Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Need someone help from someone that is very knowledgable in electronics....

Discussion in 'The Lounge' started by Emmettology 101, Nov 21, 2002.

  1. Emmettology 101

    Emmettology 101 3/4 ton status

    Joined:
    May 9, 2000
    Posts:
    8,126
    Likes Received:
    0
    Location:
    FL
    I run R/C cars and am trying to come up with a way to make a smal gadget. What I am trying to make is a small device that monitors my battery discharging.

    A little more details:

    I made a light bulb discharger for my batteries. THis is a row of 10 1156 auto bulbs wired parrellel(all pos. together, all negs. together) with a plug on the end. THis will drain an R/C battery pretty well and rather quick.
    The gadget I am trying to make will be hardwired to the bulb discharger and have the connector for the batery on the other end. It needs to "monitor" what voltage the battery is(or is letting out) and cut it off at a certain voltage. It is not good for the battery to go below 5.40v(for a 6 cell pack) so I would like it to cut-off around 5.40-5.80 or so....

    Granted you can buy these at most larger hobby stores, but I am a person that like to make things! /forums/images/graemlins/smile.gif

    Can anyone help me out and guide me in the right direction?

    Thanks!!!!
     
  2. newyorkin

    newyorkin 1 ton status

    Joined:
    May 8, 2001
    Posts:
    16,555
    Likes Received:
    157
    Location:
    Los Estados Unitos
    I'm just barely into electronics (supposed to get some hardcore training soon, though)...

    You can just use a decent sized resistor (the right value of course, which I couldn't tell you), instead of light bulbs. If you have a multimeter, find out the resistance of the lightbulb discharger circuit, and put in a resistor of roughly the same value. I'd think discharging it that quick can damage the battery, though, no? Or shorten it's life?

    Check an electronics store for a volt meter/guage (not a multimeter if you ask the kid at the counter), the kind that you wire into a circuit. You can find digital or needle, (I'd recommend needle for a circuit this small), then wire it in series to the light bulbs/resistor. Be sure the guage is rated for the max output current (amperage) of the battery.

    If you want to get nutty, you can get a couple transistors, some pc board, a switch, a couple LED's, and have it light or turn off LED's at certain voltage marks, then cutoff the circuit when voltage drops to a certain level.
     
  3. Emmettology 101

    Emmettology 101 3/4 ton status

    Joined:
    May 9, 2000
    Posts:
    8,126
    Likes Received:
    0
    Location:
    FL
    They have been using the bulb style discharger for years and I just coopied it from one you can buy from one the the big named companies. One company does use a resitor style discharger also....

    I have a multimeter and have been monitoring it like that, but was looking for somethign that would shut it down at the right time so I didn't have to keep my eye on it. The lightboard would be a neat idea and would be nice if they went on at certain votlages and then cut off. Kind of a show quality type of thing. /forums/images/graemlins/smile.gif
     
  4. landsmasher

    landsmasher 1/2 ton status

    Joined:
    Mar 13, 2002
    Posts:
    4,423
    Likes Received:
    0
    Location:
    California, The Blow Me State
    What you want is a simple Voltage Regulator. Just like the one in a car only transistorized and smaller. If you know a ham radio enthusiast he'll most likely jump at the chance to build one for you. Or you can get a book from PLastic Shack that will have one in there. Then just buy the parts and build it. You will need to do a little math in order to get the cutoff voltage right. It's called Ohm's Law... Simple really...
     
  5. Emmettology 101

    Emmettology 101 3/4 ton status

    Joined:
    May 9, 2000
    Posts:
    8,126
    Likes Received:
    0
    Location:
    FL
    Cool thanks landsmasher... I dont know of any Ham guys, but I am goign to head to da'Shack and see about that book and see if those guys can head me in the right direction on the parts.

    Thanks!!!!!!!
     
  6. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    I think the answer for you would be a heavy duty SCR. This SCR is basically a gated diode. It will let current flow through it as long as there is a biasing current on the gate. Bear with my shitty drawing.

    [​IMG]

    I used these for short circuit protection on power supply's. Get one that can handle the amperage with a gate level of 5.8 volts. The 10K resister is to keep the current from blasting throught the gate part. I believe this should work but its been a few years since I've done any circuit design.
     
  7. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    Oh yeah, the theory.

    What happens is long as there is 5.8 volts or higher on the gate, The diode will flow the current through the main connections (Anode and Cathode). Once that Voltage goes below that level, The Diode will close ( I wont go into N and P region stuff here) and no more current. You could put a voltmeter on it to watch it but it should be a hands off deal.
     
  8. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    Oh yeah #2.

    Picking the current capability will depend on what resistance you use to drain the Battery. In this case you are using a bunch of light bulbs. You could use one big fat resistor to do the same thing. The higher the resistance, The slower it will drain but it will not produce as much heat. You can drain it fast but you might have to mount the whole thing onto a big heat sink. One thing you could do is measure the resistance the light bulbs are giving you for a starting point. Good luck with it.
     
  9. Emmettology 101

    Emmettology 101 3/4 ton status

    Joined:
    May 9, 2000
    Posts:
    8,126
    Likes Received:
    0
    Location:
    FL
    Thanks Sandman. Your diagram confuses me a bit, but I am not familiar with reading circuitry diagrams.

    I will take it to Radio Shack when I pick up the parts...
    So what I would need then is a 10K ohm resitor, and a gated diode rated at 5.80v and the amprage I am running?
    The battery I am running is a 6 cell(sub c I believe), each cell is rated at 1500mAh...
    The discharger I use has a discharge rate of 21 amps(10 1156 bulbs at 2.1amp each.)
     
  10. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    Good luck with Radio Dump. You'll have better luck at an Electronics supply store.

    The voltage that the battery puts out should be printed on it. Measure the resistance off all the light bulbs hooked together. divide the battery voltage by the resistance. Now you have the current flow. Multilpy that by 25% and now you have a current spec on the SCR.

    Example: My battery puts out 12 Volts. The total resistence of all my light bulbs is 250 ohms.

    12/250 = .048 Amps

    .048 x 1.25 = .06 amps or 60 Miliamps. (this is done so you can abuse it some and the SCR wont blow)

    Now you know what current it needs to be capable of.

    Let me know if you need any more help.
     
  11. newyorkin

    newyorkin 1 ton status

    Joined:
    May 8, 2001
    Posts:
    16,555
    Likes Received:
    157
    Location:
    Los Estados Unitos
    Hey sandman, I've been trying to do something similar for my power rear window on the K5. I have a remote start unit with a trunk output (2 or 3 second closure, I think).
    I wanted to set up a circuit where the closure from the trunk option would flip a constant switch on (to power the circuit) and throw a pole on a relay simulataneously. The relay part of the circuit would reverse the polarity of the circuit's output, which would lower or raise the window. I wanted to set it up so when the current spiked (when the window reached full open or full closed and the motor load increased), the switch would return to closed.

    I think I may have some questions for you if I pick that project up again soon...

    Hey, if you guys can, pick up a copy of Microsoft Visio to draw and plan these things. I've never used any kind of cad or drawing software before, but this is really cool. I picked it up a couple weeks ago when I was supposed to be taking a different job where I would need to map out some networks... The picture below is the K5 electric fan upgrade I'm doing. The cool thing about Visio is that I've revised this circuit about 20 times already, when normally I probably would've roughly sketched it if I didn't have a mental picture, then built it and later been all annoyed at myself as I rebuilt it...

    [​IMG]


    Click here if the image doesn't show up:
    http://ice.prohosting.com/ratchy/images/truck/truckfan.html

    I was sending that my old boss to get his opinion on, that's why the resistor question's prominently displayed...
     
  12. BowtieBlazer

    BowtieBlazer 1/2 ton status

    Joined:
    Jul 15, 2001
    Posts:
    2,462
    Likes Received:
    0
    Location:
    Baton Rouge, Louisiana
    What kind of RC are you running have an old Losi XXT I have been looking to give a new home for quite some time...Lots of parts and tires and nice controller...let me know if you know anyone who may be interested...I'll send you full specs...
     
  13. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    I forgot all about Visio. I use it to keep our WAN and DNS structure map up to date. I forgot it also did electronics.

    Yeah, you can use the SCR to do what you want. You'll want to run it in parallel with the window motor and the gate line to the positive side or something. I've got the schematic around here somewhere.....
     
  14. Emmettology 101

    Emmettology 101 3/4 ton status

    Joined:
    May 9, 2000
    Posts:
    8,126
    Likes Received:
    0
    Location:
    FL
    Sandman, I was talking with another guuy who is working on the same project and he is using MOSFET transistors... Would those work in an HD SCR or is he got a totally different design going?
     
  15. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    You could do that as well. I believe those are used in whats call a "push-pull" amplifier. The circuitry to get them to work at your desired voltage will be more complicated however. Basically I think he would be using those MOSFET's like a solid state relay. You can turn your current on or off with a small voltage input. The trick is getting it to turn on and off when you want it to. You could build a circuit to do this using a Zener diode with a breakdown voltage of 5.8 volts and it would work. Using the SCR helps to creat a simpler circuit. If you do want to go the other way, I'll figure out the schematic for you.
     
  16. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    Ok, here is a way to do it with a relay (could be solid state if you want) and a Zener.

    [​IMG]

    A Zener diode is a regular diode that you can push voltage (current) backwards through. It has a "breakdown" point where it gives up and lets the current flow. In this schematic, as long as the voltage is above 5.8 volts, (you can get Zeners with all manner of reverse breakdown voltages, we'll assume yours is 5.8) The relay is on because the Zener isnt tuff enough to stop it. Once the battery power drops below 5.8 however, it can stop that, and it does and the relay opens up and stops discharging the battery. This might make more sense to build. The SCR basically combines the relay and the Zener Diode. A MOSFET can act very much like a solid state relay. MOSFET's are desighned to operate much faster as they are used in amplifiers. So the solid state relays might be much cheaper. Is it clear as mud yet? /forums/images/graemlins/grin.gif
     
  17. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    Interesting. It could be easily done with a flip flop on a chip running relays but it would loose its place when the power was shut off. Let me think about it some...
     
  18. Emmettology 101

    Emmettology 101 3/4 ton status

    Joined:
    May 9, 2000
    Posts:
    8,126
    Likes Received:
    0
    Location:
    FL
    We have a large electrical supplier here in town. Not sure if they deal with smaller stuff such as this, but we'll see. If not I'll stop at Radio Shack and see if they can help.

    Thank you very much Sandman!!!!
     
  19. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    Ok, You could do it with a momentary push button hooked up to a flip flop then to two latch circuits and that running a solid state relay with an over-current protection circuit guarding it. The theory would go like this. A momentary pulse of current from a switch on the dash would hit the single input on the flip flop. The flip flop puts power out one leg and then the next pulse, or the next time you hit the switch, It puts the power out on the other leg. It would only be momentary so that output would have to run into a latch circuit. a latch circuit takes a pulse and turns it into a solid output. You would have two latch circuits next to each other in parallel. Each latch circuit would run a solid state relay(or manual relay if you wanted) that would control the direction of the motor. Off of the motor current would be the input wire into the SCR. Or you could use another relay and a Zener diode like in the discharging circuit posted here. The SCR would supply the power to the Latch circuits So when the motor stopped turning under power, The voltage would drop (current rises) and the SCR would cut the power to the Latch stopping the whole process. Hitting the button again would run the parallel circuit and move the window the other way. Does this make sense?
     
  20. Sandman

    Sandman 3/4 ton status Author

    Joined:
    Apr 15, 2002
    Posts:
    5,653
    Likes Received:
    0
    Location:
    Pocatello, ID
    Glad to help. I have a degree in Electronics but there is no money in it. I make almost double being a Network Tech. I'm not kidding either. I used to ba a broadcast engineer at a radio station and I doubled my money into this job. I miss doing it though.
     

Share This Page