Bowthruster Battery Install

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Philt66

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Hi, apologies if this has been asked/answered many times but I have searched the forums and could not find a definitive answer.

Just had notification I can get back into my marina to work on my boat from Wednesday so I can move ahead with my bowthruster install.

The unit is 1.3kw / 130 amp. I plan to change my single 125 a/h leisure battery for 2 x 85 a/h connected in parallel and charged by the engine alternator and a Victron Blue Smart 15 A charger. Leisure bank is in engine compartment on starboard side. Suggested battery cable size is 50 mm2 / AWG 1 for a run of 5-10m.

If I sited one of the batteries in the bow, close to the thruster, would I still need to use 50mm2/AWG 1 cables for the connectors between the 2 x 85 a/h batteries? (so one battery in bow and one in engine compartment). Distance would be about 4m between the batteries.

I am fully aware of the impacts of under-sizing cables but the run is quite tricky and 50 mm cables are not that flexible.

Thank you

Phil
 
No. Fit the battery in the bow and connect with smaller cables. Don't forget to fit a fuse at the aft end of the cable and a thermal breaker at the bow battery.
 
I would use a battery to battery charger (adverc is one make) that only tops up the bt battery once the main one is full. Still need fuses each end but it does work and so far mine has been a fit and forget.
 
Boathook said:
I would use a battery to battery charger (adverc is one make) that only tops up the bt battery once the main one is full. Still need fuses each end but it does work and so far mine has been a fit and forget.
Click to expand...

The OP's plan is to split his two house batteries, leave one where it is, put the other next to the thruster, but both still wired in parallel. So a battery-to-battery charger wouldn't be appropriate.
 
The battery threads on here get more and more ridiculous by the day. The OP has a tiny installation, yet we still get suggestions of spending hundreds of £££££s

Just fit the battery at the bow and connect it to the current domestic battery with some cable, fat as sensibly possible, fused at each end. Job done.

Final point to the OP, don't swap the 125ah for 2x80ah, keep the 125ah and fit the biggest AGM you can at the bow.
 
Thank you for the replies. A battery close to the BT seems to be a common thread. I assume I should still size the cables connecting the 2 house batteries based on the BT output. potentially I could reduce to 35mm2 as run between batteries to battery and 2nd battery to BT will be less than 5m. My current leisure battery is 6 years old hence I did not want to risk paralleling with a new battery hence I went for the 2 x 85's (already purchased a pair of Advanced XD85 Dual Purpose Leisure Battery 85ah) as this will give me less electric capacity anxiety when at anchor.
 
Philt66 said:
Thank you for the replies. A battery close to the BT seems to be a common thread. I assume I should still size the cables connecting the 2 house batteries based on the BT output. potentially I could reduce to 35mm2 as run between batteries to battery and 2nd battery to BT will be less than 5m. My current leisure battery is 6 years old hence I did not want to risk paralleling with a new battery hence I went for the 2 x 85's (already purchased a pair of Advanced XD85 Dual Purpose Leisure Battery 85ah) as this will give me less electric capacity anxiety when at anchor.
Click to expand...

You don't have to, the cables will merely act as charging cables if they were, say, 10mm. But, as i said earlier, bigger is better. What you propose above is perfectly adequate. Don't forget the fusing.
 
After delays from Lockdown etc, i have now got my Bow Thruster install 99% complete. I ended up siting an 85A/H battery next to the thruster, connected with 50mm sq cables. This battery is then connected to my house battery with 16mm sq cable. I have a Victron Cyrix CT VSR between the 2 batteries. I know I need to add either a breaker or maxi blade fuses at either end of the charging circuit but I am struggling to work out what they should be rated at. Are the fuses to protect the cables or to stop the Bow Thruster from drawing power from the house battery? The charging cable run is no more than 6m.
 
The fuses are there to protect the cables and to limit the current drawn through the VSR to the maximum rating of the VSR. 16mm cable is rated at 110A and the Cyrix could be 120A, 230A or 400A, so the fuse should be limited to the lowest current rating, which in your case will be the cable. You need to fuse both cables, as close to the batteries as possible/practical.

You can fit fuses at both ends or you can fit a fuse at one end and a circuit breaker at the other (the easiest to get to). A 120A fuse at the least accessible end and a 100A breaker at the most accessible end will provide adequate protection for the cables (the 16mm cable would safe with the slightly over rated fuse for the short time it would take the fuse to blow) should ensure that the VSR is protected from overload whilst having a resettable breaker should the current be excessive.
 
It's actually quite a difficult problem when you look at all the angles.

It depends on what scenarios you choose to design for.
e.g. what happens when the bow battery is getting old and not fully charged?
At what point do you say it's more important to prevent the cables getting a tad warm than to prevent the boat from hitting the pontoon?

A thermal circuit breaker, which will allow those long cables to carry more than their long term rating for a few seconds at a time might be a good choice.
Or, arrange for the VSR to disconnect before operating the thruster.

Some installations, you won't know the bow battery is getting old until the fuse goes in the long cable and suddenly you've got nothing.
 
TernVI said:
It's actually quite a difficult problem when you look at all the angles.

It depends on what scenarios you choose to design for.
e.g. what happens when the bow battery is getting old and not fully charged?
At what point do you say it's more important to prevent the cables getting a tad warm than to prevent the boat from hitting the pontoon?

A thermal circuit breaker, which will allow those long cables to carry more than their long term rating for a few seconds at a time might be a good choice.
Or, arrange for the VSR to disconnect before operating the thruster.

Some installations, you won't know the bow battery is getting old until the fuse goes in the long cable and suddenly you've got nothing.
Click to expand...

This was one my my suggestions in another bow thruster thread, where the OP wanted to use smaller cables. I suggested a pair of normally closed relays connected in series on the VSR negative. The energising coil of one connected to the thruster left circuit and the other to the right circuits.

I think with 16mm cables the OP in this case should be OK, but if he finds the breaker tripping regularly he could retrofit the relays. No loss in trying without, the fuse and breaker would still need to be there, even with the relays in place.
 
Thank you everyone. i have a 100 & 120 amp breaker on order as access at both ends of the circuit is good. If I do get premature tripping I will follow your plan B. I have a battery voltage monitor on the BT battery so I can easily check if it is not recharging.
 
PaulRainbow said:
This was one my my suggestions in another bow thruster thread, where the OP wanted to use smaller cables. I suggested a pair of normally closed relays connected in series on the VSR negative. The energising coil of one connected to the thruster left circuit and the other to the right circuits.

I think with 16mm cables the OP in this case should be OK, but if he finds the breaker tripping regularly he could retrofit the relays. No loss in trying without, the fuse and breaker would still need to be there, even with the relays in place.
Click to expand...
I suspect you are referring to me but there have been a quite a few threads on the topic recently! I initially thought I had 10mm2 cables connecting the house bank and bow thruster battery but it turns out they were 16mm2 and I went with an 80amp breaker and 100amp fuses. Sounds like a could /should have gone for 100/120 but so far good and the relays to disconnect the VSR are currently gathering dust but will be retro fitted if needed. Thanks again for the advice. It was really helpful.
 
Ammonite said:
I suspect you are referring to me but there have been a quite a few threads on the topic recently! I initially thought I had 10mm2 cables connecting the house bank and bow thruster battery but it turns out they were 16mm2 and I went with an 80amp breaker and 100amp fuses. Sounds like a could /should have gone for 100/120 but so far good and the relays to disconnect the VSR are currently gathering dust but will be retro fitted if needed. Thanks again for the advice. It was really helpful.
Click to expand...

Yes, there have been a few similar threads lately. You could have gone 100/120, but if what you have works, no point changing. Glad to hear you got it all working and you're welcome.
 
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