Replacing Sunforce MPPT

[GypsyJohn]

I am a certified electrical moron and need guidance. I have 140W soloar panel and a Sunforce wind gen with MPPT controller. The MPPT has died, and Sunforce will not deliver a warranty replacement outside of USA or Canada (go figure - a cruising sailor leaving the waters from where he bought the unit?)

So, I am looking for a cheap option to replace the MPPT. The current from the wind gen is AC, and the maximum output is 450 watts. I am currently in Curacao, so I can get auto parts from NAPA and marine parts from Budget Marine and Island Water World.

Over to you my electrically capable fellow sailors. What should I use as a replacement?

[hellosailor]

And what converted your Sunforce AC windgen to DC for the batteries? What brand was your MPPT controller? If you were feeding AC into it, I would expect it to blow. It would also be most unusual for an MPPT controller to take the input from a wind generator, normally they need a dump regulator.

It isn't at all clear what your whole system is made up of.

[GypsyJohn]

Thanks for that Hello Sailor. The MPPT is the Sunforce that came with the Wind gen. I guess it must rectify the AC current from the wind gen, as well as control the DC to the house batteries. If the batteries are full (like that's gonna happen when you live on the boat) it stops the wind gen. Any thoughts on replacements?

[hellosailor]

Well, that's kinda curious. Sunforce's web site actually shows no MPPT controllers, and only "charger controllers" for their solar panels. But they do show an MPPT controller bundled with their wind turbine--and no specs at all for it. No manual no nothing. Apparently $250 to replace it and without any technical information, that might be your best option since with the stop switch it is not a conventional piece of equipment.

[Dsanduril]

Unfortunately I think hellosailor is pretty much right and you are SOL without the Sunforce replacement (given the credentials you cited above). If you want to go down another road...

The generator puts out 3-phase "wild" AC voltage. Wild as in not at a specific voltage. The electricity then passes through a diode bridge where it gets converted to DC, then into your batteries. Without "MPPT" when you connect the whole circuit together the generator will run at the battery voltage (the voltage gets "tamed" by the batteries). If you are in a pinch you could probably use the diode bridge from just about any car alternator. It would need to be rated for the current, but the wind generator maxes out at about 50A, so most alternator bridges would handle that. You'd also need a decent heat-sink for the bridge so that it doesn't kill itself. All of those parts should be available in pretty much any place where auto parts can be had.

What you lose is the battery charger control function(s), the wind generator will just keep putting out and the voltage will rise and rise as the batteries fill. Which means you have to keep an eye on it. The KISS wind generator works this way, when the voltage rises to the damage point on the batteries you shut down the wind generator.

Which comes to the second point, shutting down the generator. You also wouldn't have the switch on the controller for that. Presumably that switch just shorts the windings in the wind generator, but without a schematic impossible to tell. If it does, then pretty easy to build that for yourself as well.

And lastly the MPPT part, that is less critical. If it is truly MPPT then the controller manages the wild AC on the generator to get the maximum power out of it, and then converts that power to the appropriate voltage on the DC side. Without specs hard to tell just how much it benefits the system.

So, unless you really feel comfortable experimenting (or can get someone familiar with electrical work to assist) you probably need to convince Sunforce to send you a new unit (maybe you have relatives/friends in the States/Canada who could act a go-between?). The only other option I can think of is the Midnite Solar Classic, which has a wind input and bridge option. But that will set you back a lot more than $250.

[EDIT] Heck, if all you need is an address in the US PM me and I'll accept the package and forward it to you. Don't know if you have enough time for all of that, and what the shipping costs would be, but would be more than happy to do it if it helps. [/EDIT]

[Dsanduril]

Sorry for the second post, I went back and looked at the manual again, in the troubleshooting section it says:

3) With the red and black wires connected to each other, the shaft should be more difficult to turn. When the wires are disconnected it should spin freely.

This tells me the stop switch is most likely just shorting the windings, so that would allow you to put in a switch of your own to shut down the generator. Would have to be on the AC side of the diodes, a simple toggle switch would work.

[hellosailor]

"(the voltage gets "tamed" by the batteries). "
In a conventional system, maybe. But once the voltage goes high it will boil off electrolyte and that's "taming" the voltage kinda like throwing passengers under the bus in order to slow it down. Not too good for the batteries.
But if an MPPT were set up with specific design for a generator, rapidly sampling the output voltage and both up-and-downconverting that to keep it to what the batteries needed, it theory it could be much more effective than a conventional "wild" generator, although it would still need a dump or shutdown for excess conditions.
Speculating on engineering decisions like that is somewhere between useless and dangerous. Personally? When a company ventures into that kind of new territory, or makes claims that make it appear to be doing so, and they don't post ANY technical information about what they are doing?
They have zero credibility with me. I'm an honorary Missourian: "SHOW ME."

Who knows, maybe a technical enquiry to Sunforce would get some light shed on this.

[Dsanduril]

hello,

What I described is exactly how the KISS wind generator (as a commercial example) works, and every other similar system without a regulator. If your wind generator is putting out 260W the voltage in the batteries will rise until the batteries accept that amount of power. The voltage will not rise above the acceptance level for whatever power output you have (voltage/current combination). The batteries are a giant sink. With a wind generator that typically puts out maybe 10-15A (on a lucky day) you can charge even a small 300Ah battery bank for a very long time without a problem.

As your batteries continue to charge the voltage will continue to rise with the increase in SOC, generally very slowly unless the batteries are very small with respect to the generator or they are close to full charge. When the batteries reach "full" you shut off the wind generator manually. You are the charge controller. KISS argues that on a cruising boat the batteries are rarely full, and that you can use this kind of manual charge control, and I find that to be true, as long as you are willing to accept the necessary duties (I think few people are).

I've worked on and installed just about every variety of charge controller on other people's boats. On our boat I have a diode bridge and manual shutoff on the wind generator and a rheostat and manual shutoff on the 100A Balmar alternator. My instruments display voltage in the cockpit, and of course it is visible at the breaker panel. I manually manage all charging without a problem. For me it makes equalization much easier, there are way fewer parts to break, and those parts are available just about anywhere in the world.

If I had $5 for every anchorage I've been in where we had to jury rig exactly something like this to bypass a broken battery charging/monitoring system I could still be cruising There's really no guesswork here (except as to the exact wiring), a 3-phase wild generator is a 3-phase wild generator. The MPPT controller may get a little better production out of the unit, and the charge controller removes the need for you to monitor and control the thing. But, if you are stuck without the parts, and want to stick your (fallible) human brain in the circuit as the charge controller you can do this with about $15 in very common parts. I'm just trying to describe a simple solution that might be available where a more complicated one is not.

Check out this picture (found on the web, not my own work) for how simple this is:

[goboatingnow]

Why would a mppt controller be useful on a wind generator. The VI relationship is linear. It's a voltage source rather then a current source ... Confused. ( I could see a Buck/boost Ac to DC controller being useful as it would enable low speed ( lower then battery voltage ) charging to take place. But power point tracking. That has me confused ?

Dave

[Captain Bill]

Sorry to hear about your issues with the Sunforce warranty, since I was thinking of buying one. I wonder if these companies know how much business they loose by screwing their customers. Do they think people won't discuss it on the internet?

You can buy a 3 phase rectifier pretty cheaply on the internet. Just Google 3 phase rectifier and you'll get a long list. The key is to buy one that will handle both the maximum voltage and maximum amperage. I would guess that the maximum amperage would be less than 50 and the maximum voltage less than 100. The rectifier will get pretty warm at these numbers so you'll either need to provide a heat sink or buy one with a heat sink built in. That solves the ac-dc problem. As has been pointed out you can run without a regulator if you can babysit the wind generator and turn it off when your battery voltage gets high enough. You can also buy a conventional wind turbine regulator that dumps the power to a resistor or water heater element once the batteries are charged. A conventional regulator won't know the difference between the dc coming out of your regulator or that coming out of a dc wind turbine. You will not produce as much power as with the MPPT but it could get you home. For the purists who will undoubtedly point this out I know that virtually all small wind turbines are AC, the real difference is whether their rectified in the turbine or at the controller.

[goboatingnow]

That's the second thing why have load dumping resistors on a AC alternator wind turbine. I can understand why on a DC generator. But on an AC one you would just control the field current and reduce the excitation.


Dave

[hellosailor]

' you would just control the field current "
If you were using field coils and not a permanent magnet. There's a lot of variation in what gets called an alternator, vs what gets called a generator, and again, more room for error when the stuff is coming from overseas (or even domestic) without a thorough technical writing team.
I have no idea what's really in that windmill. Is it an alternator? Or a 3-phase generator? Dunno, my Magic8Ball is already on Xmas break.

[hellosailor]

Warranty: BTW I always ask people, did you buy it perhaps with a credit card that extends the original warranty for a full year? Worth checking.

Dave-
"Why would a mppt controller be useful on a wind generator."
You're right, it shouldn't be. Now, let's rephrase everything in Cantonese. I expect a lot of technical terms to get mangled in translation, and technically I wouldn't called it an MPPT controller, but something similar *could* in theory be used to continuously convert the power from the windgen, in the same way that an MPPT controller adjusts the power output of a solar panel. That is to say, what the voltage from the source is, part of the MPPT controller is a dedicated dc-to-dc voltage controller which is converting the power from the source to the optimal charging voltage, at the maximum amperage.
So let's say the windgen is turning slowly, putting out 11.8 volts, and the battery is in bulk phase and needs to see 13v. An MPPT controller, with a partial lobotomy, could be used to convert the windgen's 11.8 volts to a proper 13v, or whatever it is the battery wants to see. Similarly, if the windgen is really buzzing and putting out 22 volts, the controller would be able to knock that down to 13v at higher amperage.
So MPPT might or might not be accurate but these days? It's a buzzword and easier to use than to try explaining technical things to buyers.
Never put a "4" in a price. It's got four sharp corners on it. Numbers can be dangerous.

[goboatingnow]

It's the engineer in me I know.
I like precision

Dave

[Dsanduril]

Dave,

For the engineer in you:

http://www.tuc.gr/fileadmin/users_da...zakis/J.33.pdf

http://www.jatit.org/volumes/Vol39No2/13Vol39No2.pdf

Both of these deal with large wind generators, which have the additional control option of pitch variation. The little wind generators we deal with on boats are fixed pitch (I'll even lump in the flexible blade units here, there is some pitch variation, but not a great deal). However, the same basic principles apply, possibly more so in fixed pitch installations.

The turbine/alternator design is (should be?) optimized for the typical conditions expected by the designer. Outside those conditions the turbine does not necessarily extract the most possible power from the breeze. You may be able to extract some (how much?) more power from the same breeze by changing slightly the operating voltage. That's pretty much the definition of MPPT, walking through the various combinations of voltage and current to extract the most power. If the turbine is designed to be optimum at 13.6V output voltage in 10K of wind, and the batteries are at 13.0 in 15K of wind you may be able to extract more power by holding the alternator voltage higher and then doing the voltage conversion. As with all MPPT voltage conversion devices, once you factor in efficiency of those conversions you may not win.

I know of a couple of other small wind generators that claim to use MPPT, but I suspect the market has a hard time demonstrating gain since we don't see it everywhere as we do with solar. One problem is the extreme inconsistency in power density of the wind, which means MPPT must track very quickly. I've seen measured gains with solar MPPT, but not with wind at our scale.