cable type

[Alf Roberts]

nice one Keith.

 

although I take issue with you first post, yes of course you get bad work from professionals but you also get good. (same as the semi-pros)

Do it for years does not mean that he under stands what he is doing

 

I see many marina installation supposedly installed by competent installer and on inspection they are many basic mistakes

 

Keith

[Neil Smith]

Thanks Tony, yes I don't know a great deal about DC electrics, but learning all the time with all the positive posts but not enough to feel comfortable about tackling it myself, the sparks is coming this Friday to do first fix and that reminds me I still have to get the cable to charge the bow thruster battery.

 

Neil.

[Tony Brooks]

Thanks Tony, yes I don't know a great deal about DC electrics, but learning all the time with all the positive posts but not enough to feel comfortable about tackling it myself, the sparks is coming this Friday to do first fix and that reminds me I still have to get the cable to charge the bow thruster battery.

 

Neil.

 

And that is another potential voltdrop problem area with such a long run. If it were me I would be using something close to starter or welding cable size and even then after a good run of bow thruster use there is likely to be a fair bit of voltdrop along the length. That will r educe as the battery charges.

 

Keith may come in and make a recommendation.

[Keith M]

For the bow thruster just apply volt-drop calculation

And personally no more than 3%

Some my take me task that just my standard

 

But it is very difficult as the current chances with a bow-thruster so you have to start at max current

 

Keith

[nicknorman]

With a bow thruster cable, a lot depends on how heavily you intend to use it. If "once in a blue moon" then fairly thin (relatively!) cable will suffice and just accept it takes a long time to recharge, but if you want rapid recharge you need really fat cable or a dedicated mains charger (if you have an inverter running normally).

 

Ed: all that presumes a dedicated bow thruster battery local to the BT.

Edited January 13, 2015 by nicknorman

[Tony Brooks]

 

And that is another potential voltdrop problem area with such a long run. If it were me I would be using something close to starter or welding cable size and even then after a good run of bow thruster use there is likely to be a fair bit of voltdrop along the length. That will r educe as the battery charges.

 

Keith may come in and make a recommendation.

 

 

Just to add:

 

As these cables will have a battery at both ends they should really have a fuse at each end as well.

With a bow thruster cable, a lot depends on how heavily you intend to use it. If "once in a blue moon" then fairly thin (relatively!) cable will suffice and just accept it takes a long time to recharge, but if you want rapid recharge you need really fat cable or a dedicated mains charger (if you have an inverter running normally).

 

Ed: all that presumes a dedicated bow thruster battery local to the BT.

 

 

I agree that something like 8 or 10 sq mm cable will eventually recharge than batteries and with light use do a good enough job BUT my concern is the effect of a well discharged bow thruster battery would have on the current flow when the bow thruster is used. If the cable was fused for its own protection then a fuse will blow (I hope) but there will then be a temptation to replace it with a larger fuse that will endanger the cable..

[smileypete]

strewth this forum likes to make things complicated.

 

It isn't.

 

See post #8.

 

cheers, Pete.

~smpt~

[nicknorman]

I agree that something like 8 or 10 sq mm cable will eventually recharge than batteries and with light use do a good enough job BUT my concern is the effect of a well discharged bow thruster battery would have on the current flow when the bow thruster is used. If the cable was fused for its own protection then a fuse will blow (I hope) but there will then be a temptation to replace it with a larger fuse that will endanger the cable..

 

Agreed but there is no optimal answer I fear. (Relatively) thin cable risks being overloaded or the fuse blowing, fat cable risks whatever batteries are at the other end (engine or domestic) being flattened by excessive BT use. That is why dedicated charging is the best solution. We have a dual alternator our boat and no BT, but if we did have a BT i think I would be tempted to dedicate the 45A engine alternator to the BT batteries and use a split charge relay to charge both the engine and domestic banks from the 175A domestic alternator. Or a dedicated mains charger near the BT fed from our always-on inverter, via a relay so it was only in when the engine was running. Edited January 13, 2015 by nicknorman

[by'eck]

Despite the comments above don't underestimate the charge current draw from dedicated battery(s) after even momentary use of the bowthruster. Mine regularly draws over a 100 amps initially after just a short burst.

 

FWIW my charge cables (fused at both ends) are of 35mm2. It obviously depends on how much charge current your setup is capable of though.

[Keeping Up]

Agreed but there is no optimal answer I fear. (Relatively) thin cable risks being overloaded or the fuse blowing, fat cable risks whatever batteries are at the other end (engine or domestic) being flattened by excessive BT use. That is why dedicated charging is the best solution. We have a dual alternator our boat and no BT, but if we did have a BT i think I would be tempted to dedicate the 45A engine alternator to the BT batteries and use a split charge relay to charge both the engine and domestic banks from the 175A domestic alternator. Or a dedicated mains charger near the BT fed from our always-on inverter, via a relay so it was only in when the engine was running.

 

A slightly off-the-wall solution would to use a very thin cable (1mm or less) between the main and BT batteries (fused at each end of course). On a 12v system a 20m run of 1mm thinwall twin cable cannot take enough current to damage itself, even if the far end voltage is reduced to zero.

[nicknorman]

 

A slightly off-the-wall solution would to use a very thin cable (1mm or less) between the main and BT batteries (fused at each end of course). On a 12v system a 20m run of 1mm thinwall twin cable cannot take enough current to damage itself, even if the far end voltage is reduced to zero.

 

Yes, that would be fine, although it would take a while to recharge the BT battery!

[ditchcrawler]

 

Hello Ditchcrawler

 

What are my qualification

For just over sixteen years I was working for GPO / BT working on there power plant

Battery chargers which you can walking side, very large batteries plus generators

Running my own hire fleet in the Midlands

Being part of the UK team which help with the revision of both ISO covering DC and AC installations as can be found in the BMEEA code of practice

I also sit on the BMEEA committee

And wrote a significant number of the BMET exam questions

I also have AC qualification to Test and Certificate level

 

I hope the above helps.

 

Keith

Edit,

Sorry Keith I now realise I worded my first question very badly and it didn't really say what I meant it to. I was not questioning YOUR qualification, but WHAT qualification was required. So sorry .

 

That was not my question Keith and I respect your qualifications and shows you know your subject and can give advice, I wont go into mine.

 

My question was What qualifications do you HAVE TO HAVE to do electrical work on a narrowboat, because I don't know of any, but I could be wrong.

Edited January 13, 2015 by ditchcrawler

[Tony Brooks]

I agree with Brian, as far as I know - none. Likewise for the mechanical work as well. Gas work may be a little different but in effect not much for a non-residential boat.

 

Trouble is than many do not seem to understand that a court would consider them an expert and expect them to conduct themselves as such the moment they do or say anything the man on the bus could reasonably consider as indicating they are experts. So an add in a magazine under "engineers" would do it as would simply saying you are, but that is harder to prove.

Edited January 13, 2015 by Tony Brooks

[Keith M]

Edit,

Sorry Keith I now realise I worded my first question very badly and it didn't really say what I meant it to. I was not questioning YOUR qualification, but WHAT qualification was required. So sorry .

 

That was not my question Keith and I respect your qualifications and shows you know your subject and can give advice, I wont go into mine.

My question was What qualifications do you HAVE TO HAVE to do electrical work on a narrowboat, because I don't know of any, but I could be wrong.

Unfortuneately anybody can install both DC and AC with any qualifications

BMET would be a good way to go

Unless the vessel is residentsal and hard wired to the grid then it comes under the IET 17 edition amendment 3

Keith

Edited January 13, 2015 by Keith M

[Keith M]

And that is another potential voltdrop problem area with such a long run. If it were me I would be using something close to starter or welding cable size and even then after a good run of bow thruster use there is likely to be a fair bit of voltdrop along the length. That will r educe as the battery charges.

 

Keith may come in and make a recommendation.

A good starting point 35 mm

 

At a owners request I ran 2 x 120 mm positives and negatives for almost 0 volt drop

Keith

[smileypete]

Agreed but there is no optimal answer I fear. (Relatively) thin cable risks being overloaded or the fuse blowing, fat cable risks whatever batteries are at the other end (engine or domestic) being flattened by excessive BT use. That is why dedicated charging is the best solution. We have a dual alternator our boat and no BT, but if we did have a BT i think I would be tempted to dedicate the 45A engine alternator to the BT batteries and use a split charge relay to charge both the engine and domestic banks from the 175A domestic alternator. Or a dedicated mains charger near the BT fed from our always-on inverter, via a relay so it was only in when the engine was running.

 

For a large BT it's not a bad idea to go 24V; the high current fuses, isolators (and motor brushes!) that a large 12V BT needs can be problematic.

 

Could even charge the 24V BT batts quite nicely off 12V using a few inexpensive DC converters. Or just go 24V for the whole boat.

 

cheers, Pete.

~smpt~

Edited January 13, 2015 by smileypete

[Neil Smith]

Wow so much to think about, I have a 50 and 140 amp alts and was going to link together with a sterling alt to batt charger and possibly a 25 amp batt to batt charger so I would then be able to use smaller cable unless anyone knows a unit that restricts the amps for the BT batt in the bow about a 17 metre run.

 

Neil

[by'eck]

Wow so much to think about, I have a 50 and 140 amp alts and was going to link together with a sterling alt to batt charger and possibly a 25 amp batt to batt charger so I would then be able to use smaller cable unless anyone knows a unit that restricts the amps for the BT batt in the bow about a 17 metre run.

 

Neil

 

Why would you want to limit the charge current to the BT batts? Better that they are kept topped up as quickly and efficiently as possible. They will only draw what is needed to replace power drawn out of them. With a well engineered system this may be only a minute or two following a few second burst on the BT.

 

With 17 metres of say 35mm2 cables, volt drop won't be a significant issue and you will save money, as the batt to batt charger won't be needed.

[Neil Smith]

But with 190 amps will 35mm be enough.

 

Neil.

[Keith M]

Hello Neil

Sorry I am away from my office until Satarday at the Boat Show

 

I have just review the early posts and for volt-drop calculations require 34 meters cable 17 meters there and 17 meters back

 

I always use 24-volts

I will do the calculations on my return

 

Keith

[Keith M]

Hello Neil

I have completed a rough calculation

100 amps

At 34 meters

95mm2 will give around 0.6 volt-drop

This is a 12-volt calculation

 

I hope this will help

 

Keith

[Neil Smith]

Thanks kieth, I will wait but suspect the cable will be huge.

 

Neil

[by'eck]

But with 190 amps will 35mm be enough.

 

Neil.

 

You won't get 190 amps unless the service bank is involved, i.e paralled to the BT batteries. Even then its likely to be only a little over 100 amps and for a matter of seconds if my installation is anything to go by (12 volt Nobels 9hp with 2 x 110 Ah batteries).

 

Its really not worth worrying about excessive volt drop for just a few seconds, and will likely have zero impact on re-charge time.

[by'eck]

A good starting point 35 mm

 

At a owners request I ran 2 x 120 mm positives and negatives for almost 0 volt drop

Keith

 

This is where the volt drop calculation can be ignored to a large degree. BT use being so momentary (most have thermal cut-out to prevent prolonged use) means that a high charge current draw during and for a few seconds after use is so short as not to worry about too much. Doing the maths as your customer did is simply over the top. I suspect if the decision had been left to yourself you would have fitted a much lesser cross-section, assuming the charge cables were just that and not carrying the full BT motor current draw.

[Neil Smith]

Hello Neil

I have completed a rough calculation

100 amps

At 34 meters

95mm2 will give around 0.6 volt-drop

This is a 12-volt calculation

 

I hope this will help

 

Keith

Is there no way I can supply a lower charge current to avoid running such large cables while engine is running.

 

Neil