Diy mppt? - Page 10

Xringer · 01-02-11, 08:40 AM

Quote:

Originally Posted by fabieville

Its not from the inductor it was happening before i add it in so i am guessing its the fet and the pv panel already have the big cap across the output so what else should i do?

Also what can i do to protect the input and the output of the circuit if they are shorted?
Should i just add a high amp blocking diode that is above my PV short circuit current on both sides of the circuit?

Sometimes, larger foil caps have some inductive reactance and that can make them react more slowly than, other types, like Tantalum capacitors..
Try some Tantalum caps around 47uF or more. (Remember the voltage rating).
They might help a little.

Don't put diodes in series with your current flow. That will cause a voltage drop and power loss.
You might want to add a fuse at the battery, because it can be a source of massive current flow during a short.
Your panels will never put out more than about 130% of their rated power.

fabieville · 01-02-11, 08:45 AM

What if i accidentally shorts the input or the output what will happen?
Will it damage the fet?
I know the fet suppose to have a internal protection diode am I correct?

Xringer · 01-02-11, 10:35 AM

If you short the input to the mini, the source will supply as much current as it can.
If that's a solar panel, it might supply about 8A across the short.
But that should not hurt the FET. (Since it's not going into the FET, but into the short).

If you short the output of the mini, that will cause the board to deliver every amp the PV can provide to the short. (heating it up).
But, if it's about 8A, the FET should be fine. It should be rated to match your panel(s).
(If you are using a 20A FET and have 50A coming from your panels, kiss the FET goodbye).

However, if that shorted output is also shorting out your batteries, and you have no fuse,
your battery will try to melt the short in half. It can make your wedding ring glow a dull cherry red and sink right down to the bone.
(Yes, you might need to have the finger amputated).

That's one reason why you might want to put a fuse on your battery terminal..

I don't know what's inside the FET you are using. I have some docs, but have not
had the time to read them.. Sorry..

fabieville · 01-02-11, 08:23 PM

If i want to upgrade the mini max so that it can operate on 2 setpoints and switch between them depending on the light condition for eg. 15V to operate on low light and 18V when the sun is at its peak on the panel, what should i do to accomplish this?

Xringer · 01-02-11, 10:54 PM

Quote:

Originally Posted by fabieville

If i want to upgrade the mini max so that it can operate on 2 setpoints and switch between them depending on the light condition for eg. 15V to operate on low light and 18V when the sun is at its peak on the panel, what should i do to accomplish this?

That's what is called automatic MPPT.. The mini-max is Manual Power Point Tracking..

If you have it set for 15V, then it's going to be at 100% duty cycle at 18V.
Why would you want to pulse it at full sun?
Unless your load is a very low resistance, (That can pull a weaker PV down),
it doesn't seem logical to be pulsing the power off and on.
When it's off, no power will be delivered. Is your load almost a short circuit?

Anyways, if you really want to try something, you might try putting a photocell across the resistor above the pot.

A bit like it's used in this circuit. As brighter sun hits the photocell, it's resistance gets lower,
increasing the + voltage going down to the comparator input.

Photocell based night light by ua741 | Circuit Project Electronic
Might take some tinkering or adding a pot in series with the photocell, but
it might be able to give you a useful self-changing set-point..
Here's your chance to build something really cool..

If the photocell goes too low in resistance and increases to setpoint too much,
it might be easy to adjust it by putting a paper filter over the photocell
to reduce it's resistance drop (in bright sun).
Or by painting over part of the light window of the sensor.

fabieville · 01-03-11, 01:55 AM

the only problem with the photocell is that the circuit has to be outside which will cause losses.

Xringer · 01-03-11, 08:00 AM

Well, you could place it outdoors and run a cable out to it..
You could use some old TV coax cable..?.

Xringer · 01-08-11, 09:52 AM

I found an interesting paper about using comparators.
It does a pretty good job explaining Hysteresis. Good design info.

Analog Devices: Analog Dialogue: Curing Comparator Instability with Hysteresis

It also comes in pdf.. http://www.analog.com/library/analog...omparators.pdf

fabieville · 01-23-11, 01:51 PM

On the mini max site it stated that the speed of the maximiser's oscillations could be doubled by increasing the 100K resistor to 220K. If i double the oscillation speed will i get better performance or more efficiency for charging my battery?

fabieville · 01-23-11, 03:12 PM

The thin film panels have a high VOC typically about 70Volts and the current rating is about 1amp and they are used for grid-tie installation.

I was wondering if it was possible to build a circuit that would take that high voltage input and step it down to about 18V and step up the current at the same time typically like how the MPPT circuits operates so that it can charge a 12V battery?

Because if you look on how a advance MPPT circuit operates, it can charge a 12V battery off a 24V or 48V panel by dropping the panel voltage down to the charging voltage of the 12V battery and increase the output current at the same time. So i was just wondering what is your comment on this. Is it possible to build such a circuit?

Reason why i ask this is because these panels are very cheap. I see them on the internet for as low as $60 and it would be quite economical if you could use them to charge a 12V battery.

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01-02-11, 08:45 AM	#92
fabieville Helper EcoRenovator Join Date: Dec 2010 Location: Jamaica Posts: 59 Thanks: 0 Thanked 0 Times in 0 Posts	What if i accidentally shorts the input or the output what will happen? Will it damage the fet? I know the fet suppose to have a internal protection diode am I correct?

01-02-11, 10:35 AM	#93
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	If you short the input to the mini, the source will supply as much current as it can. If that's a solar panel, it might supply about 8A across the short. But that should not hurt the FET. (Since it's not going into the FET, but into the short). If you short the output of the mini, that will cause the board to deliver every amp the PV can provide to the short. (heating it up). But, if it's about 8A, the FET should be fine. It should be rated to match your panel(s). (If you are using a 20A FET and have 50A coming from your panels, kiss the FET goodbye). However, if that shorted output is also shorting out your batteries, and you have no fuse, your battery will try to melt the short in half. It can make your wedding ring glow a dull cherry red and sink right down to the bone. (Yes, you might need to have the finger amputated). That's one reason why you might want to put a fuse on your battery terminal.. I don't know what's inside the FET you are using. I have some docs, but have not had the time to read them.. Sorry..

01-02-11, 08:23 PM	#94
fabieville Helper EcoRenovator Join Date: Dec 2010 Location: Jamaica Posts: 59 Thanks: 0 Thanked 0 Times in 0 Posts	If i want to upgrade the mini max so that it can operate on 2 setpoints and switch between them depending on the light condition for eg. 15V to operate on low light and 18V when the sun is at its peak on the panel, what should i do to accomplish this?

01-03-11, 01:55 AM	#96
fabieville Helper EcoRenovator Join Date: Dec 2010 Location: Jamaica Posts: 59 Thanks: 0 Thanked 0 Times in 0 Posts	the only problem with the photocell is that the circuit has to be outside which will cause losses.

01-03-11, 08:00 AM	#97
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Well, you could place it outdoors and run a cable out to it.. You could use some old TV coax cable..?.

01-08-11, 09:52 AM	#98
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	I found an interesting paper about using comparators. It does a pretty good job explaining Hysteresis. Good design info. Analog Devices: Analog Dialogue: Curing Comparator Instability with Hysteresis It also comes in pdf.. http://www.analog.com/library/analog...omparators.pdf

01-23-11, 01:51 PM	#99
fabieville Helper EcoRenovator Join Date: Dec 2010 Location: Jamaica Posts: 59 Thanks: 0 Thanked 0 Times in 0 Posts	On the mini max site it stated that the speed of the maximiser's oscillations could be doubled by increasing the 100K resistor to 220K. If i double the oscillation speed will i get better performance or more efficiency for charging my battery?

01-23-11, 03:12 PM	#100
fabieville Helper EcoRenovator Join Date: Dec 2010 Location: Jamaica Posts: 59 Thanks: 0 Thanked 0 Times in 0 Posts	The thin film panels have a high VOC typically about 70Volts and the current rating is about 1amp and they are used for grid-tie installation. I was wondering if it was possible to build a circuit that would take that high voltage input and step it down to about 18V and step up the current at the same time typically like how the MPPT circuits operates so that it can charge a 12V battery? Because if you look on how a advance MPPT circuit operates, it can charge a 12V battery off a 24V or 48V panel by dropping the panel voltage down to the charging voltage of the 12V battery and increase the output current at the same time. So i was just wondering what is your comment on this. Is it possible to build such a circuit? Reason why i ask this is because these panels are very cheap. I see them on the internet for as low as $60 and it would be quite economical if you could use them to charge a 12V battery.