the alternator may not charge with a blown bulb, as it wouldn't get the excitation to get started(!). So a led instead of a bulb should be OK if you have the resistor in parallel with it, as western says. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted May 25, 2020 Share Posted May 25, 2020 Alternators need a certain amount of current flowing into the sense terminal to get them going - the bulbs are usually ~5W - so putting an LED in there that only flows ~20mA may result in the thing not charging. That's why you want a resistor in parallel with the LED. Also the LED will NOT warn you of the same failure modes because it can't flow current "backwards" (being a diode and all), so it will warn of the "usual" situation (ignition on, engine off) but not things like a dead alternator diode (ignition off, power back-feeding through warning light) etc. Quote Link to comment Share on other sites More sharing options...
Ex Member Posted May 25, 2020 Share Posted May 25, 2020 1 hour ago, FridgeFreezer said: Also the LED will NOT warn you of the same failure modes because it can't flow current "backwards" (being a diode and all), so it will warn of the "usual" situation (ignition on, engine off) but not things like a dead alternator diode (ignition off, power back-feeding through warning light) etc. Yes, but pretty much every car has a diode in the circuit to prevent the alternator back feeding the switched circuits when the ignition is turned off. In Defenders, this was adding in 1991 as the engine would keep running if there were no switched load on. Quote Link to comment Share on other sites More sharing options...
HoSS Posted May 26, 2020 Share Posted May 26, 2020 20 hours ago, FridgeFreezer said: Also the LED will NOT warn you of the same failure modes because it can't flow current "backwards" (being a diode and all), so it will warn of the "usual" situation (ignition on, engine off) but not things like a dead alternator diode (ignition off, power back-feeding through warning light) etc. Not sure about that without testing, but simple put another LED in inverted parallel, one or the other will light. Make them 2 different colours and you have that information too. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted May 26, 2020 Share Posted May 26, 2020 6 hours ago, HoSS said: Not sure about that without testing, but simple put another LED in inverted parallel, one or the other will light. Make them 2 different colours and you have that information too. Exactly, my setup has LED's in anti-parallel and a resistor to pass the necessary current, works perfick. Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted May 27, 2020 Share Posted May 27, 2020 On 5/22/2020 at 11:27 PM, Bowie69 said: In parallel, yes, that would work, in series, no. Yes, thank you, Bowie69. As I said, I'm not great on electrickery, but I do understand, now🤔! Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted May 27, 2020 Share Posted May 27, 2020 This is what's in my gauge: Quote Link to comment Share on other sites More sharing options...
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