CrawlerXJ

Replaced 90amp alternator with a 160amp. When lights, a/c, off-road lights, etc are on, voltage drop to 12.5 still. Bad alternator?

13.48 at battery nothing on
13.60 at alternator nothing on
12.50 at battery with everything on.

Checked battery, it shows 100% on batt charger. So, its charged.

This is the same as the stock alternator. Arggg

Any ideas?

Turbo X_J

Anything over 12 is fine, 8 would be a problem.

SeriousOffroad

Higher amperage does not mean higher voltage....it means higher AMPERAGE.

Voltage is regulated by the VOLTAGE REGULATOR in the PCM.

CrawlerXJ

Fair enough. I would think 160 amp would keep it at 13.5 since its huge. Maybe I am wrong.

CrawlerXJ

So upgrading is snake oil then and I bought into it?

SeriousOffroad

No, not at all. A lower amp rating means that you'll be short on amperage when trying to run high-amp draw lights, stereo gear, winch, etc.

With higher amperage available from the alternator you won't be short on available current.

Keep in mind that you aren't getting much of an increase in amperage at idle unless the alternator is rated for high amps at low RPM's.

If you need more amperage at idle, install an Extended Idle Switch.

CrawlerXJ

To be fair, this was at idle. Maybe ill try it driving.

SeriousOffroad

An extended idle switch will hold your RPM's at 1100.

Have an assistant hold your throttle to maintain 1100 and measure your amperage instead of the voltage. Then measure at idle and see what the difference is.

allevolution

Yea youre fine, One thing I would do if you need more amperage is upgrade your big 3. That is:
1. alternator to battery charge wire (+)
2. Engine block to frame ground (-)
3. Battery Ground to frame ground (-)

Also what you could do if you had to keep voltages up
(dont see why you would have to) is buy additional batteries. Or maybe an adjustable transpo regulator like I have.

but then you run into possible issues with charging voltages that are going to be higher than your battery was designed to handle and PCM also.

CrawlerXJ

I found one place to sell the big 3 upgrade. They want $100 for the kit I think. Cheaper place?

Radi

Your wiring is deficient. You are losing 0.12 volts in the short run of cable between the alternator and the battery, similar losses are most likely happening everywhere else. These are resistive losses so the more current you draw the higher the voltage losses will become. Likely can be fixed by upgrading wiring gauges and making sure all connectors, grounds, etc are clean and tight.

Turbo is right that it really isn't an issue as long as your charging voltage remains higher than the nominal battery voltage. As long as that's the case the battery won't discharge, even if you do have some losses. Once your system voltage drops below nominal battery voltage you start draining the battery.

CrawlerXJ

So, you're saying its not normal then?

Radi

It's pretty normal, but it isn't ideal. XJ's rolled off the assembly line with the smallest gauge wiring they could get away with.
If you are going to upgrade the alternator and actually make use of that additional current capacity, you also need to upgrade the wiring to carry that extra current. The OEM stuff was marginal with just the OEM loads.

What concerns me is that you are dropping to 12.5 with 'everything on' and aren't anywhere close to running the alternator at capacity. That's acceptable for now, but if you add stuff down the road- larger sound system, a winch, more lights, you'll drop down below the point where the battery is charging and go into discharge, even though the alternator is capable of supplying the current. Upgrading the wiring will keep that from happening until you hit the current capacity of the alternator.

CrawlerXJ

Better pricing than this?
http://custombatterycables.com/appli...kee_cables.htm

SeriousOffroad

You missed the part where he said his rig was just at idle.