laet

Hey Guys, Thanks for you help. Im listening and learning. Ill implement the things you said and post up results shorty. Heaps appreciated, Laet ;D

Hi all, Thanks for the info MP, very good. Well i decided to set up a little project in multisim to try and work my problem out. A pdf of my circuit is attatched. Now your eyes are probably going to pop out of your head and i bet you all think im mad, but im only learning ::) I have refined my relay values a bit so they make better sense, the coil resistance should be about 75ohms and the realy coil should draw 0.160 amps at 12 volts. Relay switches on at about 8volts. Okay, so you see how i set it up, its working but I think I need to change values or do something. I used the BD139 because its a high output transistor, I somhow thought this might be good for driving the relay, but was not sure. Now I did not really do much math here just played in multisim untill i got it half right. So my aim: To make the relay switch on at about 13+ volts, but not 12-12.9 volts, or there abouts (ie at least when alternator charging). So if this circuit is a super pooper let me know how I can improve it, should i use a different transistor, should I have a stabalisation resistor somewhere, and should i have a set up that determines when the transistor turns on and off better. The simulation in multisim is really fine with the resistor value, it will work sometimes and not others, althoug im not getting an error message. You comments and thoughts, most helpful Laet :) Circuit7.pdf

Thanks Ante, I know what you mean but I dont want to do it this way. Why u ask, cause its to hard :). Cant I just get a transisotr that will switch on at 13 volts and trigger the relay. Id rather do it like that.

Hey Guys, Thanks heaps for your replies and interest here :) Okay, Ill try to be more specific. - I have a few ther questions, but I think Its first best to outline the application. I need to hook up daytime running lights on a car (DRL's). However, they need to be automatically switched on once the car is started and once the alternator is charging the battery. As the application is for a fleet, just hooking the headlight relay to ign is no good, because the batteries will die as these cars are getting started on and off all day. So, what i need really is a 12volt 40amp mini auto relay to switch the low beam on only when the alternator is charging. Now I dont want to go off the alternator dynamo because its really hard to get to the alternator on these things. Second, I only want to use realy simple stuff if i can get away with it and I mean basic. If I have to use a transistor I will but not too many. So breaking down the problem again, i need the realay to close when i get about 13volts. Oh yeah the resistance of the auto relay is about 6.7ohms between 86 and 85. I was thinking along the lines of a voltage regulator on the negative side of the relay, also thinkg about a zener put on the postive side in series with the coil. Also maybe a voltage divider with some resistors, but I m not sure how to apply these. Anyway, have a think and let me know, id really appreciate it. It might be to hard without transistors etc, but let me know, thanks Laet

Hi All, Just want to say im really new here. My question is that I need to make a 12volt, 40amp auto relay latch on for about 10 seconds. I however only want to use a capacitor and a resistor to do it. Can this be done?? If so what values should I use and where should I put the capacitor and resistor??? I seen basic capacitor articles where it just shows a capacitor can make a relay stay on for a time, I just need to know if it can be done. I do not want to put transistors in the circuit. All comments and answers are highly appreciated. Thank you