Obsessive About Battery Banks (SOC)

Although I have the Maretron SOC program on my boat, The MFD where I monitor the SOC is on the bridge and is not readily available when on the hook, mooring or even in the slip. I wanted something that I could simply glance at when walking through the boat that would give me an immediate status of my House, Engine & bow thruster battery banks. I purchased these 12-24v volt meters from Amazon and installed them in places that are easily read. The two in the photo are under my dinette and are labeled "Engines" & "House." The second photo is forward in the master cabin by the bow thruster battery switch & is labeled "Bow Thruster." (24v bank) Now, when casually walking through the boat, I know the SOC of the various banks with just a glance. When running, they also indicate the charging volts (or lack of if the alternators are inoperative.) I also put one on the dinghy's dash.

https://www.amazon.com/gp/product/B01FH9NJ7O/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Those are volt meters, only give you a very very rough idea what SOC is, especially if there are any lads.

Excellent article on battery monitoring:

Smart Gauge Battery Monitoring Unit Photo Gallery by Compass Marine How To at pbase.com

Codger
I have Magnum BMKs, one for the engine starts and a remote for the house bank. The engine batteries are charged by a Newmar and the house bank by a Magnum inverter charger.

Your instrument tech should know all about these and how to set them up.

Do any of them give a "real" state of charge?
I have a victron 750 and have been on the victron blog asking questions to make sure it is set up right, which apparently it is.

If, for example, I run the genset to "just" 100% batts at 5pm and turn the genset off, at about 6am the next day a 23.5 volt alarm will go off when a fridge fires up and the batts are at around 80% . (Turn everything off I still have 24+v)

If I leave the genset running past 100% for say, 30 mins extra its still stuffing extra amps in at an admittedly lower rate, but still putting it in.
In this example, alarms don't kick in until several hours later in the day indicating more than 100% in the bank.
100% should be 90% and 100% should actually be 100%

On a solar day the batts are charged by midday and the panels and mppt keep doing their thing and we never get the alarms because the sun is at it again in the am with voltage still at 24.5v

Now, 18mths after install, its not an issue as I know 100% is not full.

I should have added to the above, from the Victron blog it was indicated that voltage was an indicator of state of charge.
28. something Volts is chocker for a 24v bank.

My Magnum BMK was very accurate and adjusted over the life of the batteries. Best way of verifying in my opinion is to compare to a properly conducted hydrometer test.

I recently installed the Color Control GX from Victron which interconnects with my solar controller, battery monitor/s and inverter/charger. I've got it connected to the internet via a small router and now I can see full system status and history from anywhere in the world via the website portal or iPhone/iPad app.

It has been brilliant and extremely useful to analyse some of the historical metrics.

Rhino

No dino juice charge source will get lead batts to 100%, unless running all day long.

No AH counting SoC meter remains accurate without frequent resets and close attention from the owner.

http://www.pbase.com/mainecruising/programming_a_battery_monitor

john61ct said:

No dino juice charge source will get lead batts to 100%, unless running all day long.

No AH counting SoC meter remains accurate without frequent resets and close attention from the owner.

Keeping Your Battery Monitor More Accurate Photo Gallery by Compass Marine How To at pbase.com

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I guess someone forgot to tell the generator, chargers and battery banks on my boat that. I'm very thankful they didn't get the memo.

The Magnum BMK is much more than an amp hour counter, and agree that a mere amp hour counter will not be precise as batteries age. Excellent article as usual from that guy.

Simi 60 said:

28. something Volts is chocker for a 24v bank.

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It shouldn't be as 4 -6volt golf cart batteries are used on my bow thruster bank. Although it would seem that 4-6 volt batts =24.0 volts at full charge, each 6v batt is actually 7+ volts, hence a reading higher than 24 volts.

Here's the present voltage for the bow thruster bankSorry for the cockeyed position of the photo but it does read 26.7 volts and was confirmed by the Maretron SOC program on board and the technician's multimeter.)

x2 for compass marine article and the smart meter from Balmar

RB

caltexflanc said:

I guess someone forgot to tell the generator, chargers and battery banks on my boat that.

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How large is your bank? What model batt? How are you defining Full?

Do you know the mfg spec for endAmps defining 100% Full? Do you have a shunt based BM showing amps going into the bank? Are there loads running while the bank is charging?

If your bank is depleted, getting them to 80-85% might only take 2-3 hours, but from there to 100% is at least another three, maybe five or more.

I can see a trawler with a good Alt and external VR getting there **when underway all day** as I said, but do you really run **your genny** that long every cycle?

If just for charging that of course would be silly, when just a couple solar panels could do that last 5-10% that takes over half the total charging time needed.

http://www.pbase.com/mainecruising/effect_of_charge_rate_on_agm_battery

Codger2 said:

It shouldn't be as 4 -6volt golf cart batteries are used on my bow thruster bank. Although it would seem that 4-6 volt batts =24.0 volts at full charge, each 6v batt is actually 7+ volts, hence a reading higher than 24 volts.

Here's the present voltage for the bow thruster bankSorry for the cockeyed position of the photo but it does read 26.7 volts and was confirmed by the Maretron SOC program on board and the technician's multimeter.)

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Very first link on google

A typical 12-volt lead-acid battery must be taken to approximately 14.2-14.4 VDC before it is fully charged. (For 24 volt systems, double these figures.) If taken to a lesser voltage level, some of the sulfate deposits that form during discharge will remain on the plates.
https://www.emarineinc.com/Batteries-Maintenance-101

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Do you know the mfg spec for endAmps defining 100% Full? Do you have a shunt based BM showing amps going into the bank? Are there loads running while the bank is charging?

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I used a Magnum BMK (which uses a shunt), and referenced 100% SOC on it and verified occasionally via hydrometer. The targeted bank in question was 4 6v L16 flooded, 415 AH rated but set to a realistic 395AH 24v. Had US Battery for many years, then Trojans. Typically discharged 40-50% before cranking the genset, which was a 20kw Onan. Inverter was a Magnum MS 4024, specs here: https://www.invertersupply.com/media/data/MS_series_data_sheet_revi.pdf

I seldom aimed the run time with 100% SOC in mind, but around running the electric range/oven, laundry dryer, dishwasher etc.

Although I'm a fan of Compass Marine (Main Sail) and have read numerous articles on SOC, (when at rest for 24 hrs with no load) this chart has served me well over the years. I have it on my iPhone, in my wallet & posted on the boat.

Good point Codger. While battery voltage takes some experience to interpret the results, it is a decent rough indication of state of charge.

Years ago I had a twin engine sailing catamaran with two widely separated house battery banks (one in each hull). I tried using a dual battery monitor, but could never get it to give me reasonable results. But after a few months of cruising full time I was able to use the battery voltage as in indication of SOC even making mental adjustments for the voltage drop due to small (about 5 amp) house loads.

That is what the Balmar SmartGauge does with a sophisticated algorithm that apparently is about as accurate as a shunt based integrating ammeter such as Xantrex's.

David

SG is more accurate.

Most so when bank is quiescent. More so while no charging and only small loads.

Voltage readings need full isolation for 48-72 hours before any real accuracy, and different batteries have different correspondence charts.

Same to a lesser extent with a hydrometer.

Chocker means "full"

caltexflanc said:

I seldom aimed the run time with 100% SOC in mind, but around running the electric range/oven, laundry dryer, dishwasher etc.

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And unless you ran for 5+ hours, there is no way you actually ever got to true 100% Full off dino juice alone.

No matter what any SoC meter says, even lab grade ones costing $6,000+

Your bank is not Full until trailing amps measured at the shunt falls to ~.005C, in your case 2A.

The actual spec you can get from Trojan.

Bottom line, unless you motor all day long, solar is required to finish the long tail when away from mains power. The dino juice contribution works best in the morning, before solar ramps up.

I got there in 3, sometimes as much as four hours depending on discharge % and age of bank. Your post I reacted to said:

No dino juice charge source will get lead batts to 100%, unless running all day long.

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I agree, not realistic.

Good chargers will get you there the same way as at the dock. Sure it isnt an hour or so, but not never.

Theory vs reality.

At fully discharged 50% SoC and lead chemistry I stand by what I said. Actually read the CMS article I linked to in #13?

Your charge source or batt monitor, no matter how expensive or sophisticated, simply telling you the bank is full does not count

Full means trailing amps has fallen to .005C, unless your mfg docs spec otherwise.

The last 15% takes at least 3x what the first 35% did.

Big bank or small, high CAR or not, big amps charge source, makes little difference.

Yes, if you're motoring for propulsion 5-7 hours anyway, a good alt setup will get you there.

But running an engine for an extra 3-4 hours just to trickle in an average 5-10 amps is not sensible when a $300 solar setup can do so with no noise, fuel or wear and tear.

Or just accept PSOC abuse as inevitable, buy cheap GCs more frequently.

Or spend extra buck$ on LFP or Firefly Oasis.

Your boats your choices.

OK, the science is great, but pure science only goes so far in practicality.

Like those of us sitting in the North Carolina fog bank for days, good luck with your $300 solar setup topping things off.

And while we are at it....why dont you tell everyone not to permanently mount 2 solar panels and put 2 on mounted hinges so you can akways get max efficiency by moving them around to get full sun and best angle? Much better, ecept for those that couldnt be bothered.

john61ct said:

Your boats your choices.

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What's on your boat?

"What's on your boat?"

A propane reefer , propane range /Dickinson oil fired range for wintering aboard and a 75W solar for topping off charging ,or when not in use for a season.

A LED anchor light and interior lights leave only the auto AM/FM radio as drains when anchoring.

The toilet has a lever.

I"d go with pulverized coal and wood pellets on my boat if only the marinas would catch up.

I am looking into getting a Smartgauge monitor. The Smartgauge was originally developed by Merlin in the UK. You can order direct from UK it for much less than USA prices, $120.00
Battery Monitors: Merlin Smartguage Battery Monitor (19-1001)