On 14 August 2014 13:47, Richard Savage <[email protected]> wrote:
> Hi > > > > I am testing some new Cisco ASR901’s and need to find a suitable DC power > supply that will power them up in a lab environment. The ASR 901-12C-F-D > says that it will accept: > > > > 1 GE models: > > ● DC-input voltage rating: 24 VDC, -48 VDC, -60 VDC > > ● DC-input current rating: 2.5A maximum for non- TDM variants and 3.0A > maximum for TDM variants > > > > Power connector > > 6-position 2-tier stacked connector comprising two feeds, A and B DC power > (AMPHENOL ELVA06100), and 3‑position mating connectors for each feed > (AMPHENOL ELVP03100) > > > > Does anyone have any suggestions to a Lab DC power supply? > > Buy a proper one ? :) The following won't be easy, but may be free if you have the right stuff lying around. It depends how much a "real" PSU is for this purpose and how much experience you have in-house with electronics. If you have a pile of them lying around, you could use some types of ATX PSUs (they'll need modified) as long as the outputs *and* their cases are fully isolated from each other (this needs properly checking- if the cases are at earth potential then you've just created a bigger problem) You'd chaining the outputs together in series to get +24V (2x12V) -48V (4x12V) -60V (5x12V). You'll have plenty of amps, so much that you'll definitely need to fit appropriate fuses to prevent fires and popping the mains circuit breaker should a fault occur. Personally I'd use 2A to 3A fuses (max) and 10A cables as a start, going to lower fuses is possible. the fuses will protect the wiring, any fuses internal to the router protect only the router equipment internally, so you'd need to use 30A+ cable to it otherwise ;) In the worst-case, you'd need a maximum of 11 ATX PSUs, best-case you'd get away with 7. They'll need carefully selected for their isolation designs, modified with suitable minumum-loads added and appropriate fuses or breakers for the low current you require. Get an experienced electrical or electronics engineer to modify them and connect them up, our you'll have 800*11=8 kiloWatts of DC fire on your hands, pulling 15% more than that from the mains circuit - not good. The max power draw with the router as load will be far less, minus the efficiency of each one and the static load resistors you've added (10-20W per PSU for those resistors - don't omit them!) You're talking about a quid or two for the resistors for each PSU at most, so £20 should see them modified for continuous use. Omitting these resistors could cause the PSU output (especially the -60V one) to rise to a damaging level because the offload rise will be 5x that of one unloaded PSU. You;ll quickly have a popped router on your hands otherwise. This means that this route is a horrible bodge, but I've used series chains of ATX PSUs for over several hundreds Volts of DC before in a lab environment, because with the right ones and the right modifications are very versatile - you can reconfigure them to any sum of 12V, 5V and 3.3 at high currents and both negative and positive outputs. Using discarded PSUs they are effectively free other than the offload resistors and wiring the PS_ONs together. This is *not* a job for an amateur, it needs a lot of safety thought and bench sense. The risk assessment will be several pages alone and needs done right in case someone gets killed. Done right it's as safe series connected lab-PSU setup. You also need to understand that above 60V potential (in this case, wired at minus 60 volts WRT Terra) is above the old SELV limit, so the wiring should be done by a competent professional and appropriately insulated. In particular, you need to select the cabling to match the over-curent protection, though you'll need to do that with a -48V "rectifier pack" too (they tend to boatload of amps out for whole racks), so safety requires fat wiring or fitting additional overcurrent protection. When they go wrong they are a free-running arc welder and electric heater rolled into one - imagine 30+Amps on thin cables that can handle 6A plugged into the router. If there's no fuse, the entire length wire is the fuse, so it catches fire. The foldback or crowbar probably won't sense a short at 3/4/5/6A and so keep on pumping amps down the wires thinking that it's got a rackfull of items and batteries to supply. To buy new PSUs, you can get generic 24V and 48V PSU from various sources, the 60v is less common as a cased PSU, all will need suitably enclosed and isolated from each other. You'd be looking at 30-100 quid for each as separates for low-reliability ones and they may need better output smoothing. You could buy cheaper on Ebay, 24V is a very common PSU output and there are many sources available. It's up to you to trust the cheaper ones - I'd rather use my own ATX series-PSUs. On a side note - older low-end Cisco router and switch redundant power supply inputs could be freaked by cutting up an ATX PSU <> motherboard Molex Mini-Fit Junior connector and feeding them from a single modified ATX PSU. the 5v and 12V rails were easy. Great dodge for when the internal PSU pops and you have no RPS. You may find that single pins cut from a Mini-Fit Jr fit the back of your new router too? May save you crimping your own if you are careful with a Stanley knife and have big heatsink to cover it all with a couple of good layers. -- sent via Gmail web interface, so please excuse my gross neglect of Netiquette
