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Forum Index : Solar : Experimental Multi-Phase Solar MPPT Controller

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Warpspeed
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Joined: 09/08/2007
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Posted: 03:54am 17 Nov 2019
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Its interesting though, but many ancient long forgotten techniques can still come in useful sometimes.
Cheers, Tony.
 
Solar Mike
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Posted: 10:49am 17 Nov 2019
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Module PCB completed, its been a bit of a mission to get everything inside a 100 x 100mm board. I don't have a schematic for this yet, will do this in the next few days in between renovations tiling the bathroom and kitchen, as a way of checking there are no errors.

The white hatched area is covered by a nylon insulator then an alloy right angle for mounting the two mosfets, the 4 phase boards are stacked above each other bolted to a common heat sink - each designed for 30 odd amps.
High PV and Battery current connections are made with bus bars bolted to tin plated brass right angle pcb connectors that protrude from the edge of the pcb.
Buck inductor is wound on one of  These Cores.
The ribbon cable connector with control power (12v) and drive signals plugs into all modules, note its 0v line is isolated from the modules high current lines. Edit: (Just noticed an error on this cable connection, will fix it)

Top:


Bottom:



I need to make a mother board now with CPU etc, This will also have some larger Bulk input capacitors on the PV side, output ones don't matter so much here as the battery is a near infinite capacitor.

Cheers
Mike
Edited 2019-11-18 06:12 by Solar Mike
 
mackoffgrid

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Posted: 09:28pm 17 Nov 2019
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How many turns do you need on that core for 100uH?
 
Solar Mike
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Posted: 10:05pm 17 Nov 2019
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  mackoffgrid said  How many turns do you need on that core for 100uH?


You can work it out from their spec sheet, about 25T, waiting for items to arrive so haven't tested with my Inductor saturation curve tracer.

Mike
 
mackoffgrid

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Posted: 10:43pm 17 Nov 2019
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Thanks, yes I was showing my laziness  
 
Solar Mike
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Posted: 10:33am 18 Nov 2019
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Fixed my input stuff up, all 4 PWM phase signals are now on the ribbon cable, solder blob link on the pcb selects wanted input; this is fed into InA on the chip, InB is switched by a mosfet to get an inverted input, the chips dead time fixes any crossovers.

All changes on the top layer.


Note if the DW version of the UCC21521 is used, the PS1//2 can be changed to 12-12 volts, I'm using CDW variant as the DW doesn't seem to be available in small quantities.


Time now to draw up a schematic.
Cheers
Mike
Edited 2019-11-19 05:43 by Solar Mike
 
rogerdw
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Joined: 22/10/2019
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Posted: 12:50am 19 Nov 2019
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Fascinating thread Solar Mike.

Just so I get this straight  ...  this project takes the output from one PV array and charges one 48V battery  ...  but uses four separate modules to share the charging process ???

The reason for splitting it up between multiple boards is simply to reduce the size and cost of the Buck coil and associated components  ...  four small systems is much smaller, cheaper and easier to build than one large one ???

Cheers,  Roger
 
Solar Mike
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Posted: 04:38am 19 Nov 2019
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  rogerdw said  Fascinating thread Solar Mike.

Just so I get this straight  ...  this project takes the output from one PV array and charges one 48V battery  ...  but uses four separate modules to share the charging process ???


One PV Array, correct; the battery bank voltage can be anything you want really, I have optimized components for 48v, however there is no reason why you cannot use 12\24\48\96 etc.

The buck\synchronous rectifier modules are designed to be modular, as up to four can be used on the one host controller; they all share a common CPU host PCB (yet to be designed) for control. The host board has four 10bit resolution PWM outputs at 62 Khz, each output is on a different switching phase, so when combined the system is effectively equivalent to a 248 Khz PWM buck converter, but with a lot lower losses and better efficiency.


  Quote  
The reason for splitting it up between multiple boards is simply to reduce the size and cost of the Buck coil and associated components  ...  four small systems is much smaller, cheaper and easier to build than one large one ???


Each buck module is good for 30 amps (single layer PCB) although the mosfets are rated way higher than this. At 48v x 30 odd amps approx 1500 Watts, so depending on the size of your PV array, up to 4 modules may be used to extent the charge current as required.

On another thread "3Kw Controller" I designed one that would charge to a similar output 120-150 amps. The buck inductor weighs about 2kg and I had to import the bare cores from the USA, this makes it somewhat hopeless and expensive to build.
Big currents = high I^R losses and specialized components, smaller modules can use readily off the shelf cores that are cheap and easy to wind; if your array is only a couple of KW then only two modules can be used - much simpler in concept.

MPPT controllers have gotten cheaper over the past few years (the Chinese ones anyway) 60 amp auto switching 12/24/48v are available here in NZ for <$600, all well and good until they blow up and then become unfixable doorstops. This design I hope will will allow something to be DIY that can be repaired. I need 6 of these controllers, thus motive for designing my own.

If you can build your system with correctly match PV array to battery voltage then pure a PWM controller would be a better option and way less expensive to make.


Cheers
Mike
 
rogerdw
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Joined: 22/10/2019
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Posted: 01:06am 20 Nov 2019
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Thanks for filling in the blanks Mike  ...  it's always helpful when you hear the back story.

Took me a while to go through the other thread and I can see the reasoning behind the direction you're taking.


  Solar Mike said  
MPPT controllers have gotten cheaper over the past few years (the Chinese ones anyway) 60 amp auto switching 12/24/48v are available here in NZ for <$600, all well and good until they blow up and then become unfixable doorstops. This design I hope will will allow something to be DIY that can be repaired. I need 6 of these controllers, thus motive for designing my own.


Love the idea and will be excited to see the finished design. Pretty sure I could make use of the finished product too.

Being able to be fixed if it fails is huge as well. Staggers me the amount of expensive stuff that just ends up in landfill. On a good day I have sometimes repaired boards that cost $7-8000 to buy new. I probably don't charge as much as I should, but it's still an awesome feeling knowing that it wasn't all just trashed for want of a handful of parts and a days labour.


  Solar Mike said  

If you can build your system with correctly match PV array to battery voltage then pure a PWM controller would be a better option and way less expensive to make.


What are the ideal parameters eg for a 48V battery system.

In looking at available secondhand panels, there's quite a variation in output and open circuit voltage figures  ...  hard to know just how important it is to aim for one or the other.

Thanks again for all the insight.

Cheers,  Roger
 
renewableMark

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Posted: 09:26pm 20 Nov 2019
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  rogerdw said  

What are the ideal parameters eg for a 48V battery system.

In looking at available secondhand panels, there's quite a variation in output and open circuit voltage figures  ...  hard to know just how important it is to aim for one or the other.



If you want to Pwm try to get Max amps voltage close to 30v, so when you series 2 then you have 60v or so.

If you plan to use a fork battery it will likely have bulk absorb voltage of 57.6v, so you are not missing out on much of the peak power.

When it's at float @54v you are not using all the power on tap so it doesn't matter.

When you start drawing a load the controller will up the pwm cycle to keep voltage up to the 54v.
Many controllers will have a start charge process again voltage, so if it gets drawn down too far it will start at bulk then go through the routine from the start.

The little Mad Pwm board is great, but make sure you put in on a whopper heat sink and perhaps allow for fans.

Something like this is pretty good.



If you go mppt it doesn't matter as much, just check the specs of the controller

Edit, whoops, sorry Mike I shouldn't have got your thread off track like that.
Edited 2019-11-21 07:27 by renewableMark
Cheers Caveman Mark
Off grid eastern Melb
 
Solar Mike
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Posted: 10:05pm 20 Nov 2019
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  renewableMark said   ... Edit, whoops, sorry Mike I shouldn't have got your thread off track like that.


No problem there Mark, I was going to say much the same thing, 24 volt rated panels that have a Vmp of 30 volts are readily available up to 285 watt output; so two in series is a pretty good match for a 48 volt bank.

However the common used 4mm^2 cable in any length above 10 meters is only good for 18 amps before the power losses increase too much, means every 4 x 285w panels is a separate cable run; going to Mppt has advantages in that higher input voltages can be used with less current; so greater number of panels and power output per cable run, or longer distance.

But hey if you can get hold of second hand panels at cheap prices, then a little wasted power is of little consequence, sadly NZ doesnt have a second hand market of cheap PV stuff as there were and nor will be any subsidies for PV, so the uptake is pretty low.

Cheers
Mike
 
rogerdw
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Joined: 22/10/2019
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Posted: 06:57am 23 Nov 2019
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  Solar Mike said  
  renewableMark said   ... Edit, whoops, sorry Mike I shouldn't have got your thread off track like that.


No problem there Mark, I was going to say much the same thing, 24 volt rated panels that have a Vmp of 30 volts are readily available up to 285 watt output; so two in series is a pretty good match for a 48 volt bank.

However the common used 4mm^2 cable in any length above 10 meters is only good for 18 amps before the power losses increase too much, means every 4 x 285w panels is a separate cable run; going to Mppt has advantages in that higher input voltages can be used with less current; so greater number of panels and power output per cable run, or longer distance.

But hey if you can get hold of second hand panels at cheap prices, then a little wasted power is of little consequence, sadly NZ doesnt have a second hand market of cheap PV stuff as there were and nor will be any subsidies for PV, so the uptake is pretty low.

Cheers
Mike



Thanks for the confirmation of the ratings Mike.

Regarding cabling, I wonder if it's possible to pick up some heavy second hand cable to do some of those low voltage parallel runs to reduce the voltage drop. I bought some excellent priced multicore cable to run some dmx lighting once and saved hundreds.
 
Solar Mike
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Posted: 08:11am 23 Nov 2019
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  rogerdw said  ... Regarding cabling, I wonder if it's possible to pick up some heavy second hand cable to do some of those low voltage parallel runs to reduce the voltage drop. I bought some excellent priced multicore cable to run some dmx lighting once and saved hundreds.


Whatever you use has to be UV protected, the "solar" cable has a very thick tough  black UV proof insulation, would be hard to beat... I have used 6mm mains rated conduit wire in the past for long runs buried in the ground inside a plastic water pipe.

Mike
 
rogerdw
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Joined: 22/10/2019
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Posted: 01:38pm 23 Nov 2019
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  Solar Mike said  
  rogerdw said  ... Regarding cabling, I wonder if it's possible to pick up some heavy second hand cable to do some of those low voltage parallel runs to reduce the voltage drop. I bought some excellent priced multicore cable to run some dmx lighting once and saved hundreds.


Whatever you use has to be UV protected, the "solar" cable has a very thick tough  black UV proof insulation, would be hard to beat... I have used 6mm mains rated conduit wire in the past for long runs buried in the ground inside a plastic water pipe.

Mike


Makes sense  ...  I might make a visit to some of the local scrap yards and see what's lying around  ...  though I'm not going to flaunt the law too much in that area. Thanks.

Cheers,   Roger
 
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