12v/24v tester

Don't know what is available in UK but in the states one could pick up a cheap voltmeter (VOM) for about $10. They are small and simple to use as you only want to measure DC volts for 12 or 24. Dave

Two resistors, an 18volt Zener diode, and red and green LEDs.

Assuming that all the vehicles are negative ground.

center terminal of cig adaptor plug is +

Is there power available? positive terminal -- 1K resistor -- green LED -- negative terminal Green light indicates power.

Is it more than 12 volts? positive terminal -- 470 ohm resistor -- red LED -- 18 volt Zener diode -- negative terminal Red light indicates more than 20 volts present (18 volts of Zener + 2 volt drop across LED.

Resistors may need adjusting based on maximum current rating of LEDs used.

John

Thanks John - this is exactly what im looking for. One question though....are the circuits wired in series or parrallel to each other?

(all vehicles are negative ground yes)

Thanks. Kev

Go to any electronics parts supplier, and spend a few dollars on a low cost DVM. Then buy the parts required to make up a test plug that you can plug in to the cigarette lighter for taking voltage measurements.

When using a DVM, just make sure that the meter is set to the proper range before connecting, to avoid damage to it.

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JANA _____

I was hoping someone here can help me out please. The problem is that being a truck driver (in the UK) there is no universal way of the cigarette lighters to be wired for one of the above voltages. For example, Volvo might have one cig adaptor fitted and it could be of the type thats found in cars but it migth be of either voltage. A different truck manufacturer, say Mercedes, might have the same cig socket fitted but the voltage stepped down to 12v. So theres no definate method of supplying 12v to the cab to run ancillory equipment from - and I carry a fair bit with me whenever I get into a truck such as portable TV, cooler, satnav - the list goes on. Im sick fed up of blowing the balls off my gear with 24v really! So I need a little help here as such - Id like someone to draw me a simple wiring diagram with components labelled whereby I could use a cig plug and wired to it would be a little circuit board with 2 LEDs - a green one for a

Thanks in Advance.

Kev D

voltages

Better still use a circuit that makes 12V from 12 or 24 automatically so you don't have to bother checking...

I already have a voltmeter - that wasnt my original question.

(im in the UK - dont have dollars here)

Kev

That link you posted is dead.

What you suggest is feasable and there is a manufacturer that sells 24V reducers and I have one (blown to bits though!). However there is a maximum load on them and ocassionally I exceed the load hence the need for a visual indication of which voltage is piped to which socket.

McKev.

try this: red for 24V green for 12V red 10V zener LED

My sincere thanks to all of you on helping me on this little project - you have been very considerate an I appreciate your time and effort very much.

McKev

Multimeter prices aren't too bad in the UK - I just picked up a autoranging DMM with K-type thermocouple and transistor tester for £15 at Maplin, and they're not well known for reasonable pricing! Typically a basic meter shouldn't be more than £5 if you shop around.

Wired in parallel (both are checking the same voltage feed).

Remember to verify the polarity of the LEDs and Zener diodes..

John

__ TH amd TR have an impedance of several megaohms, is there a reason to burn

__ TH amd TR have an impedance of several megaohms, is there a reason to burn

Works for me. Just tried it again.

Thanks...just worked for there. I appreciate it :)

McKev