And So It Starts,i Get Intimate With The Boat.

[Smoggy]

It's only the screw on battery leads that are frowned upon, soldering is fine, if the soldering is hot enough to melt you want to be off the boat already. 

[MargeandParge]

50 minutes ago, Smoggy said:

It's only the screw on battery leads that are frowned upon, soldering is fine, if the soldering is hot enough to melt you want to be off the boat already. 

Sorry can't say what's right or wrong just what we were told 

Kindest Regards Marge and Parge 

[Regulo]

1 hour ago, mikeyboy1966 said:

any obvious flaws in my plan?

None - but I had plenty of plans when I had my boat, about 50% never turned out as expected. So much so, that it became a running joke -

Dave: "How long will this take"?

Me: "About an hour".

Dave: "Better call the wife, and tell her we'll be home tomorrow".

[mikeyboy1966]

Quick question,

does anyone know what sort of current a diesel starter motor is likely to draw on a cold start?

im just considering the use of a mega fuse on the starter circuit,

and what size fuse I’d need.

ta

 

[Smoggy]

I would have thought a fuse of any kind on the starter lead will be pushing your luck on a cold morning, it's not a normal thing to do, that initial load must be a good few hundred amps.

[mikeyboy1966]

2 minutes ago, Smoggy said:

I would have thought a fuse of any kind on the starter lead will be pushing your luck on a cold morning, it's not a normal thing to do, that initial load must be a good few hundred amps.

I was pondering a 500 amp maxi fuse.

[Vaughan]

26 minutes ago, mikeyboy1966 said:

does anyone know what sort of current a diesel starter motor is likely to draw on a cold start?

Your Perkins 4108 starter draws 400 amps (from memory).  I believe a Nanni draws a lot less than that.

 

 

[mikeyboy1966]

Just now, Vaughan said:

Your Perkins 4108 starter draws 400 amps (from memory).  I believe a Nanni draws a lot less than that.

 

 

So in theory,

I could fuse the main starter cable with a 500amp maxi fuse.

so everything outside of the battery box would be protected from a dead short.

hmm,will ponder.

 

[Meantime]

7 minutes ago, mikeyboy1966 said:

I was pondering a 500 amp maxi fuse.

Starter cables are not generally fused, however if you do then you need to realise you will be fusing for a short circuit situation, not an overload situation, unless you seriously upgrade your battery wiring. 

A starter motor could easily draw 200 amps and will cause the voltage to drop closer to 9 to 10 volts, which in turn will raise the current to closer to 250 to 300 amps. Power = volts x amps so as the voltage gets dragged lower, the current has to rise to provide the required power. 

Your starter cable if using 25mm2 will be rated at 170 amps. This is fine because although it will get slightly warm it will not be enclosed and normally an engine will start within a few seconds. Continued attempts to start the engine are likely to flatten the battery before you can burn the cable out. However if you were fusing this cable to protect against overload you would probably use a fuse of 150 amps, which would instantly blow the moment you tried to start the engine. The fuse should be less than the power rating of the cable it is protecting.

If you wanted to use a 500 amp fuse to protect against short and overload protection you would need to upgrade your starter wiring to something greater than 150mm2 which is not practical.

So by all means add a fuse, but just be aware it will only protect against short circuit, not overload.

[mikeyboy1966]

2 minutes ago, Meantime said:

Starter cables are not generally fused, however if you do then you need to realise you will be fusing for a short circuit situation, not an overload situation, unless you seriously upgrade your battery wiring. 

A starter motor could easily draw 200 amps and will cause the voltage to drop closer to 9 to 10 volts, which in turn will raise the current to closer to 250 to 300 amps. Power = volts x amps so as the voltage gets dragged lower, the current has to rise to provide the required power. 

Your starter cable if using 25mm2 will be rated at 170 amps. This is fine because although it will get slightly warm it will not be enclosed and normally an engine will start within a few seconds. Continued attempts to start the engine are likely to flatten the battery before you can burn the cable out. However if you were fusing this cable to protect against overload you would probably use a fuse of 150 amps, which would instantly blow the moment you tried to start the engine. The fuse should be less than the power rating of the cable it is protecting.

If you wanted to use a 500 amp fuse to protect against short and overload protection you would need to upgrade your starter wiring to something greater than 150mm2 which is not practical.

So by all means add a fuse, but just be aware it will only protect against short circuit, not overload.

Got it!

all starter and batt cables will be 50 mm sq tinned.

rated at @350 amp

im only concerned with short circuit protection,

id never just keep cranking an engine,if it doesn’t start as normal there is obviously a problem.

thanks for the advice,very helpful 

[Meantime]

5 minutes ago, mikeyboy1966 said:

Got it!

all starter and batt cables will be 50 mm sq tinned.

rated at @350 amp

im only concerned with short circuit protection,

id never just keep cranking an engine,if it doesn’t start as normal there is obviously a problem.

thanks for the advice,very helpful 

Forgot to add, don't forget your battery isolator switch will generally be rated for 5 seconds at maximum rating before it will burn out as well.

[annv]

Hi Micky There is no need to fuse starter cables, on your battery picture you have not greased your terminals and you have taken both pos and neg supply cables from the same battery not recommended, see my picture on a earlier post on this file. John

[mikeyboy1966]

2 hours ago, annv said:

Hi Micky There is no need to fuse starter cables, on your battery picture you have not greased your terminals and you have taken both pos and neg supply cables from the same battery not recommended, see my picture on a earlier post on this file. John

You’ve not read my post John ,

the pos and neg will exit the box from different sides so will not be taken off the same battery,there are two more batts to fit yet.and the through panel connections ,

the box needs to have a test fit on the boat to determine cable exits

So I’ve not greased anything yet.

as this is 1st fit,no point in getting oily mitts

 

[mikeyboy1966]

I realise there is no “need” to fuse the starter cable,

the battery isolators on the boat are not particularly close to the battery bank,

id guess there is at least 3 to 4 metres of heavy duty starter cable between the batteries and solenoid/starter motor.

if there is a valid reason NOT to fit a 500amp fuse,I’ll relocate the isolator,solenoid and associated wiring to minimise exposed wiring and components.

As  things stand ,all of this cable runs around the engine bay in close proximity to other wiring/combustible materials and parts that are earthed.

Hence my concerns over a dead short circuit.

[grendel]

5 hours ago, mikeyboy1966 said:

so everything outside of the battery box would be protected from a dead short.

you have to be careful with that assumption, working as I do with mains cables and voltages, there is a calculation (i am not clever enough to remember it, but know it exists) that can be used to calculate the fault current from a direct short, the problem is that the further from the source you are the lower the fault current seen at the source due to the resistance of the cable, thus there is a point at which a fault can be present, but not allow enough current to flow to blow the fuse in a reasonable time to protect the cables and source (tyrpically we are looking at hundreds of metres with large cables (300mm2) but the same principle will apply to smaller cables at shorter distances. (eg a bow thruster circuit at the other end of the boat might not blow a 500A fuse even on a direct short.

[WherryNice]

I fused my starter cable when I re wired my boat as when I looked online it seemed to be the thing to do these days, from memory I used a 450amp Mega fuse which has never blown(BMC 1500D). Peak amperage when cranking is at zero RPM and drops rapidly once things get moving(if I remember my college lecturer correctly that is).

I crimped my terminals, using one of the cheapy chinese hydraulic crimpers off ebay, bit of a faff to use but decent results.

For charging I used a Sterling Alt to Batt charger and I have been very happy with the results and it was simple to install:)

 

[Vaughan]

18 hours ago, Meantime said:

Starter cables are not generally fused, however if you do then you need to realise you will be fusing for a short circuit situation, not an overload situation, unless you seriously upgrade your battery wiring. 

I have been thinking carefully and I don't think I have ever seen a hire boat with a fuse on the main cable to the starter solenoid.  I have seen a few (very few) with a fast fuse on the positive feed from the alternator.

Also, I have always been used to soldered terminations on battery cables, with no problem.  I would suppose that if the solder melted in a fire this would break the connection and shut off the circuit, therefore "fail safe".  After all the reason for having a battery master switch (according to BSS) is to cut the circuit when fighting a fire.

[Meantime]

4 hours ago, Vaughan said:

I have been thinking carefully and I don't think I have ever seen a hire boat with a fuse on the main cable to the starter solenoid.  I have seen a few (very few) with a fast fuse on the positive feed from the alternator.

Also, I have always been used to soldered terminations on battery cables, with no problem.  I would suppose that if the solder melted in a fire this would break the connection and shut off the circuit, therefore "fail safe".  After all the reason for having a battery master switch (according to BSS) is to cut the circuit when fighting a fire.

There's a number of things to consider here. The BSS allows for either crimped or soldered connections. I don't think you could rely on a soldered connection melting and breaking free unless it was hanging under its own weight, (which would be a BSS fail anyway as cables should be properly supported) and then if it was the live end it might drop onto an earth and provide another short. Screw terminals are also allowed providing there is the use of spreader plates between the screw and cable or the cable end is tinned, quite hard to do with a normal domestic soldering iron.

Although there are some enhancements to the BSS for hire boats, in relation to fuses it is the same. The lack of a fuse or circuit breaker on DC systems is NOT in itself a fail point for the BSS, except for charging wires, these are battery charger, invertor charger, solar or wind charge cables and anything that requires a continuous supply such as a bilge pump, memory for a radio etc.

The main emphasis for the BSS is placed upon having proper isolators, as close to the battery as possible, properly labelled and easily accessible. The ability to isolate the battery from any short quickly is seen as the most important thing.

I believe there is a move in the boat building industry for the leisure market to move towards adding battery fuses for starter motors more as a nod towards the insurance industry, rather than because they are an essential safety item.

Modern cars tend to have a built in fuse as a part of the positive terminal, but again it is only designed to blow in the event of a short circuit, not an overload situation. The fuse is not replaceable and the whole terminal has to be replaced. Off course the big difference between cars and boats is that generally speaking you can just open the door and walk a safe distance away from a car. Not so easy on a boat when it's underway.

Another big difference between cars and boats is the size of the battery, which in a car is generally sized as small as possible. A car battery with a shorted starter motor is more likely to go flat before the cables can catch fire. Most people tend to fit another leisure battery on the boat engine start rather than a smaller more suitably sized battery. Therefore there is much more power available in the event of a short circuit.

The strange thing about the BSS is that whilst the lack of a fuse or breaker on a DC system is not in itself a fail, if you do fit one and then replace the fuse with a nail, it will fail. I can understand the logic in failing it if a nail is fitted, but by the letter of the BSS you could remove the nail and fuse holder and join the cable and it would pass. (Unless off course it was a charge cable, or directly connected to the battery.

My final thought, is that the isolator being easy to get to and close to the battery is more important than fitting a fuse in the feed to the started motor. However the fitting of a fuse will protect in the rare event of a short circuit, but is unlikely to be of any use in an overload situation. I won't rush to rewire my boat, but if I was going through that exercise then I might as a belt and braces approach consider doing so. 

[Vaughan]

1 hour ago, Meantime said:

There's a number of things to consider here. The BSS allows for either crimped or soldered connections. I don't think you could rely on a soldered connection melting and breaking free unless it was hanging under its own weight, (which would be a BSS fail anyway as cables should be properly supported) and then if it was the live end it might drop onto an earth and provide another short. Screw terminals are also allowed providing there is the use of spreader plates between the screw and cable or the cable end is tinned, quite hard to do with a normal domestic soldering iron.

Although there are some enhancements to the BSS for hire boats, in relation to fuses it is the same. The lack of a fuse or circuit breaker on DC systems is NOT in itself a fail point for the BSS, except for charging wires, these are battery charger, invertor charger, solar or wind charge cables and anything that requires a continuous supply such as a bilge pump, memory for a radio etc.

The main emphasis for the BSS is placed upon having proper isolators, as close to the battery as possible, properly labelled and easily accessible. The ability to isolate the battery from any short quickly is seen as the most important thing.

I believe there is a move in the boat building industry for the leisure market to move towards adding battery fuses for starter motors more as a nod towards the insurance industry, rather than because they are an essential safety item.

Modern cars tend to have a built in fuse as a part of the positive terminal, but again it is only designed to blow in the event of a short circuit, not an overload situation. The fuse is not replaceable and the whole terminal has to be replaced. Off course the big difference between cars and boats is that generally speaking you can just open the door and walk a safe distance away from a car. Not so easy on a boat when it's underway.

Another big difference between cars and boats is the size of the battery, which in a car is generally sized as small as possible. A car battery with a shorted starter motor is more likely to go flat before the cables can catch fire. Most people tend to fit another leisure battery on the boat engine start rather than a smaller more suitably sized battery. Therefore there is much more power available in the event of a short circuit.

The strange thing about the BSS is that whilst the lack of a fuse or breaker on a DC system is not in itself a fail, if you do fit one and then replace the fuse with a nail, it will fail. I can understand the logic in failing it if a nail is fitted, but by the letter of the BSS you could remove the nail and fuse holder and join the cable and it would pass. (Unless off course it was a charge cable, or directly connected to the battery.

My final thought, is that the isolator being easy to get to and close to the battery is more important than fitting a fuse in the feed to the started motor. However the fitting of a fuse will protect in the rare event of a short circuit, but is unlikely to be of any use in an overload situation. I won't rush to rewire my boat, but if I was going through that exercise then I might as a belt and braces approach consider doing so. 

Oh Gawd, I seem to have started something here . . . 

I actually agree with most of this post but does it apply to what we are all doing on the Broads?  One point I would make is that the fitting of a domestic battery to the starter is not practical because of CCA - cold cranking amps.  The average "domestic" battery would not be powerful enough to start an old fashioned engine such as a 4108, let alone blow a fuse.

6 hours ago, Vaughan said:

I don't think I have ever seen a hire boat with a fuse on the main cable to the starter solenoid.

That is all I actually said.  It is based on my experience of running literally hundreds of hire boats.

Edited to add : Perhaps I could gently mention that I "liked" your post before I quoted it.

Edited December 17, 2022 by Vaughan
line added

[mikeyboy1966]

Things are taking shape,

I’ve spent some time looking at the seminars from pacific yacht systems.

most informative.

jeff cote seems to know his stuff ,without the normal waffle from YouTube vids.

skip thru the intro bits.

 

[mikeyboy1966]

With this in mind,

live decided not to fuse the starter circuit,as he explains the pitfalls of doing so.

but I will be looking to reduce the length of cabling to the isolator switches.

work in progress,mk 1 version.

now I have the battery isolator,and external regulator ive more questions than answers till I get down to the boat again.

[mikeyboy1966]

My initial plan was to locate the new battery box in front of the engine,

but,,,,,

this would mean zero access to the raw water pump

[mikeyboy1966]

Plan b,

required removal of the old water tank mounts

[mikeyboy1966]

Plus some other bitsnbobs

[mikeyboy1966]

Then I ran out of time,

hope to get down between Christmas and new year for more prep.