BOW THRUSTER CABLE SIZE

[emkay]

Hi techs. A litttle advice from those that know please.

 

I have a 95 k Vetus on board my 3 month old boat, during fit out the sparks called me to say that he considered the 16mm charging cables to the thruster batteries as being inadequate and recommended an upgrade to 40mm as the length of the run was a good 55 ft. Installed as recommended, however we dont use the thruster much and didn't notice a problem until it suddenly died. Testing the voltage showed no power going into the batteries even with fully charged domestics and the engine on. Sparks not interested in desnagging (anything actually) so got a local marine engineer to check. This guy is an excellent all rounder but I have no experience of his sparkie skills.

He found that the neg had been wired to the ignition buzzer in such a way that it could only charge while the buzzer was sounding, a quick check after a temporary mod on the neg (to earth) showed good current flowing to the thruster. However after 20 secs or so the 70 amp blade fuse popped, the engineer after checking the fuse told me that was to be expected as the fuse was suitable for a 15mm cable but was well below spec for a 40mm. Also recommended that the neg be wired back to the buzz bar as a permanent fix.

 

1. Does this sound right?

 

2. Original sparks doesn't seem to have an aftersales life so before I put in a big fuse (ceramic slow burn?) am I risking damage to the thruster batteries or worse?

 

3. Is warranty work always such a pain in the rear to get done?

Edited August 23, 2010 by emkay

[pmms]

Hi emkay

 

16mm (is that the actual dia or the sparkys estimate of the csa 16mm2?) seems way too small for that length of cable run. You say the run is 55ft is that the distance between charging source and the bow prop batts, in which the cable run for calculating the size of cable req is 110 ft. this will give you a cable size that will freak you out! you dont say where you are located, if you pm me I may know of someone you can contact. BTW its worth remembering that any circuit protection device should be rated at less than the capacity of the wiring/device its protecting. do you have the vetus installation instructions as they may offer guidance on the matter?

 

All the best

 

Paul M

[DHutch]

You are only using the cables to charge the battery, and with care these need not carry the current of the BT itself.

 

Ours i would say are a little small given the alternator is machine sensing, but they work, and are more like 6mm^2

 

 

Daniel

[Gibbo]

What you're supposed to have is the bow thruster batteries at the bow then the charging cables running the length of the boat. If that is the case, then 16mm will do it. The 16mm cable isn't carrying the bow thruster current, just the charge current. 16mm isn't ideal, but it will get the job done.

 

I suspect the fuses blew when the bow thruster was operated. For this reason many people don't fit fuses. That is lethal. They should be fused at both ends (because there's a battery at both ends).

 

Now we need to consider how they are charged. If they are charged form a split charge diode then that is the end of the matter. If they are charged from a split charge relay then two things have to be done. Firstly the split charge relay has to be big enough and more importantly, the split charge relay has to be disconnected each time the bow thruster is operated. This is usually done by stealing a signal from the bow thruster control panel to operate a small relay which interrupts the feed to the main split charge relay coil. Without doing this the fuses can blow each time it is used. Some cowboys cure this by fitting bigger fuses.

 

The fuses blowing after the cable was changed is probably as a result of the 16mm cable being so small that it dropped most of the voltage across its length thus the current wasn't enough to pop the fuses. But once bigger cable was installed, the voltage drop was less, and therefore the current higher.

 

The comment re the neg cable being conected to the buzzer makes no sense whatsoever.

[emkay]

What you're supposed to have is the bow thruster batteries at the bow then the charging cables running the length of the boat. If that is the case, then 16mm will do it. The 16mm cable isn't carrying the bow thruster current, just the charge current. 16mm isn't ideal, but it will get the job done.

 

I suspect the fuses blew when the bow thruster was operated. For this reason many people don't fit fuses. That is lethal. They should be fused at both ends (because there's a battery at both ends).

 

Now we need to consider how they are charged. If they are charged form a split charge diode then that is the end of the matter. If they are charged from a split charge relay then two things have to be done. Firstly the split charge relay has to be big enough and more importantly, the split charge relay has to be disconnected each time the bow thruster is operated. This is usually done by stealing a signal from the bow thruster control panel to operate a small relay which interrupts the feed to the main split charge relay coil. Without doing this the fuses can blow each time it is used. Some cowboys cure this by fitting bigger fuses.

 

The fuses blowing after the cable was changed is probably as a result of the 16mm cable being so small that it dropped most of the voltage across its length thus the current wasn't enough to pop the fuses. But once bigger cable was installed, the voltage drop was less, and therefore the current higher.

 

The comment re the neg cable being conected to the buzzer makes no sense whatsoever.

Thanks Gibbo

 

Pretty much what I expected, no idea whether a relay or diode was used but I'll investigate. ref the buzzer, all I know is that in the original wiring form the only time current flowed to the BT batteries was when the buzzer on the ignition switch was on, when the neg was earthed current flowed when the engine was running.

One last thing, why would the fuse blow when the BT was operated if the fuse is on the charging cables?

Edited August 24, 2010 by emkay

[Gibbo]

Thanks Gibbo

 

Pretty much what I expected, no idea whether a relay or diode was used but I'll investigate. ref the buzzer, all I know is that in the original wiring form the only time current flowed to the BT batteries was when the buzzer on the ignition switch was on, when the neg was earthed current flowed when the engine was running.

 

 

If the charge cable was in any way connected to the buzzer it would have blown the living daylights out of every wire in the engine panel. I suspect someone has misinterpreted something here.

 

One last thing, why would the fuse blow when the BT was operated if the fuse is on the charging cables?

 

When the BT is operated it will pull lots of amps. If the BT battery is a bit low on charge the BT will try to pull this power down the split charge cables. Thus popping the fuses. Electrons are just electrons. They don't know they're only supposed to charge a battery as opposed to power a bow thruster.

[emkay]

If the charge cable was in any way connected to the buzzer it would have blown the living daylights out of every wire in the engine panel. I suspect someone has misinterpreted something here.

 

 

 

When the BT is operated it will pull lots of amps. If the BT battery is a bit low on charge the BT will try to pull this power down the split charge cables. Thus popping the fuses. Electrons are just electrons. They don't know they're only supposed to charge a battery as opposed to power a bow thruster.

 

Thanks Gibbo, clear now. Certainly didn't mean the main BT neg to the buzzer, neg to the buzzer was a small wire probably a control one, leaving it to the experts to sort that out. Thanks to everyone for the input

[blackrose]

My BT cables running down the length of the boat are only 16mm2 but since (as the others have described), the BT batteries are at the bow next to the motor the cable size isn't a problem. My system utilises the start alternator via a relay which switches charge to the BT batteries as soon as the start battery reaches a certain voltage. I've never run out of power with this system, but it does rely on the user not over-doing it with the BT because as soon as the BT batteries are drained they wouldn't charge quickly enough to be used. This has never happened to me in practice.

 

The cables connecting my BT batteries to the motor are a lot thicker - about 60-70mm2 I think?

[emkay]

My BT cables running down the length of the boat are only 16mm2 but since (as the others have described), the BT batteries are at the bow next to the motor the cable size isn't a problem. My system utilises the start alternator via a relay which switches charge to the BT batteries as soon as the start battery reaches a certain voltage. I've never run out of power with this system, but it does rely on the user not over-doing it with the BT because as soon as the BT batteries are drained they wouldn't charge quickly enough to be used. This has never happened to me in practice.

 

The cables connecting my BT batteries to the motor are a lot thicker - about 60-70mm2 I think?

 

 

Thanks Blackrose, I'm going to do the same thing, at the moment my learning curve feels like a cliff face but this forum certainly helps.

[blackrose]

Thanks Blackrose, I'm going to do the same thing, at the moment my learning curve feels like a cliff face but this forum certainly helps.

 

This is the relay that switches the charge between my start and BT batteries. http://www.bepmarine.com/home-mainmenu-8/product-269/125-amp-voltage-sensitive-relay-vsr-

 

I don't know how it compares to other relays but it does seem to do the job pretty well. There are also some other variations on their website.

 

If you have twin alternators, I think there's and advantage of switching between start battery to BT batteries (charging via the start alternator), rather than switching between domestic batteries and BT battery (using the domestic althernator). If you think about it the start battery alternator isn't doing very much once the start battery is fully charged so it may as well be utilised for charging the BT batteries.

 

My setup is probably a bit unusual. I think a lot of people (without BTs), are paralleling their start & domestic alternators to provide additional charge to their domestic battery bank, while some people with BTs are splitting the charge between their domestic battery bank and BT batteries. Personally I don't think the latter setup makes the best use of the alternators.

 

(I have a Vetus 95kgf thruster powered by 2 x 110 a/h batteries)

Edited August 26, 2010 by blackrose

[NB Willawaw]

I'll leave Gibbo and the others to the electrical responses, but I'm intrigued that you have a 3-month old boat with these problems and nobody seems interested in any remedial work.

 

Was the original electrician employed by yourself or the boatyard ?

 

Is this a sailaway where you have employed your own sub-contractors for the specialist items ?

 

 

Hi techs. A litttle advice from those that know please.

 

I have a 95 k Vetus on board my 3 month old boat, during fit out the sparks called me to say that he considered the 16mm charging cables to the thruster batteries as being inadequate and recommended an upgrade to 40mm as the length of the run was a good 55 ft. Installed as recommended, however we dont use the thruster much and didn't notice a problem until it suddenly died. Testing the voltage showed no power going into the batteries even with fully charged domestics and the engine on. Sparks not interested in desnagging (anything actually) so got a local marine engineer to check. This guy is an excellent all rounder but I have no experience of his sparkie skills.

He found that the neg had been wired to the ignition buzzer in such a way that it could only charge while the buzzer was sounding, a quick check after a temporary mod on the neg (to earth) showed good current flowing to the thruster. However after 20 secs or so the 70 amp blade fuse popped, the engineer after checking the fuse told me that was to be expected as the fuse was suitable for a 15mm cable but was well below spec for a 40mm. Also recommended that the neg be wired back to the buzz bar as a permanent fix.

 

1. Does this sound right?

 

2. Original sparks doesn't seem to have an aftersales life so before I put in a big fuse (ceramic slow burn?) am I risking damage to the thruster batteries or worse?

 

3. Is warranty work always such a pain in the rear to get done?

[emkay]

I'll leave Gibbo and the others to the electrical responses, but I'm intrigued that you have a 3-month old boat with these problems and nobody seems interested in any remedial work.

 

Was the original electrician employed by yourself or the boatyard ?

 

Is this a sailaway where you have employed your own sub-contractors for the specialist items ?

 

Hi Mark

 

It's an unusual situation a sailway, but not ballasted, foamed or battened the fitters took all that on. The shell builder who also supplied the engine and BT etc has been fine and I have nothing but praise for the quality of the fit in general. The main problem lies with the sparks contracted to the fitters, he did a great job wiring the boat but has been almost comically averse to answering the phone or emails and the fitters seem to have no control over him. But! An email has just arrived to say he's coming to fix the BT wiring, just doesn't say when. I would say that if you are having a boat built make sure that you retain a small but tempting amount until the warranty period is up.

[Night Hawk]

Electrons are just electrons. They don't know they're only supposed to charge a battery as opposed to power a bow thruster.

 

Moving at the fabulous speed of 1.5cm per minute, they've got plenty of time to decide?!?

[mchancox]

Hi Mark

 

It's an unusual situation a sailway, but not ballasted, foamed or battened the fitters took all that on. The shell builder who also supplied the engine and BT etc has been fine and I have nothing but praise for the quality of the fit in general. The main problem lies with the sparks contracted to the fitters, he did a great job wiring the boat but has been almost comically averse to answering the phone or emails and the fitters seem to have no control over him. But! An email has just arrived to say he's coming to fix the BT wiring, just doesn't say when. I would say that if you are having a boat built make sure that you retain a small but tempting amount until the warranty period is up.

I am sure the Sparky will get everything put right if he is worth his weight in salt. You have a basice fit out here so I am intrigued to see and understand what the problems really are.

The charge circuit to the bow thruster batteries (Which should be at the bow) is relatively simple by means of components and installation. The Instrument panel (Unless it is home made) should be quite a simple fit too.

 

I look forward (Being a Boat Sparky) to seeing what hasn't gone so well.

 

 

Regards,

[Theo]

Moving at the fabulous speed of 1.5cm per minute, they've got plenty of time to decide?!?

Yes but they do push each other along so the signal passes from one end of the conductor to the other at a large fraction of the speed of light.

 

N

[Gibbo]

Yes but they do push each other along so the signal passes from one end of the conductor to the other at a large fraction of the speed of light.

 

My old lecturer likened them to old women in a post office.....

 

"They move slowy and clog the place up, but look how fast gossip gets from one end to the other"