Getting 20V out of a 12V battery

[jnb]

Inspired by a piece of kit someone at my astro society has built I was thinking of building my own power pack. Essentially a 12V leisure battery in a toolbox. But in addition to 12V I'd want to be able to get 20V for the laptop and possible 6V for some equipment. Is there some standard piece of kit I can easily wire in to get those voltages out of a 12V battery?

[TCWORLD]

How much current on the 20V Rail do you need?

What you need is a DC-DC boost convert which can step 12V up to 20V. What these basically do is convert current to voltage. So if the output voltage is higher than the input voltage, then the input current will be higher than the output current.

You can do the same thing efficiently with 12V down to 6V (in this case a buck converter).

[TCWORLD]

Or even just something like this:

http://www.mintprice.com/products/item/81323-Laptop-Power-Adaptor-DC-Car-Charger-with-8-Tips-Connectors.html

[TCWORLD]

Or even:

http://www.maplin.co.uk/p/15-24v-laptop-car-adapter-85a-9-charging-tips-a33hu

That sort of thing.

[jnb]

How much current on the 20V Rail do you need?

What you need is a DC-DC boost convert which can step 12V up to 20V. What these basically do is convert current to voltage. So if the output voltage is higher than the input voltage, then the input current will be higher than the output current.

You can do the same thing efficiently with 12V down to 6V (in this case a buck converter).

typical laptop PSU is 20V 3.5A. So something like this http://www.ebay.co.uk/itm/DC-DC-Boost-Converter-10-32V-to-12-35V-6A-150W-Step-Up-Voltage-Charger-Module-/181198105569 ? Suspiciously cheap but it's got all the right words on it

and something like this http://www.ebay.co.uk/itm/LM2596-LED-Voltage-Regulator-DC-Buck-Adjustable-Step-Down-Converter-Module-New-/200960509542? for the lower voltages?