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Unread 29-12-2013, 18:12
F Elliott F Elliott is offline
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Powering the Robot From the Battery Charger

Rookie coach alert.

During test and development, would it be possible to power the robot using the battery's AC charger without harming the controllers?

THANKS!
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Unread 29-12-2013, 18:16
Christopher149 Christopher149 is offline
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Re: Powering the Robot From the Battery Charger

Is there any reason that running from the charger would be more advantageous or convenient than plugging in the battery?

That said, I don't know about safety concerns, since I've never known anyone to bring up this idea.

(Edit: advice given wrt FRC, not FTC)

Last edited by Christopher149 : 29-12-2013 at 18:33.
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Unread 29-12-2013, 18:26
k4mc k4mc is offline
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Re: Powering the Robot From the Battery Charger

If you connected the robot to a charger, I am fairly sure you would draw too much current and burn out the charger. The charger is designed to deliver a few amps while running robots can draw a hundred amps.
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Unread 29-12-2013, 18:29
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Re: Powering the Robot From the Battery Charger

I think the question comes down to how much are you trying to run?

If it is just the electronics to make sure everything is working, or running a free spinning motor, you may be OK, but you could run out of supply amps in a hurry.

The other thing to "strongly" warn about. There are parts of the electronics that will handle reverse polarity but NONE of the speed controllers do (jag, victor, talon) do. If someone clamped the charger to the supply terminals backwards and "poof" there they go. Really easy to do.

The battery connectors will not allow that to happen, so I would recommend just using the battery, or use a dedicated bench supply rather than the charger. And if using a dedicated bench supply use the Anderson power connectors so no backwards polarity can happen. Speed controllers are expensive (we had to replace 5 last year due to a sleep / sick student trying to rush the electrical without a double check from someone else before powering things up).

If you are just running the electronics and no motors, a good wall plug 12 volt power supply would be a good alternative to using the charger.

Also if just running the electronics, the battery will supply power for a long time before needing to be charged again.

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Unread 29-12-2013, 18:30
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Re: Powering the Robot From the Battery Charger

Don't every try and power the robot off of the charger! Chargers output voltages significantly over* the 12-13v that the battery supplies and are rarely rated for enough amps to power more than the control system.

*Some chargers spike up to more than 20v.

Bottom line: Powering a robot off a charger is a bad idea.
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Unread 29-12-2013, 18:31
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Re: Powering the Robot From the Battery Charger

Quote:
Originally Posted by k4mc View Post
If you connected the robot to a charger, I am fairly sure you would draw too much current and burn out the charger. The charger is designed to deliver a few amps while running robots can draw a hundred amps.
Looks like this is for FTC instead of FRC. However, I still would advise not to use the charger to power the entire robot. If you're just powering the controller you might be fine, but add in a motor or more and all bets are off.
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Unread 29-12-2013, 18:37
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Re: Powering the Robot From the Battery Charger

Quote:
Originally Posted by F Elliott View Post
Rookie coach alert.

During test and development, would it be possible to power the robot using the battery's AC charger without harming the controllers?

THANKS!
No.

A battery charger is not simply a DC power supply. Battery chargers typically contain advanced circuitry to measure the current status of the battery and adjust the electric current available. Batteries typically charge at their fastest rate when mostly depleted, then slow down as they approach full, then provide minimal trickle-charge current to keep the batteyr topped off when its full.

You will likely get unpredictable results attempting to use it as a power supply.

Also, the typical peak output current of a FRC battery charger is way under-powered for running a FRC robot. Most chargers can only put out a few amps at most, and a FRC robot can and do draw hundreds of amps for brief periods of time.
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Unread 29-12-2013, 19:31
F Elliott F Elliott is offline
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Re: Powering the Robot From the Battery Charger

Thanks everyone!

I'm trouble shooting our FTC robot. It seems the NXT is working (ROBOTC sees it and can make it beep), I have the motor controller configured in the PRAGMA, the controller power LED is on, and the motors run with direct DC, but the motors are not running when under program control. Ive tried the simple sample programs and none of them work either. I've looked at it for about an hour and as a last resort I'm recharging the batteries. They've been charging for over an hour now.

UPDATE: Batteries are charged and the motors show as "running" in the NXT Device Control Display Debugger, but they're not running.

Last edited by F Elliott : 29-12-2013 at 20:00.
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Unread 29-12-2013, 19:50
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Re: Powering the Robot From the Battery Charger

For the VEX you could plug in the charger and battery at the same time to the controller but I really would not want to do that.

Instead I would get a power supply to act as the battery.
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Unread 29-12-2013, 22:17
philso philso is offline
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Re: Powering the Robot From the Battery Charger

The Schumacher-branded chargers I have seen used for FRC robots test to see if they are connected to a battery by measuring the voltage at the terminals before turning on their output. Your robot should not have any residual voltage on it so the charger output will not turn on and no voltage will be applied to your robot. It is also likely that the starting surges of the CIM motors will cause the charger to go into current limiting mode and/or shut down.
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Unread 29-12-2013, 22:24
Seth Mallory Seth Mallory is offline
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Re: Powering the Robot From the Battery Charger

GRT for years have been using 12 volt drills with the motor removed as power sources. Remove the motor and install long leads that you can use to power things with One drill battery will run 2 CIM motors. We use Anderson Power Pole connecters to hook things up. This gives you a variable voltage reversible polarity power source. You can add a fuse to both leadssince bioth can be positve. Walmart has their own line of 12 volt drills for 20$.
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Unread 30-12-2013, 00:03
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Re: Powering the Robot From the Battery Charger

F,
It sounds like the motor controllers are not getting power or the controller is not being addressed properly. Power wiring to the controllers are notorious for falling out unless the wire is carefully prepared and inserted.
As a new user, I have to ask if the controllers are connected to a working sensor port on the NXT brick and that they are properly looped if you are using more than one. It is possible that the cable between the first controller and the NXT is bad.
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Unread 30-12-2013, 00:07
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Re: Powering the Robot From the Battery Charger

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Originally Posted by Al Skierkiewicz View Post
As a new user, I have to ask....
You're not a new user, Al


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Unread 30-12-2013, 14:11
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Re: Powering the Robot From the Battery Charger

You'd be much better off, powering you robot off a switching PSU or an ATX psu.
An ATW PSU will typically have over-current protection and can typically handle over 20 amps at 12 volts. However, don't expect to run CIMs (CIM, MiniCIM and BAG). The BAGs draw up to 40 amps at stall!

I believe the batteries fast-charge at 3A/hr. I think the bridge consumes 1 or 2 amps, by itself. Plus, you have a cRIO, DS, and other components, like a coprocessor. So, you'd probably see magic smoke from that $100 charger you saved up for!


---------AAAHHH!!! You're an FTC, not FRC. My bad. I'll leave that up because that would be useful for FRC teams---------

Again, just get an ATX PSU and hack it so it is always on. That only requires a paperclip. Battery chargers are not meant for powering things. They are meant for charging batteries! Don't ask up why you got magic smoke if you used a battery charger to power the robot.

This is what you aree probably looking for, and costs less than a good FRC charger. (I don't know what FTC uses)

Last edited by yash101 : 30-12-2013 at 14:17.
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Unread 30-12-2013, 16:00
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Re: Powering the Robot From the Battery Charger

Ether, just testing to see who picked up on that. You pass!
I should have mentioned that it is never a good idea to power anything from a battery charger, particularly smart chargers. These devices generally test to see if a battery is connected and then will alternately turn on and off to supply current and then test for terminal voltage changes. In any case, the amount of current the charger can deliver is generally much, much less that that delivered by the same battery. In the case of the FRC battery, the charger is limited to about 6 amps max while the battery can deliver 100 times that amount when fully charged. In the case of the FTC system, the charger may be designed for NiMH batteries or the old NiCD and in either case, the charge voltage may just exceed the motor controller, it may open a fuse in the charger or it may just permanently damage the charger, controller or both. A 20 amp, 12 volt power supply might be able to run the motors but don't be surprised if the start current causes even that larger charger to shutdown on over current. An FTC motor as I remember is about 7 amps stall current.
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