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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 03-03-2015, 18:35   #16
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Re: Open Source MPPT

Thats the beauty of a commercial controller.. You can feed it anything from 17V - 150V and it will spit out the required voltage for your battery bank. This way you can use panels in series or parallel and not have any issues. This gives you flexibility to adjust your setup to reduce shading.

There are many posts about panels in parallel vs series. For me, I would rather have a single panel on one controller so I don't have to worry about a single shaded panel dragging down the network. More points of failure but also more redundancy.
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Old 03-03-2015, 22:22   #17
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Re: Open Source MPPT

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Originally Posted by travellerw View Post
Thats the beauty of a commercial controller.. You can feed it anything from 17V - 150V and it will spit out the required voltage for your battery bank. This way you can use panels in series or parallel and not have any issues. This gives you flexibility to adjust your setup to reduce shading.

There are many posts about panels in parallel vs series. For me, I would rather have a single panel on one controller so I don't have to worry about a single shaded panel dragging down the network. More points of failure but also more redundancy.

I would agree. For me lower cost multiple smaller capacity per panel mppt is best .

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Old 03-03-2015, 23:34   #18
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Re: Open Source MPPT

So the ideal setup then would seem to be having an MPPT controller for each panel using smaller sized panels. As you have pointed out this would optimize the output from each individual panel and reduce any shading issues. Maybe I should focus on supporting a modest amount of current at a really low price point to allow for say 4 panels and 4 controllers each pushing 15 amps.

Making it support a higher voltage is not a problem. I just didn't do it in the first place because I was designing with the intent to use the 24v Renogy panels and didn't see the need to spend money on 150v components. But the more we talk about it the more the larger high voltage panel seems to be not worth the hassle.

Really great input guys. So I'm gonna look into shrinking the current components to reduce cost and see how low I can get the number behind the $ sign to go.

I guess from here I'll just ask anyone to speak up for support of high voltage input otherwise I won't bother. In the meantime what ideas do you guys have for features that might be nice to have, particularly ones that require hardware present in the design. Making it 2.4ghz wireless is not a problem if someone can come up with a reason for it to be. I have no experience actually maintaining and operating one of these system while on a boat so I don't know exactly what's needed or what would be nice to have.
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Old 04-03-2015, 00:14   #19
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Re: Open Source MPPT

Thank guys for interesting discussion. Just voted for 40V. That'll do comfortably for most single panel and double serial "12V" panel installations.

If I were to build my own solar controller it would be purely for fun. No chance to gain any money when Chinese have a quality control on their products. But really, it can be very useful to be able to repair your controller on a remote island

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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.
The controller mentioned by OP is apparently older model or at least different series then the one reviewed by travellerw. So the quality and materials can be different among them. Saying that, I have one of those (mentioned by OP) installed on my boat for about 2 years and it has been been working flawlessly.
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Old 04-03-2015, 00:19   #20
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Re: Open Source MPPT

My thoughts exactly ullar. My plan is to build a prototype one for myself and if there is enough interest I can do a small run of boards, as long as we have at least 10 boards that will help reduce the price.
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Old 04-03-2015, 00:22   #21
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Re: Open Source MPPT

So the obvious question is what is the extra cost for you (development, BOM, etc) for creating a single device that can support multiple panels, each with its own MPPT controller? Seems like most boats will have at least two panels, with three or four more likely at panels get cheaper. Can you provide independent MPPT for all of these? That would be neat.

Or is it just simpler to make a single MPPT device, and install four of them?

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Old 04-03-2015, 00:34   #22
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Re: Open Source MPPT

An extremely cost conscious device that you simply buy 4 of and use 1 on each panel is what we seem to be getting at toaster. But you bring up a valid point as to the economics of having possibly redundant hardware on each board when you know for a fact that almost everyone will have 2+ boards. It might make more sense to have a master board and then additional slave boards for every extra panel. The master board would contain a somewhat powerful microcontroller to implement whatever fancy bells and whistles you guys come up with/request and all the other boards would be practically dumb maybe just a small cheap microcontroller on each board. As you mentioned there is nothing stopping someone from putting 2 MPPT controllers on 1 board; but would it be worthwhile? Idk yet.

Regardless, I would say that is a decision to be made later on in the design process when components have been decided on and what it'll all cost, otherwise it's just guessing. Right now a maximum voltage and wattage needs to be decided for each board to be able to handle.
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Old 04-03-2015, 04:48   #23
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Re: Open Source MPPT

I would disagree with the master slave idea , micros are cheap , just make a single board and people install multiple ones.

This simplifies the design as you can constrain the specs and optimise the design and cost

Dave
( I design embedded systems )
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Old 04-03-2015, 07:34   #24
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Re: Open Source MPPT

I would say 20AMP is minimum for each controller. This will support a 230-250W panel which are very popular these days.

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Old 04-03-2015, 09:51   #25
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Re: Open Source MPPT

I love tinkering as much as anyone, and have done a few custom things like a PIC mcu dimmer for our boat's strip lighting. But key factors are safety, reliability and the cost/benefit ratio. If you value your free time at say $50/hr, the hand-built route loses it's economic appeal very quickly. (On the other hand, if you are in the part of the world that has winter, such a project will help keep you sane).

Speaking personally, I would probably be content to buy a few of a known-good 20A MPPT controllers, use them conservatively (eg 15A max each), have a spare, and understand them well enough to be able to diagnose and maybe fix'em.
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Old 04-03-2015, 10:09   #26
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Re: Open Source MPPT

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Originally Posted by goboatingnow View Post
I would disagree with the master slave idea , micros are cheap , just make a single board and people install multiple ones.
Well, certain micros are cheap, some certainly aren't. I was also worried about lcd displays, data connectors, user input such as buttons, firmware flash updating, wireless modules, battery temp sensors, and who knows what else that probably doesn't need to be reiterated onto every board. But, like I said there is no way to know for certain until later on when components have already been selected so I'm not even gonna worry about it right now.

Lake-effect, I understand that this very well may not work out financially net positive for me personally but that's not the point. I'm doing it because I want to as a project. Even still I hope to add a substantial amount of solar to my boat and I don't know of any $50 30A MPPT controllers available so it's not as if I am totally reinventing the wheel for no reason. Winter or not I can't go out sailing very far for at least another year so until then I am trying to keep busy.
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Old 04-03-2015, 10:13   #27
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Re: Open Source MPPT

I use an Arduino for my MPPT controlling and there is already code out there in the public domain which can be adapted for the Atmel microcontroller chips. The base algorithm doesn't need to be complex and the processing required doesn't need to be fast (or floating point, for that matter).
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Old 04-03-2015, 10:25   #28
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Re: Open Source MPPT

Thanks for the input Zanshin. Lately I have been using the $1 @ 1 qty ARM chips. They beat the snot out of anything 8bit and for the price/performance ratio it's hard to pass them up even if the extra power isn't needed, you never know when you might find a use for it.

Speaking of algorithms, yet another reason to build my own. The video review travellerw had posted of the only affordable small MPPT I have yet to see seemed to have the world's worst PP seeking algorithm. Constantly venturing way farther into the IV curve than it ever should, and frequently giving up and outright resetting.
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Old 04-03-2015, 12:51   #29
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Re: Open Source MPPT

Someone mentioned they were interested in open source autopilot. There was a thread linking a YouTube video on a home built Arduino based autopilot. A google custom search should turn it up.

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Old 04-03-2015, 12:55   #30
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Re: Open Source MPPT

Yea, once I have solar power working my top priorities will be an open source autopilot and high contrast e-ink multipurpose display as I've noticed the current offerings seem vastly overpriced considering the screen itself is only 15$.
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