Proposed power and charging arrangements for a narrowboat

[oldfatgit]

I am in the process of refurbishing a narrow boat. My intention is to install a largish charger/inverter to provide 240V pure sine AC as a domestic supply for running a number of small loads, such as audio visual entertainment, through to a coffee machine (short burst at 1kW) and a microwave (longer usage at 750W). The 12v circuit will be for engine electrics, interior and exterior lights (LEDs throughout), diesel water heater and domestic water pump. To this end I have purchased and tested one of these which seems to be very good when bench tested with 2 old deep cycle batteries (105Ah Trojans). The alternator is a new 70A Lucas which will be fitted with one a Sterling ProReg B (already fitted to the boat).

My intention is to install and charge a large bank of deep cycle domestic batteries (probably 4 110Ah lead acid) with the same alternator via the ProReg B direct using 50sq mm copper carefully set up in a balanced circuit. When connected to shore power the charger/inverter will do the same and when alongside but not connected a good 60W solar panel will provide top up charging when the boat is otherwise electronically idle. The same 50sq mm copper will provide DC to the charger/inverter.

To charge the small ish 70Ah engine start battery my intention is to connect its positive to the domestic bank via a 10A fuze, in series with a relay (switched from the starter solenoid) and a blocking diode. The fuze is there to protect everything, the relay is to disconnect the connection whilst the engine is being started in order to prevent excessive currents being drawn on the domestic batteries and the diode will prevent the engine start battery from charging the domestic batteries when they are low and/or working hard. My view is that though there will be a voltage drop across the diode of 0.7v the set up will still ensure the engine start battery has enough charge to start the engine (which is a good starter in any case).

The advantage of this set up is that the domestic batteries are not fed from a split charge diode but direct from either the alternator/ProReg B or the charger/inverter and so I should always be able to start the engine. By using the ProReg B the large bank will be more fully charged from the reasonably small automotive alternator than would usually be the case. The system will be monitored with 2 digital volt meters (one for domestic, the other for engine start) and a single digital shunt ammeter on the domestic side showing both charging currents and currents drawn up to 100A. The DC system will be protected with a 100A fuze between the battery bank and master switch. The remainder of the circuits will have the normal measures such as galvanic isolator, fuze boards and consumer units etc.

I value your views.

 

[BabaYaga]

It seems to me you run the risk of permanently undercharging the starter battery (because of voltage drop by the blocking diode and maybe also the fuse/thin wire) which could shorten its life.

I suppose the relay in the set up is normally closed.... Would it not be better to skip the diode and use a normally open relay that is switched/closed by alternator D+?
That way the banks are connected only as the alternator begins to put out and disconnected again on engine shut down.

 

[Ex-SolentBoy]

Don't narrowboats all have generators attached to the engine?

 

[oldfatgit]

Actually, this one didn't and I get the impression that most don't. Shouldn't be necessary when cruising as the engine is on the go for hours on end. Small generators of the suitcase type seem to be on board many of those that are tied up without power and lived aboard along with solar panels and wind generators but my intention is to set this one up for cruising rather than living aboard.

 

[halcyon]

To charge the small ish 70Ah engine start battery my intention is to connect its positive to the domestic bank via a 10A fuze, in series with a relay (switched from the starter solenoid) and a blocking diode. The fuze is there to protect everything, the relay is to disconnect the connection whilst the engine is being started in order to prevent excessive currents being drawn on the domestic batteries and the diode will prevent the engine start battery from charging the domestic batteries when they are low and/or working hard.

Why not just connect the alternator to domestic bank, then fit a VSR between service bank and engine battery.

The VSR will charge the engine battery if engine running, mains charger is on or solar panel is charging. When using power it isolates the engine battery, plus it can provide link start to allow starting the engine from the service battery.

Brian

 

[Bru]

Well I'd keep it simple (electrically speaking)

Charge the engine battery off the standard engine alternator

Fit a second high power alternator charging the domestic battery bank via a Sterling, Adverc or similar controller

 

[pampas]

dont forget that the micro wave if its marked 750 watts (cooking )will require about twice that (750W) to operate.

 

[Ex-SolentBoy]

Actually, this one didn't and I get the impression that most don't. Shouldn't be necessary when cruising as the engine is on the go for hours on end. Small generators of the suitcase type seem to be on board many of those that are tied up without power and lived aboard along with solar panels and wind generators but my intention is to set this one up for cruising rather than living aboard.

That's my point. My boat has a generator built in to the engine, not as a separate item. As soon as I run the engine I have 4kw continuous so I can run all those appliances as well as a 220v battery charger.

The reason they are fitted to narrow boats is that they work very well at typical cruising speeds. If you are going to change your engine it is a no brainer really as the incremental cost is very low compared to a separate generator.

 

[oldfatgit]

It seems to me you run the risk of permanently undercharging the starter battery (because of voltage drop by the blocking diode and maybe also the fuse/thin wire) which could shorten its life.

I suppose the relay in the set up is normally closed.... Would it not be better to skip the diode and use a normally open relay that is switched/closed by alternator D+?
That way the banks are connected only as the alternator begins to put out and disconnected again on engine shut down.

Thank you. An elegant solution worth examining. When I get to the stage of installing the electrical system I will give it a try.

 

[oldfatgit]

Well I'd keep it simple (electrically speaking)

Charge the engine battery off the standard engine alternator

Fit a second high power alternator charging the domestic battery bank via a Sterling, Adverc or similar controller

Could go this route at some expense, particularly as the engine is out at the moment and so should be able to fit the extra pully etc. In addition I like the extra redundancy this puts into the system.

 

[oldfatgit]

Why not just connect the alternator to domestic bank, then fit a VSR between service bank and engine battery.

The VSR will charge the engine battery if engine running, mains charger is on or solar panel is charging. When using power it isolates the engine battery, plus it can provide link start to allow starting the engine from the service battery.

Brian

Again, great advice, thank you. An elegant and cheap option. What I am learning is that there are many ways to solve this problem.

 

[oldfatgit]

That's my point. My boat has a generator built in to the engine, not as a separate item. As soon as I run the engine I have 4kw continuous so I can run all those appliances as well as a 220v battery charger.

The reason they are fitted to narrow boats is that they work very well at typical cruising speeds. If you are going to change your engine it is a no brainer really as the incremental cost is very low compared to a separate generator.

Ah, that is what you are driving at. I shall do some research. Thank you.

 

[oldfatgit]

dont forget that the micro wave if its marked 750 watts (cooking )will require about twice that (750W) to operate.

Thank you. Will bear in mind.

 

[halcyon]

Could go this route at some expense, particularly as the engine is out at the moment and so should be able to fit the extra pully etc. In addition I like the extra redundancy this puts into the system.

Why fit high power ? as you said the engine is running for long periods, why not a small one for engine battery.

Also remember the bigger alternator / alternators require more HP, thus less available for boat propulsion.

Brian

 

[sailinglegend420]

......To this end I have purchased and tested one of these which seems to be very good when bench tested with 2 old deep cycle batteries (105Ah Trojans). .............

BEWARE

This is a non-marine inverter and so the AC earth and the DC negative may well be connected. Stray currents can then pass through the boat negative to the water and cause galvanic corrosion.

EDIT: (The chassis will also probably be connected to earth and this could easily come into contact with the boat earth, especially in a steel boat, and bypass any Galvanic Isolators. If it is a steel boat then an isolating transformer should be used and then the AC earth connected to the hull. A complicated subject to cover in a small posting about a non-marine battery charger!)

This product is a quarter the price of a marine inverter of the same size!

 

[Plevier]

It seems to me you run the risk of permanently undercharging the starter battery (because of voltage drop by the blocking diode and maybe also the fuse/thin wire) which could shorten its life.

I don't think that is likely because you have a smart regulator on the alternator, I agree it could be a problem if you didn't. If the engine battery is only used for starting and the engine is a good starter as you say, then if the starter battery is permanently connected to the smart regulator which will be governed by the needs of the domestic batteries, the starter battery could well end up overcharged! A typical engine start takes 1Ah or less and to replace that you want some time at around 14V, if you put 14.8V on from the smart reg you are not being kind to it and it will gas.
At float voltage the starter battery will be taking so little current that the diode will have little forward voltage drop.
The service conditions are so different that ideally the starter battery wants a separately regulated charging source.
The Cristec charger on my boat actually has a second diode in the battery charging circuit so that it gets less charge than the domestic battery. It's a crude way of doing it but it will have some effect when it's on boost voltage.

 

[BabaYaga]

I don't think that is likely because you have a smart regulator on the alternator, I agree it could be a problem if you didn't. If the engine battery is only used for starting and the engine is a good starter as you say, then if the starter battery is permanently connected to the smart regulator which will be governed by the needs of the domestic batteries, the starter battery could well end up overcharged! A typical engine start takes 1Ah or less and to replace that you want some time at around 14V, if you put 14.8V on from the smart reg you are not being kind to it and it will gas.
At float voltage the starter battery will be taking so little current that the diode will have little forward voltage drop.

My suggestion was based on the idea that a battery, to have a long and healthy life, should see around 14,4 V from time to time, in order to get fully charged.
Might well be the case for the starter battery behind the diode, if the smart regulator raises the charging voltage as high as 14,8 V – I don't know.
Risk of starter battery becoming overcharged (without diode)? Perhaps, on long engine runs at such a high voltage. Would certainly have to check water level now and again.
On my boat I have a switch to disconnect the starter circuit on longish engine runs. But then it is a small AGM so cannot be topped up.

 

[Bobobolinsky]

Well I'd keep it simple (electrically speaking)

Charge the engine battery off the standard engine alternator

Fit a second high power alternator charging the domestic battery bank via a Sterling, Adverc or similar controller

Depends what size the engine is, but a flat belt drive to a 120W alternator

PRM boxes have a PTO for a hydraulic drive

 

[prv]

Depends what size the engine is, but a flat belt drive to a 120W alternator

I'd go for something a little bigger than ten amps, personally

Pete

 

[oldfatgit]

BEWARE

This is a non-marine inverter and so the AC earth and the DC negative may well be connected. This can be a fatal error if the polarity on the shorepower supply is reversed (EDIT: and the neutral and earth have also been connected on the boat via some other piece of equipment, like an immersion heater that has an earth to the metal cylinder which is sitting on a metal platform connected to a metal hull, that is also earthed!) Reverse Polarity will cause all earthing points on the boat to be live, including the anodes - and AC is being fed directly into the water. Even if the polarity is not reversed stray currents can still pass through the boat negative to the water and cause galvanic corrosion.

This product is a quarter the price of a marine inverter of the same size!

Thank you for the warning and I will be careful. However, the instructions state that it is suitable for mounting in both vehicles and boats; furthermore, the instructions and the item itself bear a remarkable resemblance to Sterling's products mentioned here though they do not do a 3kW version. At the very least I will have, located near the switch panel, a domestic socket with a socket tester permanently in it so that it will be very easy to check the supply polarity and earth continuity. Furthermore, it will be easy to carry a polarity reversing adaptor so that in such an instance the situation can be remedied before the supply installation is fixed. I did consider sourcing an isolation transformer rather than a galvanic isolator as I understand that these eliminate the possibility of a reverse polarity connection but the cost, for a project such as this, appears too great.

Edit. Have just checked the item with a multimeter and , indeed, the AC earth and DC negative are not connected. However, the AC earth is connected to the inverter/charger case and bonding connection, as you would expect. So if a 12v negative is deliberately or accidentally connected to the metal hull boat it is possible that the AC earth and DC neg will become connected presenting the reverse polarity risk you describe. Therefore I think I will install some form of warning system between the 2 based on an audio continuity tester; shouldn't be too difficult.