Battery Cables & Bow Thrusters [Archive]

Landlubber

10-01-2007, 09:35 PM

A lesson for all to learn from and remember.

Recently here a luxury vessel had a small, (fortunately contained) fire in the bow thruster area. The end result was damage to the bow area and burnt out batteries etc etc. A fire at sea can ruin your entire day!

The interesting thing was this. The positive and negative cables from the batteries (series/parallel) were crossing each other at the terminals of one of the batteries. Now whether the cable became hot from excessive use or the the insulation wore through (or both) the end result was that there was a direct short in 0000 battery cable from the cross over point to the two terminals, with all the usual drama to be expected when 500+ amps gets out of the box.

Remember to be aware of crossing cables where this circumstance could be repeated, I do not think the abrasion side of the story would be correct as the boat is less than a year old, but the insulation heating up and becomming soft, leading to the copper wire touching could be a very real scenario.

Let's all be aware of this sort of problem and learn from others mistakes. I am sure we have all done similar things in the past without realising the consequences.

TerryKing

10-03-2007, 10:35 AM

(..snip..)I do not think the abrasion side of the story would be correct as the boat is less than a year old, but the insulation heating up and becoming soft, leading to the copper wire touching could be a very real scenario.

There are different types of plastic used in wire insulation, and some are rated for higher temperature. There is also the type THW? which has an additional harder-plastic coating on the outside that is temperature and abrasion resistant.

Is is well known that plastic will 'cold flow' which is slow movement and shape change with constant mechanical pressure. Of course this happens faster with 'less cold'!

I recently had a lighting fixture explode and drop a glass lens and bulb and socket right on the dining room table of my 'new' apartment here in China. It was an elaborate fixture, but done with the wrong low-temperature cable. The wire insulation 'cold flowed' after 1 month, the wires shorted and the flash / over current burned totally through the wires and dropped the lens and lamp and socket. Fortunately we were in another room when we got the loud Pop, then Bang! and all the lights went out.

NOT anywhere near as scary as unexpected smoke onboard!

I think we need to think about 2 things here: (1) The correct higher-rated temperature and abrasion type cable, and (2) mechanical restraint of cables with as many cable ties and cable attachments as needed to assure that they do not move against each other under shock and vibration.

Many years ago I was a test engineer on US Navy jet fighter planes. Every cable was tied or laced, and attached to retainers every 6 inches or so. No insulation moved and rubbed together. Maybe we need to consider offshore class boats in a similar way.

Landlubber

10-03-2007, 07:08 PM

Interesting point about the cold flow Terry, ta.
Cable rating was 105deg, which is the norm for battery cable in Chinese boats, and elsehere too for that matter.

New apartments in China, as you well know, are built for a price, they are erected in 8 to 10 minutes, often by entirely unskilled labour (there is so much development they cannot get skilled people), and the end result is what you witnessed. We have the same problem in boatbuilding, same results naturally.

Frosty

10-04-2007, 01:10 AM

I would say that the cable is insufficient, no way should a cable get that hot.

Incidentaly I use the same cables for the generator start as the anchor windlass. It is extremely unlikely that I would be using both at the same time.

If I had a bow thruster I see no reason why the windlass/ gen cables coudnt be used for that too.

My bridge windlass sw was in the on position ( dont know why but it was ) When I turned on the batt one day I did not hear the clunk or the groans of the windlass trying to pull on an already parked anchor. After 20 minutes I had smoke bellowing from the forward hatch, the damage was extensive, but not to the cables, they were re-used. The windlass and its soleniod were a melted mess. I now have an alarm on the solenoid.

A fuse would have done nothing as I have discussed this with an dc elecrical engineer. If you fused to 300 amps 280 will not blow it. 280 amps will do the same damage.

Landlubber

10-04-2007, 02:30 AM

Yeah I agree on all points Frosty, the cable may or may not have got "that " hot at all, but because they were crossed, the situation allowed the direct short from the crossover point to the single battery terminals.

A fuse would not have blown, as you say.

We are supposed to fuse a circuit at the power source, yes, but that is not actually at the batteries, it is in line outseide the battery box (as usual).

This is a tricky circumstance, often done in actual fact, but obviously (in hindsight) wrong.

Not anymore with my boats anyhow!

TerryKing

10-04-2007, 04:40 AM

The windlass and its solenoid were a melted mess. I now have an alarm on the solenoid.
Hey Frosty, please tell us how / what type of alarm you have added..

This is the kind of thing where some smart power control approach could have a "Current times time" alarm set, that would alarm when the amount of energy put into the windlass was 'too much'. Whatever you might decide that was :confused:

Landlubber

10-04-2007, 06:04 AM

I would expect a simple pietzo quartz beeper would do, it will just drive you mad while the motor is in operation, after that the power is cut off and so is the bloody noise. Such as a reversing alarm from a car would do the trick.

Frosty

10-04-2007, 06:13 AM

Personally I prefer to be the fuse on my winch. I am well aware of how hard it is working and give it a rest occasionally. I cant imagine anything more anoying than a fuse blowing just when you need it the most. If its labouring I let it rest and pull the boat up on the engines, then pull again.

The alarm is a simple 12V beeper bought from an electrical shop,--less than a dollar. It is sited under the control panel and will alarm if either station winch switch is thrown.

Some kind of timer would work,-- alloying all current to flow but say 5 seconds. Simply release the switch and switch again.

I have seen something like this in 240V for starting big motors in stages, it could be times to 1/2 second.

TerryKing

10-04-2007, 07:20 AM

The alarm is a simple 12V beeper bought from an electrical shop,--less than a dollar. It is sited under the control panel and will alarm if either station winch switch is thrown.
OK, so the Alarm sounds any time the winch is running, much like the backup alarm on trucks and busses. Is that right??

Frosty

10-05-2007, 12:08 AM

Yes exactly. When the primary circuit of the winch solenoid is activated the alarm sounds.

Its is also beneficial for other uses apart from warning me that the solenoid is energised, it would give me an indication of diagnosis. If the winch was to fail yet the alarm was working I would know imediately that it was a winch motor failure, or solenoid,-- but certainly not the primary circuit which is usually the case.

This along with an ammeter showing DC draw and a battery voltage indicator I can determine exactly what is going on.

I strongly believe that these high ampage pieces of equipment need careful consideration and you can quite easily loose your boat as I nearly did.

farjoe

11-11-2007, 12:47 AM

This thread is very interesting in trying to understand what initiates a fire on board and how we can avoid it.

Only 2 weeks ago the boat on the mooring next to mine cut loose in a storm and was drifting onto the rocks.

It is reported that the owner noticed this and immediately raced on board to avoid going aground. Apparently, when he tried to engage the screw the engine stalled due to some rope getting caught in the screw. What happened then is vage but apparently smoke was seen coming out and eventually the whole boat caught fire. The boat ended up on the rocks totally razed to the ground.

Since then I have been trying to deduce what started it. To me I would think the owner continued to force the starter motor without disengaging the engine from the stalled shaft and in the panic he did not realise he was just producing heat instead of rotation.

regards

lazeyjack

11-11-2007, 03:05 AM

seems to me likely that loaded the clamps could have been loose, melted down, sparks, , gas, bomb
properly sized cables never get warm hardly, intermittent load, let alone hot nuff to melt

Moosemiester

11-16-2007, 09:46 PM

Any high amperage device should be fused at BOTH ends of the cable both positive and negative wires.... HF SSB radios, bow thrusters, windlass should all be installed this way.

TerryKing

11-16-2007, 10:04 PM

Any high amperage device should be fused at BOTH ends of the cable both positive and negative wires.... HF SSB radios, bow thrusters, windlass should all be installed this way.

I have never seen this recommended. Why would you do this??

If the fuses are the same rating, and one blows, you have to search through both ends to find it.

The only way this makes sense is IF you had a large value at the source end, to protect against a cable short circuit, and a load-appropriate fuse at the load end. But usually this is done at the source end, protecting against both faults.

Sometimes a larger fuse and cable is used to feed a sub-panel with more than one fuse for multiple loads, but that's a different situation.

Frosty

11-17-2007, 12:04 AM

I would never fuse heavy ampage equipment. I notice that you mentioned SSb with bow thruster and windlass. SSb maybe but windlasss no'

A windlass could take 200 amps. Besides the annoying replacement or re setting to fuse /trip, If you fused it at 180 it will not blow untill you overload by 180 amps .

A windlass will haul slack chain with a small 20/30 amps but will quickly load to 200 or more. How can you fuses that?

20 amps is more than adequate to start a fire and it will continue to supply under that 180 amp value.

Personally I feel a windlass should be protected by a timer and should not be able to operate longer than say 10 seconds without re engaging.

You don't fuse a starter motor do you?

TerryKing

11-17-2007, 12:55 AM

Frosty, I think you're basically right, when the device is one you depend on working, even if it's a bit overloaded right now...

On the other hand, Smoke and Fire is Bad...

What do the big automobile manufacturers do?? They don't exactly Fuse the biggest loads, like the starter solenoid, or some A/C stuff, or the Main Power Panel feed. But they don't want uncontrolled fire and smoke, so they decide where to PUT the fire and smoke. Right at the battery positive terminal, they connect the wires for big-load devices. But they put a short (2 inches or so) piece of SMALLER wire right at the beginning. Short enough so that the added resistance is negligible. Small enough so that if there's a major short circuit upstream, that smaller wire will be the one to smoke and melt. These days they use some kind of high-temperature self-extinguishing insulation on these. In the shop manual these wire ends are called a "Fusible Link". Often the dealer will replace the whole wire, but there are aftermarket replacement ends. Maybe we should look at using these on boats??

Take a look at: http://www.madelectrical.com/catalog/fusible-link.shtml
for a good overview. A quote:
Installation and function of a Fusible Link is similar to the “cartridge type,” in-line fuse. But the Fusible Link does not deteriorate or have meltdown problems with constant use in heavy-duty systems, as the cartridge type fuse is famous for. (Chevy began installing Fusible Link wires in the main-power circuits with ’66 models, and of those old cars that are still in use, most of the original Fusible Link wires are still in place. If a Fusible Link burned out then it saved the car!)

Frosty

11-17-2007, 01:28 AM

That is for "full overload ' (a short to ground). Providing the shorted wire is bigger? If the shorted wire is smaller than the fusable link then you still get a supply and a fire.

Automotive ac is fused, compressor clutch and fan for the evaporator is all
there is to it.

A compressor clutch would be protected by 10 amp max.

Head lamps and wipers are the biggest draw along with a cigarette lighter socket.

A winscreen wiper motor would burn up with 15 amps and the "fusable link" would'nt even notice it.

masalai

11-17-2007, 02:27 AM

Well thought out wisdom, Thanks Frosty

Moosemiester

11-17-2007, 11:46 AM

Frosty

11-17-2007, 08:43 PM

"fusable link" the short word for this is fuse,--its nothing new .

The fuse you are refering to is now called a maxi fuse and is not on the starter circuit.

Maxi fuse 3--70 amps how can you fuse a starter motor that can draw 300 amps. and then when the engine is warm maybe only 200amps.

A cold morning start could see more than 300. How do you fuse a variable load.

A house is nothing like a car.

TerryKing

11-17-2007, 11:34 PM

Although I don't have a good detailed technical explanation handy, the fuse both ends method is what is taught to installers of high power radio equipment in automobiles. QST magazine (A Ham Radio publication) has had several good explanations of why this is done and I'm sure there are other places.

I've seen various references to this issue, in QST and also in some online Ham websites talking about high power mobile. There are two considerations:

Fusing BOTH the positive and negative power feeds to a radio (or other) unit. This is to protect against the negative lead (which is also connected to the radio's chassis, which is usually connected to the frame/body of the car) becoming a conductor of some OTHER device's ground/negative current. The obvious example is a failure of the large cable from the battery negative terminal to the engine block/starter. If that cable is disconnected, current from the engine/starter will flow from the (Radio) negative conductor, through the radio, to car chassis/ground. This has actually happened and smoked some radio or two.
Protecting the WIRE from overcurrent. This is one reason for fusing BOTH ENDS of the positive cable to a radio etc. IF the cable gets shorted to ground, the fuse at the SOURCE end will open, protecting the cable. IF the radio draws too much current, one of the fuses will open. Which one?? One practice is to fuse the source end with a value equal to the max current carrying capacity of the cable. There seems to be no reasonable scenario for fusing BOTH ends of the negative lead, however.

The Kenwood VHF-UHF radios I have, have fuses in both the negative and positive leads at the radio. I guess to be really safe, I should put a fuse or fusible link at the battery end of the positive wire. Using the example of a #12 positive wire, and a "4 wire sizes less for a fusible link" I'd need a short section of #16 at the battery.

I think a few of the online suggestions confuse both WIRES with both ENDS.

TerryKing

11-17-2007, 11:45 PM

Automobile manufacturers started doing this because high-current fuses used in earlier cars suffered from poor connections and failed from overheating.

Regular fuses "plug in" and are dependent on a spring pressure for a good connection. Over time, temperature cycles, vibration and environmental contamination, the contact between the fuse and its holder gets worse and worse and the contact resistance goes up. That causes heat, which makes contact/corrosion worse. An overheated fuse blows before its normal current rating. Replacing the fuse in a corroded holder doesn't last long. I've seen "3AG" type fuseholders on older boats that were green with corrosion.

"Fusible Links" solve this problem two ways:

The connection is made with a good crimp connector that makes a high-pressure large-area gas-tight connection
The joint is covered with a water-tight shrink covering. The newer ones have a remelted zone over the wires.

In an automotive or Marine environment this is a much more reliable years-long-life solution.

Some Boats have a large (100 to 200 amp) 'fuse' near the battery that feeds a main cable to the main circuit breaker panel. Good fuses have large LUGS that bolt to lugs on the cable, with lots of pressure and area. They do not rely on spring pressure in a fuse holder. I hear they are reliable.

For my own DIY stuff, I guess I'll do a few 'fusible links' when I refit my boat this Spring in Vermont.

We're all learning stuff!

Frosty

11-18-2007, 02:08 AM

Wow, we are jumping from cars to houses to boats to radios . I cant keep up with you all.

But basically the point of a protected from the environment type fuse is a good idea but you cant protect a 5 amp circuit with 30 amp fuse. Yes fuses can corrode of course and cause a problem, but its not an every day occurence.

Landlubber

11-22-2007, 10:31 PM

ANL type fuse holders are the ones to use for high current applications in boats. They are available in many sizes up to about 750 amps, so there would be very few applications that could not be covered. If the boat is drawing 750 amps through the system, it may be time to go to 24 VDC instead of 12VDC electrical systems.

Most boats using say the Vetus bow thruster of about 8hp use a 350 A slo blo fuse. The motor draw on these motors is actually about the 500 amps, which is very high indeed. Fortunately they only have a capacity to run for two minutes TOTAL in an hour, something many, many owners ignore. They seem to think that they can run them for two minutes whenever they like, but the poor old DC motor really gets to heat up with such high currents running.

nordvindcrew

11-23-2007, 08:16 AM

just another idea on the problem. I install heavy automated rolling access gates. They all have a stress circuit that shuts down the operator if too much stress is felt. No idea how they do it but they work every time. Have been told it's done two ways, one is mechanically with a switch that senses movement of the motor if it torques up too much, and the other electrical that senses the load on the motor and de-activates the solenoid. You might want to check out these ideas and see if they will work. In line with this general problem, how do you calculate wire size needed foe a piece of equipment. My brother wants to move the batteries in his boat forward to help weight distribution and can't find a clear cut way to figure the wire size.

Frosty

11-23-2007, 07:47 PM

How do you think your electric windows on your car know when the glass is at the top.

See how much the window switches are????

I bust my door switches and a new set for 1 door x 2 windows was 200 dollar.

Because its got fancy stuff in there.

TerryKing

11-24-2007, 10:12 PM

Here's what those ANL type fuses look like. They are bolt-down types which are more reliable in Marine Environment than types that only use spring pressure.
http://www.terryking.us/boatbuilding/ANL-Fuses-CB.jpg
This is from:
http://www.texasindustrialelectric.com/breakers.asp

Landlubber, or anyone, have you seen a supplier for those high-current fuses that look like a large cylindrical fuse, but they have side lugs for bolt-down holders?

And I agree that any boat running motors at 300 amps on 12volts should better be running 24 or 48 volt systems. With inexpensive point-of-use switching regulators becoming available, you can have 12 volts wherever you need it, from the 24 or 48 volt bus, and the output is a clean regulated voltage that won't have dips and surges during engine starting etc.

I'd like to find a decent 12 volt output device that runs from 18-50 volts, and has a NMEA network port so you can turn it on and off remotely, and read back the status and the current being drawn. Maybe, in my Other Spare Time :rolleyes: I'll design one...