### Author Topic: Convert 0.5V@4A to 8V@250mA  (Read 2140 times)

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#### z.s.tar.gz

• Supreme Robot
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##### Convert 0.5V@4A to 8V@250mA
« on: January 09, 2010, 06:49:41 PM »
I don't really know what to use to do that, as I've never really come across a situation like this before.
I need the absolute simplest solution that steps up the voltage. I don't need it to regulate necessarily, but that would be a plus.

Some have suggested some kind of boost device, but I don't really know what that's all about.
If someone could just point me in the right direction please.
Save yourself the typing. Just call me Zach.

#### Razor Concepts

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##### Re: Convert 0.5V@4A to 8V@250mA
« Reply #1 on: January 09, 2010, 07:23:06 PM »
A boost converter is what you will need, but from a low voltage like 0.5 volt is quite difficult, and it probably won't be very efficient.

Try searching for voltage step-up or just boost converter.

#### Soeren

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##### Re: Convert 0.5V@4A to 8V@250mA
« Reply #2 on: January 09, 2010, 07:55:55 PM »
Hi,

The 0.5V is a very optimistic estimate for when the sun is shining its absolutely highest. Most of the time the output will be between 0.25V and 0.35V (unless you live in a very sunny area and only measure it around noon). The current is proportional with the voltage, so you won't get 4A either.

You won't find a switcher that will work from a single solar cell. To be absolutely certain of power most of the time, you need at least 4 or 5 cells and to make life easier, make sure you have at least 2V (and the 2W or 4W you need) on a grey day.
Depending on how the cells are made, they can be broken in equal sized pieces and the pieces series connected to give the voltage you need. That depends on the ability to solder (or use liquid silver loaded "solder") to the chips.

I gave you a link to an efficient switcher that goes down to under 2V and I don't think you'll find anything better.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Engineering is based on numbers - not adjectives

#### z.s.tar.gz

• Supreme Robot
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##### Re: Convert 0.5V@4A to 8V@250mA
« Reply #3 on: January 09, 2010, 08:55:16 PM »
As for the whole 0.5V thing, they're actually rated above that but I figured (like you said) that the sun won't always be at full power.
Also, the last solar panels I purchased were rated well below what they could output. (Not saying that these will be able to, just saying the ratings aren't always correct)

As far as using several in series, that isn't really an option at the moment for several reasons. I'm just going to keep surfing around wikipedia until I find something that can work.

« Last Edit: January 09, 2010, 08:59:25 PM by z.s.tar.gz »
Save yourself the typing. Just call me Zach.

#### Soeren

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##### Re: Convert 0.5V@4A to 8V@250mA
« Reply #4 on: January 09, 2010, 09:31:10 PM »
Hi,

As for the whole 0.5V thing, they're actually rated above that but I figured (like you said) that the sun won't always be at full power.
Also, the last solar panels I purchased were rated well below what they could output. (Not saying that these will be able to, just saying the ratings aren't always correct)
If you measure the open circuit (=unloaded) voltage, it will be higher than when loaded appropriately.
Beware of the specs, some sellers give open circuit voltage and short circuit current and just multiply them for the power rating and that's bogus, as they cannot happen concurrently.

You cannot use the short circuit current rating, as this only exist when the cell is... Well short circuited.
And the open circuit voltage won't be seen with a load.

As far as using several in series, that isn't really an option at the moment for several reasons. I'm just going to keep surfing around wikipedia until I find something that can work.
If you're referring to the real Joule Thief (not the one there's been a commercial for here, where the name has just been "stolen", there is only one Joule Thief, as the term is coined by Big Clive who first named the circuit so, although he didn't invent the construction), you won't get there unless you have some germanium power transistors (which probably haven't got the gain required anyway).
Best result I have gotten from such circuit is down to slightly above 0.5V and only if the oscillator was started at a bit above 0.6V (how much is depending on your transistor selection) and at such low voltage, the allready not too efficient circuit is very inefficient at such low voltage.

A general rule in switchers:  The larger the difference in in/out voltage potential, the less the efficiency. (And that's why a SEPIC converter with an output at close to the average input voltage is aces here).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?