Canter with 2 alternators

Generally not, alternators are meant to have a battery connected to them to filter the output. If the alternator is not designed for operating without a battery the transients on the output can damage the rectifier diodes, the transients may also damage a DCDC.

Depending on the batteries and the alternator you may be able to charge the battery directly off the alternator without the DCDC.

Does the truck itself (lights etc) run on 12v or 24v. If 24v why not get rid of the 12v system and use a 24v to 12v Dc DC charger off the 24v system to charge the 12v battery bank.

My vehicle is 24v and I a 24v to 12v Dc Dc smart charger to charge the 12v battery. I used to have a 12v alternator to do this but it easier to just go the Dc DC charger.

You cannot run a Dc Dc charger direct from an alternator as it will kill the alternator.

Yo could charge the lithiums directly from the 12V alternator if you wished. No need for a DC-DC charger.
Just check the alternator capability and output voltage first.
Problem is those that have not done it will tell you that you can't .
Cheers,
Peter
OKA196 motorhome

As Peter mentioned you could directly charge the new batteries from the 12V alternator if they can handle the available current.
Don't necessarily believe all the doom sayers and irrelevant slow revving poor airflow alternator YouTube videos portraying rapid alternator death. Ours spins c3000 rpm at slow idle.

Our 4 cell 300Ah LiFePO4 battery has now survived 8 years of full-time travelling being charged from our 12V 100A rated Canter truck alternator at 75-80A until full. No smoke yet or if there has been there is still an awful lot left.
Any reasonably priced DC-DC charger added would severely increase charge times.

As mentioned in previous posts our setup is a little unorthodox in that we have a single battery to both start the truck with ease and supply the house behind. It has survived perhaps a few thousand 740A peak current engine starts so far.

It is common in the yachting world to run 2 alternators and the Mercedes G military are 2 running 12 & 24v,
With Lithium if the alt volts are set correctly (less that ~14.1v) then it will work fine, the problem comes if you use batteries with a inbuilt BMS and the cut in and disconnect the battery, the alternator volts will go crazy high and blow up your fridge, etc.

Have a look at a company called WAKESPEED who make a regulator for the alternator called Wakespeed-500. It is very popular in this application
Steve

thanks for the info ....