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Voltage amps power and current - I think I might not know what it is I don't know — Parallax Forums

Voltage amps power and current - I think I might not know what it is I don't know

MarkCrCoMarkCrCo Posts: 89
edited 2015-03-20 09:42 in BASIC Stamp
OK I think I'm starting to understand Voltage and current a little but I still have this uneasy feeling that it is as clear as mud to me. I switched one of my robots from the BOE to a homework board so he is less expensive. I use this one at work where other people can bump into him and I take him back and forth where I have dropped him once. The problem I have is that the homework board with this surface mount chip only operates on a nine volt battery that last all of about fifteen minutes before he resets. I solved this reset problem on the BOE by going to rechargeables but 9v rechargeables are hard to find and expensive. Will he run without killing him if I run him on 7 rechargeable AAs. This would give him 8.4V and a lot more miliamp hours. Will it fry him though? Or is the 0.6V decline going to just not work?

Comments

  • SapphireSapphire Posts: 496
    edited 2015-03-19 18:48
    It will work just fine. Even six rechargeable AA at 7.2v will probably be okay.
  • Hal AlbachHal Albach Posts: 747
    edited 2015-03-19 19:02
    The Homework board uses a LM2940-CS-5 LDO regulator rated for up to 1 amp output. Input can be anywhere from 6 Volts to 26 Volts. If you use a higher than necessary input voltage the regulator will have to dissipate a lot of heat. To answer your question, 7 rechargeable AA batteries providing 8.4 Volts will not harm your Homework board. But it does add considerable weight. You may want to consider LIPO batteries and a balance charger if you are going to be building more bots. Check out the battery & charger offerings at Hobby King. A 7.2 Volt, 2 or 3 AH battery will give you much longer run time and they recharge much quicker. A 7.2 V LIPO when fully charged will put out 8.4 Volts.
  • MarkCrCoMarkCrCo Posts: 89
    edited 2015-03-20 06:33
    Ok as soon as I hooked him up to the 7.2V his PIR sensor started melting. No damage done he still works with the 9V. He stinks literally with 7.2 Volts. The PIR is 12 mA @ 3V, 23 mA @ 5V. Do I need a resistor in the circuit now that wasn't needed before?
  • PublisonPublison Posts: 12,366
    edited 2015-03-20 08:10
    MarkCrCo wrote: »
    Ok as soon as I hooked him up to the 7.2V his PIR sensor started melting. No damage done he still works with the 9V. He stinks literally with 7.2 Volts. The PIR is 12 mA @ 3V, 23 mA @ 5V. Do I need a resistor in the circuit now that wasn't needed before?

    Are you running the PIR off of VDD (5 volts), or VIN (whatever the input voltage is)? The version A of the PIR will work up to 5.0 volts, and the version B will go up to 6.0 volts.

    The PIR would not like 7.2 or 9 volts if you run it from VIN.
  • MarkCrCoMarkCrCo Posts: 89
    edited 2015-03-20 09:10
    Publison wrote: »
    Are you running the PIR off of VDD (5 volts), or VIN (whatever the input voltage is)? The version A of the PIR will work up to 5.0 volts, and the version B will go up to 6.0 volts.

    The PIR would not like 7.2 or 9 volts if you run it from VIN.

    Vdd and it is version B with the jumper set for 15 feet.
  • MarkCrCoMarkCrCo Posts: 89
    edited 2015-03-20 09:42
    I have no idea what is happening now. I unhooked the PIR and tested the voltage at the wires with the 9V and got a perfect 5V. Hooked up the 7.2V got the same thing. Plugged the PIR back in and he works fine with the 7.2V supply. Total mystery why he started stinking and melting the first time.
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