Voltage spiking - battery in boot

[MrOizo]

Hey Peoples.

Been having a few issues with the charging system in the Supra.

A few months ago I was coming back from a trip down the line and the radar is telling me HI VOLTAGE and then shortly after it would turn off and repeat the cycle for about 10 minutes and go right again.

Ken/Kinloud helped me out by swapping the regulators from another alternator thinking this was the problem - this seemed to sort it out.

Today I when I went to go for a drive, I had the same thing happen. It's the first time this has happened since having the regulator swapped out.

Things I should note is I have a blue top gel cell battery in the boot with circuit breaker not far from it - a jaycar 100A one. Since the car had been sitting for a few weeks, the battery went just flat enough to not have enough juice to start the car so jumped it. After jumping it the circuit breaker tripped and the car was running on the alternator alone. It did it again but not too sure what the cause was.


So peoples what could be going on here?? Could the breaker be causing the issues in some way?

Any help and comments much appreciated!!

Cheers

[Malcolm]

have you got any sort of voltmeter on the car? If not then get a multimeter on it and have a look at whether it's actually spiking, or just charging to too high a voltage. On my MR2 the voltage used to reach about 16v because the fuse on the voltage sensing wire to the alternator was blown, so the regulator always thought that voltage was at 0v.

[Akane]

Once I had a dodgey battery, PowerFC read 18v..... very bright headlights too <3 No idea how a 12v can get to 18v+ but shortly after the battery died, put in a new one, sweet ever since.

[MrOizo]

I have the radar detector and the RSM as a volt meter. They both read high and then low when I have the spiking issues.

I started thinking that the battery was on the stuffed side but not sure.

I going to have a look it over today some time.

[MAGN1T]

Throw away your rubbish gel cell and put a proper battery in there. You shouldn't have any more problems.
Modded cars give far more trouble than stock ones. All modifications are a compromise.

Steve

[KwS]

I have the radar detector and the RSM as a volt meter. They both read high and then low when I have the spiking issues.

I started thinking that the battery was on the stuffed side but not sure.

I going to have a look it over today some time.

instead of just 'high' or 'low', get a real multimeter on it and actually see what voltage its spitting out.

[DeeCee]

Throw away your rubbish gel cell and put a proper battery in there. You shouldn't have any more problems.
Modded cars give far more trouble than stock ones. All modifications are a compromise.

Steve

So whats a proper battery then? Gel's are a lot better than a standard lead acid.

[MrOizo]

I have the radar detector and the RSM as a volt meter. They both read high and then low when I have the spiking issues.

I started thinking that the battery was on the stuffed side but not sure.

I going to have a look it over today some time.

instead of just 'high' or 'low', get a real multimeter on it and actually see what voltage its spitting out.

high is 15v and above
low is 10.5 and lower

It's a bit hard to measure when this happens as it's only intermittent. Will keep a multimeter in the car just in case though.

[MrOizo]

Well...

Spent a bit of time trouble shooting today and have found what I think is the 120A jaycar circuit breaker is at fault. With it in, it idles low which results in stalling. When I felt the breaker it was hot and didn't want to stay on. Not sure what's going on there

I took the breaker out and works very nice now.. No spiking or dipping that I could tell

I'll keep having a play to see what else I can find is going on.

A quick check of voltages before showed:
16v and then warning of high voltage
10.5 and then warnings of low voltages

now got a nice 13.8v chur!

[postfach]

What gauge cable are you using? How long is it? A 120A breaker might not be enough, because of the resistance of the cable and the fact that it's probably 4-5m long if it's anything like what I ran in my Soarer, the current draw will be higher than stock.

[MrOizo]

I'm using 35mm^2 welding cable and it's 4-4.5m long. All connectors are soldered in lugs

How does the resistance affect the running of a vehicle?

[postfach]

I have pretty limited knowledge about electronics, but I would imagine that even though the circuit breaker is rated at 120A, that it won't like anywhere near that kind of current flowing through it steadily for a prolonged period of time.

You say the circuit breaker is getting hot and doesn't want to stay on. Heat increases the resistance of copper, lots of resistance = voltage drop, everything starts struggling to work, stall.

35mm² should be fine up to something like 200A continuous at that length, the unknown factor here is the size of the conductor inside the circuit breaker....maybe its very small?

[postfach]

BTW I know it's a hijack, but Steve, I'm not trying to have a go at you mate but a lot of the stuff you post is a little abrasive (not the content itself mostly, but just the way you put it) and I think people would respond to you better if you took the time to explain yourself rather than chucking out short statements with nothing to back them up.

I'm sure you've probably got a whole heap of experience and knowledge, and it's cool that you're willing to share it, but it's a lot more helpful to the rest of us if we understand what you're saying.

[MrOizo]

Oh one thing is that I've had the breaker in the car for just over a year now. Should a fault like this come up earlier?

[Adydas]

CABLE LOAD CURRENT CALCULATION (BASED ON AS/NZS3008.1.2:1998)
____________________________________________________________________________________________________
Value of Volt Drop: 2.5% of 12(V), (0.3V); Route Length of Circuit: 5(m)
35 mm² PAC, PVC, Single Core, Single Phase,
Unenclosed, Touching,
____________________________________________________________________________________________________
Actual Load Current (40°C): 52.2 (A)
Max. Unit Volt Drop of Cable (conductor temp. 75°C): 1.29 (mV/A.m)
Current-Carrying Capacity of Cable: 137 (A)
Reactance (50Hz): 0.101 (ohm/km)
A.C. Resistance (75°C): 0.638 (ohm/km)
Conductor Temperature: 35 (°C)
A.C. Resistance (40°C): 0.57 (ohm/km)
Actual Unit Voltage Drop (conductor temp. 40°C): 1.15 (mV/A.m)

[MAGN1T]

BTW I know it's a hijack, but Steve, I'm not trying to have a go at you mate but a lot of the stuff you post is a little abrasive (not the content itself mostly, but just the way you put it) and I think people would respond to you better if you took the time to explain yourself rather than chucking out short statements with nothing to back them up.

.

Fair enough, It's all about reliability. The more you change from stock, the less reliable it is. Messing with the electrical system can be expensive.

The circuit breaker, best thing to do is throw it away. A circuit breaker can't work without causing a voltage drop across it. That means that the more current the alternator tries to pump into the battery, the greater the voltage drop across the breaker and the greater the difference between battery and alternator voltage.That sort of doesn't make sense but the end result is that the battery takes longer to fully charge.
That's why the breaker gets hot. When it trips out there's always a possibility of damaging something else. Lucky you don't have a V1 radar. They die at just under 15V.

There's specs and there's specs.There's also instruments and other instruments. Have you checked battery voltage at the battery?
I'm unfamiliar with where the alternator senses the voltage. Some cars sense it at the alternator itsself, others do it at the battery. Sensing voltage at the battery could cause too high a voltage elsewhere.
The battery looks good on paper until you read the fine print that mentions cell temp. Who measures that? So, small lightweight battery,not much surface area or thermal mass. Pump 130 or whatever amps into it when the car starts up. How many times are you going to do that before it fails. The proper battery is designed for the job. Maybe it's OK if you've only got a 30A alternator. Anyway I can't see the point in one when you can get a good used battery from pick a part that lasts 6 months and pay $26 and you get back $6 with your scrap one.
It's very easy to modify a car to the point where it becomes too much of a reliability problem .

Steve

[steve murch]

BTW I know it's a hijack, but Steve, I'm not trying to have a go at you mate but a lot of the stuff you post is a little abrasive (not the content itself mostly, but just the way you put it) and I think people would respond to you better if you took the time to explain yourself rather than chucking out short statements with nothing to back them up.

I'm sure you've probably got a whole heap of experience and knowledge, and it's cool that you're willing to share it, but it's a lot more helpful to the rest of us if we understand what you're saying.

hate to get on the band wagon here but hes does it on just about ever site I've ever seen!! and any reply is just like water off a ducks back to him.
modding cars is what most forums are about.
now gel cells in any race car/road car Ive done by far out perform a acid battery and weigh less and take up less room,I've used a few from helicopters which were outstanding.
now I'm sure the military wouldn't be using them if reliability was an issue, and yes steve they were gel cells.

[KwS]

arent gelcells technically superior to lead acid batteries in all ways, except for the cost to make them?

Just be thankful 'Steve' didnt start calling it a BHG like he usually does...

[captain crescent]

gell cells are far supperior from lead acid we have machines at work that will destroy a lead acid from vibration and working in weird angles etc a led acid will last about 2 or three days the gel cells last for a few years. certainlyu if i was racing or even planing to i would be putting one in there in a flash!!

[MrOizo]

Well I thought that I would say that I went for a drive past night without the breaker and everything was working mint.

I don't have a breaker in there at the moment so should put one in there.
Are there any suggestions on what to use? Guess I should visit a cad audio store.