Diode Voltage Drop

You could try using a MOSFET (very low series resistance) in line with each generator, control the MOSFETs by some voltage comparators. With more than two generators this could be tricky.

Thanks for the suggestion, but I could end up with more like 20+ of these motor/generators working together. Some sort of comparison system would be too complicated.

I was thinking of stepping up the voltage by some type of transformer so the voltage drop would be less of a reduction in the overall voltage. But I was not able to test this and I don't know the theory that well. If I did manage to increase the voltage would it increase the efficiency of the diode? What effect would it have on the diode?

Thanks

Transformers don't work on DC.

Please post a circuit diagram that shows these things doing what they are intended to do. It would save a lot of time.

As a generalisation the diode will drop less volt at lower current.

So if you assume your generator will output a fixed amount of power (Volts x amps)

Then Higher volts will be lower amps therefore the diode will drop less volt...also the volts it does drop will be a smaller percentage of the total volts. So it's a win win situation.

Have you tried 1 bridge per generator....?

The transformer idea may be flawed as you the frequency of the AC from your generators will vary considerably... or will it...what is the application? (even if it doesn't vary the transformer will need to be designed for the right frequency).

I'm sure some more electronics guys will chip in...where's Electroman when you want him???

Del

Couple of immediate thoughts off the top of my head...

1. What diodes are you using now?

2. Presumably the output is going through a bridge rectifier at some point? Can't each motor have its own bridge and then join up the 'raw' DC. (If this is rubbish and would still feed back to the other motors I appologise...it's just that its quicker to try it than to sit there with a pencil and paper trying to work it out!)

3. Use motors with higher voltage/lower current windings?

This is a subject I have thought about, but havn't actually tried...how is the brush life going to be?

That's about it..

Del

I picked up a pack of assorted rectifier diodes at the local electronics store the ones I'm using are marked "IN4004 MIC". I have some other red diodes that are marked "v4148". I also got my hands on another device marked "BYX 30 500 E7405" I think this is some type of rectifier as well but a lot bigger. This one has less of a voltage drop then the others but I only have one and can't really test it.

I think the brush life on the generators will be rather low but I'll work on that problem later. I would like to figure this out first.

At low currents you want something like a BAT85. they do the same type of diode in highter current ratings..cant remember the No off the top of my head (1N4158?) whatever..I can check tomorrow....

It's good to learn by playing about...a lot of us will have started that way too!

Have fun

Del

OK, how about connecting groups of these generators in series? What's connected as a load; what are they doing?

The generators would be linked together like a miniture wind farm for power generation. If they were linked in series would they still drive each other as motors if there were no diode at all?

Yes. Reverse current flow is not possible, because a single diode will block it. It is preventing any storage battery from turning the generators as it would as if they were motors.

The problem now resolves into keeping about the same wind speed to each generator, lest the first one should dissipate most of its generated power in turning the second one backwards, and forwarding none to the storage battery.

These things sound small. What's wrong with throwing them all out and installing a single, larger, generator that develops a higher voltage?

Space and the mechanics around the idea are the main problems with using a larger generator. Also I am under the inpression that the cost will increase with trying to parellel larger generators. Am I correct to say that a simple diode will allow reverse current if the voltage gets too high?

All diodes have a reverse bias rating that limits their operational use. From memory, the 1N4001 silicon diode has a reverse bias rating of 50V, for example. Show it 75V reverse-bias and it will go

and then the current flow will stop.

KWNish writes...

"The trouble is the power generated by these generators is very small, less then 1 volt and current in the mA range."

and

"...but I could end up with more like 20+ of these motor/generators working together."

and

"The generators would be linked together like a miniture wind farm for power generation."

-----

You're using small DC generators that each produce less than a volt and only a few mA as the generating elements in a wind farm? So, we're basically talking about generating maybe tens or possibly hundreds of milliwatts total?

Milliwatts?

I'm having a really hard time seeing the point in this, KW. Please enlighten me, won't you?

-e

I am trying to educate myself on the principles and theory of this stuff using real problems that I encounter while creating a potentially useless device. In the process I will learn more then reading a book on this stuff and in the end I may end up with a 'useful device' or discover some attributes within the theory which may allow me to develop something that isn't useless. There is little likely very little value in this for you, but I do appreciate your help in my quest.

Ah! So your objective isn't really one of building a practical device so much as it is one of educating yourself in the basic principles? That makes all the difference, KW. Good for you! From reading your original post I'd say that you've got a pretty good handle on some of the engineering problems you'll need to overcome.

Others here have adequately addressed the problem of diode drop. You can minimize diode drop, but you can't eliminate it entirely even if you use some other, non-diode approach (by using MOSFETs in place of diodes, for example). As your generators don't produce much voltage, perhaps you should answer the questions of "why not?" and "how can I get these generators to produce more voltage?"

You didn't actually say, KW, but I'm guessing that you're driving the generator shaft directly by the propeller. Is this the case? If during normal wind conditions, the propeller doesn't drive the shaft fast enough to generate a reasonable voltage, you might consider linking the prop and the generator through a gearbox which increases the shaft speed over that of a direct mechanical link. Since the gearbox trades torque for speed, you may need to use a bigger prop to increase the torque available to drive the generator. But if you try this approach, keep in mind that gearboxes will introduce mechanical losses in your system, making it less efficient overall. And gearboxes are expensive and introduce their own problems.

A (far) less expensive approach would be to select a different generator that will produce a higher voltage (in exchange for less current) for a given shaft speed over that of the generators you're using now. If this were my project, this is the direction I would take. As it is, your low output voltage means your design will suffer significant losses due to diode drops, and there's not much you can do to eliminate that. Higher operating voltages mean lower losses because the diode drop represents a smaller fraction of the available voltage. As it stands, my hunch is that you may be attempting to solve the wrong problem. As this problem won't go away, I think your solution lies in a different direction; namely, find a way to increase your operating voltage.

-e

So I can minimize the voltage drop but not eliminate it. I can still look for an effecient diode, but with the power scale I am working with I'll need to minimize the drop beyond simple diode selection or increase the voltage. Using a gear-box will work but it would need to be small. The higher the increase in speed with the gearbox the higher losses, especially when in a small package. I guess I'll need to move my research into changing the characteristics of the generator. I am hoping to use 'off the shelf' parts to conduct real tests, but I still may find what I need.

I'll do some more digging on the generator.

Thanks

Unfortunately, yes. You're stuck (as are the rest of us) with diode drops.

The generator you're now using: is it (say) a D.C. permanent-magnet motor? Do you know its specs, ie, rated voltage and so forth?

Yep; I have a couple of D.C. permanent magnet type motors, all the same. I can get them up for a couple bucks each. They are rated for 1.5V and about 12,000 rpm if I remember. I pulled one apart, it has three poles on the rotor. Not sure what difference that makes.

For the testing I have a few wired in parallel with some more motors of the same used to supply the mechanical rotation of the generators. It's easier then going out side and waiting for the wind to blow.

If I could find something that will produce a good voltage at an rpm of 600-2000 I may be able to make something work in the real world.

Is voltage increased by the number of windings in the poles, the number of poles, or the strength of the permanent magnet?

Use transistors instead of diodes, a fully switched on transistor has a much lower voltage drop than a diode.

Hi Syhprum,

Yes they do, and its a good thing to know. My concern here is that if KW's output voltage hovers around a meager one volt, a drop of even 100 mV across the transistor represents a whopping 10% of the available output voltage. He doesn't have a lot of headroom here even when taking advantage of transistors in this way. My recommendation, then, would be for KW both to use a transistor and find a way to get a higher output voltage from his generator.

I'm actually a little surprised at this low output voltage he's getting. When I've used DC PM motors as generators, I've routinely seen voltage spikes higher than one volt even when turning the shaft just hard enough to overcome cogging.

Sounds like I should double check my numbers.

Am I correct to think you need an input current to 'turn on' a transistor?

a) Check your numbers... yes ..it depends how you are measuring your voltage! An oscilloscope is best, failing that, add add a capacitor after your diode (say 1000uF), this will help you to measure somewhere near the peak voltage with a voltmeter.

b) Yes to turn a transistor 'hard on' it will need some base current.

I would always say keep it simple at first...once you have the basics working you can try more sophisticated techniques.

Del

Thaz right.

Del is still figuring out how to jack the radiator fan motor out of his neighbor's truck without being seen (and the pox on that guy's pit bull)!

Yes, a bipolar transistor requires a small base current to turn on the transistor. On the other hand FETs, MOSFETs, and their kind are voltage-mode devices, ie, a voltage (on the gate terminal) rather than a current turns on the device. Such devices do draw a transient current to charge the gate capacitance, but otherwise the gate draws practically no current at all.

An earlier poster mentioned using a MOSFET. You may wish to take a look at this Wiki page on a synchronous rectification.

That link on synchronous rectification looks very interesting.

Not sure how the wiring goes to set up the diode and MOSFET in parallel but there is a limited amount of possibilities. The key is that I need to be able to use the forward bias in the diode to switch on the MOSFET. I would like to try to set this up to test but I need a MOSFET. Could I find one in an old TV, because I have an old TV.

Mosfets require a gate voltage of about 4 up to 10 for full turn on, cant see where your 1Volt generators would operate in this system.

Schottky diode is the lowest forward voltage drop if you have to use any diode at all.

Basically your 1volt power generation is not very practical if generator speed should drop your output would be zilch

Hi KW,

A number of online surplus houses sell DC motors cheap - "cheap" (a relative term) here meaning a couple of bucks each or per package of 2-3. American Science & Surplus is one such vendor.

Some Ideas...

Low-RPM (un-geared), high-voltage (12-24V or higher) DC permanent-magnet (PM) motors are probably your best bet. If the motor runs at such-and-such RPM at rated voltage, chances are it will generate something near that same voltage when driven at the same RPM under no load.

Note: As this is an educational quest on your part, you don't really need to build your "wind farm" using lots of generators. A handful (two, really) will teach you the basic principles of linking generators together; using more generators will not teach you additional concepts, but it will cost you more money. On the other hand, having lots of generators on your model wind farm does add a certain coolness factor to the project...

For my part, I would use two high-output (high-voltage/high-current) DC PM motors rather than many small ones. And Schottky diodes. If you have a hobby store near you - one that sells RC model planes - you might find a good selection of props for your generators. If you're ambitious, you can even make your own props. Designing and building your own prop has educational value, especially if your goal is in designing an efficient one. And try different styles, say, a "wind-bucket" of the kind used by anemometers:

You can make one out of funnels and rods. If this were my project, I would build my own props and try different prop designs.

Speaking of props: use one large enough to drive your generator under the heaviest expected load, say, one of charging a dead lead-acid battery. Better yet, use a prop big enough to turn the generator shaft in a minimal wind with the generator terminals shorted together. Don't worry; for generators in your size range there isn't much of a chance of blowing them up. (While you're at it, measure the current produced by the generator under shorted conditions to see what it is maximally capable of producing). This is a "worst-case" test. As your typical load won't be nearly this severe, testing your prop/generator combo in this fashion will guarantee that the prop is big enough to drive the generator under any load.

-e

You can use precision rectifier circuitary were high i/p impedence of op-amp is used to offset voltage drop across diode to almost 0.04-0.2 V with common diodes , but here you require additional power to op-amp , also complexity of the circuit will make it impractical to impliment as far your applications are concerned , you can work on diode - capacitor voltage multiplier circuit

Hi Vikas,

Diode-capacitor multipliers work with AC only. KW's wind farm is generating DC.

-e

Hello europium

I was aware of that , KW intended to do drastic changes to his design with modifications adding gear, change motor , add step up transformer to output AC it was just a suggestion if he changed to generating AC instead of DC , well thanks

Switching to AC is not really a bad idea. I was thinking that with an AC motor of roughly equal size the current generated could be run through a step up transformer then through a bridge rectifier to switch to DC. As the voltage is higher there would be less effect by the voltage drop. The key is that the final product must have DC output otherwise it would be necessary to synchronize the AC current when placing the generators in parallel. Also I'm not sure if it is common to see cheep mass produced AC motors of very small sizes. All that I see are DC motors with permeate magnets. I would like to keep to small motors.

Transformer??? See post#6

Del

I agree with europium on the possibility that the speed is too low to produce higher voltages.

If you're interested, RS Components offers small gears as well as small gear boxes with different ratios available. That is, if you're willing to spend a little more for your experiment which, I must say, is admirable.

If the price is too much, you could try using rubber bands and handmade pulleys.

More info would be nice...

I'd suggest getting a 24v radiator fan motor of a truck and sticking a nice big prop on it via a little bit of gearing (bicycle chain/cogs?) and play with that.

Quick simple and dirty & fun....

Del

There's loads on wind microgenerators on the 'net. Try asking for pictures from a search engine, as well as text-related sites?

Others have stated, quite correctly, that one is 'stuck' with the forward bias voltage drop in a rectifier. The 1N5xxx series are all silicon rectifiers with 0.6V nominal forward volt drop, the xxx numbers determining the maximum reverse bias voltage that the device will withstand. The 1N5xxx series are as cheap as chips, and a few mistakes won't break the bank.

A sizeable germanium rectifier with a forward volt drop of 0.2 volt might be applicable here, though, being nominally smaller and more delicate, it would need to be selected very carefully.

<unsubscribes> Good luck!

If you want to keep things simple, and, stick with your original idea, nobody has mentioned looking for Schottky diodes yet. Del suggested BAT85s: which are great low power Schottky diodes. Look at these power Schottkys from SGS micro: STPS20L25CT/CG

These are max forward voltage figures (they get slightly better for lower current than shown). Also if you're not going to use their full current capacity you're better off not trying to cool them. You should be able to get these for about $2 each, but, there are two in each package.

You are right, Schottky is the simplest and best solution.

I would recommend that you up size your testing to allow the use of a car alternator, which will give you far higher outputs that can use to directly charge 12v lead Acid batteries.....

Some VW cars with Diesel engines have 120 amp 12v Alternators......Lorries and trucks have 24 volt systems....take your pick!

Using motors is not an efficient method at all, theoretically good, but totally unpractical....

As a "small" solution you might test another type of diode - your "bread-and-butter-types" are not good enough for that task.
Take the THCS400 from ZETEX, thats a high-current schottky in SMD-size.
The VF is about 250mV @ 40mA instead of 400mV.

Apart from that I agree with the other posts which recommend to use one bigger generator.
Regards Uwe

If your main problem is voltage drop, you can resolve it with a "super diode", dont know if you are aware of that concept, it uses an operational amplifier and a diode to create a diode without voltage drop, i dont think the price of the amplifiers will be a problem because nowadays your can find integrated circuits with 4 or more amplifiers for a small price. For more information: http://en.wikipedia.org/wiki/Super_diode Good Luck :)

The super diode is for signal processing, not what is needed here. It will require more power from another source to minimize the voltage drop at the generator. That kinda spends dollars to collect pennies.

Lots of good ideas have been presented but the diode drop is real and unavoidable. it can be minimized with careful selection, use a higher current, lower voltage schottky for lowest forward drop at low voltage and current. It does not seem like enough power is being generated to warrent the use of any active device or MOSFET switches. I would go to the larger output generator or, I am not sure how well this will work but you may be able to series the motor generator outputs if you tie the shafts together with a gear or belt (rubberband) system so they spin at the same speed.

All wind industry is running on brushless generators.

To play with a small one, I suggest to find (recycle) an old floppy disc drive and to take out the pancake motor. Keep only coils (very flat ones glued on the PCB) and magnets (the rotor itself) and connect them to a rectifying bridge.

Good luck!

Hello Hottech

I did try that floppy disk motor , it was able to power a set off LED`s with rectifier , regulation

Hi Vikas,

I know that the output power is very humble, but I suggested it for just understanding the principle of a brushless generator. In this case, it's not only brushless but also ironless (or coreless) which bring another huge advantage at low wind speed as it has no cogging torque!

Regards

From what I understand brushless DC motors use transistors to switch around the magnetic polarity of the coils. How can these transistors be operated if the only source of power comes from the generator itself?

Or is a brushless DC generator essentially the same as a rectified AC generator?

Both answers are No.

A Brushless motor usually have 3 fields (they are the only ones I have worked on, if there are others with more or less fields I have no expertise on them, sorry). You need to get to the field connections before the transistors and there you will get 3 phase AC unrectified.

I could not even say from memory star or delta connected, but guessing Star. But also no neutral unless you can access the point where they are connected to each other (assuming star)

How many volts at what speed etc., no idea, I have never done it....

http://cr4.globalspec.com/blogentry/3708/Shawn-Frayneâ-s-Windbelt-Uses-Resonance-Not-Turbine-to-Harness-Wind-Energy

I find this link very interesting. I ran into it before but I didn't watch the video until now. I am curious as to the frequency of belt movements, but what really interests me is the power conditioning that he says costs a quarter, and if that conditioning will allow more then one belt/generator of the same to be linked together in parallel?

As others have stated, going to a Schottky diode is going get you the lowest voltage drop. The synchronous rectifier idea has promise, but you have to come up with a control signal for the MOSFET, meaning added complexity. Have you considered a bicycle type generator? Maybe it takes more torque or RPM than you have available, but worth a look. The cheap ones can be purchased for around $10-15 dollars.

Tom

An excellent idea!!! Efficiency at low revs!!!

For my part, I've not gotten much efficiency out of those types of "bicycle generators." On the other hand, the best motor/generator I've tried has been of the rare-earth (samarium/cobalt) magnet motors. On the down side, they're expensive and from the looks of it, KW doesn't have a large engineering budget...

You're right on the engineering budget. Cheeper the better. Then again it's hard to put a price on education. As long as it's cheeper then spending the evening at the Pub I'm ok.

I'm curious to know what makes the bicycle generator diferent then the regular PM motors of the same size?

First off, AC comes out of it in response to its being turned. It's a combination of a coil and a fixed magnet (whichever one spins is not relevant).

Second, its speed-to-voltage characteristic in combination with using a filament bulb load is quite flat; it has to be otherwise the lights would go dim as speed drops and the bulb would blow as speed increases. The characteristic of a filament bulb is compatible with this, as its resistance increases with temperature.

Third, the frame of the bicycle is used as an earth return, which means it needs, and is fitted with, only one wire from the generator to the switch (if fitted) and from there to the lamps.

It is quite possible to get some DC from one. There again, one needs a diode (a rectifier), or, better, a bridge rectifier to get the most from it, so the problem of forward voltage drop is still there.

A suitable home-brew self-learn project might become:

• Find a way of using wind to turn the bicycle wheel. Mechanical attachments that permit the wheel to turn at an appropriate speed while driven by wind will take a bit of thought best expended at the local Pub with a pencil and a few Kamikaze beer mats.
• Make a connection from the generator to the storage battery via a bridge rectifier so as to convert AC to DC. What current rating should the rectifier be in order to survive the experiment?
• Add a voltmeter and an ammeter into the circuit so one can see what is going on.
• Find a windy place, set the contraption up, observe and monitor the results.

Something that might involve a few friends perhaps or, for the older experimenter, some young offspring? Take a picnic!

This is not my field, but here are some thoughts anyway:

Your post appears to imply that the generators always produce the same sign of Voltage output (always driven the same direction because of a sail or similar??)

In that case, it will usually be possible to group your generators so that members of a group see similar wind conditions. Then you can happily place members of the group in series. You can also limit the losses in any one of the generators (when it lacks power) by placing a reverse diode in parallel with each generator. This would be in addition to one series diode per group. The parallel diodes will only be operational very rarely, so you will lose very little power.

The worst problem with these simple arrangements is that only the highest Voltage generators (or series groups) contribute. That's fine if the fan RPM are reasonably similar, but not if they see very different wind conditions.

As others have suggested, you should be able to find suitably rated (small-signal)*** Schottky diodes in the catalogue of a reasonably local electronics distributor. If possible, you should aim as close above 200-mV forward Voltage at your typical operating current**, as this is about the lowest Voltage that is compatible with an adequately low reverse current (assuming your temperature range is moderate).
**If the Schottky diodes are specified for higher forward Voltage, a useful rule of thumb is that the current changes by about a factor of ten for each 60-mV change in forward Voltage (this rule often fails above about 350-mV forward Voltage, because strong injection effects and series resistance become important).

***These should not be too expensive, because they have been used in very high volume applications. I suspect US$2 is a bit steep. An alternative with slightly higher drop at the 10-mA you want could be something like the BAT721 series that give 300-mV maximum forward Voltage. This is a range of dual diodes that sells for about 0.2US$ (that's 0.1US$ per diode). Watch out that you buy the connection that you require - different for your original arrangement than for the devices in parallel with the generators.

Good luck with your project

Fyz

A few days ago I suggested that ex car alternators are a good bet, you seem to have not read my post....

Why are they a good bet you may ask? here are a few reasons:-

1) Cheap, you can get working ones from any junkyard for very little money

2) They have (in all but the oldest versions), a built in regulator and diode bridge. If you want AC, then get an old one with the separate box.

3) Are built with lugs etc so very easy to mount mechanically and can be driven by a v-belt.

3) Car ones are built to deliver 12v and trucks 24v - your choice.

4) Are designed to start outputting at quite low (under 700) RPM. Gives full output generally by at least 1500 rpm, but regulator controls voltage to make sure for instance that a max of of around 14.4 volts (cars, I would guess 28.4v on lorries) is achieved which will charge a 12v car battery. This means that you do not have to worry about over speeding or under speeding, the alternator simply does not care as long as you achieve something like between 700 to 6000 rpm.....a wide range of wind speeds....Even the 700 might not be the lower limit for some, I had a car many years ago that ticked over at 700rpm and it charged the battery. It could be that the two pulleys were optimized for low revs I have no idea anymore, something you could easily test out with a small motor...just at what low rpm usable output is still developed....

5) Electrical storage achieved with car batteries as just mentioned in 4).

6) Weather resistant to most types of inclement weather as what they had under the car bonnet (Hood for the USA) was far worse than what you will be doing to them!

7) Easily replaced with another if one should break. Most scrap yards that I have used give a short guarantee and will replace a duff one within say 2 weeks or so...

8) Is already diode isolated so that running two in parallel should not be a problem. Remember, it usually runs with a battery connected, so having voltage on the other side of the output terminals is normal. (Though I have to admit, that is a theoretical comment, I have not tried it personally, I see no problems...)

I see these alternators as being a prime source for your test project (I would be most interested as to why they would not do the job!) as they cover many of your needs without you needing you to design something both mechanically and electrically, why do you not consider one or two? A lot of your problems that you have mentioned here with your present setup would be fixed immediately by using them.....

Andy Germany

My friend, I did read your post and found to be a rather interesting and practical as a solution. I regret that I didn't place my thoughts in a comment at the time but as you can see there have been very many useful and interesting comments made here, commenting on each would be, well impractical.

You are correct in stating that a automotive alternator would be ideal for my experiments. The issue is the physical size. My original conceptual plan had many small generators (of theoretical infinite number) linked together in parallel to create a large output. I wanted to know how it would be done. My attempts to do this brought to light the problems with the diode drop. My preferred course of action is to find a way to solve the problem of the diode drop rather then adjust my original concept plan to allow the problem to exist such as increasing the size and output of the generator. The benefit to doing this the possibility of discovering a way to do something that others say can not be done. The risk in keeping to the original concept is the possibility of creating something absolutely useless. I am inclined to increase the scale of the project for this purpose, but it feels like I'm cheating. With that said I could chase the perfect diode forever and accomplish nothing in the end. It's a mater of balance. In time without success only a fool keeps his course.

Could a small polarized capacitor be used to bias the current, it would not be as sure as a shottky, but with less loss and more gain?

Guru's please explain your responses.

Don't see how a cap' can help??? (other than how I mentioned in an earlier post)

..if it's across the supply it will just charge and discharge on alternate half cycles, unless you put a diode in circuit to stop the discharge...in which case you are back to your diode drop.

If it's in series with the supply it will pass AC to some extent but not DC.

To try and utilise the polatisation is a recipe for failure. A reversed electrolytic can go bang in a spectacular fashion.

I hope this counts as an adequate explanation.

Del

<A reversed electrolytic can go bang in a spectacular fashion.>

Good reminder.

Been there. Done that. Got the T-shirt, which had to be thrown away because of all the stuff that erupted from the capacitor when it went , along with a pair of badly-soiled underpants and the carton from a box of sticking plasters that got used up shortly afterwards. DON'T REVERSE-BIAS ELECTROLYTIC CAPACITORS, dear reader!

A polarized capacitor does not do anything that a non polarized one doesn't---except: blow up (standard electrolytic), or, catch fire (tantalum electrolytic); if you try to charge it with the wrong polarity.

In my experience, the polarised ones can also be physically much smaller for the same capacity.....

Use Ge diodes. As the fwd drop is very low. PIV is well hi for the project.

if Ge Transistors are available, EB or BC junction can be used.

Very simple solution.

Haajee

Thanks for your comments. Unfortunately I am not familiar with "Ge diodes". What does the 'Ge' stand for? Also I do not know what you mean by 'PIV'? "EB"? "BC"? This may be a simple solution, but I am a simple man, and abbreviations confuse me.

GE Germanium most transistors are silicon these days.... The first ones developed were germanium and workd in the opposite polarity.

BE BC etc --- base-emitter base collector.

e.g. You can use the base emitter junction of a transistor as a diode.

If you use a transistor (of any description) as a diode, you need to be aware of the following:

a) The reverse breakdown Voltage between base and emitter is rather low (typically between 3 and 7 Volts - but check the data sheet before you blow anything up).

b) If you can afford the low breakdown Voltage, you will get the lowest forward drop if you connect the collector to the base, and use C+B to E as the diode

c) Next best for forward drop is to connect the emitter and the base together, and use the diode betweem E+B and C. This will give the rated VCBO of the device as the breakdown.

Ge for Germanium & Si for Silicon

Did you see my comment about connecting at least some of the generators in series and limiting the reverse voltage across any one of them with a diode? The loss in that diode will at most be the same as you would get in a series diode - and most of the time it won't be active - unlike the series diodes, which will always be active if ththe associated generator is providing power. (Or is there a problem in applying it to your arrangement?)

Fyz

My reply: to KWNish #13

It is a Ge Rectifier
[Fwd V Drop 0.2V 200 stands for = 500v PIV, 500=500V PIV; 14A; T_on = < 350MS

& with R suffix = Reverse in polarity
Package = Stud [for threading in a Heat-Sink Threads ?? ]

My reply to Del the cat #15:
(1N4158?) to 1N4193 type is a series of Zener Diodes;1W; 6.8V - 200V


In a series of Diodes with common 2 starting digits like 1N-40xx have the same wattage, but PIV rating varies with next 2 digits xx, e.g. 01 = 50v, 02 = 100v & 07 = 1000v.
But it is not a standard formula. PIV may be different with other series.

My reply PWSlack #10 :
It is termed "PIV" Peak Inverse Voltage to which the device is Guaranteed to withstand.

Most of the people have misleading concept on it. e.g. in a rectifier/ charger circuit
voltage applied to diode is the sum of rectified output across the DC Filter /Battery & the Peak voltage of AC supply. So in approximation x2 of the AC peak

Reply to : KWNish #17

To minimize the fwd drop; [in your case almost >50%]; but will be the least if you increase the output of Gen. As the Fwd drop of diode will remain constant [0.7v for a Si & 0.2 in case of Ge diode.

Reply to Del the cat #24
A 1000µF will drain all its output with its leakage current & take a long time to charge.
I think just 1-10µF will do do better. He should use a sensitive Voltmeter [DVM]

I feel you are replying to people who do not need one...

Indeed you quote me out of context...the question mark (!N4158?) indicated I'm not sure of the number and am mrerely trying to recall it...indeed I state I can check the actual number if required...no such request was forthcoming... I believe it was a 1N5001 I was ttrying to recall..but again don't quote me on that!

(Check my signature for confirmation)

Del

Sorry for that, Regards

Why not try another option:

If higher power is not the goal, and maybe if it is, (it just complicates the matter) just connect each generator output to an inverter circuit, which will also work as a buffer, using the generated power to feed an oscillator, (difficult with these low voltages but... ) and through transformation increase it back to whatever level you want (that's easy) Not practical, but maybe an answer to your experiment.

Wangito.

Theoretically possible, but on a practical scale basically useless. You are trying to make something out of nothing.....the losses would account for any gains....

What the original poster is trying to do on a cheap scale using many cheap motors as generators, with all its problems, will never become anything practical, too little energy from each motor, too complicated. He will at least need to find small motors where he can move the optimum commutation point to where a maximum voltage is obtained, Motors are designed to be used as motors, not generators.... I have not studied the way these motors are built today, but that might be completely impossible....if not very, very fiddly when dozens of motors are envisaged....

Furthermore, most of the motors(not all) have a commutator, which is subject to wear and tear, I would not be surprised if some motors were damaged in this area within a week of starting......they were never designed to work in this manner..

The good point is that before he has invested much time and expense, he now knows what is going to happen. He has had some really good advice and tips from people like ourself.....He should be grateful.

Grateful is an understatement… The amount and quality of the responses that have been provided here are much more then I expected. The comments made have helped me to connect a lot of puzzle pieces together. I would like very much to be able to work with and test each one of the ideas presented. It would certainly help me to understand them all in greater detail. Unfortunately time and resources are limited right now but hopefully in time I will be able to go into more detail. In the mean time I would like to thank everyone for there comments.

Over the past few days I have been involved in another unrelated project that all but took over my entire existence, I haven't been able to follow through with many of the comments made recently. I am just about clear from that so I should be able to focus more time to this now.

I get the point that I should up the scale a little to allow the use of a larger voltage generator. I can use what I learned already to optimize the efficiency. Another reason to up the voltage is for power transmission. It wouldn't make much of a difference in my little project but in theory I would need to transmit the power generated at least some distance. With the price of wire these days, a little reduction in conductor size could make a difference in the price of the system. Operating at a higher voltage will allow a smaller conductor to be used to transmit the power.

Am I correct to say that the best place to increase the voltage is at the generator? A bicycle generator creating AC power would work, but as a thought experiment designing a similar generator to produce increased voltage would increase the required torque to spin it… Correct? Assuming the frequency is not stable enough to use a transformer, and I still want in increase the voltage, could I use diodes and capacitors to make a voltage multiplier like described in this website? (http://www.reuk.co.uk/Making-Voltage-Doublers-and-Multipliers.htm) What would the losses be in a multiplier such as this?

If you wish to work with AC, and have access to off the shelf items and components, you need to have AC at 60hz, which will be a single speed of rotation that you will need to maintain. The speed will depend upon the design of the Alternator you are turning, how many poles it has etc..

AC has the major plus point that within reason you can up or down the voltage with transformers, which is not so easy with DC.....

I feel that you should start to decide what you are going to do, you know my advice which is to go for a 12v DC system and if you are able to generate/store enough of it, there are electronics you can buy/make (making is a bit dangerous!) that will convert it to the AC voltage and frequency of your choice.....I assume 115v 60hz...thats how some people in Germany make money, they generate enough to allow them to feed back into the national grid and they get paid for each watt produced.....