What does the charger that the DVD player uses now put out?
12 volts. It could also be charged using cigarette lighter in car
meaning it should be able to handle a bit more than 12 volts.
It depends on
the voltage of the batteries primarily as to the likelihood that the solar
charger you want to use can in fact be used. As far as something to step
down the voltage, if the voltage difference between the required charge
voltage for the DVD and the 16.5 volts output that the solar charger will
put out is minimal (within +- 5 volts), a step down resistor would work just
fine. If the voltage difference is much more than that, then your charge
rate will increase accordingly.
Where can I get a "step down resistor" and how would I hook it up??
Would it require soldering and a permanent change to the solar
charger?? Sorry if the question is silly as I am rather ignorant in
matters of electronics (if that already was not obvious).
Forget the resistor.
If the load your device puts on the photovoltaic (PV) array changes
while it's charging, then the voltage dropped across the resistor will
vary with the current through it, with the result that under light
loads and full illumination of the PV array the voltage out of the PV
array could rise high enough to damage the batteries or the charging
circuitry in the device.
What you need is something like an LM317 wired like this:
PV
ARRAY LM317
+-----+ +---------+
| +|-[DIODE>]---|VIN VOUT|--[Rs]--+---->BATTERY+
| | | ADJ | |
| -|--+ +----+----+ [240R]
+-----+ | | |
| +-------------+
| |
| [2.4K]
| |
+----------------------------+---->BATTERY-
Go to
http://cache.national.com/ds/LM/LM117.pdf
and particularly to "12V Battery Charger" for more detail.
A few more specifics about what youre trying to charge would help more.
Actually I would like to be able to charge a variety of devices while
away from AC including GPS, PDA, laptop computer, portable DVD, etc.
As long as they all take a steady 12V in to charge them, the circuit
above should work as long as the input voltage to the lm317 is >=
14.5V. If they need different voltages, read the data sheet to find
out how to change the LM317's output voltage. One caveat, you may
have to put a heat sink on the LM317 if the battery charging current
causes it to heat up too much.
You could also use a 7812...