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Output Voltage #98602 Sun Dec 24 2006 08:52 AM
Joined: Apr 2005
Posts: 930
S
speed 6351 Offline OP
Shop Shark
eek I have an 85 Amp alternator on my '57 GMC,and it seems to be overcharging,like 16.5 volts at anything over 600 rpm's. This voltage holds even with every electrical accessory on the truck running.I know the problem isn't related to operating speed because I ran this same alternator for about a month on this engine and it was running within specs,no problems. After it started acting up,I replaced the regulator,same problem. I had the old regulator tested,14.7 volts,just like it should be. I've also noticed recently my radio only makes sound when I rev the engine a little;at idle,it still lights up,but the speakers make no sound until it's running at 750 rpm or more. I was told by the owner of the automotive/electric shop here it may be related to a grounding issue. I have new battery cables,replaced just a week or so before the problem. My ground cable's connected to the top right bellhousing bolt,which I removed the paint from and tightened to about 50 lbs torque. There's a 10 ga. ground from the firewall to the frame.and a ground strap from the head to the firewall. I'm out of ideas. Everything is working fine (except the radio),but I'm worried that if I get on the highway with it,something's gonna go ugly. The battery still starts the truck even at below zero temps,shows about 12.5 volts when I get in the truck in the morning.Voltage goes to 9.5-10 volts cranking.I also noticed the radio falters for half a econd when I turn on the heater fan or use the stoplights. Sounds like a ground to me too,but where?? I don't think it's the alternator case,or it probably would've got either better or worse when I removed/reinstalled the alternator to replace the regulator. Any iseas?
Speed


1954 GMC 350
1957 GMC 1/2 ton
1962 Chevy C-30
1952 Chevy 6400 dump bed project truck
'98 Harley FLSTC
'66 Pontiac Catalina
'76 Chevy 1 ton Duallie
'84 Bronco II
'78 Dodge W-200
'81 Toyota 4X4 truck
Re: Output Voltage #98603 Sun Dec 24 2006 03:01 PM
Joined: Dec 2005
Posts: 324
C
Chester Offline
Member
Did you test the volt gage? try running a dedicated ground on the alt and the regulator. use a multimeter to check the voltage across the battery when running.


"It ain't a truck if you can't hose out the cab."
Re: Output Voltage #98604 Sun Dec 24 2006 06:21 PM
Joined: Jul 2004
Posts: 5,697
A
atomarc Offline
Master Gabster
speed,

This isn't a SI alternator...correct. The regulator you have replaced, the one you also had tested, (?) is a external unit mounted on the firewall or inner fender...correct.

I am not understanding what the connection is between the radio and this problem. It seems you are using the radio to help diagnose this charging system glitch.

The voltage you measured is obviously way to high. The voltage regulators purpose is to limit this value. It seems like two units have been unable to do this properly, so either both were funked up, or the root problem remains.

My first thought would not be a ground issue, but rather a question dealing with the alternators ability to 'see' system voltage and respond accordingly.

If the first regulator is still at hand, it would be interesting to attempt to adjust the voltage relay to see if you could tune it to cutout at the proper voltage.

Did you ask your auto electric person if there could be a internal problem with the alternator itself that might cause this phenomenon.

A '57 GMC is a negative ground rig isn't it?

Stuart

Re: Output Voltage #98605 Sun Dec 24 2006 08:03 PM
Joined: Jan 2006
Posts: 55
1
1947RBT Offline
Member
with the DMM are you Reeding AC or DC voltige If you are reding AC right of the alt. will vary with RPMS but After the Regulater and rectifier you shuld read about 13.5 with about a +-.05%. To me it sounds like a wireing problem to me.

Re: Output Voltage #98606 Sun Dec 24 2006 10:05 PM
Joined: Apr 2005
Posts: 930
S
speed 6351 Offline OP
Shop Shark
I heard the guy at the shop say it was a 15(?) SI;it's internally regulated.
I've been checking the voltage on the in-dash voltmeter against my multimeter,and the dash meter seems pretty accurate,considering the generic looking figures it has.
The only reason I mentioned the radio is that it's problem started at the same time the charging system wierdness started. Could be just a coincidence,but it,too,sounds like a possible ground problem. I've had taillights do the same trick until I re-grounded them.
The voltage I was seeing was both at the battery terminal on the alternator and at the battery itself.
I'm going to try grounding everything seperately and see if that makes a difference Thanks for your ideas-I'l let you know how this turns out...
Speed


1954 GMC 350
1957 GMC 1/2 ton
1962 Chevy C-30
1952 Chevy 6400 dump bed project truck
'98 Harley FLSTC
'66 Pontiac Catalina
'76 Chevy 1 ton Duallie
'84 Bronco II
'78 Dodge W-200
'81 Toyota 4X4 truck
Re: Output Voltage #98607 Sun Dec 24 2006 10:45 PM
Joined: Jul 2004
Posts: 5,697
A
atomarc Offline
Master Gabster
Speed,

This is sort of basic, so I'm sure you have investigated it. If this is a three wire unit, #2 wire out of the DA plug needs to have a good handle on system voltage to properly regulate it.

Although a touchy subject, connecting to the main BATT lug leaves little doubt you are seeing direct alternator output.

I wonder what the 'DA' in DA plug stands for??

Stuart

Re: Output Voltage #98608 Mon Dec 25 2006 02:48 AM
Joined: Apr 2005
Posts: 930
S
speed 6351 Offline OP
Shop Shark
Well,as per the auto-electrician,s suggestion I ran a seperate ground from alternator case to frame,negative battery post to frame,cab to frame,cab to block,alternator case to block and frame to block,no difference. Where's the best place to tie the #2 wire in,to get the most useful reading? Now I'm wondering if I have a faulty connection on that wire thats messing with its reading of the output. What gets me is that this all used to work perfectly,but now it doesn't. The only changes I've made to the electrics since then is I had a pinched taillight wire I couldn't see,and pulled my lights switch out to find out why the lights were going off and on. Found what looks like a circuit breaker kinda thing on there that was cycling the lights. Found where the wire was pinched and put the light switch wires back on and re-installed the switch. I'm sure I got a couple of the wires in the wrong locations because the cab markers and taillights are on with the key switch and the dash lights don't work at all. I can't imagine the lighting problems having anything at all to do with the charging problem. At that time,something was killing the battery every night,and I couldn't find that problem. I DID find that unplugging the DA plug stopped the discharge,so I wired a big toggle switch into the wire from the plug to the battery. that stopped the discharge,everything worked fine,life was good. So far so good,but then the switch failed,so I temporarily connected the wires from it to each other. Now the battery doesn't go dead anymore but I get the charging wierdness. Could those 2 wires that went to the toggle switch be the problem? Maybe I just need to replace that wire with one piece that goes the same route as before I "modified" it.
BTW-I'd think the battery would get kinda hot with that much voltage going in,but it doesn't.And looking at the volt gauge in the dash,it shows 14 volts at idle,and about 14.8-15.0 revved up. Not quite as high as I thought I'd seen earlier.
Did I mention yet that I HATE WIRING?
Speed


1954 GMC 350
1957 GMC 1/2 ton
1962 Chevy C-30
1952 Chevy 6400 dump bed project truck
'98 Harley FLSTC
'66 Pontiac Catalina
'76 Chevy 1 ton Duallie
'84 Bronco II
'78 Dodge W-200
'81 Toyota 4X4 truck
Re: Output Voltage #98609 Tue Dec 26 2006 06:06 PM
Joined: Dec 2005
Posts: 324
C
Chester Offline
Member
have you tried grounding the dash cluster? the feed back to the alt, the volt meter, and the radio usually share these conections. well maybe not the alt.


"It ain't a truck if you can't hose out the cab."
Re: Output Voltage #98610 Fri Dec 29 2006 11:49 AM
Joined: Apr 2005
Posts: 930
S
speed 6351 Offline OP
Shop Shark
I got the charging problem cleared up. Apparently the longer wire I added to connect the toggle switch to stop the current draw was the problem;I removed the addition and connected the wire back the way it was,and now the alternator charges at a rock solid 14.2 volts. I haven't a clue WHY that would make a difference,but it did. Next project is to replace the light switch. I'm not getting any power to my dash lights terminal in the light switch,and one of the sets of overload points is getting a very poor connection;it's been so hot the points aren't staying closed under normal conditions. Seems like this lighting stuff started with a pinched wire on the license plate light,and that started the lights cycling through the points in the switch. I'm wondering if during this,maybe some internal contacts in the switch got cooked,causing loss of connection or even cross-connection of circuits. I have a later light switch or two-I'll check them with my meter tomorrow and if they both work I'll try changing to one of them. BTW- would a 20A circuit breaker be enough to work on the power input wire to the light switch,to replace the points sets on the switch I currently have? I also have a 30A one if that'd be better.
I still need to find out what's up with the radio,but that's way down the list right now. Thanks for all your input-you gave me some good ideas and things to check.
Speed


1954 GMC 350
1957 GMC 1/2 ton
1962 Chevy C-30
1952 Chevy 6400 dump bed project truck
'98 Harley FLSTC
'66 Pontiac Catalina
'76 Chevy 1 ton Duallie
'84 Bronco II
'78 Dodge W-200
'81 Toyota 4X4 truck
Re: Output Voltage #98611 Fri Dec 29 2006 02:31 PM
Joined: Feb 2006
Posts: 395
D
doc41 Offline
Shop Shark
what is the toggle sw for???doc

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