Battery Charging Station

[Alan Anderson]

Originally Posted by pwnageNick

Has anyone really run into a situation where they did not have enough power in their pit?

Yes. A fuse blew at the Boilermaker regional one year, and lots of people had no power.

If teams are limited to 4 amps apiece, it's going to cause problems if anyone wants to run a shop vac. That's not an unheard of practice.

[yash101]

I'm surprised that the people setting up the regional don't bring in a 10 kW generator! That's weird because they probably know that there will be a great power usage. The only power problems we experienced were the lights going out during the Las Vegas regional, which I do not know about!

[EricH]

Originally Posted by yash101

I'm surprised that the people setting up the regional don't bring in a 10 kW generator! That's weird because they probably know that there will be a great power usage.

Yash, you're going to go talk to the folks who run the Arizona Regional about how much it costs to run a regional, and how hard it is or isn't to get that funding. You're also going to talk about past Arizona Regionals in the Coliseum, same topic. (I'm hoping some of them happen to see this and go find you to make sure.)

Once you do that, you'll understand exactly why they don't bring in a much bigger generator at this time, even if they know there may be a huge power issue.

If it works out OK this time, then we'll all have been saying the sky was falling. If it doesn't, or barely works, then I'm sure that increasing the size of generator will be very high on the list of priorities for the next event.

[Al Skierkiewicz]

Originally Posted by Alan Anderson

Yes. A fuse blew at the Boilermaker regional one year, and lots of people had no power.

If teams are limited to 4 amps apiece, it's going to cause problems if anyone wants to run a shop vac. That's not an unheard of practice.

This actually occurred because teams were using the upper limit of available power from the generator. Coupled with the warm temps that year, the electrical distro finally broke down and was too hot to go near for quite a while. It took out the pits and the FCS computers as well. Thankfully it occurred near the end of the competition day.
Putting in higher power generation carries higher distro costs and increased liability insurance. That is of course if you can find one locally.

[yash101]

Can't you hook up the pits to the cars? You may be able to generate a kilowatt!

[Alan Anderson]

Originally Posted by yash101

Can't you hook up the pits to the cars?

Please elaborate. What do you mean?

You may be able to generate a kilowatt!

How far do you expect a single kilowatt to go? Consider the power used by a battery charger, an electric drill, a soldering iron, a laptop computer, a shop vac, etc.

[yash101]

Quite a bit over here in the US. We use 120 volts, so that would be equal to 8.3... Ah. For those on 240v, you would get 4.15.

Anyways, now I really think we are getting off topic so we should create a new thread, like "Power in the Pits"

[magnets]

Originally Posted by Alan Anderson

Please elaborate. What do you mean?



How far do you expect a single kilowatt to go? Consider the power used by a battery charger, an electric drill, a soldering iron, a laptop computer, a shop vac, etc.

Your car's engine has enough power for many kilowatts (>100 kw), but the alternator and electrical system isn't designed for powering stuff. Some cars have an inverter built in, but their usually rated for only a few amps, so the alternator, charging system, and battery don't get damaged.

Teams also use a ton of power. We have an ancient computer that draws 450 watts while running video, three monitors, two pretty high power projectors, a few hundred watts of lighting, 10 robot battery chargers, and 3 drill battery chargers. We've also run all this plus a shop vac, sawzall, mini band saw, and mini bench grinder all at the same time. We don't typically run all this at the same time, but it's happened before. That's quite a few kilowatts.

[philso]

Originally Posted by magnets

Your car's engine has enough power for many kilowatts (>100 kw), but the alternator and electrical system isn't designed for powering stuff. Some cars have an inverter built in, but their usually rated for only a few amps, so the alternator, charging system, and battery don't get damaged.

Teams also use a ton of power. We have an ancient computer that draws 450 watts while running video, three monitors, two pretty high power projectors, a few hundred watts of lighting, 10 robot battery chargers, and 3 drill battery chargers. We've also run all this plus a shop vac, sawzall, mini band saw, and mini bench grinder all at the same time. We don't typically run all this at the same time, but it's happened before. That's quite a few kilowatts.

Car and light trucks (pickups and full-sized vans) have alternators that have current ratings in the range of 80 to 120A, depending on the vehicle, giving you about 1 to 1.2 kW of output power. That rating is only a peak rating for when the alternator is charging the battery after the battery was used to start the vehicle. It is very likely that the continuous current rating would be half of the stated peak rating or less so you will only get around 400 to 600 W continuous. No, the manufacturers are not going to tell you what the continuous rating is since they play the specmanship game.

All the motor driven power tools you use in your pits will have some sort of current rating printed on them if they meet the UL safety standards. The starting surge current will be several times (3 to 6 X) higher than that continuous current rating printed on the case of the tool. I blew out a 2 kW inverter running such loads off my trucks batteries during Hurricane Rita.

[Al Skierkiewicz]

Let us not forget the resistive losses of the wire at 12 volts. In vehicles you are talking a few feet at most while trying to bring that inside you are now talking 50-100 feet. Welding cable is needed to prevent the drop from being excessive.

[yash101]

In this case, wouldn't you step it up to 120/240 volts at the generator/battery/etc, and use the high voltage instead of the low voltage? Also, wouldn't you need gauge 6 wire or so, for the current traveling at 120volts?

[magnets]

Originally Posted by yash101

In this case, wouldn't you step it up to 120/240 volts at the generator/battery/etc, and use the high voltage instead of the low voltage? Also, wouldn't you need gauge 6 wire or so, for the current traveling at 120volts?

No. Most wiring in your house is (probably) 14 gauge. Your microwave is probably 12 gauge. Wire gauge has a lot more to do with current than voltage.

[Kimmeh]

Originally Posted by pwnageNick

While I did not read this entire thread...

Aaaaaaand here's why:

Originally Posted by Mr V

Looking back through the thread I see the OP is from OR which throws a big wrench into the plans for a charging station.

Since we are in High School aux gyms for most of the events power to the pits is severely limited. We will be running on generator power for the pits and 5 or 6 teams will have to share 1 20a circuit. Because of this teams will be limited to the use of 2 chargers or one 3 station charger with no more than 2 batteries charging at a time. Also note that when the pits close power will be shut off to the pits so making a plan to take your batteries with you and charge them off site on Fri night is going to be a good idea.

I love it when I can answer questions with material that was already said in the thread.

[Al Skierkiewicz]

Originally Posted by yash101

Also, wouldn't you need gauge 6 wire or so, for the current traveling at 120volts?

#6 at 100 amps will drop 0.1 volt for every 2 feet of length. At 100 feet that is 10 volts. (remember you have to calculate for both the red and the black wire.) While at 220 volts that represents a mere 0.045% at 12 volts that is 83% drop in voltage. The wire size in a residential home is calculated on the voltage loss expected in a particular length and then fit to the breaker size. Many circuits in a typical house are 15 amp breakers fed with #14 wire. If you look at typical spec sheets, appliances are designed to run down to about 90 volts.