Hi

First of all, this is not a project. I was just designing a set-up in my mind. I have very little experience of 3-phase generators. I need some help to understand the concept. Please see the attached diagram below:

For example:
A 3-phase generator, producing say 15-30VAC 10A.
A full-wave rectifier (15A) is used to convert into DC and then supply to load.

My Question:
During operation, if there is rapid switching in each phase line using some control circuit, will there be any sort of high voltage spikes?
If yes, deploying protection diodes as shown will provide the protection? If this protection set-up is not workable, can anybody suggest some better alternate?

 

Your schematic is of the standard 3 phase transformer and rectifier. I don't see what protection your "protection diodes" give you. Could you be more specific about the purpose of this circuit and about the protection diodes.

 

Your schematic is of the standard 3 phase transformer and rectifier. I don't see what protection your "protection diodes" give you. Could you be more specific about the purpose of this circuit and about the protection diodes.

Thanks for your response.

First of all, it is not 3-phase transformer.....it's a 3-phase generator.

I am driving a 3-phase generator with a powerful stream of water. To regulate the output I am currently using a motorcycle's regulator/rectifier, which is a shunt type regulator. It is working fine except that it gets quite hot. I am planning to design my own regulator. I was considering to regulate by rapidly switching off/on each phase at a preset threshold voltage.

What my actual concern is that I am not sure, if switching off a phase will cause a high voltage spike (which I expect within the winding of the generator). If there will be spikes, will the diodes provide protection against them

 

the "protection diodes" are shorting part of the three phase bridge.

 

the "protection diodes" are shorting part of the three phase bridge.

How can the diodes short the bridge?? They are identical to the diodes in the bottom of the bridge.

................ I was considering to regulate by rapidly switching off/on each phase at a preset threshold voltage.............

You will certainly generate some very BIG spikes using this method. I suggest that you consider a different way to regulate. How about a switching regulator at the output?

 

Look to how they do it in an automobile alternator. It, car alternator, does this internally.

 

If it has a wound field the same as a automotive style, then the field is easily regulated, via the slip rings.
Max.

 

Look to how they do it in an automobile alternator. It, car alternator, does this internally.

No, the generator is not automobile type. It is permanent magnet type.

 

You will certainly generate some very BIG spikes using this method.

So, the protection diodes would not do the job? Any other suggestions for protection?

How about a switching regulator at the output?

Yes, that could be done. But, I was thinking before rectification with an idea that rectifiers and the generator winding would have some relaxation when switched off.

 

......... I was thinking before rectification with an idea that rectifiers and the generator winding would have some relaxation when switched off.

To switch 3 phase power to achieve voltage regulation is very complex. What specifically are you thinking about?

On the other hand, the voltage and current you are talking about is well within the capabilities of a switching converter and would be very economical.

What is your target voltage?

 

Personally I wouldn't worry about it. SCR based AC to variable DC power converters don't have a problem with switching on and off all through each phases cycle.

If you want to regulate your output voltage I would recomend doing something other than just turning the entire AC part of the system on and off to do it and do as others have said and use a dedicated buck converter on the DC end control things from there.

Either that or keep your load dump type regulation systems in place but use a larger heatsink on it if heat is a concern to you.

 

What specifically are you thinking about?

I am thinking to design the regulator in such a way that generator winding and the rectifiers should get some relaxation. Continuous load on the winding and rectifiers make them hot, particularly the rectifiers.

My idea is to sense voltage from the output, compare it with preset threshold and then use some suitable switching devices to switch the 3-phase power.

What is your target voltage?

Target is 15V.

 

@abuhafss
Is this a battery charger?

 

@abuhafss
Is this a battery charger?

Yes, the overall setup is made to charge batteries.

 

I suggest that you look at PWM charge controllers used in solar power systems. They are cheap, readily available, and are programmed with good battery charge profiles. The voltage range of your generator/rectifier system is perfect for these controllers.

Google "Xantrex C35". It would be perfect for your application.

 

The only practical way to control the voltage of a permanent magnetic generator is to short the output as a motorcycle shunt regulator does, since open circuiting the generator will generate large and possibly damaging voltages.
Using protection diodes with the generator open-circuited will dissipate as much (or more) power than shorting the output.
Here's an article I wrote on a low power motorcycle regulator design which may be of interest to you.

 

Here's an article I wrote on a low power motorcycle regulator design which may be of interest to you.

Thank you for the link.
I'll study it and get back if any question, most probably in other forum coz here automotive circuits are not allowed, as far as I remember.

 

.............. probably in other forum coz here automotive circuits are not allowed, as far as I remember.

That ban has been removed. Go for it.

 

crutschow

Referring to your article, would you please specify how the Triple Diode CMXD2004TO should be mounted in the ambient air stream.
Should it be placed away from the body of the regulator, particularly the fins of heatsink?
Can 3 x 1N4148 be used instead of the triple diode?