DC to DC converter/regulator design?

Hi,

I have 20V PV solar panel.
I want to charge 12V automotive battery.

I would like to hack apart some electronics
and make a DC/DC converter so I can charge
the battery.

Any ideas on how to ? I was thinking of
tapping into a PC power supply after the
rectifier, and using the supply to convert
20V DC into 12V DC?

This is going in a VW camper van. I have
a few spare voltage regulators from the VW.

It looks like the VW voltage regulator
works by varying the voltage
to the "field" coil in the alternator. If
the output voltage from the alternator is
too great, it reduces voltage to the field
coil. If the voltage from the alternator is
too small, it increases voltage to the field
coil.

So, the regulator has
1)V+ input (this voltage is output from alternator)
2)V+ output (for field coil input on alternator)
3)ground
4)V+ output (to battery to be charged)

would there be a way to use this scheme to
control how many volts get to the battery?

I was thinking of maybe a variable resistor
that can be controlled by an analog input
voltage. Mimic the field coil/ alternator
with another device.

There is no coil in the solar panel.
I have "constant" voltage output from
it.

The regulator increases one of it's outputs
(output to field coil in alternator)
if the power input is too low.

the regulator decreases the output
(output to field coil in alternator)
if the power input is too high.

How to regulate +20v from PV panel with this
inverse proportional analog voltage?

Jen

 

[martin griffith]

On 26 Jul 2005 11:31:52 -0700, in sci.electronics.design
jboothbee@gmail.com wrote:

Hi,

I have 20V PV solar panel.
I want to charge 12V automotive battery.

Usually all you need is a diode in series with the SP
see
From: larwe@larwe.com
Newsgroups: sci.electronics.design
Subject: Request comments on simple solar charger
Date: 23 Jul 2005 16:31:12 -0700


martin

 

[Roger Lascelles]

"martin griffith" <martingriffith@XXyahoo.co.uk> wrote in message
news:ml0de11417cch5s2u05sekna25hgv7uv4s@4ax.com...

Usually all you need is a diode in series with the SP

Jen, this is good advice.

The "20V" solar panel is designed so it will do a good job when connected to
a 12V battery. You need to add the diode, because when it is dark the
battery tends to discharge through the panel. A lot of panels actually have
the diode wired inside a junction box on the back of the panel, so look for
the diode - a cylindrical component with a wire coming out of each end. If
you don't have a diode, buy a 50 volt or more, 5 amps or more diode from
your electronics shop. The cathode (striped) end goes to the battery plus.

Because this simple connection does not have a regulator, the battery will
gas gently when it is charged, so you will need to top it up with distilled
water sometimes. This will not reduce battery life. However, you must not
use a sealed type of battery such as a Gell or AGM type with this simple
connection.

The automotive regulator can't really help with this application. You can
buy small solar regulators for the job.

Roger Lascelles