Showmans engine generator

[ScrumpyParticipant @scrumpy]

Just to muddy the water last night a friend called with a permanent magnet motor from a small wind turbine on the can is printed 36w-12 v-24 v is this a better option for me as the size is perfect if so what regulator would I need as I have bought the LEDs these are Vaol-10 gwy4 rated 20 ma /3.5 forward voltage what ever that is there would be 50/60 of them over to you people as I find this all a black art wrong age thanks in anticipation Derek

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Scrumpy on 11/10/2016 10:38:01:

… I have bought the LEDs these are Vaol-10 gwy4 rated 20 ma /3.5 forward voltage what ever that is there would be 50/60 of them …

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First step is to undertand what that spec. means:

Each LED will draw 20 ma, when supplied with the specified 3.5 volts.

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You can connect them in series, or parallel, or any mix thereof … the voltage and current for the full set will depend how they're interconnected.

 12 parallel groups of 'four in series' running on 12 volts would seem a good start.

MichaelG.

Edited By Michael Gilligan on 11/10/2016 10:56:31

[GwilParticipant @gwil]

LEDs behave differently from incandescent bulbs – a small change in the voltage across them means a large change in the current going through them. It is always necessary to control the current somehow, usually by making the supply voltage a good deal higher than the voltage across the LED(s) and adding a resistor in series. For example to run a single white LED (3.5V forward voltage) at 20mA from a 12V supply one needs a resistor to lose 8.5V. Ideally that would be 425 ohms, which unhelpfully isn't a standard value but 470 ohms is standard and would only reduce the current slightly. Two LEDs in series would have 7V across them leaving 5V for the resistor (250 ohms ideally this time), but you have to be aware that the smaller the voltage across the resistor the more sensitive the arrangement is to variations in supply voltage and LED voltage, which can change with temperature. Series and parallel wiring works but you always have to consider how the current is being controlled.

[Tim StevensParticipant @timstevens64731]

In view of your lack of experience with LEDs and their oddities, can I suggest a way forward?

You could settle on a voltage standard for which there are many regulators around – 12volts – as used on all cars and almost all motorcycles for lighting etc. This would also make two other things easier – the supply of a range of suitable LED bulbs, without head scratching over voltages and resistors etc; and the possibility of adding a battery supply so that when the engine is not running you can display the lamps.

The wind turbine seems ideal for this sort of use, and regulation could rely on a motorcycle-type Zener diode. These will cope with an alternator output up to 150 Watts, given a sensible heat-sink (or 'radiator, in unhelpful car-type terms). This is well over the output of the 36W wind device, but a regulator which will cope with more than you have got is going to last for ever.

You will need to play with the generator driving a small pulley on the generator with a fairly big one to suit the engine, and this will tell you if these sizes are going to give you sensible output (ie that you don't need another gearbox etc).

It seems a shame to abandon the LEDs you have bought, but you should be able to get some joy by connecting a few of those you have, in series, and driving them with a car battery. If they are 3.5V each, then four in series should work, but try six and five, too. Then when you are happy that one 'set' does what you want, further identical sets can be added in parallel. And if these terms are new to you. come back to us.

And don't forget that the generator will produce AC, alternating current, but the LEDs need DC, direct current. This means you need a 'rectifier' – again a simple matter of a few quid (or lots more from a motorcycle spares shop). The wind generator may well have a rectifier within it, so check this detail. It certainly would if it was set up to charge a battery on a boat, for example, but you might not have got the complete kit.

I am tempted to say 'Bring it all round and I will try to get something going for you' but I don't suppose Ludlow is just up the road, is it?

Hope this helps

Cheers, Tim

[Tim StevensParticipant @timstevens64731]

PS I suspect that the generator shown by Ian S C is going to be too big for you (in electrical terms). It looks like a full size motorcycle stator (the outside ring of coils) and so could be expected to give 200W or thereabouts, at about 2000rpm upwards. The rotor is a home made mod, replacing an electromagnet – so it will need a big regulator too, as well as a powerful rectifier. It will also be capable of powering a boxful of LEDs.

Cheers, Tim

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Gwil on 11/10/2016 13:55:23:

Series and parallel wiring works but you always have to consider how the current is being controlled.

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Quite so … That''s why I suggested "a good start" … for the subsequent design process.

Constant current regulators are a better arrangement than dropper resistors; but whatever supply is decided upon, the basic choice of how many LEDs are in circuit is a good place to start.

MichaelG.

[MuzzerParticipant @muzzer]

There's a relevant app note from Infineon here that outlines some of the design considerations. Nothing clever about the constant current driver they are offering, as it's just a linear circuit incorporating a transistor, 2 diodes and a couple resistors.

You could easily knock something up yourself with guidance from here. Otherwise, they are ready to go, offering typically 10-60mA and up to 40V. Obviously you'd need a small PCB with heatsink or heat spreader.

[Neil WyattModerator @neilwyatt]

It's pretty easy to wire a low drop out voltage regulator as a current limiter.

Google will provide circuits & formulas

Choose the regulator for Vref as small as possible.

Neil

Edited By Neil Wyatt on 11/10/2016 16:31:44

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Scrumpy on 11/10/2016 10:38:01:

… I have bought the LEDs these are Vaol-10 gwy4 rated 20 ma /3.5 forward voltage what ever that is …

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Neil & Muzzer

I was simply doing Scrumpy the courtesy of taking this in gentle steps:

Thanks for posting the Infineon note, Muzzer … It's the obvious choice, but I had mislaid it.

MichaelG.

[GwilParticipant @gwil]

I should probably have mentioned constant current drive (like Michael G I was starting from basics) but now others have dealt with it. It is certainly the most efficient approach if you have a high supply voltage to take advantage of.

[MuzzerParticipant @muzzer]

In fact the efficiency will be pretty miserable, especially at high input voltage, as pointed out earlier in the thread but it's probably the simplest solution. For efficiency you'd want to use a switching converter but that would add to complexity. Linear have quite a range.

Something like the LTM8042 boost regulator can operate over the range 3 – 30V with efficiency over 90%, although the LT3519 is a more versatile beast specified for automotive applications.

I've not used any of these but there are a range of options, depending what you are looking for.

[ScrumpyParticipant @scrumpy]

I would like to thank every one for all there help and advise especially Tim sadly i live on the Cornwall Devon border with all the information I have my brain is trying to evaluate it all

My first decision is which of the two Outrunner motors I have I use along with the LEDs so only a regulator required but what along with other components

Do I use the permanent magnet motor from the wind turbine along with the LEDs again only a regulator required but which one along with other components

I would like to use the main body of the engine as a heat sink if one required

But I feel at this moment its away to a dark room with a drink Derek

[GwilParticipant @gwil]

Hi Muzzer

What I meant was that constant current drive is the most efficient approach if you have a number of LEDs to drive and you have a high enough supply voltage (e.g. 12V) that you can connect a number of them in series, leaving just a few volts across the regulator. Under these circumstances I'm not sure that a boost converter with its own losses followed by a constant current regulator would end up being any more efficient, and it would be more complicated. However I haven't done any real world calculations on this arrangement.

[Colin WhittakerParticipant @colinwhittaker20544]

There was a comment about why would a single diode be used for half wave rectification.

The answer, I think, is that the particular generator used was voltage challenged and the 1.2V drop from a full bridge rectifier could not be tolerated while a 0.6V drop was just acceptable.

[Colin WhittakerParticipant @colinwhittaker20544]

Re the series connection of LEDs. I think you'll find that you can daisy chain LEDs of the same colour but the different colours will need different currents to deliver equivalent brightnesses, Hence a separate circuit for each colour of LED.

[Ian S CParticipant @iansc]

The alternator in my photo has an over all size of 4" diameter x 4" length. My motor/alternator was I think from an older model ceiling fan. Derek, the motor used as an alternator on a wind turbine would probably chosen to generate at reasonably low revs, probably less than 500 rpm if it was direct drive from the turbine.

Ian S C

[ScrumpyParticipant @scrumpy]

Hi All

I have solved most of my Dynamo problems with a small wind turbine motor running at 3000 rpm I get 12 v running at 5000 rpm I get 24 volts using 60 led bulbs that are 3.5 volts each this leaves a total 21 volts all I need I think is some form of regulator to make sure I do not over speed and blow all the bulbs any suggestions would be appreciated thanks in antisapation

[Les Jones 1Participant @lesjones1]

I'm not clear exactly what you are trying to do. Is my understanding correct that you have 24 volts from the dynamo and you want to drive 60 LEDs connected in parallel so you have 20.5 volts too much ? LEDs do not behave in the same was as filament bulbs. You would drive filament bulbs from some constant voltage. With LEDs you need to control the current trough them. The current through an LED changes a large amount for a small change in voltage. The simple way to drive them is via a suitable resistance. With 24 volts available you could drive the LEDs with 10 strings of 6 LEDs connected in series in parallel. With your 3.5 volts (Approx.) LEDs that would require 21 volts. You could drop the 3 volts across a resistor in series with each string. This would be OK if the 24 volts was stable but probably would not be OK if the 24 volts was varying. You will need to specify the maximum and minimum voltage from the dynamo, The current you want to run the LEDs at and the maximum current rating of the LEDs. From that we can decide weather you can just use resistors or if a constant current circuit is required.

Les.

[ScrumpyParticipant @scrumpy]

The wind turbine states on the label 36 w – 3000rpm = 12 volts 5000 rpm = 24 volts i wish to run 60 led bulbs that are Vaol – 10 gwy4 rated 3.5 volts my question is what do I need to keep a constant voltage so that it does not go over voltage for the bulbs if the governor fails as 60 bulbs at 3.5 volts are 21 volts or have I got it all wrong any information is a great help as I find this all so confusing

[Les Jones 1Participant @lesjones1]

3.5 volts will be the nominal voltage at 20 mA current. If you look at page 3 of the data sheet you will see that the votage could be between 2.8 and 4 volts. If we base the calculation on the nominal 3.5 volts and we have 10 strings of 6 LEDs then we need a resistor of ( 24 – (6 x 3.5)) / 0.02 = 3/0.02 = 150 ohms in series with each string. As the maximum current rating is 30 mA than the maximum voltage we could tolerate would be 25.5 volts. If you chose to run the LEDs at less than 20 mA then with just the resistors it would tolerate a higher maximum voltage. (If the LED current was 10 mA then we could tolerate a voltage of 30 volts. There are three options I can see. 1 Add a voltsge regulator on the output of the dynamo to limit the voltage to about 24 volts. 2 Add a single constant current controller to controll the current to the 10 strings in parallel to 200 mA. 3 Have a constant current controller for each string controlling the current at 20 mA. (The constant current controllers would replace the 150 ohm resistors.) Option is the best solution but 1 or 2 should work well enough. We would still need to know the maximum voltage output from the dynamo to choose the components. Yet another approach would be to have a relay to disconnect the LEDs if the voltage went too high.

Les.

[ScrumpyParticipant @scrumpy]

Hi Les many thanks for your help the only information I can find is on the turbine can it states power 40 w max current 36 w with direct current that's all the information I have I would value your advice on which way to go and if you could come up with part numbers or a wiring diagram that would help me as I have stated this is all very strange to me thanks again Derek

[Les Jones 1Participant @lesjones1]

Without knowing the maximum voltage that te dynamo gives it is not possible to design a regulator. I assume that you are driving the dynamo with a steam engine that has a speed govener. Can you measure the voltage from the dynamo with the govener dissabled ad the boiler at maximum pressure. I initially thought the dynamo was just like a permanent magnet motor but this can't be the case as the voltage output of these is directly proportional to the speed which is not the case from the figures that you give. You say it gives 12 volts at 3000 RPM and 24 volts at 5000 RPM. If it was a normal permanent magnet design I would have expected it to give 24 volts at 6000 RPM.

Les.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Les Jones 1 on 01/11/2016 08:10:18:

Without knowing the maximum voltage that te dynamo gives it is not possible to design a regulator.

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I haven't tried them in a 'dynamic voltage variation' situation, but these LM2596 based voltage regulators are very effective and seem to be robust … One of these feeding into a constant current regulator might do the trick.

http://www.ebay.co.uk/itm/LM2596-DC-DC-Adjustable-Step-Down-Buck-Converter-Module-LED-USB-Port-UK-SELLER-/400858205723?hash=item5d5502ce1b

MichaelG.

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Note: I bought mine from China a couple of years ago, but the UK seller link seemed convenient.

[ScrumpyParticipant @scrumpy]

Hi All have just run the engine on air with no governor connected the pressure was set to 100 psi its working pressure the speeds were 1000 rpm 6 volts 3000 rpm 12.4 volts 4000 rpm 16.5 volts 5000 rpm 24.6 max speed unregulated 6500 rpm? 31 volts this was very erratic hope this helps Derek

[Les Jones 1Participant @lesjones1]

Hi Derek,
Here is a circuit that should do whatyou want.

It is designed for a LED current of 20mA and the transistors in the constant current circuit should be OK up to 60 volts from the dynamo. The TIP31 will need to be mounted on a small heatsink. You could use the regulator that Michael suggested in place of the two transistor constsnt current source if you want.

Les.

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