Starting Battery Sizing

[Head Sail]

I installed a 80 Ah GM style (side posts) starting battery for my 23hp diesel engine thinking it should be plenty to crank that little engine. What I am finding out is that the power to crank the engine is not really an issue, but the glow plug heating prior to cranking the engine takes so much power that the small battery has difficulty cranking the engine if the starter motor is engaged immediately afterwards. I can see the volt meter peg at 10v during glow plug heating. I have to wait 10 seconds or so to let the battery recover from the drain. Just wondering if I would have been better off with a deep cycle or is this a typical problem.

 

[Davidasailor26]

You might want to check the voltage at the battery posts themselves when the glow plug is on. You might have some bad connections along the way causing voltage drops even if your battery is strong enough.

 

[Ken Cross]

You might want to check the voltage at the battery posts themselves when the glow plug is on. You might have some bad connections along the way causing voltage drops even if your battery is strong enough.

Yep. A meter on the battery terminals is the right way to investigate this.

Ken

 

[Mark Maulden]

Yep

 

[Stu Jackson]

What I am finding out is that the power to crank the engine is not really an issue, but the glow plug heating prior to cranking the engine takes so much power that the small battery has difficulty cranking the engine if the starter motor is engaged immediately afterwards. I can see the volt meter peg at 10v during glow plug heating.

I agree with the yeps.

At least you know to not hold the glow plug button in and push the start at the same time.

Your experience is NOT unusual. The answer is ALMOST ALWAYS a BAD ground connection at the engine of the OEM ground from the batteries.

How do we know this?

Because we have had 30 years of C34 experience collected on our website (www.c34ia.org), in addition to the contributions made on this forum by folks with similar if not identical systems.

My boat is 30 years old. AGMs have their uses, but my boat ain't one of 'em. But that's NOT the issue.

You have a connection and maybe old wire issue on your boat.

Do you have a solenoid for your glow plugs? I added one for mine, which reduces start time from 30 to 15 seconds when cold. http://www.c34.org/wiki/index.php?title=Faster,_More_Efficient_Glow_Plug_Heating_with_a_Solenoid

We've been saving this stuff up for over 25 years. Come join us there, as well as here. http://c34.org/bbs/index.php/board,11.0.html

Unless you're there already and too shy to post.

My reserve bank is 60ah and works just fine for our M25 engine.

 

[Head Sail]

Thanks for the responses. I'll check voltage at batteries when I get a volunteer to hold the glow plugs on. I'm not suspecting a connection issue from the battery to the starter since the starter cranks just fine and will start without glowplugs on warm days.
Stu mentions this is not unusual for a C34 but I'm wondering if OTHER diesel engines see the same characteristics. Specifically a large voltage drop when glowplugs activated followed by a 10 second recovery period before the battery comes back up to sufficient voltage to crank the starter.

 

[NYSail]

I just went through a problem..... voltage would drop lights would flash when I should have had plenty of capacity. Turned out to be a bad connection. One day on hook and could not start batteries. Now two + days full refrig, lights, stereo etc and engine turns over immediately.
check all neg connections!

 

[Terry Cox]

FWIW, we have two engines that rely on one group 24 starting battery that has always been ample over the years. No glow plugs for the main 4JH2-TE 57HP, but the three cylinder Kubota Genset does. Onan (the Genset maker) recommends 30 second glow plug warm up. Never had an issue with the group 24 having enough juice. Perhaps something else is going on, as suggested by the previous posters.