Want to understand car behavior with kaput battery

brassplyer · 2012-03-23T06:37:14+00:00

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

Mar 23, 2012 27 Replies

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klem kedidelhopper 14 years ago

That is very interesting. I never heard that before about regulated and smooth DC. I just always assumed that (not necessarily regulated), but filtered DC was a "better" DC for all purposes, including battery charging. A properly operating battery acts as a very low impedance device that will clamp the supply voltage to it's terminal voltage. It also acts as a regulator and filter. What you said makes sense though because I've been inside many battery chargers and have never seen any kind of a serious regulator or filter for that matter. I'm curious though, have you ever looked at the output of the alternator circuit on a scope with only a resistive load, and then in normal configuration with the battery as a load? Lenny

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jim beam 14 years ago

page 18.

with battery, it's more smoothed out, as you would expect. with resistive load, it's simply bumpy as you ride the top of what is effectively six phase bumps.

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N8N 14 years ago

yes, basically an alternator output is a little choppy as it (as the name implies) is rectified AC - three phase in most (all? There's got to be an exception, but I'm not aware of it - every alternator I've ever had apart has had six diodes) cases, so there'll be six little pulses per revolution of the alternator. Generators are no better; while they natively produce DC output, it's still not perfectly smooth due to the nature of the beast. The battery does provide some smoothing effect to the voltage of the system.

nate

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gregz 14 years ago

Since an pulsating dc has many voltages, some part of the output would tend to insert charge under varying conditions. I forgot, the battery is sensitive to temperature, and requires different voltages. The battery chip designed long ago, monitored the temp, and adjusted voltage accordingly. This was a highly regulated design. Without measuring temperature, you can still regulate current. I prefer controlling current vs controlling voltage.

Greg

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Ashton Crusher 14 years ago

Interesting info. Do expensive battery chargers (the big kind on wheels) typically have this kind of capability?

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Ashton Crusher 14 years ago

I have one of those but replaced it with a similar one that also has a built in digital voltmeter readout. The second is far more useful. I can leave it plugged into the cig lighter socket and monitor the battery thru the window and read the actual voltage (the display is backlit).

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gregz 14 years ago

A regulated charger is not usually going to charge an old battery. If the battery comes back, it's because there is enough volts to generate current into a high impedance set of cells. Sometimes letting it go for at least a week might bring it back into some kind of condition.

The old battery was essentially no battery, that's why there were problems.

Greg

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