# DC to DC converter, step up

• posted

Sorry if this sounds incredibly basic.

Can someone point me to a unit of some sort to step up say, 3 volts, to 12-14 volts. Input is a wind generator I'm toying around with. When it isn't turning very fast the voltage can be pretty low, I'd like it to simply store the low voltage and when enough is stored, jump that up to 14 or so in bursts to charge a battery.

Thanks,

/g

• posted

Problem is that if you succeed in sucking out power ay low speed, you're likely to stall the rotor.

What level of power (how much current) are you working with?

Grant.

• posted

Is the 3V smooth or very lumpy? If it is smooth what you are looking for is some sort of DC-DC converter to boost the voltage enough to do the charging.

Have you tried putting some sort of load such as light bulbs onto this

3V to see how much current you can draw?

If the amount of current is very low, the converter needs to store the energy at 3V for a while and then boost some up to the battery.

If it is high enough, you can do it continuously.

• posted

If it's lumpy you could pump the lumps into the battery, no?

Yes, charge input capacitor after rectifier diodes and dump into battery when voltage (thus stored charge) gets up to a useful level.

That too.

Grant.

• posted

The converter could choke a bit on the lumps. But you can use a delumpifier, commonly called capacitor :-)

A rectifier requires a good look at 3V. If it drops a volt that'll be a

33% energy waste right there.
```--
Regards, Joerg

http://www.analogconsultants.com/```
• posted

Funny how interpretation changes upon re-reading. I was thinking wind power -> 3 phase AC -> rectifiers.

Of course one might use a DC generator :) But you'd then need a rectifier to stop capacitor discharging back into the generator.

The rectifier voltage drop doesn't waste that much power, as the voltage from generator will go up on no load until current is drawn again. So there's nothing like a 33% power loss at 3V involved by adding rectifier.

Grant.

• posted

Automotive Alternator?

...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
• posted

3-phase would be the deluxe version :-)

You could also use a FET but it must be one that reliably conducts at

2-3V, there was another thread here where Charlie wanted a reverse battery protection, subject line is "Favorite reverse bias ...", thread start date 3/16. Essentially the body diode of that FET does the initial job and when a few volts have developed the FET bridges that with its low Rdson.

I meant under load, assuming that's when efficiency really counts.

```--
Regards, Joerg

http://www.analogconsultants.com/```
• posted

They're not very efficient, they want high speed, they want rotor power, no good for wind power. Permanent magnet much better.

• posted

Really ?:-)

Check out my patents.

...Jim Thompson

```--
| James E.Thompson, CTO                            |    mens     |
• posted

Most stuff I read about is 3-phase, unless one sources a s/h big DC motor from old mainframe tape drive or something. Plus, there's no brushes or sliprings up on the pole to wear out with a PM alternator.

That would work. Because wind energy has a cube factor re: speed, there's very little one can do at the low wind speeds to extract energy.

Oh, sure. Use the FET to get that extra bit :) Or half way with schottky diodes?

Grant.

```--
http://bugs.id.au/```
• posted

Schottkys under load still drop around 500mV, why waste it if low Rdson FETs cost just a few dimes?

There was a bet going on in a German NG where someone said you can't yield 90% efficiency when converting from a fuel cell (600mV) to 30V. Well, long story short we all pitched in with some hints and then one of the guys did it, built one.

```--
Regards, Joerg

http://www.analogconsultants.com/```
• posted

The wife of a friend wondered what one could do with a bicycle wheel as a wind generator so I started to build one in tinkering mode. I removed half of the spokes leaving a fairly reasonable set for a maybe-ok angle on them. Since then it occurred to me to look on youtube and there are several there already, for example

although he doesn't have that hooked up to a generator yet. This one is cool:
This was a bit annoying and not a bicycle wheel, yet educational:
and I'd recommend it to anyone interested in this topic.

Ok with that proper stuff out of the way, back to my redneckish project. Of course the blades, for lack of a better word, on the bicycle wheel are not ideal, though there is a possibility of extending outward. I removed the bearings and synched it up so the threaded shaft can no longer turn freely, planning to couple to the generator shaft (not the same diameter, argh, well ok, slap forehead and press on). The idea is to just see what can be done with fairly easily available materials. The pipe dream would be to inspire tons of people to build something simple for themselves. So, even though I have some DC motors that I think would work well as generators, wanted to have something easily obtainable by the average household, so I dropped in to the local wrecking yard and picked up a radiator fan unit from some sort of Chevy vehicle, 1991. (Windshield wiper motors have a worm drive and not too easily removable gear housing that made them less practical, fuel pump is messy, couldn't find an automatic antenna motor, any others?). Wanted to find a newer fan motor, figuring newer would be more efficient, ran out of patience in the oily mud. Anyway, the fan itself was nice after some cleanup though I figured it wouldn't do well as a wind turbine, for several reasons (including, only about 14 inches in diameter) so I removed that part and am left with the motor, or in this case generator.

Turning the fan by hand when it was still on there I could only get about a volt out of it. No worries. Using a hand drill at max, just

10.5 volts. Now worries. The drill says 0-2500 RPM. At 2500 that's some pretty ******* strong wind, rare, bummer. So hence the question.

By the way this motor/generator has permanent magnets. Turning it slowly by hand you can feel the tug as pole pieces line up with the magnets and move past them. Not all radiator fans are like that and I'm not sure what the others are up to. Actually, without taking this one apart you can look through gaps and see the magnets and coils and inside, I'd guess 16 gage wire.

I was thinking one can pulse DC at a fast rate into a transformer and rectify the output for higher voltage DC (and proportionally lower current), with some degree of power loss in the process ("switching" power supplies). Figured there might be off-the-shelf units for that. Or it might be cool to hack a computer power supply, which I think are the switching type. I'm not familiar with solid state DC-to- DC converters.

Originally I was thinking something more primitive. Charge a cap from the generator and when the voltage reaches 3.2 or so, a zener diode triggers a transistor which both closes a switch to allow the contents of the capacitor to dump into a step-up transformer and simultaneously opens (stops) the zener path to not blow it out or waste energy. Or maybe that isn't necessary for the zener trigger side, as mentioned just use a FET instead? Or even a resistor to limit the current. So then, once the pulse into the transformer is triggered, there will be some output, however, it has to be repeatedly pulsed, can't just leave it flowing steadily or the transforming stops. Maybe charge 4 caps in parallel and discharge them in series.

I feel like a guy with a couple of hammers looking at a grand piano figuring maybe hitting it a certain way a concerto will emerge, knowing pretty much exactly enough to be dangerous.

Was hoping for a unit to buy, 3-6 volts in, and intermittently 13.8 out. Current becomes an issue? How much here, I'm not sure. Donno how best to measure the current output capabilities of the generator. Do think I have a precision 1 ohm resistor laying around somewhere if that helps. Just using my VTVM I didn't have to spin very fast with the drill to reach 8 amps (max 10 for the ammeter and didn't want to blow the fuse). That's with virtually no load. The coil, just hooking up to the two wires, measured .4 ohms.

Hmm, now after seeing that last video mentioned above I'm thinking I might prefer to scan the neighborhood for one of those exercise equipment treadmills with the "Free" sign on them next to the street by someone ready to just return to their cheese puffs. Sounds like they have fine DC motors/generators.

Now I had all of this written and was about to send, then googled DC- to-DC converters and found

Got to wondering if one could be pulled out of a dollar cell phone from the thrift shop. Eah cripes, no, seems would be too small to handle much current.

Thanks for the responses and kudos to anyone figuring they could help put this more on track (or is that this moron on track, lol).

• posted

On Mar 21, 3:18=A0am, gseattle wrote: [....]

.

Perhaps a cheap and nasty DC-DC converter can do what you want. I will fling this idea out there and see if anybody likes it:

You can get the sort of transformer that is used for door bells. Running it backwards, it will step voltage up by a factor of about

10 instead of down by 10.

You can use a bridge rectifier on the high voltage side to charge the battery.

On the low voltage side, I am going to suggest a second wind turbine like thing. A small turbine a few inches across, can work a set of points to open and close the circuit on the low voltage side of the transformer.

I expect that the efficiency will be very low but if the parts cost is low enough, the power output per dollar may be reasonable.

• posted

Wind power thinking is very new to me, and I'm probably off the beam on a few comments, but here it is anyway....

This cogging effect you are talking about would seem to couple together with blade diameter/design to set the lowest wind speed you can accommodate. (I didn't enjoy your comment about 2500RPM yielding 10V -- which implies you need to rewire the motor, at a minimum, I think.) If you want lower wind speeds to provide a useful result or otherwise use a motor with strong cogging generally, you will need to use a bigger blade system and/or better blade designs, I think. I also suspect you may need to consider practical ways to modify whatever motor system you find in a junk yard to mate better between whatever prop you use and electronic circuit on the other end.

Jon

P.S. I know you are thinking about the ease of getting a design done that is easily buildable and where efficiency isn't the primary goal, but some additional wild scattering of thoughts still occurs to me....

NACA (the precursor org to NASA) prepared huge books on the subject, by the way, as part of understanding how to couple blade systems to air, and there was (and is) a great deal of info now available on the subject. I wonder if there might be some software on the subject, even. A couple of special terms to look for might be Blade Element Momentum (BEM) and Computational Fluid Dynamics (CFD) methods. BEM is more a 2D approach while CFD provides 3D to compute flow variables and accommodate rotational effects that BEM requires empirical testing and measurement to approximate with tables. Blade tip considerations are important, but so is the blade cross section plan from root to tip. The whole design can be very important in getting the most out of the blade part.

Also, it may be possible to construct a custom blade system using existing and not overly complex polyurethane or expanded or extruded polystyrene foam and fiberglass cloth and epoxy or polyester resin construction techniques that are today used for making surf boards (which are pretty durable and very 'shapeable.') Shaping can be done in a variety of methods, including sanding but also perhaps using a few hundred watt soldering guns with appropriate copper wire spans as a "tip" to get the basic shapes worked over before going on to finer and finer approaches to get a laminar flow over a greater range of air speeds and rotational rates.

Assuming the very important issue of wind speed as a given, two parts of the system seem vital: The blade which should be designed to couple wind to motor and the motor itself. The motor design is a transducer changing mechanical torque and rotation into electrical energy and the blade is also a transducer converting translational velocity of air into mechanical torque and rotation. Everything else seems to turn on these two transducers. So that would seem to be where to focus more of one's design effort.

This makes me think of yet something else that might be a helpful project. There may be a need for a small, cheap (in other words, not too painful to lose or break or field a dozen units) device that can be placed somewhere and will continuously measure wind speeds in any remote site (battery powered, self-contained recording, and able to be placed on a tall pole top, for example.) Something that could be left there for a year would be nice so as to get a complete, annual profile to work with for later designs or comparison with other sites or just talking with engineers about what you might expect to see with commercial systems vs what you get with anything you make and test.

• posted

Here's how my wind turbine thing turned out. Thanks for your help.

Hope you like:

• posted

interesting... the nrg site has a bunch of voltage graphs. Couldn't find any infinitely more useful power/time graphs. or power/wind velocity graphs.

• posted

I liked your wind generator almost as much as the young lady in the video.

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Wow, I got all excited. I thought MooseFET was back. (till I noticed the date.) Anyone know why he went away?

George H.

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I didn't watch the whole thing. Did you say how much power you get out of it? I guess the thing about having a bigger wind turbine is the dollars/ w att output is cheaper. And then of course I could ask if you will ever mak e enough energy to pay back the 'energy cost' of all the parts that went in to your windmill. We've got a bunch of big windmills near my house. AIUI the energy pay back time is 3 to 6 months.

George H.

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