Subject:
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Lithium-Ion batteries are innocent!
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 4 Aug 1999 07:10:16 GMT
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Viewed:
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1197 times
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In lugnet.robotics, lego-robotics@crynwr.com (Tilman Sporkert) writes:
> Please note that in this particular case, the RCX is reported to still work
> with the internal batteries. That means the fault is somewhere in the path
> from the external connector to the main power "bus" within the RCX. Some
> component that is only used with the external power supply is probably
> damaged. I suspect that there isn't much more than the connector and a
> bridge rectifier that falls into this category. So either the bridge
> rectifier got burned out by an overcurrent situation, or quite simply, the
> connector doesn't work anymore. Maybe a piece broke off in the connector, or
> there's a bad solder joint on the circuit board.
I think you will find that the bridge rectifier is in the internal battery
circuit also, as the type of power socket used normally has only a single pole
normally closed switch to disconnect the battery.
I would suspect either the power connector in the RCX has a dry joint, or far
more likely there is a problem with the external battery pack & connections.
The way to check this is under-load (If you check the voltage off-load, it will
look OK even with a seriously damaged battery or bad solder joint) - get a 12V
car bulb, around say 6W, and connect this across the buisness end of the RCX
connector (i.e. exactly where the RCX would go), and measure the voltage
across the bulb.
> > From: Issac Merkle <the_gaff@hotmail.com>
> > > The more I think about it, it may be a NiMH pack, rather than • Li-Ion. I'll
> > > have to check.
> >
> > Note that both NiMH and Li-Ion can put out much higher currents then
> > alkaline cells (alkaline cells have a high internal resistance).
> > Could this
> > person have shorted across the output somehow? That would
> > probably blow the
> > motor controller because it would run more current through the controller
> > then the controller could deal with.
The motor controllers are virtually bombproof (If the manufacturer is to be
believed) - they current limit at 500mA ish, and if they overheat, they
shut down. Thus (without a major fault within the RCX) even with all 3 motor
outputs on & shorted you will only get a load of around 1.5A max.
However, anyone who powers their RCX from external batteries should put either
a fuse of about 1A or maybe a 21W 12V car bulb in series with the battery.
Also, about voltages, I think you will find that the RCX is OK up to about 17V.
Kevin.
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Message is in Reply To:
 | | RE: Don't use Lithium-Ion batteries
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| Please note that in this particular case, the RCX is reported to still work with the internal batteries. That means the fault is somewhere in the path from the external connector to the main power "bus" within the RCX. Some component that is only (...) (25 years ago, 3-Aug-99, to lugnet.robotics)
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