A note regarding Battery Monitors BMV 6005 Victron

[monte]

Just a quick note to those using battery monitors that will be obvious to some more experienced sailors but oblivious to others (like myself)
When I installed my battery monitor I expected the percentage to show the actual percentage of battery remaining, and decided this is the simplest way for me to monitor the state of my batteries.
However, as the percentage is a calculated guesstimate of amps used/amps charged it can become out by up to 20% over time. It is in fact fairly close within a few days after the batteries are fully charged but after a couple of weeks of not plugging in it could be well out because amps out are actually higher than those read by the monitor (due to Pookets law or whatever his name is). Sure the monitor applies an adjustable value for this, but its not always accurate. So after a couple of weeks of saing and anchoring, relying on solar and wind to charge the batteries, the monitor might say batteries are at 65%, but, the voltage is at 12.2V. The voltage indicates the batteries are actually at 50%. This reading will be most accurate after the batteries have rested for a while (probably first thing in the morning)

These are approximate voltages/% of charge
12v - 40%
12.2v-50%
12.4v-65%
12.6v-80%
12.8v-100%

Hopefully this will help someone (and their batteries) as it has taken me a while to figure it out!

The monitor is a good piece of equipment, it will tell the amps out, and amps in, which can be really useful, and the % state of charge is fine to use if you fully charge regularly, just don't rely on it if its weeks between fully charging your batteries.

Corrections or clarifications are welcome, I just wanted to state my views in case it helps others.
Cheers
Monte

[noelex 77]

A battery monitors SOC reading will become less accurate the longer the time from the reset parameters.
However, if well set up and wired correctly the drift should not be a large as you describe. If the monitor is consistently over or under reading with time the better monitors can be adjusted to to compensate or this. This is part of the set up. It usually involves adjusting the battery efficiency factor.

I would question your use of resting voltage as a reference. This is best a rough guide and even when compensated for temperature, battery type, and voltage meter inacuracy, significant errors can be expected in predicting SOC.

It's more likely that the battery monitor was the correct reading (if it's well set up) rather than the SOC derived from the resting voltage.

[sailorboy1]

All I can say is that if I leave the boat on Sunday and the monitor says the battery is at 95% and amps hrs-out are 15, when I come back Friday the SOC is 100% and the amp hours is 0. Somehow during the week the monitor thinks I charged the batteries somehow.

[markpierce]

Don, now I understand your avatar and title.

If I leave the Coot for several days without the charger on, my meter says the batteries are at a lower percentage of capacity.

[sailorboy1]

it is those magic batteries I have that charge themselves, but only when they are alone on the boat

[steamgoat]

Wiring & Installing A Battery Monitor - SailboatOwners.com Lots of good info here,especially in all the following posts. Bruce.

[Mark Johnson]

I have twice the solar panels that I need for my average daily use, and only cycle my 340 Ah battery bank down 10 - 20 % daily.

This means that EVEN on very cloudy overcast days, I get to 100% charged EVERY day! It just takes all day, rather than being fully charged by 11:30 AM.

With this system, the batteries last well over 10 years, everything runs better due to higher line V, I have VERY high reliability, and the Link 10 monitor re-zeros itself daily, remaining dead on accurate.

M.

[CharlieJ]

...I get to 100% charged EVERY day!...With this system, the batteries last well over 10 years,...and the Link 10 monitor re-zeros itself daily, remaining dead on accurate.

These statements, in a nutshell, are the keys to accurate readings on a battery monitor and battery cycle life that equals or exceeds the manufacturer's specifications. All lead acid (LA: flooded, absorbed glass mat (AGM), thin plate pure lead AGM (TPPL AGM) and gel) MUST be fully charged as often as possible.

When a LA battery bank is operated between 50% and 85% state of charge (SOC) to minimize operating an engine driven charging source any longer than "necessary", a properly sized bank will provide adequate service, but this mode of charging will significantly reduce the life of your battery bank. Sulphation and stratification will occur and the batteries will prematurely fail.

I start battery seminars with this phrase:
"BATTERIES DO NOT DIE ON A BOAT. THEY ARE MURDERED!"

[Cheechako]

i found a monitor more trouble than value personally for many of the reasons noted above. I should pay hundreds of dollars, crawl around running wires etc for something that requires constant oversight? The Volts are close enough for me.... all I need to know is if I need to charge! It's a bit like trying to monitor your dingy gas usage with a flo scan... heck, just lift the tank before you go!
But.... boys like their toys ... so have fun!

[GaryMayo]

This will tell you how many more times your boat will start

I love this battery monitor. I use it on a V8 powered motorcycle that has one more than one occasion left me stranded. After the purchase of this, not one surprise as I can see at a glance if it will start again.

http://www.amazon.com/gp/aw/d/B000NV...dir_mdp_mobile

[motion30]

The big value to me is learning how many amps each accessory I have uses Biggest power savings was changing to led lights

[silverp40]

Quote: "

i found a monitor more trouble than value personally for many of the reasons noted above. I should pay hundreds of dollars, crawl around running wires etc for something that requires constant oversight? The Volts are close enough for me.... all I need to know is if I need to charge! It's a bit like trying to monitor your dingy gas usage with a flo scan... heck, just lift the tank before you go!
But.... boys like their toys ... so have fun! "

There is a difference if one lives aboard or not. If this is the case and living on alternative power (not marina power) almost or all the time, then battery life is much longer with an amp monitor.

Our batt monitor installed 12 years ago has not needed Any maintenance...

[goboatingnow]

Originally Posted by Cheechako

i found a monitor more trouble than value personally for many of the reasons noted above. I should pay hundreds of dollars, crawl around running wires etc for something that requires constant oversight? The Volts are close enough for me.... all I need to know is if I need to charge! It's a bit like trying to monitor your dingy gas usage with a flo scan... heck, just lift the tank before you go!
But.... boys like their toys ... so have fun!

Arrh cheechako. I don't need no stinking voltmeter I put me finger in the air and can tell. Argh

It's as least as good as your method and as accurate.

As the man said, batteries are murdered on a boat.

Dave.

[monte]

Thanks for the input

[Albro359]

Surely you can do it with a voltmeter...
Batteries don't need to be murdered.
First start with good batteries
Then a good alternator with an adjustable external regulator.

No matter what the state of your batteries, you know that if you're down in the 11.5 volt area they're really quite discharged.
If you run the engine/ plug in shore power and they're up to 14.5 volts in a minute or two and there's no appreciable load on the engine..the batteries are sulphated, which generally means stuffed
You don;t need one of those fancy gadgets to tell you that !
Buy good batteries..keep em charged right up...when you're out there and they get down to ~50%...for me 12.4V... charge em up...and allow them to ABSORB the charge
Both my solar MPPT reg and the Next Step engine alt reg are set for 180 mins absorption time for a 525 Ah bank of AGMS
AND EQUALISE them every 4 weeks or so...even AGMs
Let the Volts rise up to 15.5 or so and keep it there for an hour or two once a month will do wonders for battery longevity and maintenance..flooded and AGM.
My AGMs have been in the boat since 2008 and they're still working well