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Semi-OT: Odd voltage gauge behavior: UPDATE 2

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Initially Posted - 04/04/2013 : 21:50:47

Driving home today I noticed the battery warning light flickering when the truck was idling, and the voltage level was low, maybe 11 volts indicated (it only reads between 8 & 18 volts, so you have to guess). As I drove home, the voltage reading kept dropping, so I turned off all non-essentials hoping I could get home. It was pouring down rain and the wiper just crept across the windshield when I flicked it on and quickly back off so I could see. It dropped below it's lower threshold on the gauge (maybe 9 volts?) when I was about 5 minutes from home and I wasn't sure I'd make it. Then all of a sudden the voltage jumped back up to "normal", maybe 14 volts?

I put my trickle charger on the dual batteries when I got home, but didn't want to stand in the rain to check the voltage. I just checked it now, and it's at 11.9 VDC after about 5 hours, so it must have been a bit lower when it started.

I'm wondering if my voltage regulator is on it's last legs, but what say you? The batteries are a couple of Sears Diehards I bought right after I bought the truck, so they're about five years old or so, but not much use since we don't use the truck all that much.

David
C-250 Mainsheet Editor

Sirius Lepak
1997 C-250 WK TR #271 --Seattle area Port Captain --

Edited by - delliottg on 04/13/2013 13:56:39

hewebb
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761 Posts

Response Posted - 04/05/2013 : 05:07:31

I have a Chevy Diesel that does that occasionally, however the low voltage only last a few minutes than slowly increases. It has done that several times in the past year. It has always been cold out (30 to 40) Truck is three years old. Sorry I have no idea what causes it, nor did the dealer when I took it in

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Dave5041
Former Mainsheet Editor

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3758 Posts

Response Posted - 04/05/2013 : 09:10:31

It could be a loose connection in the alternator circuit, but I agree that it is probably a failing alternator. It is possible that driving in heavy rain would would lubricate a slightly loose belt and let it slip until it got hot and dried a bit. Regulation is usually internal on alternators and the truck would probably be an antique if it has a generator.

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delliottg
Former Mainsheet C250 Tech Editor

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4479 Posts

Response Posted - 04/05/2013 : 11:28:10

It's a '99 Ford F-250 diesel, so "reasonably" new. I'd expect it's an alternator, not a generator. I was never in any real danger of not making it home last night, just having electrics for wipers & lights was iffy.

It's possible the belt got wet, but doesn't seem likely even if it was pouring cats & dogs for a while when I was driving home.

I plan to check the connections, this seems like a fairly likely probability, but agree, it's probably a failing alternator. Wonder how easy it is to get parts to fix the internals?

Edit: Just checked prices, a new alternator is from $85 - $400 depending on what features, amperage, etc. you want. The OME replacement one is about $140 shipped, so it's not too onerous of a replacement if it comes to that.

Edited by - delliottg on 04/05/2013 11:33:36

islander
Master Marine Consultant

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Response Posted - 04/05/2013 : 15:53:59

I wouldn't say that for sure... If it has a computer it will shut down if the volts get low enough also electric fuel pump if it has one. Check battery, Battery connections, Engine grounds but more than likely the alt. is kaput or soon to be. If it has a serpentine belt it wouldn't slip, They have belt tensioners. A V belt might slip if its not tight enough and got wet but really only for less than a min. until the squealing stops. $140 is cheap, I think the one in my old jeep Grand Cherokee was $300.

Edited by - islander on 04/05/2013 16:10:25

bear
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Response Posted - 04/05/2013 : 16:44:25

Dave, Hear in upstate New York we have Advanced Auto parts stores. Here if you drive in and think your battery etc is failing they will do a system anaylsis real quick to make sure it's the battery whatever. Of course they want you to buy the replacement fix there also. A slipping belt if it's not a serpentene belt will squeal when you gun the engine.

Edited by - on

britinusa
Web Editor

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5404 Posts

Response Posted - 04/05/2013 : 16:47:24

Check for Corrosion on the Batter terminals.

Paul

Edited by - on

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 04/06/2013 : 13:22:53

Update: got some time to look at my batteries in the truck, the tops were quite filthy, and I know you can leak current across dirty terminals, so I scrubbed both of them clean. While working on the second battery, I took my scrub brush to the negative terminal, and the connector moved! On closer inspection, the geniuses at Sears had managed to spin the retaining nut completely around, so unless you used a wrench on the retaining nut (instead of relying on the lead that it seats against to hold it), it's just going to spin. They even put a locking nut behind the first one to "hold it". I'm surprised I haven't had a problem sooner, but the truck did get a good shaking a couple of weeks ago on a rutted road, so maybe that's what triggered it. Anyway, it's all tightened up now, I've got the charger back on it (it had only risen to 12.03 VDC since the last time I updated this, another indicator of a bad connection). Hopefully the batteries haven't been damaged by the loose connection.

Edited by - on

Voyager
Master Marine Consultant

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Response Posted - 04/06/2013 : 20:28:15

David,
Battery voltage should be 12.6 to - 12.8 for a fully charged battery at rest. If the alternator is charging, the voltage should rise from 12-point-whatever V to 14.2v during initial charging, then it should settle down to the mid- 13v region after several hours.
If the alternator does that, then it's working. Never disconnect the battery from the alternator to check its open circuit voltage. You'll blow it for sure.
You could also try charging the batteries using an external charger, to see whether the batteries will take a charge. Use a digital voltmeter to check charging voltages and resting voltages. Best to try one at a time in case one is bad...
Regarding rebuilding a truck alternator, mfrs purposely remove the part numbers from the diodes so you can't suss out replacement diodes. The regulator assembly is usually also a mystery.
I've had a fair amount of success checking the forums for DIY auto repairs for my daughter's Jeep Grand Cher and wife's Saab 9-3.

Edited by - on

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 04/06/2013 : 20:43:53

Thanks Bruce, was actually an electrician in the USN, but that was 30 years ago and always good to get a refresher.

The batteries have climbed to 12.2 VDC since I tightened up the connector a few hours ago, so they appear to be taking a charge. I'm using a Harbor Freight light duty charger (same one I use on the boat), and charging some fairly large capacity batteries, so I'm not surprised it takes a while to come up to fully charged. I know my batteries on the boat are usually around 13.2 - 13.6 volts or so when I come on board, and quickly drop to 12.4-ish or so as soon as I start to load them (I like to listen to the VHF while I'm working).

I'll monitor the batteries and their charge state for a while to see if it indeed was the loose connection, or if that were just a symptom of a deeper problem.

I've found a pretty decent forum for Ford diesels where I can usually get questions answered, but if I think it's the alternator, I may just replace it and keep the core as a spare (most online stores don't want a core back).

Edited by - on

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 04/13/2013 : 14:04:52

This past week our gas grill gave up the ghost, with valves that simply locked in place. Time for a new grill. I'd been charging the batteries on the Ford for several days but the voltage had only come up to about 12.3, which I knew wasn't good news. We found a grill we liked on sale at the local Lowes (don't worry, this ties together shortly), ordered it, added a side smoker box, and Lowes would put it together for us for free. So, that was Wednesday, they'd promised the grill & smoker would be ready by Friday afternoon. So, on Friday morning, I drove into work with the truck, with no issues. At lunch time, I jumped in the truck to go grab some food, and it was reluctant to start. Having experienced nearly identical issues seven years earlier, I knew I was unlikely to get the truck to start again if I shut it off, so I drove directly to the local Sears (where I'd purchased the last two batteries) to have them do their free diagnosis. Both batteries were shot, only holding 8-ish volts under load and neither would take a charge. Unsurprisingly, the truck wouldn't even start for them to do the diagnosis on the alternator, so that'd have to wait for $273 worth of batteries to be installed (after about a $50 reduction because there was still some warranty left on the first set (after seven years!). Put the two batteries in while I walked around the corner to grab some lunch. Turns out the alternator is bad too, but they wanted roughly 2x for a replacement battery than I can get it for online, so I declined to have them install a new one. I figure I can buy a larger amp capacity alternator for less than they wanted for the OEM replacement and still be ahead labor charges to remove & install it.

They were able to get the batteries installed over my lunch hour, and I was still able to pick up my new grill/smoker at Lowes that evening. Now I just need to get an alternator ordered & installed.

Edited by - on

glivs
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836 Posts

Response Posted - 04/13/2013 : 15:57:48

About three weeks ago, my wife came home from work saying she had trouble getting her Subaru started. Assuming we couldn't get into our regular mechanic for a couple of weeks (they are usually busy), I ran it down to Sears getting in about an hour before COB. They checked the voltage and told me the alternator was shot but could have one by noon next day. I wasn't convinced so the next morning called our mechanic who said bring it right in. He found the ground from the alternator to the block was loose and dropped in a new Interstate battery - problem solved in LE 30 minutes and at a fraction of the cost quoted by Sears. Check your ground connection as a last effort.

Edited by - glivs on 04/13/2013 15:58:35

islander
Master Marine Consultant

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USA
4031 Posts

Response Posted - 04/13/2013 : 16:27:57

Sure way to kill a starting battery is to run it down, Probably due to the alt. not keeping them fully charged. Although 7yr old batteries were probably on their last legs anyhow. Get the new alt. installed ASAP to avoid running down the new batteries and damaging them.
Battery Facts
Lead acid batteries designed for starting automotive engines are not designed for deep discharge. They have a large number of thin plates designed for maximum surface area, and therefore maximum current output, but which can easily be damaged by deep discharge. Repeated deep discharges will result in capacity loss and ultimately in premature failure.

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 04/13/2013 : 18:46:48

Yeah, I'm sourcing a new alternator as we speak. Apparently O'Reilly sells an "ambulance" alternator for right around $200 that puts out more amps than the OEM replacement, so I'm going to see if I can find one of them locally. If not, I can probably get one closer to work, or simply have them order one in. I've got the batteries on trickle charge again, and it's not like I use the truck that much to begin with, so I'm not overly concerned about damaging them in the short term.

I've looked up the replacement, and it looks like a half hour job to do it, so it shouldn't be hard. If I can find the alternator, I should be able to get it installed tomorrow.

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