12v to 5v transformer

[Droopy Dick]

I'm after a 12v to 5v transformer that I can use to bike power my mp3 player.

I'm staggered that iRiver want £12.99 for one!

Does anyone know where I can find one for a more reasonable cost?

 

[Iain Hogg]

Transformers only work with alternating current so no use on the bike.

What you need is an electronic gizmo that will provide the voltage you want. O.K. so it can be done with a single Voltage Regulator IC costing a few pence but packaged up with connectors, £12.99 is not a bad price for a commercial item IMHO.

Iain

 

[Mouse]

Maplin sell a switchable voltage converter for about 10 quid, as Iain says, that's not a bad price for the official item, I think.

 

[Tarka]

I'm staggered that iRiver want £12.99 for one!

Squeak...squeak....

Assemble the following words into a popular sentence...

A shark`s arse tight as at forty fathoms.

 

[turbine_2]

Argos is where I ended up getting one from in the end.

 

[Bagpuss]

£12.99 is a good price for a little switch mode supply (electronic & lightweight) which will probably have all the right connectors and therefore require zero faffing about with afterwards...

Stick your hand in your pocket!

 

[trotsky]

12V dc to 5V dc needs two resistors and some connecting wires. Does a man of your resourcefulness not have this to hand?

<iframe frameborder="1" height="800" scrolling="auto" src="http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html" width="780"></iframe>

 

[Mouse]

Sorry it's not so simple

The voltage fom your bike will vary between about 12V and 14.5V depending on the speed of the engine and other factors.

To ensure a steady 5V supply you need to use a zener diode to drive a transistor at the very least. Even so it's true that the parts to make somehing like this would be less than a quid

 

[Iain Hogg]

Still not so simple! These solutions will only work for a limited range of load current.

What you need is a voltage regulator IC like the LM723 for example.

Spend the money you tight git

 

[trotsky]

Sorry it's not so simple

Damn you pesky kids! If it hadn't been for you my fiendish "exploding bike" plan wouldn't have fallen at the first hurdle!

 

[jkersh1]

Most GPS units although nominally 5v can be run on bike voltages with no harm. With some exceptions. Or so I've been told. Would an mp3 really care either?

 

[Fanum]

Most GPS units although nominally 5v can be run on bike voltages with no harm. With some exceptions. Or so I've been told. Would an mp3 really care either?

I think that's one we'll let you test out Jkersh.......report back with pictures of smouldering Ipods and Zens when you've completed the exercise will you???

Cheers

 

[Mouse]

High end GPS units (like Streetpilot) can run from automotive voltages, because they have a built in voltage regulator. Cheap units like the Quest don't, that's one way the manufacturers make them cheap - and that's why a power lead for the Quest costs the best part of 40 quid.

 

[jkersh1]

OK, if nobody wants to let out the secret smoke, check out Belkin for palm PDA chargers. They are 5 V, cost about $20 US.

http://catalog.belkin.com/IWCatProd...d=&Section_Id=1979&pcount=&Product_Id=161651#

 

[Fanum]

High end GPS units (like Streetpilot) can run from automotive voltages, because they have a built in voltage regulator. Cheap units like the Quest don't, that's one way the manufacturers make them cheap - and that's why a power lead for the Quest costs the best part of 40 quid.

OI!!!

It's not cheap...it's compact

THAT's why they have the power dealt with externally.....to minise the form.

So there.

 

[Mouse]

Yours is pretty compact after it was squashed flat by that traffic on the motorway!

 

[Wizard]

I thought it was rather less than compact after having bits of it fired all over the countryside by said traffic.....

Take one L7805 5Amp 5V regulator (Quid ish) and some wire, hook the input to the 12V, attach the tab to the frame using a mylar insulator & heat transfer compound (about another £1-50), and hook the output to a plug for the MP3 player. Total cost about 3 quid and ten minutes.

If you want to get really complex, stick a capacitor (c. 10p) across the input to keep out ignition noise, although I've always found the internal supression is more than adequate.

 

[(RIP) Kaister]

put a 6V bulb in series - voila =- 6V +- a bit

excellent thread - a bunch of educated people arguing a number of ways to determine a solution to a relatively easy problem - and all coming up with different yet plausible ways of acheiving it.

think laterally. - i love it.