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Bow thruster - battery type; and charging from shore power


Hawksbill

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9 minutes ago, nicknorman said:

I think discharging at 1C is their normally rated discharge current, so you’d need 3 or 400Ah. No doubt they would last longer if the discharge was kept below 0.5C but then again with the life being so long, does it matter?

 

All a bit circular as their long life depends on them being treated well, e.g. charging and discharging at 0.3C..!

 

It is suggested in the stuff I read that the higher rates they are discharged at and in particular, charged at, the shorter the life. 

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40 minutes ago, MtB said:

 

All a bit circular as their long life depends on them being treated well, e.g. charging and discharging at 0.3C..!

 

It is suggested in the stuff I read that the higher rates they are discharged at and in particular, charged at, the shorter the life. 

Fast charging is definitely bad, as it can cause lithium plating especially at low temperatures. (And of course that raises another issue if the batteries are located outside the heated space) but I think provided the discharge is limited to 1C there is no major loss of cycle life. And of course we are talking about high discharge just for a few seconds to a minute, not many minutes, so internal heating is not going to be an issue.

 

My CALB cells claim 4000 cycles to 80% DoD, and also specifies 1C as maximum continuous discharge, 2C for 3 mins and 3C for 30 seconds. Although whether you get to do that AND get the 4000 cycles isn’t clear! But considering a typical application of the bowthruster will only take a few % of discharge I think calendar life is more likely to be the limiting factor.

 

Of course the other advantage of Li is the OP’s problem of using the BT to moor, then shutting down before it can be recharged, which is ideal for them.

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23 minutes ago, nicknorman said:

And of course we are talking about high discharge just for a few seconds to a minute, not many minutes, so internal heating is not going to be an issue.

 

That may depend on who is 'on the button'.

 

I have heard, and seen, a few NB's steered by the bow thruster, you can hear them coming half-an-hour before you see them

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2 minutes ago, Alan de Enfield said:

 

That may depend on who is 'on the button'.

 

I have heard, and seen, a few NB's steered by the bow thruster, you can hear them coming half-an-hour before you see them

This can be true! But even so, I doubt the duty cycle approaches even 50% so the average discharge current would be below 0.5C

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If my understanding is correct the OP has a 24V bow thruster and  a 12 volt starter battery. This makes the common charging starter/bow thruster combination, like mine both 12 volt so easy and fitting a small solar panel keeps both charged. 24V makes it easier to combine domestic and bow thruster,  but I don't know of any dual output 24V solar controllers. So maybe the 240 charger is a good solution if worried about cooking the batteries over a long period on charge just got a 7 day time switch and charge for a few hours once a week.

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16 hours ago, Detling said:

So maybe the 240 charger is a good solution if worried about cooking the batteries over a long period on charge just got a 7 day time switch and charge for a few hours once a week.

Thanks for all your input which has been incredibly helpful - I will investigate the best way to go over the next few weeks (mainly probably between 1. using a VSR to parallel the BT and domestic  battery only when the charger is on, and 2. second mains battery charger at the bow for the BT battery). 

Just one question re the comment on concern over cooking batteries over a long period, say if on permanent charge: Would leaving a 240V charger permanently (ie when on shoreline, which is 24/7 when not running the engine, as I’m in a marina and not a live-aboard) trickle charging the 24V BT battery really be a risk to the battery - after all, that’s exactly what’s happening with the main domestic 24V bank being charged mainly 24/7 through the Combi charger when attached to shoreline? 

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2 hours ago, Hawksbill said:

Thanks for all your input which has been incredibly helpful - I will investigate the best way to go over the next few weeks (mainly probably between 1. using a VSR to parallel the BT and domestic  battery only when the charger is on, and 2. second mains battery charger at the bow for the BT battery). 

Just one question re the comment on concern over cooking batteries over a long period, say if on permanent charge: Would leaving a 240V charger permanently (ie when on shoreline, which is 24/7 when not running the engine, as I’m in a marina and not a live-aboard) trickle charging the 24V BT battery really be a risk to the battery - after all, that’s exactly what’s happening with the main domestic 24V bank being charged mainly 24/7 through the Combi charger when attached to shoreline? 

 

I get the feeling that whoever made that comment still thinks battery chargers have no voltage regulation and no ability to drop to a float voltage. Unless there is a cell starting to short, leaving batteries on charge from a modern multi-stage charger is normally perfectly safe as long as the Combi is set properly so it can't use battery power to charge the batteries when the mains fail and  whatever it's voltage profile is matches the batteries under charge.

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2 hours ago, Tony Brooks said:

 

I get the feeling that whoever made that comment still thinks battery chargers have no voltage regulation and no ability to drop to a float voltage. Unless there is a cell starting to short, leaving batteries on charge from a modern multi-stage charger is normally perfectly safe as long as the Combi is set properly so it can't use battery power to charge the batteries when the mains fail and  whatever it's voltage profile is matches the batteries under charge.

It seems most battery failures these days are from positive grid corrosion and not sulphation, possible causes are long solar charging when batteries are full and/or float charge voltages to high.

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1 minute ago, Detling said:

It seems most battery failures these days are from positive grid corrosion and not sulphation, possible causes are long solar charging when batteries are full and/or float charge voltages to high.

 

I think that you may be correct, I have never been too happy with a 13.8V float that I have seen on occasions

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On 12/10/2021 at 10:43, Tracy D'arth said:

NiFe submarine batteries would be brilliant, not many about though.

 

Depends whether the BT motor will tolerate the wide voltage range between charged and discharged without slowing down unacceptably 

Edited by cuthound
Clarification
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