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Old 20-05-2018, 12:01   #1
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Boat: Lagoon 400S2
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L400 Generator start battery

Today i have installed my LFP bank along with the victron 5000 quattro ant tested all the logic for charging. Also measured all voltages for the remaining AGM start batteries.

Big surprise - the engine batteries are full, 13.8V float on shore power, but the Generator battery has only 12V, almost empty - the boat is on shore power for 5 months with charger enabled...

A lquick look in the schematics reveals that the generator start battery is stand alone and not connected to any charging source on board, no separation diodes, nor crystec charger outputs.

I connected a crystec to the half past dead battery, and the next surprise 7.5V on the connection on the main power switch.

Some more investigation reveals the generator battery is even not connected to common ground like all other batteries on board. Who installsin the factory such a stupid set-up? Is there any hidden reason to completly separate the generator start circuit even on common ground - that I have not understood yet or is it just the french laisez-faire mentality to forget to charge the generator starter battery because european vessels usually do not buy the A/C option?

This system definitely needs a review.

Same for the factory installed inverter. Stupid set-up with excess wires around the vessel. inverter goes to a circuit braker in a separate housing next to it, 2ft away is the central breaker housing for the 220v house installation and the breaker housing for the A/C, but the inverter wires go diagonal through the vessel bellow the chart table, where in a separate DIN housing a relay takes care to disconnect the inverter when 220v shore power or generator power is available. this relay could have been placed along with the circuit breaker and directly connected to the main distribution just next to it saving 10-20 meter of excess cabling. They just throw randomly components in cavities with no plan... also lots of possible problems by using plugs everywhere to interconnect cables. really unnecessary and begging for trouble...
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Old 20-05-2018, 12:52   #2
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Re: L400 Generator start battery

Hard to imagine why you'd possibly consider a separate battery for a generator on a 40' cat. Clearly the manufacturers have given up all pretense of having them be sailboats.
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Old 20-05-2018, 15:35   #3
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Re: L400 Generator start battery

Did you buy this boat from new?


Diesel generators often charge their start battery from an alternator on the generator engine. if you have a standard lead acid battery as the starter battery and you never run the generator then I guess it would discharge slowly over time. I guess a battery combiner would solve this issue in this circumstance so it could be charged from one of the battery chargers or the house bank or the solar array.


If you don't want the weight, then easy enough to wire it to a propulsion engine start battery.
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Old 21-05-2018, 00:27   #4
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Re: L400 Generator start battery

Well, I am aware of the possible solutions. I am just angry about the engineering skills of the manufacturer.This is not a issue only on my boat, but built in since the first 400 and in continues in the 400S2, I am curious, if it is addressed in the other models, but I doubt it. When you look in the circuit diagramm, it was designed that way from the beginning. A short bridge to the breaker switch next could make the generator start battery obsolete, same can be achieved with a bridge to the house battery breaker switch. There is no reason the battery does not have a permanent connection to common ground as all other batteries have. Just saying....


btw. a battery combiner or charger output wire or charge distributor diodes would only work if the battery is connected also to common negative, what is not the casein the original dessign, a four inch cable would do the trick.
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