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Speed controller, circuit change please help?

Discussion in 'General Electronics Discussion' started by pxr5, Mar 1, 2010.

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  1. pxr5

    pxr5

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    Mar 1, 2010
    Hi, hopfully some one can help, I have a 12v motor speed controller (PWM ), to alter the RPM it uses a trim pot.
    Q, I want to use this on a car engine & use a MAP sensor to change the RPM.
    The MAP uses a 5v alterd signal,three pin.
    Is the any existing wiring diagrams for such a circuit? thanks
     
    Last edited: Mar 2, 2010
  2. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    Q; what does the trim pot on your PWM controller do (i.e. what are the voltages on its pins)?

    But to make your own PWM controller, start with this sawtooth generator. Run it from a 7.5V regulated supply to make its Vpp 5V. Feed the sawtooth to one input of a comparator and the MAP voltage to the other input of the same comparator. Let the output drive a MosFet transistor.
     
  3. pxr5

    pxr5

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    Mar 1, 2010
    Speed controler MAP sensor

    Hi, thanks for the replie, I've found this wiring diagram for the speed controler,I've drawn on a schematic diagram of the MAP sensor, I'm looking to get the speed controler to increase RPM of a electric motor in step with the air pressure sensed.
    I'm more than happy to make a contribution to the forum , ( £ ),
     

    Attached Files:

  4. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Thanks for the diagram. You may be in luck. The TL494 has a 5V reference voltage and so you can just replace the speed pot with the MAP sensor.
    The only question is what to do if the motor speed regulation turns out to be the opposite of what you need, but let's deal with that in due time.
     
  5. pxr5

    pxr5

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    Mar 1, 2010
    Easy as that?, great stuff- I'll get on to it, I'll report back soon.
    thank you much it!.
     
  6. pxr5

    pxr5

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    Mar 1, 2010
    Having replaced the trimpot with the MAP sensor, the load( in this case a 12v bulb) is shining quite bright with no air pressure applied- when air pressure is applied the bulb shines slightly brighter.
    The power rises ( good ), but not from zero to high.
    Any way of calibrating it?
    thanks
     
  7. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Air pressure? Do you have a MAP from a turbo engine? An ordinary engine, & its MAP, works with vacuum.
    If this doesn't solve the mystery then measure the voltages on pins 2, 3, 14, & MAP output.
    Also check the MAP output with its output disconnected from the controller.
     
  8. 55pilot

    55pilot

    434
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    Feb 23, 2010
    It may be helpful if you explain what exactly you are trying to do. I strongly suspect that there is a flaw or a misunderstanding in your project several steps earlier than the motor controller.

    ---55p
     
  9. pxr5

    pxr5

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    Mar 1, 2010
    Ok, I'm looking to using the speed controller as shown to control the speed of a fuel pump, the speed being dictated by ( hopfully ) the boost pressure.
    The MAP is from a turbo engine.
    I'll do the voltage checks later, thanks !
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    All the turbo charged cars I've had in the past (ok, only 2) have had a fuel pump that provides a far greater flow than required with the excess being returned to the fuel tank or shunted around the pump via a pressure relief valve of some sort..

    Why do you need to have a variable speed pump?
     
  11. 55pilot

    55pilot

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    3
    Feb 23, 2010
    That is a start. Lets take a few more steps back up for an even bigger picture. What EXACTLY are you doing and why? Lets have all of it.

    Sounds like you trying to turbocharge a NA (normally aspirated) engine. Even though this is not an engine forum, you really need to provide the big picture for people to really help you. Incomplete questions will get incomplete answers that will leave you chasing your tail.

    As for the MAP sensor, pressure sensors produces a voltage proportional to the pressure plus a constant offset. So at vacuum, the sensor may produce 0.5V and at 30" it may produce 4.5V. If you have a turbocharger that boosts the manifold pressure to 45" your sensor is only going to give you a little over 4.5V because that is all it is able to put out.

    ---55p
     
  12. pxr5

    pxr5

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    Mar 1, 2010
    I'm adding a turbo to F/I engine( I've built several carb' turbo systems ), looking at adding fuel injectors with their own fuel pump & with a rising rate fuel regulator.
    Hopefully this will enable me to add the correct fuel ratio when on 'boost'. ( modulating the fuel pressure will add/ reduce the fuel flow out of the injectors.
    Also, this will be used for a water injection system, I know you can buy systems allready however, several friends also will use this system & it will be a great project to get working well!
     
  13. pxr5

    pxr5

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    Mar 1, 2010
    Thanks for the input, the system will be in addition to whats allready running the engine.So the stock ECU will be doing it's thing & then the added injectors etc, would fatten up the fuel curve when seeing boost
    It would be far easier to use a variable rheostat hooked up to the throttle linkage I suppose!. It would just make for a slicker system!
    Thankfully no emissions problems.I'm doing this so as to save money, which would be a fair amount.
    Performance equipment can get very expensive.
     
  14. pxr5

    pxr5

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    Mar 1, 2010
    Im in the UK, so no problem re; emissions.
    I'm only increasing the fueling high up in the rev range, so it's nothing like creating a total fuel / ignition system. Now that would be real difficult!
    It's job satisfaction ! thats what motivates me.If you add up the man hours I've spent on this & other projects it would not be worth it, however self education & helping other people make it worth while.
    I understand what your saying, thanks for your help.
     
  15. 55pilot

    55pilot

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    Feb 23, 2010
    Don't have time right now for a lengthy response, but here's a quick synopsis.

    Everything you are trying to do is doable, but not the way you are trying to do it. You will have to change the MAP sensor to one that can work at the higher pressure. The final relationship between the MAP output and the pump voltage is not going to be as simple as you are hoping. You will likely have to add a microprocessor that will increase the fuel flow based on the pressure via a non-linear relationship.

    While you do all of this, what is happening with the engine's native ECU? Is it an old enough engine that it does not have an ECU and everything is mechanical?

    What are the regulations for driving this things on public roads? Will you still be able to pass emissions if your state has periodic emissions testing? If your state does not have annual testing, does it have emissions rules that you are violating anyway? You can get away with breaking those rules (if they exist) till you get caught at which time you may be facing some huge fines. If you are providing this to friends, you may have additional problems. You should look into that angle and understand what risks you are taking.

    ---55p
     
  16. 55pilot

    55pilot

    434
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    Feb 23, 2010
    Where are you located? Just because there is no annual inspection does not mean there are not limits. Almost every state in the USA has emission requirements and you are not allowed to violate them if you modify the engine and are driving on a public street. Even though no one checks it, the rules are on the books and if you get investigated for something else (street racing, car accident, ex-girlfriend/ex-wife/ex-mistress accuses you of things...) the penalties can be stiff.
    There is a reason for it. To do it right takes a lot of effort and when you have to spread that over very few sales, things get expensive. If Ford spends $10 million to create and test an engine improvement that will be used on 1 million vehicles, it will cost them $10 per vehicle. If "Joe's Performance Shop" spends $10,000 on developing and testing a mod and he is going to sell only 100 of them, he needs to charge $100 each (in addition to what it costs to manufacture the mode) just to recover his cost.

    As you go through this process, what you will find is that if you are lucky you will break even. If you make a few mistakes, you will end up spending a lot of money and a HUGE amount of time to get only a fraction of the performance you could have gotten from a properly engineered and tested performance mod.

    The bottom line is that there is no free lunch. If you want to do it yourself for your education or enjoyment, have fun and hope you learn a lot. If you are doing this to save money, you are certain to be disappointed.

    ---55p
     
  17. 55pilot

    55pilot

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    Feb 23, 2010
    Are you exempt from the annual MOT test? MOT testing includes emissions testing and if you mod the engine you are likely to fail the MOT test. What is your plan for that?
    Actually, you will have to create the the whole fuel/ignition system. As soon as your boosted manifold pressure goes past the MAP sensor's range, the ECU is not going to be able to measure the air mass and the mixture is going to get too lean, potentially leading to detonation. If you are going to boost the engine, you will have to get into the main ECU and modify it. There is no way around it.

    Even if you do a manual wastegate and keep the boost off most of the time, as soon as the engine gets boosted, you will have to take over everything to control the fuel flow. You can not just "throw in some extra fuel" without precisely knowing how much extra to put in and when to put it in. For the "how much" part, you will need detailed engine test data. For the "when" part you will need timing information. And how exactly are you going to get the standard injectors to add more fuel? This problem is far more complicated than you appreciate. There is a reason the performance mods are that expensive.
    You have a lot more to learn about how engines work than you realize. I am not particularly knowledgeable about vehicle engines, but I do know enough to be scared by what you are doing. You on the other hand know so little so as to not be worried by your lack of knowledge. As for helping others, right now those you "help" will be classified your victims.

    I suggest you spend a lot of time learning and FULLY UNDERSTANDING how engines work, how they are controlled and the legal implications of what you are doing.

    One final thought. When you boost the engine, you are adding horsepower. That puts a lot of extra load on the engine and the transmission. Have you analyzed if the engine is physically capable of handling the additional forces? What about the transmission?

    ---55p

    Edited to add: You do realize that MOT regulations require any after-market engine modifications have to have a special safety inspection in addition to the regular MOT test?
     
    Last edited: Mar 12, 2010
  18. pxr5

    pxr5

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    Mar 1, 2010
    Wow ! your making a lot of assumptions about me, with out knowing any thing about me!.
    You are mistaken, the system I will add has no connection what so ever with the stock fueling system.
    Using a wide band fuel /air monitor, a close eye can be kept on whats going on- throwing in extra fuel is not my plan.Hence my question regarding the motor controller.
    Given that I built a few turbo engines, including fabricating manifolds etc that run great proves I know what I'm doing.I have three self built Turbo bikes & one car in my garage, how many have you done?

    As to MOT's, on bikes no emissions are ever checked, also no ' special safety inspections are required on modified vehicals- I know this given I take several modified vechicals in each year. ( a fresh built car would require a SVA test = safety test )
    By the way, emissions can be easly reached by using a mix of methanol+ petrol, retarding the ignition & running hot running spark plugs! ( UK emissions are not as strict as in the US )
    Thats how I get my car MOT'd each year.
    I think you are being quite hostile to me, why?
     
  19. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    When did that change from a car engine (that requires emissions testing) to a motorcycle engine? Hope that explains why you are being seen with skepticism.

    If you are not going to modify the fuel system, how are you going to get the additional fuel into the cylinder? Are you planning to drill a new hole in the cylinder and add another injector? If not, then you either have to T into the existing system or have the injector do something other what the ECU is telling it to do and that can only be done by modifying the existing fuel system. Unless you are willing and able to explain in detail exactly what you are trying to do, you will not get useful answers.

    Regards,

    ---55p
     
    Last edited: Mar 12, 2010
  20. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    pxr5, are you planning to increase the fuel pressure in order to get more fuel into the cylinders under boost conditions?

    My understanding is that fuel injectors typically operate in an environment where the fuel pressure is regulated so that fuel volume is proportional to time.

    My assumption from your description is that you are planning to dynamically measure the requirement for additional fuel by monitoring an O2 sensor in the exhaust. When it senses a lean mixture you will speed up the pump to increase fuel pressure and thus the amount of fuel delivered per unit time the injector is open.

    Is this right?

    If it is, my first question is "How will you ensure you get higher pressure?" In my experience the pressure is regulated via a relief valve which redirects excess fuel back to the fuel tank (or to a point in the fuel line prior to the pump). If you simply increase the fuel pump capacity, the pressure will probably not change much.

    It is also my understanding that many (most? all?) fuel injected vehicles monitor the manifold vacuum in order to determine the amount of fuel to inject (this is not a requirement for a vehicle with a carburettor).

    I recall reading a long time ago about a turbo conversion of a normally aspirated fuel injected vehicle and it "just worked" up to a certain amount of boost. In this case the fuel was being injected into the manifold rather than direct into the engine so the modification for higher boost was to add an additional injector in the manifold that was triggered at high boost levels. At least in this instance the original engine management was able to deal with it -- presumably it could handle +ve pressure and also monitored the engine exhaust.

    I don't know if any of that is helpful or not.
     
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