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Could pulsing DC prevent system overvoltage? — Parallax Forums

Could pulsing DC prevent system overvoltage?

P!-RoP!-Ro Posts: 1,189
edited 2010-05-05 04:10 in General Discussion
I am looking to use my .33hp electric motor to start the engine/generate power on my robot, however considering it runs on 12 volts 1750 rpm, connecting it to my engine at the max rpm which close to 5000rpm would generate ~36v. Although I may be able to do some short term charging of the battery at this voltage, it runs the risk of boiling the battery and frying my electronics tied to it. So, although I could use resistors and regulators to lower the voltage I really don't enjoy the idea due to the high energy loss. Instead I was wondering about pulsing the power to the battery, giving it too little time to build up voltage and keeping the system voltage around 14v doing so. Does this sound plausible?

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Got 150 pounds of bot and growing.

Comments

  • kwinnkwinn Posts: 8,697
    edited 2010-05-05 03:14
    Pulsing the 36V to the battery will give a lower average voltage but you will still have very high peak currents which may damage the battery. You need to add an inductor to the circuit which would essentially make it a switching regulator. The size of inductor and switching frequency would have to be determined.
  • Mike GreenMike Green Posts: 23,101
    edited 2010-05-05 03:14
    That's what a switching regulator does. You need what's called a "buck" regulator that can handle maybe 50V (to allow for overvoltage) and has a 14V-15V output. You may be able to combine that with a charging regulator. You can also use a switching regulator to drop the 14V to 5V for the logic. It's much less wasteful of power.

    Start with the Wikipedia article on Switching Regulators (en.wikipedia.org/wiki/Switched-mode_power_supply)
  • BradCBradC Posts: 2,601
    edited 2010-05-05 03:15
    Most motorbikes have the alternator connected to the battery full time and use a shunt regulator to burn off the excess power. Connecting a motor (or generator) and letting the output float can be a bad idea. The open circuit voltage can often exceed the insulation rating in the device and cause breakdown.

    Cars don't suffer from this problem as they can modulate the field strength to adjust the output level.

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    You only ever need two tools in life. If it moves and it shouldn't use Duct Tape. If it does not move and it should use WD40.
  • P!-RoP!-Ro Posts: 1,189
    edited 2010-05-05 04:10
    I'm definitely starting to like the idea, however I don't think I want to use somebody else's board for regulating it when I already will be using two propellers which can do the job just fine. I should be able to just use the schematic Wikipedia shows to make it, and I'm hoping to be able to get a good 30amps or so out of it. Although that will be a challenge in itself I'm wondering, how can I better reduce the emf's from this method of power regulation?

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    Got 150 pounds of bot and growing.
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