Subject:
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Don't use Lithium Ion (was Re: RCX battery cover)
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 3 Aug 1999 19:13:12 GMT
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Viewed:
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976 times
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Someone sent me an e-mail reply saying that they had used an external Lithium
Ion battery pack to power their RCX, and that after a few days of use the RCX
appeared to stop working, then they discovered that it only worked with
internal batteries. In other words, they had permanently damaged the RCX by
"burning out" the external power circuit.
The problem this person encountered results from the fact that lithium ion
batteries have a very non-standard voltage of 3.0 - 4.3 volts per cell, and it
simply isn't possible to build a 9V battery pack out of them. This person
probably had 3 lithium ion batteries in series supplying from 12.9 volts (when
fully charged) to as low as 8.5-9.5 volts (after the first 90 minutes). The
12.9 volts is probably what damaged the RCX.
So I'm going to extend the warning to everyone out there -- don't use batteries
that have a higher voltage rating.
Here's the information I currently have for well-known types of batteries:
primary (single-use) cells
max. nom.
1.50 Carbon Leclanche (Zinc/Manganese Dioxide-Carbon/Ammonium Chloride)
1.50 Heavy-duty Carbon (Zinc/Manganese Dioxide-Carbon/Zinc Chloride)
1.59 1.50 Alkaline (Zinc/Manganese Dioxide/Potassium Hydroxide/Zinc Oxide)
1.34 1.33 Mercury (Zinc/Mercuric Oxide)
1.40 Zinc air
secondary (rechargable) cells:
max. nom.
2.04 2.00 Sealed Lead-Acid (Lead/Lead Oxide/Sulphuric Acid/Water)
1.40 1.18 Ni-Cad (Cadmium/Water/Nickel Hydroxide)
4.30 3.60 Lithium Ion
3.40 3.00 Lithium Metal (Lithium/Manganese Dioxide)
1.25 Nickel-Metal Hydride
and just for fun:
1.23 1.23 Platinum-Hydrogen-Oxygen fuel cell (as used on the Space Shuttle)
For each battery type I'm showing the "maximum" voltage that you get if it's
brand new, fully charged and has no load, and a "nominal" voltage that you get
after an hour or two at a standard discharge rate (which depends on the size of
the cell and the chemical type).
In lugnet.robotics, Robert Munafo writes:
> Has anyone considered the idea of using a seperate 9V battery pack to
> power the RCX? You'd have to rig up a custom cable with a lego connector
> on one end and an "AC adapter" connector on the other end, and you'd
> have to leave the battery pack's switch turned on all the time to avoid
> losing the programs in the RCX memory. But, it would make design more
> flexible because you'd then be able to locate the batteries anywhere
> that's convenient.
- Robert Munafo
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Message has 1 Reply:
 | | RE: Don't use Lithium Ion (was Re: RCX battery cover)
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| (...) It would be good to figure out exactly what the burnout mechanism was. does any other external power source work? I use a 4Ahr 12V rechargable gel-cel as used in many security panels, its no-load voltage is about 13V and I have used it for a (...) (25 years ago, 3-Aug-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: RCX battery cover
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| (...) Yeah, you pretty much have to make sure your design holds the battery cover on, for example by having beams both underneath and on top of the RCX, held together with vertical beams and connector pegs. This can be a bit of a challenge if you (...) (25 years ago, 2-Aug-99, to lugnet.robotics)
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