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  1. BobK

    battery chargers - AGM and lithium

    Link to the data sheet? Bob
  2. BobK

    Help calculating battery charging rate off Solar

    Yes, the solar charger seems to put out 5V for USB connector charging and the battery bank accepts this voltage so you have everything you need to charge the batteries. I would expect 3H to be the typical charge time. Bob
  3. BobK

    Car Battery Powered House Ideas, Questions

    If you have a generator, why waste power by charging batteries instead of running directly off the generator? Humoring your fantasy for now, the best place to put your effort would be in getting the most efficient devices possible. And don't forget the ventilation fans! Bob
  4. BobK

    So, how many "watts" is a 9-volt battery?

    The current that a battery can supply to a short circuit is not well controlled and drops rapidly with use. In other words, you might initially get 2 or 3 amps from a 9V battery, but only for a few minutes. The capacity rating of a battery tells you how long you can pull a given current from...
  5. BobK

    Come & get yer watts!!!

    First of all, are you talking about a voltage amplifier with a collector resistor, or an output stage, which is typically push-pull and the speaker is the load, usually connected to the emitters? They operate quite differently. The output stage typically has no voltage gain. Bob
  6. BobK

    DC MOTOR QUESTION

    I hate to ask this, but are the motors and gearing identical. Also, you might try swapping the two motors and see if the problem moves with the motor or stays with the axle. Bob
  7. BobK

    Op Amp not working properly LM324

    No, the output will be 0-5V. The offset is added as part of the amplifier circuit. Here is a complete practical circuit: The 5V supply should be the same one used to power the Arduino. The 5.1V Zener clamps the output voltage at a safe level for your Arduino input and is necessary to...
  8. BobK

    Heat pad project

    The power you will need depends on what you are heating, the material and the geometry, as well as the environment. Once you have determined the power, you can determine the resistance of the heating element from the equation P = V^2 * R or. R = V^2 / P One you know R you can determine a...
  9. BobK

    Heat pad project

    It would be silly to use a boost converter to power a heating element. The heating element should instead be designed for the available voltage. Bob
  10. BobK

    Invert PWM signal

    If the signal is generated by software, simply reverse the instructions that turn it on vs the ones that turn it off. Bob
  11. BobK

    Invert PWM signal

    Use an inverter, that is, a NOT gate. Bob
  12. BobK

    trying to understand amp limits? (10 vs 15 vs 16A)

    Okay. Alll you need to do is use a plug converter, not a transformer. Or just clip off the plug and put a standard 120V plug on it if you do not intend to use it on 240V again. Any amp rating will do, your device will only draw about 1A or less at 120V. Bob
  13. BobK

    Identifying a resistor

    I ran it through a calculator here: http://www.hobby-hour.com/electronics/resistorcalculator.php And it says 0.51Ω 10% That is consistent with the 0.7Ω reading you are getting. The ones that are infinity have failed open. Bob
  14. BobK

    trying to understand amp limits? (10 vs 15 vs 16A)

    Where are you getting this 250V 10A rating? There is no way that is the rating for the power supply to the tablet. If it were using that much power (2500W) it would be hotter than a space heaters, and could not be powered from a standard US outlet (120V 15A max). Can you show us a pic of...
  15. BobK

    Which transistor to choose for my regulators !!!

    I don't understand why you remain fixated on using this inappropriate 24V supply, when you can get inexpensive more efficient regulators for the voltages you need. Bob
  16. BobK

    idle: driving steppers closed-loop?

    There is no need for feedback with stepper motors. The number of steps you execute determines it's position. As long as you allow sufficient time for it to respond to each step, it will stay in synchronization. In most applications, you will need a limit switch at one end of the range of...
  17. BobK

    Turning an LED Off when voltage is applied

    Would you answer my question? Are you putting a valid logic level (0 or 12V) on each input at all times. If you are not it will not work correctly. A circuit that supplies 12V to the input sometimes and an open circuit at other times will not work. The off state must be 0V, which is not the...
  18. BobK

    Anyone know a simple circuit to make a signal generator using a crystal oscillator? (if possible)

    If they are indeed crystal oscillators and not crystals, they will output a square wave. How many pins do these have? If 4 they are oscillators, if 2 they are crystals. If they are actually crystals, look for crystal oscillator circuits which will give you sine wave at the crystal frequency...
  19. BobK

    why we use ports ?

    Why do we use ports to transport goods from China to the US? Shanghai - output port, San Francisco - input port. Of course both are actually bidirectional ports. Bob
  20. BobK

    Turning an LED Off when voltage is applied

    Did you leave the other inputs unconnected? They must all be connected to a valid logic voltage. Bob
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