Diy mppt?

[fabieville]

the mini maximizer circuit according to what i read about it is that its basically a large capacitor across the panel which can be connected by an electronic switch to the motor.So like how i already have a very large cap (12,000uf 63V) across my PV and connected down at the bottom just at where my pv would be connected to my charge controller would it give me the same results as the circuit would give me so basically adding the mini maximizer would not make sense? or does the mini will deliver more power to my battery/motor than my big cap that i have now?

[Xringer]

A capacitor alone won't gain you anything. It will smooth out the way a system operates.

The idea of the mini-maximizer board, is to get more power into heavy loads,
during weak sunlight conditions. Like starting up a big pump motor in the morning, with weak sun.

If a panel is connected directly to a motor and the sunlight is weak, the motor can't get going.
It just gets a little warm.

But, if the FET stays off for a while, and the PV charges up a little batch of power in
the input capacitor..?.
And then the voltage on the cap goes up to a max value. (Near PV open voltage).
Suddenly the higher voltage is seen by the comparator, and it switches the FET on!
The stored power is sent (High voltage and all) to the motor..
That starts the motor moving.. Once it's moving, it's easier to keep it moving..

So, high power(watts) is delivered to the motor in time slices. Little pulses. Repeating spikes of power.

Because the voltage is so high, the load can absorb more energy.
What lights up a bulb brighter? 6V or 12V??
More energy delivered over time means higher efficiency..

The energy is measured in watts.. Volts times Amps..
If you have 15A and 0.1 volts, you have almost nothing in power..
But, if you have 10A and 20 volts, you've got 200 watts..
The mini-max gets the voltage up..

It allows the panel to put out it's full rated power, but in short pulses.
Once the sun gets full on the panel, the pulses get longer.
At full sun, the FET should stay on all the time..
(Unless the load is too heavy. Like 2 ohms or a short).


~~~

If you can understand the above, then you can see how higher voltage
can be obtained from a PV in bad light conditions.
And, if you were to be charging a battery?
High voltage pluses is going to work pretty well. A lot better than direct connection..

[fabieville]

ok thanks for the very good explanation. On the circuit the output negative lead is from the drain pin foot of the fet? because i am using the mini to charge my battery and i did not put in the fast diode at the output

[Xringer]

Yeah, that's the drain on the negative side of the PV input.

Installing a diode across the output capacitor is a good idea, since there will be
some small inductive reactance in your cables.
It's reversed-biased, so it's not going to affect your battery at all.

Diodes don't have hardly any reverse leakage. Just hook an LED up backwards,
no light or current at all.. Ever.. It's a quantum mechanics thing that diodes do..

[fabieville]

I made the original mini maximizer circuit yesterday using the IRFP150N fet and i replace the 2k trimpot with a 5k trimpot because i could not source the 2k one and i did not put in the SF52 superfast diode at the output as i did not think it was necessary as i would be using the circuit to charge a battery instead of powering a pump. But when i run a test on it I could not get one part to operate like how the guy on the site said it should. This is what you must do for the testing according to the website:
connect a 12V battery to the solar input. Now check the voltage across the 6.2V zener diode (Z1). This should be roughly 6.2 volts. Set the trimpot to its mid point and measure the voltage between the trimpot centre leg and the sol- terminal. This should be about 6V. Turn the pot fully anticlockwise, then measure the voltage across the 15V zener diode (Z2). It should be about 11V indicating that the switch to the motor is turned on. Turn the pot fully clockwise. The voltage across the zener should now be less than 1V indicating that the switch is off. If you can get it to perform like this, then try it on the real thing.
I did all the steps but when i am testing the 15V zener diode i get the 11V but when i made an adjustment on the trimpot i am still getting the same 11V. It doesn't matter which direction i go with the trimpot the value for the 15V zener doesn't fall below the 1V as specify by the site that if you turn the pot fully clockwise it should fall below 1V.

Could you please tell me what i did wrong. I trace back the circuit and made sure all connections are accurate and check for any shorts and everything is correct so far. So I am wondering if is because i used a 5k instead of the 2k trimpot making my testing not going how it should. Also I did not put the fast diode at the output. So could that cause an effect on the circuit? I also replace the (2) 470uf 50V caps on the input with a (1) 680uf 200V cap. Please tell me if my adjustments where wrong and which one should be corrected. I even made the circuit on a software (circuit design suite 11) and i get to insert the right trimpot which is 2k but i did not put in the fast diode at the end again as i did not think that was necessary and i run a simulation test on the software but i still cant get the 15V zener diode to read less than 1V. So please tell me what is wrong or what do you think? I am anxiously waiting for your response.

[Xringer]

The fast diode has nothing at all to do with this problem.
As I said before, since it's installed backwards (reversed bias), it's invisible to the normal
operation of the circuit. It only works if you were to have back-EMF from a motor/inductor.

Guess #1.
It sounds like your comparator isn't switching. Check Pin 2 (Pot tap line) to make sure
that it's voltage is going up and down when you turn the pot CW & CCW.
If Pin voltage isn't changing, you are using the wrong pin on the pot.
If it is changing, then check the exact voltage change.
It MUST change above and below the reference voltage (6.2v) on pin 3.
If it's not changing above and below 6.2, it's not going to switch the FET.


Guess #2.
If it wasn't guess #1, then check your output wiring. The 15V zener on pin 7
is to protect the gate from high voltage (from the 1k5 pullup resistor).
If the wiring is all correct, change the chip. The LM311 might have been
zapped by static, or was bad from the box..

The grounds on Pins 1 & 4 are switched to the output pin(7) to pull down
the voltage. (Supplied by the 1k5 pullup resistor).
That 'Low' turns off the FET.

I'll be around this afternoon, let me know what you find.

Happy Holidays,
Rich


Linuxfromscratch.dk

[fabieville]

ok i am going to try your suggestions. by the way the pot that i used(5k) would it cause some effect on the circuit and also the 680uf cap 200v on the input??

[fabieville]

I did your Guess #1. step
It sounds like your comparator isn't switching. Check Pin 2 (Pot tap line) to make sure
that it's voltage is going up and down when you turn the pot CW & CCW.
If Pin voltage isn't changing, you are using the wrong pin on the pot.
If it is changing, then check the exact voltage change.
It MUST change above and below the reference voltage (6.2v) on pin 3.
If it's not changing above and below 6.2, it's not going to switch the FET.

When i did the above step i got it going all the way up to 6.83V and going all the way down to 6.17V
By the way when you said check pin 2(pot tap line) you mean pin 2 on the ic and then the next tester lead should go to ground comings from the input? because that was how i did it and got the results above.

[Xringer]

Originally Posted by fabieville

ok i am going to try your suggestions. by the way the pot that i used(5k) would it cause some effect on the circuit and also the 680uf cap 200v on the input??

The pot being smaller will limit the voltage range you can get,
the input cap size change will make no difference to comparator or FET operation.
Depending on your PV voltage and power output, the input cap will
have some effect on over-all circuit performance.
A smaller cap will not be as effective.

[Xringer]

Originally Posted by fabieville

I did your Guess #1. step
It sounds like your comparator isn't switching. Check Pin 2 (Pot tap line) to make sure
that it's voltage is going up and down when you turn the pot CW & CCW.
If Pin voltage isn't changing, you are using the wrong pin on the pot.
If it is changing, then check the exact voltage change.
It MUST change above and below the reference voltage (6.2v) on pin 3.
If it's not changing above and below 6.2, it's not going to switch the FET.

When i did the above step i got it going all the way up to 6.83V and going all the way down to 6.17V
By the way when you said check pin 2(pot tap line) you mean pin 2 on the ic and then the next tester lead should go to ground comings from the input? because that was how i did it and got the results above.

I'm using this image for reference. Pin 2 refers to pin 2 on the IC.

All measurements should be made with the black meter lead to ground/negative from the PV panel.

This Euro-style diagram does not clearly show the output connections
on pin 7 of the IC, and uses an oddball looking Pot drawing (no arrow).
Which is some of the reasons, I drew my own diagram.

If your reference voltage on pin 3 is 6.2v, and you can change the voltage
on pin 2 from 6.17 to 6.83 volts, the output (pin 7) should be switching.

BUT, that's not a very big voltage range.
Maybe if you put a 1K in place of the 3K3 under the trim pot,
you would get a bigger voltage range on the
5K pot's tap* line, or center (movable) connection.

*Note:
By center-tap or pot tap line, I am trying to refer to the sweep arm
shown as Pin W on the pot in this American style diagram.