How to make a battery powered slug

Try this at your own risk and only if you have some electronic knowledge; No warranty! If you are not willing to take all responsibility from doing this, then don't!

As the slug is a very versatile device, it seemed an interesting challenge to see if the slug could be battery powered. Or as RonM stated: "Never leave home without it!".

First I did some measurements. My power supply (which is not the standard one) gives 5.3 V. When the slug boots without anything connected it takes 400 mA. With the ethernet connected (but still nothing on USB) the current is about 480 mA.

This seems low enough to make battery power work. In order to get in the area of 5V it is best to use 3 or 4 batteries. When rechargeable batteries are used you'll definitely want to use 4 as these are typically 1.2V each.
For regular batteries I would recommend 3 (as that will give between 4.5 and 5 V). You could try 4. The slug itself can handle it, but it is unknown what the effect is on the voltage on the USB connector. Better safe than sorry, so stick to 3 batteries unless you really know what you are doing.

In order to battery power the slug you'll need:

• a power connector (I fried my power supply in the past, so I just cut off the connector)
• a container for batteries (and some fresh batteries)
• a piece of cable
• a voltage meter
• a soldering iron and some solder

Just solder the cable to the battery container and to the connector. Make sure that the inside of the connector is connected to the + and the outside to the -. (This is where the voltage meter comes in handy).

Put some fresh batteries in the container. Again measure that the + is on the inside of the connector. Verify also that the voltage is around 5V.
If everything is sound, connect the power to your slug and enjoy the view of the leds while it is booting.

Measurements with not-so-fresh batteries indicated that the voltage will drop when the batteries are connected (not really a surprise). I've seen a voltage drop from 6V to below 4V. The lowest I was able to get the slug running is around 3.5 V. In that case the current consumption is about 550 mA with the ethernet connected.

If you are carrying around the slug it is probably not connected to the ethernet. My guesstimate is that if you use only a single memory stick, the power consumption will be around 500 mA. This means that with a good set of batteries you should be able to power the slug for several hours. I did a test with 4 x 1700 mAh AA batteries though and there the voltage dropped from 5.3 to 3.4 V within half an hour. After disconnecting the slug the voltage rose quickly back to 5.3V. Apparently my batteries cannot deliver sufficient current for a sustained period.

It has also been suggested to use a 6V lead acid gel battery and connect this through a 7805 (or similar) voltage regulator. This has not been tested yet though. And it almost certainly won't work well: the 7805 drops more than 1V between input and output and so is unlikely to provide a reliable 5V. But a low-drop regulator like the LP38690 could work.

More simply, you could try a diode such as a 1N4001 to drop around 0.6 Volt - providing 5.4V to the Slug. At this level, you're less likely to damage USB devices than by running the 6V directly to the slug, and as the battery voltage droops as it discharges, the slug and USB devices are likely to reliably keep on going for longer.

[Tibby says: Be careful using a 1N4001 to drop voltage. If you have lots of accessories attached to your Slug, you might exceed the 1A rating!]

Also it was suggested to use an ISun Portable Solar Charger. Again not tested.

Try this at your own risk and only if you have some electronic knowledge; No warranty! If you are not willing to take all responsibility from doing this, then don't!

As part of my Slug Carputer, I am using batteries in my Honda Hybrid

To provide consistent power, and meet the power needs of the slug, I am using a 2 Carnetix 15watt, 5v Point of load converters. These devices use 10-15v input and deliver up to 3A each of clean 5v. I have 2, one for a USB 80GB HDD on Disk2 and one for the Slug with a 512MB Flash Drive1. The whole unslung portion of my carputer uses less than 1A at 12v. To power this, I have a 34AH Gel Battery (12v) under the passenger seat. This, in turn, is recharged by the starter battery. (I don't mess with the 150volt battery used for locomotion)

The best way to run from a 12V gel or conventional lead-acid battery is to use a switching regulator; linear ones will waste more than half the energy supplied as heat. Instructions for building one can be found at [http://johnarthur.wordpress.com/2008/06/08/an-efficient-voltage-regulator this page]

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