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I've been reading several threads about battery management (I was going to say charging, but it's not just about that) and am, quite frankly, confused.

 

There seem to be a number of technologies in use and I am trying to work out what would be best for us.

 

We bought our boat a year ago and moor on a marina with a shoreline so when we're there the onboard charger should be taking care of things. The only other means we have of charging is running the engine. This works fine while we keep moving but I'm concerned that we might damage the domestic bank if we moored up for a few days while cruising. The previous owners were continuous cruisers living aboard so I assume the set-up worked for them.

 

The only instrument I have to tell me what's happening with the batteries is a distribution panel with built in voltmeter and ammeter and a switch for battery 1 or battery 2

 

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Battery 1 is, I think, the starter battery and will probably fail next winter judging by the fact that it never seems to get above 12.5 V and struggled to turn the engine over in December when it was about -8 degC outside.

Battery 2 usually reads 12.7 V in the morning. We don't really use a lot of juice in summer (mostly the fridge and water pumps, I suspect) but in winter we might be tempted to check if the TV works and would also be running the Webasto as well as potentially up to 40 lights.

 

I suppose the questions I need to ask are

1. How many years does a set of batteries last if treated well?

2. How can I tell when the batteries need replacing?

3. Would it be cost effective to add one or two PV panels and a reasonable quality MPPT?

4. How much energy does a 100 W PV panel provide over the year (mounted horizontally on the roof with no attempt at tracking the sun)

 

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1. Depends upon what type/ design but as long  as they are tolerably well looked after from two years upwards. Easy to destroy in weeks though.

 

2. When it will:

a. not hold enough charge for you.

b. individual cells start bubbling/run dry/stink of rotten eggs

c. Charges fast and discharges fast.

d. Discharges itself over hours/a days.

 

When the case ends start bowing out start saving!

 

3. Yes, especially if its you leave the boat & go home but I doubt it will keep up with your domestic demand in the summer, et alone in the winter.

 

4. Someone may be logging their panels performance but its so variable I would not even consider giving you an answer, its probably a lot less than you think. Trees etc. near the mooring will affect it.

 

If you leave the boat and go home consider fitting a VSR so the solar charges both banks and it will ease winter starting.

 

 

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24 minutes ago, George and Dragon said:

The only instrument I have to tell me what's happening with the batteries is a distribution panel with built in voltmeter and ammeter and a switch for battery 1 or battery 2

As a most basic regime, if you ever see the voltage dropping close to 12.2V then either start charging by running the engine or, if it’s after 8pm, then turn everything off and go to bed until you can start charging in the morning. 

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There are simple steps you can take to help things along. A decent PV array is worth having though it won't give you much in the winter but in summer it will lessen wear and tear on the domestics. I fitted a 20w panel dedicated to the starter only cost all in about £25.00. You mentioned using up to 40 lights, hopefully they are all LED, if they are not then seriously consider changing them 

Phil 

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4 minutes ago, Phil Ambrose said:

You mentioned using up to 40 lights, hopefully they are all LED, if they are not then seriously consider changing them 

They are. And that would mean every light on the boat was lit which I hope is unlikely?

32 minutes ago, Tony Brooks said:

If you leave the boat and go home consider fitting a VSR so the solar charges both banks and it will ease winter starting.

 

VSR?

 

18 minutes ago, WotEver said:

if you ever see the voltage dropping close to 12.2V then either start charging by running the engine or, if it’s after 8pm, then turn everything off and go to bed until you can start charging in the morning. 

I hope that never happens ?

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3 minutes ago, George and Dragon said:

VSR?

Voltage Sensitive Relay. 

 

It switches on only when the voltage is above about 13.7V and will disconnect when the voltage drops to about 12.8V. You connect all your charge sources (alternator, mains charger, solar) to the domestic battery bank and the VSR between domestic and starter battery, with the ‘sense’ side (the bit that measures the voltage) on the domestic side. Many newer VSRs sense on both sides which makes installation simpler. Then, while your domestic batteries are being charged the VSR will connect the starter battery and charge it too. 

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Wotever's rule of never below 12.2V is very important and will get you on the first step to getting 2 years plus out of the domestic bank. I am worried however that you don't really know what the voltmeter is telling you. Yes, pos 2 is probably domestic but how accurate is it? I would find someone to check it with a decent multimeter so you know it is accurate. I'd prefer 2 places of decimals on the display but you should get by. I say this because you say you see 12.7v each morning. I would expect with limited overnight use and not so new batteries to be showing 12.5v or less. If you are 0.2v out, you need to know that!

The second rule is to charge until you get a low tail current. To do that you need an ammeter. Again, we need to find out what yours is telling you. Again, try and find someone with a clamp meter who can have a quick look. I am sure there maybe peeps on here who can help test the meters. Where are you....approx area only?

Certainly get some solar to help in the summer to save running the engine. No use wotever in the winter.

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14 minutes ago, WotEver said:

As a most basic regime, if you ever see the voltage dropping close to 12.2V then either start charging by running the engine or, if it’s after 8pm, then turn everything off and go to bed until you can start charging in the morning. 

This is great advice for those still on the start of the learning curve.  A 12v battery state of charge chart, easily found by Google will give more detail of what the readings mean.  Leave the monitoring on your domestic batteries except for when checking the starter battery specifically - it'll pretty much look after itself as it recovers from a start quite early with the engine running.

 

I'm assuming you have the more common sealed lead acid batteries.  One slight caveat would be that the voltage measurement should be a 'resting' voltage, so if the missus is running her hair dryer it will drop then recover.  The reading first thing in the morning will tell you how well or badly you did yesterday!  My aim is never to let my domestic batteries drop beyond 60% full, more on that lower down.

 

The good news is that you have an ammeter as well as a volt meter, which is really useful.  When charging, select your domestic batteries and watch the Amps.  They'll start high and slowly but steadily drop (the volts will steadily rise as the batteries fill), but up to 80% full is quite quick - it's not enough though.  Charge until a steady low single figure is reached - this is "tail current".  Some say 2% of your battery capacity figure, so for 440 amp hour battery capacity they go to 8.8 amps.  I think that this is not far enough - I get below 2 amps before a steady state is achieved.  You should really do this after each discharge, so ideally every day.  2 days will hurt your batteries a bit, 3 days a bit more.  Charging to less than 100% will hurt your batteries a bit, as will discharging to 60%, 50%, 40%, etc - heavier discharges hurt more heavily.  Some use 50% as their floor, I prefer 60%, others something else.  It's all a compromise harder use = shorter life.

 

There's way more, but that I hope will give you a basic idea.  Good luck!

 

Note:  There's been a few replies as I've been typing, so please forgive any repetition, conflicts or thunder stealing! :)

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1 hour ago, George and Dragon said:

 

We bought our boat a year ago and moor on a marina with a shoreline so when we're there the onboard charger should be taking care of things. The only other means we have of charging is running the engine. This works fine while we keep moving but I'm concerned that we might damage the domestic bank if we moored up for a few days while cruising. 

 

This was exactly my situation, and with exactly the same concern, when I bought my boat in August 2015. The following June I had 2 * 100W of solar fitted, although I now regret not having larger panels.

 

These have pretty much removed the concern about mooring up for a few days, at least in late spring, summer and early autumn. At least if the weather is reasonable. If we moor up for a day or more due to continuous dark clouds and rain then, depending on voltage readings, I may have to bite the bullet and run the engine but our reasons for not moving are usually more to do with good weather and a good location and less to do with a full day of bad weather. Even in bad weather we normally try to move for a couple of hours if possible in preference to running the engine without moving.

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Thanks all

 

We've been moving all day but slow running with locks and so I discovered another little issue: the inverter doesn't like the washing machine on at tickover. There was lots of beeping from the machine and it eventually went quiet - the inverter had gone into overload ? Previously the washing machine seemed fine while we were cruising at normal speeds most of the time.

I'm not sure but it looks like it's a Power Master 'pure sine wave' unit. Hard to tell as it appears to have been installed upside down

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Sounds as if it may have cut out on low voltage. As long as the voltmeter for the domestic battery is reading (say) 12.2V + at idle/off charge (guess) it suggests the inverter is suffering from volt drop, probably undersized leads for their run length.

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4 minutes ago, Tony Brooks said:

Sounds as if it may have cut out on low voltage. As long as the voltmeter for the domestic battery is reading (say) 12.2V + at idle/off charge (guess) it suggests the inverter is suffering from volt drop, probably undersized leads for their run length.

I hope it doesn't happen again, but if it does I'll be sure to check. 

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13 hours ago, George and Dragon said:

Thanks all

 

We've been moving all day but slow running with locks and so I discovered another little issue: the inverter doesn't like the washing machine on at tickover. There was lots of beeping from the machine and it eventually went quiet - the inverter had gone into overload ? Previously the washing machine seemed fine while we were cruising at normal speeds most of the time.

I'm not sure but it looks like it's a Power Master 'pure sine wave' unit. Hard to tell as it appears to have been installed upside down

George, that's not unusual at tick over with a heavier load. We have a 175 amp alternator and you can really feel/hear the load coming onto it as the revs drop when you use any relatively powerful appliance. Even when cruising the revs can drop, so sometimes it needs a bit of extra throttle to compensate for the load without speeding up.  This can need a bit of management,  particularly if passing moored boats at low revs.  If you're running the washer whilst stationary, put her in neutral and add a few revs til the engine is at a comfortable fast idle and is coping nicely with the load rather than labouring. I'd suggest not using a washing machine when transiting locks as there's enough to occupy you without faffing with the throttle.  Same goes for a hair dryer, coffee maker, electric kettle, etc.  Give it a go and see how you get on.

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32 minutes ago, Sea Dog said:

I'd suggest not using a washing machine when transiting locks as there's enough to occupy you without faffing with the throttle.  Same goes for a hair dryer, coffee maker, electric kettle, etc.  Give it a go and see how you get on.

Maybe when I get a bit more experience I'll be able to concentrate on more than one thing at a time. 

In the meantime I'll definitely make sure the washing machine stays off until we've done with the locks

13 hours ago, George and Dragon said:

As long as the voltmeter for the domestic battery is reading (say) 12.2V + at idle/off charge (guess) it suggests the inverter is suffering from volt drop, probably undersized leads for their run length.

I'm sure fatter copper would help but I probably won't go to the trouble unless it becomes a persistent problem. However, would that kind of load (assuming 260A at 12V) be a problem for the domestic batteries?

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10 minutes ago, George and Dragon said:

However, would that kind of load (assuming 260A at 12V) be a problem for the domestic batteries?

For what period ?

 

If you have 2x 110Ah batteries the answer is (probably) YES.

If you have 10x 110Ah batteries the answer is (probably) NO

 

Anywhere in between will be problematic and financially prohibitive.

 

A starter motor is drawing 100's of amps from a single battery - but only for a few seconds

Drawing 260 amps for (say) half-an hour would not be good for battery health.

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2 hours ago, George and Dragon said:

Maybe when I get a bit more experience I'll be able to concentrate on more than one thing at a time.

That's known as complacency, or familiarity breeding contempt. In locks you should have one eye for the boat and one for yourself. Leave the washing machine out of the equation.  :)

 

(Don't run it off the batteries either, unless you enjoy buying batteries!) :D

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The biggest power draw on the washing machine is heating up cold water, not the motor turning the drum. I installed a washing machine on our boat over the winter and put a thermostatic mixer valve on the water supply, taking from both hot and cold feeds. I set this up for just over 30degC by filling some saucepans from the hose with a thermometer in and run 30degC washes. The heater is never called upon so we only ever see the inverter pulling 30 to 40 Amps for the motor. I turned the engine off during a wash cycle once, when I had to wait for an hour at Bingley locks and new I had warm water.

Edited by PeterF
So it makes sense
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Perhaps it varies with different batteries but the tail current with my single 105ah Trojan is 0.38%. I know this because the amp reader on the Tracer meter settles at 0.4 amps after many hours of hot sunshine, with everything turned off.

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2 hours ago, Gareth E said:

Perhaps it varies with different batteries but the tail current with my single 105ah Trojan is 0.38%. I know this because the amp reader on the Tracer meter settles at 0.4 amps after many hours of hot sunshine, with everything turned off.

I don't know, but I'm not sure a solar controller meter can be trusted as a battery monitor - My thinking is that there are so many variations in the supply source. But I could easily be wrong.

 

The tail current on my 4 x T105s, (450Ah capacity when new, but much less more recently), tends to settle around 3A or 4A, at 14.4V, so around 1% - 2%. This is using a NASA BM2 monitor. 2% at 14.4V seems to be a widely quoted figure for considering your batteries fully charged, or as good as.

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39 minutes ago, Richard10002 said:

I don't know, but I'm not sure a solar controller meter can be trusted as a battery monitor - My thinking is that there are so many variations in the supply source. But I could easily be wrong.

 

The tail current on my 4 x T105s, (450Ah capacity when new, but much less more recently), tends to settle around 3A or 4A, at 14.4V, so around 1% - 2%. This is using a NASA BM2 monitor. 2% at 14.4V seems to be a widely quoted figure for considering your batteries fully charged, or as good as.

I was thinking the same so I did a little test: ran the engine while the solar meter was showing .4 amps. Checked the meter, it went down to zero but my clamp meter suggested .4 amps going in from the alternator. The alternator seems to override the panels which I don't understand, but there you go. It does suggest the meter is accurate though.

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13 hours ago, Gareth E said:

Perhaps it varies with different batteries but the tail current with my single 105ah Trojan is 0.38%. I know this because the amp reader on the Tracer meter settles at 0.4 amps after many hours of hot sunshine, with everything turned off.

......but what is the voltage? Are you sure the low current is not just because it has gone into float. Voltage needs to be 14.4 ish to be able to know the real tail current.

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10 hours ago, Dr Bob said:

......but what is the voltage? Are you sure the low current is not just because it has gone into float. Voltage needs to be 14.4 ish to be able to know the real tail current.

I'm not sure about that but regular looks at the meter suggests voltage stays at 14.6 until amps drop to around 0.8. It then goes into float at 13.4v, amps then drop slowly over an hour or two until they settle at 0.4. This suggests to me that the tail current is the tail current, the voltage is irrelevant, other than perhaps it taking longer to get to the tail current at 13.4v than it does at 14.6.

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10 minutes ago, Gareth E said:

I'm not sure about that but regular looks at the meter suggests voltage stays at 14.6 until amps drop to around 0.8. It then goes into float at 13.4v, amps then drop slowly over an hour or two until they settle at 0.4. This suggests to me that the tail current is the tail current, the voltage is irrelevant, other than perhaps it taking longer to get to the tail current at 13.4v than it does at 14.6.

I don't think you can claim you tail current is 0.38%. That is the current you are getting at float. I would describe your tail current as just below 1% ie 0.8amps with a bit of inaccuracy in the meter, the age of the one battery and potentially going into float too soon. 

Our 660Ahr bank, over one year old and maybe lost say10% capacity .....estimated via at rest voltage and Ahrs out....will go down to around 5A charging at 14.5v if I keep forcing the system to come out of float......which isn't easy....so that's about 1%.

Whilst it is useful...and important.... to quote voltage to two decimal places, that is a bit ott for tail current. 

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31 minutes ago, Gareth E said:

I'm not sure about that but regular looks at the meter suggests voltage stays at 14.6 until amps drop to around 0.8. It then goes into float at 13.4v, amps then drop slowly over an hour or two until they settle at 0.4. This suggests to me that the tail current is the tail current, the voltage is irrelevant, other than perhaps it taking longer to get to the tail current at 13.4v than it does at 14.6.

That can't be correct. Voltage is the pressure that forces Amps round a circuit. If you reduce the pressure you will reduce the amount of Amps being forced through the batteries so you get to the accepted "tail" current before the batteries are less fully charged than when charging at above 14 volts.

 

Remember this 1% to 2% of battery capacity is based on empirical observations not scientific measurement and calculations so the voltage its observed at is a vital [part of getting the correct answer.

 

I agree a lower voltage can and will fully charge a battery as a higher one BUT it will take a lot more time. However I am not sure 13.4 volts would do it before the batteries sulphated. It sounds  a bit low for a float voltage to me because I would expect a  float of about 13.6 volts.

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