Bow Thruster & Victron Smart Battery LFP

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neil-langford asked Jul 3, '23

Bow Thruster & Victron Smart Battery LFP

I'm getting pushback from bow thruster manufacturers when I suggest powering the thruster from the very large Victron house bank. It seems they have engineered the thruster motors to run at lower than specified system voltages, due to common voltage sag with lead acid batteries. The use of high quality LFP batteries keeps the voltage high and the thruster motors don't like it. Has anyone else come across this? Sleipner / Side Power (Norway) are one who advise against Lithium. Has anyone used Victron LFP successfully with Sleipner / Side Power thrusters?

Lithium Battery

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Stefanie (Victron Energy Staff) answered · Jul 03, 2023 at 02:41 PM

Hi @Neil Langford,

This isn't a direct answer to your question, but it might be interesting to hear Victron's opinion on bow thrusters powered by lithium batteries in general and the problems this can cause. These include smart lithium batteries from Victron.

Please see the Victron blog Lessons learned: Thrusters, Lithiums and SOC, a bit older, but still up to date.

FWIW: The bow thruster (3.5kw) of my sailing yacht is powered by the starter battery (100AH AGM). During port manoeuvres, the engine is running anyway, so this is not a problem. With larger thrusters, use a dedicated lead-acid battery bank (2 batteries in parallel or series/parallel depending on the voltage).

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Answer 1 · 2023-07-04T03:21:38Z

neil-langford answered · Jul 04, 2023 at 03:21 AM

Appreciate the very prompt feedback. We'll go with AGM batteries ..... N./

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Answer 2 · 2023-07-04T05:01:51Z

mvas answered · Jul 04, 2023 at 05:01 AM

How many amps does your bow thruster use? I have read that some bow thruster could draw, up to, 500 amps! That is more than many engine starters. 500 amps would definitely cause a voltage drop on a small lead acid battery bank. How are you calculating the size of the new dedicated bow thruster AGM battery bank?

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kevgermany ♦♦ commented · Jul 04, 2023 at 09:32 PM

I think you'll find that's why @Stefanie (Victron Energy Staff) suggested parallel batteries for larger setups than hers.

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neil-langford commented · Jul 16, 2023 at 11:33 PM

I was originally planning to use the very large smart lithium house bank, and figured capacity would not be a problem. However it seems that both Victron and the thruster manufacturers do not like this approach (see answer from Stefanie above). It seems that the bow thruster manufacturers have been forced to engineer their systems to run at low voltages - as significant voltage drop is extremely common during use. So, if you power them on a big Lithium bank with appropriate cabling, and the voltage does not drop during use, the motors can burn out(!). I know of one dealer here in Australia who had this problem. Victron also say that they do not want thruster motors on their smart lithium batteries. So, I will now change planning and use series / parallel AGM batteries, for a total capacity of about 150ah at 24vdc.

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