Re: A54 bow thruster seal replacement?

Scott SV Tengah


When I was troubleshooting my 1 year old replacement BT motor, those were the words out of the mouth of the lead tech at Sleipner USA (IMTRA). They had some trouble with lifepo4 equipped boats because they designed it to operate at much lower voltage than the lifepo4 batteries provided under load. Perhaps they were trying to get out of warranty work, but that's what they stated. Turns out my trouble was something else, btw.

Regarding the shutoff switch, apparently newer A54s came with an emergency shutoff switch in the bow locker. Olivier suggested in his survey that I install one. I did a bit of asking around and my understanding is there was an A54 that had the solenoids melt closed (probably due to high amperage as a result of low voltage) and thereafter it was recommended that you have the emergency shutoff switch and run the genset and chargers when you're using the BT. It was third hand, but I also definitely have read, more than once, the recommendation to run the genset/chargers in docking operations.

I had the Sleipner shutoff switch but it's not that waterproof and quickly failed in that sometimes wet bow locker. I now have three 450A fuses, one for each pair of batteries, installed.  I also have a third battery switch at the passage berth dedicated to turning off the BT power in an emergency.

On Mon, Dec 14, 2020 at 5:22 PM Dean Gillies <stella@...> wrote:
Hi Scott,

On Tue, Dec 15, 2020 at 11:53 AM, Scott SV Tengah wrote:
That said, lower than 22v is very plausible with normal batteries.
In an Amel, yes, but not always.
A fully charged 115Ah AGM (such as Rolls S12-128AGM) will deliver 67A for two minutes while retaining terminal voltage above 12V.  Put 12 of these in a 2S6P arrangement and you get 400A at 24V. That's almost 10kW delivered to the cable with terminal voltage above 24V. In an Amel the voltage drop at 400A would be around 2V, hence 22V delivered to the BT. However, in a boat where the batteries are located close to the BT, then the voltage drop in the cable can be much less, so the delivered voltage to the BT will be much closer to 24V. 

I find it difficult to believe Sleipner would produce a "24V" BT which does not operate reliably if powered with 24V which is exactly what LIthium batteries would provide in an Amel cabling setup.

Btw I didn't quite understand ... why (and where) did Amel ask you to install a shut off switch? I understand there is no breaker/fusing on the BT cables, which is interesting in itself.

Cheers, Dean
SV Stella A54-154

2007 A54 #69
SV Tengah

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