A (probably) simple RC circuit question

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Discussion Overview

The discussion revolves around designing a circuit to operate 12V solenoids with a specific on/off cycle that includes a gradual ramp-up to full voltage. Participants explore the use of an RC circuit and related components to achieve this functionality, addressing both theoretical and practical aspects of the design.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant describes the need for a circuit that operates solenoids with a periodic cycle and gradual voltage ramp-up, expressing uncertainty about how to implement this with the specified voltage and amperage.
  • Another participant suggests using a 555 timer and two BJTs to create the desired functionality, mentioning the use of a drain resistor and capacitor to control the ramp time.
  • A question is raised regarding the term ".5 seated amps," seeking clarification on its meaning.
  • A participant expresses a lack of familiarity with the components mentioned (555 timer, BJTs) and requests further breakdown or resources for understanding how to estimate values for resistors and capacitors.
  • One participant shares that they have built a circuit that should be adjustable for frequency and ramp time, describing it as an astable circuit based on a datasheet, though they have not tested it.
  • A later reply expresses gratitude for the assistance received and indicates a willingness to explore the proposed solutions further.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach, as there are varying levels of understanding and experience with the components involved. Multiple suggestions and clarifications are offered, but no definitive solution is established.

Contextual Notes

Some participants express uncertainty about specific terms and components, indicating a need for foundational knowledge in electronics. The discussion includes assumptions about the participants' familiarity with circuit design and terminology.

Who May Find This Useful

Individuals interested in basic electronics, circuit design, or those looking to operate solenoids in a controlled manner may find this discussion relevant.

oldguy
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Its been 30 years since my last Physics course so while I have the basic concepts I'm uncertain how to solve my current problem: I need to operate a pair of 12V solenoids (.5 seated amps, 4 watts each) with a periodic on/off cycle that gently ramps to full voltage (over about .5 to 1 sec) and then shuts off, repeating every 5-10 seconds (I'd love to be able to adjust this once my device is built and tested). It sounds like an RC circuit to me in theory but I'm lost as to how to proceed in reality at these voltage/amperage levels. I've looked into programmable controllers but this seems like over-kill for what strikes me as an essentially simple operation.

I'd love any help or thoughts on where to go to educte myself on this topic.

Thanks.
 
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one 555 and a two bjts will do what you want, use one after the 555 (5-10 second adjustable pulse) with a drain resistor and cap that determines the rc time ramp of the base of the second bjt.
 
Last edited:
what is ".5 seated amps"
 
light_bulb: Thanks so much for the prompt response--it sounds like its very do-able but I'm strictly an amateur as far as real-world applications--would you mind taking a minute and breaking it down for me (or point me at a resource for understanding your response). don't know 555 or bjts and how do I figure out where to start to estimate values for resistor and capcitor. (sorry). thanks again.

and to moe_3_moe: seated amps refers to the steady state draw when the solenoid is fully activated and in the held state--
 
i made the circuit, should be adjustable from 3-15hz, and the ramp time also. didn't test it but i figure it's good for illustration. it is an astable circuit off the data sheet with a series resistor-cap off the discharge leg that is adjustable to turn the square wave into a slight saw. once again didn't test.
 

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wow. thanks very much-that's phenomenally helpful. I'll dig in and see if I can put this together. I really appreciate your time.
 

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