[c-nsp] 7507 crashes

[Barton F. Bruce]

> Would DC power supplies be more apt to smoothly power the cisco? I've
> got an old lorain 25amp rectifier that seems like it should power it and
> some batteries fine. It had powered an old tadiran PBX that was bigger
> than a 4-draw filing cabinet.
>
> Is this a good way to go, or should I be chasing down some other path?

DC is always best IF you have dealt with the monster speed bump of 
installing CO grade DC plant.

You need to treat your batteries VERY WELL, and any old 48 VDC supply is 
simply NOT the same as a good CO grade rectifer that is designed to get 
maybe 25 years out of batteies.

The batteries need to be FLOATED at very exact voltage (depends on exact 
battery type and its specific gravity even for what are all basically lead & 
sulphuric acid variants) and cell temperature.

Your Lorain may be ok, or maybe not.

There should be no ripple torturing the cells, either. Though  a battery 
effectively can act like a LARGE cap and filter for you, you don't want to 
do that to a battery. If this is just for your 7507, and is in a private 
controlled access place with plenty of ventilation to dissipate hydrogen 
(closets and small rooms are BAD), consider 4 LARGE car or TRUCK 12 V 
batteries in series. Costco still sells ones you can top up with water, BJs 
thinks everyone is too stupid so sells sealed ones.  Leakage worries? Get 
cat-box to small morter mix sized heavy plastic trays, loaded with some 
traditional clay sorbant cat litter (NOT the modern junk) and a LOT of 
baking soda, and you can weather any leak. The + end of battery string is 
grounded. Consider a system where your non-CO grade rectifier NEVER impacts 
the battery! Run the rectifier ABOVE the battery voltage and have a LARGE 
blocking diode (or a few in series for more drop) so it directly feeds the 
7507 but not the battery and the battey is drained ONLY when the AC fails. A 
LARGE (inches in diameter and height) electrolytic cap may be necessary if 
rectifier ripple drops voltage low enough that battery would be drawn many 
times a second without it. Next MIT/ Harvard ham Sunday flea market is soon, 
drive down from Maine and you will probably find some (or LARGE UPSes, 
or...)

Then FLOAT the 48VDC battery with even a smallish QUALITY charger that may 
not even be able to carry the 7507.

Buy No-Ox-ID by the case for all your crimped power lugs and battery 
connections. Also makes great non-messy (it is a wax) lube for rack screws. 
Also polishes shoes and is used for the non-flaking rustproofing liner for 
steel water towers (has a NSF rating for this). Aluminum oxide is SANDPAPER 
and screwing steel screws into aluminum racks without No-Ox-Id is asking for 
trouble if there is any side load being carried while screwing.

Now that is all silly to do for just a 7507, but if you want to tinker, have 
fun.

You can typically BUY a used small CO grade charging bay cheap enough all 
wired up perhaps complete with some integral battery trays. Several USED 
equipment dealers in New England get these periodically.

The rectifier(s) should be able to periodically cranked up to "equalize" 
voltage to bring all cells to full charge, but no longer than necessary.

Good CO chargers are designed to work in parallel with others of the same 
model, so you can build for whatever size load you want. The battery is 
sized for how long you need to run with no AC, but you MUST have a low 
voltage cut-off lest you destroy the battery when some cells go to zero 
before others and then effectively are getting reverse charged by their 
mates. Generally better to shut down a little earlier and not destroy the 
battery.

We use 200AMP Nortel/Aztek rectifiers that take 480VAC three-phase in, and 
run as many in parallel as necessary. Each 2VDC cell is rated at 1500 Ampere 
Hours and weighs 600 pounds. A tray of 3 in parallel gives you a 4500 AH 
battery system and 24 trays (72 cells) make up the full 4500AH -48VDC 
battery. Wire a couple of these in parallel and have a 9000AH battery. 
Everything connects with MULTIPLE 750MCM 2000Volt rated DLO "FLEX" (copper 
the size of a banana) cables run in parallel.   Ideally, your diesels should 
have block heaters and be able to take full load as soon as they are up to 
stable speed. That is only about 12 seconds, so a battey this size also 
assumes the diesels may not start immediately...

Perhaps you need to be in someone's COLO that has suitable AC and/or DC 
already handled.

Don't know about 7500 supplies, but 7200 ones CAN NOT have AC and DC mixed 
(clueless bad design). A 6509 takes an AC and a DC together with no problem.

Also a chance is that it isn't loss of power but a related SPIKE that is 
zapping you. Do you have a QUALITY service entrance grade TVSS on your power 
line? Or even better appropriate grades at each breaker panel in your 
building (getting cleaner and cleaner farther away from ouside lines, while 
also snubbing locally generated crap within the building). Some UPSes won't 
filter all this stuff out.

If you had the "ALWAYS INVERTING" type UPS, there is no "should we switch 
over?" delay time at all. Get a suitable UPS.