solar panel

Hi all

I have a seimens 10 watt solar panel I bought on ebay used. I know
that solar panels have a definite life expectancy, and that when you
buy them used, you don't know how much good service you can expect
from them.

I bought it anyway, because the price was very affordable.

My question is this: In full direct sunlight, my multimeter reads 17.9
volts output from the panel, at zero milliamps. I don't understand
this reading. It is powering the internal electronics of the charge
controller it is connected to, and the charge controller requires a
few milliamps if I recall. Is my multimeter giving me a bad reading?

Any help is greatly appreciated. My email addy is bogus, any response
should be publicly posted. Thank you,

Mathew

 

Due to the internal resistance etc of the panel the voltage will drop as you
load it up (they can be shorted out without harm).
When it is connected to say a 12v battery which is what I would say it is
designed for you will see the volts drop to just above the battery terminal
volts.
That will slowly rise as the battery charges, probably up to 14volts.

 

Make sure you use a solar controller!! don't hook the panel directly up to
the battery....and also, be sure to use some series diodes to stop the
battery from draining back (if you don't use the controller).

 

Thanks for the advice SB. Actually, a charge controller is only needed
if the panel will be delivering more power than the battery is capable
of accepting during a charge period. With the deep cycle marine
battery I have, that is very unlikely with a ten watt panel. But you
are correct, a charge controller is a good peice of equipment to have
in the loop. Any decent charge controller has a reverse feed diode to
prevent power bleeding from the battery to the solar panel during dark
hours, and an additional diode is not needed. In fact, the
manufacturer of my charge controller (sun selector M8) advises against
the use of a diode with thier controllers. As I stated in my original
message, I have a charge controller attached to the solar panel.

By the way, and please take this in the spirit in which it was meant,
top posting is generally considered bad form on usenet. Just a tip.

(scroll down for response to Rheilly, see why top posting is
troublesome?)

Thanks Rheilly, If I am to understand correctly, when connected only
to my multimeter, I will read a high voltage and no amps because there
is no load. When connected to a battery (with controller inbetween) as
load, the volts drop as the amps rise do to ohms law?

Best regards,

Mathew

 

Actually, I consider bottom posting to be a pain!!
I have access to all previous messages so don't see why it's necessary to
scroll down through old messages to reply.

And the killer is those that leave the 30message thread and just add their
one liner comment on the bottom...but I digress!!

Back to the OT....I haven't played with panels less than 40W so have only
ever used controllers with our panels.
It's nice to see panels getting more effiecient...cuz that means ppl will
dump their old panels to make their system more cost efficient (although the
new panels cost more! ). Keep an eye on Ebay or something to catch the
bargains!

 

You have it, also being a 10watt panel I would consider the chances of
overcharging your deep cycle battery to be remote since the current will
never be much above 0.1amp anyway. Hardly a need for the controller in that
application although the diode would be needed.

 

No, not needed, but prefereable. I use the battery to power a 2 meter
ham radio, and I keep the battery topped off all the time. so for
topping off purposes, the controller is nice because it automatically
monitors the batterys self discharge rate and keeps it up to snuff.
After I have been using the radio, I kick in the plug in charger to
bring it up fast. I installed both the charge controller and the plug
in charger on the outside of a marine battery box. Now if only it had
wheels on it .....


by the way, is that 1 milliamp? I knew a 10 watt panel wouldn't
exactly be a hydrogen fuel cell, but 1 milliamp?

Regards,

Mathew

 

Hmmm, last time I looked 0.1 amp came very close to 100 mA

 

Thanks for the clarification. I never was too good at math ;-)