Open Source MPPT

[travellerw]

If you plan to release this as a hobbiest project, I would be very carefull about that chip. Although those chips are awsome, the soldering required is well beyond MOST hobbiest abilities or capabilities (a major reason why lots of OpenSource projects are never widely adopted).

QFN packages are something that even skilled hobbiest shy away from due to the equipment and skills required to solder them. Ovens, solder paste and stencils are not something that most hobbiest will have EASY access too. Anthing you pick, should be able to be "drag soldered".

Sounds like, instead of OpenSource you just want to make a custom charge controller as a project (nothing wrong with this), then maybe share it with 3 or 4 people. If you really want to do OpenSource, you need to consider these things or adoption will be low (which I count as failure for OpenSource). Just some food for thought.

[whiskthecat]

Good points traveller. They also offer that chip in QFP which is easily drag solderable. I just linked that one to show what chip I intended on using, not necessarily the package. Even with all the equipment QFN can be a hassle. At the same time I would likely just sell the boards with everything already soldered on or at least the more difficult ones. Open source doesn't necessarily mean assemble it yourself. The benefit here being that the software and hardware will be openly documented and free for anyone to modify/easily repair. Now that the plan is smaller individual boards for each panel it will likely be possible to get away with little or no heatsinking if low resistance SMD components are used.

[whiskthecat]

Here's something that might be a cool idea. Since my current design is 2 phase there are enough components present to allow switching it over to 2 single phase bucks. Basically you'd have one board that you could choose to use as either 2 separate 20A MPPTs or one 40A MPPT. This would allow someone to benefit from having either 2 lower 100w panels or 1 larger 250watt panel using the same board design. If you have 4 100watt panels you only need 2 boards. Thoughts?

[Zanshin]

Those ARM chips are cheap, but overkill for the intended application. The Arduino or the Atmel Studio is a great development and breadboarding platform, I don't know if the same exists for the ARM.
I like the idea of splitting the MPPT into two separate output circuits, supporting two banks - i.e. ensuring that the starter battery is always topped up and feeding the house bank.

[whiskthecat]

I've used these exact chips for a couple of projects now and I have nothing but praise for them. The development environment provided by silicon labs (formerly energy friendly micro) is free and nearly identical to Atmel studio. You can get the entire development kit that includes the full Jlink programmer for $40. I've had no problems with it whatsoever. As far as being over powered for this application, processor wise yes, but the amount of peripheral features you are getting along with the chip can not be discounted. There are never enough timers, counters, PWM's, ADC's, DMA's, comparators, etcetera, and these chips are jammed packed with them often at a lower price than an equivalent AVR or PIC alternative.

I hadn't even thought of how that would help with multiple battery banks. I just meant MPPT for 2 seperate panels on 1 board into 1 battery bank, but you are correct at that point you could divert the power to a secondary battery bank if you'd like.

[travellerw]

Originally Posted by whiskthecat

Here's something that might be a cool idea. Since my current design is 2 phase there are enough components present to allow switching it over to 2 single phase bucks. Basically you'd have one board that you could choose to use as either 2 separate 20A MPPTs or one 40A MPPT. This would allow someone to benefit from having either 2 lower 100w panels or 1 larger 250watt panel using the same board design. If you have 4 100watt panels you only need 2 boards. Thoughts?

Hhmm, me thinks something is very different in your design than commercial designs.. A 20A commercial controller can handle about a 260W panel @ 12V output or a 520W panel @ 24V output. A 40A controller can obviously handle double that. 4 commercial 20A controllers can handle about 1000W of solar with a 12V battery bank.

[whiskthecat]

The numbers weren't exact since we haven't come to a definitive conclusion on how many amps each MPPT needs to be able to support or even a maximum input voltage. All of the numbers you just listed are correct and there's no way to change them to where you can get more watts at the same amperage besides feeding into a higher voltage battery bank as you said. You can always use less than the controller supports though. Using a 20A controller on a single 100watt panel is certainly excessive overhead and wasteful, I wasn't suggesting that was all the design would be capable of. With the amperages I listed in that post you would run 2x of each panel in parallel, but that gets away from our idea that each panel should have it's own controller. I just used it as an example because it's about the range I have designed into the controller at this point. It can all be scaled up or down of course.

With this new idea of having a single board reconfigurable to be either 2 separate MPPTs or one high current one, the numbers likely would change depending on the supported input voltage. If it's decided only 40v of input is needed then it would make sense to have each phase be 10A, so the user would select the board to operate as either 2x 10A MPPT's each controlling a 100w panel (~200 watts total) or 1x 20A MPPT controlling a single 240w panel. Sorry for the confusion. If the higher 80v panels are to be supported then higher current phases would have to be implemented.

So can anyone chime in why they are voting for 100v panel support? The higher voltage panels don't appear to be any cheaper per watt and often they are only sold in large pallets for rooftop installation. They are often much larger and therefore more difficult to locate and install on deck. The only advantage I have noted of them is they tend to be ever so slightly more efficient per sq. in. They also certainly make the electronics design more difficult and costly to no benefit of anyone using the lower voltage panels and possibly slight losses. They would only seem usefull in a 24v battery bank setup which I am still assuming is not the norm.

[travellerw]

Many cruisers run panels in series due to the layout of their boats.. So 2 40V panels now becomes 1 80V panel. This is why commercial controllers support up to 150V of input.

The second reason is cost of wire. You can run smaller guage wire if you run a higher voltage panel. Since marine wire is not cheap, the savings quickly add up.

The downside of 1 controller per panel is wiring.. You need a "Home Run" for every panel. One some boats that is just not feasable or owners don't want to do it. Like everything on a boat, tradoffs. I will spend the extra work and wire to gain the redundancy and eliminate shading in a network, some won't.

[LeaseOnLife]

Originally Posted by whiskthecat

So can anyone chime in why they are voting for 100v panel support? The higher voltage panels don't appear to be any cheaper per watt and often they are only sold in large pallets for rooftop installation. They are often much larger and therefore more difficult to locate and install on deck. The only advantage I have noted of them is they tend to be ever so slightly more efficient per sq. in. They also certainly make the electronics design more difficult and costly to no benefit of anyone using the lower voltage panels and possibly slight losses. They would only seem usefull in a 24v battery bank setup which I am still assuming is not the norm.

I am looking at 255 and 345W SunPower modules for highest W/area and some shading tolerance.
57.3V Vmpp:
Sunpower SPR-X21-345 (345W) Solar Panel

The 255W panels have >=45 Vmpp

Dirk

[nimblemotors]

I hesitate to say anything...
Just making something that already exists is not very useful.

What is needed for boats that doesn't exist are microMPPT controllers that solve the problem of shading.
You want to use small single panels with a fixed voltage output so they can be all combined in parallel. Those shaded just contribute less current.
See SPV1020 which is a hardware solution.
If done well, you would have a system that is very valuable to sailors even if a lot more expensive.

Now if you want to invest a lot of time, then I think it is possible to build a lower cost system using a micro that controls multiple small panels.
As I have hundreds of small solar panels for my boat this is what I was going to try, but like all my projects many get put off and/or never finished,
but eventually I MUST HAVE a solution that isn't possible to buy today.
But the SPV1020 (or the SPV1040) is the fast way to get it done.

SPV1020:

The SPV1020 is a monolithic 4-phase interleaved DC-DC boost converter designed to maximize the power generated by photovoltaic panels independent of temperature and amount of solar radiation.

Optimization of the power conversion is obtained with embedded logic which performs the MPPT (max. power point tracking) algorithm on the PV cells connected to the converter.

One or more converters can be housed in the connection box of the PV panels, replacing the bypass diodes. As the maximum power point is locally computed, the efficiency at system level is higher than that of conventional topologies, where the MPP is computed in the main centralized inverter.

For a cost effective application solution and to minimize size, the SPV1020 embeds power MOSFETs for active switches and synchronous rectifiers, minimizing the number of external devices. In addition, the 4-phase interleaved topology of the DC-DC converter obviates the need to use electrolytic capacitors, which may severely limit system lifetime.

The SPV1020 operates at fixed frequency in PWM mode, where the duty cycle is controlled by the embedded logic running a Perturb&Observe MPPT algorithm. The switching frequency, internally generated and set by default at 100 kHz, is externally adjustable from 50 kHz to 200 kHz, while the duty cycle can range from 5% to 90% with a step of 0.2%.

The safety of the application is guaranteed by stopping the drivers in the case of output overvoltage or overtemperature.

Multiple SPV1020s can be used in a panel array with one SPV1020 per panel. Panels can be connected in series, in parallel, or series/parallel combinations.

[whiskthecat]

As always thanks for the responses guys.

The downside of 1 controller per panel is wiring.. You need a "Home Run" for every panel. One some boats that is just not feasable or owners don't want to do it. Like everything on a boat, tradoffs. I will spend the extra work and wire to gain the redundancy and eliminate shading in a network, some won't.

Well you just need 1 line per panel, I'm sure all panels could share a large ground line. I'm of your mentality as well (maximize the output of each panel and therefore the overall system) and I'd rather not add things into the design at the detriment of overall performance just so someone else can make an unnecessary compromise. I'd assume most peoples panels are near their engine room and therefore near their battery bank and controller so what's a few wires to ensure you are getting the most of those precious watts out of your expensive system. Seems like a serious case of form coming before function.

I am looking at 255 and 345W SunPower modules for highest W/area

Yup, lust worthy aren't they? I was looking at the Sunpower 435w panel with an open circuit voltage of 85v You won't want to grab onto that with a wet hand. Have you ran the numbers on how much space you are saving or how much extra wattage you can get from a given area? I hadn't done so myself yet. It seemed like they were only claiming a 2% increase over regular mono panels unless I am misunderstanding how that relates to output wattage.

It's just that the higher voltage components cost so much more and to be at the same efficiency as the lower voltage ones you will need 4 HV components where only 1 or 2 low voltage ones would have worked. The design price can skyrocket quite fast like this. Also finding off the shelf buck IC's that can handle over 40v is quite difficult so I'd likely have to design the entire thing from scratch which might be more than I want to bite off and chew.

I hesitate to say anything...
Just making something that already exists is not very useful.

I'm not entirely sure that is fair. I'm not aware of any open source MPPT controllers under the $100 mark. Certainly not any that can be reconfigured to operate as single high current or double low current units. I'm not even aware of any multi-phase controllers at all, PWM or MPPT. Saving money, engine room space, and producing more power seems like a worthwhile venture to me.

What is needed for boats that doesn't exist are microMPPT controllers that solve the problem of shading.

Could you elaborate more on this? The IC you have linked looks quite interesting but it is a boost converter. Meaning your input voltage (solar) must be lower than your output voltage (battery bank). I'd say this is almost never the case unless you have a 24v battery bank and 12v solar panels, quite an odd setup. It seems they are intending for many of these chips to be embedded into a very large panel each controlling a portion of the solar cells making up the panel. Unfortunately I don't have the mechanical skills or equipment to be manufacturing my own solar panels so this is somewhat outside the scope of this project. Besides, what we are accomplishing by using a low current and cost effective controller on each panel is exactly what that chip is doing for a much larger array. We are doing MPPT for every panel as opposed to just grouping all panels and doing MPPT on the sum of them. Optimizing each panels output individually will always beat trying to optimize them together. I'm not sure entirely how much gain this will net us depending on conditions but it will for sure help draw more power out of the partially shaded panels.

Now if you want to invest a lot of time, then I think it is possible to build a lower cost system using a micro that controls multiple small panels.

Yes, exactly that. That is the plan as of now.

but eventually I MUST HAVE a solution that isn't possible to buy today.
But the SPV1020 (or the SPV1040) is the fast way to get it done.

So back to your original remark, what I'm working on doesn't really exist. It can be implemented by buying multiple small controllers that already exist and wiring them all together but at their current prices that would hardly be cost effective. And if you just have one or two large panels...

In addition, the 4-phase interleaved topology of the DC-DC converter obviates the need to use electrolytic capacitors, which may severely limit system lifetime.

^^^This^^^ If you took a look at my BOM link you will have noticed there are no failure prone electrolytics on the list since I am using 2 phases, something I've yet to find in any currently available controller.

[travellerw]

Your assuming too much.. Not everyones panels are close to their battery banks.. Many boats have banks low near the keel. Or on a Catamaran the batteries are usually up under the mast with the panels over the cockpit. Those can be some pretty long runs because you need to go under the bridge deck.

Controllers need to be flexible to handle different scenarios.

[whiskthecat]

Controllers need to be flexible to handle different scenarios.

Fair enough. Even still with 40v Panels and a 500w system you are only having to move 12.5amps. Marine wire at that gauge is obtainable at under 1$ per foot. The difference between going in series vs parallel/multi-controller is going to be less than 50$ of wire and a possibly substantial difference in efficiency/output. The person who insists on running that in series for whatever reason can just buy one of the already available controllers and accept whatever shading losses they incur.

I wouldn't look at the question of supporting 40v vs 100v in the design as whether or not to support different series and parallel configurations. I really like the idea of one MPPT controller per panel, therefore series is out completely. The question now is are the panels that are above 40v by themselves worth support. Considering the currents being dealt with from panel to controller are already not that high if you are running a wire from each panel (Under 6amps for 240watt panels), the only benefit I see the higher voltage panels bringing to the table are the slight (as far as I know) increase in watts per sq. in. I just doubt it's worth all the hassle.

[DeepFrz]

Be careful, read the reviews as there is a lot of junk on the market. A number of sellers on eBay selling charge controllers as MPPT that are not MPPT and maybe not even properly working PWM charge controllers. There are a number of reviews on youtube that should be of interest if you are looking for cheap charge controllers. Just don't look for really cheap MPPT charge controllers as you are likely to get something else.

[whiskthecat]

Just don't look for really cheap MPPT charge controllers as you are likely to get something else.

Yup, that's why we are talking about making a really cheap one that actually works here.