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paulmw avatar image
paulmw asked

Charging circuit - house bank first?

Small sailboat, 200ah house bank, ~80ah starter battery. Question is - why recharge the starter battery first (as I see in all the Victron diagrams)? Seems to me that my 70a alternator would be best paired with the house bank, which is likely to need more (quicker) recharging - after all, the starter battery is only used to start the engine - 190a (CCA) in my case for maybe 5 seconds, maybe 0.5% of its capacity, whereas the house bank could be down 25-30%. So it seems to me the priority should be to recharge the house bank, then the starter...meaning that a 20a or even 10a Orion-TR would be fine to recharge the starter. Critiques welcome!selene-power-distribution.jpg

orion-tr smartorion dc-dc
selene-power-distribution.jpg (73.9 KiB)
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2 Answers
kevgermany avatar image
kevgermany answered ·

The assumption made in the Victron diagrams is that number 1 priority is the the engine will start when needed. I.e. starter battery always fully charged.

DC:DC chargers will only start charging once input voltage is high enough. A large house bank will take all the alternator output until almost fully charged. If the usage pattern is such that the engine isn't run until starter battery fully charged, over time there will be a dead starter battery.

An alternator will usually replace the starter current in less than a minute. House banks take hours.

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JohnC avatar image
JohnC answered ·

@paulmw

There's a risk of smoking the alternator with continuous high demand on it, possibly at low revs and poorly ventilated in a bilge. Many people have chosen Orions of specific output to control this in the Starter > House scenario. The new Orion XS has adjustable output and should be popular.

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