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Unread 23-02-2015, 08:19
dorg dorg is offline
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possibility to use charger and battery at the same time

hi everyone
i want to make a robot using the frc battery:
http://www.andymark.com/battery-p/am-3062.htm
and this charger:
http://www.andymark.com/Battery-Char...-p/am-2555.htm

the thing is, i want the battery to power the robot, and from time to time connect the charger to the battery in order for it to charge (while it is powering the robot)

is that possible?
if not, are there better solutions? battery charger and such?

thank you,
dor
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Unread 23-02-2015, 09:07
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Re: possibility to use charger and battery at the same time

The way the batteries use the cables, they are not meant to be powering the robot and charging at the same time. What most teams do is keep multiple batteries with them, and charging the other batteries while your robot is doing its function.

Last edited by Bryce Clegg : 23-02-2015 at 09:10.
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Unread 23-02-2015, 09:20
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Re: possibility to use charger and battery at the same time

You can do what you want, but you need to consider how much current the robot will use, and how often you will need to charge it, and how long it will take to charge the battery while the robot is running. The current the robot uses while charging, will limit how much current will be able to return to the battery from the charger.
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Unread 23-02-2015, 10:28
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Re: possibility to use charger and battery at the same time

Unless the charger is specifically designed to work while the battery is being used, connecting it while the robot is powered is very much not a good idea.
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Unread 23-02-2015, 10:50
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Re: possibility to use charger and battery at the same time

It is done in cars all the time so it is a theoretical possibility. You need a charger that self limits current so it is not overloaded when the system is drawing more power than the charger can provide.
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Unread 23-02-2015, 10:50
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Re: possibility to use charger and battery at the same time

It depends on the components used on the robot and the voltage range of the charger. A typical charger will charge at ~14.2 volts while a fully charged battery is only 12.7 volts. Not all chargers are the same however, but most fully automatic chargers will not exceed ~14.4 volts. So if you have any components that can't handle the max voltage the charger can supply they will be damaged. Keep in mind every time you drive your car those components that are normally rated for a nominal 13.8v are subject to that ~14.2v while the car's charger (alternator) is "on" which should be any time the engine is running.
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Unread 23-02-2015, 10:59
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Re: possibility to use charger and battery at the same time

so, if i understand you right when the charger is on and connected all my components in the robot will get the voltage it suplies 14.2 for example?

is there a way to do this without damaging my components with the extra voltage?
are there any recommended chargers for this?

to make myself clear, i am doing an autonomous robot that needs once in a while to charge itself from the AC power dock
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Unread 23-02-2015, 11:07
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Re: possibility to use charger and battery at the same time

As Alan suggests, you probably want to use a charger that is designed to do what you want to. The charger you listed above is designed to charge batteries with not other load connected.

I don't know how helpful this is, but I have an old robot called Hero 2000 that has a docking station that it can drive into, and charge. I might have the schematics for it somewhere. It uses a battery similar to the battery you listed, although it has a bit more capacity (24 AH instead of 18 AH).
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Unread 23-02-2015, 11:35
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Re: possibility to use charger and battery at the same time

sure anything will help
especially if someone could help me choose a good charger for this application
and can also answer me for the question above:

Quote:
so, if i understand you right when the charger is on and connected all my components in the robot will get the voltage it suplies 14.2 for example?

is there a way to do this without damaging my components with the extra voltage?
are there any recommended chargers for this?
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Unread 23-02-2015, 11:38
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Re: possibility to use charger and battery at the same time

Quote:
Originally Posted by dorg View Post
is there a way to do this without damaging my components with the extra voltage?
The VRM Module has a rated input voltage of 5 to 16 volts, so it can receive 14 volts. It will output 5 and 12 volts at the rated amperage limits. You can use the VRM to protect electronic circuits.

The Talon motor controller is rated for 6-28 volts, so is fine. I'm guessing that the CIM motors won't have a problem with 14 volts.
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Unread 24-02-2015, 14:49
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Re: possibility to use charger and battery at the same time

Guys,
Most smart chargers use pulse charging. While the average voltage read by most multimeters will show approx 14 volts, the peak is much higher than that. As I remember, the KOP chargers peaked at something greater than 15 volts. Do not run chargers and robot electronics at the same time. The electronics in cars are designed for all kinds of voltage swings. I remember reading an article that suggested, power supply could be anywhere between 5 volts and 19 volts with a lot of noise on the line. The charge current in an automobile is also generated by a polyphase alternator and the peaks frequency varies with engine speed.
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Unread 24-02-2015, 14:53
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Re: possibility to use charger and battery at the same time

How good of a filter is the battery?
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Unread 24-02-2015, 14:56
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Re: possibility to use charger and battery at the same time


Has anyone ever put a scope on the output of a KoP charger and looked at the waveform with a fully charged -- and with a fully discharged -- battery?


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Unread 24-02-2015, 15:11
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Re: possibility to use charger and battery at the same time

The battery is pretty good filter. On the more primitive motorcycles, not having a battery in the circuit will fry the electrics. (and more than likely a RoboRio) The better UPSs run on battery all the time with the charging circuits float charging the battery. Not to say that either of these is like the KOP chargers just that this problem has a solution.
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Unread 24-02-2015, 15:11
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Re: possibility to use charger and battery at the same time

You read my mind. Although I was just going to do it with a volt meter, since my scope probe got lost on the movie set, and I haven't replaced it. Maybe an analog voltmeter, because it would be so neat to show the students some old technlogy. And I was wondering last night where I put my dad's voltmeter...I found it around 1 AM. Won't see the little transients, but will give us an idea of what the charging voltage is.
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