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lithium and agm common ground

Atomvoyager

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Sep 5, 2021
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I'm installing Lithium "house" batteries and an AGM engine start battery on a sailboat. They are isolated on always separate circuits for safety. The solar is charging the lithium and I have a Victron B2B charger on a switch to occasionally charge the AGM from solar via the lithium bank. The engine alternator charges the AGM and I have a Renogy 40A DC-DC charger to transfer the alternator charge to the lithium bank. I plan on using a common negative bus bar for both banks. Is that OK?
 
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Yes, best option on a boat is to have all your grounds combined, and bonded to the engine/prop. If you're doing an inverter/charger and will be connected to shore power, you should also invest in a galvanic isolator as that will prevent your shaft/propeller from becoming the grounding rod for the rest of the marina.
 
Thanks. That seems obvious but I wanted to confirm since this is my first time to combine lithium and agm.
 
Don't use the prop for your negative. When it turns the connection will fail. :)
 
Don't use the prop for your negative. When it turns the connection will fail. :)
Well, unless you have a well maintained rubber soft coupling, one should always assume that your engine is electrically connected to the shaft and prop. :)
 
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