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Recent content by larryg

  1. larryg

    choosing fusible resistors

    Moira: Let me see if I can clear up the confusion - I am designing an off-line flbyack supply that must run off of 3 phase power. This supply will be inside a commerical watt-hour utility meter. Therefore, the 3 phase will come directly off of the pole (xfmr). I have seen similar designs...
  2. larryg

    choosing fusible resistors

    To help clear things up...here's a bit of background. This circuitry will be in a 3 phase watt-hour utility meter. Not a lot of power will be consumed during the normal operation of metering. However, during the daily transmission of kWh data back to the server, small bursts of power will...
  3. larryg

    choosing fusible resistors

    Hi all, I was wondering if anyone out there has any experience specifying fusible resistors for use as circuit protection in a 3 phase watt hour meter. I've looked around on the web a good bit and have not found any definitive information for how to properly use these things. Here are my...
  4. larryg

    preventing accidental charging of alkalines

    Hi all, I'm in the process of designing a battery powered device to be used in the car. The plan calls for rechargeable batteries with 12V from the car to provide charging. However, I would also like the option of using alkaline batteries. The problem arises if a customer has inserted...
  5. larryg

    preventing accidental charging of alkaline batteries

    Sdmays, Thanks for the feedback. I could see that working with fresh batteries. However, I think the larger problem will be as as such: The customer will insert alkaline batteries in the unit and use it until they deplete. At which point, they will plug in the charger, forgetting that they...
  6. larryg

    preventing accidental charging of alkaline batteries

    Hi all, I'm in the process of designing a battery powered device to be used in the car. The plan calls for rechargeable batteries with 12V from the car to provide charging. However, I would also like the option of using alkaline batteries. The problem arises if a customer has inserted...
  7. larryg

    super cap charging dilemma

    Hi All, Thanks for all the informative posts. I forgot to mention one important part of the design. In addition to providing pulse power, I need to hold up the 3.6V rail for 30-40 seconds in the event of a power failure. I apologize for not providing this information earlier. So, it seems...
  8. larryg

    super cap charging dilemma

    Hi all, Thanks for the posts. BrianG brought up a good point I had overlooked. The radio transmission sequence is on a 25% DC (1.154 ms/4.616 ms) and is repetitive. The voltage drop calculation for the burst of 2A comes out at around .8V, which is too low for the radio to handle. So...To...
  9. larryg

    super cap charging dilemma

    I'm looking for a clever and simple way to current limit charge some super caps and also allow them to be available to provide pulse power. Let me explain further: I'm providing 3.6V from a regulated output to a GSM/GPRS modem. During transmission, I need to suppply up to 2A peak for about...
  10. larryg

    Soft Start Circuit for a capacitor bank

    Hi All, Thanks a lot for all the responses. I finally got my prototype together and found that a hefty thermistor does wonders for snubbing out my inrush. And it makes the circuit quite simple. I also added an inline diode to prevent the capacitor bank from discharging thru the PSU when...
  11. larryg

    Soft Start Circuit for a capacitor bank

    Lewish, Thanks for the suggestion. I actually use some of Ametherm's thermistors in another application. I don't know why I didn't think about using one for this application. It would be a lot simpler than incorporating a resistor, relay, and control circuitry. Thanks to electricuwe for...
  12. larryg

    Soft Start Circuit for a capacitor bank

    Allow me to fill in some more details. Basically, this cap bank is being used as a PSU hold-up on power loss. I will need 3.5A for 0.5s from 28V to 18V (which is the min. voltage). This equates to around 0.2F in capacitance. This bank will be connected between the existing off-the-shelf PSU...
  13. larryg

    Soft Start Circuit for a capacitor bank

    I need to design a very simple soft start circuit for a super capacitor bank (12 4.7F caps in series). The bank will be charged to 24-28VDC. I'm thinking of using a power resistor, a relay (to shunt out the resistor when the caps are charged) and some simple control circuit. My first...
  14. larryg

    4-20mA Current Transmitter

    Morizabal, If I recall correctly, a two wire transmitter requires excitation voltage from the device it is connected to. A three-wire transmitter allows you to use an external supply (typically 15-30VDC). Some PLC's provide power for your transmitters and some don't. As for preference, if...
  15. larryg

    Need guidance re: E-stop implementation for motor drive circuit

    jw62, Thanks for the reply. Unfortunately, that project has been put on hold for awhile. However, it may rear its ugly head later this year. Your reply gave me alittle bit more to consider. Thanks. LarryG
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