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zeer avatar image
zeer asked

Using BlueSolar MPPT 100/30 to keep a PV panel at its MPP and dump power onto dummy load

Hi.


For a project, I need a device that can set and keep the operating point of a PV panel at its MPP at all times and dump the power onto a power resistor; the PV panel intended to be used in this project is the BlueSolar SPM043602402.


For this, I was considering using the BlueSolar MPPT 100/30. I was thinking of setting the constant current of the bulk stage at 20A and the constant voltage of the absorption stage at 24V (since the charging algorithm is programmable) while connecting a 1 ohm 500W power resistor across the charger battery terminals.


I believe that by doing so, the charger will operate at its bulk stage at all times (the voltage at most gets to 20V but never to 24V, so the absorption stage is not initiated). Therefore, it delivers maximum possible current (maximum possible power) to the load at all times, keeping the panel at its MPP.


Can I use the BlueSolar MPPT 100/30 in this manner?

MPPT SmartSolar
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kevgermany avatar image
kevgermany answered ·

The MPPT is designed to output to a battery, not a resistor

It tracks max power point by analysing/optimising PV power every few minutes. During this period output is not constant and drops.

You cannot set an output current, the MPPT output is basically a combination of PV power and battery acceptance.

Sorry, it's not going to work.

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Alex Pescaru avatar image
Alex Pescaru answered ·

The problem is in fact maintaining a voltage close to that of a battery at the battery terminals in order for the MPPT to have from where to power itself and start working.

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zeer avatar image
zeer answered ·

Hi @Alex Pescaru

Can't the MPPT charger be powered on by the solar panel in the setup I am describing?

Once the MPPT charger is on (by connecting a battery and solar panel), does the MPPT charger use both sources to keep it powered on or does it only rely on the battery to keep it powered on? If it does relies on both sources (battery and solar panel), would disconnecting the battery the MPPT charger powers on and "instantly" replacing it with a power resistor keep the MPPT charger powered on?

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Alex Pescaru avatar image Alex Pescaru commented ·


Experimentation is the heart of progress... :-))

I believe that I've read somewhere that there are some versions of the MPPTs that starts even if the battery is dead. Don't know what that mean, from voltage point of view, but you may try to find them.

Indeed, you could rely on others advice, but, at least in my case, it can be far removed from the truth. :-)

LE:

From SmartSolar brochure:

Fully discharged battery recovery function
Will initiate charging even if the battery has been discharged to zero volts.
Will reconnect to a fully discharged Li-ion battery with integrated disconnect function.


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JohnC avatar image
JohnC answered ·

@zeer

To keep the panel at Vmp you won't be able to limit the mppt's output in any way. It needs to exceed what the panel can deliver before it will track. So for a 360W panel and 30 Amp mppt you'll need to be feeding something that will hold up >12V and accept the full 30A.

It tracks only every 10 minutes, so consider that when you put this together.

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zeer avatar image zeer commented ·
Hi @JohnC

Will what I am trying to accomplish work (keeping the solar panel operating point at MPP) if I used a DC electronic load operating in CV mode?

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JohnC avatar image JohnC ♦ zeer commented ·
@zeer

I don't know. It may work better with a buffer (like a small battery) in between the mppt and load.

One other little thing.. You mentioned a Bluesolar mppt. The equivalent Smartsolar will allow you to graph what's happening on your phone. Watching Panel V and A when it's tracking might interest you.. I call it the 'triple dip'..

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