Current Load Calculations - Much larger alternator needed

[ETI4K]

I'm in the process of making wire harness changes that include upgrades and additions that will increase the total current requirement from the alternator/battery.  Ultimately, besides wire gauge changes, the alternator will need to be upgraded.  

For this calculation, I started with the belief that winter and summer might be very different.  Turns out, maybe not so much. 

Loads are computed at minimum charging voltage: 13.5 (arguably).

Lighting current is based on using incandescent bulbs which also will see "persistent" and "transient" use.  The persistent load comes out to about 17A, while transients total around 16A.  I took a WAG and chose 25A for both.

Some other transient loads, such as power windows, are not included. 

Audio equipment is not included.

The highest load case in this example is 134A.  If you believe in safety factor, and I most certainly do, it looks like I'll need at least a 150A alternator. 

 

Has anyone successfully used an alternator rated in the 150 - 200A range?

Edited March 26, 2020 by ETI4K

[sweatybetty]

150 amps? That means the wire from the alternator needs to be about the same size as the battery cables...........

[AZDatsun]

You should be able to put as large an amp alternator in as you see want if you can find one that fits properly.


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[ETI4K]

sweatybetty: Yep.  Looking at #2AWG. 

AZ: I was trying to find an OEM type (rather than one that's been amped up - pun intended) to ensure a long and healthy life.  I did just read that Megasquirt 3 provides control signals for about any alternator, so suddenly the process gets a lot easier.  But, as you said, it's down to finding one that fits, and I believe the higher output alternators have larger cases.  Finding the right one is tough to do over the internet.

[grannyknot]

Both the GM CS144 and the AD244 alternators are good alternatives, the modifications to fit a L series engine are minimal and both can put out up to 200 amps with upgrades. I used a GM CS144 on my first 240z and it was putting out 150 amps if needed, they are also inexpensive and available everywhere. Lots of good info on Hybridz, here is just one thread, https://forums.hybridz.org/topic/67531-ac-delcogm-alternator-swap-part-2-cs144-installation/?tab=comments#comment-634683

Edited April 12, 2020 by grannyknot

[wheee!]

I have a GM 12SI in mine. Easy mod.


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[ETI4K]

grannyknot: Thanks for the link.  That's a very helpful bit of info.

wheee!: What's the rated and actual output of yours?  Sorry if that info is posted on your excellent restoration thread.  I've only made it through 30 pages so far.

Edited April 15, 2020 by ETI4K

[AK260]

Granny lot and others beat me to it. The 12si is a well rehearsed favourite and a CHUNKY bit of kit. I do hope you will up your compression and cam duration to carry the extra weight ;)

Here’s another interesting link to read ...


http://www.edmontonzcarclub.com/pages/articlepages/alternator.html

[ETI4K]

I've been looking at the 12si for a while.  They can pack a lot of amps into one, which at 140A or better makes me nervous about reliability.  Also was looking at the CS144 which supposedly can better handle higher outputs, but they tend to be a bit pricey. Before I had decided, my brother offered me a spare he has for his Cadillac. It has a 140A capability,  PLUS IT'S FREE.

Guess my decision is taken.  It'll be easy enough to upgrade later if it can't keep up.

Thanks for the link.

[Zed Head]

Are you going to swap to the multi groove belt?  Higher output means more work on the pulleys.  I think that to "do it right" and avoid slippage you'll want to take a good look at the drive system.  Of course you'll only need it if you actually pull that amount of amperage.  Some of those loads are intermittent and could just use battery power, in between.

It would be interesting to see how much capacity is really needed.  Many people upgrade based on overall output when what they really want is idle output.

[Zed Head]

I looked for an output plot and found one in this article.  It's actually a pretty good overview, just boat-based.

https://shop.pkys.com/Installing-a-High-Power-marine-alternator-on-your-boat_b_111.html

[ETI4K]

I seriously wanted to convert to serpentine style drive.  The BHJ Dynamics damper and Sanden A/C compressor are available in 8-rib, and of course, an alternator pulley is no problem.  The problems are, I couldn't find a water pump pulley,  and to use a single belt (with A/C) requires two idlers.  Fitting them in (in CAD) was not easy.

Thanks for the article link.  I'll read it later.