I would like to charge my portable DVD player using a portable solar charger rated at 20 watts with 16.5 volts (23 volts open circuit) but am concerned that I may damage the player with too high a voltage.
Is this a valid concern?? If so, is there a device to step down the voltage from the solar charger that would not significantly affect the charging rate??
Thanx,
Jake
What does the charger that the DVD player uses now put out? 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. A few more specifics about what youre trying to charge would help more. Brian
Normally step down resistors are considered a wasteful way to dissipate excessive power but in this case, it's the sun's energy which we don't use a fraction of anyway so who cares. Just thought I'd blurb that little anecdote, ;-).
-Dave
just
Jake,
What I would do is measure the current draw into the battery when the player is hooked up to it's regular charger either from the wall or car. You've already measured the voltage. Plan on stepping down the voltage on your solar charger by an amount to equal your regular charger and assume (here's where things get a little gray) that your solar charger under ideal conditions can deliver an equal amount of current at the same voltage. Ohm's law, R=V/I should get you in the ballpark for how much dropping resistor you'll need. But you'll also have to make sure it can dissipate the amount of power it will be wasting as heat, another formula, P=(I^2)*R or P=(V^2)/R. Measure current again. If it's off it will most likely be on the low side (better than high) and you can adjust your dropping resistor accordingly to bring it up to a reasonable charge rate. Resistors of all shapes, sizes, values and power capacities can be found everywhere, Radioshack might even one. You're probably going to have to do a little fiddling to get it just right.
One other thing. Would it not be possible to just simply cover some of the solar panels to reduce the output voltage of the charger down to a safer level? You could try that too, might be simpler. Best regards,
-Dave
solar
just
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.
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).
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.
Thanx,
Jake
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
and particularly to "12V Battery Charger" for more detail.
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...
-- John Fields
What John is saying about the voltage drop across the charge resistor changing is true, however as the batteries come up to charge they will take less current and would probably be okay. Still if you can regulate the voltage as he suggested that's a better idea since you don't really know if there's any sensitive circuitry in between the battery and the charger. And as I mentioned previously you could try just covering some of the panels to reduce the voltage down to a safe level in full sunlight. Not the most technically glamorous solution but certainly simpler. Good luck.
Dave
solar
step
will
just
charge
Would this charge controller work?
-- I don't know.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.