Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 02-08-2021, 07:49   #1
Marine Service Provider

Join Date: Feb 2012
Location: Vienna, Austria
Boat: Vagabond 47
Posts: 734
Batteries SOC - State Of Charge

Please make me wise. I simply do not understand it.

For my knowledge one can only determine the SOC by measuring the batteries voltage which is, for FLA-Batteries:

12,65V fully charged
12,20V 50%
11,90V empty


So yes, I am willing to start the genset at 12,30V which I think is 60%

But how to measure it when your wind generator and solar panels give you a constant 13,6V load into your network?

Yes I am really suspicious about BMI's like the Victron BMV-702 (180€) that always tell me 100% as the cheap china instruments (30€) that do the same. One china on the house-load side another on the engine battery input and the house bank input and the funny BMI-702 somewhere else. (Iconsider it is not a bit better than the chinese ones but a lot more expensive)

I have the ONE and ONLY input(A2B, Solar, Wind, 230V CHarger and else...) at an Victron Battery Isolator and 3 Outputs.
House Trojan FLA, Bank

Engine FLA closed, Single

AGM, Single


As far as I do understand it BMV's claim to list the difference between in and out.


So, by all means I should have to fix the loads at the Victron Battery Isolator too to have an Input and an output at the same terminal and to connect the shunt between the battery and the BI's terminal?

And how effective is this method of measure?

Thanks.
moseriw is offline   Reply With Quote
Old 02-08-2021, 09:32   #2
Senior Cruiser
 
tkeithlu's Avatar

Cruisers Forum Supporter

Join Date: Feb 2012
Location: Carrabelle, Florida
Boat: Fiberglas shattering 44' steel trawler
Posts: 3,681
Re: Batteries SOC - State Of Charge

Disclaimer: there are battery gurus on the forum who can talk circles around me when it comes to batteries.

So, let me just speak from experience as a non-guru battery user. I have house bank, engine starter, genset starter, and OMG backup battery in the wheel house in case the house bank gets flooded in the seawater sense. The two starters are on theiir own alternators and v oltage regulators and the rest charges from two choices, the battery charger (sophisticated, from shore, genset, backup genset) and a Balmar alternator with its own voltage regulator (sophisticated, programmed).

One point: Life is easier around batteries if you keep all the same sort, in my case, flooded and Duracell from Sam's Club.

Second point: I doubt that you are learning anything from the BMV that you ould not already know with a good permanently mounted voltmeter and a battery tester. My voltmeter for batteries has a rotary selector switch that lets me choose the one to check upon. Everything charges at the same voltage (13.4) and sits at the same (12.8) so life is simple. Then, I recently retired my old-fashioned resistance battery tester for one of these:

https://www.amazon.com/dp/B07Z67MMGC...mcd_asin_0_img

It quickly tests the batteries when I have a question, but really, how often does that happen if you keep your batteries properly charged? It should not be a big part of your life. It just gives you a heads up if a battery is starting to fail or an alternaor is not doing it's job, but then, you knew about the alternator because you weren't getting 13.4 any more.
__________________
Never let anything mechanical know that you are in a hurry.
tkeithlu is offline   Reply With Quote
Old 02-08-2021, 09:53   #3
Marine Service Provider

Join Date: Feb 2012
Location: Vienna, Austria
Boat: Vagabond 47
Posts: 734
Re: Batteries SOC - State Of Charge

Nah, in fact I wonder about the super computer systems that tell you about the house batteries and says your rate is 76,37%

Is this true? Can I install a unit that will give me this information with one click?
Frankly I do not want to dismount my rack two times a day to mount a battery tester.
I have them stacked vertically (topmost base is around 1,6 m) and there is not really much space
when you have 4 racks.

Really enough trouble filling up the water once a year,
moseriw is offline   Reply With Quote
Old 02-08-2021, 09:57   #4
Registered User

Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft Catalina 381
Posts: 2,365
Re: Batteries SOC - State Of Charge

As long as the batteries get topped off periodically to allow the meter to re-calibrate, a meter that knows how many amp-hours have gone in and out, as well as the current amps flowing in/out and voltage, along with the capacity and Peukert exponent of the batteries can produce a pretty good estimate of how charged they are. Certainly one that's good enough for most purposes.
rslifkin is offline   Reply With Quote
Old 02-08-2021, 10:01   #5
Marine Service Provider

Join Date: Feb 2012
Location: Vienna, Austria
Boat: Vagabond 47
Posts: 734
Re: Batteries SOC - State Of Charge

rslifkin thank you. So it seems that I have not mounted the shunts correct and have to work on the right position.
moseriw is offline   Reply With Quote
Old 02-08-2021, 10:07   #6
Registered User
 
glenn.225's Avatar

Join Date: Jan 2008
Location: Kingston, ON
Boat: Albin Vega 27'
Posts: 361
Re: Batteries SOC - State Of Charge

Perhaps have a look and read over this: https://marinehowto.com/installing-a-battery-monitor/ and this:https://marinehowto.com/programming-a-battery-monitor/



Rod has a lot of excellent marine electrical info/guides (as well as a lot more) on his site.



Maybe the Victron battery monitor isn't perfect but I've found mine pretty good. Going on 9 seasons on a set of Trojan T105's.
__________________
Glenn
glenn.225 is offline   Reply With Quote
Old 02-08-2021, 13:27   #7
Registered User

Join Date: Jun 2013
Location: canada
Posts: 3,724
Re: Batteries SOC - State Of Charge

Quote:
Originally Posted by moseriw View Post
But how to measure it when your wind generator and solar panels give you a constant 13.6
With a battery monitor... the one you listed.

With a big ac charger you could guess closely using absorption amps. But not with small solar or wind chargers.
smac999 is offline   Reply With Quote
Old 02-08-2021, 13:31   #8
Registered User

Join Date: Jun 2013
Location: canada
Posts: 3,724
Re: Batteries SOC - State Of Charge

Quote:
Originally Posted by tkeithlu View Post
Disclaimer: there are battery gurus on the forum who can talk circles around me when it comes to batteries.

So, let me just speak from experience as a non-guru battery user. I have house bank, engine starter, genset starter, and OMG backup battery in the wheel house in case the house bank gets flooded in the seawater sense. The two starters are on theiir own alternators and v oltage regulators and the rest charges from two choices, the battery charger (sophisticated, from shore, genset, backup genset) and a Balmar alternator with its own voltage regulator (sophisticated, programmed).

One point: Life is easier around batteries if you keep all the same sort, in my case, flooded and Duracell from Sam's Club.

Second point: I doubt that you are learning anything from the BMV that you ould not already know with a good permanently mounted voltmeter and a battery tester. My voltmeter for batteries has a rotary selector switch that lets me choose the one to check upon. Everything charges at the same voltage (13.4) and sits at the same (12.8) so life is simple. Then, I recently retired my old-fashioned resistance battery tester for one of these:

https://www.amazon.com/dp/B07Z67MMGC...mcd_asin_0_img

It quickly tests the batteries when I have a question, but really, how often does that happen if you keep your batteries properly charged? It should not be a big part of your life. It just gives you a heads up if a battery is starting to fail or an alternaor is not doing it's job, but then, you knew about the alternator because you weren't getting 13.4 any more.
Nothing you have posted here aswered his question on how to determine Soc under charge.
smac999 is offline   Reply With Quote
Old 02-08-2021, 13:40   #9
Registered User

Join Date: Jun 2021
Posts: 222
Re: Batteries SOC - State Of Charge

The battery voltage determines what your voltage meter reads regardless of the solar or wind turbine voltage. They simply "try" to maintain the voltage desired but the batteries pull it down to to slightly above their current charge/voltage level.
EngineerRetired is offline   Reply With Quote
Old 02-08-2021, 13:51   #10
Registered User

Join Date: Aug 2016
Location: Long Island, NY
Boat: Cal 33-2
Posts: 297
Re: Batteries SOC - State Of Charge

With FLAs, just get one of those cheap battery testers from an auto parts store that checks the SG of the battery acid. That plus a halfway decent DMM to measure the voltage is all you really need. Total cost under $25.
__________________
S/V First Tracks
1985 Cal 33-2
JimsCAL is offline   Reply With Quote
Old 03-08-2021, 09:13   #11
Marine Service Provider

Join Date: Feb 2012
Location: Vienna, Austria
Boat: Vagabond 47
Posts: 734
Re: Batteries SOC - State Of Charge

EngineerRetired Well Voltage is not really the thing that makes you happy with a set of 6 Trojan T-125 in a very close rack.

JimsCAL same with tools that have to be mounted ord inserted.

When I fill up water I have to get every batteriey out of the rack.
moseriw is offline   Reply With Quote
Old 03-08-2021, 09:17   #12
Marine Service Provider

Join Date: Feb 2012
Location: Vienna, Austria
Boat: Vagabond 47
Posts: 734
Re: Batteries SOC - State Of Charge

But the solution is clear: I will check these HoTo's and adopt the gauges

https://marinehowto.com/installing-a-battery-monitor/ and this:
https://marinehowto.com/programming-a-battery-monitor/

Well I am an IT-Pro and coder (7 langs or so) but electronics and coding in a car or boat is pain in the a for me. My car is an 1997 Toyota Hiace. The only electronic component is the clock.

"What I do not have can not brake"
moseriw is offline   Reply With Quote
Old 03-08-2021, 11:52   #13
Registered User

Join Date: Feb 2006
Location: Eastern Caribbean for the 2020 season then east coast or Panama
Boat: Lagoon 470 cat
Posts: 570
Re: Batteries SOC - State Of Charge

Moseirw - had the same issue with my 6 GC house bank, except it was also under a bunk in the "storage cabin". Real PITA to ck water so it didn't happen as often as it should have. Not cheap but the semi-auto filling system is worth its weight in gold. Have special caps that replace the standard ones which are connected by tubing. I just put the end of a tube in distilled water and pump a squeeze bulb until there is back pressure.



Have saved untold hours of moving s___ to check the water. Not cheap but a mental health (nd battery) life saver.
Moontide is offline   Reply With Quote
Old 03-08-2021, 16:55   #14
Registered User

Join Date: Jul 2016
Location: Traverse City, Michigan
Boat: Hinterhoeller Niagara 35
Posts: 219
Re: Batteries SOC - State Of Charge

The battery fill systems mentioned are well worth the price. Like many, our bank is in a tight spot under a quarter berth.

IMO: Unless you have a power hungry boat with a big battery bank and a genset, expensive battery monitors are not] worth the price.

KISS: When we are on the mooring, our solar runs the fridge and the anchor light. When we are cruising, when the teakettle is on the stove (propane), before the solar is doing anything and we are using minimal battery power, I note the battery voltage. This gives a very good measure of battery condition. We never in practice see our batteries below 75%.

Cost: A digital panel mount voltage meter - $20

A very important part of this approach is a careful energy budget. That is knowing how much power your boat actually uses, and matching your battery capacity and your charging system to those needs. It is also important for us small and mid-sized (under 36') do-it-yourself cruisers to not load up our boats with all the electrical comforts and spend our time worrying about running our batteries flat instead of trimming sails and steering a true course.
Boatwright is offline   Reply With Quote
Old 03-08-2021, 22:41   #15
Registered User

Join Date: Mar 2012
Location: On board in Leros, Greece
Boat: Hunter Legend 420 Passage
Posts: 857
Re: Batteries SOC - State Of Charge

Quote:
Originally Posted by moseriw View Post
For my knowledge one can only determine the SOC by measuring the batteries voltage which is, for FLA-Batteries:

12,65V fully charged
12,20V 50%
11,90V empty
.....
But how to measure it when your wind generator and solar panels give you a constant 13,6V load into your network?
To answer the original post (OP):

The DoD can be estimated by measuring the battery bank voltage, but the difference between a fully charged battery and one that needs charging is only 0.5 volts, so a digital voltmeter is essential. An analogue or moving coil voltmeter cannot give such accurate readings.

At a DoD of 50% their voltage should be 12.2 volts, but this is with no loads. At only 25% DoD it will be about 12.5+ volts. Different brands maybe different and the age of the batteries may also have slightly different voltages to their published values.

The most important point here that often confuses even the professional is that these voltages are 'open circuit' voltages - that is the voltage under 'no load' and 'no charge' conditions. This is difficult to achieve as there is always something drawing a current or maybe some charging from solar. If you have solar that is difficult to disconnect then the 'No charge' will only occur at night.

This ‘no load' voltage state is also defined as the voltage when the battery has been allowed to 'rest' with no discharge or charge for several hours, depending on the battery type. It is difficult on a boat to disconnect all loads for two hours - so disconnect just one of the batteries.

To achieve this 50% 'no load' voltage of 12.2v you may have to let the batteries go down to about 12.05v, with a current draw of about 5 amps, The safest way to isolate just one battery is by lifting the EARTH lug. Having positive cables floating around a boat is not a good idea! Leave this isolated battery for two hours and see what the open-circuit voltage of this disconnected battery comes back up to. If it's up to 12.2v then at 12.05v, with a discharge current of 5 amps, your bank was at 50% SoC. Try this at different discharge currents to determine what voltage the batteries can fall to before they reach 50% DoD.

Reconnect the battery to the bank and next time you do this test disconnect a different battery. If all batteries are in the same condition then the results should be the same.
sailinglegend is offline   Reply With Quote
Reply

Tags
batteries

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
USCG documented my state registered boat, do I need to tell the state? AmericanVagrant Rules of the Road, Regulations & Red Tape 23 21-02-2020 15:07
thomasow' SAR and regulating charge current w/ SoC john61ct Electrical: Batteries, Generators & Solar 47 23-01-2019 11:24
Measuring State of Charge (SOC) at almost full troubles rgleason Electrical: Batteries, Generators & Solar 80 07-07-2018 21:12
Washington State purchase with out-of-state residence cyclepro Dollars & Cents 7 06-06-2011 08:55
State by State Nonresdient Regs Stoney Rules of the Road, Regulations & Red Tape 2 10-06-2008 08:52

Advertise Here


All times are GMT -7. The time now is 23:53.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.