Power and Bow Thrusters

[purplerobbie]

I have two very heavy cables running from my batteries to my bow thruster.
They run the anchor windlass too.
I phoned Lofrans with a problem on my windlass and they said i would be better off mounting a battery in the bow and running a cable from the batteries at the back to charge it?
Then running both off the battery

Could i just mount the battery and use the heavy cables that are in place? Just attach them to the battery?
Would that work?

I have 3 110 amp hr batteries at the moment one for the engine and 2 domestic.
I'm going to make the 3 110's for the house bank and add a 85 (ish) amp hr for engine starting
Would 85 amp hr be ok for starting a 40hp engine?

Then get another 110 for the bow.
This could be isolated from the house bank

Thoughts?

Rob

 

[sailinglegend420]

Interesting question - but too complicated to really answer fully without more info.

What current does the Bow thruster and the Windlass take?

What diameter is the cable feeding them at the moment?

What current does your alternator deliver?

What distance from the battery to the windlass?

All these will determine exactly what you should do - which is not always the advice you might get.

At the moment the set-up is a bodge! A bow thruster could be taking hundreds of amps - which is why a long cable is not the answer and a dedicated battery next to the bow thruster is the needed. This battery must have a charging cable that is big enough to deliver at least half of the maximun current that your altrnator can deliver - otherwise the voltage drop along the cable will not charge the battery quickly enough before you need it again.

The Windlass should be on a separate cable from the starter battery - again a very large cable is needed to minimise the voltage drop to less than 3% when a large current is passing through.

If you Gooogle "AWG cable size" there are lots of sites that will help you with the correct size cable. The tables usually take the length as the distance to the load and back to the battery.

 

[halcyon]

The basic system charge system is as below. avoid diodes they have to much volt drop, use a relay. Bow thruster can use between 200 - 800 amps so you need to plan, your existing cables may well be ok for charge currents.

Sort out your equipment loadings first, also check with bow thruster and winch manufacture regarding what size battery they recommend to run them. Then do not forget your fuses.

Brian

 

[purplerobbie]

Winch 60 to 115 amps acording to the Lofrans and the best i can find on the thruster is about 300 amps (which came as a shock)

If i was to cut through the cable the wire part would probably be about 15 to 20mm in diameter

The distance apart has got to be 25ft+ (boat is 34ft)

The alternator is a tricky one. i would assume it is the standard one that goes with the engine No more than 50amp?

If i'm putting a battery at the bow would lead acid be ok?
Could i attach the windlass to the same battery?

Rob

 

[jimbaerselman]

15 - 20mm diameter - now that is a thick cable, absolutely fine for the winch amperage, and probably satisfactory, if not ideal, for the bow thruster. You advisor may have been assuming a much thinner line.

That line is well over-specified if you wanted to charge a bow battery. And yes, nothing wrong with lead acid at the bow, and yes, you'd attach the winch too.

However, an advantage of keeping just the one battery for start, winch and thruster, is that you won't have the complexities of having to charge three battery banks. Balancing the charging needs of two banks is bad enough . . . either relays, or diodes with battery voltage sensors suffice.

For optimum battery lives your two battery banks should be different types. The starter/winch/thruster has to deliver very high amperages for short durations, so it doesn't need to be a high ampere hour capacity (lots of plate mass and acid per cell, not so much surface area), but it must have a high Cold Cranking Amps (CCA) ability (lots of thin plates, ie, surface area, per cell). The CCA should be around 600 to 800 - your engine spec will advise, and so should the bow thruster spec. A typical car battery, in fact.

Your domestic battery will be all about ampere hours, rather than amps. So called 'deep cycle' design.

 

[Chris_Robb]

The way I have my bow thruster and lofrans connected is with a bow battery - with both connected with isolation and overload switches on each unit. The battery is connected to a Sterling Battery to Battery charger connected to the engine battery. The connection to the bow battery with 25mm sq felxible cable. You need this size of cable as you cannot afford any voltage drop, or otherwise the bow battery wont charge properly.

The system works well and was easy to install. You will need to borrow some heavy crimping gear.

 

[jimbaerselman]

[ QUOTE ]
Sterling Battery to Battery charger

[/ QUOTE ] Does anyone know if that is a voltage sensitive relay?

 

[steveallan]

Not just a relay

http://www.sterling-power.com/products-battbatt.htm

Steve

 

[vyv_cox]

My windlass runs perfectly well on welding cable run from the battery bank in the stern. I guess the wire diameter is 10 - 12 mm. The windlass has an 800 watt motor. Having another battery forward seems like needless complication and hassle, not to mention the loss of stowage.

 

[1611]

I fitted a 1000watt windlass with a 35 ft run of 16mm cable from my starter battery. I agree with Vyv why complicate things. I never use the windlass without the engine running so the size and type of battery need not change. I would assume that you would also be using your bowthruster with engine running and not necessarily at the same time as the windlass.

 

[jimbaerselman]

Thanks Steve. Interesting product. If well designed, that should remove the chattering problems with using mechanical voltage relays in conjuction with intelligent chargers.

 

[Chris_Robb]

Paul - I think the ampage on the bow thruster is 3 times the winch, so whilst I agree with you on the winch - my old boat had that set up, and had no problems, I think you would have to have some very fat wires indeed for the thruster. The alternative set up with a battery up front with a battery to battery charger works extremely well, again requiring 20-25 mm sq cable.

 

[purplerobbie]

[ QUOTE ]
My windlass runs perfectly well on welding cable run from the battery bank in the stern. I guess the wire diameter is 10 - 12 mm. The windlass has an 800 watt motor. Having another battery forward seems like needless complication and hassle, not to mention the loss of stowage.

[/ QUOTE ]
The lofrans i have has a 1000w motor and the bow thruster is about 3hp The cable is so thick it wont run properly round anything
It is thicker than most hose pipes.
I can run the bow thruster for about 30 secs before it cuts off.
SidePower say this is because it heas taken too much out of the battery at this point

Rob

 

[purplerobbie]

[ QUOTE ]
At the moment the set-up is a bodge!

[/ QUOTE ]
My whole boat is a bodge!
From the incorectly fitted engine to the chart table that will only open 4 inches because someone choose the worst place you could ever fit a bilge pump switch.

No gas locker and a gas system which is leathel
A hull that has a cross section of glass-water-foam-water-glass
The top 6 inches of which is made of compost?
A deck that i dont think had one plug in it
Rigging that was too short and was held together with shackles
The worlds first sails made of celophane (maybe they have just got that thin i think they are made of celophane)
An electrical system which is frankly shot i dont think there is one wire on the whole boat which is clipped up
The fresh water system had a 12v pump and a foot pump neither of which worked.
A shower that isnt connected not that it matered as none of the pumps worked
and a respray done by stevie wonder.
Would you like me to continue?

Rob

 

[jimbaerselman]

Your bow thruster, at 3hp takes about 300 to 400 amps. That's about 6 ampere hours a minute. So (as I said above) ampere hours don't count here. And, for that matter, having your engine running and providing a charging current is also trivial . . .

Check the CCA (or CA - crank rating) of your battery. A rating of 400 would give you 30 seconds (give or take an inch) before the battery delivery voltage dropped below 7.2v, a typical cutout figure. If you want more time, a battery CA of 1,000 sounds more realistic - that would give you 60 seconds or so.

A better approach though, is to use the thruster in shorter bursts, allowing recovery time between each burst. Good high CCA batteries recover their voltage very quickly once the demand is off. Lots of spare AH lying around there!

Incidentally, check the cutout voltage setting on your bow thruster - it may be a higher figure, around 9v or so. In which case, you get even shorter an operation time.

All this assuming the batteries were fully charged at the beginning.

 

[vyv_cox]

3 Hp = 2.25 kW. At 12 volts the current would be 187 A. This is not enormous compared with the current drawn by a diesel starter motor, and well within the capacity of a practical cable run.

 

[jimbaerselman]

The HP quoted should be the output. Allowing for inefficiencies, that means a rather bigger amperage input.

 

[Anonymous]

Exactly what problems are you experiencing?

Like others here, I have cables from my main batteries to the bow, for both the bowthruster and windlass. I wouldn't dream of installing a battery up there given that the cabling is already in place...if I was designing a new system I would consider it but I wouldn't change an existing system.

I suspect the the problem you are experiencing is relay chatter, if you have an up/down relay? If so, I have a way round it which works well but confirm that's the problem first.