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Low power consumption server with integrated car battery UPS

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I wrote in another post how I simply attached a car battery to a standard market UPS to give it even more juice; in that occasion, several users commented how I committed several shortcomings regarding the assembly.

Also taking into consideration that comments, this morning I rearranged the power supply of my home server to make it more silent and power efficient/independent.

On a side note, most comments were centered about me using thin cables to connect to the battery, with the reason that a car battery can deal a lot of amperes together, making a thin cable overheat, leading to possible fires. At first I credited them, but then I realized something, for which they should also get back to earth: we are not talking about shorting the battery leads for test purposes, but about using a day-to-day load, especially since it’s a low-power home server that together with accessories drain maximum 60W, which is 5amperes at 12V voltage.
Enter PicoPSU: you get a little toy able to give out up to 95W constant power (with my own model, but they make them up to 160W), which is 8amp at 12V. There is an 8 amperes current flowing through the cable running from the barrel connector of the PicoPSU… now please go and check the thickness of those cables. If those are enough for 8amps, how should 220v cable not be enough for 5 amps (tops, make it 4 on a regular basis)?

Back to us, my idea was to save the most possible on power waste, and have a silent PC that could sustain moderately long blackouts.

Ingredients:

  1. Your favourite hardware configuration for home server/automation (I bought a D510MO from Intel, with a dualcore D510 64bit Atom, put 2GB of RAM on it, a PCI DVR card, and a 2TB Samsung disk, the cheapest I found)
  2. A picoPSU power supply or something similar (I bought for roughly 20€ off the US a PicoPSU80, rated for up to 95W max, but I’ll need way less than that)
  3. A decent 12V power adapter, preferably fanless, that can manage the load you’re going to put under it, plus some more (mine came from China, but it’s ISO and CE compliant, and apart from the build quality which looks sturdy, it can take up to a nominal 120W load, that is 10A@12V)
  4. A car battery, must not be new, but should be able to hold its charge for a while, otherwise it’s pointless to use it

Here goes.

server insides
This is how deserted the tower case (courtesy of someone who abandoned it near a garbage can) looks, but it's fine, as I have the space, and I want air to be able to circulate freely inside without needing fans.
12v barrel connector on tower case
Detail: I used a pre-existing screw hole used to hold in place the old PSU, enlarged it with a drill, and fitted the PicoPSU barrel connector inside. Notice the thin cables coming out of the connector (those are apparently perfectly safe for 8amperes).

NOTICE: Be ABSOLUTELY careful when handling the following step: never, Never, NEVER make it so the battery leads are shorted together, or you will be in for a GREAT amount of PAIN, including, but not exclusively limited to: electric shocks, fire, tools welded to other tools or to the battery or to rings (NEVER wear rings or similar metal things on you while doing this). Additional word of advice: when connecting a cable, make sure the other end is either not naked, or if you removed the coating already, put a strip of insulating tape around it, you don’t want it to make contact around; this is especially true when you have both cables connected, as the naked ends may make contact between them. When you are about to connect the battery to the load, uncover a cable end at a time (first the positive, then the negative), and not both together.

car battery negative lead
In the "car battery ups" post I wrote, several people criticized how I made the connections to the battery, both plug-wise and cable-wise. This time, I used cables 3 times larger, and since I didn't have a proper car battery clamp, nor wanted to buy one/disassemble from somewhere, I just curled the copper wire around the lead. Ugly, but in the end it's as much effective as a regular clamp (try and confute). I only had ground cables that big, so who cares, I just tagged them with coloured tape to tell them apart.
cabled car battery
Sexy. This is the final result: didn't have red insulating tape either, so I used black for negative, and white for positive.
cabled 12v 10A 120W power adapter
The cable panel for my adapter, large white cable is 220V mains input, ground cables are battery leads, and grey ones are the load (server + lcd monitor + modem/router + other stuff). Before you go and start bashing me because it's ugly: I don't care, it works and it's safe. Also, it's not visible in this picture, but each cable has its own white/black tape tags to tell if it's positive or negative lead.

Results were as following: I plugged the battery leads while the ac adapter was already powering the server, and no problem whatsoever popped up; after I did it, the wattmeter I was using immediately went down quite some figures, as the charged car battery was sharing the load together with the 12V PSU. With this setup, I can plug in/out the mains plug with no effect whatsoever on the server: load, PSU and battery are all in parallel, so it 220V inlet dies, the battery takes all the load with no hassle.

Currently, the wattemer is showing quite a lower load, since the battery was all charged: I expect it to slowly raise until full consumption, which should be little more than 42W (full stuff load, plus something more to keep the battery charged).

 

What would have you changed, and what do you like/dislike about this mone-morning project?