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

Hi, this is Amy from the Alte Store. I just did a video showing you the difference
between using a 60 cell 20 volt solar panel and a 70 cell 24 volt solar panel to charge
a 24 volt battery with a PWM charge controller. So I'm going to do the same thing but with
an MPPT charge controller. So now I'm using the midnight kid. And this is a MPPT charge controller. So I've got my cheat sheet. I've got a Canadian solar 280 watt panel that
72 cells so it's 24 volts. And I've got a SolarWorld 275 watt panel 60
cell. So it is very hot out so the voltage of these
solar panels has dropped dramatically and you can check out that other video I will
show you some of the voltages there because of the heat. But what I want you to remember is that battery
manufacturers recommend about 28.8 volts to charge a sealed battery. So let's see what we get with these solar
panels. And I do apologize about the wind, it's picked
up. So we're starting with a 24 volt solar panel. I've got it connected to the midnight kid
and it is charging the batteries.

I can look and see coming out of that solar
panel I've got 30.6 volts now that's just a little bit higher than what the recommended
28.8 volts was for charging my charge controller. It's getting a little later in the day so
the sun isn't as intense as it was earlier. But I think this is still really good to see. So we've got 30.5 volts going into the charge
controller 27.79 volts coming out and 7.1 amps. Now when I was doing this earlier when it
was actually mid-day I was actually seeing about 6 amps coming out. So the MPPT charge controller is certainly
boosting the output of this and getting my maximum output. So now lets switch this around and see what
outputs we get using the 60 cell 20 volt solar panel.

Okay? Okay so I've got the 20 volt solar panel. And again this is a 275 watt solar panel vs
the 280 watts so very similar. But the big difference is it's putting out
a lower voltage because it only has 60 cells. So if we take a look, it's putting out about
30.5 volts into the charge controller 26.3 volts into the battery 5 amps. So I'm getting a full amp less from this 20
volt solar panel than from the 24 volt solar panel.

And that's significantly more of a change
than you would see just because of that 5 watt difference in their ratings. So I am absolutely not getting as good power
out of my 20 volt solar panel into a 24 volt battery they really do prefer to matched up
nicely even with an MPPT charge controller. An MPPT charge controller can take a higher
voltage and drop it down to a lower voltage battery. But most MPPT charge controller with a couple
of specialty ones that are exceptions. They need to have a higher voltage going into
the batteries. So it's ever so slightly higher. Like I'm dropped down to 29.8 volts so it's
a little bit higher than where the battery bank wants to be charging at. Again AGM wants to be charging up around 28.8
volts so I barely have the voltage and this is really full sun. If a cloud were to go by I would not have
higher voltage, I would probably have higher voltage in the battery than my solar panel.

So it really does make a difference of having
a 24 volt 72 cell or 2 12 volt 36 cell panels wired in series to make your 24 volts. If this was winter time it would probably
not be as bad because when it is cold, the silicon voltage goes up in solar panel. So it would probably work better in the winter
but in the summer when it's hot. It's probably well in the eighties right now. The voltage of these solar panels really drops
down and just doesn't efficiently charge these batteries. If this was a flooded battery it wants to
be up around 30, 31 volts. I'm really not going to be able to give it
a good full charge, with a 20 volt solar panel. So while it looks like yeah everything is
cool, it's charging, it's not going to give it that really big top off. It's going to be at risk of being in a partial
state of charge which most batteries do not like to be.

So while it will appear that it's working
okay, you're going to shorten the life of your batteries. So just important note to keep in mind 72
cells for a 24 volt battery. This is Amy from the AltE Store, I hope this
was helpful, if so give us a like and a share, and be sure to subscribe to our AltE Store
Channel so we'll send you notifications when we've got new videos. And make sure to go to our website at altestore.com
where we've been making renewable do-able since 1999.

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