Flashing batttery light - what's it going to be?

Lawrence
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Joined: April 11th, 2006, 4:50 am

Flashing batttery light - what's it going to be?

Unread post by Lawrence » July 14th, 2017, 1:06 am

Hi guys.
Having a problem with my charging system. Couple weeks ago, on my way to town, my battery light stayed on all the way. I went straight to the electrician, who ended up servicing the alternator, including rewiring the rotor and new brushes. He also changed the slip rings.

The following week, I noticed the battery light flashed every time the car was turned off, or I slowed down. A couple days, in addition to that, sometimes after a ride over corrugations especially, the light would pulsate at idle.

I took it back to the electrician who tested the system and he didn't find any problem. What could be the cause of this ?

mydmax
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Joined: August 4th, 2011, 10:43 pm

Re: Flashing batttery light - what's it going to be?

Unread post by mydmax » July 14th, 2017, 9:16 am

I would not think an auto electrician would press apart the rotor to rewire it.
Why would he have to rewire it anyway? Unless he broke off the wires to the slip rings, then he would need to rewire.
Most would not do that but simply replace the rotor and it would have new slip rings anyway, and be cheaper I would think.

If the light comes on when slow running, it indicates the alt output is low and possibly diode failure and you now have only 1 of the 3 phases working and therefore 1/3 of normal output happening at present. That will result in the light coming on when the alt output is low and cannot keep up with the engine system demand.

If the light comes on when the headlights are turned on, that also backs up that theory.

The repair may not be a good one.

Lawrence
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Joined: April 11th, 2006, 4:50 am

Re: Flashing batttery light - what's it going to be?

Unread post by Lawrence » July 14th, 2017, 11:52 am

I suspect it wasn't repaired properly either. Tried turning on the headlights one evening while it was flashing and it stopped. I think I will have to have another electrician look at it again as the previous one wouldn't have done a proper job.

Yes, one of the wires on the rotor was broken. Could have been while he was servicing the alternator. Had to carry it to a place that rewires motors.

Thanks Mydmax.

mydmax
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Joined: August 4th, 2011, 10:43 pm

Re: Flashing batttery light - what's it going to be?

Unread post by mydmax » July 14th, 2017, 1:17 pm

IF and only IF the slip rings were worn too far would a repairer change the slip ring unit. Great care must be taken to preserve the wire ends from the rotor. If broken, the rotor may have to be pressed apart and rewound and then the new slipring fitted.

I would be very surprised if the rotor was rewound though. Far too much time for the $$$ which could be charged.
That must be working because it is charging, but the voltage and amp flow deficiency under load is the concern. As mentioned, if it comes on when headlights are ON, then a diode is not connected, open circuit, or shorted internally.
Usually a shorted diode flattens the battery. A not connected or open diode means the 2/3 drop in output but near normal voltage can be acheved on light load.

With engine running and headlights on full, perhpas a demister or two, will use ALL of the available current output and the light will appear or will be dull, because at that state the battery is slowly going flat. ie not being topped up.

There are auto electricians and there are "Auto Electricians". Like mechanics, some have good abilities, the majority don't, but can recognize wire at 3 paces in a good light.
PS: Although then working as a mechanic, I ran the Auto elec repairs for a Vic roads region while in my 3rd year of apprenticeship, so I have done a few alternator repairs, including slip ring changes.

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