What do battery management systems do and do you need them.

[dominicebs]

What do battery management systems do and if you don't have one then what are the implications in terms of things you need to do

[bottle]

Battery management:

 

Your eyes and a Smartgauge is the simplest. Now supplied by this company Merlin Power Store

 

Never let your batteries go lower than 50% SOC (State Of Charge).

 

Charge batteries to at least 95% SOC

 

Regularly Charge to 100% ( depending on usage, once a week or or once a month, preferably with a three stage charger supplied by a shoreline)

[smileypete]

What do battery management systems do and if you don't have one then what are the implications in terms of things you need to do

Just tell when it's time to charge the batts, and tell when they fully charged enough.

 

If your budget doesn't stretch to a Smartguage or similar, a £4 digital voltmeter and £20 shunt ammeter will do.

 

cheers, Pete.

~smpt~

[blackrose]

Battery management system is quite a broad term which might encompass a few different types of equipment.

 

I've heard people using the term to describe external alternator regulators for example, which are used to boost the voltage from your alternator. The consensus seems to be that if your alternator(s) are fairly modern then auxiliary regulation is not required, although despite this many users report good results.

 

Then there are battery monitors mentioned above, which most users find very useful to show them when to start and stop charging their batteries. If you don't have a battery monitor or a connected voltmeter, then you'd have to take regular voltage readings with a multi-meter, or just make the mistake of charging when your lights start to dim!

Edited August 27, 2012 by blackrose

[blodger]

Having 100 watts or more solar panel charging the batts through a decent solar controller is a good battery management system IMHO

[Paul C]

I think a lot of it depends on the way you use your boat. If you don't cruise much, live aboard it, don't have a shoreline (and battery charger), don't have (much) solar power, have a single low power alternator on the engine and use elecricity intensively then you'd potentially have a large drain on the batteries and need to run the engine for a long time to recharge them. Conversely, if you simply use it for leisure and each time you visit the boat, go out cruising, and don't have much in the way of electrics, go home in the evening (so no lighting), including turning off the fridge, then you're probably generating more power than you use. If its somewhere in between, battery monitoring could be useful. Of course, you might have a fault in a component eg alternator or one of the batteries, and a battery monitor would show up the fault (or at least, the effect of it if significant).

 

Personally, I like the Smartguage and am seriously considering getting one, but there is a new version of it out in approx November so I'm waiting for that.

[Chalky]

Depends on the type of battery.

 

With a lithium battery they are very complex and safety critical bits of kit (lithium batteries are very energetic when they let go). They will monitor battery voltage and current, control the charge rate by sending instructions to the generator / charging system, control the battery cooling system, control the battery isolator systems and safety interlocks, manage the charge balance between cells (using either bleed off circuits (resistors) to bring all cells down to a common level or using active balancing to move charge between cells), monitor battery temperature and also give an accurate state of charge.

In a lithium battery they will monitor each individual cell and manage that particular cell and its operating parameters. One of many reasons why lithium batteries are so expensive.

 

For a lead acid battery they're a lot simpler and usually indicate Volts, Amps and State of Charge (with differing levels of accuracy)

 

For a lithium battery they are absolutely critical. For lead acid you can manage without them, but they're highly recommended if you want to maximise the life of your batteries.

Edited August 27, 2012 by Chalky

[blodger]

There is no BMS that does not rely on common sense ang knowledge by the human that looks after it. So start simple and keep it simple. The solar is automated by its controller so is a good starting point that might obviate the need for extra alt, alt controller, generator, etc. Every boat is subject to individual use that means tailoring batteries and their support system to. There are no categoric/definitive answers just what works for others boats and usage.

[bizzard]

It must be worth going to examine HMS Belfast's landline arrangement, it being a permanent moorer.

Edited August 28, 2012 by bizzard

[Gibbo]

a £4 digital voltmeter, £20 shunt ammeter, a pile of books, a load of learning and a couple of years experience will do.

 

I fixed that for you.

[smileypete]

I fixed that for you.

(Oh dear the pointless Gibbo arguments have started... )

 

I could teach them in 5 minutes, tops, if someone posts to learn how I'll answer.

 

OK if you really want to fret whether your batts state of charge is 55%, 50%, or 45%, buy a £150 SmartGauge.

 

cheers, Pete.

~smpt~

[Gibbo]

Ok. Teach us, in five minutes, how to tell the state of charge of our batteries, using a voltmeter and an ammeter, for all possible situations anyone might meet on a boat.

 

I won't hold my breath.

[dor]

If by BMS you mean Sterling, Adverc etc, then what they do is increase the alternator's regulated voltage. And despite all the marketing speak, not a lot more. If you have an old alternator that is regulated at 13.6 - 13.8 volts, then the charging current will be limited, especially the last 20% or so of the charging period. If you increase the regulated voltage to say 14.4V then you will get much faster charging, and more complete charging. Newer alternators are generally regulated at 14.0V or more which helps. Now you can either buy an external regulator for about £200 and get the higher charge rate, or, for most alternators, you can find an internal regulator to replace the OEM one for about £15. If it is regulated at 14.4V it will do most of what an external regulator will do, without overloading your batteries (unless you run your engine regularly for 10 hours or more at a time - even then it is debatable as the charging current reduces significantly as the battery charges up.

[blodger]

What do battery management systems do and if you don't have one then what are the implications in terms of things you need to do

You will probably realise by now that you have opened a oneupmanship issue similar to pump out v cassette.

 

You either have a Smartguage or aspire to have one and make do with hydrometers, voltmeters, ammeters, bits of string and chewing gum.

 

ETA I am in the second group

Edited August 28, 2012 by blodger

[Keeping Up]

What about those of us who don't have a Smartgauge and don't aspire to one, but instead relish the joys of watching moving-needle ammeters and voltmeters (but I do have an Adverc)

[David Schweizer]

Ok. Teach us, in five minutes, how to tell the state of charge of our batteries, using a voltmeter and an ammeter, for all possible situations anyone might meet on a boat.

 

I won't hold my breath.

 

I seem to remember this debate taking place more than five years ago. I also remember the outcome, but will wait to see if history repeats itself.

Edited August 28, 2012 by David Schweizer

[Gibbo]

I seem to remember this debate taking place more than five years ago. I also remember the outcome, but will wait to see if history repeats itself.

 

Yes. Good job I wasn't holding my breath.

[blodger]

What about those of us who don't have a Smartgauge and don't aspire to one, but instead relish the joys of watching moving-needle ammeters and voltmeters (but I do have an Adverc)

witchcraft!

[David Schweizer]

What about those of us who don't have a Smartgauge and don't aspire to one, but instead relish the joys of watching moving-needle ammeters and voltmeters (but I do have an Adverc)

Those of us who grew up with cars that had lots of moving needles and switches are not intimidated by them, I am quite happy with all my dials which tell me all that I need to know. (I do have a Sterling advanced Alternator regulator though).

Edited August 28, 2012 by David Schweizer

[Pretty Funked Up]

witchcraft!

 

deep voodoo

[smileypete]

I seem to remember this debate taking place more than five years ago. I also remember the outcome, but will wait to see if history repeats itself.

Can't remember TBH, what sort of debate would you like?

 

cheers, Pete.

~smpt~

[Gibbo]

Still waiting for the 5 minute lesson on how to determine SoC from volt and ammeters.

 

Can't do it can you!

[Theo]

Still waiting for the 5 minute lesson on how to determine SoC from volt and ammeters.

 

Can't do it can you!

 

I hesitate to tread into such hallowed regions but how about:

 

1. Get a copy of the battery manufacturers data sheets and find from them a table of open circuit pd v. soc

2. Buy a really accurate voltmeter.

3. Wait for some hours with the batteries completely off load and charge.

4. Measure the offload/offcharge voltage to 2dp

5. Relate voltage measured to Soc from the table discovered in 1.

 

Is that it?

 

Nick

 

Ducks, runs for cover and decides not to log on for a week until it all dies down.

[Gibbo]

I hesitate to tread into such hallowed regions but how about:

 

1. Get a copy of the battery manufacturers data sheets and find from them a table of open circuit pd v. soc

2. Buy a really accurate voltmeter.

3. Wait for some hours with the batteries completely off load and charge.

4. Measure the offload/offcharge voltage to 2dp

5. Relate voltage measured to Soc from the table discovered in 1.

 

Is that it?

 

Nick

 

Ducks, runs for cover and decides not to log on for a week until it all dies down.

 

That will do it. The pertinent point being the "Wait for some hours".

[Chalky]

I've got a set of curves (derived from a set of tests) that also include temperature effects - there is a temperature effect of about 10% between +20 & -40 for the batteries I've got.