I'm in kind of an odd situation in that I need a LOWER output alternator for my 99XJ (to play nice with the BMS of a lithium battery) and I see that the 98/99 is rated at 90amps. However, the 99 has a plug and the 97/98 seems to have two studs. Are these the same charging systems just with a different method of attaching to the CPU or are they different in some way that makes them incompatible? It would be great if I could just strip the plug wires and use the earlier alternator. Having a hard time finding information so any replies are much appreciated. I'm also wondering if a 117A alternator ever actually reaches max output. If it's only charging at 90 or below in real life then I'm good already!

Others can help more than me , but I think it will be ok as long as you make the plugs compatible (by cutting & joining)

They are Denso 90A and they are regulated by the PCM, so as long as the systems are similar, it should work, but ur wise to research

However, I am thinking it may be better to consider another dual battery controller that can cope ??

The alternator will only put out what the total system requirements are...It doesn't magically throw out the full amperage unless there's something calling for that much draw... Not sure what you're doing but the biggest factor for the lithium battery charging system upgrade is the temperature sensor and some type of charging cut-off if you're retrofitting it...

Unfortunately dual battery costs me more weight and space than I can afford, and fortunately this battery is rated for the use, just need to keep the alternator within spec.

Good point, but the battery manufacturer list the battery as compatible to drop in to an alternator system as long as the alternator is within the recommended charging amps, so I'm thinking the internal BMS can't regulate how 'thirsty' the battery is, meaning maybe it can pull more than is healthy for it if there is an available charging source?

Full alternator output capability is usually rated at 6000 rpm. You'd need to measure the crank and alternator pull diameters to figure out what that translates to in engine rpm. I think the alternator pulley is 2-1/4" and the balancer is 7" which would mean full output capability around 2000 rpm. You're saying the full rated output of the alternator is higher than your bcm can handle? I would expect the BCM to only pull as much current as it needs to charge. PCM will control the alternator output current to maintain the voltage.

I would think the same but they are very specific about the max amps of the charging source, so apparently that is not a function of the BCM. I'm trying to figure out the best way to put it under load and just check the amp output simulating the maximum output at say, 3000 rpm. I read the with PCM regulated alternators, the PCM decreases the alternator output when the engine is loaded heavily (like going uphill) and increases it when the engine is under less load (going downhill) to get a bit more HP out of the motor. Not sure how to simulate that part of things.

You might be able to locate an oversize pulley too. The racing guy use them to free up a few extra HP.

fwiw my '98 & '99 had the same alternators. Of course that might be an export/RHD thing or, given the age of the vehicles, either, or neither, of them was original.

For the purposes of trouble shooting I briefly use my spare '96 alternator which isn't actually as different as it first looked & the '98 now has a replacement listed for XJ's but needed the charging wire connection changed (as it pointed in the wrong direction) and the pulley replace because it was too big (an alternative might've been a longer belt, but I only learned about buying belts by length, rather than application, later0.

So, pretty much like awg said, if they're about the same size & the mounting lugs line up, all the rest can be made to fit/work.,