1/2/Both/Off Switch >>> Alternator Diodes

[rardiH36]

My alternator is Yanmar OEM 1980 vintage. After all these years, still puts out charge voltage when the engine is running!

My 1/2/Both/Off switch is wired so that "OFF" totally removes both my batteries from the alternator charge circuit. I know that moving the switch to off when the engine is running causes a spike of "whatever" that can result in the alternator's solid state circuitry (the diodes) to fritz out.

But what about the opposite? If I start the engine with the switch in the "OFF" position, and then move it to say (both) to connect the alternator charge current/voltage back to the batteries, will that cause damage?

This is reason I am asking. I want to see if the heavy duty Li-Ion jump starter I have for my car will start my boat's Yanmar engine with absolutely no (zero) assist from any 12v battery still in the circuit. Even a very depleted battery will still have some residual voltage/amperage left that might assist the jump starter. I have already successfully started the engine with a pretty depleted 12v lawn motor battery substituted into my boat's battery circuit. With the normal batteries disconnected. In this "experiment", the alternator is sensing the load of the lawn motor battery. So all is good.

My concern about these Li-Ion jump starters is that when connected normally, do they also direct voltage/current towards attemtping to recharge what might be totally dead batteries? If it takes me say 30 seconds between the time I connect the jump starter cables to the battery posts before I actually push the start engine button, might there be not enough reserve still left in the jump starter to start the motor? The way around this scenario is to disconnect the batteries from the circuit and start the engine with only the Li-Ion jump starter. Then after a successful startup, turn the 1/2/Both/Off switch back to 1 or 2 or BOTH so the engine's alternator can begin to recharge the boat's dead batteries.

Thoughts?

 

[Davidasailor26]

Lots of factors to consider here. The risk to alternators happens when they’re putting out lots of amps to a battery and then suddenly have no sink for that current, causing a voltage spike. If the switch is already Off then there can’t be any current going to the batteries, thus no risk of a spike. What I don’t know is if the lithium booster itself could be a sink briefly after the engine starts, and if it will suddenly shut itself off or if unplugging it would cause a spike, without having other batteries in the circuit. If the boost pack doesn’t absorb significant current from the alternator then I’d guess there’s no risk of that, so your strategy could work. But I’ve never looked at the exact functioning of those boost packs to see if they absorb charge that way, so your mileage may vary.

Practically speaking though these boost packs are generally built for starting much larger engines than most of us have, even with dead batteries. I have one and I figure if I ever use it I’ll just connect it in parallel with the start bank the way its instructions suggest.

 

[rardiH36]

David26,

Gosh you are a quick typist and very good at getting your thoughts together in short order!

Thanks your comments. One realization that I have is that compared to most newer cars (and maybe also newer boats?), which I believe now have very efficient brushless starter motors, my 1980 starter motor is a real current hog. It protests unless my two group 27 deep cycle batteries are pretty much fully charged. Hence the Li-ion jump starter probably needs to have virtually 100% charge to devote to my start engine task. I have looked up on the internet for information whether these jump starters don't actually put anything out until the sudden demand of the ignition switch being activated. But I haven't been able to find a clear answer. If they don't do anything until the sudden demand for starter motor current, then maybe my concerns of the jump starter depleting itself into the dead battery might not be warranted. But I don't know.

 

[dlochner]

It shouldn't take both batteries being fully charged to start the engine, unless the batteries are pretty old and have lost much of their capacity. If that is the case, then new batteries should be at the top of the list. Also make sure the battery connections are clean. It may also be time for the starter to be rebuilt with new brushes.

To test the the starter with the batteries, disconnect the negative lead from the battery and connect the negative lead from the Jump starter to the battery's negative lead. The Jump starter positive can go to the battery's positive. Place the switch on 1 or 2 depending on which battery you are using.

 

[Davidasailor26]

It shouldn't take both batteries being fully charged to start the engine, unless the batteries are pretty old and have lost much of their capacity. If that is the case, then new batteries should be at the top of the list. Also make sure the battery connections are clean. It may also be time for the starter to be rebuilt with new brushes.

+1 for all of this. Connections and crimps can fatigue over time; and some older boats weren’t designed with much margin for error in their wiring harnesses. If starting is iffy I’d check the voltage at the starter when cranking, and compare that to the voltage at the battery posts. If the difference is significant then start tracing wires to see where the drop may be coming from.

 

[Rick Webb]

If the test is will the jump starter alone start the boat? But you are concerned about the alternator remove the concern by removing the belt and taking the alternator out of the equation.

 

[east coaster]

Maine Sail aka marine how to has a couple of great articles on battery switches, alternators and wiring. I don't have one but Sterling makes a device that stops/prevents alternator damage if switched off while running. It's all on marine how to website.

 

[Stu Jackson]

This is reason I am asking. I want to see if the heavy duty Li-Ion jump starter I have for my car will start my boat's Yanmar engine with absolutely no (zero) assist from any 12v battery still in the circuit.

Then just disconnect the boat batteries. Remove the (-) from the battery's post(s). Should be easy to do. Keep thre jumper pack connected so the AO has somewhere to go. Then shut down engine quickly.

 

[rardiH36]

So many good suggestions from very knowledgeable boaters. I have taken everything "onboard".

I wasn't clear about both batteries being "pretty much fully charged". If one of my two batteries is at max capacity (i.e. at say 11:00am when the solar panel charge controller shows +/- 14v), then it on its own will will start my engine without hesitation. But if the other battery is say reading 12.2V, and I use only that battery, the starter motor will protest before turning over.

Several years ago (and many hundred starts since then), I did remove the original equipment starter for inspection. Quite obvious was the brushes were severally worn. I remember finding online a supplier who sold me a complete new brush plate which I installed. Before closing the starter back up, I did the tests specified in Yanmar's service manual. And I took care to clean the armature. So I am pretty confident that my starter motor is OK.

As to the observation that "older boats weren't designed with much margin for error in their wiring", I fully agree. Just last month I disconnected all of the lugs at both my batteries, at the 1/2/both/off switch, and at the starter motor. All the interfaces were clean. But for sake of good measure, I gave all the interfaces another cleaning before reconnecting. I am not at my boat right now, but from memory the cables between my batteries to the switch and then to the starter are 8 gauge. The total distance between the batteries to the switch to the starter is about 7 feet. I am thinking that 6 gauge might have been the norm only several years after my 1980 construction? I have often thought to replace with larger cable. But the old stuff still does its job!

Good suggestion to remove the alternator belt. Then check that the jump starter on its own will make the engine run.

My question though is still in doubt: Before actually turning the engine start key (or pushing the button), do Li-Ion jump starters when connected per the instructions also direct voltage/current to recharging the 12v battery? Tomorrow I will attempt a new experiment: Using my 2005 Toyota. Firstly deplete my old 12v lawn mover battery to virtually dead. Remove the leads from my Toyota battery. Replace with the lawnmower battery. But also put my Volt/Amp meter in line between the jump starter and the 12v lawnmower battery. See if any current is passing through. If not, then the mystery is solved. The jump starter doesn't do anything until the starter key/button is switched on and the jump starter senses a significant sudden demand for current.

 

[Stu Jackson]

My question though is still in doubt: Before actually turning the engine start key (or pushing the button), do Li-Ion jump starters when connected per the instructions also direct voltage/current to recharging the 12v battery?

Wouldn't that depend on how & what it is connected to when it is turned on?