Running 12 volt (LED's) and 24 volt, without changing ...

[duncombemu]

This is very difficult to explain, so I'll just explain what I want to do.

I have just finished converting a school bus into a Motor home. I want to tow behind the 'bus' my old 1960 model VW Beetle. I've converted the rear lights (tail/brake, direction indicators), to LED's. But this is where it gets complicated (for me anyway).

The car is a 12 volt system (as usual) and the bus has a 24 volt system. So if I attach the trailer plug from the bus to the car's rear lights, we would get 24 volts going to these lights, thus destroying them in the process. This is where I'm getting stumped.

What I'd like to have is, a circuit that can run 12 volts when I'm driving the car and still have the rear lights (LED's) operative when the car is 'plugged' into the 24 volt bus. I'm sure someone would know how this could be done. I've tried to find on 'the Web' and help myself, (a circuit that can perform this task), but I've found nothing.

Could someone supply me (or point me in the right direction), with a circuit diagram or information, of how I could build a system that could run either voltage, without the hassles of having to unscrew the lenses and change globes/LED's, every time I attach to the bus, or use the car by itself?

In other words, a circuit that can operate with either voltage, without overloading or destroying the LED's and so making the system automatic.

Regards,
Mark

 

[zaph1]

Convert the output from the bus to 12v and change nothing on the beetle.

Are you sure the rear connector and lights are 24vdc? I couldn't imagine a trailer connector being anything other than the standard 12vdc. Have you checked with a multimeter? I can see the inside of the bus running at 24v, but not the lights.

 

[wp100]

Re: Running 12 volt (LED's) and 24 volt, without changing ..

Hi,

What is the current for each of the led lamps ?

 

[pranam77]

You may use a 24 to 12 volt regulator which will then supply your cars loads. But before we come to a conclusion which one to constuct and use, you need to measure the full load current (AH) of your car wiith all the laods ON.
Cheers

 

[IanP]

Re: Running 12 volt (LED's) and 24 volt, without changing ..

On the 24V line you have to use a step-down voltage regulator (switching or linear, depending on the current of the LEDs), then connect both voltages through diodes that will work as an automatic switch - whatever voltage is present - it will be supplying the LEDs .. see attached picture ..

Details of the step-down device can be discussed later, once you provide info on the LEDs current requirement ..

IanP

 

[duncombemu]

Re: Running 12 volt (LED's) and 24 volt, without changing ..

IanP,
Quote ... once you provide info on the LED's current requirement ...

Please let me know how I can 'measure' the current of the LED's, so I can let you know.
Regards,
Mark

 

[IanP]

Re: Running 12 volt (LED's) and 24 volt, without changing ..

G'day mate,
The easiest way would be to use a clamp-on dc ammeter ..
**broken link removed**
Question is, do you have somehing like that? or, what meter do you have?

IanP

 

[duncombemu]

Re: Running 12 volt (LED's) and 24 volt, without changing ..

G'day mate,
The easiest way would be to use a clamp-on dc ammeter ..
**broken link removed**
Question is, do you have somehing like that? or, what meter do you have?

IanP

IanP,
I don't have a clamp-on-meter, but I do have a DMM, that can measure amps. Will this be OK to use? Now, how would I measure how many Amps I'm using?
Thanking you for your help so-far.
Regards,
Mark

 

[wp100]

Re: Running 12 volt (LED's) and 24 volt, without changing ..

Hi,

You would probably be best measuring the current to each lamp / set of leds rather than trying to read the load of all the lamps.

If all the lamps use the same type and amount of leds then you really only need to measure the one lamp.

Prepare your meter with the range switch on the highest DC AMPS setting, usually 3A or 10A, and move your leads into the 10A and COMMon sockets.
If you have crock clips, put them on the end of you leads.

Now connect the COMM lead to the +12v terminal of your 12v battery and the 10A lead to the POSITIVE lead of your lamp. Make sure they are all well secured .

Take the NEGATIVE lead from your lamp , and with a insulating pair of pliers etc, hold it firmly onto the Negative terminal of the battery. - it may spark a bit as you connect it.

Your meter should now be giving a reading, which should stabalise quicky.

 

[IanP]

Re: Running 12 volt (LED's) and 24 volt, without changing ..

Do whichever way you fill comfortable with ..

I prefer to use a voltmeter and a shut resistor .. see attached picture .. then I = V / R ..
There is a fuse inside your DMM on mA/A sockets and if current is unknown it may be really easy to blow that fuse ..

IanP

 

[duncombemu]

Re: Running 12 volt (LED's) and 24 volt, without changing ..

Thank you IanP and wp100, for your help. I've now sorted it with your assistance.

What did we do before 'The Internet'?

Kind regards,
Mark