How to manage 2 batteries for diesel conversion?

[Luhrs28]

Hi guys:

I'm mostly over in the Resto section, posting about putting a GM 6.2 diesel in my old Luhrs 28 footer. My question tonight is about how to manage the 2 batteries. Unlike most of you I need both batteries connected to start my engine. But what I'm wondering is what do I run on while I'm cruising around and maybe anchored for a couple of hours listening to the stereo.

Plan A) Only have the switch in the "Both" position when starting the engine, then switch to just 1 battery. But my problem with that is then the alternator is only charging one of the batteries while running.

or:

Plan B) Leave the switch in the "Both" position all the time. (except I'll switch them both off when docked of course)

I like plan B 'cause it's just simpler. Does anybody see a reason why I can't run in the "Both" position all the time?

Thanks,

Bert

 

[Silvertip]

Re: How to manage 2 batteries for diesel conversion?

What makes you think only one of the batteries is being charged when the switch is in the BOTH position. BOTH parallels the two batteries so BOTH will be charged. Either you explained what you want to do incorrectly or you misunderstand how the switch works. It works exactly as labeled. I also question if you need both batteries to start the engine, why do you even need a switch? Diesel trucks have as many as six batteries in parallel and a switch is not used. What makes your installation special??????

 

[Luhrs28]

Re: How to manage 2 batteries for diesel conversion?

Silvertip: Go back and read what I wrote under "Plan A". I said only 1 battery would be charging after switching to just 1 battery.

And yes of course the whole setup can be done without a switch, but in my opinion it's important to be able to switch both batteries to OFF while docked.

 

[Luhrs28]

Re: How to manage 2 batteries for diesel conversion?

It's a GM 6.2 liter diesel. In a truck with this same engine the 2 batteries are connected in parallel all the time. They both power the glow plugs for 5-6 seconds, then as soon as the glow plug light (and relay) shuts off you hit the starter and both batteries power the starter.

A diesel needs fast cranking speed to start, and to do that with 22.5:1 compression takes a big starter that draws a lot of juice. The cables have to be #2 AWG minimum.

 

[sasto]

Re: How to manage 2 batteries for diesel conversion?

Are you running a generator on your Luhrs?.... Onboard battery charger?... That would mean something different.....if not, maybe a simple parallel switch activated from the console during start-up...keep the selector switch on "house"...hit the momentary switch at the console activating a solenoid (similuar to the one in your starting system), which parallels the batteries....the alt will charge the "house" and not the start battery.

 

[boatmanalso]

Re: How to manage 2 batteries for diesel conversion?

I've always been able to start my engine on one battery but what I do is start the boat with the odd or even battery depending on if it is a odd or even day.

 

[dlngr]

Re: How to manage 2 batteries for diesel conversion?

So what good would it do to anchor for a couple hours and run the stereo,and only kill one battery ??

 

[Silvertip]

Re: How to manage 2 batteries for diesel conversion?

With or without a switch, if it takes two batteries to start the engine and you kill or deeply discharge one of them, your engine will not start. Therefore to prevent that you need a third battery for the accessories. Parallel the two starting batteries and put those on BAT 1. Run the accessory battery to BAT 2. Everything on the boat should connect to the COM terminal on the switch (except bilge pumps) for optimum versatility. Run on BOTH for charging or BAT 1 or BAT 2 depending on which needs charging the most. If you don't want the starting batteries paralleled when away from the boat, install a simply ON-OFF battery switch between them.

 

[fishrdan]

Re: How to manage 2 batteries for diesel conversion?

What size are the paralleled start batteries, group 29, 31? How about using a single D6 or D8 industrial battery, that should have plenty of capacity to start your diesel, they are non-marine batteries though. Interstate has a 4DM marine battery, 120#, 1645 cranking amps.

 

[Luhrs28]

Re: How to manage 2 batteries for diesel conversion?

Yes Silvertip I was thinking the same thing, a 3rd battery is probably what I need. But I'm not that happy about adding another 60 lbs. of permanent weight to the engine compartment. The diesel engine is already heavier than the original Chrysler gas V8.

I could mount the 3rd battery up towards the bow, but then I need long cables to get back to the switch. Hmmm.