Battery Isolator, ACR or Battery to Battery Charger

[DaveBMusik]

Just wondering what everybody uses?
The more I learn, the more I don't know :)

I have a simple Guest Isolator http://www.marinco.com/en/2530 coming off the alternator.
This seems to have worked OK as the batteries have lasted eight years.

As I look to replace my four T105's and Group 27 Start Battery, I keep wondering how my Balmar 110 alternator / ARS-5 charges the house bank efficiently without frying the start battery.
I'm considering 2-3 110Amp 12 Volt Firefly batteries -suggested Balmar settings: Start Delay 30 sec., #High Voltage Limit 14.4V, Compensation Limit 14.8v Fac. Default, Bulk Voltage 14.4V, Bulk Time 30 min., Absorption Voltage 14.3V, Absorption Time 60 min., Float Voltage 13.4V, Float Time  6 hrs.
If I don't go with Firefly's, I'm considering four Trojan Reliant T105 AGM's.
I'm am unsure about a start battery in either case.
I also have 200 watts of solar, Blue Sky MPPT with very customizable charge parameters along with a Xantrex True Charge 40 with just three basic battery settings.

A Sterling Battery to Battery Charger https://shop.marinehowto.com/products/sterling-power-60a-dc-to-dc-slash-battery-to-battery-smart-charger-star-new-star
seems to be the ideal solution but is it really necessary?

Thanks to all of you EE's out there!

Dave
   

[Dave Spencer]

Dave,
Others more knowledgable than I will likely chime in but I would suggest dropping the Isolator and going with some kind of Echo Charger.  The one you referenced to Mainesail's site looks like an excellent choice.  I have a less expensive and less capable Xantrex Echo Charger and it has served me well for many years.  http://www.xantrex.com/documents/Accessories/Auxiliary-Battery-Charger/Echo-charge-OwnerGuide(445-0204-01-01).pdf
Starting batteries live a fairly easy life and they aren't discharged very much at all during their starting duty cycle so the demand to recharge them after staring the engine is very low.  Here's a video from... who else... Mainesail showing how starting a 44hp Westerbeke uses about a tenth of an amp hour.  https://www.youtube.com/watch?v=nrQXnqNOI9Q
When I look at the Guest Isolator manual downloaded from the link you provided, I think I'm seeing that proper operation means there is a 0.4 to 0.6V drop across the isolator making it very difficult to precisely set the optimum battery charging voltage from the otherwise excellent system that you have.   I may have misinterpreted the meaning of battery isolator testing but here's the manual wording:
******
Battery Isolator Testing
1. Remove all wire connections from the isolator.
2. Setup a digital multi-meter (DMM) in the diode test mode.
3. Connect the red probe from the DMM to the alternator input (A)
and the black probe from the DMM to the battery output terminal to be tested. A good isolator connection will show a reading of 0.4 to 0.6VDC.
4. Connect the DMM black probe to the alternator input (A) and the red probe to the battery output terminal to be tested. A good isolator connection will show a reading of OL.
5. Repeat steps 3 and 4 for the other battery output terminals.
*******
This means the finely tuned output voltage from the alternator is reduced by 0.4 to 0.6V before it gets to the batteries.  This is a large discrepancy in the battery charging world.  Even if I've misunderstood the manual and it's less than that (isolators always introduce some voltage drop), it doesn't make sense to introduce a preventable voltage drop between the alternator and the batteries.
If you go with an Echo Charger, the precisely set alternator regulator focuses on optimally charging the house batteries and ignores the starting batteries.  The echo charger will provide the required charging voltage to the starting battery when the voltage to the house batteries reaches a certain point; in the case of my Xantrex, 13.0 V.

In summary, my thought is to drop the isolator and go with whatever kind of echo charger you think is best.  I suspect the charging performance for your house batteries will improve significantly. 

Other comments?

[mainesail]

Definitely upgrade from the diode isolator. There are very, very few good uses on a boat for diode based isolators these days. While the Firefly batteries are great they are near impossble to get right now. I still have, and use on my own boat, the original Firefly battery tested for the Practical Sailor PSOC article in 2013-14. It still has its original capacity. This battery has literlly been beat to $hit. 

In regards to the Trojan AGM's, these are a relativelyt brand new product line for Trojan and long term real world longevity data has not been established. The "carbon" in the Trojan's is not at all the same as the pattented carbon foam used in the Firefly, and nowhere even close.

I would not put my own money on the Reliant AGM's, at this point in time, when we have other known good quality AGM's from the likes of Lifeline, Northstar, Odyssey, Rolls & Full River that are already out there. Perhps in a few years I will, but only time will tell.

So long as the start battery and house bank charge at similar voltages, within about 0.1V to 0.2V, an ACR can work fine and is essentially no differnt than most multi-output smart battery chargers. 

If you want a true dedicated seperate charge profile for the start battery, and one that can be used with any charge source, then the best option is a Sterling Power B2B charger such as the BB1230. Products such as the Echo Charger and Balmar Duo Charger are simply voltage followers and do not offer an independent charge profile from what the house bank is seeing. All these can offer is a voltage cap/limit.

[DaveBMusik]

So long as the start battery and house bank charge at similar voltages, within about 0.1V to 0.2V, an ACR can work fine and is essentially no differnt than most multi-output smart battery chargers. 

Sorry about my ignorance.
Will the ARS-5 profile pass through the start battery and ACR or should the alternator be connected to the house bank first?

https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

[mainesail]

So long as the start battery and house bank charge at similar voltages, within about 0.1V to 0.2V, an ACR can work fine and is essentially no differnt than most multi-output smart battery chargers. 

Sorry about my ignorance.
Will the ARS-5 profile pass through the start battery and ACR or should the alternator be connected to the house bank first?

https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

House bank first is most optimal....

[Stu Jackson]

.
Sorry about my ignorance.
Will the ARS-5 profile pass through the start battery and ACR or should the alternator be connected to the house bank first?

https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

Dave,

The simple sketch in this thread (Basic Battery Wiring Diagrams  This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html) - Dave's wiring diagram.jpg - shows it.  AO to house bank first.

[DaveBMusik]

Thanks Stu! I have seen so many diagrams it was hard to know what to do.

[Stu Jackson]

Dave,

Glad to help.  I "captured" that one because I felt it was the clearest one showing the major components.  Further down in that topic (Reply #1) is a more detailed one that, interestingly enough, is identical.

I've always recommended getting the "big picture" before getting into the nitty gritty details.

Those two diagrams are the ones I selected to show both.

Editorial:    There is a common misconception, usually promoted by folks from the UK who are  notorious for their fears about engines not starting, that prefers the AO to the start (or reserve) bank.  The fallacy of this approach is that the house bank always needs more amps in than any start bank (except for just when you're leaving your slip after being plugged in).  Running more current through an ACR or VSR or whatever device you choose to automatically charge the second (house) bank makes little sense just because you incorrectly ran the AO to the start bank.

Of course, by running the AO to the house bank, you can even turn off your 1-2-B switch without incurring any damage.  B is for Both, which is just like using a VSR except manually!