Re: 12volt or 18volt that is the questiion..
| Subject: | Re: 12volt or 18volt that is the questiion.. |
| From: | Fred Jutsum |
| Date: | Fri Apr 26 18:00:08 1996 |
was apparently designed for 12 volt operation because the dissipated power is approximatly
half the max rating of the part. When you increase the supply to 18 you then cause the
regulator to dissipate near the max its rated for. I happen to work as an engineering tech
for a company that manufactures silicon integrated circuit components. I asked the design
engineers what they thought about the situation and what the effects of running a part near
its max rating for extended periods. They explained that a circuit should be designed so no
part dissipates more than half the max rating for any length of time. Extended periods of
anywhere near max rating will cause the part to deteriorate and fail prematurely. In this
circuit the failure may be either an open or a short in the regulator. Open circuit will not
cause much other problem except the motor may run continuously which could be a problem. A
short on the other hand will be a big problem because it will place the full 18V supply on a
lot of parts that were intended for 5V. The motor sense leds and optical sensors will be
history and damage may even result to the mother board. I asked the engineers for advice and
here it is.
Install a different regulator like a 7805C that is rated for a lot more power and the
troubles will be over. They dont exactly fit in there though. The other possibility is to
sink away the excess heat. They said a heat sink is better than nothing but the part is
still being pushed too hard and will still have a shorter life than normal. I have made some
heat sinks out of .005" brass to push over the regulators and used the white heatsink
compound to help transfer heat. This is only til I figure what to do for a permanent
solution. I hope this helps you all to understand the problem and that you must do something
or the motor circuits will eventually fail at 18 volts. It not only is the dec motor thats
involved because the RA motor has the very same regulator on its circuit board.
Good luck, Fred Jutsum fjutsum@micron.net Boise, Idaho
