What battery for 30hp diesel?

Xfaxman · Jul 5, 2013

alchemysa said:
Hmmm, this not looking good. Not a lot of replies so far but the general advice seems to be that 650cca should be sufficient. Perhaps I do have an electrical problem, or the new battery is dodgy. (I'll put it in my 4WD and see how it goes.) I've gone to some effort to ensure I have good earth and good contact at the starter but perhaps its still not good enough. I've got 12v at various test points but that doesn't mean I'm getting all the boot I need.

The voltage at the starter will let you know what the problem is. Measure the voltage of the battery with the probes on the terminals, not the cable clamps. 12.6 is full charge. The voltage should be be the same both places while cranking.

This video shows what I mean. Starter Voltage Drop - YouTube

TedLaRue · Jul 5, 2013

The starter gets power through a solenoid relay (electrically controlled switch). I don't know your machine. Sometimes these solenoids are external devices, with a heavy gauge wire from the battery to the solenoid, and another one from the solenoid to the starter, and also at least one or maybe two small gauge wires attached to the solenoid. And sometimes they are built into the starter unit. I think it is safe to say that newer machines have them built into the starter unit (the starter motor and bendix).

Xfaxman's advice to check the voltage at the main starter terminal when you are cranking is an excellent idea. Building on that, if the voltage there is ok, then there are two possibilities: (1) if your solenoid is not part of the starter unit, then your starter motor may have problems (2) if the solenoid is part of the starter motor unit, then the contacts inside the solenoid may be oxidized as JasG suggested in an earlier post.

CliffordK · Jul 5, 2013

You don't need AH, unless you're planning to crank the engine over for an hour or so before it starts.

CCA is probably somewhat more representative of the battery.

Odyssey Batteries makes some excellent, albeit a little expensive batteries. If their PC2150 battery won't crank it over, then you have issues.

Anyway, it doesn't hurt to try connecting two "good" batteries in parallel (12V, plus to plus, neg to neg).

How big is your battery cable? Perhaps it is undersized for your power draw. I also assume your battery is "new". Does the battery hold at least 12.6V overnight?

Here is a pretty simple load based Battery Tester from HF.

alchemysa · Jul 5, 2013

TedLaRue said:
The starter gets power through a solenoid relay (electrically controlled switch). I don't know your machine. Sometimes these solenoids are external devices, with a heavy gauge wire from the battery to the solenoid

Solenoid is separate. Battery is brand new and cranks my 4WD over just fine so it should be OK. When I touch power directly to the starter it spins OK so I hope thats OK too. So hopefully the problem is just my cables. I'm just using 2 pairs of quite heavy jumper leads at the moment. I doubled them up to run parallel, so I had 2 clamps to earths and 2 clamps to a flat bar bolted to the solenoid terminal, plus they were separately clamped to large bolt on battery terminals. I thought this would give me sufficient contact to happily turn over this quite small engine for a 'bench test' but perhaps not. I'll have to get some proper bolt on cables. It looks like my problem is stupidly self inflicted. My original question of whether the battery is big enough seems to have been answered. Thanks gentlemen.

The pic attached is from the manual. Its actually a marine engine.

Xfaxman · Jul 5, 2013

alchemysa said:
Solenoid is separate. Battery is brand new and cranks my 4WD over just fine so it should be OK. When I touch power directly to the starter it spins OK so I hope thats OK too. So hopefully the problem is just my cables. I'm just using 2 pairs of quite heavy jumper leads at the moment. I doubled them up to run parallel, so I had 2 clamps to earths and 2 clamps to a flat bar bolted to the solenoid terminal, plus they were separately clamped to large bolt on battery terminals. I thought this would give me sufficient contact to happily turn over this quite small engine for a 'bench test' but perhaps not. I'll have to get some proper bolt on cables. It looks like my problem is stupidly self inflicted. My original question of whether the battery is big enough seems to have been answered. Thanks gentlemen.

The pic attached is from the manual. Its actually a marine engine.

Yep, the clamps are the problem. I would expect 3-400 amp initial draw and no start cranking draw of 200-275 amps, maybe more on that new old diesel. Hard to get that much current through the small contact area of jumper cable clamps.

Are you going to put this engine in your Honda Farm Bike? :laughing::laughing: