Power your Classmate PC with this cable

After reading about the extensive problems with teams’ Classmate PC’s dying, and anticipating a greater problem as the season goes on, I have developed a simple solution that I am happy to make available to all teams who wish to purchase it. Pictured below, this cable plugs into a standard FRC robot battery, and provides a fused cigarrette-lighter socket to plug a power inverter into. This adapter cable can be used with an inverter to re-charge the Classmate PC when an outlet is not available (such as in the pre-match lineup). It is also quite useful for scouting teams in the stands, and outdoor demonstrations.

Purchasing will be handled through RobotWires.com. Orders placed today, and tomorrow should arrive in time for teams competing at Week 4 events.


Whats the black gizmo in the middle?

The piece in the middle is a weather-tight fuse holder with a 15-Amp automotive blade type fuse inside.

We made one of these and it works very well, we also use it for out pump to keep our tires inflated.

I had a similar solution made a couple years ago for the bus ride to Atlanta - my laptop only had a 2 hour battery life, and we had a bunch of old batteries.
Very simple to make.

I suggested my team use it for the upcoming regionals, I think they were planning on it anyway.

Hmm… wouldn’t it be more efficient (not having to deal with the AC->DC->AC conversion) to keep it DC?

One end has the same battery connector, the other has the barrel connector for plugging in directly to the laptop. In the middle, all you need is a simple 12v->20v converter, which is a little bit of circuitry: http://english.cxem.net/car/car4.php

It looks like you aren’t the only one getting into this business: http://www.andymark.biz/am-0626.html

For something like this, “quick and easy” usually trumps efficiency.

it is interesting that you did this…
We actually built one of these on the fly during the elimination matches at Oregon. It saved our bacon on the field…

By the way… scuttlebut is that some regionals and possibly the Championships will have AC available at the Driver’s stations to plug in the classmates…

Just a rumor

It would be a good step…


At Arizona they announced at the end of Friday that there would be power at the driver stations Saturday. Saturday morning they announced there would be no power at the driver stations.

More efficient, yes.
More compact, yes.
Safer, yes as there is nothing over 20 volts.

You can buy a 12vdc-20vdc converter from www.powerstream.com,
make sure that you get the 5.5mm-2.5mm plug and exceed 2 amps,
and then change the cig plug for a battery connector.

Or, you might drop into Radio Shack and buy the
iGo anywhere NetBook charger, which has both a
110 volt and a 12 feed, RS part number 273-377

Lots of teenagers playing with inverters makes worry about safety!


These both look like good solutions, but a bit expensive ($40+). I figured many people already have inverters they use in their car, and the only missing link for these folks is something to safely connect it to the battery with.

Gold star for including the fuse. Those of you making your own, consider this a necessary feature. The battery is capable of very high currents and needs protecting.
Myself and others are lobbying hard to provide power at the driver’s station for the Classmates. After two weeks of regionals with teams failing to compete due to batteries dead or dying during finals matches should have been enough but there is no word yet.

My inverter has an integral 40a fuse, so in some cases an additional fuse may be unnecessary.
But it must have one somewhere.

The only thing i would caution Mark - if you’re hooking the inverter up through something like this (which provides a 12V car power socket to hook up to the input to the inverter), having an in-line fuse as shown at the beginning of the thread is a good idea. I doubt anyone’s worried too much about the safety risk the inverter presents (as every inverter I’ve seen includes a fuse), but if the inverter isn’t present and the cable is plugged in, the power socket on the end is wide open to being shorted. In cars, these sockets are protected by their own inline fuses, and the same should happen here.

In our case, we had taken an inverter, snipped the power cable, and hooked it up straight to the Anderson connector. In this situation, the on-board fuse for the inverter provides sufficient protection against shorts, as there are no removable intermediate connectors prior to that fuse.

Good point.
It also may get used in the future for other purposes with devices that lack a fuse.

We have one of these, but for competition we’ve wired the Inverter directly to an Anderson connector.
The extra connection through the 12v car power socket is a potential point of failure, so keep your eyes on the inverter power status light and the Classmate DS power display to be sure it really is running.