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

[Clive S]

Not good, I pulled the PSU out tested the capacitors they read 45v I discharged them with a light bulb setup. Then tested unplugged the capacitors from the recitifer and turned it back on and tested the output of the transformer diddly squat. There's 240v going in but nothing coming out.

Well that shows the caps are OK.
Now check to see if you have continuity between each winding pair on the transformer after you have disconnected it fro the rectifier
I doubt the AM882 has blown the transformer. Did you have it working at one time or is this the first time you powered it up

[Desertboy]

Hi, right I have continuity on only 3 of the 4 coils one of the primaries has no continuity I assume this means thhe thermal fuse blew and I'm pretty screwed. Going to get another multimeter to test it with to be sure but not looking good.

[Nickhofen]

Can you take a resistance measurement at the coil that you do not have continuity? If you put your multimeter at continuity scale you get a bazing sound of a reading only if resistance is low,I think up to 10 ohm but I am not sure if it is a little higher or change between the brands of the meters,if resistance is higher you have to take a measurement with the ohmmeter.

[Desertboy]

Can you take a resistance measurement at the coil that you do not have continuity? If you put your multimeter at continuity scale you get a bazing sound of a reading only if resistance is low,I think up to 10 ohm but I am not sure if it is a little higher or change between the brands of the meters,if resistance is higher you have to take a measurement with the ohmmeter.

I've ordered another transformer, will check the existing transformer though

https://www.maplin.co.uk/p/2x50v-100...nsformer-a74qj

It's 50v per output core

I hope there's no issue going oversized with a 1000va transformer but I didn't realise they had 625va one and this was 1/2 price same make as rapid.

Saved enough cash on the transformer that I just managed to buy a new AM882 as well with fast shipping.

Normal version not am882h.

One good bit of news the new parallel port card came I fitted it and parport recognises it so linuxcnc should at least work and I bet mach 3 does to.




I got it wrong before there's no continuity between blue and grey OR violet and brown but there is continuity between grey and violet I guess this means both thermal fuses are blown.

One question about the new transformer I know I wire on the input side the brown and blue to the mains, the grey and violet together as before. On the output I wire the orange to the black and the yellow to the red then wire them to the the rectifier is that correct?

Would wiring a 5amp plug fuse to the PSU input give some protection to without tripping out in normal usage?

[Neale]

Would wiring a 5amp plug fuse to the PSU input give some protection to without tripping out in normal usage?

I suspect that 5A might be a bit small and might blow on switch-on, although you will probably get away with it. Typically, a standard fuse will blow within 10sec with a 2x overload, so that might be OK. For normal running, you are unlikely to be drawing anything like 1000VA (which is a touch over 4A in practice) most of the time, if ever, so that's well within the fuse rating. I use a 10A MCB on my own machine feeding all the PSUs (although the stepper driver PSU is the most power-hungry) and I haven't had it trip yet.

Unfortunately, the fuse is very unlikely to protect the equipment and that's not really why it's there. In practice, the fuse blows just after the equipment fails! It's really there so that in the event of a serious fault that draws excess current, the wiring isn't going to burst into flames. In the case of elecronic components, it's well-known that the transistor is the fastest fuse on three legs...

[Desertboy]

Right I'll get 1 of these mcb's tomorrow to wire the PSU through
https://www.toolstation.com/shop/p26107

and 2 10 amp ones, one for the spindle and one for the twin 3 pin wall sockets.

I am going to wire 32amp to the junction box soon so might as well plan for the future.

[Clive S]

Right I'll get 1 of these mcb's tomorrow to wire the PSU through
https://www.toolstation.com/shop/p26107

and 2 10 amp ones, one for the spindle and one for the twin 3 pin wall sockets.

I am going to wire 32amp to the junction box soon so might as well plan for the future.

I think you might want a D rated one with that big transformer