Bowthruster?

[PaulRainbow]

On the left all the fuses are commoned onto a vertical busbar. I think the three cables are equal length and come from three batteries.
The cables on the right are all independent feeds for different systems. The cable at the top, hidden in the ducting in this picture, is on the little horizontal busbar probablly because it wont bend round the corner.

Doesn't sound ideal, can you double check how those three cable are connected to the batteries and how the batteries are connected together ?

Also, how far from that fuse to the thruster and what size cables ?

 

[goeasy123]

Doesn't sound ideal, can you double check how those three cable are connected to the batteries and how the batteries are connected together ?

Also, how far from that fuse to the thruster and what size cables ?

The three cables are of equal length from the three nearby batteries and the cable to the bowthruster is big enough (as I remember, over spec'd}. The fuses are at the back of the boat as near to the batteries as possilble. The thruster is at the front. Therefore a long cable. Not ideal, but it all works.
Changing any of this doesn't solve the immediate problem of the fuse getting hot. It doesn't make sense to me having 12mm dia. wire carrying 300 to 400 amps of current and then putting that through the plate of a fuse that's 20mm X a little over 0.5mm. All that heating is robbing the bowthruster of power. Shortening the high current carrying path is still going to have the same heat generated no matter where the fuse is.
Is there an alternative solution, like a breaker, that avoid the heat generation? If so which one?

 

[PaulRainbow]

The three cables are of equal length from the three nearby batteries and the cable to the bowthruster is big enough (as I remember, over spec'd}. The fuses are at the back of the boat as near to the batteries as possilble. The thruster is at the front. Therefore a long cable. Not ideal, but it all works.
Changing any of this doesn't solve the immediate problem of the fuse getting hot. It doesn't make sense to me having 12mm dia. wire carrying 300 to 400 amps of current and then putting that through the plate of a fuse that's 20mm X a little over 0.5mm. All that heating is robbing the bowthruster of power. Shortening the high current carrying path is still going to have the same heat generated no matter where the fuse is.
Is there an alternative solution, like a breaker, that avoid the heat generation? If so which one?

If " it all works", " the cable to the bowthruster is big enough" and "Changing any of this doesn't solve the immediate problem" it sounds like you are good to go

I asked some basic questions regarding the current setup because you asked for some help and advice.

There will be millions of ANL fuses out there, carrying their rated currents, without issue. If you don't want to look at what could be causing your problem, that's fine by me, good luck with it.

 

[Wing Mark]

The three cables are of equal length from the three nearby batteries and the cable to the bowthruster is big enough (as I remember, over spec'd}. The fuses are at the back of the boat as near to the batteries as possilble. The thruster is at the front. Therefore a long cable. Not ideal, but it all works.
Changing any of this doesn't solve the immediate problem of the fuse getting hot. It doesn't make sense to me having 12mm dia. wire carrying 300 to 400 amps of current and then putting that through the plate of a fuse that's 20mm X a little over 0.5mm. All that heating is robbing the bowthruster of power. Shortening the high current carrying path is still going to have the same heat generated no matter where the fuse is.
Is there an alternative solution, like a breaker, that avoid the heat generation? If so which one?

That's how fuses work.
They warm up.
At a certain current, after a certain time, they melt. Fuse even.
The voltage drop at rated current should not be much, it is not robbing much power.
It is a loss that the designer should have taken into consideration.

Your problem is not heat generation in the active bit of the fuse, it is not mounting it correctly, with the nuts etc which are part of the design.

You could look at the thruster documentation and see if a suitable breaker is recommended.

Just because it's 'only 12V' doesn't mean it's safe to change stuff randomly.

 

[goeasy123]

That's how fuses work.
They warm up.
At a certain current, after a certain time, they melt. Fuse even.
The voltage drop at rated current should not be much, it is not robbing much power.
It is a loss that the designer should have taken into consideration.

Your problem is not heat generation in the active bit of the fuse, it is not mounting it correctly, with the nuts etc which are part of the design.

You could look at the thruster documentation and see if a suitable breaker is recommended.

Just because it's 'only 12V' doesn't mean it's safe to change stuff randomly.

That's useful to know. Thanks.

All the bits fitted apart from the cable come with the thruster and it's all installed as recommended... as far as I can tell.

I still have the problem of a lot of heat being generated, apparently by design and in a place were it might be considered dangerous.

 

[PaulRainbow]

That's how fuses work.
They warm up.
At a certain current, after a certain time, they melt. Fuse even.
The voltage drop at rated current should not be much, it is not robbing much power.
It is a loss that the designer should have taken into consideration.

That's absolute nonsense.

 

[PaulRainbow]

That's useful to know. Thanks.

All the bits fitted apart from the cable come with the thruster and it's all installed as recommended... as far as I can tell.

I still have the problem of a lot of heat being generated, apparently by design and in a place were it might be considered dangerous.

Only useful if you wanted to know some pure nonsense.

Electrical systems are not designed to get hot and melt their fuses and fuse holders.

But hey, if it suits what you want to hear, go with it.

 

[Wing Mark]

That's absolute nonsense.

How do fuses work then?

 

[[2574]]

Those thumbscrews are pants Rob, bin them and fit some new brass nuts.

Thanks Paul, you're talking my language!

 

[Wing Mark]

That's useful to know. Thanks.

All the bits fitted apart from the cable come with the thruster and it's all installed as recommended... as far as I can tell.

I still have the problem of a lot of heat being generated, apparently by design and in a place were it might be considered dangerous.

No, it is not 'as intended'
You've inserted a bunch of high electrical resistance, high thermal resistance stainless between the tab connections of the fuse and the buss bar it's connected to.
Just be cause it's shiny doesn't mean it's a good conductor.
Stainless is not a good material to use here.

When you are messing with hundreds of amps, you need to be as meticulous as when you are using hundreds of volts.
A very small resistance x a pretty big current =a significant voltage drop. Multiply that by the current again and it's suddenly a lot of power!

PaulRainbow was right about one thing. Fit proper brass nuts (or a proper fuseholder and suitable fuse).

 

[goeasy123]

ot a good material to use here.

When you are messing with hundreds of amps, you need to be as meticulous as when you are using hundreds of volts.
A very small resistance x a pretty big current =a significant voltage drop. Multiply that by the current again and it's suddenly a lot of power!

PaulRainbow was right about one thing. Fit proper brass nuts (or a proper fuseholder and suitable fuse).

ot a good material to use here.

When you are messing with hundreds of amps, you need to be as meticulous as when you are using hundreds of volts.
A very small resistance x a pretty big current =a significant voltage drop. Multiply that by the current again and it's suddenly a lot of power!

PaulRainbow was right about one thing. Fit proper brass nuts (or a proper fuseholder and suitable fuse).

The same high temperature was present even when the whole assembly was brass??

 

[PaulRainbow]

How do fuses work then?

Google is your friend.

 

[[2574]]

Google is your friend.

From RS Components:

Fuses are very simple components. Inside each is a thin metal strip or wire called a resistor that forms a link in an electrical circuit. A number of different metals are used to make resistors. Tinned copper wire is a popular choice. This is copper which has been coated in a thin layer of tin to protect against corrosion.
This resistor will melt in response to the heat generated by the excess current, breaking the circuit and stopping the flow of potentially hazardous voltage. Fuses do not produce sparks, gas or electrical discharge.

 

[Wing Mark]

The same high temperature was present even when the whole assembly was brass??

Old, corroded brass?
At these kinds of power levels, things need to be proper, and will have finite life on a boat.

The original setup obviously worked for some years without issue?
So putting it back to 'as new' should be OK.
Alternatively fit something better, like a different fuse and holder or a breaker.

 

[Wing Mark]

From RS Components:

Fuses are very simple components. Inside each is a thin metal strip or wire called a resistor that forms a link in an electrical circuit. A number of different metals are used to make resistors. Tinned copper wire is a popular choice. This is copper which has been coated in a thin layer of tin to protect against corrosion.
This resistor will melt in response to the heat generated by the excess current, breaking the circuit and stopping the flow of potentially hazardous voltage. Fuses do not produce sparks, gas or electrical discharge.

That's cringe-worthy in several ways.
Beyond "it's a bit of metal with some resistance, so it gets warm when passing current. Too much current it melts.." it misses the point on almost everything.
Fuses are made of carefully chosen alloys . As they warm up, their resistance increases, so the heat increases quickly and they blow at a carefully designed point.
Voltages don't 'flow', currents do.
Fuses can produce sparks if misused. They can produce gas.
'Resistors 'are generally designed to have a relatively constant resistance.

 

[goeasy123]

Old, corroded brass?
At these kinds of power levels, things need to be proper, and will have finite life on a boat.

The original setup obviously worked for some years without issue?
So putting it back to 'as new' should be OK.
Alternatively fit something better, like a different fuse and holder or a breaker.

I don't think it has worked without issue. There are two other posters in this thread that have reported the same issue. I believe the design of the installation is marginal.
I've cleaned everything, put it all back to original, including clean brass. I've checked the current which is always well below the 425A fuse rating. I can pin point the source of the heating as the blade of the fuse between the ceramic housing of the fuse and the mounting post. I assume that's normal?
On reflection, all the other, lower current circuits are wired directly to the posts of the fuse holder. This one and only high current circuit is wired through a short busbar with only this one connection. I think this has been done to act as a heat sink and/or to protect the sheathing of the cable from the heat.
It's still a concern, that while it is functional, it is generating a lot of heat in an enclosed space under the bedding in the rear cabin.

 

[Wing Mark]

The electrical resistance of the 'ear' on the fuse should be something like 10^-5 ohms. I don't have the dimensions to get it exact.
Say 1000A in rush current, something like 10^-2 volts, 10 watts peak?

If this was my problem, I'd be putting a voltmeter across it and checking the peak volt drop.
The brass buss bar is a bit suspect. Brass is a variable thing and has a much higher resistivity than copper at the best of times..
It's much better mechanically than copper though.
Again it might be worth looking at the peak volt drop.
Replacing the brass with thick copper might help.
Or even adding a strip of copper.
That's sounding like a bodge, but such silly-big currents in 12V are never elegant.

But I can't help suspecting it's a contact resistance problem as much as the bulk metal resistance.

Another possibility is that the fuse could be faulty?
A crack in one of the 'ears' maybe? Perhaps hidden by the ceramic?
That would up its resistance.
Obviously trying a new fuse is not a cheap option unless you have a spare handy.
Which is always a good idea.

 

[ean_p]

I don't think it has worked without issue. There are two other posters in this thread that have reported the same issue. I believe the design of the installation is marginal.
I've cleaned everything, put it all back to original, including clean brass. I've checked the current which is always well below the 425A fuse rating. I can pin point the source of the heating as the blade of the fuse between the ceramic housing of the fuse and the mounting post. I assume that's normal?
On reflection, all the other, lower current circuits are wired directly to the posts of the fuse holder. This one and only high current circuit is wired through a short busbar with only this one connection. I think this has been done to act as a heat sink and/or to protect the sheathing of the cable from the heat.
It's still a concern, that while it is functional, it is generating a lot of heat in an enclosed space under the bedding in the rear cabin.

My two pen'th worth though I'm sure many will disagree........
If the two photo's that you posted are current then the cleanliness of the mountings leave a lot to be desired. The buss bar (left side) looks to be scratched with abrasive , the washers have verdigris on the surface and the plate fuse appears to be sandwiched between a nut and a washer rather than clamped between two washers. What is the material of the washers, the nuts and the studs(bolts).
Contact the manufacturer of the fuse holder and ask about a new holder and fuse or if possible just the spares for the mounting. That would mean 3 washers each side and at least 2 brass half nuts each side, (the top tension nuts can be stainless or what ever though accepting Pauls comments about the thumb screws I personally used to quite like them if used with a non ferrous wave washer to maintain pressure.) and a wide section spring washer to keep the pressure on. Ideally the mounting stud should be brass too as it lends good conductive mass to the assembly. All contact should be through a washer so from the busbar you would have a washer , a nut, then a washer , then the fuse , then a washer then a spring washer / wave washer then a nut either brass or steel. If you get no joy from the holder maker then try a quality electric forklift spares supplier or company as they use this equipment as standard. Items like the washers and nuts are not the usual engineering stuff from the likes of B&Q as they are (the washers) of a thicker cross section and the nuts have a broader shoulder to give more surface contact, which is what its all about. If you can't get joy at the above then try the makers like SIBA or Bussman. Should that bring no joy then you may have to pay the inflated rates of Victron, Littlefuse or BEP. I would expect the fuse to be about £3-£4 where I see Victron is selling for £12 + I think!
At the end of the day you need them clean and bright and really in the present condition only new gear will suffice. You need to have an appreciation of how high 450 amp is and what handling it entails! A poor contact of any sort is your enemy here!
Last thoughts are that its a shame your busbars aren't tinned as that would have saved some head ache and secondly, the cable next in line on the bussbar looks like it has poor surface connection as you can see the edge of the cable shoe hole showing under the nut. Finally change the stainless screw on the auxiliary's (water pump etc) to a brass nut and bolt with wave washer etc if you can't re site them altogether!
Farnells list a few 500amp DC rated circuit breakers and the cheapest is £1800 up to £6000............ with a middle price Square D unit weighing in at 14" x 9" ! I'm sure you can find much cheaper and smaller....!
Enjoy!

 

[goeasy123]

Thanks. Food for thought. I've got new brass on the way. including wavey washers.

 

[goeasy123]

Problem solved.... I think.

The posts of the fuse holder are too far apart. One end of the fuse does not reach far enough to make good contact with the brass washers it's clamped between.

The boats out of the water so I haven't been able to test it yet.