12v help

[TonyWig]

I want to run some LED lights (meant for use in a car) from mains.

Can I just use a plug-in transformer from an old Xmas tree (or similar) that has a 12v output ?

Apologies if this is a dim question.

Thanks in advance
Tony

 

[Chri5]

What's the spec for tha lamps 12v DC and .......... watts / amps / m amps.

Do the lamps connect to a LED driver, and then on to the 12v system ?

 

[TonyWig]

It's a halfords interior flashing LED set. 12v DC, 30mA, 360mW.

 

[ericmark]

The mains supply is AC so the reducer needs to convert to DC. The output should be 13.2 volts DC but likely 12 V DC will be close enough.

There are many items that use 12V DC from train sets to CB radios and the latter did have some good cheap power supplies in the hay day.

Power is the next thing. If you were using for example a lamp rated at 6W then at 12V it would use 0.5A or 500ma and you may find a plug in transformer to provide that power.

As you go up to 1A the transformers that plug in become more rare and often they have only an intermittent rating.

A car battery charger rated at for example 8A will provide 8A at 12V but at 13.2V this will be only about 2A so one has to be careful on selection.

Most transformers have a VA rating. This is nearly the same as watts. So a 6W lamp needs a transformer with over 6VA. VA as name suggests is Volts x Amps so at 12 Volt at 60VA transformer will provide 5A.

 

[TonyWig]

Many thanks. Clearer to me now.

I have two sets (or maybe three) of the LED sets detailed above.

Am I right in thinking that since I need two lots (I have two sets of LEDs) of 12v DC, 30mA, 360mW which would more than adequately be covered by a standard battery charger.

Given I want to run these lights for 4 hours max (as a one off) then I could use a standard battery charger and just rig up some cabling to run them from?

Or am I so far from reality I should forget it ?

 

[bernardgreen]

which would more than adequately be covered by a standard battery charger.

I wouldn't run the LEDs from a standard battery charger as the output voltage maybe several volts higher than 13 volts when supplying only a low current of 60mA Only when running at a few amps will the voltage be dragged down to the nominal battery voltage

Given I want to run these lights for 4 hours max (as a one off)

Then use batteries to remove the need for cabling

You could invest in a 12 volt battery such as http://www.tlc-direct.co.uk/Products/TSB2.html which when charged will provide 60mA for many hours and then be a usefull power source for other uses.


Or even less expensive ( about £4 ) use two of these http://www.tlc-direct.co.uk/Products/PB4R25.html for a one off use.

Other battery sources are available

 

[ericmark]

Likely the standard battery charger would work them. However the rectified AC from a battery charger is not the same as the smooth DC used in a car so without have a battery across the terminals it may cause damage to the lights although unlikely.

I did a Google for CB power supply and between £10 second hand and £32 new so that would seem best option.

But a 12v 1A power supply can be as low as £2 seems sold for CCTV supplies.

So if it was me I would try one of the CCTV transformers which should be continuous rated. However I used one to power my satellite box and although supply rated 1.5A and box draws max of 1A it failed after 3 months. So returned to using power supply for my amateur radio rated at 10A. That is many years old and still going fine.

Because your lamps will run off a switched mode supply and CB and Amateur radio in the main will not the units for what you want are much smaller. However they don't seem to last as long.

 

[TonyWig]

Many many thanks for all the advice and info.