1985_K5_Silverado
1/2 ton status
You might have just found the cause of your trouble.BranndonC said:
CK5
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Alt not charging correctly?
- Thread starter BranndonC
- Start date
add more than one ground. make sure to wire wheel the metal before attaching the ground wires. I always add one to the frame from the block, the body/cab to the block, cab/body to the frame, and the bed to the frame.
roadnotca
3/4 ton status
onetonbb74 said:
"dummy" alt light??
What do you mean by a "dummy" alternator light?...if its in the wire that excites the alternator feild windings,it can affect the charging rate if the bulb is the wrong one,burnt out, or hooked up incorrectly..
My 74 K20 had similar problems,I found after installing several alternators that the wiring under my dash was butchered by a previous owner that installed a "custom" aluminum dash with gauges like a stock car would have..and he interrupted the flow of current to the alternator feild when he unplugged the OEM printed curcuit plug from the old dash cluster!..
The weird thing was my truck would start cold fine,but crank slowly and kill the battery when hot..wait awhile,and it would start right up--so I suspected "heat soak" or a starter problem..but every starter and alternator I put in from "good used" stock I had did the same dam thing!..and my voltmeter the "butcher" installed would show NO charge immediately after starting,unless I revved the motor up to 2200 rpms,then it would kick in and charge normally--this was due to the dash cluster wiring being disconnected.(how come it decided to charge after I'd rev it up is a mystery??)..
I had to run a new wire,hot only when the key was on,to the white wire on the alternator 2 prong plug,with a # 194 bulb spliced inline as an "Alternator" light..that solved the delayed charging problem!..
My truck was rusty everywhere,and I noticed a big improvement in cranking speed and brightness of my lights when I added more ground wires from the motor to firewall,and to the frame..this could be your problem too,just not having a ground strap to the firewall can cause lots of electrical wierdness!..
What do you mean by a "dummy" alternator light?...if its in the wire that excites the alternator feild windings,it can affect the charging rate if the bulb is the wrong one,burnt out, or hooked up incorrectly..
My 74 K20 had similar problems,I found after installing several alternators that the wiring under my dash was butchered by a previous owner that installed a "custom" aluminum dash with gauges like a stock car would have..and he interrupted the flow of current to the alternator feild when he unplugged the OEM printed curcuit plug from the old dash cluster!..
The weird thing was my truck would start cold fine,but crank slowly and kill the battery when hot..wait awhile,and it would start right up--so I suspected "heat soak" or a starter problem..but every starter and alternator I put in from "good used" stock I had did the same dam thing!..and my voltmeter the "butcher" installed would show NO charge immediately after starting,unless I revved the motor up to 2200 rpms,then it would kick in and charge normally--this was due to the dash cluster wiring being disconnected.(how come it decided to charge after I'd rev it up is a mystery??)..
I had to run a new wire,hot only when the key was on,to the white wire on the alternator 2 prong plug,with a # 194 bulb spliced inline as an "Alternator" light..that solved the delayed charging problem!..
My truck was rusty everywhere,and I noticed a big improvement in cranking speed and brightness of my lights when I added more ground wires from the motor to firewall,and to the frame..this could be your problem too,just not having a ground strap to the firewall can cause lots of electrical wierdness!..
BranndonC
3/4 ton status
thanks! I installed a new ground today from the battery to the frame. and it still didnt help, i was charging fine at first, but then i stopped somewhere, and when i started it to go home, it was charging at the mid-low 13.X volts.... I think it may be the LED causing the problem, would there be a problem with too large of a bulb? IE a tail light bulb? I have one laying around that I could use.
roadnotca
3/4 ton status
Only two more to go, engine to frame and firewall to frame.
2 things that might help, are to defintitely get a ground from the battery to the engine!!! The alternator bracket should have a nice little hole with a threaded bolt in the top of it just for that purpose, the starter cant get enought juice if the ground isnt attached to the block, remember the engine is sittting in rubber mounts and the likely hood of a 0 ohm short between the mounts and the engine is low.
Second an easier way to find a slow draw on a battery is to take a flashlight bulb, (radio shack for under $1) and a set of aligator clips, and disconnect the ground lead from the battery, connect one terminal from the bulb to ground, and the other to the battery's gound lead. MAKE SURE THE KEY IS OFF AND NOTHING AFTERMARKET IS ON! EXTREME CURRENT WILL POP THE BULB!!!! If nothing is on and the bulb is lit, even very dimly, (Helps to do this in a dim lighted garage with someone watching the bulb), then you have a slow drain, get under the dash, and start pulling fuses from the fuse block until the bulb goes out. When it does the fuse that made it go out, is the circuit with the slow drain.
Simple but effective.
Second an easier way to find a slow draw on a battery is to take a flashlight bulb, (radio shack for under $1) and a set of aligator clips, and disconnect the ground lead from the battery, connect one terminal from the bulb to ground, and the other to the battery's gound lead. MAKE SURE THE KEY IS OFF AND NOTHING AFTERMARKET IS ON! EXTREME CURRENT WILL POP THE BULB!!!! If nothing is on and the bulb is lit, even very dimly, (Helps to do this in a dim lighted garage with someone watching the bulb), then you have a slow drain, get under the dash, and start pulling fuses from the fuse block until the bulb goes out. When it does the fuse that made it go out, is the circuit with the slow drain.
Simple but effective.
BranndonC
3/4 ton status
thanks for the help 69_chevy, i do have one from the block to the battery, that was the only one i had before yesterday, And i'll test for a slow drain. I checked before, and there was not one, but who knows, there could be one now
ProJunkRacing
1/2 ton status
79k20350 said:also dont store the battery on concrete it can drain it and f up the experiment
that is a myth
BranndonC
3/4 ton status
ok, so I put a bigger bulb (not tail light but dash light size, 1/2 wide maybe) and the light now turns itself off and it was charging at 14.4, i let it idle for a while, it warmed up, still 14.4, then I pull out of my parking spot, make a u turn, and face nose in to my spot (I was nose out before) and now its charging 13.5 or so... what gives?
Bulbs..
I used a #194 side marker bulb as an "Alternator" light on my trucks I added an internally regulated unit in place of the OEM externally regulated ones,and my 74 K20,with its "custom" dash that disabled much of the original harness curcuitry..the #194 bulb is the correct resistance needed in the #2 wire on the plug on the alternator.(what GM uses originally!)...too much resistance will lower the output of the alternator,it reduces the current flowing in the feild windings..lower current there = less output....so if you used a #1157 taillight bulb,it could have reduced the output a bit..
You might have an intermittent connection at the wire, on that plug that activates the feild in the alternator..usually a brown or white wire on a GM harness,not sure if painless uses OEM color coding or not..
Most times a GM alternator won't charge,or is undercharging is due to no current getting INTO the alternator feild..--its not a magic device that makes electricity out of thin air,it NEEDS 12V IN, to get the 14.5 volts OUT!..if the voltage is there,then its probably a bad diode trio or regulator causing the trouble..but I find wiring problems in 90% of the trucks I've dealt with..and now have about 6 "spare" alternators with NOTHING wrong with them thanks to friends who run right to the parts stores or boneyards and buy another alternator without diagnosing the real problem,assuming its the alternator at fault..
There is a good site on alternator tech you can find by typing in "Alternator Secrets" on Google...tells all about how they work,how to get 110v out of one,even use one as an arc welder....a bit too in depth perhaps,but it does explain a lot of things I never understood about them until I read it..
I used a #194 side marker bulb as an "Alternator" light on my trucks I added an internally regulated unit in place of the OEM externally regulated ones,and my 74 K20,with its "custom" dash that disabled much of the original harness curcuitry..the #194 bulb is the correct resistance needed in the #2 wire on the plug on the alternator.(what GM uses originally!)...too much resistance will lower the output of the alternator,it reduces the current flowing in the feild windings..lower current there = less output....so if you used a #1157 taillight bulb,it could have reduced the output a bit..
You might have an intermittent connection at the wire, on that plug that activates the feild in the alternator..usually a brown or white wire on a GM harness,not sure if painless uses OEM color coding or not..
Most times a GM alternator won't charge,or is undercharging is due to no current getting INTO the alternator feild..--its not a magic device that makes electricity out of thin air,it NEEDS 12V IN, to get the 14.5 volts OUT!..if the voltage is there,then its probably a bad diode trio or regulator causing the trouble..but I find wiring problems in 90% of the trucks I've dealt with..and now have about 6 "spare" alternators with NOTHING wrong with them thanks to friends who run right to the parts stores or boneyards and buy another alternator without diagnosing the real problem,assuming its the alternator at fault..
There is a good site on alternator tech you can find by typing in "Alternator Secrets" on Google...tells all about how they work,how to get 110v out of one,even use one as an arc welder....a bit too in depth perhaps,but it does explain a lot of things I never understood about them until I read it..
roadnotca
3/4 ton status
This one's a keeper
BranndonC
3/4 ton status
thanks, i'll look for that bulb. Do you think it'd be the same for a cadillac alt from a 1976 caddy?
The current through the number 2 wire doesn't actually control the alternator output. Changing the resistance in the number 2 wire does change the current in the wire which adjusts the RPM the alternator turns on. Lower resistance = more current = lower turn on RPM. Once the alternator is on the field current is supplied by the alternator itself through the diode trio as disel4me described.
1 wire alternators don't have a #2 terminal. Permanent magnets inside the field generate the voltage needed to turn the alternator on. They have to be spun up to a certain RPM to make enough voltage to turn the alternator on. Once on the alternator powers the field throught the diode trio just like a standard alternator.
1 wire alternators don't have a #2 terminal. Permanent magnets inside the field generate the voltage needed to turn the alternator on. They have to be spun up to a certain RPM to make enough voltage to turn the alternator on. Once on the alternator powers the field throught the diode trio just like a standard alternator.
surpip
1 ton status
also might want to check for a good connection on all the points, back of alt. batt. etc, just make shure everything is clean and tight
BranndonC said:
I just went through the same thing as you (I think). I rewired my 1980 K20 using a Painless wiring harness and aftermarket dash (Dakota Digital). I was using the stock v-belt alternator for years and it would not charge at idle, but would after I blipped the throttle (self exciting). I ran it that way for years and never really thought about it. I then swapped in a BBC and used a serpentine setup with a new style alternator. It would not charge for squat. I also noticed that my Optima Red Top died from the constant deep unchargeing. I bought a new battery but that did not help. After some phone calls and research, I found that the white exciter wire was not getting 12 V which it needs. When I installed my DD dash it did away with the dash light and subsequently the 12 V going to the exciter. I read my painless wiring harness book, found the wire under the dash (white #914 be careful as there is another white wire in the same harness that can fool you) and hooked it up to a keyed on ignition switch with an inline resistor (of at least 35 ohms of resistance). The charge lights acts as the resistor, but if not used, you need to install a resistor inline.
Hope this helps.
more Bulbs...
I've always used a #194 or #168 bulb on GM alternators I install on old farm tractors and other equipment that had old fashioned generators..since GM used those bulbs in the dash on OEM wiring,I assumed they had the proper resistance..
I see "10 ohm resistor" in my wiring diagram on trucks equipped with voltmeters rather than idiot lights..you NEED resistance there,because if the regulator SEES a full 12 volts at the #2 "sensing" terminal,it will assume the battery is fully charged,and send little amperage to the battery to charge it..
I don't dispute the fact the amount of resistance will alter the RPM at which the alternator "kicks in" and starts charging...but I was always taught controlling the voltage at the #2 terminal is what determines the amount of amps it will crank out...all the text on building a welder out of a GM alternator says to apply a FULL 12 volts to the feild,for "maximum voltage and amperage output"...one set of plans I read even showed one setup that uses the dimmer in an old headlight switch to adjust the volts and amps of the welding alternator,by turning the knob and varying the voltage supplied to the field coil ..that and the rpms its turning at...
My 74 K20 would somehow "energize" itself even with no current at the #2 wire when I'd rev it to about 2500 rpms..it must have had enough residual magnetism in the windings to "kick" it in!..it was not a gentle "kick" though,I blew a few diode trios,a regulator,headlight bulbs, and a few ignition modules until I figured out the cause,and fixed it!...
I've always used a #194 or #168 bulb on GM alternators I install on old farm tractors and other equipment that had old fashioned generators..since GM used those bulbs in the dash on OEM wiring,I assumed they had the proper resistance..
I see "10 ohm resistor" in my wiring diagram on trucks equipped with voltmeters rather than idiot lights..you NEED resistance there,because if the regulator SEES a full 12 volts at the #2 "sensing" terminal,it will assume the battery is fully charged,and send little amperage to the battery to charge it..
I don't dispute the fact the amount of resistance will alter the RPM at which the alternator "kicks in" and starts charging...but I was always taught controlling the voltage at the #2 terminal is what determines the amount of amps it will crank out...all the text on building a welder out of a GM alternator says to apply a FULL 12 volts to the feild,for "maximum voltage and amperage output"...one set of plans I read even showed one setup that uses the dimmer in an old headlight switch to adjust the volts and amps of the welding alternator,by turning the knob and varying the voltage supplied to the field coil ..that and the rpms its turning at...
My 74 K20 would somehow "energize" itself even with no current at the #2 wire when I'd rev it to about 2500 rpms..it must have had enough residual magnetism in the windings to "kick" it in!..it was not a gentle "kick" though,I blew a few diode trios,a regulator,headlight bulbs, and a few ignition modules until I figured out the cause,and fixed it!...
I think we are on the same page diesel4me. Full voltage on the input would generate max power. I agree with you on the residual magnetism too. I bet that alternator came on with a vengeance.
I forgot that SI alternators are 10 ohms. The newer CS alternators use 35 to 300 ohms. 10 ohms would be a 12V bulb rated at 14.4 watts. Anything close would probably work.
I said earlier that the #2 wire is the one that the light or resistors hooks to. That might be wrong. Either way it's the small white wire on SI alternaotrs.
I forgot that SI alternators are 10 ohms. The newer CS alternators use 35 to 300 ohms. 10 ohms would be a 12V bulb rated at 14.4 watts. Anything close would probably work.
I said earlier that the #2 wire is the one that the light or resistors hooks to. That might be wrong. Either way it's the small white wire on SI alternaotrs.
