Add Electro-Max to your list of replacements; the ability to kick out 90% of rated output at idle makes it a winner in my book.
Your 4 t105's are 450 AH's, 25% of that for bulk charging would be 115 ah, with a echo for the rest. The Electro-Max 100 would do, and is possible without having to go with v-belt and expensive pulley mod's.

That's what I'm looking at for my set up.

 

My .02..

Ample Power - Makes a reliable regulator but it really lacks in the options & programming area. They also do not answer phones and only do tech support via an on-line forum. I stopped using them a while ago due to the lack of support and lack of programming options. Still, they build a reliable regulator

Xantrex - Just google Xantrex tech support.... The Xantrex XAR regulator is made by Balmar for Xantrex, enough said... Why buy Xantrex when you can buy the Balmar and get Balmar support?

Balmar - IMHO the best support in the industry. Dale, Tom, Rick & Rich are always available and bend over backwards to help. The Balmar regs are very programmable to do what ever you need or want.

Your Bosch alt is likely internally temp compensated via the voltage regulator. Some Hitachi's, Valeo's etc. are the same way. When they heat up they reduce voltage which in-turn reduces current output. It is a self protective feature but one that leads to chronic undercharging on boats with large banks..

You may find that the alt does the same thing if using the Balmar alt temp sensor. These alts were never designed for high output applications and don't cool as well as an alt built for extended high output run times. The difference is the Balmar temp sensor can be adjusted and you can also limit the field to allow the alt to run at say a max of 50A vs. the 65A it is rated for. It can likely run at 45-50A all day long without over heating or going into temp limiting but you'd need to play with the field output to figure this out......

 

My .02..

......
Your Bosch alt is likely internally temp compensated via the voltage regulator. Some Hitachi's, Valeo's etc. are the same way. When they heat up they reduce voltage which in-turn reduces current output. It is a self protective feature but one that leads to chronic undercharging on boats with large banks..

You may find that the alt does the same thing if using the Balmar alt temp sensor. These alts were never designed for high output applications and don't cool as well as an alt built for extended high output run times. The difference is the Balmar temp sensor can be adjusted and you can also limit the field to allow the alt to run at say a max of 50A vs. the 65A it is rated for. It can likely run at 45-50A all day long without over heating or going into temp limiting but you'd need to play with the field output to figure this out......

Thanks Maine... I'd be quite content if I could get up to 50AH steady while motoring... that would mean the ability to recharge the bank in approx 3-4 hours vs 10-12 it would take now... Now even with a relatively low bank, while I charge at 35A or so for 10 minutes it's soon down to 10A or less. Not satisfactory.

Add Electro-Max to your list of replacements;

Hadn't heard of that one.. will check it out. Thx.

 

I agree with MaineSail 100%. As usual.

However, I believe you'd be better served if you could possibly squeeze out enough $$$ to replace that alternator, as well as add a good external charger.

You can find Balmars at decent discount prices, but one I've been very happy using with clients is the PowerMax alternators sold by Hamilton Ferris. I've been using the 125A model (about $458) and de-rating it to about 100A using the Balmar MC-612 or MC-614 regulators.

The PowerMax's are very well built and will easily put out 100A for as long as you need it. And, you don't need any fancy upgrade to the belt drive system. A single 1/2" or even 3/8" belt will do the trick at this output level.

There are good discounts available on the older MC-612 regulator, too, which I prefer to the newer MC-614.

Bill

 

I have the Balmar ARS-5 series, works great. You can save some $$ by going with the ARS-5 vs. the MC series. My boat yard said ARS does everything you need just fine. They were right.

 

You can get a 90A Leece Neville alternator for less than $200, and they make alternators for Balmar. Why spend more than you have to?

 

On Mainesails advice we replaced our old Hitachi with an ElectroMax 100 ( last one where no sepentine belt is needed. and 614 Balmar Max regulator. The amount of amps generated by it at the lower rpm range was far superior to the Balmars. We purchased it with a temp sensor as well.

It amd the Mastervolt 3 stage charger were the last piece to complete our electrical system upgrade. Have noticed a much better greater amp charge into our 6 volt agms at normal operating ( 2700 rpm) and idle for our Yanmar 3GMF