Weird Voltage Readings

[Gc01]

So today and yesterday I started my Yaris Mk1 and I plugged in my FM radio transmitter that tells the voltage of the Battery from the cig lighter port, It usually comes up with 13.9 volts. For the past two days its fluctuated between 12.8 volts and 13.3 volts which is usually. When I use my OBD scanner and record the volts its the same thing but when i look at my multimeter while the car is on it shows at 13.9 or 14 volts when I put the probes on the Battery. so is it a fuse or relay that is damaging. I was worried it was the alternator but I'm not sure.

[Mooly]

Use your meter to measure the voltage at the lighter socket before assuming that anything odd is going on.

[Gc01]

13 hours ago, Mooly said:

Use your meter to measure the voltage at the lighter socket before assuming that anything odd is going on.

So I started the car this morning and I checked the 12V socket and it came up with 13.5. I checked the Battery again and it said 14.04

[furtula]

I would trust the multimeter more than the fm transmitter.

 

[Gc01]

I think it might be a fuse problem

[Mooly]

I doubt you have any problem tbh. The Battery voltage is the absolute and your multimeter readings show it is being charged correctly. The voltage does vary on older alternators depending how hot/cold they are. So its not necassarily an unchanging fixed value. That is deliberate and designed to really hammer a charge into a cold Battery on a cold day. It could be closer to 15.5V under those conditions but soon comes down. It can be as as low as 13.5 or less on a really hot engine and ambient temperature.

The voltage at the socket should be similar to the Battery voltage but having said that it also depends on what current draw is 'tapped off' from the wiring along the way. The dash and other accessories (heater/A/C/Radio etc) may well be on the same feed and so they will pull that voltage down even though the source (the battery terminals) are relatively constant. Any current drawn along the length of a wire cause a volt drop to occur on that wire.    

Does the lighter socket heat up the lighter correctly?

That is a high current consumer (around 10 amps or more) and that would highlight any problem with high resistance fuse/fuse holders/relays and so on.

I think you are worrying over nothing tbh.

 

 

 

[Gc01]

9 minutes ago, Mooly said:

I doubt you have any problem tbh. The battery voltage is the absolute and your multimeter readings show it is being charged correctly. The voltage does vary on older alternators depending how hot/cold they are. So its not necassarily an unchanging fixed value. That is deliberate and designed to really hammer a charge into a cold battery on a cold day. It could be closer to 15.5V under those conditions but soon comes down. It can be as as low as 13.5 or less on a really hot engine and ambient temperature.

The voltage at the socket should be similar to the battery voltage but having said that it also depends on what current draw is 'tapped off' from the wiring along the way. The dash and other accessories (heater/A/C/Radio etc) may well be on the same feed and so they will pull that voltage down even though the source (the battery terminals) are relatively constant. Any current drawn along the length of a wire cause a volt drop to occur on that wire.    

Does the lighter socket heat up the lighter correctly?

That is a high current consumer (around 10 amps or more) and that would highlight any problem with high resistance fuse/fuse holders/relays and so on.

I think you are worrying over nothing tbh.

check out this 

This explains my problems and what could be the problem to it 

[Mooly]

You seem convinced you have a problem somewhere and... and I'm not seeing that based on what has happened so far. You haven't mentioned any actual problems or fuse blowing. Also I would at this point only trust readings from a known good multimeter and what you have shown so far looks pretty normal to me.

If you are still not convinced then you need to approach it logically and that means proving or disproving that the voltage difference between socket and Battery can or can not be accounted for by current draw along that path... and then look at whether the individual current draws of such things as the fuel pump and all the things you mention are correct which is easier said than done.

I genuinely do not think you have a problem.   

 

 

[Gc01]

Oh and I was using the multimeter on the cig lighter and it was showing 13.5

[stantheman1]

If you shine a light into the cigarette lighter chances are that the positive contact point will be tarnished or have slight pit marks due to use, if so that will account for the volt drop due to its resistance.

[Gc01]

I dont use the cig lighter I just use the socket

[stantheman1]

I meant the socket, shine a light into it and see.

[Gc01]

Just now, stantheman1 said:

I meant the socket, shine a light into it and see.

Yeah its clean

[stantheman1]

When I say clean I mean shiny and chrome looking clean as most that I've seen are not otherwise your's must have have little to no use. 

[Gc01]

Just now, stantheman1 said:

When I say clean I mean shiny and chrome looking clean as most that I've seen are not otherwise your's must have have little to no use. 

yea it hasnt been used alot. when my dad bought the car in 2012 the owner plugged out the cable to the 12v socket so we always thought it was broken he didnt use it till 2017 till we tried to fix the radio. And even then he didnt use it much the past year and 4 months the car has been in the drive coz it was getting repaired.