Half-decent source for 5V regulated DC-DC converters!

Electrical & Ignition

  1. Gerald Morris

    Gerald Morris Senior Member

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    Greetings Moparians!

    Having read The Oracle of the Honorable Mountain (Ehrenberg) on using the venerable 7805 IC regulator to replace the Victorian antique behind the gas gauge, I went in search of some 7805s to make up a few of these for folks.

    New Egg carries stuff already done. I recommend these, as the 1.5 amp maximum from a single LM 7805 doesn't go far in our old dashboards, as "R.E." should know! I advise you to get a 10 amp supply, which will easily power any USB items you may want to plug in in addition to the old stuff.

    My only concern about this stuff is its point of manufacture. IFF I find a good vendor of GOOD 78XX chips on our side of the oceans, I'll post links.

    For the 10A adjustable set:

    LTC3780 High-efficiency power supply module DC 5-32V to 1V-30V 10A Automatic Step Up Down Regulator Charging Module - Newegg.com

    Single 7805 based unit:

    LM7805 three terminal voltage regulator module 5V voltage stabilized power supply module - Newegg.com

    There's more, but its all more sino-sludge. They do electronics somewhat more reliably than repopping American car parts, though this shouldn't comfort folks much. Ehrenberg's article is old, but maybe you can still buy the ICs from Stateside vendors as listed.
     
  2. bnz84

    bnz84 Active Member

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    I was looking too and there is a bunch of them on Amazon too. Mostly low amp like 1.5 or 3. But 10-15a is there too. Search for "Step down" or "buck converter" or Drok or just "voltage reducer." Of course there is the RT Engineering guy who makes his own. And there is this video that shows it being done. I will use one of these options.
     
  3. 78Brougham

    78Brougham "Chump" FCBO Gold Member

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    I have no Friggin' idea of what you are talking about...:rofl:
     
  4. jct

    jct Senior Member

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  5. 78Brougham

    78Brougham "Chump" FCBO Gold Member

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    Using it for what?
     
  6. bnz84

    bnz84 Active Member

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    These voltage reducers/regulators are attached to the back of our gauge cluster and turn 12volts into a steady 5 volts which then power the gauges. These regulators are common on many body styles. They can last but are very low tech, relying not on circuits but heating wire coils and resistance and "stuff". When they do go or if you just want to be proactive people look for "solid state" circuits with solder and boards and newer "stuff". The ET engineering guy's is cool because he reuses the original box and adds his own guts. But its $50. You can easily get cheaper circuit boards to do the same thing. They got really common when USBs connectors were spec'd to use 5volts also.
     
  7. 78Brougham

    78Brougham "Chump" FCBO Gold Member

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    Guess I never needed to replace one in my 40+ years of owning dozens of Mopars.

    Good info to know though, thanks.:thumbsup:
     
  8. Gerald Morris

    Gerald Morris Senior Member

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    Its cool man. Rick Ehrenberg wrote up a bit on how to replace the old power supply for the dash lights, gas gauge & such. Its a good read, and might work for some folks. I'm not sure if 1.5 amps at 5 V, a mere 7.5W is enough juice for the gas gauge AND one's instrument panel lights, so I figured a more robust 5V supply would be better. IFF you like USB gadgets, then you REALLY owe it to your self to scale up to at least 10A at 5V. THAT should supply ALL your low voltage desires.
     
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  9. Gerald Morris

    Gerald Morris Senior Member

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  10. 3175375

    3175375 Senior Member

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    I have been reading the posts and references with interest.
    As an electronics engineer (retired), I am concerned about noise being produced by a converter. With all of the electronics that we now use, many of them are succeptable to noise caused by switching power supplies and / or ‘chopping’ power supplies.

    The LM7805 voltage regulator doesn’t produce much noise as it doesn’t ‘switch’ the output to achieve the average output voltage value of 5 VDC. That is why it requires a heat sink, that is attached to the hole of the 7805.
    Regarding current output, the 7805 is limited.
    The 12 VDC power form running around a vehicle is inherently dirty, as the alternator, and relays switching on and off create noise on the 12 VDC ‘bus’.

    Secondly, by simply adding a 7805 provides no output current limiting protection and no fuse / circuit breaker protection if a short exists or is presented to the 7805.
    Now a filament type incandescent light bulb that is used to illuminate your dash instruments is very robust and forgiving), but dimmable LEDs and more importantly, electronics such as GPS receivers, radios and other modern conveniences that are in our present vehicles and ‘toys’ are and much of them are designed and manufactured in China (read: JUNK) and extremely susceptible to input power quality - in fact, they expect 5 VDC to be rock solid as if they are connected to Hoover dam.

    The ultimate way I believe to correct the delivery of 5 VDC to the dash (and any added USB ports one might add) is to install a DC to DC converter AND current limiting / fuse / breaker capability. Also remember that a fuse or circuit breaker is to protect the wire.

    How easy might it be to short out a USB or other interface (me thinks very)?

    Procuring a 5 VDC DC to DC converter is simple, but they aren’t cheap and many are probably junk.
    I worked on military instrumentation systems and a decent DC-DC converter for 28 VDC to 5 VDC was sharp (1000+ US$) as aircraft 28 VDC is horribly dirty.

    I am going to do a little research on how I might come up with something that is off the shelf that doesn’t cost 1k$+.

    FYI, I also worked on radars that we installed on testbeds that presented such wild dynamic current loads that we would trip the generator control unit (GCU) safety control circuits on a jet and we had to install a massive, big and heavy power conditioning unit (basically an electronic equivalent of a shock absorber) to eliminate the issues.
     
    Last edited: Jun 18, 2020
  11. Mike66Chryslers

    Mike66Chryslers Senior Member

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    The voltage limiter doesn't power any of the instrument lights. Those are still connected to your full system voltage, just through the dimmer switch, which is a simple potentiometer (variable resistor). The voltage limiter is just to power the gauge movements and sensors: gas gauge and oil pressure if equipped.

    The problem with a 7805, as has been noted, is that it can fail SHORTED if it overheats. That would put full system voltage through your gauges and fry them. That happened to me with a circuit I was experimenting with once, and burned out an expensive microcontroller chip I was programming.

    I would recommend not combining the gauge voltage limiter circuit with any other function like charging USB devices. It might seem like a cool idea, but not worth the risk of plugging in a device and which affects your gauges. USB power supplies are cheap and small. Wire-in a separate one and hide it elsewhere in the dash close to where the USB plug will be.

    While I could build a voltage regulator circuit myself, I like the RT-Eng replacement regulators. They are a plug-and-play direct replacement if your original voltage limiter is the external plug-in style and not built into one of the gauges. They also have built-in current-limiting in the event of a short circuit.

    IMO the best things you can do to eliminate noise in the C-body electrical system are to replace the electromechanical voltage regulator (the one which controls your alternator output) with an electronic one, replace the points ignition with solid state, and make sure you're running carbon-core spark plug wires and ensure the insulation on them is good so they don't "leak" EMI. This should cause a significant improvement in electrical noise at the source.

    Beyond that I wouldn't over-think the noise filtering. I think that, when retrofitting electronics in an old car, it's easiest to consider the noise filtering requirements at the point of use, based on the type of load.

    LED replacement bulbs will not be damaged by ripple on the power supply, and you're unlikely to see any flickering from them at the frequencies you're talking about. Any plug-in devices for automotive use such as GPS or aftermarket stereos should be designed to accommodate the variable conditions of automotive power supply and have adequate noise filters built into them already. GPS units have a battery built-in, which acts like a large capacitor, and their own internal power supplies with noise filtering.

    If audible noise comes through on the stereo/amp speaker output, there are passive LC filters available to install inline on the power wires, or you can certainly design one. An equally important consideration IMO would be to route high-impedance audio signal wires to ensure they don't pick up any radiated EMI from surrounding wires/devices, and ensure that all high-impedance audio wires are shielded and not simple twisted pairs. (I'm talking about signal wires between stereo head unit and external amp, not between the amp and speakers.)

    The original voltage limiter powering C-body gauges was very crude, and the electro-mechanical sensors and instrument movements were designed to handle a very noisy environment. They will not be affected by transient voltage spikes from relays or high-frequency ripple. Using a more stable voltage regulator, even a noisy switch-mode one, will be a drastic improvement.
     
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  12. 3175375

    3175375 Senior Member

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    @Mike66Chryslers , I agree with almost everything you have stated. However, I have seen LED indicators fail, root cause unknown, but I suspect that they did due to poor design, manufacturing techniques, noise spikes and/or over voltage.
    In my career, I witnessed failures of solid state devices fail in referenced root cause situations. And the expense of discovery of the root cause was excessive in time and cost... Hence, my concerns.
     
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  13. 3175375

    3175375 Senior Member

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    One more thing, as long as the public continues to procure ‘drop-in functionally equivalent’ components and subsystems with inherent design and manufacturing flaws (buy on price only and not total value), the situation will only worsen as the developers and manufacturers of quality components are driven out of existence.
     
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  14. Gerald Morris

    Gerald Morris Senior Member

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    I knew the dimmer is a wound, toroidal pot, but labored under the delusion that the attenuated voltage was being dimmed. In retrospect, obvious nonsense, given that same dimmer dims courtesy lights in rear pillars. Mea culpa, error mihi. I got my oil pressure on a purely mechanical gauge and need to tighten the little 1/8" copper compression fitting if I tire of oily fingers every time I toggle my pusher fan on. The Torture Never Stops.....

    AGREED! Reckon if I ever put the original instrument panel back in I'll use the RT-Eng reg myself. Purpose built for the job beats home brewed experiments most any day. Good to know the fault in the 78xx regs. I'll steer clear of them then.

    I LIKE my old school Kettering breaker point ignition, and tune it very fine, but regarding the rest of the 19th Century tech, I'm in total agreement with you. Good to have learned a couple good facts from this today. Much Obliged!
     
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  15. Mike66Chryslers

    Mike66Chryslers Senior Member

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    If you worked in military/aviation I'm not surprised that your component verification and root-cause failure analysis procedures would be very thorough. I'm an embedded systems engineer (hardware and software) with experience in high-speed digital communications, though not military/aviation. I have friends in that area though and they've told me stories about how rigorous their unit testing and design reviews can be.

    I'm sure we could swap some interesting stories (which would bore everyone else here). I've had numerous cases where a "pin-compatible" component was electrically compatible, but the API was different. We also have to contend with Chinese knock-off electronic components which have been labelled and sold to us as the real thing. This is especially problematic where a designed-in component has gone end-of-life from the manufacturer and we had to buy some leftover stock from a third-party distributor so we could continue building products.
     
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  16. 3175375

    3175375 Senior Member

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    Yes, there is a significant root cause analysis effort for ‘gripes’ in military systems. However, most of the equipment I worked on was instrumentation / support gear and we (team of people) that were responsible for ALL aspects of the ‘queer’ stuff that we had to add to make an F/A-18 radar think it was in an F/A-18 and not in the 727 that we used as a testbed.
    Software was also included in the responsibility.
     
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  17. 3175375

    3175375 Senior Member

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    FYI, I am writing a book about my engineering career. I have the chapters defined and started to populate them, all to have it lost electronically. Something that I may do this winter (re-start writing it). Title is ‘Living the Dream as an Aviation Engineer’
     
  18. Mike66Chryslers

    Mike66Chryslers Senior Member

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    Sign me up for a copy!
     
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