charging problems

Hello,

Starting late last summer the original battery in my '91 Miata would run
down after a week or so of use, so I got in the habit of leaving it
hooked up to my trickle charger when I wasn't using it. I replaced the
battery, but ran that one down probably three or four times (after the
2nd time or so it was obvious that I had a charging problem). What's
kind of strange is that I tested the output of the alternator using a
voltmeter across the battery terminals and it seemed pretty good, I
can't recall exactly, but think that it was at around 14 V.

I had the alternator checked at my local auto parts store and it wasn't
up to snuff. He said that the alternator could be generating 14 VDC,
but not putting out enough current to charge the battery, which seemed
plausible. I bought a rebuilt alternator and installed it. Then after
several months of use my battery was dead again. I put it on my trickle
charger for a couple days and according to the lights on the charger it
seemed okay.

I had the same autoparts store that I bought the alternator from check
out the output and it was good. The device that he had purported to
measure the output in watts from the battery, so it should be a better
test than just measuring the voltage.

The dude at the autoparts store noticed that my battery terminal was a
bit loose on the post, and felt that that might be my problem. You can
twist it back and forth by hand, but you can't pull it straight off by
hand, not ideal, but I'd think adequate as far as electrical contact goes.

I ran a couple wires from the battery terminals into the passenger
compartment and then drove around with the multimeter hooked into these.
The battery checked out at 12.5 V with everything turned off. When
the engine was running it wa s over 14 V, generally at or above 14.2 V.

I went for a 200 mile trip and it was staying at at or above 14.2 V,
when I stopped it was up to 12.75 V. The next morning it was around
12.75 V. When I drove the 200 miles home the voltage was staying at at
or above 14.2 V, when I stopped it was up to 12.75 V again. I thought
that maybe by letting the car sit for weeks at a time and driving it for
short trips mostly (I use a motorcycle as my main transportation), I had
run down the battery.

I then let my girlfriend use my car for a week and the battery ran down
again. Is my battery toast from having been run down several times and
that's the reason that it won't hold a charge.

The way that I have the battery charger and voltmeter hooked up is that
I have a couple ring connectors under the nuts on the battery terminal
clamp bolts and a short wire crimped to the ring connector. On the
other end of the short length of wire I have a female bullet connector
crimped onto. So when I connect my voltmeter, trickle charger, etc. I'm
going through the battery terminals.

Any ideas?


-Eric

Volts don't charge the battery, amps do. Years ago they used to put
ammeters in cars which was a useful gauge. Then they put in voltmeters
which are pretty much worthless. Same with testing a battery - if you
don't put a draw on it, the voltage means nothing. Charging a Miata
battery incorrectly pretty much toasts it forever. It needs to be slow
charged (2 amps) back to full capacity. As to why it ran down, that
could certainly be the alternator. Do you have an aftermarket alarm
system on the car - they usually create drawdown problems with dark
current. Also, your lose terminal is creating problems you can't
readily see. If it's lose enough to twish, then it's lose enough to
allow corrosion to build up between it and the terminal. Sounds like
you should invest in some new terminal ends, clean the posts well and
put the connectors on so that you can't twist them. At this point, you
may also need yet another battery.

Tom
92 Red

Eric Goforth wrote:
> Hello,
>
> Starting late last summer the original battery in my '91 Miata would run
> down after a week or so of use, so I got in the habit of leaving it
> hooked up to my trickle charger when I wasn't using it. I replaced the
> battery, but ran that one down probably three or four times (after the
> 2nd time or so it was obvious that I had a charging problem). What's
> kind of strange is that I tested the output of the alternator using a
> voltmeter across the battery terminals and it seemed pretty good, I
> can't recall exactly, but think that it was at around 14 V.
>
> I had the alternator checked at my local auto parts store and it wasn't
> up to snuff. He said that the alternator could be generating 14 VDC,
> but not putting out enough current to charge the battery, which seemed
> plausible. I bought a rebuilt alternator and installed it. Then after
> several months of use my battery was dead again. I put it on my trickle
> charger for a couple days and according to the lights on the charger it
> seemed okay.
>
> I had the same autoparts store that I bought the alternator from check
> out the output and it was good. The device that he had purported to
> measure the output in watts from the battery, so it should be a better
> test than just measuring the voltage.
>
> The dude at the autoparts store noticed that my battery terminal was a
> bit loose on the post, and felt that that might be my problem. You can
> twist it back and forth by hand, but you can't pull it straight off by
> hand, not ideal, but I'd think adequate as far as electrical contact goes.
>
> I ran a couple wires from the battery terminals into the passenger
> compartment and then drove around with the multimeter hooked into these.
> The battery checked out at 12.5 V with everything turned off. When the
> engine was running it wa s over 14 V, generally at or above 14.2 V.
>
> I went for a 200 mile trip and it was staying at at or above 14.2 V,
> when I stopped it was up to 12.75 V. The next morning it was around
> 12.75 V. When I drove the 200 miles home the voltage was staying at at
> or above 14.2 V, when I stopped it was up to 12.75 V again. I thought
> that maybe by letting the car sit for weeks at a time and driving it for
> short trips mostly (I use a motorcycle as my main transportation), I had
> run down the battery.
>
> I then let my girlfriend use my car for a week and the battery ran down
> again. Is my battery toast from having been run down several times and
> that's the reason that it won't hold a charge.
>
> The way that I have the battery charger and voltmeter hooked up is that
> I have a couple ring connectors under the nuts on the battery terminal
> clamp bolts and a short wire crimped to the ring connector. On the
> other end of the short length of wire I have a female bullet connector
> crimped onto. So when I connect my voltmeter, trickle charger, etc. I'm
> going through the battery terminals.
>
> Any ideas?
>
>
> -Eric

Killing even a new battery "flat" is not good, and, in my experience, causes
permanent damage - it will never work as good as it should.

Sounds to me like you are familiar with using a DVM - voltages all sound
normal. My guess is you have something draining the battery. Perhaps your
girlfriend is doing something different like leaving the radio on and the
motor off. Another thing to try is pull one wire off the battery and measure
the current draw with an amp meter while the vehicle is just sitting there,
everything turned off. There should be almost zero miliamps. DO NOT try
starting your car with the amp meter (DVM?) hooked up as that will fry the
meter.


"Eric Goforth" > wrote in message
...
> Hello,
>
> Starting late last summer the original battery in my '91 Miata would run
> down after a week or so of use, so I got in the habit of leaving it
> hooked up to my trickle charger when I wasn't using it. I replaced the
> battery, but ran that one down probably three or four times (after the
> 2nd time or so it was obvious that I had a charging problem). What's
> kind of strange is that I tested the output of the alternator using a
> voltmeter across the battery terminals and it seemed pretty good, I
> can't recall exactly, but think that it was at around 14 V.
>
> I had the alternator checked at my local auto parts store and it wasn't
> up to snuff. He said that the alternator could be generating 14 VDC,
> but not putting out enough current to charge the battery, which seemed
> plausible. I bought a rebuilt alternator and installed it. Then after
> several months of use my battery was dead again. I put it on my trickle
> charger for a couple days and according to the lights on the charger it
> seemed okay.
>
> I had the same autoparts store that I bought the alternator from check
> out the output and it was good. The device that he had purported to
> measure the output in watts from the battery, so it should be a better
> test than just measuring the voltage.
>
> The dude at the autoparts store noticed that my battery terminal was a
> bit loose on the post, and felt that that might be my problem. You can
> twist it back and forth by hand, but you can't pull it straight off by
> hand, not ideal, but I'd think adequate as far as electrical contact goes.
>
> I ran a couple wires from the battery terminals into the passenger
> compartment and then drove around with the multimeter hooked into these.
> The battery checked out at 12.5 V with everything turned off. When
> the engine was running it wa s over 14 V, generally at or above 14.2 V.
>
> I went for a 200 mile trip and it was staying at at or above 14.2 V,
> when I stopped it was up to 12.75 V. The next morning it was around
> 12.75 V. When I drove the 200 miles home the voltage was staying at at
> or above 14.2 V, when I stopped it was up to 12.75 V again. I thought
> that maybe by letting the car sit for weeks at a time and driving it for
> short trips mostly (I use a motorcycle as my main transportation), I had
> run down the battery.
>
> I then let my girlfriend use my car for a week and the battery ran down
> again. Is my battery toast from having been run down several times and
> that's the reason that it won't hold a charge.
>
> The way that I have the battery charger and voltmeter hooked up is that
> I have a couple ring connectors under the nuts on the battery terminal
> clamp bolts and a short wire crimped to the ring connector. On the
> other end of the short length of wire I have a female bullet connector
> crimped onto. So when I connect my voltmeter, trickle charger, etc. I'm
> going through the battery terminals.
>
> Any ideas?
>
>
> -Eric