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5V Voltage Regulator

Discussion in 'Automotive Electronics' started by TP380Z, Apr 14, 2016.

  1. TP380Z

    TP380Z New Member

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    Hello Everyone,

    I have a 1965 Barracuda and I think the 5V voltage limiter for my gasoline and water temperature gauges is on its way out. There more about this device on this page:
    http://www.allpar.com/history/mopar/electrical2.html

    On my car, the voltage limiter is contained within the gasoline gauge and I think it would be easy to bypass it with fiber washer on the 12V gauge terminal. The Allpar article recommends replacing the mechanical limiter with a 7805 regulator. I checked the resistances in each gauge and both have 20 ohms. Full-scale on each of the sensors is 10 ohms. Each leg of the parallel circuit is 30 ohms so I calculate the total 5V draw from the instrument regulator would be 0.33 amps. I believe a 7805 regulator would have to dissipate up to 3.1 W of heat to run my gauges.

    Building a instrument regulator based on a 7805 device would be straightforward enough but I thought I would see if there were any better way of doing this. From reading the posts here and on other sites, I've come across the following recommendations
    I'm leaning more towards using the DE-SW050 but I would like to know if there are any other options I could look at. Any suggestions?
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Use the TO220 version of the 5V regulator, and bolt it to the car... (infinite heatsink)

    If you ever listen to AM radio, run as fast as you can away from the switching regulators.

    The worst part of an original mopar was the bimetal regulator. Why the hell would they duplicate that crappy behavior in that RTE "limiter"? Me-thinks that is like "oxygen free" speaker wire...
     
  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Who on earth would listen to crappy AM in the 21st century? :D
     
  4. dave

    Dave New Member

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  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    We have a bunch of Rush fans and Bible Thumpers that still use AM out here in AZ.
     
  6. TP380Z

    TP380Z New Member

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    Thanks very much for your quick replies.

    That would be the easy way but where's the challenge in that? Besides, old alternators (mine has a 35 A rating) have poor output at idle so I'd also like to conserve power as much as possible.

    I still have the original AM radio because 1) I want to keep the original look and 2) basically very few twin shaft radios fit in the dash (see Radio Upgrades). This winter, I had the radio refurbished and upgraded to FM with the Aurora FMC-1 FM Tuner. I see that Dimension Engineering has is a 470µF capacitor on the DE-SW033 data sheet. DE told me that this would only be necessary if my device is ripple sensitive. Noise suppression capacitors were common in old cars. Wouldn't a properly-sized capacitor eliminate any noise issues with a switching regulator?

    The old Mopar gauges are thermal devices, which means they have a slow response. I think the RTE applies full 12V power like old mechanical device to allow the gauge to quickly display the sensor reading before slowing its response.

    Wouldn't the RTE Limiter essentially perform much like the DE-SW050?
     
  7. Willen

    Willen Well-Known Member

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    AM radio is an amazing invention. Others are just its copies I think. If AM totally disappeared from the earth, many hobbyist and new comers to electronics would feel very sad. Awesome tiny AM detectors are very interesting circuitry to do and to understand and to amaze people (eg crystal radios, matchbox radio, catwhisker detector etc)
     
  8. TP380Z

    TP380Z New Member

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    It's a bit disappointing that AM music stations are slowly disappearing but there still a few good stations I've been listening to here in southern Ontario (CFZM-AM740 Toronto, WJJL-AM1440 Niagara Falls).
     
  9. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    35A@14V is 490W. The power wasted in the linear regulator is (14-5)V*0.2A ~= 2W, so the "efficiency" of switcher is a bogus argument...

    I have used a 5V reg in several older cars, and it works fine...

    The "noise suppression" capacitors are use to suppress hash from the alternator/generator brushes; they have nothing to do with filtering "ripple". The battery is the best ripple filter you can obtain, and you already have one...
    The switcher generates RFI, so it couples into the receiver's antenna directly. No amount of capacitors on the radio will make the slightest difference.

    So you are willing to pay $$ so that your gauges initially "peg" before they start displaying the correct information?
     
  10. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    One of the reasons that AM radio stations are disappearing is because of the interference from Chinese switching power supplies...

    Some reading...
     
  11. TP380Z

    TP380Z New Member

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    My alternator does not put out 35 A at idle. My voltmeter shows more like 12V at idle so it seems to me to be barely keeping up with demand..

    I thought the RTE limiter was a bit too pricey for my needs and I don't have a problem with waiting a few more seconds for the gauges to stabilize. I am just trying to find the best option over the old mechanical limiter.

    As for RFI from a switching regulator, would it be possible to enclose it in a metal box?
     
  12. bountyhunter

    bountyhunter Well-Known Member

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    No. You have to understand there are two types of EMI: conducted and radiated. A switcher creates both. A good capacitor may reduce conducted EMI on a given line, but radiated EMI spews like radio waves. The only thing that stops it is either electrostatic shielding or magnetic flux shielding.
     
  13. bountyhunter

    bountyhunter Well-Known Member

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    Yes, that will help. It will stop electrostatic EMI (like radio waves) but not very effective on magnetic flux that comes off transformers and inductors.
     
  14. spec

    spec Well-Known Member Most Helpful Member

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    Hy TP,

    Are we going to see a picture of the '65 Barracuda. :)

    300mA would not bother the alternator. By the way, unless you want to keep the car original, why not fit a modern higher output alternator.

    You need to very careful about connecting electrolytic capacitors across the 12V line on a car (auto). The ripple current is the problem. I leaned the lesson the hard way.

    I'm pretty sure that the switching regulator will be fine if you wanted to go that way. That is exactly what your alternator regulator is- and the worst type. If push comes to shove you can put the switch mode regulator in a can to screen it.

    spec
     
    Last edited: Apr 16, 2016
  15. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Alternators do use a type switch-mode regulation where the Alternator Voltage Regulator switches the voltage to the field winding (alternator rotor) fully on and then turns it off. Unlike the SMPS Buck Regulator the OP is likely to buy from EBay, the AVR switches on/off 30 to 150 times per second, which causes no detectable RFI at 0.5 to 1.5MHz, partly because the current through the alternator rotor is continuous due to the huge inductance of the rotor winding. The spectrum of the AVRs switching rate is such that you would be receiving the several-thousands harmonic at 1Mhz, which has no detectable energy...

    Contrast that to an SMPS that switches at 250KHz. It is really hard to suppress its fourth harmonic to prevent it from clobbering 1MHz..., tin boxes notwithstanding....

    Alternators can and do generate some RFI, but it it is wide-band hash due to brush arcing as the brushes ride on the copper slip rings in the rotor. This can be suppressed by mounting a shunt capacitor (with very short leads) right on the alternator (like these). These are effective in suppressing radiated RFI in the 100kHz to several MHz range. This capacitor has nothing to do with filtering alternator ripple, which is an entirely different kettle of fish...

    I have a lot of experience installing LORAN and ADF VLF receivers in boats and aircraft. LORAN utilized 100kHz while ADF uses 190kHz to 1.5MHz, and if the alternator filter was missing, reception range would be diminished. Listening to an AM car radio, if the alternator filter is missing, the alternator hash can be heard as a bacon frying sound, especially while tuning weaker AM radio stations.
     
    Last edited: Apr 16, 2016
  16. Mikebits

    Mikebits Well-Known Member

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    We have a comedy AM talk radio show that I listen to all the time while driving. All the good talk radio shows left to Satellite radio.
     
  17. spec

    spec Well-Known Member Most Helpful Member

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    The spectrum from a square wave depends on the speed of the rise time and fall time of the edges not on the PRF.

    I am not saying that there might not be problems with a SM regulator but what I am saying is that they would not be insurmountable and quite simple to sort. I too have much experience with fitting AM radios to cars. At one time that's all there was for us poor students.

    Talking about interference generators, you won't get a better radiated and conducted source than from the 12KV upwards spark gap transmitter that fires the plugs.

    spec
     
    Last edited: Apr 16, 2016
  18. TP380Z

    TP380Z New Member

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    [​IMG]

    Nippondenso externally regulated alternators are a common upgrade but it involves some work. On cars like mine, the full output from the alternator runs through the ammeter with a 12g wire. I have a 90A denso alternator from the junkyard but still have to modify the brackets and wiring.

    I'm still very new to electronics. What is that lesson?

    I've previously upgraded (back in late 80s) from the single field alternator with mechanical regulator to dual field alternator with electronic regulator (from a 72 Scamp). Are you talking about the mechanical or electronic regulator?
     
  19. spec

    spec Well-Known Member Most Helpful Member

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    Wow! what a beauty. Thks for posting the picture of your Barracuda.
    The last time I had a ride in a 'yank' car was around 1959 when a couple of us were hitch-hiking in Suffolk, England. We couldn't believe our luck when a white convertible T bird (I think) pulled up.

    Oh I see, you have it all in hand. :)

    (1) Capacitors have a maximum ripple current rating.
    (2) They also have a maximum surge current rating.
    (3) Ripple current is basically the AC current passing continuously through a capacitor which heats the capacitor up and can cause expansion and/or gassing. This in turn, in extreme cases, can cause the capacitor to explode.
    (4) Ripple current is caused by ripple voltage, rather like a resistor where the voltage across the resistor causes current to flow through the resistor.
    (5) The 12V line on a car can have a substantial ripple voltage, under certain circumstances, depending on the design of the alternator, the regulator type and condition, the integrity of the car wiring especially the alternator earth, and the condition of the battery. Worse still, the 12V line has an extremely low impedance as anyone, who has accidentally (purposely) put a shorting wire across an auto battery, will know. :D

    Average pre 1970 UK cars were very basic, and having any kind of radio was considered to be decadence in the extreme. As a result, I spent a lot of time experimenting with installing radios and even cassette players in old cars. I also modified valve (tube) car radios which had failed mechanical inverters (very common), to solid state inverters. Some of the radios were standard portable types rather than auto types and, as you can imagine, the interference, both conducted and transmitted, was horrific and, surprisingly, also with the cassette recorders.

    Anyway, to cut a long story, I designed a fantastic 12V filter which did the job wonderfully. But one cold morning I started the car and after about ten minutes there was an almighty explosion from under the dash: one of the large electrolytic capacitors in my super filter had spewed its guts all over the place. The moral of the story is that it is best not to fit a polarized capacitor (electrolytic) across the auto 12V supply line. Even non polarized capacitors need to be the right type capable of withstanding the harsh environment in a car.

    You could fit electrolytic capacitors to the 5V output of a switching regulator though.

    Mechanical regulators of all sorts: alternator, dynamo, fuel gauge and of course the awful mechanical inverters in valve radios were always a nightmare in all respects. Although some of the German sets with mechanical inverters were OK. Not only were mechanical regulators unreliable/inaccurate, but they also threw out a load of hash. The later solid state regulators are much better in all respects, but still generate harmonics because of their switching action.

    Just one word of caution. The sender voltage in a car is safety critical. As you probably know, the sender in the petrol (gas) tank is a wire wound potentiometer with a law tailored to the geometry of the tank. The danger is that the wiper of the potentiometer could cause a spark with obvious consequences. There are regulations, I cant remember them now, about the nature and amplitude of any voltage in a flammable environment, so this is an area to be aware of.

    spec
     
    Last edited: Apr 16, 2016
  20. bountyhunter

    bountyhunter Well-Known Member

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    The ugliest EMI comes from the resonant frequency caused by the transformer and inductor's leakage inductance. When the switch snaps off, it rings in the 10MHz - 50 MHz range which is really nasty.
     
  21. spec

    spec Well-Known Member Most Helpful Member

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    As you say, SMPS' generate all sorts of hash, but my point is that it is quite simple to keep it out of your system by a combination of good layout, screening and filtering.

    In terms of low risk, a linear T220 voltage regulator, with a power overhead of 3W, is the obvious way to go as already stated. That is what I would do, with a 10 Ohm 5W (1W dissipated) bolt-down resistor in series with the input. But the OP has stated that he would like to push the frontiers and use a switch mode approach. :)

    spec
     

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