[Sydo]

Howdy at idle which is 600rpm both my LED Lightbars will turn off and then keep going on and off also can't run my LED strips in canopy. When I increase revs to around 750rpm everything is fine. So obviously the alternator doesn't make enough voltage at 600rpm is this correct or is alternator on its way out ? Would it just be a simple matter of turning idle up ? Just fitted Micks HID headlights as well

 

[simmoevo]

What's the voltage of the batt when engine is off and when running? Led light bars depending on the model should operate between 9-30v. If your batt is down on charge and the alt is not regulation properly it can drop below 9v. The light bars will turn off under this.
On the other hand you may have a faulty relay or the light bar is faulty and drawing way too many amps and lowering the voltage.
You need to test the voltage in the off state, engine running state, light bars off engine off, light bars on engine off, engine on light bars off and engine on light bars on.
Also check the operating rpm your alt is supposed to work it's usually written on the side of it. Your idle may well be too low.

 

[Sydo]

Thanks mate. Haven't got a volt meter. Will get my sparky to check it out. Brand new yellow top battery as well. Strange why the LED strip lighting doesn't work either at those revs. They draw bugger all.

 

[Sooty_10]

Do your self a favour and go buy a multimeter. Handy to have to diagnose all sorts of 12v electrical issue. Odd that strips lights aren't even working though, as they draw bugger all. Especially with a fairly new yellow top. The lights should stay on no matter what the alternator is doing as long as the battery has sufficient charge. Can you still start the car normally? Or are you jump/roll starting it? If you can start it then the lights should stay on and work for a fair while, especially the strip led's.

 

[Sydo]

Yep starts fine. Led strips will also start working with higher revs. Wonder if the new HID headlights are draining too much. I will adjust idle up to 750rpm

 

[drivesafe]

Hi sydo and if your motor is starting with out any problems but your lights are playing up, it sounds like a wiring problem.

Again, as Sooty suggested, get yourself a multi meter and do some investigating.

 

[Sydo]

Hi sydo and if your motor is starting with out any problems but your lights are playing up, it sounds like a wiring problem.

Again, as Sooty suggested, get yourself a multi meter and do some investigating.

yes but only at 600rpm above that is fine ??

 

[drivesafe]

Hi sydo, that doesn’t rule out a wiring problem.

You can have a poor connection causing a resistance point in the electrical system that is causing a voltage drop. This is a very common problem found in dual battery setups

By revving up the motor, you may be raising the CURRENT in the system enough to allow the voltage to rise just enough to get the lights going.

Again, Sooty’s suggestion of getting a multi meter is the first step towards finding the problem

 

[sudso]

Sounds like bad connections to me too. Voltage too low to light up LEDs wouldn't even turn your starter motor

 

[Leethal]

Are the light bars on the cabrack?

Remember your tray is an appalling earth, it sits on the body work via plastic blocks, and patrols have very little chassis earth anyway. If the light bars and canopy light are earthed to the tray, then run a good bare metal earth from tray to body work of cab (or direct to battery) and problem solved.

Earth faults are the source of 90% of electrical evil.

 

[Sydo]

Both on bullbar Lee

 

[Leethal]

Sorry I forgot about this thread.

As Sudso says, voltage too low to power an LED certainly won't start the car.

Can you check the earth to the body work? It obviously has a reasonable earth to engine or it wouldn't start, but can you humour us and bolt a decent cable (or even just a 6mm or two to confirm a suspicion) from the battery negative to a good clean earth on the body work? An M6 captive in the inner guard will suffice.

Or... Earth the LED bars on the bullbar directly to the battery and see if that eliminates the problem, which would confirm it's an earth issue, which I think we all suspect it to be.

 

[Sydo]

Went out again tonight. Idles on 600rpm led bars go on and off. Build revs up to 750rpm no problemo

 

[drivesafe]

H Sydo, have got a multi meter yet?

If you have, try measuring the POSITIVE ( + ) voltage at the LED bar at idle and with higher revs, but also measure the NEGATIVE ( - ) voltage at the same times.

This should get you started on where to look for the problem.

 

[Sydo]

Had a Sparky check it out. 2nd Battery is shagged which was causing isolator to cut in and out therefore LED bars were going on and off. Make sense ?

 

[Leethal]

Only if for some odd reason your LED bars on the front are powered from second battery.

 

[Sydo]

New second battery is in and all good now. Isolator light still goes on and off but LED's are staying on

 

[drivesafe]

Hi Sydo and good to hear you got it sorted.

Had your shagged battery dropped a cell. As this would explain why your LED lights could only work once you revved the motor.

With a dropped cell, if it was shorted internally, the shagged battery would pull high currents and at idle, your alternator was probably not producing enough current to over come the current draw of the shagged shorted battery.

In any DC circuit, if the current draw exceeds the current supply, the voltage of the circuit will drop.

In your case, with the alternator at idle and not producing enough current, the voltage automatically drops in the hole circuit.

This would account for the LEDs not working and your isolator turning on and off ( this is common and is called oscillating ).

When you increased the revs, your alternator was able to produce a higher current output so the voltage was able to rise, and this voltage rise allowed the LEDs to work.

So yes, what the sparky told you does make sense.

 

[Sydo]

Cheers mate. he said the battery was at 230CCA. Rambled on about something else

 

[Sydo]

Well problem not entirely sorted. Isolator still clicking on and off at idle ONLY when both front LED Lightbars are on. Switch either off and isolator is working fine