Old car LED headlight issue advice please - Page 1
Forum section: electronics / beginners

author: Prefectfan
author_rank: Newbie
timestamp: April 19, 2024, 10:36:06 am
content: Hello,This is probably a simple to fix but unusual problem. I have an old car, it’s almost 90-year-old and is very basic. It has a generator, which through the use of ancient magic allegedly manages to provide approximately 6 volts and round 10 amps max. There is no voltage regulator as is common on later cars, instead using a movable extra third pickup brush in the generator to control how much current it produces, just how it does this is a complete mystery. There is no other control circuity in the car.In order to see where I was going at night, I fitted a pair of LED headlight bulbs which are many times brighter. But my issue is that even at higher engine speeds they occasionally flicker very noticeably, especially on high beam. As the ammeter is showing a positive value, I’m assuming the LED’s are either picking up RF interference from the ignition as that is just copper wires or more likely the supply from the generator is in fact very choppy, something probably hidden by the old filament bulbs.Also, when I connect my digital meter to the battery to read the voltage, the reading is all over the place and I may fit an analogue voltmeter to the dashboard next month but I’m assuming this is a product of the choppy supply.To solve my problem, I was thinking of fitting a smoothing capacitor to the LED’s but do not know how to calculate what value of capacitor or diode to get. All I know is there is about 6 volts, and the LED is possibly around 3 amps (estimate). I have no idea of the frequency of the choppiness which would be changing anyway with engine speed.I this enough information to suggest a value or do I need more?Thanks, Scott.

author: flaotte
author_rank: Contributor
timestamp: April 19, 2024, 10:55:46 am
content: does it has battery?you can try adding generic 6V battery, that should help with the issue.Setting new power wires from the battery and keeping control with relay will help too.

author: Prefectfan
author_rank: Newbie
timestamp: April 19, 2024, 11:55:46 am
content: Hi, yes it has a 6v lead acid battery for starting as normal. The generator feeds into it when charging.

author: Prefectfan
author_rank: Newbie
timestamp: April 19, 2024, 12:06:19 pm
content: This is the wiring diagram

author: Gyro
author_rank: Super Contributor
timestamp: April 19, 2024, 12:09:47 pm
content: It may be worth checking the brushes and guides on the generator, they may be bouncing. Yes, the thermal mass of filament headlamps would mask this.P.S. The wiring diagram does show a cutout for the generator, it would be worth checking the contact surfaces and spring.

author: CaptDon
author_rank: Super Contributor
timestamp: April 19, 2024, 12:54:13 pm
content: I was not aware that anyone was producing LED car headlamps for use with 6 volts? You could try adding a bulk capacitor at the headlamp switch. Something on the order of 4700uF to perhaps 10,000uF rated at 16vdc. The third brush generator output would normally be smooth except it would have brush / commutator noise. I will look at your drawing for a cutout relay in line with the generator. When the cutout relay is working to control voltage it may pulse and bounce the battery voltage around .5 volts. That may cause some of the flicker. The LED lamp should have constant current regulators which should tolerate voltage fluctuations without flicker. Perhaps the voltage at the bulb is to low for the current regulators to function properly. Can you measure the actual voltage at the lamp? 6 volt systems should run at 7.2 volts at the battery when charging. The voltage at the generator will be a bit higher and the voltage at the accessories a bit lower but you want 7.1 to 7.2 at the battery to maintain a proper charge.

author: xvr
author_rank: Frequent Contributor
timestamp: April 19, 2024, 01:56:01 pm
content: Be aware that huge voltage surge (up to 40V IMHO) in car power net is a very common thing. If you would install any electronics do not forget to add protection circuits or ensue that electronics can withstand that voltage surges.

author: Prefectfan
author_rank: Newbie
timestamp: April 19, 2024, 02:02:10 pm
content: Thanks, those are very interesting reply's. I have cleaned the points on the cutout relay before but have not set it as I didn't really understand what it was doing apart from disconnecting the generator when switched off. I never considered it might be doing anything else like regulating the voltage. I did try to measure the voltage across the battery while charging but my digital meter does not like it, so I think I need to get an old analog one to get a meaningful reading and I'll check what I'm getting at the lamps too. The flashing does seem quite random and quite pronounced so maybe it is related to that relay operating. It did work perfectly once with no flashing at all and I was delighted until I found out the fan belt had fallen off...Oh yes, there is a UK company called classiccarleds who sell them, they have quite a range. I have replaced all the bulbs in my car with them and the current requirement is now about 1/4 of the old bulbs and really bright.

author: CaptDon
author_rank: Super Contributor
timestamp: April 19, 2024, 02:23:27 pm
content: My old 48 international truck had that weird positive ground thing also. Many older vehicles were made that way. I flipped it to negative ground. The starter doesn't care about polarity and the generator was easy to re-polarize. I found out that generators were not specified as positive or negative ground but were polarized during installation often by leaving the fan belt off and jumping the cutout relay to run the generator as a motor for a few seconds. I did also have to switch the polarity of the ignition coil primary leads. It had a + and - terminal. The gauges worked with no modifications, they were King-Seeley hotwire gauges. Also had to reverse the ammeter leads if I recall. I wonder if the cutout relay has some sort of permanent magnetic bias? once the contacts close it seems they would be unable to open since the battery voltage would continue to energize the coil even when the generator came to a stop? Those systems were weird. We had a third brush 6 volt generator on an old Gray Marine flathead 6 cylinder. It never gave any problems. My 48 truck had a more complex regulator with current and voltage regulation as well as a cutout relay. It had 3 relays under the cover and two or three power resistors under the base.