Battery Monitor Shunt Wiring Best Practise

[nicknorman]

1 minute ago, Keajre said:

Hmm yes I see.

 

Should there be two fuses, one from each off the two positives that go into the switch, or just one on the output of the isolator.  Just that if only one of the output of the isolator, if either of the two positive cable connections to the isolator came loose and touched hull, it would cause the same issue. Or is that overkill?

It is bad practice to fit a fuse inside a battery box. A blowing fuse is a source of ignition, a battery produces explosive hydrogen. Mixing the two is not a good idea! So there will always be some unprotected cable, but the idea is to keep that as short as possible, minimising the probability of a fault there. So keep the battery isolator switch near the batteries  and keep the fuse near the isolator, but not on the battery side of it. Make sure the wiring between battery positive and fuse is “bulletproof” ie protected and secure, not touching other wires or anything it could chafe on.

[Keajre]

5 minutes ago, nicknorman said:

It is bad practice to fit a fuse inside a battery box. A blowing fuse is a source of ignition, a battery produces explosive hydrogen. Mixing the two is not a good idea! So there will always be some unprotected cable, but the idea is to keep that as short as possible, minimising the probability of a fault there. So keep the battery isolator switch near the batteries  and keep the fuse near the isolator, but not on the battery side of it. Make sure the wiring between battery positive and fuse is “bulletproof” ie protected and secure, not touching other wires or anything it could chafe on.

More good advice, what would I do without Canalworld, thanks again

[nicknorman]

I’m a bit puzzled by the block labelled “inverter”. Is it an inverter, or a Combi? If it is an inverter, why are there connections to engine battery and shore power?

 

I therefore am guessing it might be a Combi. If so, you might want to consider connecting the Combi positive directly to the domestic batteries (not via the isolator). This allows the batteries to be kept on shore power charge with all domestic circuits disconnected by the isolator. The fuse then allows the power to the Combi to be removed (removing the fuse) for maintenance etc,  although some people like to fit a separate isolator switch just for the Combi supply (we don’t have this so of course I don’t think it’s necessay!)

3 minutes ago, Keajre said:

More good advice, what would I do without Canalworld, thanks again

This is covered in the BSS. If you haven’t already trawled through the electrical section of the BSS check, please do so! You don’t want to do a whole lot of work only to have a BSS fail and major rewire required!

[TheBiscuits]

I like this thread.  Instead of the usual

"Should I buy an XYZ?"

"Yes they are great. Buy two."

"No, my friend's Aunt had one and it didn't work."

"I bought two and they have different readings." 

[OP wanders off much more confused]

type of thread we have an OP that asks a question having obviously done some research. 

He then understands more about the issue and then considers related questions and gets further feedback on these.

This is Canalworld at it's best.

 

[Keajre]

2 minutes ago, nicknorman said:

I’m a bit puzzled by the block labelled “inverter”. Is it an inverter, or a Combi? If it is an inverter, why are there connections to engine battery and shore power?

 

I therefore am guessing it might be a Combi. If so, you might want to consider connecting the Combi positive directly to the domestic batteries (not via the isolator). This allows the batteries to be kept on shore power charge with all domestic circuits disconnected by the isolator. The fuse then allows the power to the Combi to be removed (removing the fuse) for maintenance etc,  although some people like to fit a separate isolator switch just for the Combi supply (we don’t have this so of course I don’t think it’s necessay!)

Yes its an inverter / charger.  The way I want it is to be able to do split changing.  So that is a three position switch on the positive of the batteries (which also acts as an isolator).  Allows me to use just bank 1, or just bank 2 or both at once.  If one of the two 6v batteries were to fail, I can isolate that and just use the other bank.  Also allows me to fast charge just half the batts if I ever needed to (over 500 AH with all four (c20)).  99% of the time it will be in the ‘both’ position using all four batts.

When I am on shore power, the inverter does pass through, so current for the 240 never leaves the domestics and it doesn’t invert.  The charger is float charging the batteries while on shore power and the domestics are isolated from any load. Although 12v systems do still feed from the batteries, which is turn is powered by the charger (or Combi).  SO in effect, no amps leave the domestics when on shore power.

So not sure I entirely follow the benefits of connecting directly to the domestics, but perhaps I missed your point.

6 minutes ago, TheBiscuits said:

I like this thread.  Instead of the usual

"Should I buy an XYZ?"

"Yes they are great. Buy two."

"No, my friend's Aunt had one and it didn't work."

"I bought two and they have different readings." 

[OP wanders off much more confused]

type of thread we have an OP that asks a question having obviously done some research. 

He then understands more about the issue and then considers related questions and gets further feedback on these.

This is Canalworld at it's best.

 

:-)

[Robbo]

26 minutes ago, nicknorman said:

It is bad practice to fit a fuse inside a battery box. A blowing fuse is a source of ignition, a battery produces explosive hydrogen. Mixing the two is not a good idea! So there will always be some unprotected cable, but the idea is to keep that as short as possible, minimising the probability of a fault there. So keep the battery isolator switch near the batteries  and keep the fuse near the isolator, but not on the battery side of it. Make sure the wiring between battery positive and fuse is “bulletproof” ie protected and secure, not touching other wires or anything it could chafe on.

I use terminal fuses, makes wiring easier as well as no unprotected cable, the fuses are ignition protected.

[Keajre]

22 minutes ago, nicknorman said:

This is covered in the BSS. If you haven’t already trawled through the electrical section of the BSS check, please do so! You don’t want to do a whole lot of work only to have a BSS fail and major rewire required!

Got my BSS cert a few months ago, though I don’t think it was very thorough.  Just had a look through  

 

The one thing I might have a problem with is the ventilation.  Batteries are in a newly made battery box.  The back is open, so lots of ventilation there, but the no actual vents anywhere in the engine bay.  The unintended ventilation comes in via the deck boards, which are not an air tight fit.  Plenty of air can circulate I’m sure but Ive no way of measuring that.  I have 520AH of capacity, and the BSS guide talks about a fan to encourage ventilation if Charing over 150 amps.  I’ll be charging based on 10-13% of the C20 rate of the batteries.  So 60 amps in the bulk phase of the charge.  I would surmise gassing would be fairly minimal, apart from when equalising where it would increase.  However I would have the deck boards up and caps open during equalisation as I’d be checking specific gravity readings at those times.

 

However, am I 100% compliant? No.  Don’t think I ever would be entirely, its extremely detailed and in some cased over the top.  Some things are mandatory, like our conversation about fuses and such like, but I think sometimes it goes a little too far.  Just my opinion 

Does the hydrogen of a gassing battery lighter than air?  I guess it must be, thinking back to the periodic table (one electron and one proton).  So it would in theory escape through the gaps in the deck boards.

[nicknorman]

13 minutes ago, Keajre said:

Yes its an inverter / charger.  The way I want it is to be able to do split changing.  So that is a three position switch on the positive of the batteries (which also acts as an isolator).  Allows me to use just bank 1, or just bank 2 or both at once.  If one of the two 6v batteries were to fail, I can isolate that and just use the other bank.  Also allows me to fast charge just half the batts if I ever needed to (over 500 AH with all four (c20)).  99% of the time it will be in the ‘both’ position using all four batts.

When I am on shore power, the inverter does pass through, so current for the 240 never leaves the domestics and it doesn’t invert.  The charger is float charging the batteries while on shore power and the domestics are isolated from any load. Although 12v systems do still feed from the batteries, which is turn is powered by the charger (or Combi).  SO in effect, no amps leave the domestics when on shore power.

So not sure I entirely follow the benefits of connecting directly to the domestics, but perhaps I missed your point.

:-)

If you can switch between you two domestic battery banks, then you will confuse the battery monitor! What you propose is “abnormal” but I suppose not harmful. Generally it is always best to leave the entire bank in circuit. As you suggest, I suspect you will always have the switch in “both” position. And thus personally I wouldn’t bother with a multiway switch!

The point with the Combi supply is for if/when you leave the boat for a long period on shore power, as we do. We turn off the battery master switch but the Combi remains in circuit, keeping the batteries trickle charged. If you never plan to leave the boat for long periods, it’s not something you’ll want to do. However in general with these things, it can be better to go along with normal practice rather than re-inventing a (different) wheel.

Just on the point about Combis on shore power, you don’t mention the make of Combi but most have a switch with 3 setting, off, on and charger only (or something like that). If you leave the inverter on, should the shore power trip  you don’t notice until the batteries are completely flat and the lights go out, If you leave the switch in charger only, when the shore power trips you know straight away. So we always leave ours in “charger only” when plugged into shore power.

[nicknorman]

9 minutes ago, Keajre said:

Got my BSS cert a few months ago, though I don’t think it was very thorough.  Just had a look through  

 

The one thing I might have a problem with is the ventilation.  Batteries are in a newly made battery box.  The back is open, so lots of ventilation there, but the no actual vents anywhere in the engine bay.  The unintended ventilation comes in via the deck boards, which are not an air tight fit.  Plenty of air can circulate I’m sure but Ive no way of measuring that.  I have 520AH of capacity, and the BSS guide talks about a fan to encourage ventilation if Charing over 150 amps.  I’ll be charging based on 10-13% of the C20 rate of the batteries.  So 60 amps in the bulk phase of the charge.  I would surmise gassing would be fairly minimal, apart from when equalising where it would increase.  However I would have the deck boards up and caps open during equalisation as I’d be checking specific gravity readings at those times.

 

However, am I 100% compliant? No.  Don’t think I ever would be entirely, its extremely detailed and in some cased over the top.  Some things are mandatory, like our conversation about fuses and such like, but I think sometimes it goes a little too far.  Just my opinion 

Does the hydrogen of a gassing battery lighter than air?  I guess it must be, thinking back to the periodic table (one electron and one proton).  So it would in theory escape through the gaps in the deck boards.

If the box is ventilated, that is fine. It is all about the concentration of hydrogen - so a small amount of hydrogen in the small volume of the battery box could be an explosive mixture, the same amount of hydrogen in the much larger volume of the engine bay won’t be explosive. Yes hydrogen is lighter than air, but all gases tend to diffuse /mix to some extent, it’s not like say oil and water.

 

dont have the battery caps off during equalising, you get bubbles bursting which spits tiny droplets of acid and will, over time, make a big mess of the surrounding area. Check the battery makers instructions but I would either leave the caps in place, or just loosen them slightly.

Edited February 18, 2018 by nicknorman

[Keajre]

3 minutes ago, nicknorman said:

If you can switch between you two domestic battery banks, then you will confuse the battery monitor! What you propose is “abnormal” but I suppose not harmful. Generally it is always best to leave the entire bank in circuit. As you suggest, I suspect you will always have the switch in “both” position. And thus personally I wouldn’t bother with a multiway switch!

The point with the Combi supply is for if/when you leave the boat for a long period on shore power, as we do. We turn off the battery master switch but the Combi remains in circuit, keeping the batteries trickle charged. If you never plan to leave the boat for long periods, it’s not something you’ll want to do. However in general with these things, it can be better to go along with normal practice rather than re-inventing a (different) wheel.

Just on the point about Combis on shore power, you don’t mention the make of Combi but most have a switch with 3 setting, off, on and charger only (or something like that). If you leave the inverter on, should the shore power trip  you don’t notice until the batteries are completely flat and the lights go out, If you leave the switch in charger only, when the shore power trips you know straight away. So we always leave ours in “charger only” when plugged into shore power.

Yes it would confuse the battery monitor its true.  I would almost never use that switch.  The main use case is if one battery fails, I can isolate the fault.  I suppose that is an unlikely scenarios and even if it did happen would be simple to manually isolate the faulty bank.  Split charging might be useful, but again, probably not ever going to do it.  And would have to ‘re-sync’ the Battery Monitor after.

 

I live onboard, if I ever go away for a long period, say on holiday, I turn off all systems, disconnect mains and leave the MPPT / Solar to keep the batteries topped up.  Seems to work well.

 

The inverter charger is a Victon Multiplus.  Yes it has that function.  If I go away I have it switched so that if the shore fails the invert stops.  Saves it draining the batteries down.  It’s a decent inverter, you can log into it with a laptop and configure a whole raft of settings.  It’s set to cut out at 11.8 volts.  Generally I’d avoid going below 12.2v, but its just to stop it damaging the batteries.  

6 minutes ago, nicknorman said:

If the box is ventilated, that is fine. It is all about the concentration of hydrogen - so a small amount of hydrogen in the small volume of the battery box could be an explosive mixture, the same amount of hydrogen in the much larger volume of the engine bay won’t be explosive. Yes hydrogen is lighter than air, but all gases tend to diffuse /mix to some extent, it’s not like say oil and water.

 

dont have the battery caps off during equalising, you get bubbles bursting which spits tiny droplets of acid and will, over time, make a big mess of the surrounding area. Check the battery makers instructions but I would either leave the caps in place, or just loosen them slightly.

Ah yes, I remember reading somewhere how many parts per million of hybrogen in air before it causes explosion.  Ok good, so with open battery box and sensible charging I should be ok.  

Didn’t know that about the equalisation phase, will check with Trojan (they are 145s)

[Keajre]

The other issue, they are not tied down, and BSS recommends they should be.  They say that if they move, the cables could come into contact with the hull, valid point.  But my battery box envelopes the batteries nicely, no possible way cables or terminal ends could touch the hull.  The box they are housed in cannot fall into the bilges and there is a steel ‘step’ and a bar that would stop them. Cannot fall back more than a few centimetres  (although BSS says 10mm) as they are on top of the swim next to a steel wall (the outside shell of the boat).  They weigh 130KG, so if something smashes into the boat that hard, I have other more pressing matters :-).  And since its fused (or will be), all good I think 

Edited February 18, 2018 by Keajre

[nicknorman]

3 minutes ago, Keajre said:

Yes it would confuse the battery monitor its true.  I would almost never use that switch.  The main use case is if one battery fails, I can isolate the fault.  I suppose that is an unlikely scenarios and even if it did happen would be simple to manually isolate the faulty bank.  Split charging might be useful, but again, probably not ever going to do it.  And would have to ‘re-sync’ the Battery Monitor after.

 

I live onboard, if I ever go away for a long period, say on holiday, I turn off all systems, disconnect mains and leave the MPPT / Solar to keep the batteries topped up.  Seems to work well.

 

The inverter charger is a Victon Multiplus.  Yes it has that function.  If I go away I have it switched so that if the shore fails the invert stops.  Saves it draining the batteries down.  It’s a decent inverter, you can log into it with a laptop and configure a whole raft of settings.  It’s set to cut out at 11.8 volts.  Generally I’d avoid going below 12.2v, but its just to stop it damaging the batteries.  

OK fair enough on the usage/co figuration front.

Just on the minimum voltage setting on the Combi, I think you may be conflating two different things.

Yes it is inadvisable to discharge below 12.2v or so (lower if traction or semi-traction batteries) but that is the rested no-load voltage.

When you take a significant load from the batteries, the voltage will dip much lower but that is fine. It is about not going below ~50% SoC, it is not actually about not going below 12.2v regardless of load.

if you take a big current drain from the batteries, and especially if they are traction or semi-traction batteries (eg Trojans) and especially if the batteries are cold, you will find a big voltage reduction on the battery terminals. I think 11.8v is thus too high a setting and you will get below that easily, even with well charged batteries but say a 2kw inverter load.

Bottom line is that an inverter low voltage cut-out isn’t a good way to protect against over-discharge of batteries under normal usage.

2 minutes ago, Keajre said:

The other issue, they are not tied down, and BSS recommends they should be.  They say that if they move, the cables could come into contact with the hull, valid point.  But my battery box envelopes the batteries nicely, no possible way cables or terminal ends could touch the hull.  The box they are housed in cannot fall into the bilges and there is a steel ‘step’ and a bar that would stop them. Cannot fall back more than a few centimetres  (although BSS says 10mm) as they are on top of the swim next to a steel wall (the outside shell of the boat).  They weigh 130KG, so if something smashes into the boat that hard, I have other more pressing matters :-).  And since its fused (or will be), all good I think 

They don’t have to be tied down, just secured. So for example when I fitted Trojans to our battery box, these had a smaller footprint but were taller than the original batteries. I simply put some lumps of wood in the new gap between the batteries and box, so the batteries couldn’t move. Job done!

[Keajre]

Other small issue, it says NO circuits should return by the earth (via the hull).  All wires should have two cables for positive and negetive.  Fine, 99% do.  My horn however doesnt.   It comes back via the hull through the earth cable and back to the batteries that way.  Can’t see how that could ever cause an issue.  It states about ‘electolytic’ and suggests about personal safety.  Can’t see the harm in it personally 

Edited February 18, 2018 by Keajre

[smileypete]

ISTR that it's best to connect the DC bond to the hull from engine block and not somewhere near the batts. That way if a return cable starts to go faulty there's less likely to be fault currents going via DC bond though the hull and then porp shaft or some other way.

Also ISTR there can be some current diverted even if the return cables are good, Keeping Up had this problem.

Maybe on the diag you could put a dotted line round the starter and two alts to represent the engine block, this would then be connected to starter bank -ve, negative bus bar, and hull instead of showing direct connections.

In practice this may be done from a starter mounting bolt as the starter takes the most current, though engine marinisers may do things differently.

50 minutes ago, nicknorman said:

If you can switch between you two domestic battery banks, then you will confuse the battery monitor! What you propose is “abnormal” but I suppose not harmful. Generally it is always best to leave the entire bank in circuit. As you suggest, I suspect you will always have the switch in “both” position. And thus personally I wouldn’t bother with a multiway switch!

Yeah it is fairly esoteric but might come in handy for a year round off grid liveaboard. (the question being - how would you best eq your batts in winter without long hours of engine or genny running?)

But only around 0.5% of boaters will face this situation, and to answer such questions will invite 'expert hell', so best do what you suggest and use a single bank and isolator.

Edited February 18, 2018 by smileypete

[Keajre]

10 minutes ago, nicknorman said:

OK fair enough on the usage/co figuration front.

Just on the minimum voltage setting on the Combi, I think you may be conflating two different things.

Yes it is inadvisable to discharge below 12.2v or so (lower if traction or semi-traction batteries) but that is the rested no-load voltage.

When you take a significant load from the batteries, the voltage will dip much lower but that is fine. It is about not going below ~50% SoC, it is not actually about not going below 12.2v regardless of load.

if you take a big current drain from the batteries, and especially if they are traction or semi-traction batteries (eg Trojans) and especially if the batteries are cold, you will find a big voltage reduction on the battery terminals. I think 11.8v is thus too high a setting and you will get below that easily, even with well charged batteries but say a 2kw inverter load.

Bottom line is that an inverter low voltage cut-out isn’t a good way to protect against over-discharge of batteries under normal usage.

They don’t have to be tied down, just secured. So for example when I fitted Trojans to our battery box, these had a smaller footprint but were taller than the original batteries. I simply put some lumps of wood in the new gap between the batteries and box, so the batteries couldn’t move. Job done!

Yes I recognise and agree.  Resting voltage after several hours (24 ideally) shows SoC (or the amount of sulphuric acid in the electrolyte).  With a large load being draw, it would go below 12.2 I get that, and that’s ok.  I think 11.8 is too high, I’ll be honest I haven’t checked it recently, I think it is actually lower for those very reasons. 

 

The Trojan manual says to maximise lifespan, don’t discharge to more than 80%.  I assume that means 80% discharged, ie 20% left.  The suggestion seems to be as they are traction batteries you can safely dischartge down to 11.66 volts (resting voltage of course).  I was planning on not discharging below 20% SoC.  So 12.5 if I can help it.  I have seen the graph data showing the massive reduction of cycles you get when discharging to these lower percentages.  

 

The inverter is 3kw.  I generally never pull more than 20-30 amps.  I have a washing machine but I’ll be running a generator for that when I am out cruising.  There are some times when 200 - 250 amps will be pulled, as the Inverter performs its ‘power assist’ mode.  Takes a few seconds to kick in, initially the entire load (iron or washing machine) comes from the inverter as its starts to grab power from the generator.  Genny is a pure sign wave 2.2 (bursts to 2.5) khw.  For some reason, when I have it connected through the shore power line into the inverter, even though it could happily power said device on its own, and even though the inverter is doing ‘pass through’ only at that time, it causes the genny to stall immediately.  If I plug the same load (say washing machine) DIRECTLY into generator, its no problem.  So I have to use the power assist function and do some from batteries and some from Generator, even that sometimes causes the genny to stall.  In those cases I have to setup a separate load to pull from the genny, enough to get its RPM up and delverying current, then try again which usually does it.  Its a real pain. Sorry, going off topic here.

 

Good, my battery box sounds compliant then, thanks.

[Keajre]

17 minutes ago, smileypete said:

ISTR that it's best to connect the DC bond to the hull from engine block and not somewhere near the batts. That way if a return cable starts to go faulty there's less likely to be fault currents going via DC bond though the hull and then porp shaft or some other way.

My hull / common earth is bonded to the engine supports (the steel supports the engine sits on).  THat in turn is on four rubber blocks to prevent vibrations.  So I often wondered why it was there and not elsewhere.  Yr saying that would stop current arking on the prop?  The hull of the boat is connnected to the negetive of the battery I notice after a couple of ‘incidents’ haha.  So that earth bond must be connected to the rest of the hull somehow.  Perhaps the rubber feet have a steel connection through them.  Not sure. 

[smileypete]

OK I modified the diagram in paint rather than try and describe things in words:

Also I moved the fuses to the battery end.

There are a few other bits and pieces that might be worth a mention, but need to go out now, will try to get back to this later...

One thing that springs to mind (now I've uploaded it ) is there needs to be a fuse in the starter batt charge cable, at the starter batt end. There are some different ways to connect the starter alt to the starter batt, some bypass the isolator if the cable is short and well protected, some add a fuse instead.

Edited February 18, 2018 by smileypete

[Keajre]

Thank you,  are three fuses needed, surely one fuse after the isolator on the domestic side is ok?  

The inverter earth connects as you’ve illustrated so I’ll correct that in master diagram thanks.

So the earth connected to the engine should also connect to the hull at a common location for 12v as per your indications?  At the moment common earth for 12v systems is ALL on the engine bracket.  In theory that is a kind of ‘floating earth’ as the engine is suspended on rubber mount points. Is that bad practise?  Sounds ideal to me, because it would stop current returning via the hull in theory, which is what is supposed to happen right?

I have to go out too and wont be able to reply until tomorrow but looking forward to continuity of this thread :-)

Edited February 18, 2018 by Keajre

[Keajre]

Oh the starter battery charge cable coming from the inverter / charger is only a 4amp float current on 4mm cable.  I was going to put a 10a fuse in there, but is it really needed? 

 

Ref starter connection to start batt, I decided to do it via isolator, someone told me it was best practise but I didn’t actually check that myself

Edited February 18, 2018 by Keajre

[system 4-50]

2 hours ago, Keajre said:

For some reason, when I have it connected through the shore power line into the inverter, even though it could happily power said device on its own, and even though the inverter is doing ‘pass through’ only at that time, it causes the genny to stall immediately.  If I plug the same load (say washing machine) DIRECTLY into generator, its no problem.  

Sorry, are you saying you have the genny connected to the shoreline at this point?

[Keajre]

1 minute ago, system 4-50 said:

Sorry, are you saying you have the genny connected to the shoreline at this point?

Well the Genny is connected to the AC input of the inverter, using the same line the shoreline would use, at that point.

[system 4-50]

1 minute ago, Keajre said:

Well the Genny is connected to the AC input of the inverter, using the same line the shoreline would use, at that point.

but not at the same time that the shoreline is live?

[Keajre]

Just now, Keajre said:

Well the Genny is connected to the AC input of the inverter, using the same line the shoreline would use, at that point.

If I put a 1kwh load on the genny (it has two outputs), THEN try to draw a load through the inverter, its fine.  It does pass through.  My theory here is that the inverter calls for far more than the genny can give, expecting an induction load (very high peaks at the start etc) and the genny immediately powers off.  Strange as usually you’d get a red overload light on the genny for 6 seconds before it switches off.  Here, its just switches off straight away.  

 

So its the difference between what the inverter expects (it thinks it shore power) and what the genny can give (in an instant).  That is where the mismatch must be I guess.  

1 minute ago, system 4-50 said:

but not at the same time that the shoreline is live?

No this is when I am out cruising.  When I moored up I have 16A 240 shoreline, no need for genny

[system 4-50]

sorry for the distraction, just didn't know how to interpret the description. 

[WotEver]

38 minutes ago, Keajre said:

Oh the starter battery charge cable coming from the inverter / charger is only a 4amp float current on 4mm cable.  I was going to put a 10a fuse in there, but is it really needed?

Yes. The fuse is to protect the cable. 

1 hour ago, Keajre said:

Thank you,  are three fuses needed, surely one fuse after the isolator on the domestic side is ok?  

Yes. The fuses are to protect the cables, so unless all the cables are 70mm² then each one needs its own fuse, appropriately selected to suit the circuit / cable size.