DECsystem-1090 (KL10) power requirements

From: Eric Smith <eric_at_brouhaha.com>
Date: Tue Sep 29 17:30:04 1998

Tony Duell wrote:
> But I was arguing that it would be possible for an enthusiast to run and
> maintain a KL10. I stand by that statement...

Since I (half-)own a KL10, I'd like to believe so also. I'm just pointing
out that it's not going to be easy.

> I was only considering the CPU rack. I was comparing it against a pretty
> full 11/45 system as there are a number of those owned by enthusiasts,
> with a number of peripherals on them, which they keep going.

By CPU rack, do you mean the entire 3-bay cabinet (which still does not
include peripherals), or do you mean just the CPU card cage in the center
bay?

> The ECL requirements (-5V _at_ 400A say total) are not as bad as I'd have
> thought. That PSU could be replaced (temporarily) with a switcher to keep the
> machine running.

My plan is to replace it with Vicor power supply modules, which include
DC-DC converters and AC-DC front ends.

The VI-HAM front ends accept a wide range of AC input voltages, and produce
about 300VDC for input to the DC-DC converters. They are power-factor
corrected which is vital to minimizing the necessary circuit amperage.
Each VI-HAM handles 600W.

The DC-DC converters are available in 2V 40A and 5V 40A models; 5.2V is well
within the adjustment range. They have remote sensing. It is important to
the KL10 power layout to maintain separate remote sensing power supplies for
each section of the backplane, hence it is *NOT* a good idea to replace the
original nine 5.2V 35A supplies with a single 5.2V 315A supply.

The DC-DC converters are rated at a minimum efficiency of 80%, so the
maximum load of 1918W may require 2397.5W from the front end modules.
In principle four of the 600W VI-HAM modules should be sufficient for this,
but I'm inclined to go with five VI-HAM modules and distribute the loads in
order to not run them quite so close to the maximum rating.

The VI-HAMs are rated at a minimum efficiency of 90%, and a power factor of
0.99. So the AC input will have to supply 2664W, which will be under 12A
at 240VAC. This is about 72% efficiency (minimum), almost twice the
efficiency of the original linear supplies.

Assuming that the rest of the KL10 power supplies (which are not power factor
corrected) don't end up requiring more than 18A at 240VAC, I should be able
to operate the KL10 from a common 30A circuit.

Of course, we haven't even discussed memory, peripherals, and cooling yet.
The Ampex 4 MW memory box requires a few KW. RP06s and TU78s use hefty
amounts as well.

>> DEC didn't waste any more money on regulators than necessary, so it is
> Actually, that's not always true! In many cases on 11's, the PSUs are
> overrated by quite high margins. The 5V 25A regulator was a standard part

What I meant was that although they used 25A regulators for all of the 5V
supplies, and I'm sure that none of them are actually run at close to the
current limit, they wired the machine with as few 25A regulators as they
reasonably could. They didn't have four 25A regulators each being used
for 5A, for instance, when a single regulator would do.

>> a safe assumption that a fully configured system will use most of the
>> available DC power, which for just the +5V supplies alone is 1860W.
>
> OK, call that 2kW. Erring on the safe side, lets say we need 3kW input to
> the (modern) SMPSU that we'll use to replace the ECL supply.

Agreed.

> Say 1kW for
> the other lines. That's 6kW. Not at all impossible to find. In fact I
> think I've had that sort of total power in my machine room at once already.

No, I expect that the rest of the KL10 will require at least another 2kW
or so, not the 1kW you suggest.

However, your total of 6kW suggests that perhaps you really meant 3kW for
all the non-ECL power.

Cheers,
Eric
Received on Tue Sep 29 1998 - 17:30:04 BST