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Oh Blimey I bought a CNC Lathe !!!!

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awemawson:
Fred, as far as I can tell, remembering I have no circuits of this AC servo drive, two of the three phases are brought into this board, rectified, and chopped, the chopper / oscillator using this transformer as a load (and possibly feedback on one winding). As you can see from its size its a high frequency transformer with I suspect a ferrite core rather than iron. I agree Meggering it is a good idea that I hadn't thought of as presumably the primary is at a few hundred volts.

Fred Bloggs:
Sir

As I thought the Power supply is to generate on board LV DC supplies and as such the DC level on the primary on the transformer will be floating around 325 volts (SQR 2 (1.414) x 230V AC)  :zap: Be careful!!!

You could wire in an external supply to power the on board electronics and power it all up on the bench first then fit the board back into the system to see if the rest of the system works okay!!- Either way a bit of a risk, I have done it a few times myself.

I have fitted supplies to equipment before, got it to work and decided to leave well alone as it did the job, this included doing a very quick rush job were I left the 0-30V DC Thandar lab supply inside the equipment as they wanted to start production within that day, finally got the supply back when the company shut the line down and moved production abroad :bang: 3 odd years later :Doh:

Best Regards

Fred

lordedmond:
yep been there done that

most risky one was a lash up supply for 80vdc ( dont ask why the funny volt try the manufacture instead ) all it was doing was to supply the sync panel for the 441hz supply for a number of IBM mainframes for a large UK bank it ran for a year , the risk was the downtime £40 million every five mins  :zap:


Fred I do doubt that the logic dc volt would be floating that would be very dodgy indeed any disconnected plugs around the system would float up  BTW i though it would be root 3 (1.732) ?

Anyway back to the plot good luck with sorting what is becoming a rats nest of problems with no drawing and prop parts Sir you have my condolences


Stuart

awemawson:
The machine internally works on 100v AC - there is a three phase transformer bringing my 415v three phase down to 100v three phase. This particular board on the AC servo drive pick off two of the three phases to use as it's source - so probably about 170 volts phase to phase. When I've plotted out more of the circuit of the switched mode converter I'm going to power it from a Variac and bring the volts up slowly as I watch & measure.

Fred: I megger'd the transformer winding to winding with my (ex GPO - shows how old it is!) 500v megger and confirmed that there is no leakage - it was a good idea though - thanks.

This little bit of the circuit is generating quite a few independent supplies some of which I suspect are used on the drivers for the 'H Bridge' output power FETs and as such need to float as the H bridges (two of them as there are two AC servos in the unit) are powered by the rectified 100v three phase. Not really practical to supply external replacements as I don't know what they should be anyway!

I must spend some time this evening plotting out more of the circuit - I got diverted this afternoon sorting out my poor dog that had to be spayed this morning and dismantling the penning in the lambing shed and converting it to a shearing shed ready for when the sheep have their next haircut. Don't you find life gets in the way of doing what you want to do!

(anyone want some sheeps wool?)

Fred Bloggs:
Stuart

SQR of 3 is used when working with 3 phase power systems.

For example with a star connected 400 volt phase to phase system the phase to neutral voltage (single phase) is 400/(SQR3) = 230volts

 :smart:

SQR2 is the value used to convert a measured AC sinewave voltage (RMS or root mean square) value to its peak especially when you are charging capacitors up. The peak voltage of the sinewave will be present across the smoothing capacitors, the voltage measured will fall as load is put onto the circuit and will have an increase AC ripple component as the capacitor is discharged more heavily. That is why you have to use some form of electronic regulator (either series or shunt regulators or switch mode regulators) when you power up electronics via mains transformers with rectifiers and filtering/smoothing capacitors.

Sorry ladies and gentlemen of the forum if my explaination is not very good - I'm one of lifes doerrs not teachers :lol:

Best regards

Fred

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