Narrow boat electrics

[studentspark]

Narrow boat electrics

Just trying to understand the setup.
I have attached a quick diagram of how I think it all goes together.

Just wondering about the optimum setup and best way to transfer between 230v and 12v circuits, and the best way to manage the battery.

Thamks View media item 84822

 

[davelx]

I'm using a Victron inverter/charger with a SmartBank Advanced split charge controller - the Victron has the transfer switch built-in to automatically switch between inverter power and shore power and the Smartbank handles charging both Engine and Service banks from the Victron or the alternator as required, with a manual override to link engine and service banks to enable the engine to be started from the service battery in the event that the engine battery is discharged.

 

[JohnW2]

There is presumably something not quite right about the connections you show between the outputs of the generator, alternator and CU - there presumably needs to be transfer switching on the outputs of those items (and the lighting and sockets circuit would obviously not be joined!).

Kind Regards, John

 

[ericmark]

We considered the idea of a change over switch or relay but the problem was shore supply and inverter supply were different ratings some items would have tripped the shore supply.

So we went down the two separate circuits using blue and white sockets so we could easy identify which was which.

At the time we had not seen the grid sockets today I would use black and white grid sockets but then it was standard sockets.

Because the inverter was required to have an A type RCD not an AC type. This as a result meant could not use RCBO's as could not get them as A type.

The battery bank was 4 x 160 Ah leisure batteries 3 being domestic and forth for engine only. We had two separate alternators one domestic and one engine both were rated 80A. The charger was a twin output a trickle for the engine battery and a stage charger for domestic.

There are cheap battery chargers as in this link but also there are some integrated systems the Sterling system is popular this combines the output from both alternators and uses pulse charging for the domestic battery.

Earth is another problem ideal way is an isolation transformer but common to just put diodes in the earth so no current flows until it exceeds 1.2 volt.

There are three basic types of battery charging.
1) Float charge. This will charge a battery but takes some time.
2) Step charging. This charges at 14.8 volt per 12 volt battery until 90% charged then it drops voltage to 13.4 volt for last 10% so recharges battery faster. However it relies on the battery not being used while being on charge.
3) Pulse charge. It keeps switching off for a few seconds and monitors the off charge voltage and then adjusts the charge rate.

Most mains battery chargers over 15A are stage chargers, Most alternators are float chargers (although often a lifted float voltage). Most solar panel and wind chargers are pulse chargers.

The Sterling alternator to battery charger kids the alternator into thinking the battery voltage is low so using a switch mode system it charges the battery using a pulse charging system.

The graph from the Sterling site explains how it reduces the charge time. It can charge the same battery in 3/4 of the normal charging and with narrow boats leaving the battery part discharged is a major cause of early battery failure.

Talk to milk float and fork lift users and traction batteries should last around 4 years and with care can last up to 7 years. Talk to narrow boat owners and it's a new set every year. This is in the main because they are never fully charged.

Inverters also are split into two types. True sine wave and simulated sine wave. Some items don't like simulated sine wave. Up to around 1000VA you can get away with a 12 volt system but at 3500VA it really needs 24 volt system. The problem is with 12 volt getting the FET's to load share. It would seem many cheap simulated sine wave inverters use an array of car blade fuses to both protect each FET and to give a small resistance to get them to load share.

At 12 volt cables are also very thick and it's hard to find battery isolators to take the 250 amp and when a battery isolator fails it can damage the inverter. At 24 volt current is halved so no problems with finding an isolator. We used a welding lead bayonet connector as we could not get a reasonable priced battery isolator.

Our simulated 3kW inverter with 6kW peak gave out expensive blue smoke after trying to boil a kettle which was only 2.4kW the idea was to run the washing machine. To run a washing machine from a simulated sine wave inverter the washing machine has to also have inverter control. Only one we could find where the manufacturer said it would work off the inverter was an LG. Today there are other washing machines with inverter drives.

 

[ericmark]

Sorry missed the generator. The normal way is all lights 12 volt that means they don't go out when no engine running or shore power. Assuming using an inverter generator fitted on main engine then the easy way is for it to go to an in line 16A socket next to the shore supply. When shore supply is available the socket just dangles but when it's not available then the generator is plugged into the shore supply plug. That way it's impossible for both to be connected together. My son also had a cable length of the boat with bulkhead plug at bow and a in-line socket at the stern so if the shore supply was closer to bow this acted as an extension lead bringing power to the stern.

The generator control power does require an earth direct to the hull so when plugged in the diode (Galvanic Isolator) is bypassed.

Where a bow thruster is fitted there is often an inverter to charge a battery at the front from the main batteries at the back. The split charge relay or even worse blocking diode means there is a volt drop bow to stern so instead a DC to DC inverter is used. You can have 12 volt in and 24 volt out or 24 volt in and 12 volt out so the boat can have both a 12 and 24 volt system.

For vehicle use a firm called Durite or Gordon Equipment also make the blocking diodes and DC to DC inverters. Likely cheaper than Sterling and with fresh water likely no problem with a narrow boat. I would not want to use them with salt water craft.

Also be aware caravan suppliers often have the same stuff as a ship chandler at much reduced price.

 

[Jackrae]

FETs, unlike transistors will load share automatically and do not suffer the thermal run-away problems that transistors do. The insertion of resistance to "effect load share" is a total waste of time and energy. If you want an example have a look at a model aircraft or racing car power module and you'll see numerous FETs all wired in parallel quite happily. Basically, if a FET takes too much of the share it heats up, its resistance rises so it then passes less current = thermal stability. In a transistor set-up, if it heats up its resistance decreases and it takes even more current = thermal runaway.

You can of course save battery power by using LED lights rather than incandescent lamps, but I'm sure you are already down that road.

 

[ericmark]

Be it field effect or bi-polar they are both transistors. I did not design the inverter I just observed how it was constructed and it had a blade type auto fuse feeding each FET.

However once the FET's started to die then quickly you got a run away situation big mistake was having no indication when a fuse opened so until blue smoke escaped one had no idea something was going wrong.

With bi-polar if current is removed then it stops conducting so fails save but with a field effect remove voltage in it conducts so does not fail safe.

The problem was although they would repair the inverter I had to post it back to China although advert said not made in China and then also stung with import duty to China so cost half the price of the unit to send it back for repair. Boat was sold before second one failed and when it did it was replaced with true sine wave type.

The theroy was to charge the batteries from a 4A shore supply and use the batteries as a buffer so we could run washing machine which needed around 10A but in practice it was a failure.

it seems a little odd where it shows generator feeding both 230 vac and 12 vdc the inverter generators I have seen only produce 230 vac and the DC generator is a separate unit although both driven by the prime mover.

We did consider a stand alone generator but diesel for a narrow boat can be bought duty free for heating and power but a small petrol generator you would pay duty on the fuel also the water cooling on the prime mover also heated the boat so far better to use the prime mover engine.

The problem was it needed the engine removing to fit a replacement pulley to drive the 5 matched V belts to the inverter generator which was clearly a big job.

A diesel stand alone generator is too noisy and also rather large and space is at a premium on a narrow boat.

In hind sight it would have been worth the effort to fit something like the "Travel Power" there is a 3.5, 5, and 7kW version from the general look they are converted vehicle alternators I have seen similar items made into welding sets as well. But the main point is because of the inverter the prime mover does not have to run at a set speed 3000 rpm = 1000W and 5500 = 3500W but output always at 50Hz.

After giving up the narrow boat we found there are special inverters which will allow 4A from shore and when over 4A required the inverter grid ties to supply the extra but by the time I found they existed the boat had gone.