One last question or two tonight for those who subscribe to this theory.
Do you think that if a battery has a CCA of say 500 amps that the battery applies that 500 amps to the starter motor when the key is turned?
If the headlights are turned on a for a few seconds do you think the CCA jumps upward a bit: say to 505, 510, or whatever?
Fiction
Well, here’s the daily stats from the guinea pig. First test this morning and the vehicle has not been started in 2 days so the battery is not at the optimum 12.6 volts.
Battery voltage - 12.24 volts.
Battery voltage after 5 seconds of lights on - 11.81 volts.
Starter current draw (cold engine) 300 amp surge, 185 amps @ 11.8 volts constant.
Second test this evening. (Not quite as cold as the morning)
Battery voltage - 12.51 volts.
Battery voltage after 5 seconds of lights on - 12.08
Starter current draw (cold engine) again, 300 amp surge, 185 amps @ 11.8 volts constant.
Since it’s claimed that turning the lights on warms the battery this amount must fall into the minutae category as my digital thermometer provided the same temp reading to tenth of a degree; and both case and electrolyte were tested before and after the lights were turned on.
(In regards to the current draw of 185 constant keep in mind that is bit high due to a high mileage starter (original) and a cold engine with cold oil. With those 2 factors removed the current draw would likely be in the 125 amps range.)
Someone want to show me where in those stats the “extra power” is coming from?
Keep in mind that the closer that battery gets to 10.2 volts the odds of the starter motor not cranking the engine goes way up.
Those who think turning on the lights aids in starting should consider the more likely possibility of a failing ignition switch. Cold weather can screw around with the contacts inside and one on/off cycle can perform a miracle.
i’m surprised some respondents say that wd-40 doesn’t hurt rubber parts.you do have to be careful with some of those chemical spray products.many years ago,i had a broken/+stuck passenger-side motor mount in a '84 GTI.i used some spray stuff that was supposed to loosen rusted bolts,etc.it ate right through the rubber center of the mount,and i was left with the rusted steel cylinder seized in the mount’s sleeve.boy was that ever a pain to remove!
Doesn’t the car automatically shut the lights off as you crank the engine? Doesn’t the car automatically shut off all electrical accessories when you turn the key? If this is the case, why would it matter whether the lights were on or off?
I vote FICTION!
As the originator of this post I must now vote FICTION. Another piece of bad advice from a mechanic,so he said, trying to create more problems for people and more money in the pockets of the dishonest and/or unknowledgeable mechanics. Geewhiz, will the truth ever rise to the top? Thank GOD for the honest mechanics and others who think more of people than money.
Amen !
A few years back, after dark on a summer’s eve, my wife and I were on the way home when we came upon a car stalled at an intersection. So we did the neighborly thing and stopped to help. The other driver reported that the battery seemed fine because the lights and radio worked, but he couldn’t start the engine. The driver did what seemed like common sense: turned everything off and tried to start the engine. After looking the car over under the hood for a bit and verifying that the lights worked and the car wouldn’t start, I suggested turning the lights on and starting the engine. It worked. We saw them to their home nearby and went on our way.
So why turn the lights on and /then/ try to start the engine? I thought that there might be corrosion in the major connections. The starter solenoid circuit would not be enough of a drain to get current flowing through the corrosion layers, which don’t have to be very thick. And if the solenoid couldn’t move, the starter wouldn’t roll over. The lights are a large resistive load, so they don’t depend on anything but a simple circuit. I figured that once current was flowing from the battery, the solenoid would work - which it did! It could have been a fluke, but it worked!
We have a theory shift,Previously the theory of why this worked was that the load of the lights heated the acid in the battery increasing the batterys available current output.
Theory shift,Now the theory is the current demanded by the load (the lights) passing through a corroded or high impedience connection “zaps” this connection restoring it’s low impedience design features.The OHM’s law stuff I am comfortable with,now we need to get the Chemistry and Physic’s Departments involved.
This situation should be able to be duplicated on paper and in the Lab. We must know what our corrosion is made up of and what effect passing current through this “mix” does.
Myself I dont let may cables become corroded or use questionable batterys so I cannot add annecdocal (don’t know about the spelling there) evidience.This type of eviedience is my least favorite.
So does anyone with the chemistry or physics background care to put some effort in this somewhat interesting discussion on this cold Sunday morning? Anyone care to present a lab experiment (in theory) for this situation?
Oh my gosh, oldschool! You’ve got it! It must be quantum physics where an object (usually an electron, or a photon) will suddenly appear at a place removed from where it was a moment before. For the millions of electrons, in a large amperage charge, to do this all a once is unprecedented. Astounding!
Well, I prolly didn’t make myself clear. I’m not proposing an alternative theory for the case posted at the beginning of this thread. I just thought that I’d post an anecdote that showed that turning on the lights and starting the car was not what I’d usually try to do, and propose a theory for why it worked.
I think that you are right and the situation could be duplicated in the lab. I dunno what went on that night in the car; I just reported my theories and the facts. Who knows what really went on under the hood?
But there are precedents for similar behavior. Semiconductors act in a similar fashion. A transistor will not turn on until base current is supplied. A diode will not conduct in the forward direction until the band gap voltage is exceeded. (That’s a simplistic answer, but close enough for what I mean here.)
So maybe there was some corrosion acting as a semiconductor barrier. And maybe there was something else going on with the wiring that night. I’d like to see someone come up with an explanation that would either disprove my theory or show that it is possible.
Exactly what I was getting at.I have no idea where hellokit was comming from with his reply.
Myself, I still consider the situation fiction or myth, but something has to be going on for the myth to have the legs it does.
We usually think of electrical punch-through at much higher voltages. Now, we have a new theory of low voltage punch-through. Man! This is stimulating!
If there’s any benefit to be had by turning on the lights first (which is very doubtful), it’s because you’re heating the battery. Simply trying to start the car would heat the battery a lot quicker, and without draining any energy from it first, as turning on the lights would.
So I call bull—t on this one. Fiction.
The person that came up with this is probably the same person that thinks that hot water will freeze faster than cold water.
The starter draws less if the engine is easy to turn, more if it’s harder to turn. If the engine takes 200-amps to turn it over, the starter draws 200 amps from the batter, whether you have a 500-amp battery or a 2000-amp battery. If you have a big-block V8 on a cold day, and it takes 900 amps to turn it over, and you have an 800 amp battery, it’s going to draw the full 800-amp capacity of the battery and still probably not turn. If you have a 1000 amp battery, it will still only draw 800 amps, taking what it needs.
Just the same as your household circuits being protected by a 20 amp circuit breaker—that 60 watt lamp you plugged in is only going to draw 60W (or around ? of an amp at 120 volts)–it’s not going to use the full 20 amps just because it’s available.
I would guess that the temperature effect (on the battery) of turning your headlights on would be equivalent to holding a candle under it for 30 seconds or whatever time. A few calculations to debunk this theory.
A 700 CCA battery (at 70 F) will have only 436 CCAs at 0 Deg F.
http://www.bgsoflex.com/ccatemp.html
Cold Cranking Amps are typically calculated at 10.5 Volts, or in other words, it?s a measurement of what load to bring the battery down to 10.5 V.
A fully charged battery with no current draw should measure something like 12.7 volts.
Thus the battery (effective) internal resistance is R = E/I = (12.7-10.5) / 436 = 0.005 ohm.
High Beam headlights are usually around 65 watts, so current draw at 12 volts. I = W/E = 65/12 = 5.41 amps.
Two bulbs = 10.82 amps.
With your headlights on, and your battery fully charged, the heat generated (power) will be. Watts = E * I, E = I * R, so Watts = I^2 * R = 10.82^2 * 0.005
Heat generated = 0.59 watts
In 30 seconds, 0.59 * 30 = 17.7 Watt-seconds. = 17.7 Joule
Joule is a standard measurement of energy, and 4.187 Joule will heat 1 gram of water 1 deg C.
Assume battery has roughly equivalent specific heat as water. Don?t know this, but don?t wanna figure it out right now. The answer will tell you that even if I’m off by 50% then it still won’t work.
Assume battery weighs about 20 pounds, = 9072 grams.
With those assumptions, the battery temperature would rise
17.7 / 9072 / 4.187 = 0.000466 Deg. C.
I was wrong, it isn?t the same as holding a candle under your battery, it?s less than that.
Even cranking your engine for 30 seconds wouldn?t significantly warm your battery.
Assume 200 amps cranking current.
200^2 amps * 0.005 ohm = 200 watts
200 watts * 30 seconds = 6000 J
6000 / 9072 / 4.187 = 0.158 Deg C.
I would guess that the temperature effect (on the battery) of turning your headlights on would be equivalent to holding a candle under it for 30 seconds or whatever time…I was wrong, it isn?t the same as holding a candle under your battery, it?s less than that.
I would like to suggest that holding a lit candle under your battery can result in some very unpleasant consequences. Please don’t try this when your battery dies.