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.

Re: Battery powered DS help
 

No.

Fuses do not protect devices. They protect wires from a device failure. Note that the only way to blow a fuse is to draw too much current. The only way for the router to draw too much current is for it to fail. A fuse cannot protect the router from itself.

A fuse might protect against the application of too high a voltage, but only if the device's power input was designed to survive overvoltage and to draw lots of current in the process.

Re: Battery powered DS help
 

We lost a protective switch earlier this year. We were using a cellphone power supply with the correct voltage rating, but a lower amperage rating. The switch tried to pull too much current, the cellphone power supply fried, and that fried the switch in turn.

It was a deperation move when we were at West Michigan and they announced they were out of DS's, and we only had 1 working port.

We'll be working on something a little more robust and easier to lug around than one of the 12V batteries...

Re: Battery powered DS help
 

I believe the original IFI backup battery was 700 maHr but many teams purchased packs that had greater capacity. 1400 maHr seemed to be the norm.

The router unlikely had an electrical failure. Have you tried using the "return to factory default" procedure to load the original settings? Wall wart power supplies are rarely regulated, so electronics already have internal regulators. The WRT610N requires 1.5 amps at the power input.

Tom, I think your description is that you were using a battery from a cell phone to power the router. Or were you using a cell phone charger/ power supply to power the router. In any case, a failure to provide 1.5 amps at 12 volts nominal might have caused the router to corrupt it's firmware settings making it appear dead. The factory restore procedure or a reload of firmware may bring it back to life.

Re: Battery powered DS help
 

Alan, it was our sacrificial switch that died - we never killed the router. For whatever reason, we found it VERY difficult to find a switch at ratshack or officedepot that ran off 12 volts - they all seem to run off 6V.

Again - this was something done in desperation when we realized that if our last port died, we were out of the competition. We ran out the morning of to find the components. After realizing we couldn't find a switch that ran at 12V, we ran back out and got a cellphone car charger that provided .7 amps at 6 volts. We wired that into one of the 12 volt batteries to provide 6 volt power for the switch.

The car charger died, and the switch died at the same time. I can only assume the switch pulled too much amperage, fried the charger, then fried itself. It will no longer power up, so I would guess we killed the voltage regulator, though I never bothered to check.

Re: Battery powered DS help
 

Tom,
It is hard to know what the output of a battery charger could be. The 0.7 amp rating could be a "peak" rating based on a pulsed output. Since the switch does not present the same load as a battery would, the charger may have put out a really strange waveform. There are a few protection devices that could be in series with the power input on the switch that may have failed, and may be replaceable if a qualified person were to open the device. In most cases, I do not recommend the use of a charger as a power supply. It seems that many devices are designed for the lower voltage with the advent of lower voltage requirements for microprocessors. 3.3 volt interface electronics are becoming common as well, hence the move to 6 volt power inputs.