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Decreased charge time, surely! B2BC's used to be expensive but are perhaps better value now and the better charging performance worth the investment. I still tend to think in marine terms where an engine might run for 12 hours a day and there might be charging current available from somewhere - genset, aux or propulsion, for much of the daily load cycle. As such it's not so important to get charge into the service batteries quite as fast. In wiring terms the only real difference is that it will require more substantial negative connections than the low-current sensing wire of the relay. It will also probably require free airspace for cooling.
OT but does anyone remember Lucas 4BD split charge diodes in oilfilled cans like ignition coils? Found a few of those in my old service stock the other day dating from the mid 70s, including a pos-earth (common cathode) one. Only any good with a battery sensed regulator of course, and sure enough there were battery sensed 4TRs, 14TRs etc in the kit. And even a NOS 3AW warning light relay for the venerable 11AC. But I digress...
I do,vaguely,the 11ac was standard on some Jags,and various small Perkins,etc...what a mass of components,compared to today's gear.
Control units,field relays,and a bumble-bees heart of an alternator buzzing away at the end!
I appreciate your scenario re split charge relays,but with limited depletion,and use by your good self,problems would be rare.
In situations where there is not a "dedicated" charge alternator,as such,say just a vehicles standard fitment,and the aux batteries are flattened by a liverie's kid's laptop and lighting use...the 40A it tries to pull when that relay closes,plus the vehicles ancillary use,just murders the poor alternator.
Found one 2 year old MAN 18 tonne truck,with a 45A alternator as standard! Retro-fitting a 120A upgrade,was £850,12A current limited B2B unit was £70,so,customer had change for a new Stubben (saddle)
As a kid,i used to stalk an old auto-electrician,he had a very bad hunchback,and temper to match,but i learned many things...one was his reluctance to clip a Durite ammeter on,when testing charge rates,preferring to ask "can yer keep yer 'and on the casing,more than a couple of seconds?" ...a "yep" would mean no further discussion
As for my lock gate analogy,it IS possible to open them against a filled lock,or the upper level...just requires a Yale strongback or pull-lift,slung across the gate beam ends...don't ask...all i remember was THAT was the easy bit,removing all the old safes and shopping trolleys obstructing the sluices was a messy pain