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add light to 1930s fuel pump

Discussion in 'LEDs and Optoelectronics' started by morris8, Mar 22, 2014.

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  1. morris8

    morris8

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    Mar 21, 2014
    Hi,

    I'm not sure how to phrase this in electronic terms - I have a 1930s SU fuel pump that works with a solenoid attached to a diaphragm. When powered the solenoid draws the diaphragm towards it, but also closes the points connection so the diaphragm returns to it's normal position - creating a pull/push of the fuel forcing it through the one-way valves.

    This creates a characteristic 'click' which experienced drivers listen out for when they start their cars. Normally it 'clicks' every few seconds but if there is a problem it can stop altogether or click several times a second (and ends up spraying fuel over the engine!).

    So I guess the electronics description is an electromagnet relay which is getting its supply via it's own normally-closed relay points... right?

    My problem is I want to add a light in the dash for every click.. this is what I've tried:

    I added an LED in parallel to the points, but it only lit when I connected/disconnected the relay manually - when it clicked at its normal speed there was no light.

    So I added a 2200uF capacitor in parallel, thinking it would be charged in an instant and keep the LED on for a second. Again - manually operating the relay and its perfect but in normal operation nothing lights up. I then added a diode to make sure the capacitor wasn't discharging through the fuel pump... no change.

    I'm beginning to think that the LED start up time and the capacitor charge times are much larger than the solenoid connection time and there's no way this is going to work. Is there anything else I can try? The only rules are it needs to cope with a rather electronics-unfriendly 6V-9V range full of transistor killing HV surges...

    Thanks...
     
  2. duke37

    duke37

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    Jan 9, 2011
    It is a long time since I had to thump an SU fuel pump to make it work.

    As I understand, the contacts are closed when the fuel pressure is low and a stroke is initiated to pump some fuel. If the pressure is not sufficient, this will be repeated and the pump clicks at a few times per second. When the pressure is sufficient, the clicks stop and the pump will only click again when fuel is used or leaks.

    To detect the current pulses, you will need a resistor or inductor in the feed to the pump and a circuit to drive the led. To keep voltage drop low, I would prefer an inductor or current transformer triggering a 555 to stretch the pulse and drive the led.

    A plug in box in series with the supply will avoid any modification of the pump which would be necessary if taking the voltage across the contacts.
     
  3. morris8

    morris8

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    Mar 21, 2014
    Yes! Spot on... I have an old UBA carb and the overflow squirts petrol over the exhaust manifold when the float valve is worn... it's easy to fix at ignition time with a thump on the float bowl but I can imagine it happening at traffic lights and being unaware... so I thought a light would make a nice simple project...

    Can you confirm that the clicks are just too short to expect a capacitor or LED to work without another circuit? I assumed the charge would flow into the capacitor until it's resistance exceeded that of the solenoid, giving some sort of power to the LED.

    It's a long time since I played with a 555 but I guess you are saying an inductor in series receives the power impulse to the solenoid (ie it triggers when the click happens) and it has it's own 6V circuit with capacitor to keep the LED on for a second or so?

    Can you say why the inductor is needed? If the 555 received a trigger direct from the pump contacts wouldn't that work? Or would it work but kill the 555?

    Lastly, is there a name for this type of circuit so I can google it?

    Many thanks...
     
  4. duke37

    duke37

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    Jan 9, 2011
    My first car was a Morris 8. I used to do 200 mile journeys in it. The thought of doing this now would be mind bogling. I could travel at 55mph but had to slow down when the engine got warm as the big ends would rattle. It was ideal for tavelling in London, the Rolls Royces would give me a wide berth.

    I am not sure what the circuit of the pump is. The contacts will be in series with the solenoid but may be connecting the solenoid to earth or connecting it to the incoming power. The circuitry to use will differ which is why I suggested using the supply current and not going inside the pump.
    There will be a high voltage pulse when the solenoid is turned off which could be used.

    A resistor in the supply will drop voltage, if you go for 1V to activate a transistor, this may be too much drop for a 6V supply. A current transformer could give a large output voltage on turn off. A Hall effect device could be clamped on the wire to detect current, I have never used these.
    Both the transformer and the Hall effect device would give isolation which would help to reduce interfering spikes.

    A 555 can be used to give a pulse of standard width and will drive a led directly. Look up 555 edge triggered monostable.

    It would help to know the resistance and inductance of the pump and the supply voltage.

    Are you anywhere near Derbyshire?
     
  5. morris8

    morris8

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    Mar 21, 2014
    Oh good... I'm a newcomer but it has become my daily ride now. My aim is to figure out every aspect of it without actually changing anything permanently, and I've got loads of questions if you have the time! Unfortunately I'm in sussex which is probably several breakdowns away :)

    Accessing the pump is pretty easy - it has a cap with the live connection poking through. You can open the cap to get to the points. The points carry the live current down to earth. It works equally well with either earth but mine is negative. I'm currently working on a spare on the bench.

    Getting the resitance is easy (1 ohm) but the voltage is difficult - the car voltage varies from 5V (when trafficators are on!) to 9V when dynamo at full pelt with (I think) a full battery (and it is a nice 6.5V when headlights on and dynamo is supplying the power). Adding the HT coil spikes and I wanted to keep it robust with a capacitor and an LED I have hanging around that works on 12V (but also lights up on 6V).

    If I have to go semiconductors then I think a separate circuit is necessary and I like the idea of the hall effect device... does it wrap around a live wire? Or does it need to detect the solenoid magnetism? Can it also detect other things like the HT coil sparks? Or detect if the brake lights are working?

    In the back of my mind I thought I'd like to end up with an arduino controlling LED flashers and add some accessories like a brake fluid float and oil temperature gauge and tis fule pump light may be a good place to start... I just didn't think I needed to start on it quite yet.

    If I ordered a hall effect sensor that was pretty versatile can you recommend a spec? Some seem to be 3-pin and some are 8-pin and I haven't even begun to look at their ranges or how you use them!

    Thanks,
     
  6. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    I have had a mull and if you are happy about getting wires out of the pump, here is a simple circuit which should work.
    Note that it is polarity sensitive.
    Is negative earth used on 6V systems or have you changed polarity.

    I had a look at SU pumps and see that the later ones have a diode across the coil to save the contacts. I have included one here.

    If you have a spare pump you could try it on the bench.

    If it was me I would consider a solid state voltage regulator next, set to 7V.
    Batteries did not last long, probably due to overcharging and I got rid of my Morris 8 partly because driving in the gloom was not safe. I moved up market with a 12V Austin A35 van.
     

    Attached Files:

  7. morris8

    morris8

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    Mar 21, 2014
    I appreciate that duke... it's pretty similar, I think, to what I tried except I don't have a D1 (my old pump has nothing there and my new pump, on the car, has a small capacitor and I assumed my big capacitor performed the same role). I shall try it on the bench with D1 and see if it helps.

    The car should be negative, but I got it a couple of years ago with positive earth so I changed it back... on my series 1 there is no voltage regulator except the dashboard switch summer/winter/headlights - remember them?

    I'm finding the 6V lights pretty useless as well and I am planning for 3W LED lights to help being seen but not sure what to do with the headlights - I don't want to convert to 12V. I also plan for a 7.5V zener and power transistor to regulate the power but I'm still tinkering with the 3-brush dynamo to get the most stable output (rather than generate and dump it). Trouble is 6.5V is good for 2x3.2V white LEDs but useless if the trafficator arm is up and there is 5V free!

    Alternatively I have some buck boosters to get a stable 12V 60W out of the 6V battery which will be good for plenty of 3W LEDs, on a separate circuit, or I can presumably run them off a 12V 7A battery which is charged by the buck booster...

    Anyway, I didn't know about inductors so I'm going off to read about them and will try the pump with a D1 later on tonight.
     
  8. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    D1 is there as a flyweel diode. It passes current when the coil is switched off. This limits the voltage seen by the points.
    The small capacitor that you have passes current for a very short time on switch off so that the points can open before a strong arc is generated.

    The 1000µF capacitor needs to store an appreciable amount of energy to light the led. The polarity is wrong to help the contacts.

    I like your idea of a hall effect device fixed to the side of the pump but experimentation would be needed to determine the available flux.and device orientation.

    It is not a buck booster. Boost puts the voltage up, buck puts the voltage down. There are devices (SEPIC) which will do both but these are quite exotic.

    The three brush dynamo was before even my time. I think there was one on my father's Morris Cowley which doubled as a starter but often broke its drive chain.
     
  9. morris8

    morris8

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    Mar 21, 2014
    Well I tried it and unfortunately there was no difference... it works when switched manually but not when the pump is activated. I think I read that the solenoid is an inductor, and they drop voltage (or is it current) before the magnetic field is created, so I thought I would drop the LED resistor and just try it without a resistor hoping they'd be 3V or so... but again nothing. I'm beginning to think that it's difficult to do this in series with the pump. I may try it with a 12V battery tomorrow to see if it's the pump voltage drop and the circuit is almost there but I'm not sure useful that would be.
    If I used an inductor as a trigger to a 555, do I need one that is 2-coils with one passing the pump current or can I get away with a single coil that wraps around the live wire?
    Thanks,
     
  10. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    The pump is a resistance and an inductance. When connected the current will rise gradually depending on the inductance and will settle at a level depending on the resistance.

    The pump will pass about a thousand times the current that the led passes so will appear as just a piece of wire if connected in series. If you are connected in series and the led has a limiting resistance, then the pump will do nothing.

    Show us a sketch of what you have done.

    The diagram I posted shows the led circuit connected in parallel with the pump coil. If the pump clicks, then there must be power there and the led should light. Note that this is polarity sensitive. D2 will stop any current if you connect the wrong way round but D1 will pass current and you may get fused wires and a blown diode, perhaps better leave it out until you get the led circuit working.

    Wrapping a coil around the supply wire will do little, the wire orientation is wrong. You will need a diddy transformer which will need designing and making to suit. If you use point protection, either a capacitor or diode, then the transformer output could be low.

    I have just telephoned a neighbour who may have an SU pump which I could borrow for testing. This may take a few days. He said he had had 8 Morris cars. He now runs a Riley but this has a mechanical pump.
     
  11. morris8

    morris8

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    Mar 21, 2014
    Ha, I was very tempted by an Riley RMF with 12V and already have offers for my M8 but I'm so impressed that a 1937 car does everything I need without complaint I've decided to keep it a while yet... my other eye is on a stag or herald which is far less sacrilegious to modify!
    I did a schematic sketch likes yours and realised it was D1 which was missing but if I'm making a mistake it won't show up as a schematic... I'll try and draw the actual wires and connections instead. I am not using the same diodes/capacitors as you've specc'd, just ones I've got handy but I'll see if I can figure them out.
    My benchmark has been - it works perfectly if I make/break the contacts... but it has always failed if I activate the pump (which of course is draining power and doing all those inductance things I don't really have a grasp of!)
    Thanks for contacting your friend and going the extra mile - I really appreciate it.
     
  12. morris8

    morris8

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    Mar 21, 2014
    Well, I've redrawn it and can spot the difference between it and your drawing, but I'm not sure how to correct it.

    In my one it's the same as yours except when I connect the pump - I've drawn that as a dotted line at the top.

    Without the pump connected, the points will switch on the LED and the capacitor will keep it lit for a second.

    When I connect the pump I'm guessing the power goes straight to earth and ignores the 'circuit'.

    That certainly fits the results, but I haven't figured out what I can do about it!
     

    Attached Files:

  13. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    1. Get rid of D!, this protects the points but adds complications. You can replace it later.
    2. Connect the circuit across the coil.

    The circuit you show has the circuit always connected between earth and earth so there will be no input.

    My neighbour cannot find an SU pump, he has even more junk than me !
     
  14. morris8

    morris8

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    Mar 21, 2014
    Sorry, I'm useless at this, do you mean like this?
     

    Attached Files:

  15. duke37

    duke37

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    Jan 9, 2011
    No, it is not connected across the coil (in parallel).

    Move the wire which is connected to one contact to the other contact. Look at my original diagram.
    The idea is that the capacitor is charged whenever the coil is energised. The led is lit for a little extra time until the capacitor is discharged.
    The diagram you show will give an indication whenever the ignition is on.

    You are almost there !
     
  16. morris8

    morris8

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    Mar 21, 2014
    I'm glad you said that because in my mind's eye I had drawn the route back to earth before the switch (amendment attached) but looking at this morning I can only assume I was too braindead!

    Now, if you tell me this is wrong then I shall cry :)

    Also added where I think D1 should go for completeness...
     

    Attached Files:

  17. duke37

    duke37

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    Jan 9, 2011
    Please don't cry, there has been enough water in the south.
    This looks promising.

    You have not shown where you intend to connect D1. It should go directly across the coile with the cathode (marked with a bar) towards the positive input.
    Note that the diode will need to pass the full coil current for a very short time. Some information that I have seen says that the pump takes 3A. You say that the coil is 1 ohm so that would be 6A. Diodes can be overrun for a very short time but even so, I would not go for smaller than 3A. If the diode is not labelled, then the lead diameter can give some indication of diode capability. This diode could create sever problems if it goes short circuit so a good one shouild be fitted.

    The diode should be fitted inside the pump and connected with short leads. The rest of the circuit could be behind the dash.
     
  18. morris8

    morris8

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    Mar 21, 2014
    Doh, I didn't save and upload it correctly - have done so now.

    When you say D1 has to carry the full load of the current, I take that as meaning it has to resist carrying the current, right?

    I shall try the circuit out tonight and if it works will go out and get some rated diodes and try it properly.
     

    Attached Files:

  19. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    That looks right. However, I have had a look at the construction of the solenoid. The armature is solid so there will be in effect a shorted turn which will restrain the flyback voltage to some extent. Also, the pump will work for quite a while without modification so I would not bother fitting D1, you are not going to do 50000 miles/year !
    The diodes which were added in some cases, perhaps all, were zener diodes to limit the voltage to a specific level and were connected differently.

    The coil is an inductance so the current cannot be stopped instantly. When switched off, the full current goes through the diode for a short time until the current has declined. It only passes current during the turn off transient.

    If you have dismantled an ignition coil where a high voltage pulse is wanted you will see that the armature is made from a multitude of wires to reduce eddy currents.
     
  20. morris8

    morris8

    13
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    Mar 21, 2014
    Success! Thanks Duke, I would never have figured out not to keep on connecting the circuit earth to the car earth... I think something is eluding me here so I've decided to add an LED when the trafficators or lights are on... trafficators have a coil so it's easy but does the LED have to be connected across the coil? For the headlights, does it have to be across the bulb connections? I would have thought so, simply because of voltage drop or resistance or something... but as the LED resistor has a higher resistance I'm not sure why the LED can't be added before the coil. Dumb question I know but if I can make sense of this i think future circuits will be a lot less bother.

    Secondly, as I have your attention :) I'm going to try a flashing 555 circuit for the dash indicator so I thought I'd give your triggered monostable idea a go. I did a 'touch activated monostable'. However, for the trigger, I wasn't sure what commodity sensor I can plug in... a hall effect sensor is on my shopping list but I have an aftermarket tachometer that wraps around the HT coil and displays RPM - this obviously detects voltage so I'm wondering what the name of that circuit it, and whether it's simple to adapt the principle to a 555.
     
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