"It contains circuitry that monitors the voltage and switches the batteries together for charging or apart for use when not charging."
Great , but why bother, with costly complex electronics??
There is no charge unless the engine is running , so joining the house to the start batt , after engine start is all that is required .
Maybe because a VSR can work with multiple charge sources, does not require key on excite, and some, like the Blue Sea version, are extremely reliable.
I can't even count how many Blue Sea ACR's I have sold or installed over the years but it is many, many hundreds and I have yet to see one
actually fail. Sure a few of them got miswired (only three wires but still that can apparently get messed up) and the owners claimed they were not working but in the end it was a DIY wiring mistake and the ACR was actually fine.
The Blue Sea ACR in-particular is one of the most reliable pieces of gear I have come across in the marine market. I say this when I currently have two failed Mastervolt Battery Mate low volt drop mosfet isolators in my trash bin as well as an old school diode isolator..
Rather than using
gimmickry, in an attempt to protect a cheap relay, like some VSR makers try, Wayne K. spent a long time working on the actual contacts for that relay so they could handle the abuse of the designed duty.
The "solenoids" used by most builders (Cole Hersee etc.) are quite often not up to that duty and I replace a quite a lot of them that have failed. Builders such as Hunter, a number of Downeast builders and numerous others used cheap solenoids over the years that have cost a number of my customers some good money on towing when they failed without warning.
I have a customer with a thruster circuit that burned up five paralleling solenoids over a few year period. This all at total cost to him, from various boat yards, of well over 1.5K in repair and trouble shooting bills. None of the yards ever solved the problem because they kept replacing a relay that could not handle the amperage or duty cycle.
When I was called in the problem was obvious and solved in about three or four minutes of glancing at the system and builder schematic.. His Blue Sea ACR has been plugging away now for over 8 years, in this same system, with zero issues. It also charges both banks, via solar, when his boat is on the mooring at his island house.
While those relays are certainly inexpensive they can be less than reliable with the current that can be expected to pass through them on many boats.
For a few dollars more you can get excellent reliability, start isolation, charging from multiple sources etc. with a product actually designed from the ground up for the task. One of the first things I noticed Marlow did when they bought Hunter Marine was to do away with the unreliable Cole Hersee key-on solenoids for paralleling. I can't even recall how many of those I have replaced that have failed, but it is far more than I ever should have..
