Battery powered DS help
 

My team is planning on changing our DS and wireless router to enable it them run on battery power instead of just off of the adapters, so I would like to know if anyone knows what the mAh rating and the full charge on the old 7.2volt backup batteries is?

I haven't been able to see what the normal voltage is, and picking out resistors is slightly difficult without this information. Also I would appreciate knowing if I can just ignore the fluctuations in total voltage caused by a full charge and just use a 2.4 volt change in my calculations.

Re: Battery powered DS help
 

I don't know what kind of "changing" you plan, and I don't understand your reference to picking out resistors.

The Driver Station will run perfectly on 9 volts, and it has no problem being supplied with 12 volts. The router is designed for 12 volts, and will probably work with 9, though it's not specified to be able to.

Re: Battery powered DS help
 

As I interpret this, you want to use two of the old 7.2V backup battery (14.4V total) to run the DS and router, and you want to make a voltage divider with a resistor.
I have two better ideas for you:
First, you could go to RadioShack, a hobby store, or numerous internet sites and buy a larger NiMH rechargeable battery pack and charger. A ten-cell pack will have a nominal voltage of 12 volts.
Second, you could purchase a voltage regulator chip (such as the LM317T) from a supplier like DigiKey or Mouser, and rig up a 12V regulator circuit. This would be far more reliable, even as the batteries discharge or if their is a current fluctuation in either the router or DS.

Re: Battery powered DS help
 

Since both the Driver Station and the Linksys WRT610N router are customarily powered by 12 volts DC, why get fancy? Just use a robot battery wired to a couple of Size M power connectors and be done with it.

Re: Battery powered DS help
 

Thats exactly what our team members did, they used a previous years battery and hooked it up with quick disconnects.

Our team was at the public library recently for a Science Night, where we ran the robot for over 2 hours constantly. We had to change out the robot battery every fifteen minutes, but the Driver Station battery lasted all evening long.

Re: Battery powered DS help
 

I agree with Alan on this one. However, you could use a PD to boost your 7.2V up to 12V.

In general, using resistors for power regulation is a BadIdea(TM). Since they don't have any feedback mechanism, they vary wildly with input and output conditions. If you use a series R, you need to know your load current well - unfortunately, most logic devices only draw power when they need it, so you will swing around quite a bit. If you use a resistor divider, you can partially alleviate the low idle current problem by replacing it with a high idle current problem.

Use a linear regulator or a switcher, (almost) always.

Re: Battery powered DS help
 

Hmmmm... just lost SECOND router using battery power. I think we are going to start using fuses; I would recommend the same to you...

Anyone else lost a router?

Re: Battery powered DS help
 

Our pneumatics this year needed to be charged as close as possible to the match time, so we operated our DS remotely with a robot battery all the time. Just paralleled the DS power cable into a battery quick connect cable. I believe we operated the router this way several times also and never had a problem.

Re: Battery powered DS help
 

I'm curious to know what failure you believe a fuse would prevent.

Re: Battery powered DS help
 

excess current

Re: Battery powered DS help
 

Excess current is not a failure. It is the result of a failure.

It is also the cause of additional failures, most notably burned wires, and it is those secondary failures which a fuse protects against. But the original fault which led to too much current in the first place won't be affected one way or the other by the presence of a fuse.

Re: Battery powered DS help
 

Both routers had the symptom of plug it in and nothing happens and I've ruled out polarity as the problem both times and >12V the second time. at this point linksys has accepted router 1 under warranty, so I have no plans of opening router 2 to inspect. The only other thing I can think of is a difference in impedance from power supplies. Worst case a few ohms difference, in which case the router is designed to handle that change in current, but that's my only theory at this point. That is what leads me to fuses. This will also protect against someone using the rig with battery power >12 V in the future. true, I won't be able know for sure what the actual failure is, but at least I won't have to worry about $160 secondary failures.

So, unless anyone can tell me what we're doing wrong, I'm going to be using fuses, and I stand by my suggestion that others do the same.

Re: Battery powered DS help
 

I am looking for mobility, so I was looking more towards using 2 of the 7.2 backup batteries from past years, but I cant find the amp hour rating them. Does anyone have any idea what it might be?

After looking around I think I will do a LM317T circuit on the batteries, but I would hate to buy all of the stuff and then find that it lasts for 10 minutes or something.

Re: Battery powered DS help
 

Well the fuse would protect against a device failure. So it would make a difference by protecting the router.
http://en.wikipedia.org/wiki/Fuse_(electrical)

Re: Battery powered DS help
 

To draw enough current to blow a fuse there would already have to be some sort of failure in the router. While a fuse may prevent further failures from occurring, the router does not have any components that are user serviceable for most teams so the extent of the failure is not really relevant. Fuses are meant to prevent further failures and fires, they do not prevent the initial failure.

Also, odds are that there are one or more fuses already contained in the router to prevent a fire in the case of a failure resulting in over-current.

EDIT: The link you posted actually does a pretty good job of describing what a fuse does and doesn't do.