Hi all,
I am a equp. tech. at a golf course. I have very little exprience with electronics. So here is my problem. i have a stator that has an output of 40vac. I want to put led lights on it. so I need to reduce the voltage. The lights are 9-24vdc 27w.
any help would be greatly appreciated.
thanks.
Greg

 

You can use a Single Diode 1N4007 as an half-wave rectifier to give you 20V, or you can use a transformer to lower the voltage further and a bridge rectifier to give you DC.

 

I'm not sure what you mean by "Stator". What actually is your 40VAC supply? And how much power can it supply?
How many lights?
If you have multiples of pairs, they could be wired in series so the will now be 18 to 48V. Then add a rectifier to convert to DC.
But more info would help. Are these LED lamps, and what types? (data sheets, pictures...)

 

You can use a Single Diode 1N4007 as an half-wave rectifier, to give you 20V, and a 680uF smoothing capacitor will give you DC, or you can use a transformer to lower the voltage further and a bridge rectifier to give you DC.


View attachment 149146

thanks, dodgydave Ill give this a try and let you know how it turns out.
thanks again,
Greg

 

I'm not sure what you mean by "Stator". What actually is your 40VAC supply? And how much power can it supply?
How many lights?
If you have multiples of pairs, they could be wired in series so the will now be 18 to 48V. Then add a rectifier to convert to DC.
But more info would help. Are these LED lamps, and what types? (data sheets, pictures...)

Hi dendad,
a stator converts the rotating magnetic field to electric current. All small air cooled engines have some type of a stator
this stator is a 10 amp 40vac output. Yes LED lights, 2 of them 9-24vdc 27w
thanks,
Greg

 

Hi Greg.
I did not realize you were running from an alternator so now that makes sense.
As your lights can handle 24V each, can you get a third? Then just wire them all in series and add a rectifier bridge to the alternator 40V output.
The alternator rectified output will give about 56V peak so that is why I think a third LED light will make it easier. Just 2 will only give you a 48V rating while 3 will be 72V max. Well below the 56V peak of the alternator.
Otherwise, a buck converter could be used to drop the volts down.

 

You can use a Single Diode 1N4007 as an half-wave rectifier, to give you 20V, and a 680uF smoothing capacitor will give you DC, or you can use a transformer to lower the voltage further and a bridge rectifier to give you DC.


View attachment 149146

Just going to a half wave rectifier will not drop the volts to 20V.
The output will still be about 56V unloaded (40x1.414). And even when loaded, the peak volts will be close to 56V with high ripple and that will pop the LEDs.

 

Just going to a half wave rectifier will not drop the volts to 20V.
The output will still be about 56V unloaded (40x1.414). And even when loaded, the peak volts will be close to 56V with high ripple and that will pop the LEDs.

No it wont, half of 40V is 20V, adding a capacitor will take it to 28V .

 

No it wont, half of 40V is 20V, adding a capacitor will take it to 28V unloaded .

You do not get half volts when you half wave rectify so no, it is not 20V. Under no load conditions, the output volts will be 56V, just the same as if there was a full wave bridge there.
There is still the same peak volts there, just half as many per second as full wave.

 

What planet are you from !!

There is no need to get abusive. If you doubt me, just grab any transformer, add a diode and cap and measure it.
You will find I am right. It would be very handy if what you say is correct, and it would save a lot of hassle, but unfortunatly, it is not.
For instance, why would we use a voltage doubler, that is 2 half wave rectifiers in series, if the output volts would be doubled by just using a full wave bridge?
And actually, the peak volts out of a full wave bridge will be one diode drop less than a half wave rectifier.

 

No it wont, half of 40V is 20V, adding a capacitor will take it to 28V .

Dodgydave,

All you have to do is look at the diagram you posted to see that you are wrong. It shows the capacitor charging to to the peak voltage of the input wave, which, as dendad said is about 40 * 1.414 = 56.6V. The diode will drop that to about 56V.

Depending on the size of the capacitor and the current drawn, the average may very well be 20V, but the peak is always going to be 56V, and with a large enough capacitor and small enough current draw the average can be close to that.

Bob

 

Thanks Bob.
Along similar lines, I have a customer who has a valve that took 0 to 10V in to operate. They thought "we have a 24V PWM source so if we limit the PWM to about 40% that equals 10V..."
Well, after they blew up a couple of valve controllers, they decided to ask advice!

I can go to sleep now as it is "tomorrow" here

 

Hi dendad,
a stator converts the rotating magnetic field to electric current. All small air cooled engines have some type of a stator
this stator is a 10 amp 40vac output. Yes LED lights, 2 of them 9-24vdc 27w
thanks,
Greg

Can you control the magnetic field in your generator with a variable voltage or is it fixed using magnets?

 

I don't think the TS has considered that the outout voltage will change with the speed of the engine.
Dave, I think on a small engine they will use permanent magnets. If it had a field coil like a car alternator it's output could be controlled.
I agree with dendad and Bob that you are wrong about half wave rectification giving half the output voltage. (Unless there is no capacitor and you are considering the average.)

Les.

 

Hi Greg.
I did not realize you were running from an alternator so now that makes sense.
As your lights can handle 24V each, can you get a third? Then just wire them all in series and add a rectifier bridge to the alternator 40V output.
The alternator rectified output will give about 56V peak so that is why I think a third LED light will make it easier. Just 2 will only give you a 48V rating while 3 will be 72V max. Well below the 56V peak of the alternator.
Otherwise, a buck converter could be used to drop the volts down.

Hi dendad,
Not enough room for a third light. I have tried a buck converter, but i did not consider that I would a peak 56v. Now i know why converter burned up,it was 50v input.So if I get 75v input converter it should work? I have been at this for 3 weeks I have seen a lot of smoke, i have learned a lot of ways NOT to hook up LED lights.
Thanks again for your time,
Greg

 

Can you control the magnetic field in your generator with a variable voltage or is it fixed using magnets?

How about using a transformer to step down the 40 volts to 20 volts? A transformer wit a center tapped winding of adequate current rating would be the easy way, put the 40 volts across the full winding and then take the 20 volts across half of the winding. Just be certain to not short-circuit any of the other connections on the transformer. Of course, if the engine system does not deliver a fairly nice sine wave then all of the suggestions so far are way off, even mine. If the 40 volts off the stator are intended for battery charging use then it is probably not at all suitable for any other purpose. At least that is my thinking, since battery charging does not demand a nice waveform.
And I did not understand what the poster meant by "I have a stator" either. Many folks fail to consider that those of us who are not present with them have no knowledge of the context that their posting relates to. In addition, my mind-reading ability is very poor.

 

Yes, as MisterBill2 says, something like this..
https://www.ebay.com.au/itm/TST100W...324171?hash=item1a3846f58b:g:EasAAOSwg8tZ7O1f
It has 2 x 24V windings, and 100VA power rating.
Just make sure the primary is left not connected.
To work out the phasing, put the 2 secondaries in series, power the primary and measure the output volts across to secondary ends. If it is 48V, all ok. If it is zero, swap one secondary around.
Once you get it wired ok, hook the alternator across the secondary ends.
Then you should get half volts from one secondary end and the middle connection.
Remember to isolate the primary connections so they do not touch anything as you will have mains like voltages there.

Also, there is this..
https://www.ebay.com.au/itm/high-vo...194470?hash=item5b446fb126:g:aLcAAOSweUFakeJl
They may be "Fake" as the end of the link gibberish says
I have no experience with these, but if you bridge rectify your 40VAC, add a decent electrolytic cap to give the 50+ volts DC, a couple of these may work on. One for each lamp.

 

Hi all,
Well I tried half-wave rectifier, no good. Then a full-wave rectifier and wired the lights in series,with a different set of lights with higher input voltage. I NOW HAVE LIGHTS!!!! Now I can get the other machines wired up.
thank you all for all the help.
Greg