Alternator sizing question

[65 drop top]

I’m about to order a new wegner front drive for my ls3. I can choose either a 170 or 225 amp alternator. Car has all the common electronics such as efi, electric fans, A/C, electric fuel pump, power seats, power windows, stereo etc. so I thought i should order the 225 amp to leave me plenty of room. I have an AAW highway 22 which has a 175 amp mega fuse. Will ordering the 225 amp alternator blow the fuse? Can I upsize the megafuse? What are you guys doing, are you finding the 170 amp alternator sufficient? Thanks in advance.

[dontlifttoshift]

It's the idle output that matters and the 225 should do better there. You would have to work pretty hard to need 225a ever but needing more than 120 at idle is a possibility. Picture 850w fan, hot as balls outside, AC on full blast, etc. That said, the 170 is usually fine in most applications.

Yes, you can upsize the fuse but remember the fuse is there to protect the wire and it should be also upsized accordingly.

[dhutton]

A 225 amp alternator can deliver 225 amps if needed but it doesn’t unless needed. Hard to imagine you would need more than 175 amps fuse but you could upsize it if needed. Here’s a 250 amp.

https://www.summitracing.com/parts/bss-amg250?seid=srese1&ppckw=pmax-stock-replacement&gclid=EAIaIQobChMIp5iUncXAigMV1pjuAR1TGAI1EAQYASAB EgKKqvD_BwE

In theory you should use a larger gauge wire but honestly I don’t think it’s necessary. The increased voltage drop will be minimal.

Edit: Donny says upsize the wire so I would take his advice…

[dontlifttoshift]

lol! arent you an EE?

The fuse really won't matter as it is on the feed from battery/starter to the fuse panel and only really protecting that circuit anyways.

What I didn't put in the other post, I have yet to max out a 170 amp alternator in any application.

[dhutton]

lol! arent you an EE?

The fuse really won't matter as it is on the feed from battery/starter to the fuse panel and only really protecting that circuit anyways.

What I didn't put in the other post, I have yet to max out a 170 amp alternator in any application.

Yes but I have been schooled too many times disagreeing with you Donny… :razz:

Don

[ULTM8Z]

Yikes... even my factory 140 amp 2001 Silverado alternator seems to do just fine on my Camaro...

EFI, pretty decent stereo system, power-hogging Ford Taurus two-speed cooling fan, A/C, etc..

Voltage never goes below ~13.8-14.0V even at idle, at night with the lights and A/C on...

[Hotwire]

Don't change the fuse, it's there to protect the highway 22 wiring system. Should you run an aftermarket stereo with amp, the amp SHOULD have it's own power wire to the battery so you'd never have that draw across the existing harness or fuse..

[dhutton]

Doesn’t the highway 22 have two mega fuses? I assumed we were discussing the one dedicated to the alternator feed and it doesn’t supply the fuse block etc.

If anyone is interested the derating curves and thermal performance are detailed in the spec sheet. Max load decreases considerably as ambient temperature increases.
https://www.littelfuse.com/assetdocs/littelfuse-datasheet-mega-32v?assetguid=9fe0cd60-17bf-4fd7-b18d-977d32179af9

Don

[65 drop top]

Doesn’t the highway 22 have two mega fuses? I assumed we were discussing the one dedicated to the alternator feed and it doesn’t supply the fuse block etc.


Don
This is how I plan on wiring it

[65 drop top]

Also, on the topic of alternators, Wegner’s website says “ Standard Internal Fan 170 Amp 1 Wire or GM 2” . What is the better method?