filtering electrical noise in a vintage auto. - Page 1
Forum section: electronics / projects

author: rmhc
author_rank: Newbie
timestamp: February 19, 2024, 10:22:36 pm
content: I am the sometime proud sometime frustrated owner of a vintage auto. I have fitted temporarily an LED voltmeter to check generator function and I was upset when it died a short time after I started the engine. By 'short time' I mean minutes not hours. The spark plug wires are copper cored so should my first step be to replace them with suppression wires and/or suppressed spark plug connectors? I have heard in the dim distant past that capacitors should be connected at various places on the vehicle to filter noise on the power lines.I would be very grateful for any and all information on this subject to clean up the power line on my car. Thanks in advance. Richard C.

author: Kim Christensen
author_rank: Super Contributor
timestamp: February 20, 2024, 12:33:45 am
content: How "vintage" is it?ie: Does it have a battery?It is more likely that voltage spikes on the low voltage wiring are killing the voltmeter. I doubt that messing with the sparkplug wires would help. Do you have a link, spec, or part number for the voltmeter?

author: Stray Electron
author_rank: Super Contributor
timestamp: February 20, 2024, 01:51:28 am
content: I have a Hell of a Lot of experience with antique vehicles, what do you want to know?I doubt that your automobile's electrical system killed your voltmeter. Anyhalf descentmeter should have been able to handle far higher voltage than your automobile is capable of generating.What kind of vehicle do you have and is the generator/alternator stock or is it something else? A voltmeter isn't really going to tell you much about your vehicle's electrical system. Particularly a digital meter, they react too slow. My advice is to start by buying a decent analog meter, one with a 10 or preferably 20 Amp amp meter. Tracing current flow will usually tell you more than looking at voltages. What are your symptoms of "electrical noise" and what is your concern?Your spark plugs had no connection to your VM dying. Unless you probed a spark plug wire while the engine was running. Post up what kind of voltmeter you had and what kind of vehicle and what kind of charging system.Current antiques; 1952 M38A1 and a 1966 CJ-5, both 100% stock.

author: rmhc
author_rank: Newbie
timestamp: February 21, 2024, 08:06:53 pm
content: Stray Electron,First many thanks for your input. The car is 1934 R-R with dynamo and transistorised V. Reg. built by myself. I just wanted to have the V meter to check system voltage for my general interest that the Dynamo & V.Reg. are doing what they are supposed to do. ie. charge the batt. to 14.2 volts while on the road. The V. Reg. is a Bosch unit modified to work with the Henry Royce' Dynamo which is a 'B' type with the Field powered by the Reg. The Bosch Reg. is designed to work with 'A' type dynamos where the field is connected to the positive brush and the Reg. then provides the ground for the Field winding. Field resistance is 3 ohms. THe V meter is a small LED unit from-you guessed it Amazing Amazon- It took a crap soon after I started the engine, apparently from spikes on the DC. Is that a reasonable assumption???I appreciate ant help you may offer as I also think that phone chargers etc could be at risk . RMHC.See Attachment.

author: Kim Christensen
author_rank: Super Contributor
timestamp: February 21, 2024, 09:12:32 pm
content: Most likely the cheap Amazon meter is simply a piece of junk but....It could be that the PNP transistor you added could be adding too much gain and causing the regulator circuit to become unstable. But this shouldn't destroy any decent meter.ie: If you put a multimeter across the car battery when the engine is running does the voltage sit at a steady voltage of around 14.2V or so? Or is it fluctuating all over the place?As long as the battery is in reasonable shape (If the car starts) then it should filter out most of the generator hash. Any quality device designed to be powered from a car's 12V system should be fine with this level of noise. But an intermittent connection between the battery's negative terminal and ground, could cause problems after the engine starts when vibration causes the battery to get intermittently disconnected.

author: floobydust
author_rank: Super Contributor
timestamp: February 22, 2024, 02:38:59 am
content: The chinese voltmeter modules (did you delete the URL?) i.e. LED 3-digit 0.28" I have use a ME6203 voltage regulator+ series '5819 Schottky diode S4.Which gives a ballpark +36V/-40V transient rating, not tough enough for an older car IMHO.The vehicle will have dirty, noisy power. It's the ignition system, it's the dynamo brushes arcing.Capacitors can help (at the noise source) but transient overvoltages are always happening. I dislike adding a lot of parts to vintage vehicles.I did read Dr. Hugo Holden's work with the the Bosch 30019/Lucas RB106. I don't know it's voltage limits, the MJ2955 is rated 60V which is likely the limit for transient tolerance.If you want to run electronics, cell phone charger etc. in the car I would (at the cig lighter) put in a very big TVS to clamp surge voltages likeSM8A27which is commonly used in automotive ECU's. Then you will not damage things. It clamps to around 27V max. Add capacitors - at the coil power and dynamo if possible.For radio (mainly AM) reception, resistance spark plugs or wire are used. I think you have shielded wiring for that.Check you have both grounds proper. Battery(-) high current to engine block for the starter motor/dynamo, as well as battery(-) to vehicle frame/chassis. Two wires. I wonder what the voltage regulator ground point is. If it's on the firewall, then that is not the engine block, you get a different potential depending on lighting loads (headlights, brake lights) as they are grounded to the chassis. Electrical noise could also make the voltage regulator act a bit weird. I'd have to find a Bosch schematic but assume it's got filtering.

author: Stray Electron
author_rank: Super Contributor
timestamp: February 22, 2024, 04:23:53 pm
content: Quote from: rmhc on February 21, 2024, 08:06:53 pmWhoo! Nice ride! Yeah, the electrical system looks like the ones that I dealt with in my 1950s MGs. I agree with what some of the other's have already said, about not wanting to make too many modifications to an antique car. That said, the used to make capacitors in metal cans that had a tab on them and that could be bolted to the outside of the dynamo (or other places) and the wire lead could be attached to the dynamo output and they would dampen those voltage spikes. I don't know if those are still available or not. I have some NOS ones here but it sounds like you're in the UK so shipping would be prohibitive. "Generator Whine" as it was called in the US was always tough to deal with and some people make elaborate noise filters using multiple stage filter sections chokes and capacitors. The filter design is really the same as the filter used in the old transformer based DC power supplies. It's just a very low pass filter designed to remove as much of the high frequency electrical noise as possible.Oh, I guess I should point out that they do still make absurd looking automotive noise filters for the Audio-Phool crowd. I saw one a couple of years ago that had six LARGE capacitors tied together with flashy looking gold plated bus bars and a built in DC voltmeter on it. I think the owner told be that they sold for about $200. But you don't need anything like that.But to your case, yes, I think your meter probably died pretty much on it's own. There may be some "high" voltage spikes getting to it trough the electrical system but as I said, any decent meter should be internally protected up to 100 to 200 volts and you shouldn't have any spikes of anywhere near that voltage.Somebody on here that has more knowledge of that field than I do, might want to suggest some sort of MOV that you can install at your power outlet that will guarantee that no electrical spikes exceed 16 or so volts. That should completely protect any electrical item that you use in the car. I'm assuming that your car has typical 12 VDC electrical system with the negative side grounded to the chassis, but let me know if that's not the case. A lot of American cars of that age run on 6 VDC and some were positive grounded.Are far as your ignition wires go, Do you have a radio in the car that you're trying to use when the car is running? If not, then I wouldn't worry about the radiated RF noise. When I did have a radio in my old cars, I used a short piece of the resistive spark plug lead between the ignition coil and the distributor and used solid metal wires from the distributor to the spark plugs. That worked just as well as using all resistive wire and the wires lasted much longer.

author: rmhc
author_rank: Newbie
timestamp: February 22, 2024, 10:16:31 pm
content: Floobydust,Many thanks for the helpful reply to my problem. I contacted Dr Holden before I built my Voltage Reg. and he was very helpful. Will the TVS you suggested SM8A27 be enough to clean up my dirty 12v. power? I see Vishay have some TVS with clamping V. as high as 500V- 1.5KE400CA for example. How does the SM8A27 connect into the cct? I don't know enough about the subject to feel confident without help from people like yourself.I can get condensers for old time ignition systems easily to put on Dynamo positive and the ignition coil to ground which has been suggested also. I can get behind the dashboard to connect at the ammeter terminals easily which is the main supply wire for the system.I really appreciate your help and I look forward hearing from you again. RMHC.

author: rmhc
author_rank: Newbie
timestamp: February 22, 2024, 10:46:45 pm
content: Stray Electron,Many thanks for your help and suggestions to quiet the noise on the electric system on my old car. I can get condensers that were used on old point style ignition systems and connect 1 to dynamo pos. and to the coil pos. The car is a 12v. negative ground system with the 3 brush Dynamo modified to work with a Bosch regulator. I just wanted the el-cheapo LED voltmeter to monitor the system voltage, and I also want to protect plug in devices such as phone chargers etc. Again many thanks. RMHC.

author: floobydust
author_rank: Super Contributor
timestamp: February 23, 2024, 03:16:46 am
content: As long as the cap's construction and wiring is decent - if they or the wiring to them short, it's a fire from the overcurrent, and they would be located under the hood where it's hot with vibration too. I've never looked for 125°C rated capacitors around 0.2uFSimplest fix, I would just add that very large TVS across the cig lighter jack, with a capacitor. Could use one or two5kWin parallel as well, if the 6.6kW part I mentioned is not to be found. I would consider TP5KP24A.Watch the (cig lighter) fuse isn't crazy big, if the TVS is suppressing large, regular transients for the entire car, it might heat up. They fail short. So 5-10A.

author: Randy222
author_rank: Frequent Contributor
timestamp: February 23, 2024, 04:11:00 pm
content: Quote from: rmhc on February 22, 2024, 10:46:45 pmNot sure how far you want to go to fix such noise issue.Adding extra ground straps between various frame and engine areas, back to a junction near batt gnd, also helps. Adding a 24v ceramic cap right on gen +v output also helps.As for filtering specific lines of power (to radio, to a power jack for cell phone or other), adding DC-DC converters with some filtering before/after can help. On 12v system, dc-dc boost to 24v, add some filtering and feed that to dc-dc buck back down to say 12v, then add some filtering on that output and feed it to your "sensitive" lines. With old vehicle noisy gens, using shielded power lines helps keep EMI out of the wire. In the 5A area, that can fit into a small project box that you mount somewhere.

author: rmhc
author_rank: Newbie
timestamp: March 01, 2024, 07:34:39 pm
content: Hi Floobydust,Many thanks for your very helpful email. I have now got 2. SM8A27 and 2. 5KP6.5 diodes for my old car. I looked at the datasheet for theSM8A27's but could not work out which terminal was positive. Also you said the 5KP5.5 fail short circuit so need to be fused?. Does this apply to the SM8's??? Which should I use at the accessory lighter socket to protect phone chargers etc ? Sorry to bother you like this but my introduction to electronics was over 60 years ago and I am a little rusty!!! RMHC.

author: floobydust
author_rank: Super Contributor
timestamp: March 02, 2024, 12:04:02 am
content: That's a great start with using the big TVS diodes to clamp transients and surges.Always have a fuse upstream in case of any short-circuit. I'm not sure what the cig lighter fuse presently is, but an inline fuse+holder is OK to add and even a few amps is plenty so a 3-5A fuse I use. It would blow if you used a high current load, like an actual cig lighter or tire air compressor though. My Toyota has a 1A fuse quite the joke, skinny wire too.SM8A27fat pad is the anode which connects to ground (-ve). I have just tack soldered them onto the back of the cig lighter jack.The slightly smaller TVS5KPseries the band or stripe end is the cathode which would connect to power (+ve). What part did you get? It should do nothing below around 22V which is a 5KP22A or 5KP24A. Not a 5.0 that is a 6.4-7V part you want it doing nothing with normal voltages on the electrical system.

author: rmhc
author_rank: Newbie
timestamp: March 17, 2024, 12:44:53 am
content: Hi floobydust,First many thanks for your help. I have installed 3. SM8A27's one at the lighter plug to protect phone chargers etc. another at the input to the V. Reg. to protect the MJ2955, and the last at point to protect auxiliary ccts. Is there any benefit in placing 5KP22's in parallel with the SM8's?? The 3 SM8's are fused to prevent problems should they fail. I really appreciate your help. RMHC.

author: floobydust
author_rank: Super Contributor
timestamp: March 17, 2024, 03:23:55 am
content: I think you're well covered. A single SM8A27 is plenty good to protect a load like a cigarette lighter outlet and phone charger etc.It's hard to know how electrically noisy the whole car is. If it's bad, there's lots of hash, SM8A27 can take it but if you see one fail and the fuse blow, then it's time to do more. I don't expect that at all. For the MJ2955, one TVS is good to protect it and both will end up helping protect the car electrical spikes.The two TVS diodes (SM8A27, 5KP22) are a bit different, so when they are in parallel one type can be hogging most of the surge before the other. They don't share that well. I can't see benefit to adding them, it's just that the parts with leads are easier to work with despite slightly lower surge energy rating.Linkto Dr. Hugo Holden's conversion schematic for those following along.

author: amyk
author_rank: Super Contributor
timestamp: March 17, 2024, 05:43:29 am
content: If you're going to fit a voltmeter, I recommend an analog one --- besides being more period-appropriate, it'll naturally filter out the spikes due to its inertia, and be more robust against them too.

author: MarkT
author_rank: Frequent Contributor
timestamp: March 17, 2024, 09:55:50 am
content: Ironically you'd chosen the only type of voltage measuring device that could be damaged by automotive electronics - a multimeter is definitely the way to go, these have lots of series resistance to protect themselves and are self-powered by a battery (although some analog one's need no power).The unit you used is powered from the thing its measuring and a large spike on that will/did kill it.My multimeter is rated category III, that's never going to suffer in a vehicle as 600V isn't going to happen... Note that analog meters can be damaged if on the wrong setting, a digital multimeter with a fast bargraph as well as digital display is perhaps the best compromize for robustness and utility.With a multimeter you do have to be careful about measuring voltage after measuring current - make sure you have the leads in the correct socket before measuring voltage...

author: floobydust
author_rank: Super Contributor
timestamp: March 18, 2024, 01:10:15 am
content: Actually a cheapola Aliexpress digital voltmeter should survive the smaller transients now, until you get confidence the charging system is OK. Or maybe the CHG lamp is enough.Some of the Smiths or VDO gauges are really nice I do miss those in modern cars. I'm out west and snow is forecast. No vintage auto's on the roads for a while yet.

author: rmhc
author_rank: Newbie
timestamp: March 26, 2024, 03:58:33 pm
content: Hi floobydust,I have the SM8's installed in 3 places and the el cheapo digital voltmeter is still alive, Thanks to you.Do you know of a small- 1 1/2"- analog voltmeter I could use, I prefer it to the digital . I have looked at Ebay and other places but they are all 2 inches diameter. Once again many thanks for your timely suggestions, RMHC.

author: floobydust
author_rank: Super Contributor
timestamp: March 26, 2024, 08:20:47 pm
content: I think you are covered, it's based on my experience to add the big TVS as you have as basic transient coverage. If I'm wrong let me know here. Next level is adding filtering - capacitors, maybe a choke.I have looked at analog automotive gauges for voltage and wasn't happy with them.Most have a useless, huge scale like 8-18V. One volt is enough difference between good and trouble I think.Even at 10V the lead-acid battery is 99% dead, so no need to go down to 8V. In terrible cold -35°C/-31°F I have seen 15.5V as normal charging voltage. My multimeter collapsed, nervous breakdown after boosting that Jeep, hands froze lol. At 18V your battery is boiling over at best. I think 10-16V span is better.Decent, smaller than 2"/52mm gauges I have not seen. Even big brands likeAutometerare shit with 8-18V span, as if their designers have never driven a car. You can't glance and see trouble, pic related smaller 1-1/2" or 38mm but ICK.Smiths, Stewart Warner have some with lower span but still big size.Classic Instrumentslook nice, I'd hit them up.