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Old 12-07-2016, 11:04 AM   #1
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Battery Light On Dash Comes On Intermittently

Hi Guys,

I've got an issue with my 98 Chevy Express 3500's battery (low voltage) indicator coming on while the van is running.

The first time I noticed this was one morning when I started the van and happened to look down at the scangauge to see that the voltage was only 11.4 volts. I immediately looked on the dash to see the battery light illuminated. I shut the van off and started it back up and voltage was back to normal (13.4-ish on scangauge) and the light was off. I hadn't noticed this happen again, until...

This morning while driving in to work, I looked down to see that the same thing was going on. Voltage was at 11.4 and the light was on. It's possible this has happened before without me knowing it, but I am pretty constantly checking the gauges while driving via the scangaugeII. I got to a spot where I could shut the van off for a second and it made no difference, still low voltage and light on. Then I stopped at a couple lights and pulled into my work parking lot to find that everything was back to normal (13.5 volts and light off)

I have a surepower isolator that separates my two house batteries from the starting battery. Often I will use the battery switch inside the van to switch over to the house batteries while parked so that I can listen to the radio on breaks.

My questions are as follows:

1. Could that battery switch have anything to do with this issue?
2. Does it sound like an isolator going bad?
3. Could it be the alternator? (I'm leaning toward this, because it seems that the battery voltage reading at the scangauge and dash light must be on the alternator side, before the isolator, no?)

I replaced my serpentine belt, idler pulley and belt tensioner just a few weeks ago, but this issue occurred both before and after that fact.

Thanks!

capn
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Old 12-07-2016, 11:46 AM   #2
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I'm going with alternator
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Old 12-07-2016, 11:48 AM   #3
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Capnkurt, just for the sake of clarity, can you confirm if your Surepower unit is a separator or an isolator? A model number would be helpful. At first glance, I'm thinking that this is most likely an alternator/regulator issue, but I believe in data first, conclusions second.
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Old 12-07-2016, 11:53 AM   #4
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Thanks, simplesez. I'm thinking you're right. If not the alternator itself, perhaps some wiring going to/from the alternator might be bad. Looking at some of the wiring under there tells me it's original to 1998.

I went back out to the van to start it up and now I can't get any charge at all. This is the first time that this has happened, so I'm guessing that whatever has failed in the alternator has finally done so for good.

Is it possible that a failing alternator could do so in the manner I described? Can they be charging one minute and not the next, only to repeat that cycle that several times?

Thanks,

capn
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Old 12-07-2016, 12:00 PM   #5
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Hi Glider,

I most definitely do have an old isolator. It's a surepower 16023A. It appears to be the one installed by smb south back in 98.

Thanks,

capn
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Old 12-07-2016, 12:08 PM   #6
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Capn, I'm still thinking alternator, but if you want to do an experiment, you can eliminate the isolator from the system. That isolator has three posts: one from the alternator, one to the chassis battery, and one to the coach batteries.

One option for isolation is to simply disconnect the coach battery lead, but leave the alternator and chassis battery leads in place.

A further option is to pull the alternator and chassis battery leads from the isolator, and join them together. This fully eliminates the isolator from the system. If you still have your charging issue with the isolator out of the system, you know the problem has nothing to do with the isolator or the coach battery system.

Remember to disconnect your positive battery leads before mucking with wires...
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Old 12-07-2016, 12:15 PM   #7
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Thanks, Glider. I'll check this out.

capn
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Old 12-07-2016, 12:17 PM   #8
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In case it is helpful, I am attaching a sketch I did of the electrical system from my old Roadtrek. Most of the sketch is not relevant for current purposes, but it does show the relationship between the alternator and the two different battery systems.
Attached Thumbnails
97D-190P_Isolator_Setup.jpg  
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Old 12-07-2016, 01:02 PM   #9
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Hey Glider,

Thanks for the diagram. Shouldn't I be able to test the output of the alternator also by hooking up a meter to the alternator itself at the point it connects to the isolator? If I'm not getting 14.4 volts at that point (with the engine running) that would indicate the alternator is bad, no?

Thanks,

capn
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Old 12-07-2016, 01:21 PM   #10
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Start with the basics first. Have the battery terminals been cleaned? Are all wire connections snug? I bad connection on the signal wire (which on your van may come off the battery lead) can easily cause the alternator to drop out.
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