Kingsly John - Everything You Didn't Need To Know!
Kingsly John - Everything You Didn't Need To Know!

Random Chaos

Tue Sep 11 02:55:15 IST 2007

Low Power Computing (Pt-1) a.k.a. Dealing with Unreliable Power Supply

A few months ago, my UPS which had been powering my computers and routers since 2003, almost gave up the ghost, luckily I managed to get it repaired at no cost. But it was time to get a new power backup system in place.

The old UPS, an APC Backups RS-1500 with a BR24 Battery Pack used to power my machines(~300Watts of load) for around 1-1.5hours. Which wasn't anywhere enough to deal with the power outages in Bangalore. My iBook's 5.5+ hours run time and GPRS that helped me get through them over the past 2 years.

After a thorough search of the UPS market, I found it hasn't changed much and I was already at the top of the consumer segment in terms of run-time. And going any higher would require paying a considerable premium(almost 2x) for enterprise grade equipment. And would still not have complete freedom from power cuts.

The best off-the-shelf solutions I found were, the APC 1KVA Sine Wave Inverter(which I'd have to plug my current UPS into) But that would set me back by around INR30k(for inverter, batteries and cabinet) and only guarantee around 5-6 hours of backup. And the Su-Kam "High Frequency" Sine Wave inverters which seem to be technologically superior to the APC one. But I wasn't able to get run-time charts or any other technical information from them. The Su-Kam model is more expensive than the APC one but seems to be worth it.

But I wasn't keen on adding another 120kgs of equipment into my already cramped bedroom unless it gave me total freedom from power cuts. Considering "planned" 8 hour power outages happen almost once a month. And unplanned ones could last longer. I was looking at a minimum of 12 hours of backup hopefully with an option to further extend the runtime by adding more batteries.

Spoke to a few people working in the UPS industry and the consensus was that it wasn't possible to get the kind of backup I wanted for my kind of load.(Apparently generators exist for exactly that reason!)

So decided to work the other way and lower my current load to ensure that I have a functional system with minimal power consumption and then look at extending power backup.

The biggest load saving I could think of was to replace my 19"CRT with a LCD Panel, but I found that the LCD panels in India are overpriced junk. They seem to be geared towards folks that will use it at 1024x768. Most of the 19" models don't do 1600x1200, and those that do cost more than the price of two 17" LCDs that can do 1440x900. (The Viewsonic VA1703WB seems to be the most value for money in the indian market.)

My 19" Philips 109s4 is pretty energy efficient, even though it's supposed to operate at 80 Watts since I operate at very low brightness and use a predominantly black screen it's usually around 50-60W. So There won't be much savings from switching to an LCD. Around 10%(30Watts) if I went for a single screen and even lower in case of a dual-head setup.

The biggest power hog turned out be my Athlon XP 2600+ based desktop, which was consuming almost 150Watts even when idle. Found an utility called athcool which managed to chop off an amazing 35-40 Watts of load! My work isn't CPU intensive and so the machine is at 1-2% CPU utilisation most of the time and has been powered on almost continuously for the past 3-4 years. I could have shaved a few thousand rupees(around 1000Units) off my electricity bill had i found it earlier.

Since the bulk of my work was still done on my ~7 year old headless P3-733 which had been slowly dying away over the past few years(video card/SMPS/hard disk). I decided it was time to retire it and replace it with something really low power.

Decided to work within the quoted price for the APC Sine Wave Inverter of ~INR30k and ensure I got equal or better battery backup.

Phase 0

Since the lowest power device I own is my iBook, I decided to see how long I could run it on a regular UPS.

I picked up an APC Backups RS-1000 and a battery pack for ~INR10K, which would be necessary to power my Desktop even if it wasn't useful for the low power computer

Sat May 20 10:42:17 IST 2006 LOADPCT : 2.0 Percent BCHARGE : 100.0 Percent TIMELEFT : 1080.0 Minutes
Sat May 20 23:27:13 IST 2006 LOADPCT : 2.0 Percent BCHARGE : 028.0 Percent TIMELEFT : 382.0 Minutes

For anyone wanting to work uninterrupted a low-power laptop as your primary machine is the best option

The UPS + my iBook's internal battery would have lasted for over 20 hours.

The most energy efficient CPU that was readily available in the market was the Via C7 which was available from a whole lot of mini-itx motherboard manufacturers.

The price i got quoted for the only indian vendor that replied back fast enough was around INR10,500+shipping. Luckily a friend's colleague was returning from the US and was agreeable to carrying one down for me (Thanks Zac! :-), So I ordered an Jetway - J7F2WE1G5 from Mobile Computing Solutions for USD170(~INR 7200) Free shipping all the way to Bangalore and a saving of over INR3000.

So a couple of weeks later, I had my newest computer complete with DDR2 and SATA support and with a 1.5Ghz CPU which never used more than 12Watts! And a total power consumption of 45watts (including routers/switch/voip etc)

Picked up a 1GB stick of Kingston DDR2, a 80GB SATA laptop disk and a thin cabinet. for around INR7000 in total.

Phase 1

The resultant power backup at the end of phase 1...

Mon Sep 3 11:06:49 IST 2007 LOADPCT : 10.0 Percent Load Capacity BCHARGE : 100.0 Percent TIMELEFT : 372.5 Minutes
Mon Sep 3 16:30:26 IST 2007 LOADPCT : 10.0 Percent Load Capacity BCHARGE : 033.0 Percent TIMELEFT : 123.0 Minutes

So for a total spend of INR25000, I had a brand new computer and UPS allowing me to work uninterrupted for about the same amount of time as I would have been able to by spending INR30000 on an Inverter!

Ok that's not entirely accurate since currently my desktop(and CRT) still runs on my old UPS and shuts down after about an hour and I have to switch to my laptop. But I can now access most of my data on the headless box and use DSL+wifi and it's way better than having 100kgs of batteries lying around in my bedroom.

Over the coming months/year, I am contemplating running the new computer and the routers etc directly off a 12V battery. Which should minimise losses from converting from 12VDC-230VAC and back to DC again to power the devices. A small car battery should be able to run my current equipment for over 24 hours.

That along with a low-power desktop replacement will make the next part of this entry sometime in the future!

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