HP6572A 20V 100A 2kW PSU teardown - Page 1
Forum section: electronics / testgear

author: nctnico
author_rank: Super Contributor
timestamp: October 14, 2015, 02:58:31 pm
content: I recently bought this one because it might be useful for an upcoming project:Due to the missing knob I got it cheap. Since cheap = good ...The bad thing is that it is heavy (nearly 30kg!) and rather large.Let's open it up for a safety check and to see if it has been set for 220V - 240V operation...Hello beasty!Counter clockwise from bottom right: we can see a mains filter; a big transformer-ish inductor (maybe some crude power factor correction?); the input rectifier; capacitors; Mosfet primary switchboard; low voltage power supply transformer; front panel; output transformer; output rectification & filtering; current shunt; more filtering and finally the output bus-bars.A closer look at the mains entry section:The fan and the output transformer. Yes, the output transformer is wound using copper braid! Another interesting feature is that the wires from the primary Mosfets to the output transformer run freely through the case. One would expect this to cause a whole lot of EMC problems but appearantly the ferrite beads are enough.A big dual diode is used for rectification; this indicates this power supply uses some kind of flyback topology. Another inductor performs output filtering. Notice the small board besides the rectifier diode: this is the snubber board.Further down the path there is the current shunt and more filtering. Notice how the bus-bars run over the PCB. This power supply has a very low output impedence. The thick bus-bars probably help with that. The 2 MOSFETs (these look so small compared to the rest) are for the 'down programmer' which discharges internal/external capacitors when the voltage is lowered or the output is disabled. I have not looked at what the current sinking capabilities of this PSU are.The fan is easy to remove for cleaning:Let's see if we can fire this baby up. First it needs a new mains lead. HP got a bit cheap and simply positioned the input mains filter so that the faston press-on contacts are available at the rear of the case:Talking about cheap: HP choose to use modular jack connectors for several board to board connections. Great for temporary connections like a telephone but in equipment which needs to work for decades?Anyway... lets flick that switch... Woohooo! it works! The numbers look a bit wonky though. All in all I'm not a fan of LCD screens on test equipment.Still some things to do. This really needs some cleaning! Where is the vomit smiley?Time to take the front panel apart:The rubber key mat is easy enough to clean. I also wanted to replace that optical encoder with the broken shaft. I tried to buy this part from Keysight (which responded promptly) but unfortunately this PSU is an older version for which they no longer have the right encoder. I would need to change the front panel circuit board which would set me back at least 1400 euro. I'm thinking about replacing it with a mechanical encoder but finding the right one is tougher than it looks because of the long shaft. I decided to put it back together for now. After all it is still possible to set the current limit using the keypad. Maybe that is more convenient in de long run.A peek inside the broken optical encoder:Fortunately this PSU comes with a temperature controlled fan so the noise is bearable and it has an output enable/disable button (I often add an output enable switch to PSUs). Another nice feature is that the current limiting can work as an electronic fuse. If it hits the limit it will shut the output off. OTOH: there is a capacitance of about 80000uf at the output. This can do some serious damage even with the down programmer discharging the capacitors quickly. If a circuit is damaged by a few mA of excess current it is likely to be destroyed anyway. Maybe I'm right by calling it an electronic fuse: a fuse is there to prevent fire not protecting a circuit against excess currents.Another thing I noticed is that the case is excessively large. They could easely have made it 20cm shorter by building it more compact. The heatsink has very few fins; a shorter heatsink with more fins would have been just as effective especially since the components are not spread very evenly over the heatsink. It looks like a 'safe bet' standard chassis for a wide variety of equipment. I also miss the aluminium frame and casing made out of sheet aluminium you find on older HP equipment. The HP6572A's outer shell and frame is made out of steel which probably adds a lot to the weight. If the case where shorter and lighter it would also be easier mount in a rack (no need to support the rear). I also have a few HP6012A power supplies (1kW) which are much older but also much lighter.All in all a nice addition to my lab but I won't be using it daily.

author: bitseeker
author_rank: Super Contributor
timestamp: October 15, 2015, 03:12:26 am
content: Thanks for the teardown. Looks like cleaning it out will be a bit of a project too!