voltage drop?

[modmonster2008]

Does anyone know about voltage dropping problems? While i was driving my supra earlier today the battery voltage was above 12 by 2-3 marks, but when i was driving it home, the voltage was below 12 and my radio started to turn on/off and lights are dim, but when i press on the gas the voltage increases, i know the belts and the alternator are new, but i have no idea what the cause for this is, any help would be greatly appreciated, thanks!

 

[benchwarmer]

Get your battery tested, sounds like it's not holding a charge correctly.

 

[modmonster2008]

yeah seems like the right answer, ill get it checked out tomorrow, but if needed replacement, what battery would be recommended for the supra?

 

[AJ'S 88NA]

Check your grounds.

 

[Clip]

the advance auto/autozone batteries will do fine, iirc they're called autocraft and duralast. besides, they've got a good replacement warranty

 

[MrWOT]

Go get 2 heavy duty 2ga (only $2 more than the 4ga) battery cables from autozone that have an avail ring terminal post on them) a length of 4ga bat cable that will reach from your neg bat post to your trans. You will also need some ring connectors that will fit your 4ga cable and your chosen battery terminals. All of these need be connected to uncoated surfaces where they will make good contact.

2 bat cables:

Alt to bat pos
eng block to bat neg

4ga cable

trans to ring terminal bat neg.

That will keep all of your voltages pretty consistant.

 

[modmonster2008]

alrighty thanks!

 

[dumbo]

i would bet its prolly not your bat, check your connections(cables, if in good shape dont go bad overnight). when your car is running your alternator keeps everything powered. and seeing how you step on the gas and lights get brighter... id say alternator (new ones aren't always perfect)

and voltage drops are just that, basically high resistances in the circuit, corroded,dirty,loose terminals.

 

[suprabad]

MkIII's are real sensitive to a bad battery, everything from eratic voltage and charging to hot start issues.

Check the battery first.

 

[SupaMan]

MkIII's are real sensitive to a bad battery, everything from eratic voltage and charging to hot start issues.

Check the battery first.

re-he-he-he-ally? I did not know that. Ive been telling my aunts boyfriend the cars been acting weird since i bought this 'new' battery and its been eratic voltage and having hot start issues. hmmm this just backs up my point he just thinks im paranoid but i know my car. :biglaugh:


im sure everybody has said it but ground wires are important i plan on replacing mine pretty soon their the originals and im not takin any chances.

 

[Nick M]

Get your battery tested, sounds like it's not holding a charge correctly.

Considering that batteries don't hold a charge ever, that doesn't mean much. They are either discharging or charging, the rate changes with load and charge.

 

[benchwarmer]

Considering that batteries don't hold a charge ever, that doesn't mean much. They are either discharging or charging, the rate changes with load and charge.

When a battery fails the internal resistance exceeds its capability to chemically separate charges and you experience a voltage drop. Since this statement is nearly meaningless to the majority of people, the phrase "you're battery is not holding a charge" is as valid a way to say your battery is going bad as any other.

 

[dumbo]

MkIII's are real sensitive to a bad battery, everything from eratic voltage and charging to hot start issues.

Check the battery first.

weird, please continue, do you konw what makes them so sensitive?? ecu?? i cant see why a battery not taking a charge could effect lights, stero, and voltmeter with the engine running? the alternator powers all those things.

 

[Nick M]

When a battery fails the internal resistance exceeds its capability to chemically separate charges and you experience a voltage drop. Since this statement is nearly meaningless to the majority of people, the phrase "you're battery is not holding a charge" is as valid a way to say your battery is going bad as any other.

So sulfating is your explination to "not holding a charge"? Best just not comment if you can't explain it for somebody.

So you just prefer to pump out bad information rather than explain it? :nono:

That sure helps a lot. Because there isn't any bogus information passed on automotive boards.

 

[modmonster2008]

btw the voltmeter shows 14+ volts if i charge the battery for a week and put it back in, but after a while the voltmeter shows 12 even with the engine running, after a day or so...

 

[dumbo]

btw the voltmeter shows 14+ volts if i charge the battery for a week and put it back in, but after a while the voltmeter shows 12 even with the engine running, after a day or so...

charging your battery for a week seems a little long even for a trickle charge,
and the volt meter will prolly be reading your battery voltage, then as your accesories drain the bat, and the alternator not charging, your voltage drops.

if you got a amp clamp and a multimeter, wait till the voltmeter in your car reads 12volts, check how many volts your alternator read, and see what the amp clamp reads, porolly very low current from the alt to the system.

or if your not sure, just pull your alternator and bat, i think canadian tire can test them both for yah, nice and easy way to know.

 

[Tire Shredder]

a battery has nothing to do with the running state of an engine. once started, you should be able to remove the battery terminals (although, you shouldn't) and the car will still run.

The alternator should be supplying a surpluss of power to run the vehicle's electronics, and giving the leftovers to the battery for storage later (when you blast your stereo, run your seats or start your car later).

now, it sounds to me that your alternator is on it's way out since it drops at lower RPMs so you should keep an eye on it and be prepared to replace it. As mentioned, it's a good idea to upgrade your power and ground wires with some 4 gauge wire. The mk2 supra inheritantly has low charge levels at idle when the cars get older, simply because there is a large amount of resistance in the small gauge, corroded wires.