Jump to content


Member Since 04 Apr 2011
Online Last Active Today, 08:59 AM

Posts I've Made

In Topic: Newbie Questions re 12v Power Inverters

Yesterday, 08:34 AM

I naively thought a 3 pin plug was a 3 pin plug and would be wired the same as a standard 3 pin 240v plug! Obviously not the case? I wasn't suggesting cutting off the lighter connection, just connecting it via a 3 pin to lighter adapter connector but the only 3 pin ones I have seen are 2amp not 10. There are 2 pin to lighter rated at 10amps but these seem to be 2 square pins?


The 3 pin socket holes on the boat look quite small pins. I am of course making the assumption that these are 12v sockets. There are 240v ones but they of course are 3 pin square ones.




You are comparing chalk with cheese but with possibly a lethal outcome - DC requires only two connections positive and negative, 240v AC mains three, live, neutral and protective earth.


If at all possible use dedicated low voltage DC sockets for your 12 volt distribution. For external use suggest these waterproof non-reversible plug/sockets.





For internal the Hella/DIN range are far superior to the awful although sadly common cigar lighter sockets which are hardly fit for purpose. See Alan 's post above!




The sockets are available as panel or flush side mount. Typical rating 10 amps. Both are available at most chandlers or from mail order marine suppliers.


The three round pin connectors I think you were referring to were designed to supply household mains table lights etc. Their rating was 240v 2 amp I believe. Whilst they do the job for DC distribution there is an unused pin and no convention as to which is positive or negative - best stay away  IMHO.  

In Topic: Are single-handers the pariahs of the system?

28 July 2016 - 03:29 PM

Not me, when I boat I don't hang around, often catching crewed boats up and helping them through the locks.
Help is often appreciated but rarely needed and I dont hold people up, if they are faster I let em through.


Ditto smile.png

In Topic: Inverter Wiring

27 July 2016 - 12:34 PM

When a piece of equipment is supplied with an external fuse, like a car radio, that fuse is provided to protect the equipment. You will note that it is at the equipment end of the supply cable.


If the fuse is located close to the equipment then clearly it won't protect the larger part of the cable run. Both can be protected by locating fuse or breaker of similar value at the distribution panel though. Isn't this how most are wired?

The feed to that piece of equipment will be fused at the battery end. That fuse is most certainly to protect the cable.


Any circuit, and a high-current load such as an inverter is no different, is fused at the battery end for one reason only and that is to protect the cable. There are no exclusions to this - that is the purpose of the fuse.


No in answer to both of those points in bold, it can protect both, see above

If you wish to protect the equipment externally then it should be fused at the equipment end of the cable as in my car radio example above.


Why specifically, again referring to above?

If an overloaded combi doesn't shut down of its own accord (or blow internal fuses) then it is a poorly designed piece of equipment.


Well I'll come clean on this one and say its a Sterling Combi. The estimated temporary load was probably in the order of 4kW which had already tripped the 16 amp shore supply when the inverter took over. It could be argued that the equipment was rugged enough to take the short term abuse, and as said its still working fine. TBH I was surprised it didn't shut down although it was on Charles Sterling's recommendation that I fitted the 500 amp fuse, which I remember considering a little high at the time.



To sum up I will say that in general most DC equipment isn't fused internally. Like it or not, but I accept this on two points - it keeps the price down - it allows easy accessible external fusing without the complexity of effective double fusing.


Finally another example where equipment fusing saved me a lot of money. My Sealand Vacuflush pump with very low mechanical gearing temporarily stalled (you can guess why wink.png  )  although its normal current draw was only 8 amps it tripped the 16 amp dedicated panel breaker and consequently lived for another day. A new motor was listed at well over £100! 


I've already admitted there are situations where only the cable fusing needs to be considered, when there is further dedicated fusing further down the line, but please don't argue against the hard facts I've provided.


FWIW in over 20 years of cruising covering nearly 60,000 nm I've never had a cable burn out. I have witnessed a catastrophic melt down on a near brand new £750,000 Oyster yacht though, so am most certainly aware of the importance of cable fusing allied to adequate gauge for the task.

In Topic: Inverter Wiring

27 July 2016 - 10:33 AM

Sorry, but you can't refer to someone as an 'expert' if he believes that circuits should be fused to protect the equipment.

First link found at random - see the first Q&A:
http://www.xantrex.c...h Doctor-_4.pdf


I didn't say that the fuse wasn't to protect the cable as well, more that it's value should be chosen to protect the equipment. By default then the cable will also be well protected assuming an adequate gauge has been employed. Your linked document highlights the importance of correct cable choice.


There are many examples where a manufacturer chooses to recommend an external user provided fuse in the fitting instructions. In other cases it's included in the fitting kit but still external to allow easy replacement. I would be amazed if you are not aware of this already. If the manufacturer has chosen to include and internal fuse then fine the cable can be fused to protect it. Ditto if the cable is feeding a distribution network with a range of equipment.


Furthermore I provided clear examples where my comments regarding fusing to protect equipment were upheld with particular reference to the topic, but which you seem to have ignored.

In Topic: Inverter Wiring

27 July 2016 - 08:36 AM

Hi all,


I`m going to be fitting a Victron 3000 inverter soon and could do with a little advise regarding cable size.


Reading the Victron manual they advise using 90mm​2 cable for runs up to 5 mtrs and 120mm​2 for runs between 5 and 10 mtrs,

my run is between 5 and 6 mtrs.


At present I have 70mm​2 cable, as the inverter has 2+ and 2- terminals  would it be possible to run another 70mm2 cable along side the original giving a total area of 140mm ​2​ ?


If so I presume both positive cables would need to go through the same battery isolator but be individually fused, at present there is a 250 amp fuse fitted, so I would need to fit a similar one in the new cable.


Any advise would be much appreciated.





If at all possible I would aim to reduce the cable run from battery to inverter. A 12 metre return run is really too long assuming you were quoting distance between. I would also do the job properly and source a singe run of the correct gauge cable for each leg. You can see yourself the issues that can arise otherwise - think simple but robust with heavy current cabling. 


Please also ignore comments that the fuse is only there to protect the cable. It most certainly isn't. Thinking should be to choose fuse to protect equipment then cable size and connections to minimise volt drop for given cable run at max load. A 400 amp fuse should be ok in your case.


I can qualify above when a 500 amp fuse blew feeding an accidentally overloaded 3500 watt inverter. The 70mm2 cables didn't get remotely warm but the inverter did blush.png Without doubt it saved my Combi which is still working fine three years later. Ditto 600 amp fuse on my fouled bowthruster although it had thermal overload protection as well.