Showmans engine generator

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

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.

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

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.

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

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.

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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.

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

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.

Hi Len many thanks for all your time and help that you have put into this challenging subject but could you just clear a few points ( F1 -500 ma what voltage would I require ) ( R2 R3 is it 6RB or 6R8 ) also if I went down the line of Mike s suggestion how would I wire it up sorry for being so thick on this .

I'm sure many people will have read the posts on generators producing light , I feel quite humble to think that so many people have helped on this project thank you ,and I'm sure many people in the next few years will read these posts with interest Derek

Derek,

The resistor value is 6R8, or 6.8 ohms, or blue/grey/silver in colours on its body....

The fuse just needs to be a standard 20mm glass fuse at the rating specified....( try your local Maplins)

As for building the circuit or wiring it up, what did you have in mind?

Thanks everyone for your help a test set up has been made and it works