Quote:
Originally Posted by de_
I checked with tech support at Sparkfun.com since they sell a lot of this stuff.
The 100v volts will only provide a mildly discomforting shock due to the very very small current available. Not remotely life threatening.
The rule says 24v relative to the robot common buss. It is possible to design inverters whose outputs are totally isolated from the inputs (think isolation transformers). So if you use a voltage meter between the common buss and any output HV wire on the inverter, it reads 0 volts. Lab power supplies should be an example where the outputs are completely isolated from any of the input power lines. Else its not usable in a situation that needs differential power.
Unfortunately according to Sparkfun, its 12v inverter input common wire input is connected to one of the output wires so if you measure the robot common to the other HV line you should see 100v AC.
Oh well. Back to robots
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If you really wanted to, you can cut that wire, but you should be careful to keep things on either side of that isolation transformer completely isolated, but it would likely be ruled illegal still, due to violating the "magic safety rule".
You use isolation things like this all the time when measuring with an oscilloscope. Typically, the ground clip on a scope is grounded to earth ground. When you'd like to measure the voltage between two different signals, you'd short the one with the ground clip to earth ground. This can be a serious issue if the thing you're measuring is referenced to earth ground (as most wall-powered electronics are). If you put an isolation transformer on the equipment's power supply, the equipment is no longer grounded. Then, wherever you clipped the ground clip, you'd reference that point to ground.
100 volts is not some magic number to be feared. A balloon rubbed on your head (or a robot driving on carpet) will have 10's of times the voltage to ground, but is not dangerous because the amount of charge on the balloon is too small to produce any significant current.
This is one of those judgement call rulings. Obviously, the high voltage from a balloon rubbed on a head is safe, but the high voltage transformer for your CRT display isn't. Al, who is the lead robot inspector, has said that it is illegal, not be because it is over 24 volts to the negative terminal of the battery, but because it's just unsafe.