Want to understand car behavior with kaput battery

I wanted to see if I could rejuvenate a battery that's dead and several years old but never saw much use. Sat in a car that mostly sits in the garage.

I stuck it in my '89 Toyota Cressida, cleaned the terminals on the battery and the cable ends, hooked them up and jumped it with the good battery. Car fired after a sluggish crank and ran but it idled high and the idle never really came down even after the car got warm. Normally when warm it idles around 600 RPM in gear. With this hinky battery it would idle in gear around 1000 and about 1500 in neutral. Also noticed the lights flicker from time to time.

After running around for about 15 mins, turned it off, no restart. Not even enough juice to get a grunt out of the starter. Okay, clearly the battery is beyond salvaging. Put the good battery back in, everything back to normal.

So - why was I seeing the symptoms I was seeing with that DOA battery in place?

Thanks

Reply to
brassplyer
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That battery is probably shorted internally and your lucky it didn't just blow up or burn out the regulator and alternator.

The battery being shorted would max out the alternator which doesn't leave a lot of power for anything else. None of the computer items would have been seeing the correct voltage which is why it didn't run right.

Normal car batteries can handle about one time going completely dead and being recharged, IF they get charged real soon. Let them set around and they sulfate up and short internally, then you have a doorstop.

Reply to
Steve W.

what he said.

furthermore, you should never try to charge a battery in this way for the reasons steve states, particularly if its condition is "unknown". use a proper regulated charger, then test the "charged" battery with a high draw load tester. if it passes that test, /then/ you can put it in a car.

Reply to
jim beam

for $20, it's crazy not to have one.

Reply to
jim beam

You would need to place a voltmeter on the battery to see what was going on. But a battery with a low charge could drag down the car's voltage...

That would be like a large electrical load to the car computer. And the computer would run the car at high RPM's to generate more electricity.

Car computers are also designed to increase RPMs when there loads like A/C or the engine is cold.

As for charging a low battery, that can take 24 hours with a battery charger. If it is too low, some chargers will not turn on. You can get a charger to start charging by jumping the battery with another battery.

A battery which is 12.75 volts with the charger removed is fully charged. And if it holds that charge overnight without the charger connected, then the battery is holding a charge.

I don't think that battery could be recharged if it was totally dead though?

Reply to
Bill

incorrect - open circuit voltage tells you nothing about battery health.

incorrect - open circuit voltage tells you nothing about battery health.

incorrect - open circuit voltage tells you nothing about battery health.

i don't understand - if you don't know this stuff, and you clearly don't, why do you "answer"? as questions about /why/, sure, but "answer"???

Reply to
jim beam

given the symptoms dead and won't take any charge at all been sitting for a long time

I'd vote for serious sulphation instead of shorted. You're lucky you didn't blow up some electronics with high peak voltage out of the alternator without battery buffering the average.

Reply to
mike

You need a new battery as well as new tires (spare included) you may have damaged the alternator.

Reply to
NotMe

My guess would be opposite that of Steve. The battery had very little to no conductance or damping of the alternator output. A good battery acts somewhat as a capacitor and stabilizes the alternator output. It would be similar to starting your car then taking off a battery cable. Watch your lights flicker and electronics go poof due to high voltage.

Reply to
Paul in Houston TX

Odd stuff can happen to the ECM when voltage is not optimal. If it runs well with the good battery I would not lose a lot of sleep over it.

nate

Reply to
Nate Nagel

ok, so here's a fuller explanation of why open circuit voltage readings are not a measure of battery health.

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that is the basic electrolytic cell that is in a battery. the voltage measured between the two electrodes is a function of the two different materials used for anode and cathode [lead and lead oxide respectively].

ok, good so far - we have our electrodes in electrolyte, and we can measure a voltage. now what? we need to be able to draw current!

current is a function of the area of the electrodes, not their material. two electrodes of 20ga wire produce the same voltage as two plate electrodes of 10 sq ft. but the current each will produce is many orders of magnitude different.

with these points sorted, how is this relevant to testing a car battery?

as a battery ages, or is abused, the electrodes can decay or their surfaces degrade, and this /effectively reduces their surface area/. the materials are still basically the same [surface chemistry aside], so they can still produce the same voltage. but as the surface gets pitted, sulfated, etc., the active areas reduce, and thus their current capacity reduces.

thus, the only effective measure of a battery's health, is to see if it can sustain a voltage while under heavy current draw. if it can, its active surface areas are either wholly or mostly healthy. as current draw drops, the active surface areas have reduced. eventually the battery is unable to produce sufficient current to do its job and needs to be replaced.

to summarize, measuring open circuit voltage is a complete and misleading waste of time. to anyone tempted to repeat the bizarre and underinformed usenet myths about different open circuit measurement protocols, no matter how well intentioned, please don't.

Reply to
jim beam

My two cents, get one of these gizmos and don't lose it. You will find it most useful and easy to use when messing with car batteries and charging systems.

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Reply to
Mr. Austerity

Nate Nagel wrote in news: snipped-for-privacy@news1.newsguy.com:

Agree.

Devices that operate at logic voltages are often very sensitive to voltage levels. Below a certain threshold, they may operate, but not correctly. I guess that's a characteristic of semiconductors.

Plus, if power is very briefly interrupted, the device may also continue operating, but that slight gap in power delivery can cause the logic circuits to lose or change some of their states, and get "confused". The device then exhibits odd behavior which is corrected on a reboot.

Reply to
Tegger

whoa whoa whoa. that is so fundamentally not true, you have no idea. the whole point of "logic voltages" is that they're /insensitive/ to voltage levels other than those sufficient to switch them. i.e., they're /not/ sensitive to noise in the way analogs are. that's why we use them.

don't guess and then misinform.

you're just guessing.

Reply to
jim beam

Probably noise.

If you want to try charging a battery, on slow charge, give it at least a week. It will work, or work not. In any case, it will be poor.

Greg

Reply to
gregz

some of the newer fancier chargers, e.g. ctek, have a "Recondition" mode. It may or may not work. If this is a one time deal it may not be worth the price of the charger to avoid replacing the battery. (I bought one because I am trying an AGM battery in my Jeep rather than a conventional one, and that was the charger recommended by the manufacturer. If you'd seen the acid all over the place when I bought it, you'd understand. Kudos to the Jeep engineers for providing a plastic tray with a drain that went through the inner fender; I still had to replace all the cables though.)

nate

Reply to
Nate Nagel

Tegger said

These two statements are true for simple logic IC's but not for engine controllers.

Engine controllers are designed for hideously noisy environments.

They monitor the battery voltage and reset before entering a voltage where they cannot operate. Further, they are designed for brief interruptions of voltage.

This is not so say a vehicle will not do some odd things under low system voltages. Even graceful entering/exiting a reset state can cause some weird things.

Reply to
Homer.Simpson

First, I use a 0 - 60V regulated supply having a adjustable constant current output. In the case of an automotive battery that is NOT sulphated, regardless of what the terminal voltage is I would adjust the power supply voltage output to around 20V. Then I set the current at about 2A. I connect the supply and it's terminal voltage is then equal to the battery voltage. Over a 14 hour period as the terminal voltage comes up the supply will produce a constant 2A into the battery. At the end of the 14 hours a good battery will read about

13.50V. If at this time the battery reads 12V or less there is a dead cell, and unless you feel like cutting it open and doing surgery, (I knew a guy that used to do this), it's junk.

For those who like to tinker with things, you can sometimes "rejuvenate a sulphated battery. I've done this and actually gotten them to work again. You can tell very quickly if a battery is sulphated because it behaves like an open circuit. That is when connected across a power supply, no matter how high you raise the voltage the battery will not draw any current. In the case of a sulphated automotive battery, I would set the supply voltage to 60V and set the current for about 1A. Initially you won't see anything happen. If this "Frankenstein battery" will in fact rise from the dead, after awhile you may start to see the current meter start deflecting sporadically. At first these might be very small deflections. The deflections may get bigger and with them you may notice the supply voltage meter reading drop along with the current spikes. That would be the suphation breaking up and the battery starting to draw charging current. If all cells rejuvenate you will see a final terminal voltage of around 13.5V after a day or so. If not it's worth about 4.00 as scrap.

This is relatively safe if you keep the current low. However, I would do this outside away from people and pets. Keep in mind that this does not always work and all cells may not come back. And even if they do there's no way to predict how much electrode material is actually being revived. But it's an interesting experiment. Lenny

Reply to
klem kedidelhopper

That's what I was thinking - resetting to baseline settings without having a chance to "learn" the vehicle's particular sensors and how the engine responds to them.

nate

Reply to
N8N

while the constant current is good, smooth regulated d.c. is terrible for charging vehicle batteries. it can cause [dendritic] spikes to grow perpendicular to the plate surface, and if they grow far enough to touch, game over.

the best charging current is half rectified a.c. since that breaks up the spiking effect. and in fact, that's what "desulfating" chargers do

- they "noise" the charging current with up to 2MHz to disrupt the spikes, and if you're lucky, re-dissolve them.

Reply to
jim beam

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