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Power Supply Problems - What is ideal, what is dangerous? — Parallax Forums

Power Supply Problems - What is ideal, what is dangerous?

nrk752nrk752 Posts: 8
edited 2006-05-24 12:50 in General Discussion
I need some advice regarding power supplies for Javelins using either the Javelin Stamp Demo Board or the Board of Education.· I forgot to buy power supplies with my Javelin starter kits, so I first used 9V batteries, and then some power supplies I had laying around.· I used a·9V 200mA power supply which worked fine.· I used a 12V 300mA power supply which works fine but I noticed that the voltage regulator gets hot and the Javelin itself seems warmer than with the 9V 200mA power supply.· Then I also used a 12V 1A power supply.· This third supply burned one of my Javelins.· There was a smell, a little puff of smoke, and it was dead.· This was on a Javelin demo board.· The board seems to be fine but the module won't load programs and while its connected the LED on the board glows more dimly than usual.· Now I have noticed that it says in the manual to use the 7.5V 1A power supply.· But on the table of acceptable power supplies it says the Javelin module on the Javelin demo board is capable of using the 7.5V 1A, the 9V 300mA, and the 12V 1A.· I wasn't using the same 12V 1A power supply that parallax supplies, but it still doesn't seem like my module should have burned.· Now I am afraid of using any different power supplies·in case·I burn another $90 module.·· So my questions are:

Does it matter if the power supply is regulated or unregulated?· Are most generic wall bricks regulated or not?·

I have some 9V 650mA unregulated power supplies.· Are they going to·damage my Javelins?·

Is 7.5V safer for the boards than higher voltage, or is it a question of too much total wattage, or is it·just the supply being unregulated that caused damage?

Comments

  • Peter VerkaikPeter Verkaik Posts: 3,956
    edited 2006-05-22 13:42
    The javelin itself has a switch mode regulator that is capable to work with
    power input voltages up to 30V (at pin24). In my applications I always
    use a stabelized 24V 3A supply and never had any power problems.

    The regulator on the javelin demoboard (and other boards) are
    fixed voltage regulators, so supplying higer power input voltage
    leads to more power dissipation in those regulators.
    When using these boards and using the generated 5V, it is
    best to use a 7.5-9V power supply to not overheat the board regulators.

    Are you sure you didn't put in the javelin the wrong way?

    regards peter
  • nrk752nrk752 Posts: 8
    edited 2006-05-22 18:14
    Well, I suppose its possible I inserted it backwards, but there's no way to know now since I removed it. I think more likely is that there was something weird about that power supply, or maybe a flaw in that particular Javelin. Regardless I will try my other 9V power supplies and hope everything works out. Thanks.
  • nrk752nrk752 Posts: 8
    edited 2006-05-24 12:43
    I just figured out why my Javelin burned out. I took a closer look at the power supply. It outputs AC. OOPS!
  • Peter VerkaikPeter Verkaik Posts: 3,956
    edited 2006-05-24 12:50
    I always put·a 1N4001 diode between the power terminal and javelin pin 24.
    It is a cheap failsafe against wrongly connected power (and AC power).

    regards peter
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