Very Low Voltage with Accessories on - what is normal?

Hey guys,

I'm super frustrated with this situation and trying to crowdsource some new ideas or diagnostic approaches from the impressive brain-trust on this forum.

I've scoured the posts here trying to improve my low voltage situation at idle. I may just need new cooling fans (mine are stock), but I'm not totally convinced there aren't other factors at play because I feel like my idle voltages are too low when I start adding accessories. The other day on the road the with the headlights on at max A/C on the voltage dropped below 12V too many times, and my understanding is it started impacting the spark and fuel pump, the voltage couldn't recover and the battery died a slow death. Luckily I noticed it dropping, and made it home just as the battery died as I was pulling in.

Here's the voltages I'm reading at idle with a multimeter across the pos/neg posts in the bulkhead area behind the passenger seat.

Headlights on + Max A/C - 12.0V (it holds low 12's for a minute or so but then drops to 12.0V)
AC on Speed 1 - 12.9V
AC on Speed 2 - 12.7V
AC on Speed 3 - 12.4V
AC on Speed 4 - 12.2V dropping to 12.0V in under a minute
AC on Speed 4 at 1750 RPM - 14.3V
Just cooling fans from otterstat, no cabin fans - 12.5-12.9V
Vent mode, no AC, just cabin fans Speed 4 - 13.5V
Just headlights 13.8V
Headlights + cooling fans 12.8V

Car off - 12.5V
Running with no accessories steady at 14.1V

Battery light comes on in accessories mode

I've got a 1-year old DCMH alternator, 2-year old battery, alternator belt is tight, tried a battery swap, updated fuses and fuse block, relays and relay terminals, I've swapped the changeover relays (the gold kind), checked the connectors for corrosion even at the washer bottle, I've cleaned as many grounds as I can find including the one on the chassis for the cooling fans, DMCH also put in an additional ground from the frame to the engine, and I've ran a jumper cable from the cabin fan shroud to the neg battery post. No joy on any of those.

My cooling fan relay runs very hot - always has. I was using Dave's solid state fan-fail relay and it worked great for awhile, but it also ran very hot and eventually cracked under the excessive heat I presume, and now I'm just running the 20 amp in-line fuses for each cooling fan. When I was using Dave's fan-fail relay I don't recall seeing the low voltages, but I'm not totally sure, and I don't really understand how they would have improved the voltage, but that and a water pump install was the last thing that changed before I started noticing the low voltages.

I'm out of ideas except for getting new cooling fans - mine are stock and the motors show some rust on them.

Sorry for the long post, but if you made it this far it'll help weed out suggestions and maybe you have an idea I hadn't though of?

Much respect to you all out there dealing with this machine, but hell if it ain't worth it when she's running good! :driving1:

Bad connections don't increase load current, it drops load current. So don't go chasing that. It sounds like your cooling fans should be changed but my guess is your alternator is bad. When it was new did you have low voltage problems? If a diode in the alternator goes bad it's current output drops in half.

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Originally Posted by Bitsyncmaster

Bad connections don't increase load current, it drops load current. So don't go chasing that. It sounds like your cooling fans should be changed but my guess is your alternator is bad. When it was new did you have low voltage problems? If a diode in the alternator goes bad it's current output drops in half.

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You may be onto something Dave. 2 years ago I got a new DMCH alternator and it started dying a year after install. Battery light would come on, output was very low driving. I never bench tested it, DMCH just replaced it and the problem was fixed. But now I'm having electrical issues a year later, albeit different symptoms, which started after the water pump was installed which I noticed because water pump bearing grease started spraying all over the belts. The water pump got replaced, but maybe the residual grease on the belts is causing some belt slippage at high alternator loads? I do still see some residual grease on the belts. I've wiped them down a bit but there is still some there and maybe it lubed up the pulley walls. I'm not even sure if belt slippage would explain low voltage only under high accessory load. The belt tension seems pretty tight. It deflects in the middle about 1/2" if you push hard.

Maybe both alternators where fine and there was just a little grease spraying on them causing them to slip? Do you think bench testing the alternator will reveal anything given it seems to charge the battery fine when you rev it and the battery light doesn't come on this time, but maybe something in voltage regulator is damaged. Not sure if a bench test will reveal that. But this is the best lead I have right now.

From your voltage readings is seems the alternator is not keeping up as the load increases. Yet the 14 volts with little load would normally be considered acceptable. You might want to clean and tighten the main alternator power connection. However, Dave is spot on about diode bridge failures impacting capacity. The alternator is fairly easy to remove and many auto parts stores have a test stand available to evaluate. Take them both in and have them tested.
Ron

It is normal for the voltage to decrease when you have a lot of load on the electrical system and the motor is idling. The alternator can't output at it's full rated capacity at idle. The battery is supposed to hold the voltage up for a short period of time, like when you stop for a traffic light or a stop sign. Otherwise you are moving and the motor isn't idling. If you think you have a problem clean ALL of your connections, make sure the belt is not slipping (even if it is tight it can slip if it is glazed or the wrong size), and have the battery load tested. Make sure you don't have your rear window defroster on, it is easy to hit the switch with your elbow and not realize it.

Cleaning grounds and installing a ground bus, along with getting rid of that stupid bundle of brown wires from the alternator to the bulkhead and replacing it with a thick battery cable, all solved my voltage issues back when I was dealing with them.

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Originally Posted by dn010

Cleaning grounds and installing a ground bus, along with getting rid of that stupid bundle of brown wires from the alternator to the bulkhead and replacing it with a thick battery cable, all solved my voltage issues back when I was dealing with them.

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I have the stupid bundle of brown wires from the jump post to the bulkhead post, but good battery cable from jump post to starter to alternator with very clean connections. I could replace that but it has to go stupid brown wires once its in the bulkhead. I see if I can find a battery wire from jump post to bulkhead. :thumbup:

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Originally Posted by David T

It is normal for the voltage to decrease when you have a lot of load on the electrical system and the motor is idling. The alternator can't output at it's full rated capacity at idle. The battery is supposed to hold the voltage up for a short period of time, like when you stop for a traffic light or a stop sign. Otherwise you are moving and the motor isn't idling. If you think you have a problem clean ALL of your connections, make sure the belt is not slipping (even if it is tight it can slip if it is glazed or the wrong size), and have the battery load tested. Make sure you don't have your rear window defroster on, it is easy to hit the switch with your elbow and not realize it.

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Yall have me concerned it could be alternator/belt related even though its only a year old and the belts seem tight. I'm elbow deep in this, there's no reason I shouldn't pull the alternator get it bench tested and put new belts on that don't have grease-residue on them. I have them sitting in my garage. At the very least it'll help me rule it out.

It's been a while since I've messed with the original engine/configuration, but I'm pretty sure that the bundle of brown wires is supposed to go from the alternator to the bulkhead post (not the jump post). The Jump post should only have one battery size wire going down to the starter.

Also, while you can try new belts, I don't think that is your problem. You'd probably get squealing if it was, but the alternator spins pretty freely, unlike the AC compressor for example that would really have trouble if there was grease on a belt.

Already mentioned in this thread is lower output due to a slipping alternator drive belt. Not mentioned as a cause of belt slippage is an incorrect drive belt. Use a known-good belt that meets specs. A Gates 7495 is one such belt.

Citations below, slightly edited, are taken from the Knowlegebase article about alternators from DMC Classic - including how to prove belt tension is adequate (use a wrench):

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"4 - Set the correct belt tension. Nominally the belt should be tight enough that the belt will deflect 1/2 inch when pressing with your finger. A better indication is to try to turn the alternator main shaft clockwise with a wrench. You should see the belt turn the engine slightly rather than slip at the alternator pulley. Too tight is better than too loose. A loose belt will slip under load and greatly diminish the output of the alternator just when you need it the most.

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The # 1 Reason for Premature Alternator Failure Including "No Output" Is a Slipping V-Belt!

In the good old days when all cars needed was a 40-60 amp alternator, slipping belts were not a common problem. Now that we need 100 amps and up, it has become a real issue. The higher the amperage, the more resistance an alternator has, and it takes more power to turn the pulley. Therefore the belt has to be tighter to prevent slippage. Most of the time the alternator belt doesn?t make a squealing noise when slipping.

Signs of belt slipping:

• Little or no output, discharged battery
• Alternator pulley extremely hot and starting to discolor
• Belt sticking to pulley or belt glazed or cracked
• Rust on alternator shaft
• Belt dust collecting on fan and front alternator housing
• Belt riding too deep in pulley groove
• Bearing noise

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Originally Posted by Rich

Already mentioned in this thread is lower output due to a slipping alternator drive belt. Not mentioned as a cause of belt slippage is an incorrect drive belt. Use a known-good belt that meets specs. A Gates 7495 is one such belt.

Citations below, slightly edited, are taken from the Knowlegebase article about alternators from DMC Classic - including how to prove belt tension is adequate (use a wrench):

>
>

"4 - Set the correct belt tension. Nominally the belt should be tight enough that the belt will deflect 1/2 inch when pressing with your finger. A better indication is to try to turn the alternator main shaft clockwise with a wrench. You should see the belt turn the engine slightly rather than slip at the alternator pulley. Too tight is better than too loose. A loose belt will slip under load and greatly diminish the output of the alternator just when you need it the most.

>
>

The # 1 Reason for Premature Alternator Failure Including "No Output" Is a Slipping V-Belt!

In the good old days when all cars needed was a 40-60 amp alternator, slipping belts were not a common problem. Now that we need 100 amps and up, it has become a real issue. The higher the amperage, the more resistance an alternator has, and it takes more power to turn the pulley. Therefore the belt has to be tighter to prevent slippage. Most of the time the alternator belt doesn?t make a squealing noise when slipping.

Signs of belt slipping:

• Little or no output, discharged battery
• Alternator pulley extremely hot and starting to discolor
• Belt sticking to pulley or belt glazed or cracked
• Rust on alternator shaft
• Belt dust collecting on fan and front alternator housing
• Belt riding too deep in pulley groove
• Bearing noise

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Yeah those are enough potential issues that its worth looking at the belt slippage, especially since I'm taking the alternator off. It seems tight enough based on the deflection. I don't know how one gets a socket on that pulley without removing the asbestos muffler heat shield, but what I have done is push on the alternator fan blades with a wrench and its extremely hard to get it to slip/rotate. If belt dust can get it to slip maybe that bearing old grease residue is causing some slippage. The sides of the pulley's where the v-belt grips are black from heat from belt friction I presume but unless you all tell me your pulleys are super shiny I assume that's normal. I'll consider all these things after I re-assemble after the alternator bench test.

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Originally Posted by dn010

Cleaning grounds and installing a ground bus, along with getting rid of that stupid bundle of brown wires from the alternator to the bulkhead and replacing it with a thick battery cable, all solved my voltage issues back when I was dealing with them.

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I'm 90% sure mine goes red battery cable from alternator to starter, red battery cable from starter to jump post, then brown cable bundle from jump post to bulkhead post. And red battery cable from starter to battery. I'll verify tonight.

Pulley test
No socket wrench. Use a 22mm open end or combo wrench on the alt pulley nut. Even a 7/8in wrench will do.

My pulley surface is shiny where belt contacts it. Belt is smooth but not glossy or glazed.

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Originally Posted by TheFover

I don't know how one gets a socket on that pulley without removing the asbestos muffler heat shield

The sides of the pulley's where the v-belt grips are black from heat from belt friction I presume but unless you all tell me your pulleys are super shiny

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I think Dave wins. Load test points to bad alternator see pics. I also see what looks like bearing grease on the back side of the alternator too. This means this is the second alternator that has crapped out on me in 2 years, and I know these are good units so I'm no really sure what causing this, but I'm just going to replace my cooling fan motors too since the car is apart since I was cleaning 30 ground points and checking every connection. I'll report back when I get it all back together to confirm my idle voltage is back to normal when everything is installed.

Thanks again everyone for the help. Dave you're an invaluable resource here and I'll be getting another solid state fan-fail unit as soon as I get everything fixed.

Also please guys remember to post you're resolution to any issue you have so poor saps like me don't read 10 pages worth of posts and never find if what fixed the issue. Although I do understand often you fix multiple things at a time when the car is apart and you're sure exact which one fixed the problem.

Attachment 71690

It probably is less stress on the alternator if you don't let the battery get to low. When the battery is low your pumping a lot of current just to charge the battery. Maybe keep a trickle charger on it.

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Originally Posted by Bitsyncmaster

It probably is less stress on the alternator if you don't let the battery get to low. When the battery is low your pumping a lot of current just to charge the battery. Maybe keep a trickle charger on it.

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Overtightening the belt can cause the bearings to run hot and then the grease melts and comes out. The grease can also damage the internals of the alternator so it won't work right (it gets on the commutator and brushes). If the alternator is always working hard it can overheat and melt the internal voltage regulator and/or the diode bridge, especially if your battery is always chronically undercharged. If you have a bad battery it will kill the alternator and if you have a bad alternator it will kill the battery. That is why you must always test them both if there is a problem. When I don't use my car I put a Battery Tender on it for 1 day once a month and a day before I use it. That way the alternator only has to "put back" what it took to start the motor.

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Originally Posted by David T

Overtightening the belt can cause the bearings to run hot and then the grease melts and comes out. The grease can also damage the internals of the alternator so it won't work right (it gets on the commutator and brushes). If the alternator is always working hard it can overheat and melt the internal voltage regulator and/or the diode bridge, especially if your battery is always chronically undercharged. If you have a bad battery it will kill the alternator and if you have a bad alternator it will kill the battery. That is why you must always test them both if there is a problem. When I don't use my car I put a Battery Tender on it for 1 day once a month and a day before I use it. That way the alternator only has to "put back" what it took to start the motor.

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Yeah I agree with all this. I would leave it on a trickle charger all the time if I could, but the car spends a lot of time in a storage unit where there is no power source, so I just disconnect the battery. But even after sitting for a few weeks or more with the battery disconnected I should probably charge it up.

I'm pretty sure the belts weren't too tight - they had had 1/4" of deflection, but then again the water pump bearing busted recently too, so who knows maybe it was.

This thread is a good reminder that I also need to figure out what's going on with my system. Lately my volts have been lower even while driving. Though yesterday while out I my volt meter was spiking way up and my blower fans were going at crazy high speed. Only when I unplugged an accessory from the cigar lighter and turned the radio off, did it return to normal. Weirdly, when I plugged the accessory in a moment later and turned the radio back on, the voltage was fine. This freaking car sometimes. LOL