“Luggable” power pack
Paul and I are leaving on a cross-country train trip next week, for Jen and Shawn’s wedding in Colorado. I’m sure the view will be great, and I’m bringing a handful of books- but Paul and I are geeks and we need our electro-doodads. If only we had a way to run our Nintendo DS and PSP for the ~30 hours that the trip will take…
I sifted through my stockpile of junk, and came up with this:
It’s kind of like a mega-size Minty Boost, or a heftier version of the Kensington power pack. The Minty Boost weighs in at about 6 Watt-hours, depending on the AA cells you use. The Kensington pack is rated at 7 Watt-hours, with a Lithium Ion battery. This brick occupies the middle-ground between the Minty Boost and a car jump-start battery, weighing in at 84 Watt-hours. It should run and charge a Nintendo DS for at least 30 hours.
It’s built almost entirely from junk that I had lying around the house: (Your house may vary.)
- 12 Volt 7 AH Lead-calcium battery
- Aluminum box, in my stockpile of project enclosures
- Receptacle end from a cigarette lighter extension cable
- DC-DC converter from an old Nokia phone charger (for a phone I no longer use). Swapped a resistor with a trimmer pot for 5V output.
- USB sockets from a dead 4-port hub
- Heavy duty wires and quick-disconnect plugs from a dead UPS
- Odds and ends: Switch, mounting hardware, fuse holder, wire nuts, foam weather-stripping, JB-Weld epoxy, heat shrink tubing, LED, resistors
Parts I had to buy at the local Fry’s:
- 10 Amp fuse (Pack of five for a few dollars)
- 12V 1 Amp lead-acid battery charger ($20)
- Cigarette lighter plug for the charger ($2)
Now here’s hoping that nobody thinks it’s a “hoax device”…
P.S. I’m still working on the Robot Odyssey DS port and in fact there are some interesting bits of UI working now- but I haven’t quite reached another blog-worthy milestone yet.
Ooooh, it came out nicely! Good job.
I don’t know much about the internals of batteries, but I know that they can slowly lose charge over time even if not being used. Do you know how long this one will hold a charge when not in use? Also, how long does it take to charge to full? (Is there any type of indicator for when it is fully charged?)
I’m used to charging my DS and my (borrowed) PSP using a standard wall-plug; do USB versions exist, or are yours custom-made as well?
Thanks!
I know very little about the condition of this battery.. it seems to work pretty well, but I got it from a friend in high school, and it was used at the time.. so it’s at least 10 years old now. But, lead-acid batteries are quite hearty.
There is no charge level indicator on the battery box itself.. that would be handy, but I’m lazy
The charger I’m using does have an LED that tells you when the battery is fully charged. A full charge takes overnight, but it should be able to top off a partially discharged battery in a few hours. This isn’t a deep-cycle battery, so it’s best not to discharge it too far.
Paul has a USB charging cable for his PSP.. I think it’s standard equipment?
For the DS, there are some 3rd party USB-to-DS cables. I got a package at Fry’s for $15 that included two such cables, a car charger, and an AC adaptor.
If it’s 10 years old and was not kept routinely topped off, there’s a good chance that sulfation has significantly reduced its usable capacity.
Be careful using old SLA batteries from UPSs. The general rule is that those small UPS batteries should be used for no more than about 5 years. After that point failure rates become very high, and are usually in the form of leakage, swelling or venting or extreme overheating. Obviously leakage of the acid is dangerous, and the gas that can be vented from these batteries is hydrogen, which is highly explosive.
I’m not saying this to discourage your use of SLA batteries at all. I just highly recommend that you buy new ones for your trip.
Question?
Great idea and a nice, clean implementation.
How are you going to transport it? It looks like it could use a handle on top…
True. I don’t remember ever storing this battery in a totally dead state- I think I had occasion to dust it off and charge it at least once every few years
(Worst case, this battery is toast, I recycle it, and get a replacement for about $20..)
Re: Question?
A handle might help.. I was probably just going to sit it in one of the pockets on my backpack
Thanks for the advice. I’ve definitely seen some UPS batteries in bad condition.. I had an old APC UPS with two smaller 12V SLA batteries, and both batteries had swollen to the point of being hard to remove from the UPS. Presumably this was due to prolonged overcharging.. I’ve heard that the plates can actually grow in length if you float charge for a very long time.
This battery is pretty old, but it’s seen very little use. It wasn’t from a UPS, it was from a friend who used it to charge model aircraft batteries. I don’t think he used it too heavily, and I’ve only ever used it for very intermittent portable applications.
I’d be more worried if I were subjecting it to high charge/discharge rates, but I’m mostly discharging it at around 0.2 A and charging at 0.5 A or so. I’ve been monitoring its temperature, and even at discharge rates of 6 A or so, I haven’t noticed any increase in temperature.
Do you still think the battery is worth replacing?
I’d still suggest replacing, but if you know it’s been fairly lightly used, you’re charging it slowly and keeping an eye on it, and there’s no bulging of the case I suppose you should be ok.
If there’s any bulging though it needs to go.
Awesome luggable, Micah. Have a great trip and don’t forget to look outside the train from time to time.
I built mine into a rolling suitcase. But I also used a 45 AHr battery which is way heavier. But I run laptops off it (~25W power consumption with the laptop “idle”). Then I added a WiFi client, access point, and two patch antennas, and built myself a “WiFi repeater”.
Every train i’ve been on in the last 10 years has had 120v standard electrical sockets in every car at every seat powered by the giant onboard generators in the engines. I know this is kind of besides the point though, and the box IS pretty cool