Interested minds ... (boat electrical systems, the 'Big picture').

[wakey_wake]

On 06/10/2024 at 21:07, T_i_m said:

Do we normally add the service valves to the accumulators or is it just another thing to go wrong?

 

On 06/10/2024 at 21:27, Tony Brooks said:

In my experience, so-called service valves tend to readily seize up. Anyway, turn the pump off, open a tap, when water stops flowing close it, and turn the main water valve off near the tank, [...]

 

I've never serviced my accumulator and wasn't expecting to. It accumulates apparently was well as it did 30 years ago... I have no idea whether it's a diaphragm or bladder, or plain steel box / bladder with a hole. It's vertical so it presumably drains when I winterise.

 

However the top comment on the Screwfix page T_i_m linked points out that it should be a service item because it's a dead leg, hence a place to harbour Legionella.

 

Currently I keep my drinking water separately (the 5l "Hydr8" bottles are my current favourite, seen in larger Tescos, and with a nice stout handle) but life would be simpler if I had confidence that the plumbing is safe to drink from.

[Tony Brooks]

20 minutes ago, wakey_wake said:

However the top comment on the Screwfix page T_i_m linked points out that it should be a service item because it's a dead leg, hence a place to harbour Legionella.

 

In boats the accumulator is in the cold supply, so nowhere near warm enough to breed legionella AND it is not a deal leg because water flows in and out of it, that is water with the chlorine that was put in at the water works. we are not discussing expansion vessels on domestic boilers which is used for the central heating water, not the water gong to the taps etc. The contents of the central heating system does not change for fresh every time you turn the tap on.

 

The expansion vessel on a boat might harbour legionella, but the water is still changed frequently. If it worries, you simply locate it in the cold supply to the calorifier between the calorifier and NRV.

 

 

[wakey_wake]

4 minutes ago, Tony Brooks said:

In boats the accumulator is in the cold supply, so nowhere near warm enough to breed legionella AND it is not a deal leg because water flows in and out of it, that is water with the chlorine that was put in at the water works. we are not discussing expansion vessels on domestic boilers which is used for the central heating water, not the water gong to the taps etc. The contents of the central heating system does not change for fresh every time you turn the tap on.

 

The expansion vessel on a boat might harbour legionella, but the water is still changed frequently. If it worries, you simply locate it in the cold supply to the calorifier between the calorifier and NRV.

 

Thanks Tony, sounds like I have misunderstood the risk factors for legionella - I thought it could grow anywhere quiet. I have no idea what it considers food... it must eat something there in the dark?

 

So yes, the accumulator does have a flow. That's its purpose and it just needs to be on a short enough leg off the cold supply to get "fresh" regularly. Mine is.

 

I don't have a NRV on the cauliflower. At first I assumed there would be one, and was surprised to find none. Then I realised the cold accumulator serves the hot side too (saving cost and space of a second accumulator), because of the lack of NRV, so it seems like a sensible choice and it guarantees the pressures are balanced.

 

What's the advantage of the NRV? I can't think of any process which would send a significant amount of hot water out the bottom of the tank into the cold supply. The only reason I can think of is if we expect the hot tank to be leaching lead from older plumbing, and therefore "less clean" than the cold supply.

 

In a house system, there is often no cold accumulator. With the pressurised hot tank (more common these days than header tank in loft), an accumulator is absolutely needed. It seems to follow that an NRV is needed there because otherwise pressure fluctuations from usage in the cold supply would tend to drain heat from the bottom of the hot tank. That doesn't answer why the hot accumulator is normally put on the hot top of the tank, instead of the cold bottom feed as you described...  there is a need for correct ordering of isolation taps vs accumulator but it's not hard.

 

 

(I still refuse to drink from hot taps, having been taught that as a kid. Even now I realise the reason was growing up with a header tank, and yes we did have animals fall in and taint the hot supply... but I cannot bring myself to drink from a modern pressurised hot water tap! Sometimes, being rational means understanding what irrational choices I make.)

[T_i_m]

5 hours ago, MtB said:

 

And notwithstanding all of the above, battery capacity varies, depending on how fast you are discharging it AIUI.

 

Understood, although you would have thought with a bit of 'fuzzy logic' a battery capacity meter could get pretty close? Ok, things like 'time left' are unlikely to be accurate because it can't predict random functions but it might be able to consider repetitive stuff.

 

I have a 'smart' electric storage heater that, when power is applied it 'knows' it has 8 hours of power available, it knows the external temperature and it's core temperature so delays its power on time to the latest it can, ensuring there is sufficient time to hit full charge by the last knockings (otherwise it would be losing heat earlier than ideal).

Edited October 8, 2024 by T_i_m

[Tony Brooks]

14 minutes ago, wakey_wake said:

What's the advantage of the NRV? I can't think of any process which would send a significant amount of hot water out the bottom of the tank into the cold supply. The only reason I can think of is if we expect the hot tank to be leaching lead from older plumbing, and therefore "less clean" than the cold supply.

 

 

To prevent hot water expanding back down the cold system towards the accumulator. That, in theory, could be a legionella risk, but my system was like yours and i 20 years never had a hint of a legionella infection. Anyway, that small amount of how water gets flushed into the calorifier each time you open a hot tap, where it should get hot enough to kill the bacteria.

 

18 minutes ago, wakey_wake said:

In a house system, there is often no cold accumulator. With the pressurised hot tank (more common these days than header tank in loft), an accumulator is absolutely needed. It seems to follow that an NRV is needed there because otherwise pressure fluctuations from usage in the cold supply would tend to drain heat from the bottom of the hot tank. That doesn't answer why the hot accumulator is normally put on the hot top of the tank, instead of the cold bottom feed as you described...  there is a need for correct ordering of isolation taps vs accumulator but it's not hard.

 

No, in a house system, the thing is an expansion vessel for the water in the CENTRAL HEATING circuit. It also does the job of the small tank in the roof. It has nothing to do with the water coming out of the taps because if it did, you would have to use the filling loop each time you opened a tap.

 

 

 

21 minutes ago, wakey_wake said:

That doesn't answer why the hot accumulator is normally put on the hot top of the tank, instead of the cold bottom feed as you described...  there is a need for correct ordering of isolation taps vs accumulator but it's not hard.

 

 

Because at least one calorifier manufacturer supplies the calorifier with the ancillary valves already fitted, so it is easier for the fitters to fit it in the hot pipework.

[ditchcrawler]

1 hour ago, Tony Brooks said:

 

In boats the accumulator is in the cold supply, so nowhere near warm enough to breed legionella AND it is not a deal leg because water flows in and out of it, that is water with the chlorine that was put in at the water works. we are not discussing expansion vessels on domestic boilers which is used for the central heating water, not the water gong to the taps etc. The contents of the central heating system does not change for fresh every time you turn the tap on.

 

The expansion vessel on a boat might harbour legionella, but the water is still changed frequently. If it worries, you simply locate it in the cold supply to the calorifier between the calorifier and NRV.

 

 

Of course it also depends on the pipe run length to the accumulator, on a boat its measured in inches, in an industrial situation it could be measured in yards and the water just move back and forth along the pipe. Screwfix have no idea where and how its going to be fitted.

[David Mack]

4 hours ago, IanD said:

and the conclusion is that if you want the same effective battery size when powering heavy loads (1 hour discharge) LFP batteries only need to have 20% of the nominal capacity of LA...

Saying that will lead some to conclude you can use a 20Ah LFP as a starter battery!

🙂

[Gybe Ho]

1 hour ago, Tony Brooks said:

 

In boats the accumulator is in the cold supply, so nowhere near warm enough to breed legionella AND it is not a deal leg because water flows in and out of it, that is water with the chlorine that was put in at the water works. we are not discussing expansion vessels on domestic boilers which is used for the central heating water, not the water gong to the taps etc. The contents of the central heating system does not change for fresh every time you turn the tap on.

 

 

Your post has caused me to question the validity of my plumbing design for water. I will have three expansion tanks:

1. Central Heating as supplied with the Webasto diesel heater kit.
2. A conventional accumulator just downstream of the main water pump and strainer.
3. A second accumulator/expansion vessel on the calorifier inline with pressure relief valve.

There is also an overtemp safety mixer to bring the HW temp back down to 60 degrees if superheated by an engine.

[Tony Brooks]

16 minutes ago, Gybe Ho said:

 

Your post has caused me to question the validity of my plumbing design for water. I will have three expansion tanks:

1. Central Heating as supplied with the Webasto diesel heater kit.
2. A conventional accumulator just downstream of the main water pump and strainer.
3. A second accumulator/expansion vessel on the calorifier inline with pressure relief valve.

There is also an overtemp safety mixer to bring the HW temp back down to 60 degrees if superheated by an engine.

 

Apart from the Webasto it all looks perfectly standard without seeing a piping diagram.

 

 

I know some of the Webasto diagrams show the use of such a thing, but I have reservations. Boat central heating systems have antifreeze in them both to stop it freezing AND prevent corrosion. I think the Webasto may use an aluminium heat exchanger, so I would be very wary of running with life expired antifreeze. The antifreeze part will be OK, but not the corrosion inhibitor. They must also be filled with a water-antifreeze mixture, not one and then the other.

 

Now consider how you are going to top up the system and cover any small leaks with a sealed system using an expansion vessel. you can't use a filling loop from the domestic water system because antifreeze is poisonous. Also think about how you will refill after changing the antifreeze. I don't have an answer, but on my own boat I would prefer a conventional header tank with a car type pressure cap set to the pressure Webasto recommend. then you can take the cap off and just pour the mixture into the system. it will pressurise itself as it heats up.

 

[nicknorman]

44 minutes ago, Gybe Ho said:

 

Your post has caused me to question the validity of my plumbing design for water. I will have three expansion tanks:

1. Central Heating as supplied with the Webasto diesel heater kit.
2. A conventional accumulator just downstream of the main water pump and strainer.
3. A second accumulator/expansion vessel on the calorifier inline with pressure relief valve.

There is also an overtemp safety mixer to bring the HW temp back down to 60 degrees if superheated by an engine.

Regarding 3, it is better to have the expansion vessel on the inlet to the calorifier just after the NRV. If it is at the outlet, then it fills with water when the calorifier is heating. Then several hours later it has cooled down. When you turn on the tap, this cold water comes out of the hot tap and you have to run off more water to get it to come hot, than if you had the vessel at the calorifier input.  But in neither case is there a legionella risk because water is flowing in and out of the expansion vessel routinely and the expansion vessel spends most of its time empty.

[Gybe Ho]

44 minutes ago, nicknorman said:

Regarding 3, it is better to have the expansion vessel on the inlet to the calorifier just after the NRV. If it is at the outlet, then it fills with water when the calorifier is heating. Then several hours later it has cooled down. When you turn on the tap, this cold water comes out of the hot tap and you have to run off more water to get it to come hot, than if you had the vessel at the calorifier input...

 

It would have taken me years to diagnose that problem, if ever.

[Tony Brooks]

2 minutes ago, Gybe Ho said:

 

It would have taken me years to diagnose that problem, if ever.

 

Yes, but it seems at least two of us do/did not have this problem. It all depends upon the length of pipe between the last cold tap and the calorifier.

[Gybe Ho]

2 hours ago, Tony Brooks said:

Apart from the Webasto it all looks perfectly standard without seeing a piping diagram.

 

 

Not a conventional diagram, part circuit diagram part physical layout.

 

 

Edited October 8, 2024 by Gybe Ho

[Gybe Ho]

6 hours ago, Tony Brooks said:

 

Yes, but it seems at least two of us do/did not have this problem. It all depends upon the length of pipe between the last cold tap and the calorifier.

 

Thinking some more, given a cold system the cold water accumulator and the calorifier expansion accumulator(?) will equalize. When the HW temp increases the volume of water displaced into the expansion tank will be whatever 55l water expands by as it is warmed, say 4% or about 2 litres.

 

Once the tank is up to temperature and HW is drawn at a tap, the two accumulator pressures will equalize as the calorifier accumulator expels it 2 litres of coolish water back into the base of the calorifier and then no more risk of transient cold water slugs when further HW is drawn.

 

What happens as the HW calorifier cools when the boat is not occupied. We don't want the calorifier to suffer negative pressure physical stress. At this point my head explodes, I suppose as the system cools if the calorifier expansion accumulator cannot contribute a further 2 litres under negative pressure then 2 litres of cold water is drawn though the NRV and sucked from the main cold water tank.

 

At least I now understand why calorifiers can explode from cyclical thermal expansion pressure stress if the over pressure relief valve does not work and/or the expansion accumulator is missing. I suppose a long run of a more flexible type of plastic pipe in the HW system helps e.g. my diagram above.

Edited October 8, 2024 by Gybe Ho

[Tony Brooks]

Just now, Gybe Ho said:

What happens as the HW calorifier cools when the boat is not occupied. We don't want the calorifier to suffer negative pressure physical stress. At this point my head explodes, I suppose as the system cools if the calorifier expansion accumulator cannot contribute a further 2 litres under negative pressure then 2 litres of cold water is drawn though the NRV and sucked from the main cold water tank.

 

The valves in the pump will allow flow from tank through the pump, but not the other way, so you are correct, the contracting cooling water draws water from the tank. The same applies to the NRV.

[David Mack]

If your cold water accumulator is charged to cutout pressure, then as the calorifier cools, and its expansion vessel pressure reduces, once it is below the current cold water accumulator pressure, cold water will flow through the NRV until the pressures have equalised. This will continue until either the pump cut in pressure is reached, in which case the pump will run until the system including both accumulators has reached cutout pressure, or if the pump has been switched off, then the pressure will continue to drop. In this latter case no water will be drawn from the tank as the static head (if any) will be too low to overcome the pressure required to open the pump valves in the flow direction.

[T_i_m]

So, I managed to get onboard mates Nb today and sat on the engine whilst trying to work out / mark up the wiring.

 

Things we found easily. Battery +Ve connection from the solar controllers goes though a fuse but no isolator but the -Ve does connect to the 'right side' of the 100A shunt (so would be considered by the BM).

 

The cables to the Victron measure ~18mm OD and marked 'Welding cable' so probably have a fairly thick insulation. They both go straight to the battery (eg, the wrong side of the shunt (for good reason as it's only 100A capacity). I found this online ...

 

Conductor (mm²)    Nominal Current Rating Amps    Max Outside Diameter  (mm)

            95                                  500                                           17.9

 

Does that seem likely?

 

The domestic battery alternator +Ve connects to the battery +Ve via an isolator.

 

There is fuse in a +Ve of the battery to the VSR but the other side of the VSR goes via an 100A fuse then off somewhere toward the cabin (as yet unknown). This suggests the VSR is working more like a LVD like I think I first suggested?

 

The link from the starter battery -Ve goes directly to the domestic battery -Ve (bypassing the  100A BM shunt (for good reason if domestic alternator is 175A)).

 

Pinned down the temperature probe for the Victron bolted to a +Ve domestic battery terminal.

 

I can't find where the starter alternator output connects to the starter battery +Ve but it may be via the starter motor +Ve terminal? There is a removable key isolator on the stater battery +Ve.

 

We haven't yet pinned down the wiring to the bow thruster or the cabin 12V 'fuse' (MCB) box.

 

I would like to strip back the HV cable near the Travel Power alternator as they look like they could be bent / broken / damaged. I now have the info from the TP label and know it's a 2007 model product No is 991 00 10-08 so that might help me find the manuals.

 

If I was to fit the BMV-712 Smart shunt I think I might need a short link cable at least as large as the one to the Victron Combi (8mm lug DM end and 10mm shunt end) and then either fit new 10mm lugs to the solar -Ve,  battery -Ve link and Combi -Ve cables and fit the straight to the shunt, or add a small bus-bar block (using another short M10 (shunt) to M8 (bus bar) lug link cable to the bus bar presenting 8mm studs.

 

I think I need to fit the new shunt and BMV-712 asap so he sees it working and then we could look to improving the general layout and features of the rest of the wiring around the battery area.

 

 

[Tony Brooks]

Welding cable is often used in boats because it is usually very flexible despite its large size. Whether 500 nominal amps is enough depends upon the out and back run length because you need to consider volt drop.

 

It is very likely that the starting alternator connects to the engine battery via the starter motor positive main terminal.

 

There are no regulations requiring an isolator in the solar controller to battery line, but there is nothing to stop an individual fitting one. It is one of the BSS exemptions (charger circuits). So that bit is fine.

 

[Gybe Ho]

52 minutes ago, Tony Brooks said:

Welding cable is often used in boats because it is usually very flexible despite its large size. Whether 500 nominal amps is enough depends upon the out and back run length because you need to consider volt drop.

 

 

I read somewhere that welding cable is not a good choice for confined spaces on a boat because its insulator does not have a high melting point. The explanation being that the cable is designed to operate outdoors or in large ventilated spaces where elevated environmental temperature is not a concern. Have you heard the same?

[Tony Brooks]

3 minutes ago, Gybe Ho said:

 

I read somewhere that welding cable is not a good choice for confined spaces on a boat because its insulator does not have a high melting point. The explanation being that the cable is designed to operate outdoors or in large ventilated spaces where elevated environmental temperature is not a concern. Have you heard the same?

 

No. That may have been true when it was cotton covered rubber insulation, but as far as I know it is now some form of PVC, just like the rest of the cables. Anyway, apart from under fault conditions, I can't see any cables on a boat getting hot enough to melt and even if they did, they would have to catch fire to produce fumes.

[Gybe Ho]

13 hours ago, David Mack said:

If your cold water accumulator is charged to cutout pressure, then as the calorifier cools, and its expansion vessel pressure reduces, once it is below the current cold water accumulator pressure, cold water will flow through the NRV until the pressures have equalised. This will continue until either the pump cut in pressure is reached, in which case the pump will run until the system including both accumulators has reached cutout pressure

 

 

Interesting I had not thought about cooling of the calorifier while living aboard with the water system at operational pressure, which would be the more typical case for me. A cooling calorifier during the night would be an explanation for a phantom trigger of the cold water pump in the small hours I guess?

[T_i_m]

1 hour ago, Tony Brooks said:

Welding cable is often used in boats because it is usually very flexible despite its large size. Whether 500 nominal amps is enough depends upon the out and back run length because you need to consider volt drop.

 

It is very likely that the starting alternator connects to the engine battery via the starter motor positive main terminal.

 

There are no regulations requiring an isolator in the solar controller to battery line, but there is nothing to stop an individual fitting one. It is one of the BSS exemptions (charger circuits). So that bit is fine.

 

Thanks for the reply and info Tony.

 

I think the biggest issue he may have re volt drop at the moment is tired batteries. ;-(

 

The plan (FWIW) is to replace the short link cable between the domestic battery -Ve and the shunt with a much higher capacity (win) and probably shorter (win) cable but then moving the Combi -Ve to the shunt +Ve (lose). If I can get a couple of 10 mm hole lugs onto the shunt +Ve I could make one the Combi -Ve (win) and another a short link to a bus bar or terminal with 8mm dia fastenings for all the other -Ve's.

 

I remember cautions re connection sequence of the Eperver Tracer (battery on first) meaning I'd have to disconnect the solar input somehow (unscrew one input wire).

 

My manual crimper only goes up to 50mm2 and my hydraulic, 70mm2 ... so it looks like I'm going to have to buy a bigger one. 😉 Looks like they are about 40 quid online?

[Batavia]

39 minutes ago, Gybe Ho said:

 

I read somewhere that welding cable is not a good choice for confined spaces on a boat because its insulator does not have a high melting point. The explanation being that the cable is designed to operate outdoors or in large ventilated spaces where elevated environmental temperature is not a concern. Have you heard the same?

Welding cables come with many different types of insulation - PVC is used but a synthetic rubber would normally be preferred due to its superior abrasion resistance.  One of the better types is 0361TQ - double insulated with an EPR inner and HOFR outer, temperature rating to 85 degC - but this is probably overkill for your application!

[T_i_m]

1 minute ago, Batavia said:

Welding cables come with many different types of insulation - PVC is used but a synthetic rubber would normally be preferred due to its superior abrasion resistance.  One of the better types is 0361TQ - double insulated with an EPR inner and HOFR outer, temperature rating to 85 degC - but this is probably overkill for your application!

Thanks for that and yeah, without a complete re-wire I think it would be overkill. ;-(

[Tony Brooks]

5 minutes ago, T_i_m said:

My manual crimper only goes up to 50mm2 and my hydraulic, 70mm2 ... so it looks like I'm going to have to buy a bigger one. 😉 Looks like they are about 40 quid online?

 

Or modify a nut splitter to do indent crimping as per the instructions somewhere on here. I can't seem to find the thread.