Victron BMV602 synchronization question

Sefuller

Sefuller

.
May 6, 2010
472
1984 Oday 39 79 Milwaukee
Just received my battery monitor today and looking forward to installing this weekend. Glancing through the manual, I noticed it says the monitor needs to be synchronized (when the batteries are on the charger and the charger has entered float mode) and they recommend doing this once a month. As we are on a mooring and rarely connected to shore power, I was hoping to use the battery monitor to tell me when I needed to charge the batteries and to determine how effective the time we spend motoring is at charging the batteries. Having to connect to shore power once a month sort of defeats the purpose. I am wondering just how critical are these monthly synchronizations?
 
Maine Sail

Maine Sail

.
Feb 6, 1998
11,709
Canadian Sailcraft 36T Casco Bay, ME
Sefuller said:
Just received my battery monitor today and looking forward to installing this weekend. Glancing through the manual, I noticed it says the monitor needs to be synchronized (when the batteries are on the charger and the charger has entered float mode) and they recommend doing this once a month. As we are on a mooring and rarely connected to shore power, I was hoping to use the battery monitor to tell me when I needed to charge the batteries and to determine how effective the time we spend motoring is at charging the batteries. Having to connect to shore power once a month sort of defeats the purpose. I am wondering just how critical are these monthly synchronizations?
Click to expand
Synchronizations when "known full", using battery net acceptance, are critical to the best performance of a battery monitor. I prefer manual synchronizations only and physically program out the auto-sync feature...

What is "known full" or as I prefer to call it "cruiser full"? Simply put:

With the battery terminal voltage at 14.4V or greater the bank is only accepting less than 2% of its capacity in current..

It is very simple to determine cruising full..

Check Battery Terminal Voltage - is it 14.4V +/- (absorption) at the battery terminals?

Check Net Current Flowing Into Battery - is it less than 2%, 1.5% of "C" etc.?

If yes to both, then the bank is pretty much full. Whether you use 1% 1.5% or 2% is a personal preference.. 1% acceptance takes a lot longer to get to than does 2%..

I have been using this method for 18-20 years as my go to to know when to manually re-set my battery monitor to keep it as accurate as possible....

All you need to know is the battery terminal voltage and net current being accepted by the bank.

Best practice would be to turn off DC loads when doing this, especially if you have a marginal charge source such as a small charger or small alternator.

If doing this with the alternator be sure you are above the alts cut-in speed and at an RPM where you know it can produce more current than the 2% etc...


If you are on a mooring then you will want to somehow get the batteries back to full every two weeks or so. Alternators on sailboats simply do not have the run-time to do so.

You would be wise to invest in a 15-30W solar panel and controller if on a mooring. Batteries will begin to sulfate at any charge state below 100%. Sulfation is like cancer of the battery..
 
B

Benny17441

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May 24, 2004
7,173
CC 30 South Florida
I was thinking of a battery monitor to simplify my life. Thanks Stu for sharing the "gotcha" thing. I think I will stay with my voltmeter which I have learned to read and yields adequate results.
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,047
Catalina 34 224 Maple Bay, BC, Canada
Benny, as a regular here you'll know that many other skippers do just that. You'll also recall that many of us recommend that the first thing new skippers do is to get a battery monitor, since not every skipper is knowledgeable about battery chemistry.

I continue to maintain that most skippers can do an Energy Budget (in their sleep, in their heads or on a spreadsheet) but where a battery monitor SHINES is determining what has gone back into the bank, as a result of battery acceptance, a sadly misunderstood concept that continues to recur with alarming frequency.
 
Sefuller

Sefuller

.
May 6, 2010
472
1984 Oday 39 79 Milwaukee
Thanks for the replies -

I have a better grasp of the synch process now. Lots of information in the link Stu provided. My battery set up consists of a house bank with 2 batteries which I installed in 2006, (I am very embarrassed to admit I don't remember if they are 6 or 12 volt), and a single 12 volt "starting" battery. Last season I rewired the glow plugs with a relay, and eliminated the long ammeter loop in preparation for a panel replacement which I did this summer (replacing the dreaded Universal M25 wiring harness). We rarely if ever use battery two, relying on the house bank for starting and house loads. As I mentioned, we rarely connect to shore power, usually in the spring before launch, and perhaps once or twice during the season. I have a TruCharge 20 charger when we are on shore power, but just a standard 55(?) amp alternator. I am actually surprised the batteries have lasted this long, but our usage is pretty light and I take care not to discharge them deeply. I have mostly led lighting in the cabin, occasionally use the autohelm, most frequent consumers are domestic water pump, washdown pump, radio, stereo, and inverter for tools and computer.

Will the monitor tell me the amps being delivered by the alternator, or how do I determine that? What is the cut-in speed of the alternator, and how do I know when it is delivering more than the 2% current?
 
Stu Jackson

Stu Jackson

.
Feb 26, 2004
23,047
Catalina 34 224 Maple Bay, BC, Canada
Sefuller said:
Will the monitor tell me the amps being delivered by the alternator, or how do I determine that? What is the cut-in speed of the alternator, and how do I know when it is delivering more than the 2% current?
Click to expand
Glad to help, and your description was very good.

The BM will tell you what's going in as well as what's going out (if, of course, wired properly). Both your shorepower charger and the alternator out (hopefully to the house bank, not the C post, but for this it doesn't matter).

The OEM alternator, if you have an M25-series engine, will be 55A, you're right. Without an external regulator, the internal regulator will output as soon as the alternator starts turning. No "cut-in speed," just lower voltage at lower engine speeds.

When you program the BM to the AH of your house bank, YOU do the calculation: 2% of a 200 AH house bank is 4A, right?

Here's some links to Battery Acceptance:

Battery Acceptance by Stu http://c34.org/bbs/index.php/topic,4787.0.html

Battery Acceptance (a very good Maine Sail presentation and further discussions) http://forums.catalina.sailboatowners.com/showthread.php?t=114054

Battery Acceptance Observations by Maine Sail
http://forums.catalina.sailboatowners.com/showthread.php?p=674108&highlight=battery acceptance

Overcharging with Combiners or ACRs The MYTH:
http://c34.org/bbs/index.php/topic,7052.0.html

You seem to be on the right track, good luck. Please let us know if you need anything else. Our "Electrical 101" on our C34 website, included in those links, has a LOT more information, a LOT of it have links to Maine Sail's articles, both on his website and here on co.com. Some good highlights in those links.
 
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