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View Poll Results: What panel voltage should be supported?
under 30v (keep price low) 3 12.50%
up to 40v (compatible with most panels) 9 37.50%
up to 100v (allow large panels) 12 50.00%
Voters: 24. You may not vote on this poll

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Old 02-03-2015, 11:02   #1
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Open Source MPPT

I was looking into designing my own open source MPPT solar charge controller due to the lack of low cost ones available on the market. The only one I have found at a reasonable price has been this one. Even still I'd prefer to have an intimate knowledge of everything on my boat and buying one without open documentation precludes that.

So far I have completed the bill of materials for a sub $50 500w dual phase synchronous buck controller that would work nicely with the cheap lower voltage (under 40v) panels such as these offered by Renogy. Shortly before getting ready to pull the trigger on ordering the parts for a prototype build, the higher voltage panels caught my eye and of course I'd like to at least match the aforementioned chinese controller (which claims to accept up to 150v) in functionality. Back to the drawing board.

So would anyone be interested in such a thing or is everyone pleased with the current offerings? Is there anything you wish your current charge controller did/did-better or didn't do at all.
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Old 02-03-2015, 18:09   #2
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Re: Open Source MPPT

Interesting series of YouTube videos here on building one from scratch...


MPPT Solar Charge Controller #1 - Introduction and Voltage Measurement: http://youtu.be/MSz4-cr3EJw
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Old 02-03-2015, 18:20   #3
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Re: Open Source MPPT

Thanks for the link. It looks like Julian has some code written I might can take a look at before I start writing mine. As stated I'm still in the hardware design stage and I'm shooting for 500watts of capacity at least. Does this seem an adequate amount? I suppose I want to target a number that's large enough to be more than the average person would need but not so big as to increase the price unnecessarily.
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Old 02-03-2015, 20:06   #4
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Re: Open Source MPPT

Boats tend to keep adding more panels and I would suggest designing to 600 watts.
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Old 02-03-2015, 20:35   #5
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Re: Open Source MPPT

I posted a review a while ago about this controller.. Still haven't used it in a marine environment, but it has worked well in testing.

I have an EE background and was impressed when I tore it down. Real brand name components and a solid design.
Affordable MPPT Charge Controller
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Old 02-03-2015, 21:23   #6
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Re: Open Source MPPT

I plan on running my batteries in parallel for a system voltage around 12v. I would imagine 12v is more common than 24v+ on most sailboats? Many of the chinese controllers like to claim high wattage numbers under the condition that you are running a 24v system or more. Perhaps I should design to a price point as opposed to a wattage and just see what that gets me. I'd think using quality components and keeping it under $150 would be nice and maybe sway some of the people who prefer to add another panel instead of an MPPT controller.

Awesome input travellerw! I was really searching for a tear down of one of those well priced controllers but I was coming up with nothing on google. I was quite worried it would be dodgy components in there, but Jamicon and UCC are far from the worst. Now I am almost tempted to just buy one of those if I wasn't so damned cheap and curious to try building my own.

It certainly doesn't look like they cut any corners cost wise. I even see a few tantalums in there, no idea why. So I'm guessing there are 2 large inductors in series under that black potting compound. I had found a tear down of a morning star as well and it was also single phase. I find this kind of odd. All signs point to multiphase being nothing but advantageous, Julian also has the same remarks at the end of his youtube series. Large inductors aren't cheap and I wouldn't be surprised if that is the most expensive part of the controller. Perhaps it's the lack of drop in multiphase buck controller IC's that operate at high voltages. It was difficult to find the one I intended to use in my sub 40v design. I'm planning on doing the buck control from scratch if I do try and make an 80v+ design.

Here is the 40v bill of materials cart if anyone is interested.
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Old 02-03-2015, 21:25   #7
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Re: Open Source MPPT

Quote:
Originally Posted by whiskthecat View Post
I was looking into designing my own open source MPPT solar charge controller due to the lack of low cost ones available on the market. The only one I have found at a reasonable price has been this one. Even still I'd prefer to have an intimate knowledge of everything on my boat and buying one without open documentation precludes that.

So far I have completed the bill of materials for a sub $50 500w dual phase synchronous buck controller that would work nicely with the cheap lower voltage (under 40v) panels such as these offered by Renogy. Shortly before getting ready to pull the trigger on ordering the parts for a prototype build, the higher voltage panels caught my eye and of course I'd like to at least match the aforementioned chinese controller (which claims to accept up to 150v) in functionality. Back to the drawing board.

So would anyone be interested in such a thing or is everyone pleased with the current offerings? Is there anything you wish your current charge controller did/did-better or didn't do at all.
Not sure you are interested in comments on a business plan or whether or not you can build a better mousetrap than the Chinese (i.e. higher quality)

As for business plan your margin has to be razor thin a $50. Features sell stuff so you'll need to think about that. I would consider a controller without feature rich remote monitoring. Then it's a matter of support, and reputation. Higher end cruisers will probably go name brand. I know I would/did (morningstar).

As for building a better mousetrap, I am sure you can. The space is super crowded already at the lower end.

Good luck.
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Old 02-03-2015, 22:05   #8
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Re: Open Source MPPT

I've written a reply to your post travellerw and Ed but I am new to the forum and have just realized that using any hyperlinks or images requires moderator approval so I guess we will have to wait a few hours on that one but it includes a link to my current BOM.

Ex-Calif, I'm interested in all comments and my main goal is nearly hobbyist in the sense that I just want to do it on principle. If I can make a small profit off of it while also putting a decent controller in peoples hands well that's great too, every little bit helps when you are boat broke. I'm sure the more expensive name brand controllers are great and all but as many have pointed out you can often just spend the money on an additional panel and come out ahead once you consider the price of the controller. Of course this doesn't work when you start running out of deck space and hence the need for MPPT arises.

As for the market being crowded at the low end, it is and it isn't. Most have reported the vast majority of chinese charge controllers to be complete junk. Lying about their functionality or outright not working. Short of the single model I mentioned in my first post that travellerw has confirmed as being of acceptable quality there really isn't much else out there workable under the $200 range.

Regarding bells and whistles, they can often be added at the cost of development time and not really any significant hardware cost. I have a nice little software library I've compiled from my own and open source code to do wireless communication with less than 3$ of components. This in combination with a laptop or even a small standalone lcd display could grant you a myriad of features especially once you consider it will all be open source and free for anyone to add to or modify.
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Old 03-03-2015, 00:59   #9
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Re: Open Source MPPT

Definitely interested...

If you saw my other post regarding an integrated charger / inverter / genset-shore-inverter switch + solar and wind power management, you know that an mppc is only part of a larger pi shield I'd like to see be developed.


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Old 03-03-2015, 08:37   #10
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Re: Open Source MPPT

Quote:
Originally Posted by whiskthecat View Post
I've written a reply to your post travellerw and Ed but I am new to the forum and have just realized that using any hyperlinks or images requires moderator approval so I guess we will have to wait a few hours on that one but it includes a link to my current BOM.

Ex-Calif, I'm interested in all comments and my main goal is nearly hobbyist in the sense that I just want to do it on principle. If I can make a small profit off of it while also putting a decent controller in peoples hands well that's great too, every little bit helps when you are boat broke. I'm sure the more expensive name brand controllers are great and all but as many have pointed out you can often just spend the money on an additional panel and come out ahead once you consider the price of the controller. Of course this doesn't work when you start running out of deck space and hence the need for MPPT arises.

As for the market being crowded at the low end, it is and it isn't. Most have reported the vast majority of chinese charge controllers to be complete junk. Lying about their functionality or outright not working. Short of the single model I mentioned in my first post that travellerw has confirmed as being of acceptable quality there really isn't much else out there workable under the $200 range.

Regarding bells and whistles, they can often be added at the cost of development time and not really any significant hardware cost. I have a nice little software library I've compiled from my own and open source code to do wireless communication with less than 3$ of components. This in combination with a laptop or even a small standalone lcd display could grant you a myriad of features especially once you consider it will all be open source and free for anyone to add to or modify.
The charger I posted is $100 for a 20A charger (150V input, 12/24V output) with a huge feature set. The 30A version is $140.
1. MPPT
2. Remote monitoring
3. Software monitoring/configuring
4. Field upgradable firmware
5. Battery temperature montoring/shutdown
6. User adjustable values for everthing
7. Brand name parts
8. Attractive, heat disipative design.

Seriously, there is no way you can beat that value.

I would really love to see you focus your energy on something that makes more sense with less competition. How about an open source Autopilot.

Seriously it makes way more sense since the current offerings are all overpriced designs using Micros that are 10-15 years old. Heck 3/4 of the work is already done if you base it on an existing RC flight controller. The Naze32 or even the KK2 board would be suitable for this task.

I think you would get my more reward going down that path, but thats just my opinion.
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Old 03-03-2015, 08:41   #11
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Re: Open Source MPPT

Sounds interesting Keelsidedown but I am not 100% certain exactly what you are getting at. Mind describing in more detail what all you are trying to accomplish? Adding mosfet switches to turn external loads on and off is not a problem and many of the cheap controllers offer this. The catch being it is difficult to get a big enough bus/terminal to switch large amounts of current. Often 10 or 20 amps is all that can be switched reliably through wire screw terminals. Perhaps fat and thick copper traces combined with screw posts would be better.

What do you intend to gain from coupling/integrating an inverter? Inverters are much more common than MPPTs and therefore much cheaper per watt. I doubt I could design one any better than an already affordable unit with decent reviews.

I've yet to fully outfit my boat so there are probably things that come in to play I haven't even thought of or encountered yet. Please explain.

Ooops, this is Whiskthecat. I've accidentally posted from my buddies account.
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Old 03-03-2015, 08:53   #12
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Re: Open Source MPPT

Quote:
Seriously, there is no way you can beat that value.
Well you might be right and as I said I am almost tempted to drop the project and just buy one of those. But, at the same time I am almost certain I can beat that value and I am more in the market for a 60A controller in the $100-200 price range.

My current design is already at 30A at around 50$ and this is all very preliminary with no heavy optimizations. All of the features you've listed I am more than confident in implementing with the exception of the mechanicals (heatsink & case design), but I have some friends who can help out there.

Also, in regards to the autopilot. My boat has the steering wheel axle protruding into the cabin wall and there's a nice little sprocket just begging to be coupled with a stepper motor. So I certainly plan to implement my own (at least rudimentary) autopilot. But before I can get there the boat needs electrical power.
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Old 03-03-2015, 10:01   #13
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Re: Open Source MPPT

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Originally Posted by whiskthecat View Post
Well you might be right and as I said I am almost tempted to drop the project and just buy one of those. But, at the same time I am almost certain I can beat that value and I am more in the market for a 60A controller in the $100-200 price range.

My current design is already at 30A at around 50$ and this is all very preliminary with no heavy optimizations. All of the features you've listed I am more than confident in implementing with the exception of the mechanicals (heatsink & case design), but I have some friends who can help out there.

Also, in regards to the autopilot. My boat has the steering wheel axle protruding into the cabin wall and there's a nice little sprocket just begging to be coupled with a stepper motor. So I certainly plan to implement my own (at least rudimentary) autopilot. But before I can get there the boat needs electrical power.
Quick suggestion.. You are probably better off with 2 - 30AMP or 3 20AMP controllers than 1 60AMP controller. It has multiple advantages (and a few disadvantages), not the least is redundancy. If your controller blows up, you are at 1/2 or 2/3 capacity and not dead in the water.

So if already have a 30AMP design, then build 2 of them and call it done!
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Old 03-03-2015, 16:34   #14
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Re: Open Source MPPT

I'm interested in this. I have two 85W panels and a BlueSky 2000e mppt controller, which all work fine. I'd like to add more panels, and like the look of the 100W Renogy panels. But the 2000e only supports 20A at 12V so I'm wondering about adding a second MPPT controller. (Would this work OK, having two controllers trying to charge the same battery bank?)

But another controller would cost more than the 100W panel does.... so yes, I'd be interested in an open source controller. I'd be happy to help with testing, etc. I currently am working on an Arduino project related to solar power (at home, not on the boat), but am certainly an amateur at this stuff.

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Old 03-03-2015, 18:23   #15
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Re: Open Source MPPT

That's a good point travellerw, I was too focused in to think of it on a broader scale and just use them in parallel. The only problem with my current design is it can only accept an open circuit voltage of 40v and I've specced it at 30Amps. I have no idea which panel voltage is the most common but it seems like a lot of people on this forum are using the 24v panels so this would be fine. Someone locally is selling extras from their house installation and these are 80v panels at 450w. I really want one

But the 24v panels are just as cheap and probably more manageable controller wise. What voltage panels do you guys have?
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