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Old 04-10-2020, 07:38 PM   #1
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Solar Charge Controller Confusion

I have read books.
I have watched videos.
I have experience with residential and marine wiring.

But I can't get a definitive answer to the following question.

When one thinks about a 40 Amp MPPT Controller, should one be thinking of 40A being the most that can come in or the most that can come out?

So, in other words, can a 60A controller slam more amps into the batteries, or at a faster rate, than a 40A controller using the same battery bank and the same solar panels?
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Old 04-10-2020, 07:41 PM   #2
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Sorry, but the correct answer is IT DEPENDS.


What is the limiting factor:


Sun/solar rays
Size and efficiency of solar panels
Solar controller
Wiring from solar panels to controller and onward to batteries.
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Old 04-10-2020, 08:31 PM   #3
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I'd say it depends on the manufacturer and how they define their controllers charge capacity. I know that a 15 amp victron MPPT controller will deliver 15 amps maximum to the batteries.
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Old 04-10-2020, 09:25 PM   #4
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Both.

Put 40 amps in and get 40 amps out.

Controllers don't make electricity, they convert it.

Volts X amps = watts
Watts ÷ volts = Amps.
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Old 04-10-2020, 09:49 PM   #5
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A 60A can, potentially, charge 50% faster than a 40A, provided you have a large enough array and sufficient sun exposure.

Figure about 6A per 100W. 1000W of panels = 60A controller.
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Old 04-11-2020, 05:32 AM   #6
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Pioneer,
I figured a 100W panel with an approximate OC voltage of 22.5V would produce only about 4A.

What am I getting wrong?
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Old 04-11-2020, 05:58 AM   #7
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Quote:
Originally Posted by Brianna View Post
Pioneer,
I figured a 100W panel with an approximate OC voltage of 22.5V would produce only about 4A.

What am I getting wrong?
if that 100w panel is truly giving 100% to controller at 22,5 V.. it will give your 12V bank around 7A of charge rate in a perfect world.. so the reference to 6A is realistic

It is math , take loss into equation.. 100 watt panel is not 100% efficient, the wiring gauge, lenght is a huge factor once you stack panels.. blah blah..

Some will series panels to have extra volts with the same amps going into controller as it may be a better configuration but sun exposure to the panels is just as big and confusing to some...
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Old 04-11-2020, 07:26 AM   #8
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Quote:
Originally Posted by Brianna View Post
Pioneer,
I figured a 100W panel with an approximate OC voltage of 22.5V would produce only about 4A.

What am I getting wrong?
100 watts ÷ 12.6 volts = 7.9 amps.

Charging takes some voltage. 100 watts ÷ 13.5 volts = 7.4 amps thru a MPPT Controller.

MPPT controllers convert high volts from the panel to usable voltage to the batteries.

PWM controllers clip off any volts above usable, wasting them.

That's parked on the equator, at high noon, on a perfectly clear day.
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Old 04-11-2020, 08:58 AM   #9
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Quote:
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When one thinks about a 40 Amp MPPT Controller, should one be thinking of 40A being the most that can come in or the most that can come out?
Answer - controllers are spec'd for battery amps. They have a limit on input watts from the panel too but the point of MPPT is to adjust the impedance the panel sees so that it is always delivering the most watts (not the most voltage, or most current) it can for the illumination it has any given second.

You can never get more _power_ from something than you put in. There can be voltage and current conversion but the power (minus efficiencies) will be the same. A controller cannot deliver more power than what the panel provides.

Solar panels are not linear devices. A "100W" panel only produces (under spec'd conditions) 100W at a particular matched load where the voltage times current equals 100W. At both lighter and heaver loads the delivered power will be less. This is the premise that an MPPT controller operates - it adjusts the load the panel sees to always keep the voltage and current points where power delivery is maximum, constantly adjusting for the amount of light hitting the panels and ambient temperature.


Here's a pretty good illustration of panel output and loading:

https://cdn.shopify.com/s/files/1/25...15144934584182

Quote:
60A controller slam more amps into the batteries, or at a faster rate, than a 40A controller using the same battery bank and the same solar panels?
No. A controller cannot have more output power than input power.

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Old 04-11-2020, 09:54 AM   #10
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^^^ True.

However, if the panels are capable of maximizing the services of a 60A controller, it would be a waste of panels to install a 40A controller. We don’t know the size of the proposed array. Even if they are starting with 640W and planning to expand to 1280W later, it would make sense to install a larger controller now.

A 60A will charge faster than a 40A on a coach that is parked in Tucson on June 20th, with 1280W solar and a 600Ah battery bank.
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Old 04-11-2020, 10:08 AM   #11
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As long as the peek output of the panel does not exceed the controller rating, a larger capacity controller will NOT produce more power.

The controller manages power, does not make it. BUT some controllers by their technology will be more efficient and transfer greater power.

What I do not like about most controller is the very light weight connections. They are just being cheap.
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Old 04-11-2020, 11:04 AM   #12
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If you're trying to size your controller to your PV array, I'd just use this Victron calculator:

https://mppt.victronenergy.com/

In the case of a Victron MPPT controller, I do know that you can feed in more amps than it's rated for, and it will just clip off the top and only output the rated amps to the battery.
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Old 04-11-2020, 11:42 AM   #13
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Thanks everyone.

This is where i'm at right now:

My existing EPEver 40Amp MPPT controller can take in up to 150V and a maximum of 530 watts from the PV array.

Soooooo.....
I think I will go with (5) 100 watt panels in series which will be about 100VDC and only 500 watts on that equator day I have planned for June 20th.

Since I only have about 500 usable Ah of storage in the batteries (for now) this should be a good step 1.
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Old 04-11-2020, 12:35 PM   #14
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...So, in other words, can a 60A controller slam more amps into the batteries, or at a faster rate, than a 40A controller using the same battery bank and the ***same solar panels***?...

Answer = NO.

The 60a controller can handle a larger PV array than the 40a controller, so if a larger PV array then can charge at a faster rate.
Quote:
Originally Posted by Brianna View Post
I have read books.
I have watched videos.
I have experience with residential and marine wiring.

But I can't get a definitive answer to the following question.

When one thinks about a 40 Amp MPPT Controller, should one be thinking of 40A being the most that can come in or the most that can come out?

So, in other words, can a 60A controller slam more amps into the batteries, or at a faster rate, than a 40A controller using the same battery bank and the same solar panels?
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