phantom battery drain / alternator question

[btoran]

over the winter i was working on my spider in my garage and accidentally left the fuel pump on for a few hours. next day, battery was dead so i trickle charged it back to 13.5 volts. i have been driving the car short distances this spring without any problems, until this past weekend.

this weekend i took the car for a 45 drive to an autoparts store to pick up gear oil and i again forgot to turn off the fuel pump. this time, it could not have been running for more than 10 mins while i was in the store. when i came out, the car wouldn't start, no juice at all. the autoparts store lent me a battery booster thing and it fired right up and i drove it right home.

at home, i checked voltage at the battery with a multimeter and found 10.3 volts, so i trickle charged it over night and it came back up to 13.5 volts. i then left the car alone for 24 hours and checked with the voltmeter at different times during the day and noticed a slow voltage leak. within a 24 hour period, voltage dropped to 12.8.

the car started up and i took it out for about 20 mins of spirited driving at high revs. when i got back, i checked voltage again and it dropped to 12.6 volts.

i'm not sure how old the battery is. it came with the car when i bought it last summer. is this as simple as needing to replace the battery or might there be another problem? My shop installed mark's 95 amp alternator, and i'm concerned they may not have connected it properly. how do i tell if it is connected and working properly? if i rev the car while it's sitting in the driveway, should i notice an increase in voltage at the battery?

[spidernut]

Have your battery load tested. Most places will do it for free. It may be at the end of its life cycle and just need to be replaced.

[wizard124]

With the car running, check the out put of the alternator. The big bolt with the heavy wires attached should read 13-14 volts, you should have about the same reading at the battery. Assuming the alternator has an internal voltage regulator.

As for a possible battery drain. I would compare the battery voltage or drop over a period time. Then disconnect a terminal and compare how the battery voltage holds.

Why not wire the fuel pump through the ignition switch so you you wont have to remember to switch it off?

[btoran]

thanks guys. i'll check alternator output and test the battery myself (disconnected from car) and then at a service station.

[So Cal Mark]

the red warning light should be on with the key on/engine off, then extinguish with the engine running. The warning light circuit is used to excite the alternator, so if it doesn't light then the unit is not energized

[majicwrench]

THe battery SHOULD read 12.6 volts fully charged, and will slowly drop to that reading no matter how hard you charge it. Seeing it drop back to 12.6 over time is normal and fine.
First thing you need to do is wire your pump properly.

Test charging system. Check battery volt sitting, should be 12.6v or close. Start car, rev engine a bit. Voltage should go up, 13-15volts. Turn a few lights on, voltage should stay up, 13-15v.
If voltage does not come up, you have a problem. Could be as simple as loose belt.

When you drove home and volt was 10.3, this is not good, it indicates that charging system not working. Check as above.

[spider2081]

Most parts stores sell a volt meter that plugs into the cigar lighter. Some of them even check alternator diodes. Usually less than $15

[btoran]

so i ran some tests. when i got home i checked the battery and it was steady at 12.7 volts. then i turned the car on and set the throttle, which revs the engine and voltage DROPPED to 12.35 volts. i turned the car off and the car read 12.5 volts.

me thinks the alternator is running in reverse, sucking volts from the battery. i wouldn't put it past the shop to have mis-wired it. here's a picture of the connections. does anything look wrong?

[majicwrench]

Good job on the testing. The alt is not "running in reverse" it just isn't working. When you have the engine running, the various electrical items are drawing current, thus you see the volt drop. If you were to continue running like that, battery would go dead.
Mark pointed out the first thing.....the alt/battery light on dash should come on when you turn key on, before starting car. Then it should go out once car running. Does it??

[btoran]

the light at the bottom of the tach is red when i turn the ignition key one click and then goes out when the car is running.

i'm thinking either:

a) the shop wired the alternator incorrectly. is there any way to tell from the picture if it connected properly or since the light is working, should i assume it is connected correctly?

b) the alternator is defective. this is possible, but unlikely in my opinion. is there any way i can test the alternator output somewhere other than at the battery? perhaps at the alternator itself? if so, where and how?

b) if A and B check out ok, it would seem there's an issue with the car wiring itself. without running all new wiring, is there any way to test this?

[majicwrench]

Mark may be able to tell from pic, I do not know how his alt wires in.
You can test alt output at large terminal on back of alt. It should read basicly the same as the battery, engine running or not.
Belt has to be tight enough. Can you put a socket on alt pulley bolt and spin alt without engine turning?? (engine off of course:)

This is my minor pet peeve with all this aftermarket "stuff", it gets crappy install job, testing becomes more difficult, (who knows how that is supposed to wire in??) then folks wonder why they have issues. The stock stuff works well, and I can look up specs, wiring diagrams etc etc and know exactly how it works and how to fix it should it fail.

Done with my little gripe. Let us know.

[btoran]

majicwrench - thanks. can you point out on the photo where to test output on the alternator? Thanks.

mark - can you pls check the pic to see if the wiring is correct and if not, can you let me know how the wiring should be? thanks.

[majicwrench]

You should have one, larger terminal on back of alternator. LIkely the large black wires in the lower part of pic go to this terminal.

[btoran]

update: i spoke to mark and it seems the cables are connected properly. i removed the black rubber boot covering the large terminal on the back of the alternator and tested output there, which was 14.51 volts. i then checked at the battery and got a very similar reading (14.5 vs 14.51 volts).

it seems the alternator is putting out the correct voltage and the voltage is getting to the battery, so what changed?

it may be that removing the rubber boot shifted a cable around for the better. i'll double check all the connections and re-test over the next few days. i'll also take the battery in for a test, just for giggles.

thanks much to majicwrench for his suggestions and to mark, who was very patient as i ran a few tests while we were on the phone together. great customer service and support.

[manoa matt]

They say most electrical problems are ground related. Check the battery negative/ground wire connection to the body, it should be clean and tight. If the ground wire is not good, the alternator tests that it is charging the battery, but it will not. On almost every spider I work on the original green cable has shrunken and pulled back insulation around the terminal ends. The twisted copper wiring is usually semi-untwisted and shows signs of corrosion. Replacement ground cables are available at any autoparts store for about $6. I generally don't advocate throwing money and parts at the problem until its properly diagnosed, however for the small price, replacing that cable makes sense.