voltage drop?

[wrx884]

Hey just been out crusing round n i was playin with the trip computer trying suss it all out wen i came across the battery reading now it dont seem normal 2 me but mayb im wrong? i know the VT doesnt do this but while driving i was gettin 13.5 -13.6V then wen i stopped at traffic lights on idle it dropped right down 2 11.8V wats causing this? alternator? earths? sound system? crap battery? just wondering wat the voltage should b on idle?

[immortality]

battery voltage shouldbe maintained around 14volts, doesn't matter if it's idling/cruising, load or no load. if oyur worried, check the voltage at the battery first

[PRH]

A lot depends on the load of your accessories,not all alts will keep up at idle.
Phillip

[wrx884]

with the car turned off the battery sits on 12.8V

PRH so u think i need 2 re-wind or get a new or bigger alternator? its a calais so it has all the lighting accessories + running 2 amps and 2 subs but even with them turned off i get that 11.8V reading at idle

[totq]

Your cruising voltage of 13.5-14v or so is correct, but below 12v at idle is not (should be around 13v).

I would suggest your alternator's regulator may be faulty, if so, and if possible just to replace the regulator only, replace it.

To check, take it out and inspect the carbon contacts, if its nearly all worn, then the regulator is finished.

[immortality]

my VN will maintain 14volts at idle with load (high beam, air, rear demister, radio, hazards etc)

as totq mentioned, your regulator is probably stuffed. if the carbon brushes are worn out then have a good look at the slip rings also, they too are probably worn in which case either a rebuilt or new alternator is your best option

[commsirac]

I think you need to specify where you are getting your readings? off the trip computer?
You have measured 12.8V at the battery with a budget multimeter?
What does the multimeter measure across the battery when the motor is idling? at 2000rpm?

Depending on what car we are talking about? the alternator should be capable of providing 14V across the battery at idle, and at least 13V with all your accessories switched on.
At 2000rpm the reading should also be at 14V, no more than 14.4V. If the battery is flat then it will provide a high current load on the alternator and voltage supply can be lower.

Im guessing perhaps that there is only a problem with the voltage readings on the trip computer and where it is measuring that voltage from.

[wrx884]

I think you need to specify where you are getting your readings? off the trip computer?
You have measured 12.8V at the battery with a budget multimeter?
What does the multimeter measure across the battery when the motor is idling? at 2000rpm?

Depending on what car we are talking about? the alternator should be capable of providing 14V across the battery at idle, and at least 13V with all your accessories switched on.
At 2000rpm the reading should also be at 14V, no more than 14.4V. If the battery is flat then it will provide a high current load on the alternator and voltage supply can be lower.

Im guessing perhaps that there is only a problem with the voltage readings on the trip computer and where it is measuring that voltage from.

Its the VP calais... but like i said in the 1st post i was playin with the trip computer so yeah i got those readings while driving.

Wasnt till after i got out of the car and tested the battery switched off it read 12.8V with a mulitmeter. just checked on idle at the battery then its 14.3V weird... so does these mean my cluster is giving false readings? y is it out? i noticed last nite my lights got brighter as i put my foot on the accelerator aswell i assumed that was coz i havent upgrade my grounds in the engine bay tho?

i was drivin 4 a couple hours and was a wamish nite at 24-26 degrees could it b heat related?

[PRH]

Well from what you have said ie 2 amps and 2 subs you may well have low voltage at idle,if its keeping up while your cruising IE 14 volts there is most likely no fault with the regulator,what i would be doing is to place a clamp meter over the battery cables and see just exactly how much all your accessories draw,i know not too many members are gunna have one but take to an auto electrician and ask them to check it for you.
I installed a 130 amp alt in this peanuts car some years ago and he came back whinging that the lights where flickering,i put a volt meter on with the duke box crankin and sure enough away it went even with the engine running at speed the volt meter was dropping to about 10 volts in time with the music !!!!!!!!, had a look in the boot and he had 5 amps and enough crap to run a disco at the MCG,he ended up fitting a bigger battery to ofset the voltage spikes,and i have heard of a vehicle in Adelaide with 2 x 160 amp road handler truck alts to feed his system.
Phillip

[wrx884]

Well from what you have said ie 2 amps and 2 subs you may well have low voltage at idle,if its keeping up while your cruising IE 14 volts there is most likely no fault with the regulator,what i would be doing is to place a clamp meter over the battery cables and see just exactly how much all your accessories draw,i know not too many members are gunna have one but take to an auto electrician and ask them to check it for you.
I installed a 130 amp alt in this peanuts car some years ago and he came back whinging that the lights where flickering,i put a volt meter on with the duke box crankin and sure enough away it went even with the engine running at speed the volt meter was dropping to about 10 volts in time with the music !!!!!!!!, had a look in the boot and he had 5 amps and enough crap to run a disco at the MCG,he ended up fitting a bigger battery to ofset the voltage spikes,and i have heard of a vehicle in Adelaide with 2 x 160 amp road handler truck alts to feed his system.
Phillip

I see where ur goin with that and it makes sense 2 but i did a test 2 see if it would change i turned off my headunit cuttin power 2 the amps and drove around 4 a bit thinkin mayb the alt just needed 2 play catch up? but it didnt seem 2 change the readings.

[wrx884]

edit: double post woops

[commsirac]

Its the VP calais... but like i said in the 1st post i was playin with the trip computer so yeah i got those readings while driving.

Wasnt till after i got out of the car and tested the battery switched off it read 12.8V with a mulitmeter. just checked on idle at the battery then its 14.3V weird... so does these mean my cluster is giving false readings? y is it out? i noticed last nite my lights got brighter as i put my foot on the accelerator aswell i assumed that was coz i havent upgrade my grounds in the engine bay tho??

As suggested previously if you are maintaining 14V at the battery at idle with various accessories switched on there is nothing amiss with your alternator or regulator. Regulators can play up with temperature, after the car has warmed up etc, and you really need to monitor it whilst the car is being driven. If the headlights are flaring with rise in rpm, that means your voltage is fluctuating, this will happen regardless of suspect earths to the lamps which will generally just make the lamps get less voltage then they normally do. So it sounds like there is a problem in the alternator area there or with earthing in the charging circuit or even a battery connection . Does the trip computer reading agree with the reading you got with the multimeter at idle?

If you want to get the total current used by your accessories, you dont have to visit your auto elec. Using the voltage drop at the battery will give you a reasonable value. Here's how to do it. With the motor stopped: Turn the headlights on for 15secs and measure the voltage at the end of the 15secs across the battery. Turn off the headlamps and record what the voltage returns to in 30 Secs. There will probably be a difference of 0.2-3V or so. The headlamps 2 x 55W + parkers + instrument lights will represent a load of ~12 Amps. The amount the voltage drops is directly proportional to the amps being drawn. Repeat the procedure with whatever accessory you want to measure the current of. so if 0.25 V drop represents 12A, then if an item causes a 0.5V drop , that would represent 24Amps etc.

[wrx884]

As suggested previously if you are maintaining 14V at the battery at idle with various accessories switched on there is nothing amiss with your alternator or regulator. Regulators can play up with temperature, after the car has warmed up etc, and you really need to monitor it whilst the car is being driven. If the headlights are flaring with rise in rpm, that means your voltage is fluctuating, this will happen regardless of suspect earths to the lamps which will generally just make the lamps get less voltage then they normally do. So it sounds like there is a problem in the alternator area there or with earthing in the charging circuit or even a battery connection . Does the trip computer reading agree with the reading you got with the multimeter at idle?

If you want to get the total current used by your accessories, you dont have to visit your auto elec. Using the voltage drop at the battery will give you a reasonable value. Here's how to do it. With the motor stopped: Turn the headlights on for 15secs and measure the voltage at the end of the 15secs across the battery. Turn off the headlamps and record what the voltage returns to in 30 Secs. There will probably be a difference of 0.2-3V or so. The headlamps 2 x 55W + parkers + instrument lights will represent a load of ~12 Amps. The amount the voltage drops is directly proportional to the amps being drawn. Repeat the procedure with whatever accessory you want to measure the current of. so if 0.25 V drop represents 12A, then if an item causes a 0.5V drop , that would represent 24Amps etc.

I havent tried these tests yet but b4 i do i wanna ask u somthing i noticed wen i had the car idling in park i was gettin around 13.2-5V as soon as i dropped it into drive it went right down 11.9, 12.2 (thats the gear it was in wen i was driving the other nite) now that was checking off the trip computer. Now u say i should check these from the battery but am i better off gettin a 2nd helper 2 put the car in drive (not park) 2 get the better readings? will/should that make any difference?

[commsirac]

I think you need to establish how accurate the trip computer voltage reading is. Was it the same as the multimeter at idle, is it the same as when you switch on all the accessories etc,......if you are sure its the same, then the readings you are getting when you put it into gear are too low and you have alternator problems. If you can replicate the 11.9V at standstill, should be easy to measure with a multimeter at the battery. Sounds unlikely though as the battery in a state of good charge will probably stay above 12V if its just powering the ingition for a while even if its not getting anything from the alternator.

[PRH]

Ok have you been stuck up with a flat battery at all????????
NO......... THEN DONT WORRY ABOUT IT, as said in the last post who knows how accurate the volt meter in the climate control is and where it senses from.
Phillip

[Just_a_stocker]

If the alternator is good and your battery is good then the amps are probably drawing a bit of current.

Maybe try turnin the sounds off and probe the alternator at idle, should be about 14V.
battery settled should be about 12. 5 - 12.8.

11.8 is a bit low so your battery may need an upgrade (how old is it).

but depends on the load your drawing from it, when it stops at the lights it will not spin as fast hence will not prouduce as much current.

Thing is do a check and see if your alternator is puttin out 14 V or so, if it is then your battery needs an upgrade.
not sayin the current one is stuffed but it might not be able to handle the current your drawing with the amps and things.



cheers

[wrx884]

OK just did a heap of tests on dash and at the battery drove it around how i did that nite with all lights on ect... 2 get it all up 2 tempreture dont know how old the battery is as it was in the car wen bought tho i can tell u its not a known brand name (that i know of)

Apollo maintenence free 520CCA/100RC

On Dash display (No ACC on at idle) second readings at the battery
P: 13.8/13.9
D: 13.5/13.6

With just headlights on
P:13.4/13.7
D:12.2/12.9

All ACC on (lights, aircon, stereo up ect...)
P:10.5/12.4
D 10.5/11.9

At this stage stereo started 2 cut in and out didnt do that b4 so im guessing its the altenator or regulator?

Drove around with 13.8 with no ACC on but sat on 13.5 with all ACC on thats on dash display only tho but tried keepin the idle at 1000RPM and they were bout the same at the battery.

[wrx884]

Ok have you been stuck up with a flat battery at all????????
NO......... THEN DONT WORRY ABOUT IT, as said in the last post who knows how accurate the volt meter in the climate control is and where it senses from.
Phillip

i havent yet been stuck with a flat battery but it has been flat b4 wen my ignition module months ago was stuffed i flattened it doin tests so it had been charged up after that but i wanna try avoid gettin that flat battery if this is the start of it.

[PRH]

Ok cant remember how to get the voltage up on trip puter,give me a reminder and i'll go see what the one does in me ute,i assume your talkin about ya VP,OK
Phillip

[wrx884]

Ok cant remember how to get the voltage up on trip puter,give me a reminder and i'll go see what the one does in me ute,i assume your talkin about ya VP,OK
Phillip

Yes im talkin bout the VP lol hold down mode and reset wen u start ur car, u should see the digital speedo, press mode and it should show u the voltages.

[commsirac]

On Dash display (No ACC on at idle) second readings at the battery
P: 13.8/13.9
D: 13.5/13.6

With just headlights on
P:13.4/13.7
D:12.2/12.9

All ACC on (lights, aircon, stereo up ect...)
P:10.5/12.4
D 10.5/11.9
.

Sorry, cant really offer any suggestions as Im struggling to comprehend what the 8 voltage readings above represent. What is represented by P and D and the two readings next to them. The second readings? battery values are the D values or the numbers after the / sign?

[wrx884]

P= Park
D= Drive

1st reading is the dash reading and the 2nd after the / is from the battery sorry tried 2 make it as simple as i could with out writting a novel

[PRH]

Ok this is what i did,set the trip computer to volts,
run the engine at idle about 750 rpm in drive,
with the headlights on high beam,aircon on high (auto) and the cd playing John Williamson.
Now the volt meter in the dash cluster read 11.9 volts, the multimeter on the battery read 12.6 and the clamp meter read a charge of 1 amp.
Now this sounds about what your getting correct,so in other words put the bloody bonnet down and go out for a drive and forget about it LOL.
P.S dont play with the trip computer any more OK,and remember the old saying a little bit of information can be dangerous.
Phillip

[wrx884]

Ok this is what i did,set the trip computer to volts,
run the engine at idle about 750 rpm in drive,
with the headlights on high beam,aircon on high (auto) and the cd playing John Williamson.
Now the volt meter in the dash cluster read 11.9 volts, the multimeter on the battery read 12.6 and the clamp meter read a charge of 1 amp.
Now this sounds about what your getting correct,so in other words put the bloody bonnet down and go out for a drive and forget about it LOL.
P.S dont play with the trip computer any more OK,and remember the old saying a little bit of information can be dangerous.
Phillip

hahaha i would definatly agree 2 that and no doubt the cluster isnt relaible but after my amps cutting out from not gettin enough power 2 them doesnt make that sound so reasuring lol mayb its thet battery then? mine was droping below 12V (unlike urs) in drive so that explains y they cut out.

Did u drive ur car around 1st 4 bout 10 15 mins and let it get 2 operating temp? thats where i seem 2 notice the changes more.

[Just_a_stocker]

just drive into a battery place they will check it with an instrument for free.
Takes about 30 seconds, then at least you will hav peice of mind.

a seemingly good battery can be bad under heat and current draw

cheers