Arduino DC - DC Converter

I am working on building a arduino based dc-dc converter for my wind turbine. I have 260 ft of wire from the turbine to the house and am loosing more than half my power in wire losses at 12V. I want to build a 60V generator and send 60V DC (7% loss) to the house then the arduino chops it through a H-Bridge circuit, feeds it to a step down transformer to drop it to 12V. Rectifiers then convert it back to DC.
Mosfets are 400V 35A PNP and NPN (so they don't fry if the turbine goes open circuit)
Transformer is custom wound Primary 42,52,57 turns and Secondary 8,10,12 turns
Arduino Uno board using pins 1-4, I'm bit banging to keep it simple and allow for adjustable dead time between transitions to prevent shoot-through.

Problem I am having is that this is my first transformer project and I have no idea what the primary wave form should look like. Signal from arduino is crisp, signal from mosfet bridge in open circuit has slow fall times (first picture). This can be cleaned up by adding a small resistor across h-bridge output (second picture). When connected to the transformer it turns into a mess (third picture) I have a 100uF cap on the power side of the mosfet driver. Dead time is exagerated for diagnostic purposes till I know this is safe to operate. Does this look right or am I missing something?

Buy a converter that makes AC mains voltage. At your house, you can use a common power supply to make 12V.

I see so many problems. A step-up converter with a transformer and mosfets is not the easiest thing. That requires a good circuit or you will loose the same amount of power in that circuit. I doubt if that circuit is capable of putting a serious amount of energy into the transformer.

Why is that generator producing DC, rather than AC? Starting off with AC may make it all easier.

I've heard on this forum before that lots of power supplies that are designed for 220V AC can in fact handle DC as well (though 60V may be a bit low, they're usually rated for 85V and up). After studying their circuits a bit, that seems quite sensible to me indeed, as if I understand it all orrectly they typically first rectify the current, then chop it to a high frequency AC, pass it through a transformer, rectify again, and finally use a buck or boost type converter to get to the correct output voltage.

Do some research and experimenting!

Hi,
Have you done any calculations with regard to the operating frequency and the impedance of the transformers windings?

You are using a modified square wave into your transformer, this will produce harmonics and distort the "square wave" due to the current flowing out of phase with the voltage potential.
Each time you switch the H-Bridge OFF you have a collapsing magnetic field in the transformer windings, this produces a back EMF, being unloaded because the H-Bridge is OFF, this back EMF will be many many times higher than the 12V you are switching.

What MOSFETs are you using?
Do they have internal Source to Drain protection diodes?

I would think if you start trying to apply load you will have major MOSFET failure.

  • Where do you get your 7% loss, this can't be total, have you included the losses in going form DC to AC and then AC back to DC?
  • Is your transformer on a I-E core or a toroidal core?
  • What is the power rating of the turbine?
  • What gauge wire were you using when you had 12V DC transmission?
  • What do you mean by "Transformer is custom wound Primary 42,52,57 turns and Secondary 8,10,12 turns"

Can you post a wiring diagram of your transformers plesase?

Tom.... :slight_smile:

I've heard on this forum before that lots of power supplies that are designed for 220V AC can in fact handle DC as well (though 60V may be a bit low

Probably from me. The ones I tried worked perfectly well from 50V. I suspect, but have not tested, that they have a lower power capability with a lower input voltage.

I am afraid that I cannot see what an Arduino could possibly have to do with a power converter? :roll_eyes:

Do you know for certain that the output of the generator is DC? I mean, is it a DC generator with a commutator and brushes? If not then the output will be AC and will have a rectifier on the end. Remove the rectifier and you have AC, possibly 3 phase.

Then investigate how it is controlled, this is pure speculation but maybe you can get it to produce a higher voltage at AC.

You are going to have to make a very efficient converter to get enough savings in your cable to overcome the additional losses from doing a conversion at both ends.

I'd be looking at thicker cables carrying only the raw output from the generator and put all the electronics at the house end.

Agreed. An off the shelf power supply would do the job without the need of an Arduino in the mix. Too simple and straightforward a solution, lets not use that.

@OP: if you still want to go the Arduino way, go for the ATtiny85 or ATtiny861. They have a high speed timer running at up to 64 MHz, meant for operating brushless motors and switching power supplies. For that reason the high speed timer has three output compare outputs.

The ATtiny861 output compare signals operate two(!) pins each even: one normal and the other inverted, specifically for operating H-bridges. It even offers programmable dead time.

Furthermore, don't mess around with trying to drive your MOSFETs with BJT transistors or other hacks as seen in your schematic. That makes them operate way too slow. You will have to use MOSFET gate drivers to stand a chance of getting them to switch properly and fast.

That's beyond anything I've done.... If I was doing this I'd expect to fry a few transistors/MOSFETs during development & testing...

On the generator-end you could buy an [u]"inverer"[/u] to get 120VAC (or 240VAC). Then, use that as regular household power or if you really want 12V, plug-in a power supply at the other end. Totally guessing but you could probably get 70-80% efficiency with an inverter plus a power supply.


I also don't understand the purpose of a programmable microcontroller - Most power supplies don't have a processor or any software unless they have "advanced" features like programmable voltage or programmable current limiting, etc.

You didn't mention current (Amps) or power (Watts).

Off-the-shelf power transformers are usually designed for 50 or 60Hz sine waves (regular AC power). With square waves or higher frequencies I don't know what would happen. Of course there are special transformers used in switching power supplies and DC-DC converters.

Are you using an automobile alternator at the turbine? If so, use it to charge 12V batteries at the turbine site, which power a 110 or 220 VAC inverter for power transmission to the house.

Line losses go down as the line voltage goes up.

Lots of comments to reply too, thanks!
Turbine is turning 2 smart drive motors from washing machines rewired to produce 15V, these are 3 phase brushless motors then feed rectifiers on top of the tower, dc is then sent to the house. Cable is 2 runs of 10AWG wire for 4 wires total, running 12V I'm 60%+ wire loss, at 60V this puts me at 7% wire loss. Even with 500kcmil ($$$$) wire I would still have 20-30% wire loss at 12V so that's simply not an option, I need to get the voltage up. I didn't realize to power limitations of iron core motors when I started this project so I want to build an axial flux air core alternator to replace the undersized smart drive motors and wire it to 60V.
I thought I could send 3 phase to the house and wire a 3 phase transformer to step the voltage down but after consulting a wind turbine pro he advised me the axial flux alternator would need to cut in at 16HZ, the transformer capable of handling such a low frequency would be huge and making it 3 phase would need to be even bigger resulting in too much cost and transformer loss. So a dc-dc converter was the next idea.
To answer the other questions the transformer was removed from a large battery charger, its an iron shell type I-E core design. I found calculations online and rewound both primary and secondary to suit my needs. Primary is 3 strands 14AWG aluminum with taps at 42, 52 and 57 turns for fine tuning performance if needed. Secondary is 3 strands 8AWG copper with taps at 8, 10 and 12 turns. One note is that I am testing this at 12V as I don't have a 60V power source available, from my limited understanding this shouldn't hurt anything as its usually over voltage that puts the transformer into saturation.
I can't remember the mosfet numbers but they are 300-400V, 35A, internal diodes included and full avalanche rated. Switching frequency for the transistor drivers I wouldn't think would be an issue as its only running 60Hz.
The calculated 7% power loss is only for the transmission line to the house, I could always go higher if needed but would prefer to not go into the high voltage range.
The turbine is DIY built and should put out 800W with1000W peak, the current smart drive setup only handles 500W and the turbine is overspeeding in high winds, only 200W is actually making it to the house.
My dump load is currently running off an Arduino UNO and SSR and is running perfectly. I tried a mosfet driver chip but somehow fried it so I figured it would be ideal to use an Arduino instead then I could incorporate both into the same unit later on.
My question is what should the primary waveform look like? I know square wave wont be pretty but once I get this figured out I will try the modified sine wave design I also found on this site, basically switching variable pwm during each cycle to get closer to a sine wave form but I need to get this stage figured out first. I like the idea of having an inverter at the tower but any factory unit will safety trip due to wild voltage from the turbine, having a battery out there to smooth things out would be a problem as the inverter would drain the battery down when there is no wind and it would then freeze when it gets down to -35. I basically need a wind buck controller but such a thing doesn't exist in our current market so I'm building something instead.
Any help or input is greatly appreciated!

Thank you for the comprehensive comments and feedback.

One of the difficulties I have (and I suspect others have) in answering questions is correctly judging the knowledge of the person asking. It is quite clear from your comments that you know far more about this than I first assumed.

I don't have anything useful to add that I and others have not already stated so I wish you well with your project. I will keep monitoring this thread as I am interested to find out what happens in the end.

Good luck with your project.

++Karma; // For an interesting discussion.

That's understandable, you really don't know anything about a person over text. Guess its experiment time, see if I can get that waveform cleaned up. The circuit works im just scarred of putting power through it since it doesn't look right to me.

How much current / power does the generator(s) produce at nominal conditions? If generators were geared up to the 50 to 100 Hz range, you might use a commercial used / salvaged 3 phase transformer to kick the voltage up to the 60 VAC range and drop the unknown current by a factor of 5 for transmission to the house. Not at 23Hz though.

Hi,
Thanks for answering our questions, so comprehensively.

Can you post a basic block diagram of how you want to lay your system out?
The 12V (15V) to 60Vdc inverter will need to be researched a bit more, squarewave and modified squarewave inverters are inherently noisy EMR wise.

Where do you have your Dump Load in the system?

Can I suggest you find a say 2Amp Secondary mains transformer with the step-down ratio reflective of your step-up ratio and see what waveform you get.
The inductance of the windings appears to be having an effect.

Your DIY transformer, is a bit of an unknown quantity at the moment.

As I mentioned the switching from ON to deadtime will be a problem.
There is one solution that comes to mind, although simple in principle can be difficult in practice to implement.

Tom... :slight_smile:
PS. I think you know your method is how the windfarms connect their array of turbines and how long distance undersea power transmission is accomplished.

Have you investigated using large, surplus UPS devices that run on 12 volt batteries? They usually put out modified sine waves. I see bunches of them at the local recycle center. I have three in the garage that you could have! The AC waveform is 60Hz at 120 volts and would be easily stepped up to 240 volts for transmission to the house.
Paul

Hello, I have no intention of stepping up the voltage at the tower. The new alternator will be wound to put out 60V 3 phase AC so the step up wont be necessary, what I am working on is the step down at the house just before the battery bank. I should see 60V at 13-17A (800-1000W) from the new alternator.

Gearing up the alternator would be great but adds to the complexity of the turbine. After seeing what this thing goes through in a storm the drive would somehow need to be robust and reliable in very harsh weather, this drive would also add to start up resistance and if it ever fails the turbine will overspeed and self destruct that's why I was hoping to stick with the direct drive setup if possible.

I don't see any voltage spikes on the scope from the collapsing field so I'm kinda thinking the diodes in the mosfets are doing their job, the short collapse back to almost 0 after the transistors switch on looks weird so maybe you are right about that, how do you go about narrowing this down? I used the equation Turns = V/4/Meters squared/Hz/Tesla to calculate how many turns I needed given voltage (60V), square cross section of the transformer (0.003575Msquared), the frequency (60Hz), and the desired flux (1.2 Tesla). Multiple taps on each coil allow for adjustment in case I'm a bit off.

My dump load currently is connected straight to the battery bank through a solid state relay. My solar controllers are set to 14.7V and the dump load controller is set to 14.8V so it basically wastes any extra power the battery bank sees from the turbine but not the solar. I was hoping to incorporate the dump load into this project so the excess power can be dumped before it gets to the batteries. I also have a 12V actuator mounted on the turbine head to force and hold the tail into full furl position so I can shut the turbine down when not needed. The plan is that a single Arduino in this converter could manage these tasks simplifying the setup but I need to get the step down converter figured out first.

So you have 3 phase AC at the tower, and 4 wires from there to the home.

Why not 3 phase AC to the home? You only need 3 wires for that, and you have 4. Then at the home you rectify this AC to DC and step it down to 12V (possibly with a regular power supply).

I think it's definitely worth trying out an off the shelf 12V power supply. Less fun for sure but the currents you're dealing with are prone to give you a bit too much fun (fireworks are supposed to happen at certain days of the year only), and the main goal I believe is to get reliable power to your home.

Hi,
Thanks for the diagram.
I at one time serviced a 3phase 1Kw turbine, it was 110Vac, it was 120m of wire away from the battery/control system.
(Because it was in a 30m mast.)
The 3phase was cabled to the battery/control room as AC, then transformed (using 110Vac mains transformers) and rectified at the batteries.
The dump load was at the control room and applied across the 3phase when needed.

A very simple and workable solution, as the waveform was sinewave using 50Hz designed transformers did the job.

Tom... :slight_smile:

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