Questions on an Electronics Expert

[Raymond HodgesParticipant @raymondhodges20973]

Hello there

I know very little about electronics although i am able to read a circuit diagram, and solder components onto a PCB, but thats all.

Q1 In a circuit a Bridge Rectifier is required (12v 2A), does it matter how big the Rectifier is so long as it is more than that required.

Q2 How can i establish what type of a transformer i have not knowing the primery voltage or the output.

Thank you

Ray

[Raymond HodgesParticipant @raymondhodges20973]

Electronics

[frank brownParticipant @frankbrown22225]

A1, if the transformer is delivering X volts, then the voltage of the diodes must be 1.4 times X volts or greater.

A2. Very difficult, the best way is to get a bit of low voltage AC, say 6V from a bell transformer and wire it to a low voltage winding (thick wires) and measure the input voltage from your bell transformer and the output voltage on the other windings. eg, voltage from bell transformer = 4V, voltage on windings, 17 V, and 80v. This would mean that the 80V winding was the mains (230V), the 17V would be 17/80 X 230 ~ 45V and the 4 V winding was actually 12V.

The actual power depends on how hot the transformer can get. Best to compare with a known example.

Frank

[John HaineParticipant @johnhaine32865]

Q1 basically no, as long as the diode breakdown voltage is as Frank says, bigger is fine.

Q2 – that method is not recommended! If the low voltage winding you connected to was 4v say there would be 230 v on one of the other windings. Also it may not even be a mains transformer, could be an audio one. Frankly I suggest that you buy the transformer you need so you have a known quantity. You could post some photos of what you have?

[WALLACEParticipant @wallace]

Don’t forget there’s going to be a 0.7v drop across each diode….

There’s a very good freebie programme – Google ‘PSU Designer’that can simulate simple power supply circuits.

W.

[WALLACEParticipant @wallace]

Wrt to 2 – someone with a bit of experience would get a fairly food idea on the type – and if a power tranny – the wattage or ‘VA’ just just by looking at it – a 50VA transformer for example, is pretty much the same size as any other 50VA one. The primary and secondary windings I would identify and quantify by using a meter and ‘Variac’ – that’s probably a little too dangerous if you have limited experience with messing about with potentially lethal mains voltages.

W.

[Les Jones 1Participant @lesjones1]

Hi Ray,
A1
If you are using a large capacitor after the bridge rectifier I would suggest using at least a 4 amp rating bridge rectifier as the current will be in the form of short high current spikes.

A2
I agree with John Haine's comment that you should obtain a transformer with known ratings. I would not consider using a transformer unless I at least knew the primary voltage.

Les.

[Harold Hall 1Participant @haroldhall1]

Ray

The following web pages deal with AC to AC and AC to DC conversion, the latter, particularly using a transformer, rectifier bridge and possibly an added smoothing capacitor. You may find this useful. **LINK**

Harold

[Raymond HodgesParticipant @raymondhodges20973]

Well i am overwhelmed i didnt expect quite as much advice thank you all.

The bridge rectifier required in the circuit is a 50v 4A, i have a 1000v 25A Bridge rectifier wold that work?

I will take the advice from John Haine an Buy one.

Your link Harold, i will try to understand it a bit more.

Ray

Edited By Raymond Hodges on 26/12/2014 21:43:02

[Les Jones 1Participant @lesjones1]

Hi Ray,
The 1000V 25 amp bridge will work fine. I was going to suggest using a 12 volt 50 watt lighting transformer but looking on eBay all the lighting transformers advertiseed are the electronic type which will not be suitable for your application.It may be cheaper to buy a ready made 12 volt DC power supply. Some idea of waht you plan to power with it would help with with recommendations.

Les.

[Raymond HodgesParticipant @raymondhodges20973]

Thank you Les

I am making a Spark eroder, or EDM, and i do have a lot of electronic bits and pieces which i am trying to understand a bit more about.

I have built one as described by Mike Cox 1 on his web site, it works but very slow.

At the moment i am gathering information on what works with what, trying to keep the whole thing as simple as posible.

Ray

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