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automotive automatic relay — Parallax Forums

automotive automatic relay

TCTC Posts: 1,019
edited 2006-03-22 07:03 in BASIC Stamp
I am installing a 2nd battery into my car. I would like to make a BS1 to monitor the tachometer from the motor, when the tach hits a set speed (around 600 RPM), there would be a delay (around 30sec to 1min) to let the charging system stabelize, then turn on a 200 amp relay to connect the 2nd battery.

my question is could someone please point me in the right deraction.

thanks TC

P.S. sorry for the bad spelling.

Comments

  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-03-18 08:19
    Well a 200amp relay is huge. I am sure that the coil and mechanics of it are very substantial as it has to 'kick in' without a lot of sparking and bouncing.

    Essentially, the BS1 will put out tens of millamps of 5 volt power at tops. So you have to move that signal up to enough amps and automotive voltage [noparse][[/noparse]about 12 volts, right?].

    You have two options: solid state and electro-mechanical.

    The advantages of using another relay [noparse][[/noparse]the electro-mechanical] are that you can completely isolate the 5 volt side from the 12 volt side with a 5 volt relay AND you can use a Double Pole switch to completely, and redundantly, turn it off. The disadvantages are a bit of noise and it is slower.

    The advantages of using solid state are really unclear to me as they never completely turn off, the SSRs are often larger than the mechanical relays, they generate heat, and you can only shut down one side with one relay. Still, it is an option that many people prefer as being more 'high tech'.

    What is clear is that you have to protect your solid-state circuits [noparse][[/noparse]including the BS1] from 'fly back' voltage from the relay coil. This is done with a diode. And, it is better to nearly completely isolate the BS1 from the 12volt automotive circuit.

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    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 3/18/2006 8:22:07 AM GMT
  • ChrisPChrisP Posts: 136
    edited 2006-03-18 10:35
    Use an opto isolator on one input of your stamp to count ignition pulses over a set period using the Count command. This will give you a rough idea of RPM, sounds like it would be plenty close enough for your purposes.

    Then use another pin of your stamp as an output·to drive·a fet/transistor/relay/ssr (your choice) to actuate your larger relay.

    Roughly it would be,
    Count ignition pulses over time period
    If Pulses are greater than whatever = 600rpm
    Start·pause for 30 seconds
    verify ignition pulse count
    Turn on relay
    If Not
    Turn off relay

    Then you have an automatic relay to only tie your stereo battery to the engine battery when the car is running. Just taking a shot in the dark at what your doing.

    Chris
    ·
  • TCTC Posts: 1,019
    edited 2006-03-19 00:59
    Starting with Kramer.· The 200 amp relay I have chosen is SR200 from stinger car audio (http://www.stingerelectronics.com/web/prods/fans.asp) I was going to use ULN2003 driver to control the ground while the positive would be hooked to ignition switched. So if I ever shut the car off the relay could not stay on.
    ·
    Now for Chris. Would you know where I can info on using an opto isolator? The only thing I know about opto’s is that there is a LED for the input then there is a phototransistor for the output. But I don’t know how to work with the output. I think the picture gave away my true identity, but you are right. I do not want to put too much of a load on my alternator just after startup. I was also thinking of adding an A/D converter to monitor the main battery, and if the voltage is not up to 13.5 volts then the BS1 would wait longer until it is, then it would start the count down.
  • bushibushi Posts: 12
    edited 2006-03-19 05:00
    Here's a diagram that'll get you started. The opt drives a larger transistor that drives the relay coil. You'll have to do a little leg work on the larger transistor to find one that works with the sr200. I tried to hunt down some specs on the sr200 but couldn't find anything definitive. The diagram shows the circuit connected to a PC parallel port but should also work with a Stamp. Please note the diode across the relay coil. Very important to have that or the discharging coil will fry the circuit when the coil is de-energized.

    Good Luck!




    www.electronicsforu.com/efylinux/circuit/nov99/panel.gif
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-03-19 06:08
    Stringer's web site doesn't have a search function, so I cannot locate the SR200.
    So I have no idea of its power requirements for the input.

    It could easily exceed the abilities of the ULN2003 and cause it to self-destruct. Probably won't hurt the Stamp though.

    It would be best to measure the coil's resistance and do some math. One properly sized FET with diode protection is all you really need on the output.

    For the RPM input , the ignition spark data will usually give you the RPM x the number of engine cyclinders.
    So to get an actual figure, you merely reverse the the formula.

    Of course, if you have a fancy two spark plug per cylinder arangement or Deisel, this would not be the case.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • ChrisPChrisP Posts: 136
    edited 2006-03-19 15:50
    TC, The bike NOS/Shifter setup I'm working on uses opto isolated inputs over in projects. http://forums.parallax.com/showthread.php?p=559030

    About 2/3's of the way down, the second set of schematics. There its using switches tied to the opto's but it could just as easily be a coil negative.

    Its exactly like you said, an LED input with the appropriate current limiting resistor, and then the phototransistor output to your micro controler so now your input pin from your stamp/micro is no longer directly electricaly connected to the voltage, and switched to current instead of voltage based to reduce noise.
  • TCTC Posts: 1,019
    edited 2006-03-21 00:16
    Bushi:·· thank you for the diagram; I think I have it figured out to modify it for my tach input. I too could not find any info on the sr200 so what I thought I would do is use a standard automotive relay (it’s coil current is well under 500mA) for the ULN2003 and it has the clamp diode built in. then from the automotive relay to the sr200.

    ·
    Kramer:·· to view the relay, go to the link from above and scroll down about 2/3 the way down. And you can see the relay. ·As I told Bushi I am going to use an automotive relay to control the sr200. Thank you for the formula. I think I might have an idea. Using PULSIN measure the time it takes to go from ON-OFF-ON with the car running, Then put that into memory, and if the time is ever less then I would know if the motor is to speed, if not wait. (Shorter pulse = more tach, longer pulse = less tach). It sucks I was going to use the fuel injector but the ECM (Engine Control Module) knows if there is anything on the injector line. So I have to get a module to take the data bus (CAN Bus) and provide a tach signal.

    ·
    ChrisP:·· Your project is very interesting. I was going to do something like that a few years back for my ’69 Charger R/T. I was going to make a NOS controller for it. But I found out that after I spent the time and money I would have NOS’s controller, so I just bought it.
  • stamptrolstamptrol Posts: 1,731
    edited 2006-03-21 23:54
    TC,

    Going back to your original problem, the marine industry has many devices to allow two batteries to co-exist. They can allow simultaneous charging, individual or parallel discharge. Either automatic or manual operation.
    Look at any marine products distributer for "Battery Isolators".

    Cheers
  • TCTC Posts: 1,019
    edited 2006-03-22 01:36
    Stamptrol I tried to use a Diode Battery Isolator but my alternator would not charge the batteries. On a lot of new car alternators if there is no battery load it will not charge.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-03-22 07:03
    That 'formula' was from a 1962 high school electronics project.

    If you are not into 'very beautiful' cable, you can buy your battery cables by the yard at an welding supply.· They sell large diameter red and black for arc welding.· They also sell the end fittings which need to be 'sweat soldered' with a butane torch.· Very flexible, very durible.

    Stamptol is right about the 'marine industry' as many boats use second batteries for saftey lighting when moored at night and a dozen other things. They would be much more helpful with variations from the standard automotive set-up.

    Many marine engines are just modified automotive engine blocks, both desiel and gasoline. The supporting electrical systems transfer quite easily. You can also get bigger alternators to charge a huge bank of batteries.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 3/22/2006 7:06:26 AM GMT
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