Too much voltage to headlights?
- Thread starter HTMLmopars
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This is good but should not relate to temperature.
So what is going on?
During warm up the alternator is recharging the battery, and its also running at higher rpm (fast idle).
So the question is what voltage is the alternator output when;
a) the battery is recharging
b) the headlights are on
c) just running with no lights or electric accessories.
Also check if voltage of the alternator's output varies with rpm.
See above.
There may be enough resistance in the circuits that causes increasing voltage loss with increasing current through the resistance.
Result is the regulator is seeing a lower voltage.
Regulator then brings the alternator's output voltage up until the regulator sees the right voltage range.
But then the output at the alternator is at significanly higher voltage.
With the relays connecting the headlights almost directly to the alternator's output, they see that high voltage and draw more current.
For limited power supply yes P=I x V
For an alternator Power is usually only maxed out when there is a high demand at idle rpm (slow idle).
With car/truck ammeters, the curent shown is only current to and from the battery.
When higher voltage available to the battery, it will draw more current.
So that is why the ammeter sometimes will show higher charging with higher voltage.
It could be one of two conditions.
When the battery is not fully charged, the higher the resupply voltage the more current it will draw.
When a battery is fully charged but connected to a power supply over 15 Volts current will flow through it anyway. Instead of charging it will cook off the liquid.
If the second is suspected, its worth checking the voltage at the battery terminal while the ammeter is showing charge.
It's really a shame our only choice in some instances are good used OEM parts. They'll dry up one day.
Ya it is a shame. I've been hording good used parts for years to have available for my cars. Nobody makes a decent motor mount these days. Can remember when NAPA was the standard now most of their parts are crap.
Here's an example of how resistance in the output circuit can impact voltage.
The battery state of charge is low. That's why its drawing 20 amps at 13.9 V.
If/when the battery is fully charged, the alternator only has to power the ignition. That's only a few amps even with electronic igntion.
Lets say its 5 amps.
So that's 5 amps through the resistance in the output line.
V=I x R
V = 5 amps x .06 ohms
V = .3 Volts
Everything works like normal until the lights and other stuff is turned on...
A somewhat similar situations would be if there is resistance after the main splice, either on the battery feed or the feed to the key switch and ignition.
Bottom line is to check the voltage and the ammeter under the conditions suggested in my previous post. That will show if its an overvoltage problem.
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67Dart273
Well-Known Member
Actually some regulators ARE sensitive to temperature, and the flat 70/ later one is temp compensated
65-440
Well-Known Member
Any progress on this? I just changed the headlamps on my 70 dart for the 3rd time since installing a relay harness. When it happens both low beams go out at the same time. Charge voltage is good, a bit low at idle but mid 14's at cruising speed. Whats the absolute max voltage these sealed beams can handle before they blow? I imagine it's a bit north of 15v!
Or if the regulator is not properly grounded. Or if any of the charging system connections are a bit corroded and causing high resistance. The regulator can sense a false need to charge and will do whatever it takes to satisfy this false demand. I had a poorly grounded regulator on my 66 and it was charging 18 volts, boiled the battery and burned the headlights out when I turned them on.
Red's '72 Dart
Well-Known Member
I got my charging system under control by replacing the field wires. I ran 14 gauge wire from the alternator to the regulator. With a relay powering the circuit. 13.8 volts at idle with no load, 13 volts with full load(all lights and the blower motor running on high). 14.2 volt at cruising speed. I also have a 4 gauge wire for the charge wire going straight to the battery(with a 100 amp circuit breaker).
65Val
Average Length Member
Sounds like you’ve basically created CrackedBack’s workaround either accidently or on purpose.
67Dart273
Well-Known Member
Worth repeating "I guess."
ANY voltage drop in the path between battery and VR will cause overcharge/ over voltage even though the VR is correctly operating.
1....If there is ANY voltage drop between battery NEG post and the VR ground (mounting flange) whatever that drop is will be added to the charging voltage. That amount of drop WILL be affected by other car powered circuits sharing the same ground path. "That is" if say, the only path is a dirty, loose ground jumper between battery NEG clamp and the body, if there is 1/2 volt drop there, then 1/2 volt will be added to the VR set point and the battery will "see" 1/2 volt high from 14 nominal
2...If there is ANY voltage drop in the hot side, each point at which voltage drop is generated ADDS to a total which will cause that overcharge voltage. The path, generally, for stock vehicles is Battery POS post---to starter relay big stud-----fuse link-----bulkhead connector (RED ammeter wire)-----to the ammeter----out on BLACK ammeter wire----to welded spice------to ignition switch connector----through switch---out igntiion switch connector on DARK BLUE "Ign1" run wire-----back out through bulkhead connector---------to ignition ballast and branch off to VR
So add up each separated point, each terminal, the switch connector, the switch, the bulkhead (twice) and so on.
HOW TO CHECK for voltage drop. There are a couple of ways. How I do this:
A....Turn key to "run" with engine off. Stab one probe of voltmeter into top of battery POS post. Connect other probe as close as possible to VR IGN terminal. DO NOT disconnect any wiring. You will read a small voltage, the smaller the batter. Anything over .3V (3/10 of one volt) check into why. Chase it down and find where its coming from. In the case of either connectors or ign switch, IT CAN CHANGE due to changing "bad connection."
B....Ground.......Run engine at fast idle to simulate "low cruise" RPM. Run this check first with all accessories off and again with lights, heater, etc operating. Stab one probe of your meter into top of NEG battery terminal. Stab other probe into the mounting flange of the VR. Again, the less reading the better. Zero would be perfect. If much of anything reads, improve the grounding between battery, block,and body
ANY voltage drop in the path between battery and VR will cause overcharge/ over voltage even though the VR is correctly operating.
1....If there is ANY voltage drop between battery NEG post and the VR ground (mounting flange) whatever that drop is will be added to the charging voltage. That amount of drop WILL be affected by other car powered circuits sharing the same ground path. "That is" if say, the only path is a dirty, loose ground jumper between battery NEG clamp and the body, if there is 1/2 volt drop there, then 1/2 volt will be added to the VR set point and the battery will "see" 1/2 volt high from 14 nominal
2...If there is ANY voltage drop in the hot side, each point at which voltage drop is generated ADDS to a total which will cause that overcharge voltage. The path, generally, for stock vehicles is Battery POS post---to starter relay big stud-----fuse link-----bulkhead connector (RED ammeter wire)-----to the ammeter----out on BLACK ammeter wire----to welded spice------to ignition switch connector----through switch---out igntiion switch connector on DARK BLUE "Ign1" run wire-----back out through bulkhead connector---------to ignition ballast and branch off to VR
So add up each separated point, each terminal, the switch connector, the switch, the bulkhead (twice) and so on.
HOW TO CHECK for voltage drop. There are a couple of ways. How I do this:
A....Turn key to "run" with engine off. Stab one probe of voltmeter into top of battery POS post. Connect other probe as close as possible to VR IGN terminal. DO NOT disconnect any wiring. You will read a small voltage, the smaller the batter. Anything over .3V (3/10 of one volt) check into why. Chase it down and find where its coming from. In the case of either connectors or ign switch, IT CAN CHANGE due to changing "bad connection."
B....Ground.......Run engine at fast idle to simulate "low cruise" RPM. Run this check first with all accessories off and again with lights, heater, etc operating. Stab one probe of your meter into top of NEG battery terminal. Stab other probe into the mounting flange of the VR. Again, the less reading the better. Zero would be perfect. If much of anything reads, improve the grounding between battery, block,and body
BillGrissom
Well-Known Member
I see 14.3 V with engine running in my modern cars, with a cigarette-lighter voltmeter and no cabin loads. Much above that is "too high". I think 13.5 V is acceptable. Insure that the Vreg ground is good, should measure no more than 0.1 V higher than BATT-. Make all measurements w/ black lead on BATT-. Don't rely on the rusty sheet-metal mounting screw at Vreg, but run a solid ground wire. Ditto for all grounds, as later cars did since 1980.
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