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Alternator Volts

Hossbaby50

Hossbaby50

3/4 ton status
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How many volts should the alternator be turning out? I did a little rewiring this weekend and now I have more volts being pumped out by the alternator. I basically shortened up a power lead that runs the interior power supply.

The battery is at 13.13 volts with the truck off.
The alternator is pumping out 14.75 volts. Is this to much or is this ok? before it was putting out somewhere in the neighborhood of 14 volts or so.

Is 14.75 volts to much for the alternator to be pumping out or not? Just want to make sure.

Harley
 
You measuring at the back of the alternator?

I found that testing in various locations (fuse panel, battery, alternator) gave a fair bit of difference in voltage.

I don't think 14.75 is too much, although that's a bit more than what mine runs at idle. After rebuilding mine it's about 14.4. Usually the "drop" by the time you hit the fuse panel is on average .5 to 1V from what I've seen.
 
It was 14.75 at the back of the alt, at the battery, and also at the power post on the firewall that runs the power for the inside.

Basically what I did in the rewiring was run heavier gauge wire throughout the engine bay to help with with the voltage draw of the rock lights, ecm, winch, fuel pump, etc.

I ran 8 gauge wire from the alt. to the battery for charging. I ran 8 gauge wire to the power post on the firewall (fused). The power to the firewall post is now provided directly from the battery instead of from the starter post. The alternator exciter wire is still hooked to the firewall post.

Could the voltage gain just be from taking a fair amount of wire out of the system to the to the firewall post? I know that less wire = less resistence = more voltage to the firewall post correct?

Harley
 
Yeah, it could be all that, don't forget that you changed connections too, which are typically not in real great shape.

I'm assuming measured at the alternator, before/after rewiring the output was the same, just less everywhere else?
 
I didn't measure it before the rewiring because I didn't think about it. I just measured everywhere else after the rewire. I just remember that the gauge usually read around 14 volts before I rewired. I only notice because the gauge reads higher now then it did before the rewire.

Harley
 
I am at 14.5+ (just checked) so I don't think that your out of range.
 
Sounds like a good thing too me. You probably got rid of some dirty connections. Mine puts out 15V under heavy load conditions.
 
Sounds like your voltmeter is getting flaky and reading high. The battery voltage should measure 12.6-12.8 volts when the engine is off. 13.6-14.3 is normal charging volts.
 
The 14.75 number was read with my multimeter. I checked the volts after I noticed the voltmeter was reading higher then before it was rewired.

Harley
 
when do you test the battery?

Give it a few minutes, and the battery should drop down to 12.6 after the truck has been running.
 
In my expirence this should be about right with the modifications you made. People in the car audio world do this all the time for their amplifiers. i have seen it done with 0 awg before, and it is quite common. Seems to me that doin this is a good idea for people runnin offroad lights and especially wenches because you maximize altornator output.
 
I've been told that up to around 15V is OK under running conditions, especially when the battery is being charged by the alternator.

Once you get over 15V, you risk overcharging, overheating and blowing up the battery. I had to swap out a brand-new voltage regulator recently because it kept sending 15.8V to the battery!!!!

In car audio circles, 14.4V is the "Magic Value" and is considered perfect supply voltage for amplifiers, etc. Many folks will try to get more voltage than that into the charging system to account for voltage drops along the way so that the equipment really "sees" the 14.4V at their power supplies.
 
Not that this really means much to you Harley, but I've been playing around with Tunerpro RT (PROM editing software) and in the MAF .bin (format of the PROM "file") there is a table the ECM uses titled "Injector Pulse Width Correction vs. Battery Voltage" and there are values from 0VDC up to 25.6VDC! At 20.8VDC though, the injectors apparently shut off, if I'm reading the table right.

Just thought it was interesting since you are running TPI and this was a voltage question.

When I went hunting this year, I noticed the voltage in my truck was swinging rapidly between about 12 and 14 volts under a steady load, and I was worried it might screw with the injection. Surprisingly (or not) there was no difference when I got the alternator working correctly (and with more voltage at idle) than there was when there was an obvious problem.
 
when i took my newly rebuilt alt back to the shop to get it looked at ( bad gauge AND multi meter said 19-23 volts)

they checked it in and out of the truck and in the shop 14.4 is perfect right where you want to be:waytogo:
 
If you hear the battery venting or boiling while charging, the voltage is too high. If it's an Optima, you're hurting it. Same is true if the battery is unusuaully warm while being charged. If you can't touch the case w/ bare hands it's too much voltage.
 
I had a problem with a short in my electrical about 8 months ago that would shoot my alternator voltage up to over 22 volts of power being charged out. My TPI never shut off till I turned it off. This may have been because it was taking power from the battery though which obviously didn't have 22+ volts coming from it.

The TPI did kick the code light one telling me there was a problem with excessive voltage though. I already new this though because my voltmeter was spiked to the top.

Harley
 
Harley, how is this new design holding up? I've got a 140amp alt I'm wanting to put in and I've been rethinking the original wiring config. and wanting to spice it up a lil bit.


Hossbaby50 said:
It was 14.75 at the back of the alt, at the battery, and also at the power post on the firewall that runs the power for the inside.

Basically what I did in the rewiring was run heavier gauge wire throughout the engine bay to help with with the voltage draw of the rock lights, ecm, winch, fuel pump, etc.

I ran 8 gauge wire from the alt. to the battery for charging. I ran 8 gauge wire to the power post on the firewall (fused). The power to the firewall post is now provided directly from the battery instead of from the starter post. The alternator exciter wire is still hooked to the firewall post.

Could the voltage gain just be from taking a fair amount of wire out of the system to the to the firewall post? I know that less wire = less resistence = more voltage to the firewall post correct?

Harley
Click to expand...
 
Sofar so good. I have driven the truck a decent amount and went on a trail run last weekend with no problems. I have bypassed around alot of my stock wiring to make it easier to follow if something goes wrong. When I had the problem on the trail last time it took me about 5 minutes to trace down the problem and have my truck running again.

Harley
 
high voltage!

Our altenator tester at the parts store had a digital readout--it said an internal regulated GM altenator should put out 13.5-15.5 volts,that was considered "normal"--I guess because you are jumping the wires with test plugs on the machine rather than having it connected to the stock harness in the vehicle its possible the regulator "sees" a different voltage signal than it would at the "sensing" wire when installed in the vehicle(I think its the white wire on the 2 prong plug that senses the voltage and tells the regulator to raise or lower the voltage)...I read something about that wire having a resistance built in to make the regulator work properly..without it it might overcharge..:confused:

I've also read that different gauge battery cables than stock can cause the amp meter to read higher than usual,even though there isnt any more amps than before...:confused:

I dont think I'll ever fully understand electricity!!--just when you think you got it all figured out,the rules change!--

I know how a wire a house,lights,motors,etc--then I bought a 3 phase compressor!!!:yikes: :eek: :eek: --still havent figured that thing out!--its got more wires than I can handle--and I dont like playing with 220V!!.( and I cant run it here anyway,no 3 phase current in on my street!).:blush:
 
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