More on ACR with Battery Chargers

Maine Sail · Feb 17, 2016

Dan,

The P12 is a pretty cool charger but IMHO the "pre-float" is more of a marketing tool to separate their product from others. With an ACR all batteries will be at the same voltage from 13.0V (combine) until the house bank reaches the absorption voltage set point where again they will be at the same voltage. There is no "over voltage" during bulk..

The article below will explain anything you ever wanted to know about ACR/VSR/Combiners:
Making Sense of Automatic Combining Relays (LINK)

When we consider that the last few % of charge is the least efficient, and takes the longest, I just measured the last 4% of capacity on an AGM at 3.5 hours, using an ACR is highly unlikely to cause any over-charging. If anything the 4 hour absorption limit of the P12 may be a bit on the short side especially as batteries age & sulfate. This charger is still ONE charger with ONE charge profile. What it does is allows you to set a time limit & current limit on output 2 & 3. When that time and or current limit is reached that output has another diode tossed into the output path dropping the voltage by .5V - .6V for that output. If you have an ACR there is nothing wrong with using that feature but I don't see it giving you any more longevity on a start battery than you would see with an ACR. With ACR's it is not uncommon for me to see start batteries out last two or more house banks despite being combined when charged with the house bank. Our biggest worry in the marine market is sulfation from under charging and not over charging.

The P-12 is a cool charger, well built, yet quite expensive. The 40A P12 sells for about $585.00 and the 40A Sterling PCU we can sell for $315.00. That is a pretty huge price difference, $270.00 more, on a 40A charger.

Maine Sail · Feb 17, 2016

Dan_Y said:
Interesting. Thanks Maine Sail, I appreciate your input!

Also remember that the ACR has not been charging any differently than any multi-output charger with one charge profile and multiple outputs has been for eons. If start batteries are getting over charged, by getting the same absorption time as the house bank, then they have been for well over 30 years by every multi-output smart charger out there yet the start batteries in almost all cases outlast the house banks..

Again not a bad idea, it's a solid product but you pay a large premium for it.