Jaahn wrote:

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Hi Dorian 

Your search for knowledge is admirable  I do not claim any expertise in this area other than my reading and ownership.  I have said before that previous research has shown that lots or even most, of the cheap MPPT regulators are fakes. I have relied on other tests done in the past to compare some brands. But if you look at the size of the enclosures and the heat sinks for the units it is certainly obvious some units look and are sized like PWM regs. This applies IMHO to Australian retail offerings as well as Ebay. 

For a MPPT reg to work well it needs two functions. First function which you are pursuing, it needs to be able to take input at a higher voltage than the battery and 'convert' that to battery voltage and increase the current proportionally. That is the current gain promised by MPPT regs, but is actually just the 'buck' regulator, not the MPPT part.

The second function that is not mentioned in most advertising or elaborated on, is the actual MPPT part of the control system. There must be a 'smart' controller which will periodically 'test' the input and out put against some parameters and adjust the output to get the maximum current. This IMHO, is what sorts out a good unit that tracks fast and has a good program to extract the maximum power from the panel under all conditions and sun exposure. Indeed it is called Maximum Power Point Tracking. A poor quality unit has a very slow and clunky adjustment to the continuous changes of input and battery condition. Indeed the cheap ones probably do almost nothing in this area to track the maximum power point, or even actually nothing at all.

Of course after the battery has reached the set voltages the unit reverts to PWM regulation anyway. The extra power available is not used at all. 

Jaahn        

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Many of the mid range MPPT controllers use a ROM map and compare inputs to this topographical map to determine the best input voltage. It is not uncommon to see some MPPT controllers holding the input voltage at 16v, yet the true Vmp is down around 15v or less. This is the result of a limited range programmed into the ROM with 16v being the lower limit.

MPPT controllers that can perform both buck and boost function suitable for charging 12v batteries, AND, do it efficiently, are large and expensive, well beyond the average caravan set up. We use them in off grid house installs and there are some out there at very reasonable prices if you know what you are looking for as far as what to buy and what to avoid.

T1 Terry 

I've been trying to make sense of the Projecta range of solar controllers. AFAICT, there are no MPPT offerings in their range. In fact their web site makes no mention of the charging mode, except in some, but not all, instruction manuals.

Here is a 60A unit:
https://www.projecta.com.au/solar-panels-controllers-products/autautomatic-1224v-60a-4-stage-solar-charge-smart-controller

In this example the manual does refer to PWM technology, but there is no mention of it on the product page:
https://www.projecta.com.au/s/SC220-245-260-Instruction-Manual.pdf

Similarly, there is no mention of PWM or MPPT on the product page for the SC330D, or in its product manual:
https://www.projecta.com.au/solar-panels-controllers-products/automatic-1224v-30a-4-stage-solar-charge-premium-controller-with-remote-control
https://www.projecta.com.au/s/SC320-330-Instruction-manual-brx5.pdf

However, there is an indirect reference to "Mode:PWM/MPPT" in the "Real-time monitoring" flowchart in the manual for the remote control unit:
https://www.projecta.com.au/s/SC300D-Instruction-manual-93yp.pdf

But ... the recommendations on page 2 state that the "solar charge controller SC300D [is] suitable for use with solar charge controller part numbers SC320 & SC330", neither of which claims to support MPPT.

This begs the question, how are the "PV vol. and cur. values" measured in PWM mode? The example in the manual shows ...

PV voltage = 17.5V
PV current = 15.2A

Battery voltage = 13.8V
Battery current = 5.2A

Load voltage = 13.8V
Load current = 10.0A

Does the PV output switch between 17.5V/0A and 13.8V/15.2A, in which case the battery current would be a peak reading rather than an average?

Edit: In retrospect, the current values only make sense if they are averages. The PV voltage must be the panel's open circuit voltage.

This is whats on the Solar panel leads before the regulator. When its charging theres a steady voltage. When the battery is charged the regulator is pulsing ON/OFF to give an average voltage at the battery of 13.8V.

The screenshot shows a panel voltage of 14.7V at the regulator and 13.5V at the battery during charging. This voltage drop (1.2V) suggests that the MOSFETs have a much higher RDSon than specified in the datasheet. Maybe they are fakes?

Same on the outside, but different on the inside:

https://www.amazon.com/gp/product/B01MU0WMGT/

The one with "less components" appears to have an extra MOSFET (4 versus 3).

The microprocessor is an STM 8:

https://www.st.com/en/microcontrollers/stm8-8-bit-mcus.html?querycriteria=productId=SC1244

It has a 12-bit ADC, so I would think that the voltage and current readings would be very accurate.

The more I read, the more confused I become.

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/19316-are-you-killing-your-batteries

Greater than 90% of all of you are killing your batteries from deficit/severe under charging, and following the manufactures recommendations are only making it worse.

With a commercial charger you start charging in Bulk until you hit about 80% SOC, then switch to Absorb which lowers the voltage a bit, current slows down and tapers to 2% of C. (about 6 clock hours) then you switch to Float and your battery continues to charge overnight and becomes saturated and fully charged by morning.

Well guess what? It is impossible for you to fully charge a lead acid battery on Solar unless properly oversized by design which you likely failed to do to start with. Even a properly designed system is going to come up short in winter months. There is just not enough Sun Hours in a Day to fully Saturate your battery.

Battery manufactures are getting slammed with warranty claims from Renewable Energy users. The claims are a result of chronic under charging and sulfated batteries. Many manufactures have revised their charging procedures for RE users. They have done away with Bulk Absorb, and Float voltage Algorithms. Today they aim at Maximum Smoke. Trojan calls it a Daily Charge of 2.47 vpc which use to be roughly Equalize voltage levels. What they are doing is forcing your Charge Controller to operate in Bulk mode or Max Smoke from Sunrise to Sunset. Still may not get your batteries fully charged. But still significantly more power stored than setting the voltage to a lower value.

So what do you do? Well what you should have been doing from the start. Use your Temperature Compensating Hydrometer to find the right voltage if there is one. For roughly 90% of you there is No Voltage High Enough you can set your controller to get the batteries fully charged up, because you do not have enough panel wattage to begin with. For those of you who find yourself in that situation, all you can do is limit the damage by cranking the voltage to MAX, and then every couple of day run the genny to get your batteries back to 100%.

Since its imposible to use a hydrometer as suggested on sealed batterys. I purchased this unit on Ebay for $50, to check state of Health & internal resistance. I keep a record of what the readings are when purchased & fully charged. This then gives me some idea as to how good my batterys are. The 75Ah AGM is quite old & does not have a lot of usable capacity. The 120Ah AGM is only about 6mths old. The tester also can check altenator output & ripple, also cranking test.

Hi Dorian

In your quest, you certainly should look at the new post Custom 6x20 watts solar setup with MPPT. A very neat setup and he has given screen shots of his monitor which show the panel outputs and the battery inputs for the Victron MPPT regulator. Very instructive to see how they all work under different condition of battery voltage and various sun power input. He is getting full power + out of his small system with a quality MPPT reg.

Jaahn  

PS thanks also to DeBe for very instructive inputs to this thread with real workbench pictures and dismantled regs.

dorian wrote:

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Thanks, I did see that thread.

The Victron web site is very impressive. I found the following document to be a very good read:

https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf

According to the white-paper, the best arrangement for multiple panels is series rather than parallel (in MPPT mode). The benefits are lower IR power losses in the cable runs, and greater usable panel voltage under low irradiance conditions. I see that there is another discussion about connecting two controllers to the same battery, either PWM or MPPT. ISTM that those people who are using two MMPT controllers with two panels might be better off wiring the panels in series and going with a single MPPT controller.

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 The problem there is the total open circuit voltage. No point in getting an MPPT controller that can handle more than 120vdc, WA I believe it is as low as 115vdc unless you are a licenced electrician within the state you are doing the job or and testing or rectification work on the system. This means unless the licenced sparkie is licenced in every state, they can not work on their own solar set up unless they are at home

The average 12v nom. panel has a 20vdc open circuit voltage, so 5 panels in series is about the max, so unless the custom 6 x 20w panels have an open circuit voltage less than 20vdc, the person working on the system must have a full electrician's licence within that state, even though the system is only 120w.

Crazy yes, but them is the rules. If anyone gets injured or dies due to a heart problem while they are in contact with any part of a building that can come into contact with the system and it is found that the system open circuit voltage could show greater than the threshold that the licencing requirements and it wasn't connected and certified by a licenced electrician, the person that did the work, any person after that that did any work on the system and the owner of the system could find themselves fronting a "please explain why you should not be tried from manslaughter" type situation.

I have no idea how far the long arm of the law reaches as far as supplying equipment that could be used to build such a system or advice given to someone regarding building such a system, but it does fall into same category as giving advice on 240vac wiring and how to do it or fix it

T1 Terry

DeBe wrote:

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Don't see a problem with high voltage if you read what the person has done. If you read the thread he has set it up with 3 lots of 2 panels inseries giving 32.5V into the regulator.

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 Hi Debe

Correct. Terry should have looked at the posting.

To make a comment on the series use of panels. Quite some time back when I was researching regulators, PWM and MPPT, I came across some testing of the concepts. I have not seen it since but it made sense at the time. While there are benefits in putting lots of panels in series, mainly the lower resistance losses or the reduced copper cost, on a small installation like a van or MH this is just small beer really. The extra charging from the higher voltage at low solar insolation is almost nothing due to the low power available at that time anyway.

In that testing I recalled that the maximum efficiency of the MPPT system was when the input voltage was not too far above the battery voltage, perhaps (by memory) +30-50%. This involved less conversion losses in the electronics. The recommendation was to use about double the nominal panel voltage by using two panels in series. That is what I have done and been happy with the results. I note that is what has been done in the 6x20W solar setup, AND he has shown how well it works.  No high voltages to worry about either ! Victron also says that ! 

I have found that the long leads do need to be generous size to get the best output. But the cable cost is a one off to get double the gauge for not much more cost. When I had portable panels I had long cables to make it easy to chase the sun if I was in a bad spot. Who put those bloody trees there ????  

Jaahn

 PS 6x20W panels could use another configuration to limit the losses from long leads. 2 strings of 3 panels in series. Just saying for other people who want ideas.     

-- Edited by Jaahn on Wednesday 16th of January 2019 06:30:39 PM

I've been reading about PV panel materials. Wikipedia states that GaAs panels are the most efficient, but also relatively expensive. In an attempt to find out just how expensive they are, I found this:

https://www.alibaba.com/product-detail/Gallium-arsenide-solar-cells-made-transparent_60808115115.html

The panel is rated for 320W and its dimensions are 1960 x 992 mm. That's 165W / sq m.

Here is a polycrystalline panel:
http://www.centsys.co.za/upload/CENTSYS%20Documentation/0_07_B_0133%20200W%20Solar%20Panel%20Specifications%20sheet-29062015-NG.pdf

It is rated for 200W and is 1320mm x 992mm. That's 153W / sq m.

The difference in power output is only about 8%.

dorian wrote:

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I've been reading about PV panel materials. Wikipedia states that GaAs panels are the most efficient, but also relatively expensive. In an attempt to find out just how expensive they are, I found this:

https://www.alibaba.com/product-detail/Gallium-arsenide-solar-cells-made-transparent_60808115115.html

The panel is rated for 320W and its dimensions are 1960 x 992 mm. That's 165W / sq m.

Here is a polycrystalline panel:
http://www.centsys.co.za/upload/CENTSYS%20Documentation/0_07_B_0133%20200W%20Solar%20Panel%20Specifications%20sheet-29062015-NG.pdf

It is rated for 200W and is 1320mm x 992mm. That's 153W / sq m.

The difference in power output is only about 8%.

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The real difference between panel designs and output does not show up by comparing STC results, they actually reflect just about nothing of how the solar panels will function when out in the Australian mid day sun.

The fact most RV panels are flat mounted on the RV roof with very poor heat transfer away from the back face of the panel (because there is a trapped air pocket there) means true testing needs to be with the panel temp above 60*C and the ambient temp more like the temp likely to be found in free camp site throughout Australia. Even the NOCT results are with a panel temp of 45*C an ambient temp of 20*C, can you see that occurring anywhere in an Australian summer?

We do have an Australian solar panel manufacturer, Tindo, check out what type of panels they build and ask why that technology and not the other, the engineers answers will give you a good insight into why papers written in Europe have very little relevance in Australian conditions.

t1 terry

Baz421 wrote:

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Hi

a lot of this is over my head but I a question now please,,, based on previous,,,,

Is the Victron MPPT 75 15 controller a genuine MPPT or PWM in disguise?

 Cheers Baz

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 Hi Baz 

Victron make good gear and they perform as they claim. So a genuine MPPT unit.

My disclaimer: I own one and some inverters.

Jaahn

I should have looked more closely. The Alibaba panel lists GaAs under Specifications but Polycrystalline Silicon under Quick Details. I guess that explains the unremarkable 17% efficiency figure.

Here is the datasheet for a monocrystalline silicon Tindo panel (17.1 - 18.0% efficiency):
http://www.tindosolar.com.au/wp-content/uploads/2018/05/300W-Tindo-Karra-data-sheet.pdf

Here is an Alta Devices single-junction GaAs cell/panel (26% efficiency):
https://www.altadevices.com/wp-content/uploads/2018/04/Single-Junction-Tech-Brief.pdf

Not only is Alta's power output impressive, but the temperature coefficient is -0.09% per deg C. The Tindo panel has a corresponding coefficient of -0.41% per deg C. This means that for a roof temperature of 65C, a 200W GaAs panel would lose about 3.6% or 7W whereas the monocrystalline panel would lose 16.4% or 33W.

http://www.tindosolar.com.au/learn-more/temperature-coefficient/