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Unexpected Expenditure


Parahandy

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36 minutes ago, Horace42 said:

I have already got a similar meter on my boat. I use it all the time - mainly set on  '% capacity' so I always see how well the batteries are charged.

Oh-oh!  Beware Horace: as WotEver alluded to, if it's something along the lines of the NASA or Victron BMV which use a shunt to measure current, these things often say 100% long before the batteries really are, so it can trick you into thinking your batteries are full when they're not. 

 

If you can also read Amps on your meter, I believe it's better to monitor Charging Current as you charge and use tail current to assess when your batteries have stopped taking further charge, i.e. because they're full.  The Amps will drop off as the batteries fill, so watch for a steady lowest tail current figure. Two percent of your battery capacity is often quoted (e.g. 400 ah bank capacity would suggest an 8 amp figure at fully charged), but that's a bit high for me. I'd be looking closer to a couple of amps, but the important thing is that it steadies out. 

 

If you can, I'd also recommend you monitor voltage whilst discharging - you can find a resting voltage based table through Google which will give you another indication of your state of charge.  Amp hours used shouldn't be far off, but use your % state of charge reading only as a rough guide and don't rely on it, particularly as an indication of when to stop charging. Don't be overly optimistic about the battery capacity figure you give the meter either - the cheaper the battery perhaps the less likely it is to meet what's written on the label and it will be diminishing.

 

Battery monitoring is contentious and difficult to get your head around, but the above is my quick and dirty thoughts on it in case it helps. :)

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45 minutes ago, rusty69 said:

Don't start im off again (you know who....... And I don't mean Lord Voldemort). 

The problem is that his petulant repetition might prevent someone considering one, which could be a shame. 

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I've got a Victron 702 monitor. 4x 110. Ah batteries. I watch the monitor and charge until the charging amps reduce to 4 . something. Am I being lied to, as this was suggested ages ago by a respected member on here. Even on a long cruise does the amp reading go less than 4. 

I don't want to defunct my batteries too soon.

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2 hours ago, Sea Dog said:

Oh-oh!  Beware Horace: as WotEver alluded to, if it's something along the lines of the NASA or Victron BMV which use a shunt to measure current, these things often say 100% long before the batteries really are, so it can trick you into thinking your batteries are full when they're not. 

 

If you can also read Amps on your meter, I believe it's better to monitor Charging Current as you charge and use tail current to assess when your batteries have stopped taking further charge, i.e. because they're full.  The Amps will drop off as the batteries fill, so watch for a steady lowest tail current figure. Two percent of your battery capacity is often quoted (e.g. 400 ah bank capacity would suggest an 8 amp figure at fully charged), but that's a bit high for me. I'd be looking closer to a couple of amps, but the important thing is that it steadies out. 

 

If you can, I'd also recommend you monitor voltage whilst discharging - you can find a resting voltage based table through Google which will give you another indication of your state of charge.  Amp hours used shouldn't be far off, but use your % state of charge reading only as a rough guide and don't rely on it, particularly as an indication of when to stop charging. Don't be overly optimistic about the battery capacity figure you give the meter either - the cheaper the battery perhaps the less likely it is to meet what's written on the label and it will be diminishing.

 

Battery monitoring is contentious and difficult to get your head around, but the above is my quick and dirty thoughts on it in case it helps. :)

Thanks for taking the trouble to explain. I am fairly laid back over technical issues.  The precision of the 'numbers' are important when necessary - but somewhat academic to me when cruising when everything is working (what am I going to do with the precise knowledge!) - but useful when things go wrong - like the batteries not charging - or on unusual heavy load - where my 'Victron BMV' can drop to 60% (or is it 50%) - not that it matters unless I try using the microwave oven - when the inverter complains and shuts down on auto. But having said that I usually preserve battery power by running the engine anyway at the same time for the few minutes of cooking.

In any case I have got voltmeters and ammeters all over my boat to monitor 'this and that'. It was the 'Smartgauge' bit that caught my attention and curiosity - hence the question - but thanks to your answer perhaps it's first name should be "Notso"

 

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14 minutes ago, Nightwatch said:

What is this telling me?

That it’s not an ammeter?

 

That the voltage is probably quite good but bearing in mind the (lack of) accuracy of such gauges it could be anywhere between 13V and 15V. 

 

The one thing it doesn't tell you is how charged your batteries are. You need an (accurate) ammeter for that. Or a hydrometer if the batteries are wet and not sealed. 

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16 minutes ago, Nightwatch said:

I picture of the ampmeter on the control panel. The charging ampsare at 8.4 ish. Engine just above idle. What is this telling me?

 

IMG_1672.JPG

Don't know what it tells you. But if it was on my boat it would tell me my battery is charged - and I would be more than happy

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5 minutes ago, Horace42 said:

It was the 'Smartgauge' bit that caught my attention and curiosity - hence the question - but thanks to your answer perhaps it's first name should be "Notso"

I think you misunderstood Sea Dog’s post. The SoC gauges that tell lies are the shunt based ones. The ONLY one which is close to accurate is the SmartGauge. Obviously a faulty one won’t be, so this is MtB’s cue to jump in with a fatuous comment about them 

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2 minutes ago, Horace42 said:

Don't know what it tells you. But if it was on my boat it would tell me my battery is charged - and I would be more than happy

Don’t know how you work that out. That’s one thing that it most certainly isn’t telling anyone. 

24 minutes ago, Nightwatch said:

The charging ampsare at 8.4 ish.

How big is the bank?

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8 minutes ago, Horace42 said:

Don't know what it tells you. But if it was on my boat it would tell me my battery is charged - and I would be more than happy

I'd be looking for 14.4-14.6v to say it was getting somewhere near charged - and then only if the tail current was about 1% of bank size.

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I think often people overcomplicate things when it comes to battery management. I have a small cheap volt meter (£5 on eBay) permanently plugged into bu 12v supply. It tells me everything I need to know about the state of my batteries. 

 

When the engine is running (or the batteries are being charged from an external source) it tells me nothing. But when I am actually drawing from the batteries it tells me everything I need to know. With a fully charged set of batteries it reads around 14.5 volts. As the hours and days go on that figure falls to 13, 12, 11.. Once I reach 11v I know te batteries are close to exhausted. I have very occasional dropped as low as 10.5v without a total loss of power. 

 

It is very simple and it has worked really well for me for years. The only stipulation I would say is - use the same device plugged into the same point. That covers for any inherent inaccuracy in the device itself and for any variance in the voltage at various points in the supply.

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8 minutes ago, WJM said:

I think often people overcomplicate things when it comes to battery management. I have a small cheap volt meter (£5 on eBay) permanently plugged into bu 12v supply. It tells me everything I need to know about the state of my batteries. 

 

When the engine is running (or the batteries are being charged from an external source) it tells me nothing. But when I am actually drawing from the batteries it tells me everything I need to know. With a fully charged set of batteries it reads around 14.5 volts. As the hours and days go on that figure falls to 13, 12, 11.. Once I reach 11v I know te batteries are close to exhausted. I have very occasional dropped as low as 10.5v without a total loss of power. 

 

It is very simple and it has worked really well for me for years. The only stipulation I would say is - use the same device plugged into the same point. That covers for any inherent inaccuracy in the device itself and for any variance in the voltage at various points in the supply.

Oh - to live in such a simple world.

Happy for you.

  • Haha 3
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34 minutes ago, WotEver said:

Don’t know how you work that out. That’s one thing that it most certainly isn’t telling anyone. 

How big is the bank?

I have 4 x 110 Amp hr batteries . 440 Amp hrs. This I have put into the monitor.

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16 minutes ago, WotEver said:

Don’t know how you work that out. That’s one thing that it most certainly isn’t telling anyone. 

How big is the bank?

I can't explain it - I don't work anything out - the voltmeter meter reading tells me something about my batteries that I am happy with - and it does not matter whether the batteries are fully charged - they might be half charged for all I know - but as long as there is enough charge to operate everything OK then that is all that matters. 

 

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34 minutes ago, Nightwatch said:

I have 4 x 110 Amp hr batteries . 440 Amp hrs. This I have put into the monitor.

Then ideally I’d be looking for half the current you quoted - nearer 4A than 8A. But I’d want to know the accuracy of that little voltmeter ‘cos that 4A should be at a charging voltage of 14.4V or more. 

9 minutes ago, Horace42 said:

I can't explain it - I don't work anything out - the voltmeter meter reading tells me something about my batteries that I am happy with - and it does not matter whether the batteries are fully charged - they might be half charged for all I know - but as long as there is enough charge to operate everything OK then that is all that matters. 

 

Well yes, that is all that matters. So as long as you don’t mind replacing your batteries yearly then you’re right, you can just half charge them. 

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30 minutes ago, Nightwatch said:

Engine still running, Victron now reading, 4.75 amps and voltage is 14.3.v. I'm going to run the engine as long as I dare. I'll report back.

You’re at the high 90’s now (maybe 98%/99%) so don’t worry too much about going any further :)

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