Thread: ebay power supply
Thanks (& sorry for labouring the point! )
For anyone wanting to order a few of these - the seller will allow collection via your own courier.....& Parcel2Go will deliver upto 25kg to your door for about £7.50 in total (the ad says they weigh 2.5KG each, so factoring in some 'headroom', you could therefore get 9 PSUs into the one Parcel2Go delivery - can't imagine you'll be popular with the driver though!)
Last edited by HankMcSpank; 25-07-2009 at 09:47 PM.
So after the sage of parcel farce, parcels 2 go etc was it possible to get to around the 40 volt mark ?
.John S -
http://cgi.ebay.co.uk/NEW-UNUSED-50V...item587e03d24d knockout price.
i bought two of these a while a go before seeing this original thread and still not got round to powering them up let alone start to tweak them. i would be very interested in anything further found out about them on the voltage drop front. My drivers can do the full 50v volts but would be happier at a few volts lower to save the possible crispy bacon burn factor. By the way i picked mine up direct from the old fellow (i live in Swindon)If the nagging gets really bad......Get a bigger shed:naughty:
Adding up the costs of a diy cnc machine continues to make my eyes water so finding these makes for a refreshing change :)
In theory the output from the opto isolator should be wired to a feedback pin on the main PWM controller chip. If memory serves me correctly and the chip follows convention then the function of this feedback pin is very simple:
if the voltage on this pin is above a certain threshold value (around 2.5v perhaps) the PWM controller switches off and if the voltage on this pin is below said threshold the PWM controller switches on - this is how the output voltage is regulated.
As the PSU already has some way of varying the output voltage there may be some additional complications but all that should be needed to decrease the output voltage is a change to a single resistor such that the voltage on the feedback pin is increased by about 20% for a 40v to 47v output range (ish).
Disclaimer: I know enough to hurt myself and nothing more :)
I'd have thought the way they do this is to modify the duty cycle of a PWM stream. I'm tempted to order one - it appeals to the lazy mountaineer side of me ("I want to climb it because it's there" or transposed to this particular situation "I can't be arsed to climb a mountain, so I want to get the voltage down on this 50V PSU because erhm it's not 45V")
The problem is that the design doesnt directly match the reference application schematic for the controller chip, and has a third-party board full of SMT parts that appears to do the opto-isolated feedback with at least one custom chip on it... Also there appears to be three power supplies in there, the main 50v job from a 400vDC rectification and two others, one of which is a -ve rail.
As we know there is a input pin who's voltage controls the output. This goes into the SMT board and I believe this voltage drives a current source (as per the reference model) that controls the feedback circuit, however I was unable to identify that part on the board and suspect its inside the custom chip. Also there is obviously some sort of comparator on it to drive the 'in regulation output and control the current limit' but again suspect this is inside the custom chip too.
The result of all of this is I was unable to find an easy way to change the control range. I believe the necessary resistor(s) to change are on the SMT board but I cannot yet identify them. And then other pressures overtook the time I had available...
I bought one ages ago (as a result of this thread) and just plugged it in. It's been running the machine ever since.
Open circuit my supply measures 42.7V (the data sheet spec is 42.8V +/- 0.5V, so no worries).
The data sheet calls this voltage "out of regulation" (ie. there's less than 5.5V or more than 13.5V on Ucr). I haven't checked what happens when I put voltage on Ucr, because the "out of regulation" voltage is the one I want, and it seems to cope with load OK at 42.7V. The 4.3 signal diagram on the datasheet (attached) is the useful one.
On my machine Ucr (pin 28) is just floating, but I should probably tie it to ground to avoid surprises. I haven't bothered because, well, it just works.
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