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05-04-2005, 20:00

Ralph D. wrote:

> <HLS@nospam.nix> wrote in message
> news:qosde.218$1o3.136@newssvr12.news.prodigy.com. ..
>
>>"Ralph D." <not@anytime.com> wrote in message
>>news:I-KdnQCBq7Qw3ujfRVn-2A@giganews.com...
>>
>>
>>>Yup. Even went so far as to put a set of adapters on to change the side
>>>terminals to posts on it after using my twister brush on the posts.
>>
>>Actually
>>
>>>like it better that way and will go with them when done.
>>>
>>
>>I seem to remember that the ECM on some of those earlier cars were very
>>sensitive to voltage levels, and I suspect you may have experienced this.
>>
>>
>
>
> So... here's an interesting thing I thought about along these lines:
>
> Used to be that we just disconnected a battery terminal after a jump to see
> if the issue was the battery or regulator/charging. Of course they now say
> not to do that as it messes with the computer, so... If the car is running
> off of the battery and the battery dies, how is that any different from
> disconnecting it?

If its running and the battery "dies," the battery is still there acting
as a big somewhat inert resistor/weak battery in the circuit. It can
still damp out any rapid variaitons in voltage and stabilize the system.
When you pull a terminal connection off with the engine running, you're
basically running the alternator into an open circuit apart from the
small loads that may or may not be running (ignition system, etc.) The
alternator and voltage regulator need more damping in the system in
order to produce a stable voltage, and without the battery there to
serve as the damper the voltage may swing very high and low. It was
actually bad to do that test even 20+ years before computers, because it
can easily blow the diodes in alternators. It was reasonably safe to do
when cars had generators and vacuum-tube radios, though.

05-04-2005, 20:00	#6 (permalink)
Steve Civilians	Re: 88 2.5 Charging System Ralph D. wrote: > <HLS@nospam.nix> wrote in message > news:qosde.218$1o3.136@newssvr12.news.prodigy.com. .. > >>"Ralph D." <not@anytime.com> wrote in message >>news:I-KdnQCBq7Qw3ujfRVn-2A@giganews.com... >> >> >>>Yup. Even went so far as to put a set of adapters on to change the side >>>terminals to posts on it after using my twister brush on the posts. >> >>Actually >> >>>like it better that way and will go with them when done. >>> >> >>I seem to remember that the ECM on some of those earlier cars were very >>sensitive to voltage levels, and I suspect you may have experienced this. >> >> > > > So... here's an interesting thing I thought about along these lines: > > Used to be that we just disconnected a battery terminal after a jump to see > if the issue was the battery or regulator/charging. Of course they now say > not to do that as it messes with the computer, so... If the car is running > off of the battery and the battery dies, how is that any different from > disconnecting it? If its running and the battery "dies," the battery is still there acting as a big somewhat inert resistor/weak battery in the circuit. It can still damp out any rapid variaitons in voltage and stabilize the system. When you pull a terminal connection off with the engine running, you're basically running the alternator into an open circuit apart from the small loads that may or may not be running (ignition system, etc.) The alternator and voltage regulator need more damping in the system in order to produce a stable voltage, and without the battery there to serve as the damper the voltage may swing very high and low. It was actually bad to do that test even 20+ years before computers, because it can easily blow the diodes in alternators. It was reasonably safe to do when cars had generators and vacuum-tube radios, though.