Electronics > Projects, Designs, and Technical Stuff

Power line filtering in a vintage car

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robzy:

--- Quote from: basinstreetdesign on January 06, 2020, 05:00:35 am ---Good luck.

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Thank you very much for your post! That is very helpful. The addition of a diode in series with the circuit makes a lot of sense when it comes to protection from negative transients.


--- Quote from: duak on January 06, 2020, 06:14:57 am ---robzy, the two capacitors I mentioned above should be connected in parallel.
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Ah, that makes sense. I was totally misreading your post.


--- Quote from: duak on January 06, 2020, 06:14:57 am ---That being said, if you have a 'scope, it'd be a good time to use it.  We've all proposed solutions to what we think are the problems.  It may be that there's something else that needs special attention.
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If I had a scope I wouldn't dare to put it anywhere near this car ;) The proposed solutions have been very helpful, I've just ordered some parts, and I'll put together a new circuit on the weekend.

jfiresto:

--- Quote from: Psi on January 05, 2020, 10:13:10 am ---... If you want a bit more protection, add a 0.1 ohm 5W series resistor and chunky ~3000W  ~40V TVS diode to GND on the input side of that reg.

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Is the tenth ohm resistor necessary? I ask because an ISO-16750-2 load dump pulse generator for verifying such things has an internal resistance of 0.5–4 ohms. The last unsuppressed generator I designed for was 80V @ 2 ohms.

langwadt:

--- Quote from: Psi on January 06, 2020, 06:00:05 am ---
--- Quote from: langwadt on January 06, 2020, 05:38:58 am ---
--- Quote from: Psi on January 05, 2020, 10:13:10 am ---LM2937IMP regs are automotive rated and have built in 60-V transient protection. (buy them from legit source, there are fakes out there which are just normal regs)


If you want a bit more protection, add a 0.1 ohm 5W series resistor and chunky ~3000W  ~40V TVS diode to GND on the input side of that reg.

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not need to use as little as 0.1 Ohm when you only need maybe 100mA at 3V

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That was to protect the TVS, but if his overall power needs are that low then the thin power wire to Vbat is enough to add some resistance.

We have 36V 4000W TVS diodes on our automotive gear and, even then, they occasionally do pop.
However we need to drive 10A loads, so our cables to Vbat are quite thick.

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sure for high current, but if the load is only 100mA@3V you might as well  use something like 10-20 Ohm

amyk:

--- Quote from: robzy on January 06, 2020, 02:12:54 am ---- You're correct in noting that it isn't just the ignition system, but also generator, regulators, and fuel pump. I confirmed that my multimeter still glitches when the generator is disconnected, but that doesn't mean it wasn't a problem in its own right.

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70-year-old car with an electric fuel pump? :o

Gregg:

--- Quote from: amyk on January 07, 2020, 02:51:37 am ---
--- Quote from: robzy on January 06, 2020, 02:12:54 am ---- You're correct in noting that it isn't just the ignition system, but also generator, regulators, and fuel pump. I confirmed that my multimeter still glitches when the generator is disconnected, but that doesn't mean it wasn't a problem in its own right.

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70-year-old car with an electric fuel pump? :o

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In post #5 OP stated the vehicle has a Lucas voltage regulator.  That should be a clue as to why it has an electric fuel pump.  Lucas electrics in vehicles are legendary (not in a good way).  I know from experience, I have a 1957 MGA.
Maybe Lucas and Murphy were drinking buddies.
Edit: Additional information.  Perlux ignitors (may be listed as Pertronix  Ignitor) are available for most older vehicles and use hall effect sensors to replace the points.  Resistor ignition wires may be of some help.

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