New build with recycled parts on a ridiculous budget 120cm*60cm work area

[Davek0974]

Just an observation - are you running the primaries in series (240v) or parallel (115v) ??

If series the you need to connect supply to blue and brown with grey/violet joined.

If parallel then connect blue/violet and grey/brown then connect supply to to those pairs.

Just an observation as said but easy to ignore those little dots on the transformer winding pictures ;)

[Desertboy]

Just an observation - are you running the primaries in series (240v) or parallel (115v) ??

If series the you need to connect supply to blue and brown with grey/violet joined.

If parallel then connect blue/violet and grey/brown then connect supply to to those pairs.

Just an observation as said but easy to ignore those little dots on the transformer winding pictures ;)

I had it wired blue and brown to mains 240v, grey and violet joined on the input side. On the output side orange and red to the rectifier, yellow and black joined. This was a dual 25v output core.

This time with the 1kva transformer I'm going to wire the input the same (it's a dual core 115v input). The output I will join the orange and black and then wire to rectifier, join the yellow and red and to rectifier. (Dual core 50v output, I want 50v out to feed into the rectifier so I get my 68-70v out for my drivers.)

[Desertboy]

If I add a precharge circuit to this, could I use a type B mcb I guess the capacitors have a large inrush which might trigger the type b mcb but when charged you would have better protection with a type b than a type c? I have some adjustable time delay relays (0-30mins) 10amp I could use so the precharge circuit always comes on say 1 minute before the PSU powers on.

If so how the hell do I make one I read something about precharge resistors but have no idea where to start.

[Desertboy]

Came today but missing the top metal plate! I think the one on my old transformer will work fine but still poor maplins I do have both rubber protectors.

I was hoping it would straight swap but not so sure it will I might just get away with it and a hammer ;)



Not going to wire it up until I have an MCB, replacing the rectifier as well, going to leave the caps in place.

Think I traced the problem to a poor crimp causing the initial problems and we think my friend reconnected the bridge rectifier backwards on the output but no one can be sure.

[m_c]

There's a reason transformer manufacturer's usually recommend slow blow/time delay fuses, and this thread has just proven why.

Fit a 10A MCB to a 1KVA transformer, and there is a high probability the transformer winding will fail before the MCB trips.
1KVA roughly equals 4 amps, so taking a type B MCB, it takes a minimum of 6 seconds at double the rated current for it to trip. So taking that 10A MCB, that's 20A, 5 times the transformer rated current, or over 4KW flowing for 6 seconds. Do you still think that MCB will do much good?

I personally just use a time delay fuse rated around 120% of the transformer rating. If you blow it, you're doing something majorly wrong, and it's far cheaper than a MCB.

As for cheap multimeters, they rarely have a fuse for the amp setting, which is likely what will of caused the problems. A sudden short on the power supply, as well as causing the transformer to fail, will of likely burnt something out in the power side of the AM882. If you were to strip it down, you could at least check the main power supplies are still functioning.

Also, if you strip the outer covering of the transformer, you might find the fuses near the outside of the windings, so it could potentially be a relatively easy repair.

[Desertboy]

I am going to have a look at fixing the transformer, there's a good vid on you tube it doesn't look that hard if the fuse is near outside but at £41 for a 1kva I couldn't resist. Maplins still have a new 625va transformer (50v) for £30 which I'm seriously tempted (Have enough bits to make a 2nd PSU) and also try and fix the original one or they have an 800va (45v) for £35. I have 7 caps now and 2 new rectifiers so it's cheap PSU for betty bigger sister Already planning ;)

Would these be suitable slow blow fuses?
http://www.ebay.co.uk/itm/5-CERAMIC-...A3euImkU3PFBZg

These look plug compatible in which case I'll put the PSU on a plug for ease.

When I first got the Am882 it had a dodgy connection I changed the plug and it was fine but I do wonder if the connection is dodgy on the board open it up couldn't see anything from the top need to take it out properly and look underneath

I am going to complain to Chinese I bought it off as they "offered" 1 year warranty but also got it on my CC so will see if I can get a refund through them.

At the moment this is going to a normal plug socket which is connected to an MCB in the board (16amp) on a side note my shitty 24v psu tripped it so I chucked the PSU in the bin was £7 ebay special. But it didn't trip whenthe psu blew in fact it didn't even blow the 13amp fuse in the plug and my pc stayed on connected to same power in.

[Davek0974]

I would not bother with pre-charge, this supply is not big enough to need it, as long as the rectifier is big enough to take the inrush as well as a slow-blow fuse in the input it should work fine.

Pre-charge is easy with a resistor in the output before the rectifier, maybe 10r 25W and a timer relay which shorts out the resistor after maybe 2s would do it but i wouldn't bother myself. Pre-charge is more used with supplies that have very large capacitors/higher voltages.