I agree that removing either of the battery leads would serve his intent.
If I were going to do this, I would also turn on the high beams and any
other large resistive loads I could.
In my mind this would serve two goals:
Make sure the that the alternator is doing more than putting out an amp
or two,
and provide a way to minimize the spike you could get.
The spike would come from the alternator as it adapts from supplying a
large current to charge the battery to the lower draw of an engine at
idle. Without the battery in the circuit to absorb this, you can get a
large voltage spike.
Despite the alternator manufactures' warnings, what is being proposed is
regularly done in race cars with cheap battery cut off switches.
Eric Schieb
On 6/26/2011 4:12 PM, Larry Alster wrote:
I think Lloyd means taking the negative off the battery so the car is
running on the alternator only and not drawing from the battery.
Larry Alster
91 Miata White Knight
92 Miata Silver Bullet
92 Miata Honey B
04 MSM MX-5 Whooosh
06 WRX STi Subie
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Eric Schieb
Sent: Sunday, June 26, 2011 3:07 PM
To: [email protected]
Subject: Re: Checking alternator?
Which cable is the "negative cable"?
I suspect on a '91 that there is
a large positive output wire headed to the battery,
a small wire to energize the field in the alternator,
and a small wire to run the lamp on the dash.
The ground is handled through the frame of the alternator.
Alternator manufacturers typically DO NOT recommend disconnecting the
large wire while the engine is running. They typically talk about
voltage spikes damaging things.
Can you put a volt meter on the output wire? If you are getting voltage
levels above what the battery was at before starting the car, the
alternator is outputting something.
However, this is based on experience with alternators of that period and
not specific Miata knowledge.
Eric Schieb
On 6/26/2011 3:52 PM, Lloyd Broussard wrote:
I think my alternator is going out. Will removing the negative cable while
the engine running tell me if it's putting out juice. I know this is
really
old school, but it's a quick check.
The car is a '91 with a Link computer.
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