Getting 13.5v on output of alternator. Only getting 13v at positive post on my battery...I should have the same voltage correct? What gauge wire is everyone running for this cable? I plan to get an ohm reading on this wire tomorrow...just making sure Im going down the right path...

Thanks

Cody

 

Are you having some sort of problem?

 

You won't have exactly the same voltage, as there is always loss over any length of cable. That does seem excessive, however, since that is not a very long cable.
Increasing the gauge of cable will decrease the voltage drop. However, the cleaning of cables and connections almost always decreases the voltage drop. I looked at mine and it looks like a 4 gauge, but it is difficult to tell exactly. (Autozone claims it is 4 gauge, btw.)
You can Google wire gauge calculator and find what the expected drop should be for the gauge of cable given the length. Here is a sample: http://www.powerstream.com/Wire_Size.htm
Go to the bottom of the page and enter the data and press calculate. I get about a 1.7% drop might be expected, which would be around 0.2 volts, rather than 0.5 volts. Changing to a 2 gauge (which Autozone also offers) will cut the voltage drop in half.

 

No big problems, but voltage is
Dropping under 13v and coming close to the red.....I thought .5v was fairly excessive drop. Planning a long drive next week and want to have everything up to par....

 

Do you have and underdrive crank pulley? If you do, did you get the alternator pulley as well.

 

No under drive pullies.....

 

Welps, cleaned all cables and it got a little better. Getting .4 voltage drop now. Curious to what others are getting from Alt post to battery post?

 

Well seems like I have been lazy and the problem persists. Really noticeable when the temperature starts approaching the triple digits here in Texas. I plan to replace the alternator wire in the next week or so and hopefully my issue will be fixed. The voltage gauge on the dash is getting close to the red. Ill report back if the new wire corrects the issue.
These readings were taken after the car idled for around 20mins.

 

Clean your grounds too, body ground, engine ground

 

Checked out mine..With positive lead on alternator post and negative lead on battery post I get about 0.1 to 0.08 volts voltage drop between alternator post and battery post. With negative lead on either firewall ground terminal post OR battery ground post and positive lead on alt I get 14.51 at alternator and w/ positive lead on battery post I get 14.44 at battery.. my cars been sitting about a week and battery was taking a charge , probably reason for the 14++ higher voltage reading. By verifying same voltage w/negative on firewall and then battery ground that also verifies ground from bat to chassis is OK. NEXT I turned on AC, blower on max, bright headlamps and radio to get a full load on the alternator (max current to battery through the wire). The voltage drop increased to .25 volts across the wire. Still only half of what you are seeing w/no load. I suspect you may have a defective crimp at alt end or at the splice into batty cable near the post. I did not check resistance in the wire as that would have required disconnecting it from the alternator.

 

What's the battery voltage with the engine shut off, it should be at least 12.5 volts. If it's lower than 12.5 you need to charge your battery up. With the engine running the voltage should be between 13.5-14.5 volts at the battery.

 

Well, I should have spent that $5 last year. Went to Autozone and picked up a 4ga cable and I'm only seeing .08-.09 voltage drop between the ALT and the BATT. I ohmed the old cable and didn't see a huge difference between the 2 cables. Guess the old cable was just seeing more of a increase in resistance as the ambient temp increased during the summer months. BATT voltage at gauge cluster remains above 13V even with AC on.
Hopefully, this helps someone else out there someday!