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Car voltage spike...
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Posted by: GDG76

My buddy may sell me his old car for me to use as a beater so I don't put so many miles on my new truck.

It's a 91 Dodge Stealth that has 105K miles...he says (and I trust him) that the only issue he has with it is that every so often, the voltage will spike high, cut out the radio for a second and then everything goes back to normal. The car never even stalls.

Any ideas what this could be? From my limited knowledge on cars, I thought the battery regulated voltage spikes. At the price he's willing to sell it to me for, it would be insulting to take it to a mechanic so I'm just willing to accept it if it isn't major. Since it runs well other than that, I'm kinda willing to take my chances...

drew

Posted by: Raj

Could be that something is slack somewhere in the electrical wiring or grounding of some key electrical component.

Posted by: bgreen5

Electrical transients in automotive systems are not uncommon. But voltage spikes where you can immediately "see" effects on instrumentation indicate a problem.

Does he just notice the radio cutting out, or is the effect visible in other areas... like the instrument cluster for example?

If it's just the radio, there might be a problem with the harness/connector to the radio. Or, a loose grounding strap/bolt that is affected by vibration.

If it's happening in other areas (e.g., instrument cluster, A/C system, interior/exterior lighting, etc.), you may have a defective alternator. Does he ever see the gauges ever flutter or dip? Or does he ever notice the interior lighting suddenly increase in intensity when this happens to the radio?

"Normal" vehicle electrical systems typically exhibit a voltage around 12.8V (battery voltage w/ ignition off) or 13.8V with ignition on and alternator up to snuff). The voltage can vary between 9V to 16V depending on the battery state-of-charge and/or condition of the alternator. These are rough numbers, but you get the idea.

Most vehicle electrical and electronics systems are designed to tolerate and function "normally" with voltages in the range of 9V to 16V, and even 19V in some cases. 19V is pretty rare, and represents a failed alternator. Electronic modules are even designed to survive to 24V for several minutes (representing a double-battery jump-start), although normal functionality is generally waived until the voltage returns to normal.

Where am I going with all this... oh yeah...

The voltage regulation these days is built into your alternator. The battery itself acts as a giant capacitor that can compensate for large transient currents, but it's the alternator that keeps the voltage steady (or, tries to, anyway).

There is a phenomenon called "load dump" which occurs when large loads are switched on and off... high current items like headlamps and A/C system, etc. Load dump can also occur if the battery experiences a sudden disconnect (via loose/faulty wiring or terminal connections). This can be as high as 40V to 60V, but is very brief. Again, most electronic modules in automotive systems are designed to withstand this kind of (typically brief) transient.

Bottom line: Check, in this order...

1) Check all cables & connectors running from the battery

2) Get the alternator checked

3) Hope the problem is not buried too deep in some other part of the electrical system

Good luck!

Posted by: retrodog

In other words:

Buy the car and turn the radio off. ;)

:D

Posted by: JYoung

you refer to a Dodge Stealth as a beater? :eek: ;)

Posted by: Uther

The word "spike" is copyrighted by Mr. Spike Lee. You should expect a call from Johnny Cochrane anytime now for your flagrant misappropriation of the word "spike", and it's use without prior written consent. The authorities have been notified.

Posted by: bgreen5

quote:
Originally posted by Uther
The word "spike" is copyrighted by Mr. Spike Lee. You should expect a call from Johnny Cochrane anytime now for your flagrant misappropriation of the word "spike", and it's use without prior written consent. The authorities have been notified.

And I do hope the estate of Spike Jones plans to sue Spike Lee into oblivion.

http://www.geocities.com/SunsetStrip/Palms/1440/spike3.gif

Posted by: GDG76

I expect the paper work from Mr. Lee anyday now. Everyone should expect requests for depositions that you thought of Mr. Lee's name when you read my thread title.

He just recently (within a year) had the alternator replaced. I think that's where the issue is too but both the dealer and the place that installed the alternator can find nothing wrong with it. And it's definitely system wide, not just the radio. I think it's just that the radio doesn't have the proper protection as it was an aftermarket shoddy install. I plan on replacing it with XM anyway so I can fix that.

He's had it in the shop and they never see the issue. Since he's giving it to me for so cheap I'm just gonna take the chance and take it to some different places and get their opinions or start reading up on the electrical system myself and hope the protection is sufficient til I figure it out.

And I guess beater was the wrong word. I'm thinking of buying a house that is about 35 miles from work and I'd rather not put those miles on my new Silverado since i have this cheap alternative.

drew

Posted by: trojanrabbit

You may still get a large voltage spike depending on where the problem is. If there's a load dump/grounding problem deep in the harness away from the battery, the battery will do little to stop it because of the inductance/resistance of the harness.

In a car of that age, I'd start suspecting corroding connectors and/or grounds.