9v to 12v

[floydster]

I have some 9v devices that I'd like to connect to 12v batteries. How easy is it to make something to stop them "blowing up"? The voltage converters that I've seen in Maplin look really bulky and I don't really want a converter that's bigger than the equipment I'm connecting.

Thanks,

Floydster

[aminorjourney]

Hi Floyd,

I would suggest you build a simple 9V Regulator circuit.

John (Meeester John AKA Anacrocomputer) helped me make a 5 V regulator for my City El so I could power a 5v voltmeter from the main 12V supply. It's dead easy to make and shouldn't be a problem at all !

Oh, and best of all? It's very cheap to make!

[anachrocomputer]

Quick question: how much current will the 9V devices need to draw?

Building a small 9V regulator should be straightforward, but it all depends on how much current you need.

[floydster]

Quick question: how much current will the 9V devices need to draw?

Not a lot, only about 200mA.

Floydster

[aminorjourney]

In which case I reckon you'll be laughing but John can suggest components for it

[electric cat]

any chance of a circuit diagram?

[Tim]

As the currents and voltages are small, why not just use a series of diodes?

Memory suggest that each diode will drop about 0.6 volts, so 5 diodes will produce the 3 volt drop that you want.

I've got some radio control gear that's nominally 6 volts running off a small 9 volt battery for space reasons using this approach.

[EVguru]

You need a 7809 regulator;

http://www.maplin.co.uk/Search.aspx?cri ... A&DOY=6m10

for example.

[floydster]

How to you wire it up?

Floydster

[Deker]

Hi Floydster.

Just come to this post, I may well be in arrears.

You ask "How to you wire it up?

The 78 series voltage regulators are dead easy to wire up.

With the device facing you, looking at the printing,
there are 3 legs, left to right,
1 = + in,
2 or middle = negative,
3 = + output which is the last 1 or 2 digit number of the regulator i.e. 7809 = 9 volts or 7812 = 12 volts.
It is recommended to add really teeny weeny capacitors to the output and negative terminals, however Iv used these 78s without the caps, no probs.

An easier method is to use diodes, in "Daisy chain" formation. The IN 4001 will drop .6 to .7 volts each. max current = 1 amp, the same as the 78 series regulator.
An alternative diode which can handle 3 amps BUT give up to 1.2 volt drop is BY396P, available from RS components, RS number 629-3539, they are supplied in packs of ten. And cheap.

A word of caution, 78 series regs, do come in lower current ratings, the metal tag is also a negative connection. They may need a heatsink, if they get too hot - may go short circuit, that is pass the maximum input voltage.
They will pass max volts if the negative connection goes open circuit, i.e. broken wire.

Any more info, just ask.

Deker.