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12th November 2006, 13:22 | #21 | |
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A relay is not a good idea - the contacts won't handle continuous on/off switching. Its better to use a mosfet, protected by a flywheel diode. Maplin sell them. HUF75337P3 part no UE47B. You also need a 3.9v diode from gate to ground and a 4k7 resistor in series with the 10v pulse lead from the fbh. I'd recommend a 3amp diode across the mosfet as well. Ron Last edited by Roverron; 12th November 2006 at 13:47.. |
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12th November 2006, 13:37 | #22 |
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Hi
You probably have RAVE,but just in case you haven't then the following Quote may assist "After 20sec.the ECU starts to operate the 'dosing' pump at 0.7 Hz. The fuel entering the combustion chamber is ignited by the glowpin." If an analogue DC voltmeter is used on pulsing DC it may only register 10v or so. Needle may not be seen to pulse up and down . Hope this info may be of some use. Thanks , Simpsora |
12th November 2006, 13:45 | #23 |
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In fact, just got back from Maplins.
One comment that was made is the "driver" may be a problem. To explain, When I get the 10V and connect it under bonet to a relay, the voltage drops to zero and there is no click. The suspision is there is not enough current to drive the relay, or equally the solenoid. Got a few more tests to try . . Scotty, the pin I was testing is no.6 (just to the right of pin 3 that gets grounded). It would be really usefull to know if anyone else gets 10V with a working pump . .. |
12th November 2006, 13:53 | #24 | |
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There would enough to drive the mosfet, they need a a few microamps! |
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12th November 2006, 14:01 | #25 |
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Hi
if the ability to provide the required current to drive the pump is suspect (even if volts are there) then then this would throw suspicion on an internal circuit (ie the .7 Hz pulse circuit)of going wrong, ie high resistance,which may be pre-curser of failure. |
12th November 2006, 14:15 | #26 | |
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This is true, but rather than replacing the internals of the fbh, or even the whole fbh, if there is enough current available to drive a mosfet, then this would be much cheaper. Ron |
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12th November 2006, 15:18 | #27 |
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FBH burner
Hi Roverron
what you are suggesting would work (as MOS FEt's have extremely high input impedence) However , this would be 'working around' problem rather than pinpointing the real cause, which may be as simple as 10 pence resistor going increasingly high resistance till it fails altogether .When this happens there would be no output to drive MOS FET solution. That's why a copy of webasto circuit diagram/ component layout would be very usefull. Thanks, Simpsora. |
12th November 2006, 16:17 | #28 |
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If I can delay or avoid the cost of replacing the internals of the FBH for a few pence then why not?
In fact Maplins suggested a Medium Power lenear transistor (TIP120) Just need to remember my base collector emmoter stuff now to be able to use it! |
12th November 2006, 19:00 | #29 | |
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Ron |
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12th November 2006, 19:33 | #30 |
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FBH burner
Hi There,
Yes, roverron's circuit suggestion should work ok for you Johnfol, go for it and let us know how you get on. However ,for those of us who have no remaining vestige of pump pulse (including mine )then restoring correct operation of circuit within webasto remains the best way forward (possibly) . Anybody ever successfully got a defunct webasto working again? (not including complete replacements or retro fits etc) Also, as webasto's (fitted as standard) must all be coming on for 5+yrs . old approx. then it may be an age related fault! Thank's,Simpsora |
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