So then I could just add another 8 gauge wire and run it with the existing wire to the battery?

Why do you guys keep saying to fuse the charge wire when the original isnt fused?

 

Adding an additional charge wire isn't going to help if the alternator can't put out enough power. I took a recording of the current draw this morning. I'll try and put it on the pc when I get to work

Sent from my Telegraph using IB AutoGroup

 

Here's what I did



And yes, I will pull the wire away from the stud on the CAC clamp.

 

https://www.dropbox.com/s/tkexmja1m3...alternator.pdf

 

I get that, but it was suggested maybe the charge wire is causing a voltage drop. I'm assuming that means someone is suggesting the wire might not be up to the task because of size or because of age/resistance.

 

Awesome post!!!

At what ambient temp were these readings taken? Any accessories on the truck running at all during this (headlights, heated seats, etc)?

Also, any chance I could grab your permission to use this PDF on FICMrepair.com to better show customers the value of moving to a larger alternator?

 

I would have never guessed these things are needing well over 200 amps on a cold start. Well, here's hoping I continue to remain trouble free on what I've got. I'm going to keep with the 140 amp unit for now and take some more readings for comparison. It is showing higher voltage at speed, so it's probably better. I'll keep the original in the tool box as a spare I guess. There's just no way I'm going to spend $350-$500+ on an alternator. Thanks all for the comments and for taking those amp readings.

 

DC Power has a YouTube video..:

http://youtu.be/1J9SkmprZm8

Josh

 

I haven't measured the actual length of the factory charging wire, but assuming a five foot length, the 8 gauge wire supplied by the factory sees 3% voltage drop at just under 71 amps (see Voltage Drop Calculator). I use 3% because the National Electric Code in housing opted to pick that percentage drop as the magic allowable, but you can fiddle with the numbers to your liking to get your desired benefit.

The cross-section of an 8 gauge wire is 16.5 kcmil. Adding an additional 8 gauge wire, netting essentially 33 kcmil cross-section of wire (like what a singular 5 gauge wire would be), drops the voltage drop in half, to about 1.48% (per the calculator).

Now...take our factory 110 amp alternator default. They do 100 amps at their peak when hot. At 100 amps, the voltage drop is 4.23% with that singular 8 gauge wire, meaning that 14.9 volts would become 14.27 volts. If someone had the factory 140 amp alternator and we assume a hot output amperage peak of 130 amps, that drop is 5.5% for a yield of 14.08 volts (presuming in each of these cases an internal voltage regulator of 14.9 volts like what many of the DC Power units have - I know that this isn't the case for the factory alternators, but you get the idea).

Of course, should someone want their 270 amp alternator to take up 100% of the 235 amps that MisterCMK's Fluke meter indicated for a load at 235 amps, 14.9 volts becomes 13.42 volts with the 8 gauge wire (for a nearly 10% voltage drop (!), but drops only to something like 14.7 with the addition of a 1/0 wire like what is supplied in the DC Power cable kit.

So...for an individual application, you'd want to look at your max amperage capabilities of your alternator and then have a total cross-section of wire (the combined kcmil amount) such that your voltage drop is minimized.

Or...you could skip all of this mumbo-jumbo, pick up a 1/0 cable kit from us, and know that you are all set!

 

Hah! I had forgotten that they did that, but had recalled that they threw in a 1500W stereo (which a whole lot of guys just don't have, so see it as not applicable to them...). Thanks for the reminder!! With MisterCMK's permission, maybe I'll link to both!

Of course, the larger conversation is that these tests are done when it is nice and comfortable outside. The quick amperage drop off seen on Mister's log is because of a warmer ambient temp. That same test done on a nice 0 degree winter day would keep the amperage draw up for materially longer - like, for two minutes - stressing the living crud out of an otherwise happy FICM.

 

Thanks for the Picture! Anyone see a reason not to run the extra charge cable to the Driver's side Batt?

 

Not a *huge* commercial for the passenger side, but it's worth noting that the load against the passenger side battery is higher (starter, glow plugs), even if the batteries ARE electrically connected.

 

Thanks Ed -- I'm electrically challenged where you actually understand this stuff. I was thinking the passenger side is getting the charge current already and running the extra charge wire to the other battery would help balance the circuit some.

It's always been my passenger side batteries that have gone first -- many times the drivers side is still good! But I always replace in pairs...

I also just want to say thanks for participating here -- you are a valued resource for us all!

 

Maybe it might be a good idea to rotate the batteries every 6 months,that way the battery frame gets a break and lasts a little longer with stock wiring.Personally I run big marine cable and it does the job

 

I hadn't thought of that Per4mance. Certainly isn't going to hurt anything. Maybe on the big "spring clean-up" I could add pulling the batteries, top em off, clean em up, and put em back in the opposite sides.