# Can you charge a 24V battery with a 20V solar panel and PWM charge controller?

Hi this is Amy from the altE Store. You might have seen the videos that we've
done showing the difference between a 60 cell and a 72 cell solar panel, a 20V and a 24V
solar panel. So what I wanted to do was show you some real
world usage of it, of trying to use either of them to charge a 24V battery bank. Now a lot of people will call up and say I've
got a 60 cell solar panel, and I want to charge a 24V battery bank with it. Can I? Because when I measure it, I'm getting say
39, 38V out of it, open circuit voltage, so shouldn't that be plenty to charge a 24V battery
bank? The problem is, as you might have seen in
another video we did, with heat.

When it gets hot out, the voltage output of
solar panels drop pretty dramatically. So it's about 88 degrees out right now, which
for a northern girl like me, it is really hot! I know this is probably a lovely day for you
guys down south, but any way… So I did measure the voltage of these panels,
and the temperature. So I'm going to show you after measuring the
open circuit voltage. The temperature of the panels was about 140
degrees Fahrenheit. Now when solar panels are rated, they are
rated at 77 degrees Fahrenheit or 25 degrees Celsius. So these panels are almost twice the temperature
that you would have at standard test conditions. I also measured the intensity of the sun,
and it's right at 1000W/m2, so we've got perfect sunshine, I've got the panels at a nice angle
so it's facing the sun, really the only thing that is different from the standard test conditions
is the temperature.

It's hot. So let's take a look at the panels behind
me. They look a little bit different, but really
they are practically the same. This one over here is a Canadian Solar 280W
72 cell panel. So you'll see it's got 6 cells down and 12
cells across. Now this panel over here is a SolarWorld 275W
panel. It's a 60 cell, so it's got 6 cells down,
and 10 cells across. So the 24V panel is 2 rows longer than the
60 cell panel. The reason that they look a bit different
from each other color wise, is this one is in fact a mono crystalline, so we see it's
a little darker, and it's got the rounded corners that create those diamonds in the
middle.

And this is a poly crystalline, so they are
made out of blocks. So it does look a little bit different, but
the ratings of them are very similar, so I think they are really very close and so should
be able to give you a good demo here. So let's measure the Canadian Solar 72 cell
panel, the 24V panel. The open circuit voltage is measured at 44.6V.
And again, it's hot out.

I'm just going to measure right across, and
I'm measuring 38.5V. Again, Voc was 44.6V, so that's nothing against the panel, that's
just the way solar panels behaves when it's hot out. So now let's go over and measure the 60 cell
panel. I'm tucked back here so I'm not shading it,
now this is a 275W 60 cell panel, its open circuit voltage is 39.4V. I'm measuring 34.1V. So again, it's a little lower than the Voc
was, because it's hot. So different types of batteries like to be
charged at slightly different voltages. According to Trojan Battery, their flooded
batteries, they want to be charged anywhere from 29.4 – 30.96V for their flooded batteries. And their sealed AGMs are somewhere around
28.8V. Now different charge controllers, some of
them let you set what voltages to use, and some are just fixed based on what type you
tell it that you are charging.

So for the Morningstar ProStar that we are
going to be using, their flooded setting is 28.8V, and can equalize up to 30.2V. And AGM
is anywhere from 28.3 to 28.7V. So that is right around, a little low, but
right around what Trojan says they want their battery to be charged at. So let's take a look, we're going to keep
those numbers up, because they are the numbers that we are striving for. So I am first going to plug in the 24V solar
panel to the charge controller to the 24V battery bank, and we'll see what kind of numbers
we get out of that.

Alright, so now we've got our 24V solar panel
plugged in, and if we look at our meters, we are getting 31.9V connected from the solar
panel to the charge controller, and then out to the battery, I'm seeing 27.7V. So I'm seeing about 5.9A. So this is really
actively charging this battery. So now let's turn that off and pop over to
my 60 cell panel, and see what we get. OK, so I've got my 60 cell, 20V solar panel
plugged into this 24V charge controller, to the 24V battery bank. Now I'm seeing 29.1V going into the charge
controller, about 27.7V to the battery, and 5.19A. So it is in fact charging, and that
29V, that is slightly above, by maybe a volt what the rating was, what the ideal rating
was.

So what this shows is great, if I've got really
good sun, I'm going to be able to charge. So, <sigh>, this is a tough one, because yes, it kind of works, and in the winter, I bet it'll work great, maybe in the winter we'll do this exact
same thing on a nice cold day. But if you are trying to get the best output,
the best charge for your battery bank for the healthiest battery bank, you really do
want to use either a 72 cell, or two 36 cell, 12V panels in series, to get that 24V. There's a reason they picked these size solar
panels to charge batteries. The 36 cell for 12V and the 72 cell for 24V. These are the really good voltages to charge
a 24V battery. A 60 cell panel, the reason you see so many
of them out there, these were designed for grid-tie, so they don't really care about
if they have a high enough voltage to charge a battery, they're not.

They are not going to be charging a battery,
they are made for connecting directly to a grid tie inverter and powering your house
through the grid tie inverter. Not through the battery bank. So, I think that this shows you that, yah,
it kind of works, but not as well as it could if you did a 72 cell solar panel. OK? I hope this was helpful, if so, give us a
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