Re: Powering the Robot From the Battery Charger
 

You need one of these DC 12V 10A 120W Switch Power Supply: http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

Or a 30A version DC 12V 30A 360W Switch Power Supply: http://www.amazon.com/SUPERNIGHT-Swi...ef=pd_sim_hi_1

you would want to wire up a three pronged plug extension cord to the AC in & ground.

Re: Powering the Robot From the Battery Charger
 

Most battery chargers attempt to be a constant-current source and make no effort to regulate their voltage. They let the battery do that by taking the current until the voltage drops down to the level of the battery. The charger watches that voltage to tell when the battery is charged.

With no battery there, the voltage is likely to be quite a bit higher than you would expect for a "12" volt charger.

And the circuitry in smart chargers will further compound that. Good ones will recognize there is no battery attached and shut down.

The DC regulation on many chargers is also poor. They are often puslating, unfiltered DC and could damage sensitive electronics.

Don't ever attempt to charge a battery while it's attached to the robot (or other device.)

Re: Powering the Robot From the Battery Charger
 

Does anyone know whether or not the above cautionary advice also applies to charging installed auto batteries?

Re: Powering the Robot From the Battery Charger
 

I think it would because a similar technology is used. That would make the charger think the battery is charging, when it isn't, which could possibly lead to a battery problem, like an explosion in extreme cases!

Also, just get a good atx psu. They can handle tons of amps and can be purchased for very little money! The power output is so high that loading it down would give you the bang for the buck :D.

One nice thing about ATX PSUs is that they have 5v and 3.3v rails built in, which can be useful for powering/testing different parts of the robot without using the 12v supply. Also, they are actively cooled, so while you will have a space-heater, it won't overheat way too easily.

Also, the regulation in ATX power supplies is very precise. You don't want to feed 12v2 to the mobo. You want a much higher precision than that, e.g. 12v01! That can eliminate some variables with voltage surges when you are testing or finding a problem.

Check this out, and also have a crack at the reviews!

A 1000-2000 watt supply with many powerful 12v rails is what every team should try to invest in, especially when you can get a decent one for about $100 and a fancy one under $200!

Re: Powering the Robot From the Battery Charger
 

Thats the strangest thing i have seen, a computer power supply for external use? Im guessing for use in a Test Bench or something similar.

Re: Powering the Robot From the Battery Charger
 

Ether,
Are you asking about the charging system in your car? Modern vehicles use an electronic form of battery charging. In older cars, they used stepped resistors to regulate charge current. The alternator output voltage is controlled to provide something higher than the terminal voltage on the battery. Typically some where between 14 and 15 volts. I read a paper a few years ago that stated the vehicle electrical system is one of the most harsh environments encountered in modern electronics. Power supplies vary from 7-8 volts to more than 18 volts and noise and various other transients even higher than that.
Cheap, line operated, automotive chargers simply rectify the output of a transformer and apply that to the battery. Some may have switched resistors to limit charge current. Smart chargers do a whole lot more.

Re: Powering the Robot From the Battery Charger
 

Not exactly. You can get them quite cheap (if you look), and they can handle tremendous amperes of current. They also have large internal head sinks and large fans, meaning that the thermal capacity is even higher!

Re: Powering the Robot From the Battery Charger
 

Power supplies like this are designed for bench use and for embedded controllers that use a standard or single board computer as part of the system. A plastic sign cutter I use has just such a high current computer supply. The 2D system uses stepper motors to drive the cutting head to mass produce things like the door signs you see at the doctor's office.

Re: Powering the Robot From the Battery Charger
 

I was referring to Doc Wu's comment about battery chargers:

The DC regulation on many chargers is also poor. They are often puslating, unfiltered DC and could damage sensitive electronics.

And his cautionary warning not to use them on a battery which is installed:

Don't ever attempt to charge a battery while it's attached to the robot (or other device.)

... and wondering if that applies to an installed auto battery.

In other words, is the electrical system on most modern autos designed so that charging the battery (with an external smart charger, without disconnecting the battery) will not harm the car's electrical system?

I've heard many opinions about this, but haven't yet found anything authoritative.

Re: Powering the Robot From the Battery Charger
 

In general there should be no problem. The cheap chargers while having an unfiltered output will be supplying this directly to the battery which will tend to flatten the output waveform to approximately the terminal voltage of the battery plus voltage dropped across the internal resistance and any resistance in the charger clamps. So while the unloaded voltage may exceed 20 volt peaks, the loaded voltage will be lower. The current will spike during charging but the current is going directly into the battery. Even fully charged, the excess current (once the charger voltage exceeds the charged voltage of the battery) is converted to heat in the battery. Remember that the output voltage of the charging system will change with engine RPM while the voltage regulator is trying to compensate while changing alternator field current.

Re: Powering the Robot From the Battery Charger
 

I'm glad to hear that. I've been doing it successfully for years and always wondered if I was just cheating the hangman.

I vaguely remember adjusting the "voltage regulator" in my 68 Camaro in the dead of winter by bending something.

Re: Powering the Robot From the Battery Charger
 

Those regulators required specific distances on the contacts of the relays in the regulator. The relay field coil(s) was part of the charging circuit.