My skiff can carry 2 batteries that are connected in the normal method on a 1/2/both switch. I am considering a lithium for position 2, as that battery is the only source for a TM (via dedicated breaker). Understanding that the #2 battery (lithium) cannot be used alone as a cranking battery, could it be in used in the BOTH (parallel) configuration to start the outboard if battery #1 is compromised? That would split the alternator output between a lithium and an AGM for the duration of that run. What say y’all? TIA
Short answer. I don’t do it. The voltage difference will hurt the batteries. Second if your outboard is not recommended to run on lithium then don’t do it.
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No, it’s a yamaha. I had this crazy thought that I could start it that way and run it for a while, then stop and switch to the AGM battery and maybe get it to start and head home. I can always pull start it…
My understanding is the problem with using lithium for cranking is that when the engine is running if the BMS shuts the lithium battery off suddenly it can damage the engines charging components. If my cranking battery died I would use the lithium to crank the engine but then switch the battery back to the AGM. My Mercury allows for a lithium cranking battery but I am running a AGM. Easiest solution is carry a NOCO jump pack for dead battery.
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Yes, I have a jump pack. Good option. And I have always heard that it is unsafe to operate the battery switch while the engine is running.
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I say YES!
And agree that the alternator will be loaded with the resistance of the AGM in the BOTH position.
Since the actual voltage inside your lithium is higher than your AGM, it will probably be charging your AGM as soon as you switch to BOTH.
And if your switch has “Ignition Protected” on it you can switch from BOTH back to 1 after you get your outboard started.
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Great info @MariettaMike . Thank you.
Found this in the description for PERKO switches:
Selector switches are designed with a “make before break” feature. This allows switching between the “1”, the “ALL” and the “2” positions while the engine is running.
Some great information.
I do not recommend, you re mixing batteries with very different voltages. The Li will see a surge and pending the BMS may or may not be able to manage it. Second is your outboard will also experience the same said surge. This can cause long term issues. Finally you may be able to start and idle the engine but pending the stator voltage output and the Li BMS this can cause the BMS to go into protect mode, shutdown and your outboard will shutdown.
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I usually have my jump pack on the boat, but when I planned out my electrical systems I purposely went with 3-12v lithium trolling batteries on purpose when wiring to 36v. My batteries all sit next to each other in the console. If I ever in a need of a jump I can disconnect trolling motor battery wiring and hook it up to my 12v lead acid engine starting battery without a switch and hopefully give motor enough juice to crank. Then once running I can remove those jumper wires.
Haven’t had the need to test it yet, but it should work.
Same idea. I don’t know why I couldn’t start the motor in BOTH, then switch to ONE (lead acid). Hope I don’t have to test it…
Not with the newer switches.
You need to be careful, look for something like the following pending the switch manufacture.
Note our Blue Sea 6007 boat battery switch has make-before-break contacts. This means as you rotate from 1 to 2 to BOTH, the next position is closed before the previous position opens. This allows for safe switching between 1, 2 and both while your engine is running without damage. Never rotate through position OFF though with the motor running, if may damage the engine. So always rotate through BOTH while changing from position 1 to 2 while the engine is running.
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Yes, thanks @iMacattack . I checked that my Blue Sea switch is “ignition protected” and “should never be switched to OFF before securing the engine”. Honestly, this would not be my first back up option. This has been a good discussion. Thank you all.
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