Flickering Battery Warning Lamp - Defender Source
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  #1  
Old September 29th, 2015, 11:29 AM
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Flickering Battery Warning Lamp

My wife said that the battery light was flickering yesterday. I have checked out the alternator and there is no slipping and the voltage seems to be charging/alright when cold. When I briefly looked last night, it seemed that the output was low, high 12's, low 13's for output. The battery was at 12.4v.

I have extra regulators and I am going to pick up brushes (only $3) to have them on hand. I also have a HD Bridge Rectifier coming as it was a mod I was going to do anyway (it is a Mean Green Alternator). So I have all the parts to rebuild it if it comes to that.

But I wanted to understand the light on the dash. From what I understand, it is fed with a hot from both the battery and the alternator to both sides of the lamp. Yes, hot to both. That way, when you first turn on the truck (not started) it illuminates as it gets battery voltage from just the battery. When alternator starts up, it gets both battery and alternator voltage so as long as they are close, it doesn't light up. But if the alternator starts to fail, then the light again sees more voltage on one side than the other and then lights up. Is that the process on these warning lamps?

I am guessing I just have low voltage from the alternator which usually is the brushes as I haven't changed them forever. I figure when I open it up, that will be obvious so I figure I'll have the other components on hand.

Any other ideas of what a flickering battery light would be from?
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  #2  
Old September 29th, 2015, 11:33 AM
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It can light up if there is a failed diode in the rectifier as well. You get AC across the light. The AC damages electronics, so be careful. You really need to get it on an alternator tester to see what is what.
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Old September 29th, 2015, 01:59 PM
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I have access to a hand held oscilloscope so I will check that this afternoon. But what I am noticing is I am getting 13.5V cold and once I've driven for about 30 miles and things are hot, I am getting 12.9...
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Old September 29th, 2015, 02:53 PM
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Quote:
Originally Posted by Davis View Post
My wife said that the battery light was flickering yesterday. I have checked out the alternator and there is no slipping and the voltage seems to be charging/alright when cold. When I briefly looked last night, it seemed that the output was low, high 12's, low 13's for output. The battery was at 12.4v.

I have extra regulators and I am going to pick up brushes (only $3) to have them on hand. I also have a HD Bridge Rectifier coming as it was a mod I was going to do anyway (it is a Mean Green Alternator). So I have all the parts to rebuild it if it comes to that.

But I wanted to understand the light on the dash. From what I understand, it is fed with a hot from both the battery and the alternator to both sides of the lamp. Yes, hot to both. That way, when you first turn on the truck (not started) it illuminates as it gets battery voltage from just the battery. When alternator starts up, it gets both battery and alternator voltage so as long as they are close, it doesn't light up. But if the alternator starts to fail, then the light again sees more voltage on one side than the other and then lights up. Is that the process on these warning lamps?

I am guessing I just have low voltage from the alternator which usually is the brushes as I haven't changed them forever. I figure when I open it up, that will be obvious so I figure I'll have the other components on hand.

Any other ideas of what a flickering battery light would be from?
Maybe it was oil pressure ...
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Old September 29th, 2015, 03:21 PM
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No, it was battery--she is sure and I have switched to a crank driven oil pump and pressure is great. She wouldn't make that mistake as we have an RRC so she is used to seeing the oil light :-)
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Old September 29th, 2015, 03:21 PM
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Fix or replace asap before it kills something else on the truck.
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Old September 29th, 2015, 04:03 PM
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Originally Posted by Davis View Post
I have access to a hand held oscilloscope so I will check that this afternoon. But what I am noticing is I am getting 13.5V cold and once I've driven for about 30 miles and things are hot, I am getting 12.9...
You need more than 13.5... should be about 14.2 minimal.
Your alternator is not putting out enough voltage and yes you described how the ig warning light works.
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Old September 29th, 2015, 11:43 PM
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I am just gonna refresh it. I winched a lot on Sunday, so probably stressed diodes. I have an HD bridge rectifier arriving Friday and picked up brushes today. Already have a spare regulator, so gonna do it all this weekend. Bearings seem fine so I'll just do an electrical refresh.
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Old October 4th, 2015, 03:59 PM
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I think the issue came from that the previous day I did a ton of winching helping remove slash from my buddies yard. Probably stressed the diodes. Regardless, I was planning to upgrade the internals to my Mean Green Alternator (which is based on the Delco CS144). I installed an HD Diode pack, replaced the brushes, and put in an HD regulator (14.8V due to my Odyssesy 2150 battery) and everything is running perfect. 40 minutes to remove and replace, from disconnecting the battery to starting the truck back up after the rebuild--pretty darn quick for this kid...
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Old October 4th, 2015, 04:58 PM
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What voltage do you have now?
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Old August 12th, 2016, 09:03 AM
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Just bumping this...

When I start my truck the battery light illuminates, as soon as I touch the throttle it goes away and stays off. Any ideas?
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Old August 12th, 2016, 09:06 AM
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Quote:
Originally Posted by st0k3d View Post
Just bumping this...

When I start my truck the battery light illuminates, as soon as I touch the throttle it goes away and stays off. Any ideas?
Could be as simple as a lose or old belt.
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Old August 12th, 2016, 09:07 AM
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Originally Posted by Kevin88RRC View Post
Could be as simple as a lose or old belt.
Ok, thanks. They seem decently tight but you never know. I have new belt(s) to install anyway. I will check it out this weekend. So many loose ends to tie up on this thing...
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Old August 12th, 2016, 09:19 AM
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Originally Posted by st0k3d View Post
Ok, thanks. They seem decently tight but you never know. I have new belt(s) to install anyway. I will check it out this weekend. So many loose ends to tie up on this thing...
I have the exact same issue...I'll be interested to see what you find!
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Old August 12th, 2016, 09:21 AM
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Most likely worn brushes that are making intermittent contact with the commutator.
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Uncle "Richard" Douglas has a Land Rover with big wheels that never gets stuck... until he breaks something so it won't go. Uncle Douglas always breaks something. - Anna Crowther at the Conclave 2012 (AKA Carburetor Neck)

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UD: "Just Power through it man!"
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Old August 12th, 2016, 09:55 AM
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Quote:
Originally Posted by rdavisinva View Post
Most likely worn brushes that are making intermittent contact with the commutator.
Ok maybe local shop can rebuild alternator if need be
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Old August 12th, 2016, 10:10 AM
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I routinely buy brush sets and replace them myself.
You'll need to disassemble the alternator to install.

The smart Germans at Mercedes built alternators that have a brush set and regulator assembly that you can replace while the alternator is still in place on the engine. Super convenient.
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Uncle "Richard" Douglas has a Land Rover with big wheels that never gets stuck... until he breaks something so it won't go. Uncle Douglas always breaks something. - Anna Crowther at the Conclave 2012 (AKA Carburetor Neck)

"What's with this death wobble, Uncle Douglas, I can't keep it in 1 lane?"
UD: "Just Power through it man!"
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  #18  
Old August 12th, 2016, 10:26 AM
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Quote:
Originally Posted by rdavisinva View Post
I routinely buy brush sets and replace them myself.
You'll need to disassemble the alternator to install.

The smart Germans at Mercedes built alternators that have a brush set and regulator assembly that you can replace while the alternator is still in place on the engine. Super convenient.
It depends which alternator. The normal 65A Lucas model has the regulator and brush assembly that comes off with three bolts from the back in seconds. I find the brushes can simply get stuck from mud and just need to be freed up.

It is a common part you can find in the US as well or through a Rover parts place.

RTC5670


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  #19  
Old August 12th, 2016, 11:25 AM
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Quote:
Originally Posted by rdavisinva View Post
I routinely buy brush sets and replace them myself.
You'll need to disassemble the alternator to install.

The smart Germans at Mercedes built alternators that have a brush set and regulator assembly that you can replace while the alternator is still in place on the engine. Super convenient.
Ok cool. I can do that. I have disassembled/reassembled alternators before for powdercoat.

------ Follow up post added August 12th, 2016 12:25 PM ------

Quote:
Originally Posted by Red90 View Post
It depends which alternator. The normal 65A Lucas model has the regulator and brush assembly that comes off with three bolts from the back in seconds. I find the brushes can simply get stuck from mud and just need to be freed up.

It is a common part you can find in the US as well or through a Rover parts place.

RTC5670


Nice hopefully this is the one I have.
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  #20  
Old March 12th, 2017, 12:39 PM
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Wanted to update on this. My truck has persisted to have this startup battery lamp issue. Start truck up, battery lamp on, lightly blip throttle, light goes off and stays off. I thought it would end up being my alternator worn as it was original. I just recently installed a 75? Amp alternator. That tractor one. I replaced the charging wire from the double 12 gauge? to a solid 4 gauge to the power block. I also installed a tachometer that gets signal from the proper terminal on the alternator. Sure enough this issue persists, additionally it affects the tachometer too. The tachometer reads nothing until I blip the throttle, light goes off, all is well. If the truck has been used recently sometimes it doesn't happen. It is more of a nuisance then a problem but I would like to solve it.

Thoughts?
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