The best I can do is give you a bit of the theory of operation and maybe some suggestions here. I've done a bit of snooping around with how the DC/battery connection works on the option 11C supplies. You can find the whole writeup on my site, but the relevant information is probably scattered through the doc. There's a pinout for the 5 pin connector down at the bottom. http://www.dms-100.net/telephony/meridian-1/DC-PSU-howto/

To run through the pinning real quick, there's an earth pin, two battery returns (where 'return' is positive since it's -48V), and the battery supply (-48V). I haven't had the pleasure of actually seeing how the battery box is wired (I'd be interested in pics if you get a chance) but I imagine the breaker is in line with the battery supply line, and then has some extra contacts or maybe even an extra trip coil that leads to pin 1 to indicate to the AC supply whether the breaker is on or off. Pin 1 is what controls the state of the battery LED and controls whether a fault is reported on the terminal, IIRC. Pin 1 may also give the Meridian side the ability to trip the breaker in the battery box, without having one here I don't really know.

Anyway, moving to the supply, the AC model is basically two parts: the first is AC input, ~54VDC output that doubles as a battery charger (we'll call this the 'AC board'). The second is ~54VDC input to convert to all the different voltages that go on the backplane (5/12/15/48/90VAC/whatever, we'll call this the 'DC board'). When the supply powers up, there's a relay that closes that you can see here, on the DC board. That relay is what ties the batteries into the supply, putting them directly in parallel with the output of the AC board. That's why you can't cold start one of these on battery, you need the AC side first to make that relay close.

Anyway, it's unlikely there's a fault on the backplane that could result in the battery breaker tripping out that wouldn't also result in the AC board having problems, seeing how the two go in parallel.

Given you've replaced everything, the only thing I can think of is some kind of wiring fault. How did you perform the load test? unplugged the AC? batteries in the right way around? maybe a battery terminal that isn't quite on right, so it survives fine under charging currents but it opens up under real load?

Have you still got the original power units?. There are 4 hidden dip switches under the metal grill on the top (I think?) and some of them apply when standby power supply is used.

Firebird Scrambler

Nortel & Avaya Meridian 1 / Succession & BCM / Norstar Programmer

Website = http://somertel.net
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