routercnc_MK3

[routercnc]

Bit of an update.

Wired up the PSU caps last weekend and did a final check before switch on. so glad I did because I noticed that for some reason I'd connected the black cable to the positive side of the caps and red/white to the negative! I dread to think what would have happened if I'd switched on. I know electrolytics don't like that sort of thing and have seen small ones explode and unravel. These ones are much bigger! I always wear eye protection in the garage whatever I'm doing but it still would not have been pleasant.

So I switched the spade terminals over out of the rectifier so -ve went to -ve on the caps etc and switched on. Got 72V DC output so was happy with that. The type D 6A MCB did not trip so another good sign. I switched off and unplugged everything.

I then thought about re-soldering the cap cables so I wouldn't get confused with the wire colours if I needed to change anything in the future, but realised I had a problem. There was 70V DC stuck in the caps and the cables were therefore live. I tried discharging them by touching them on the power supply pins of one of the drivers but got a blue spark. I think this was because I couldn't really make a quick decent connection on the bare wire touching a small pin rather than anything untoward.

In the end I de-soldered one of the 10k resistors from the power module board (that held the capacitors) and managed to wedge/rest it across the pins of one of the caps. It took about 1 hour to discharge to 0V, probably not helped by the contact being quite light between the resistor and the capacitor.

This did get my thinking though about the voltage that the 12V DC relays would be switching across their terminals, and I wondered about the lifespan of the contacts. This coupled with the fact that if I e-stop the machine then there would be 70V DC floating around in the control box. So, the relays all came out and the drivers will be hardwired to the PSU. This solves both problems in one.

The PSU will be switched by a 25A SSR which is now on order. I looked for a contactor but they are all 24V and I only have 12V. I thought about changing to 24V but then would need to consider the LEDs, the pump, and cooling fans etc which are all 12V. So staying with 12V assuming SSR does the job. Here is the updated wiring drawing:

[ edit - spotted some copy/paste errors in the layout diagram above since posting so have corrected those ]

I've also just received a few more bits from Chalon components to form a second rail to house most of the DC side including power distribution, safety relays, etc. Here is an update of the control box layout: