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Forum Index : Electronics : Another MPPT controller

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poida

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Posted: 09:05am 16 Nov 2021
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  Murphy's friend said  

Pin 6 @ 7 of the FOD3182 are linked by a PCB track.


good. This rules out #3 in my list of worries
wronger than a phone book full of wrong phone numbers
 
poida

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Posted: 09:11am 16 Nov 2021
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  Murphy's friend said  

I  did the 'E' and 'F' cal. amps set up with 8 Amps flowing through the allegro sensors in the right direction. I used the nano display to show that, did not think of measuring the sensor output voltage directly but will do that next.



With this 8 Amps, I want to see the LCD show something like 8 Amps
Any large number will do for now, but I guess you have already calibrated it to
some degree.

And one more thing:
You can choose a mode of operation while in the menu.
You can choose "calibration" mode.
This will disable PWM and mppt search etc. to just run while showing
the voltages and currents and temperatures.
Make sure that is not enabled too, next time in the menu.
wronger than a phone book full of wrong phone numbers
 
poida

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Posted: 09:19am 16 Nov 2021
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  Murphy's friend said  OK, While I have been sitting here watching that CRO trace something in the nano woke up and the pulse tops are  up to 50us wide at times. Output power shown is around 55W and 1A Iout which tallies with the battery voltage.

I ran the batteries down a bit before that to entice charging but that is quite poor at present. How much charge current could I expect with nearly full width PWM pulses?


AS a rough guide the mppt will find the best input voltage that gives the highest output power and run at that.
It depends on the input voltage/current/power and the battery voltage and the
battery target voltage.

In my case my battery needs only 10 Amps or so to take it from 52 to 54V
when it is nearly 100% charged.

Lithium probably will need a lot more than that to bring it up from 52 to 54V

The mppt controller will not produce an output much more than the target voltage.
Maybe 0.1V more now and then.

At 3pm at your place I expect maybe 90V and 10 Amps (if cloudy) as a possible max power.
That's 900W, or about 18 Amps at 50V output.
Efficiency will be 92 to 95% most of the time.

The mppt is basically a power IN = power OUT minus 5% sort of device
when it has a load that keeps the output voltage lower than the target voltage.
wronger than a phone book full of wrong phone numbers
 
Murphy's friend

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Joined: 04/10/2019
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Posted: 07:18am 17 Nov 2021
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  poida said  

The Gate should show about 15V pulses compared to the FET's Source pins
which is the inductor connection.



Its working now, simple problem but it took a while to find. I blame old age and reduced eyesight for selecting a 2K7 instead of a 270R resistor in series with the FOD3182 LED.

Still have to re calibrate the current sensors, they show around 3 times of what's actually the charging current. Their output is in the correct (going positive) direction though

I'll let it run like this on the bench for a while.

A question: the fourth line shows MPPTxx, the Absorb voltage, then a 3 digit number that changes up or down a little (what does that indicate?) and last are 3 dashes.
 
poida

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Posted: 08:24am 17 Nov 2021
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beauty! I was beginning to wonder where you are and a visit to just get it working..
(oh, W.A. A $2K flight one way...)
But it was the low current drive to the opto-coupler diode.

Recalibration of current sensors is very important.
Do you have a cheap DC current clamp meter such as
a Uni-T UT210E. Quite useful.
But there are other ways to calibrate (see previous posts)

The 4th line shows with the 3 digits the PWM width in clock pulse units.
It's not important for anyone really, but I liked to see it.

the last 3 dashes show when it's in MPPT mode.
Once the battery gets up to near the target voltage, it changes to
ABSORB and then it shows the absorb time or FLOAT time.
wronger than a phone book full of wrong phone numbers
 
Murphy's friend

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Posted: 10:21am 17 Nov 2021
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Yes, I'm sure you would enjoy that expensive visit to Perth , you could even leave your mask back home (if they let you in)   .

I do have a reasonable clamp meter, it does AC and DC current which I used for the current measurement.

A somewhat different method (than a fence wired brick in a bucket of water) is used for a high current load, in case you are interested:
A big 12V lithium battery powers a cheap 12V inverter. I select the 12V current by plugging in different 230VAC light globes. A 100W flood light gives me 8Amp at battery voltage. I could even fine tune that with a Variac.

Thank you for the 4th line info, I'm the curious type if you didn't guess that already.
 
Murphy's friend

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Posted: 10:05am 19 Nov 2021
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Mounted on the wall and working now. Here is what it looks like:



A closeup of the display, late afternoon and only a small charge going in my batteries:



Now I have to wait for a hot sunny day to see how it *really* performs
 
poida

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Posted: 09:21pm 19 Nov 2021
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This is good to see.

When it gets some sun and a battery in need of a charge, it will
put out up to 45 Amps until:
1 - the battery voltage gets to the target voltage
2 - the heat sink gets too hot and it needs to reduce current
3 - not enough coming from the panels

Further details of what is shown on the LCD.

The star next to the output voltage means the controlling is
due to battery voltage being equal to the target voltage.

You might be lucky soon to see instead a star next to the
output current, this means output is now limited by
the max current setting, 45 Amps.

If instead you see a '!' next to the output current, then
the heat sink temperature is very high and it is now limiting
the output current.

I forget if you have built fans in this.
But when the heat sink has the fan commanded to be running
you will see a star in front of the heat sink temp.
Same for the toroid temp.
wronger than a phone book full of wrong phone numbers
 
Murphy's friend

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Posted: 07:20am 20 Nov 2021
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Thank you for that info Poida, I was wondering what that star meant.
Here is what I got this morning, I think I can add another 500W of solar panels before reaching the 50A current sensor limit (I set 'L' to 50.00) .



You may notice the low temperature readings, these had me confused until I worked out the sensors read backward. I replaced the thermistors with 10K trimpots, at 10K I get around +25 degree displayed. Reducing the trimpot resistance (as a NTC sensor does when it gets hot) shows a decline of the temperature readout.
The heatsink got barely warm with the 42Amp current.

Following the thermistor connections on your schematic was not easy and I am wondering why there is a choice of the pull up or down connection. I'm sure you had a reason but I can't think of it. To me, connecting one side of the thermistor to ground and pulling the other side up via a voltage divider would be all the program requires?

You can see on the schematics I posted earlier how mine is wired, I set '3' on the menu to 0.
Please advise what I did wrong so I can get that temperature readout  show the real thing.

You also mention a "fan ON and fan OFF temp setting in the menu which I left as your default settings.
BTW. I cannot find how you drive the fan on your schematic so I run mine independently of the nano with its own fan control module (this has its own NTC sensor as well).
 
poida

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Posted: 10:17am 20 Nov 2021
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The 10K NTC thermistors according to your schematic have one wire going to ground.
That means "3" menu needs to be 0 (zero)
If you have that in place already and you see -5C then something is wrong.
No idea what right now.
It's always best to play with the NTC inputs with a 10K pot and see how it performs
to get a feel for it.
8.2K = 30C
6.7K = 35C
5.6K = 40C
3.9K = 50C


50 Amps is for sure no problem.

If the voltage and current inputs are calibrated well, maybe to the nearest 0.2V
and 0.2 Amps then this mppt controller is doing a good job of converting the
62.8V at 37.1 Amps input into something the battery can handle.

62.8 x 37.1 = 2330 Watts input
54.5 x 41.0 = 2235 Watts out
efficiency is output / input which is
2235/2330 = 96%
Only 4% is lost as heat
95 Watts heat, distributed across the inductor and heatsink mainly


In your case there is no fan control from the firmware so we can forget about that stuff I mentioned above. It's up to your separate fan control system.

But the heat sink temp could cause the output current to be reduced should it
get hot enough. It depends on your settings for "A" and "4"
"A" is the max HS temp and should it get to that, output current limit will be
limited down to zero.
"4" value is where the output current starts to be reduced from 50 Amps.

So you maybe give a value of 50 deg C for "4" and maybe 65 deg C for "A"
This will mean output current will start to be limited to less than 50 Amps
at 50 C and by the time it gets to 65 C output current will be limited to zero Amps.

I made the brainboard able to handle NTC connected to 5V and to ground
selected via a jumper because Nicks board has the NTC connected to ground
and Wiseguy's boards have them connected to 5V
The brainboard had to handle both cases. My 2 mppt controllers use Nicks' boards
Edited 2021-11-20 20:29 by poida
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wiseguy

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Posted: 02:52am 21 Nov 2021
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  poida said  
I made the brainboard able to handle NTC connected to 5V and to ground
selected via a jumper because Nicks board has the NTC connected to ground
and Wiseguy's boards have them connected to 5V
The brainboard had to handle both cases. My 2 mppt controllers use Nicks' boards


Where the two thermistor locations are on my PCB, there are 3 pads, if you use the two pads located within the yellow square labelled as +5 then the thermistors are connected to +5V and as Peter stated you have to use the correct menu option and link the two 10K resistors as pull downs on Peters board.

However if you install the thermistor using the centre of the 3 pads and the pad just adjacent outside the yellow square then the Thermistor is connected to Ground and will behave just likes Nicks board, that is you use the two 10K resistors on Peters board (P4) as pull ups.

When I looked at your schematic Murph it appears that you also have thermistor pull ups on your power board.  I think they should be removed, as with links on Peters brain board in either position or even with the link removed, all combinations will result in misleading temperature readings ( the link removed will give  almost normal results with a bit of error).  The best solution is to remove the two pull ups for the thermistors on your power board.  If that is too difficult to do, then removing either R8 or R9 on Peters brain board and not installing the P4 link or removing both R8 & R9 & then it doesnt matter if the link is installed or not in either position, should get your temperatures reading correctly.
Edited 2021-11-21 12:59 by wiseguy
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
Murphy's friend

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Posted: 04:11am 21 Nov 2021
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Thank you for that input wiseguy. FYI, I made my own PCB's and there is NO thermistor connection or track for them on the power board at all. The thermistors plug straight into my (own style) brain board where the pull up resistors are also located.

I did not like the 10 way ribbon cable idea so all my brainboard inputs are via individual shielded cables. The thermistors are re cycled ones at the moment but I also have new ones and will try them out shortly.
BTW, I did like your PCB power board layout and mostly copied it (minus the 10 way ribbon cable socket) .

I got confused by that odd way to connect the thermistors, it was obviously done to suit some  else's thermistor arrangement as well. When I did my brain board artwork I was not yet fully aware why that system was used.
 
wiseguy

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Posted: 04:34am 21 Nov 2021
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Aha. I should have looked at your schematic more carefully - I didn't realise that you had made your own brain board as well. Have you fixed the temperature errors yet or is it still a work in progress ?  I would be interested to know what caused the issue.
If at first you dont succeed, I suggest you avoid sky diving....
Cheers Mike
 
Murphy's friend

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Posted: 04:49am 21 Nov 2021
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Yes, its fixed now. Cause? another senior moment at the menu inputs .
Enough said

This MPPT rocks. I saw 50Amps charging this morning, over 2.7KW!
Heatsink barely warm to touch, now with the NTC's reading correctly I get more accurate figures next full sunshine morning. It looks like the fan might get bored doing nothing in this unit.
The 1oz PCB tracks also have no problem with the 50 Amps,  thanks to that good layout wiseguy .
 
poida

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Posted: 10:25am 21 Nov 2021
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good hear this further progress, again.

With the massive heatsink you have used, I suspect it's just a matter of learning
how your build works during a day of good sun and solid charge currents.
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Revlac

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Posted: 12:25pm 21 Nov 2021
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Nice work Murph, Also The explanation that Peter and Mike have posted is great and will help in completing the one I'm working on.
Cheers Aaron
Off The Grid
 
Murphy's friend

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Posted: 02:21pm 21 Nov 2021
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Thank you Aaron, I wish I had those explanations before I started but then I probably would not have learned as much about what makes a MPPT tick.
 
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