Voltage drop

[2drXmobb]

Hey everyone it's been a long time since I posted a thread. So I have a 94 blazer with a 6.5 and I have been having issues with voltage drops. Originally the voltage would sit at 11 volts I tested the battery and alternator both came off barely at the threshold so I replaced 1 battery and the alternator. This brought the voltage up slightly. I then replaced all the grounds and power wires with a quad star kit and now it's at 13 volts idle with no load. When I turn on my AC it dips back to 11-12ish volts. Not sure what the issue is. Any ideas?

 

[H2814D]

Could be a number of things. You should remember, though, that you have a 31 year old vehicle (the 94's came out in 93) and like most other electric motors (the one in your air conditioner fan), their efficiency deteriorates with age and use. So your fan motor may be drawing more amperage than your alternator can keep up with and that is dropping your voltage down. It could be your alternator is just not keeping up with the total amperage draw, or you could have a bad battery or alternator, even though you say your replaced both of them.

You also mentioned you replaced 1 battery. Do you have two batteries running off of the alternator? The other battery may be bad and that may be drawing down the excess alternator amperage.

Is this a new problem, or has it been this way for a while? Do other things drop your voltage, or just the AC? Lights? Radio? Idle with brakes on?

 

[Cadillacmak]

Hey everyone it's been a long time since I posted a thread. So I have a 94 blazer with a 6.5 and I have been having issues with voltage drops. Originally the voltage would sit at 11 volts I tested the battery and alternator both came off barely at the threshold so I replaced 1 battery and the alternator. This brought the voltage up slightly. I then replaced all the grounds and power wires with a quad star kit and now it's at 13 volts idle with no load. When I turn on my AC it dips back to 11-12ish volts. Not sure what the issue is. Any ideas?

I am an electrician, more information is helpful. Are you testing for voltage with a good meter or your factory gauge? With it running, and a bunch of electrical on, test at the alternator then test at the battery, and then test at fuse block. If you have a lot of voltage drop between these, it could be your wiring. Auto wiring is historically under sized compared to the other industries, and a little corrosion does a lot to drop voltage. The smaller the wire, the more resistance which equals less voltage. Some times its as simple as cutting off the ends back to better wire and installing new ends, sometimes you need to replace the whole cable. Clean connections also, dirty connections also equals resistance, which is less volts and more amps, putting more stress on the cables, and the snow ball starts rolling.

 

[2drXmobb]

I just bought this rig not long ago, previous owner states it's always been at 11-12 volts. I bought a wire kit from quadstar similar to the pt wire kit. Changed all the wires to 2-0 gauge . Brought the volts up to 13 at idle but under load it dips to 12 volts with AC and lights . I'm using the factory cluster gauge . One battery is probably 3 years old and going out but it passed with 12 volts not sure if I want to throw more money on it just to change parts. The previous owner mickey moused a lot of wires I've cleaned a lot of it but I'm stumped. I haven't changed the wire to the starter yet but I'm not sure if that would change the volts. It starts up fine no problem.

 

[scott2093]

Are you testing for voltage with a good meter or your factory gauge?

I'm using the factory cluster gauge

You're not saying you're testing your voltage using the dash gauge are you?

 

[Cadillacmak]

I just bought this rig not long ago, previous owner states it's always been at 11-12 volts. I bought a wire kit from quadstar similar to the pt wire kit. Changed all the wires to 2-0 gauge . Brought the volts up to 13 at idle but under load it dips to 12 volts with AC and lights . I'm using the factory cluster gauge . One battery is probably 3 years old and going out but it passed with 12 volts not sure if I want to throw more money on it just to change parts. The previous owner mickey moused a lot of wires I've cleaned a lot of it but I'm stumped. I haven't changed the wire to the starter yet but I'm not sure if that would change the volts. It starts up fine no problem.

Test with a meter and compare to your factory gauge, they are typically a volt or two off.