Power on boats

[viewer]

Might be an old subject, but very interesting.
One of the ways that HV cables can be run through a town is under the towpath. There must be magnetic & electric field close to the moored boats. Would they be large enough to have any effect?

The original questions might still be relevant to those seeking to start work today and looking in the forum for any information.
I'm restoring an old dinghy and have needed power tools on site. The generator seemed fine with voltage showing a steady 240 but after it killed two machines I decided not to use it. Might have been a coincidence but..
Using a 1000W inverter worked well with the tools I needed such as detail sanders or other small machines, but it wouldn't power a 750W belt sander.

 

[ericmark]

Glad to say no longer my problem but what we considered was the battery charger was class II so not importing the earth and only using the battery charger from shore power would remove the electrolysis problem. Also shore power was limited to 4A in my sons marina.

Idea was then to use a 3kW inverter to 6kW peak to supply all 230 volt power. The idea was sound but the inverter was not. It burnt out completely once and second one also started to fail.

In the inverter we had there was an array of 16A blade car fuses one for each FET so if one FET failed only that one was taken out of service. However the design did not seem to power share between FET's as it should and as they started to fail more load was placed on the remaining FET's and the current limiting design was also compromised by the failures in other words it was a load of rubbish from china.

There were also problems with the RCD protection as with a simulated sin wave the original RCD would not work. Cable sizes from battery were huge and would be hard to bend so we used twin 35mm² as 70mm² so hard to work with.

Finding an isolator able to handle 300A was also a problem we had considered using welding bayonet plugs and sockets.

This was all still work in progress when the boat was sold. The electrics were not the only problem the wood burning stove also presented problems with chimney too short and not enough head on the water supply so used twin 12 vdc water pumps clearly these must not fail hence twin and having something go wrong with an inverter which removed supply to water pumps could result in steam everywhere.

Glad it's no longer my problem. Even the stage chargers were a problem as if you used power while charging batteries could be over charged and once it went to stage 3 volts needed to drop to 11.5 before it would restart stage charging.

 

[paulc2]

Glad to say no longer my problem but what we considered was the battery charger was class II so not importing the earth and only using the battery charger from shore power would remove the electrolysis problem. Also shore power was limited to 4A in my sons marina.

Idea was then to use a 3kW inverter to 6kW peak to supply all 230 volt power. The idea was sound but the inverter was not. It burnt out completely once and second one also started to fail.

In the inverter we had there was an array of 16A blade car fuses one for each FET so if one FET failed only that one was taken out of service. However the design did not seem to power share between FET's as it should and as they started to fail more load was placed on the remaining FET's and the current limiting design was also compromised by the failures in other words it was a load of rubbish from china.

There were also problems with the RCD protection as with a simulated sin wave the original RCD would not work. Cable sizes from battery were huge and would be hard to bend so we used twin 35mm² as 70mm² so hard to work with.

Finding an isolator able to handle 300A was also a problem we had considered using welding bayonet plugs and sockets.

This was all still work in progress when the boat was sold. The electrics were not the only problem the wood burning stove also presented problems with chimney too short and not enough head on the water supply so used twin 12 vdc water pumps clearly these must not fail hence twin and having something go wrong with an inverter which removed supply to water pumps could result in steam everywhere.

Glad it's no longer my problem. Even the stage chargers were a problem as if you used power while charging batteries could be over charged and once it went to stage 3 volts needed to drop to 11.5 before it would restart stage charging.

Plenty of boats do have a good electric and plumbing system with none of the issues your son encountered. There is a bit of a knack to fitting things on a boat, needs a bit more knowledge than simply copying how things are done in a house.

 

[SimonH2]

As to diodes my worry is how often they are tested? All it needs is some one to used an insulation tester or an earth loop impedance tester and the diodes can pop we all hope those electricians working on boats are careful but problem is those not use to boats may very well test as they would with a house and be unaware of the damage which could result.

My concern would be that in the event of a fault, you could easily blow the diodes. Lets face it, if you "short" a circuit then you may well get a fault current into 3 figures - in fact I think this may be required in order to guarantee short disconnect times. I guess it'll be less dramatic on a boat with some extra cable in the supply, but with prospective fault currents from a typical domestic supply into 4 figures, I can't see how a 25A or 35A diode bridge will survive anything but a "soft" fault.
Diode packs from automotive alternators may be a useful source of high-current bridge rectifiers.

RCDs won't help here - they may disconnect the supply, but they won't limit the fault current during the disconnect time. I wouldn't consider anything less than 'kin big stud diodes with 100+ A ratings. Even then I'd be slightly concerned. I'd certainly want a permanently fitted tester (battery and bulb ?) so the earth diodes could be tested every time a breaker was reset, and every time a shore supply is hooked up.

I don't think routing testing should be a concern. IR testing wouldn't be a problem as L&N wouldn't go near the earthing diodes. Continuity testing would also be OK unless you were applying large currents in excess of the capacity of the diodes - though I could see it causing confusion for a sparky when he gets odd readings !