Engine Starting Video / Real World Amp Load Data

[Acoustic]

Hi All,

I saw a need for something often debated but rarely ever clarified.

Many sailors/boaters often believe that you need to switch back and forth between your house bank and your start bank or as I prefer to call it, "emergency bank" of batteries for engine starting.

The truth is you don't. Switching back and forth from bank 1, to bank 2, only leads to eventual human error, as has been reported here and elsewhere all to often. By switching back and forth you will, in due time, fry your alternator diodes with a mental lapse or via a crew member who's been asked to switch banks.

The reality is that your system should be wired to prevent this but that's another subject for another day and most will never get this far down the project list. I am simply trying to prevent any more fried diodes with this video!

Another mis-truth that is often perpetrated amongst sailors is the absolute need for a "starting" type battery to start your small diesel engine.

This video will show why it is not necessary to use a thin plate high CCA rated battery to start a small auxiliary diesel engine. The max load when starting my engine, a four cylinder 44hp, is 132.5 amps for less than two seconds. Any deep cycle marine battery you can find will have a LOT more than a 130+/- CCA, CA or MCA rating.

Start batteries don't, and won't, generally last as long as a true thick lead plate deep cycle battery so dollar for dollar deep cycles will generally cost less in the long run.

You should not be afraid to use deep cycle batteries for your starting/emergency bank or to start your engine using your house bank. I've always started my engine on my house bank. Hopefully this video will give some of you piece of mind around the subject of starting and how little it actually consumes.

What Happens When My Engine Starts Video (LINK)

Or click the photo:

Stats:

Engine - 2003 Westerbeke 44B, 44hp four cylinder diesel (marinized Mitsubishi).

House Bank - 2 Group 31 batteries 120 ah rated each / 240ah bank

Glow Plugs - They consumed between 30 and 56 amps for about 8-10 seconds.

Starter - Max draw of 132.5 amps for about two seconds.

Battery Monitor - Xantrex XBM




Disclaimer: Some engines may take longer to start than mine does but the data will still be similar and close. All in all we're still only talking about perhaps a tenth or two of an amp hour to start a small aux diesel..

[hellosailor]

Nicely done, Acoustic! Makes you wonder why no one ever documented it that simply before.

Of course, you've got glow plugs and a co-operative engine, rather than the "roooga-roooga-rooooga" beasts that some other boaters have.[g]

[Acoustic]

Originally Posted by hellosailor

Nicely done, Acoustic! Makes you wonder why no one ever documented it that simply before.

Of course, you've got glow plugs and a co-operative engine, rather than the "roooga-roooga-rooooga" beasts that some other boaters have.[g]

Hence the disclaimer.. Still, it's not the load most think it is!

[S/V Antares]

Thanks for the video. You are correct, Even very large Diesels do not pull a zillion amps as some believe, The more cylinders the faster the start.

I have a separate starting battery because human error can lead to a dead or very low house bank

[Charlie]

I can't believe I enjoyed that video. It was interesting. Thanks for sharing Acoustic.

[hellosailor]

I got to the same conclusion the paper way. [Warning, mathematics ahead!]

2 kilowatt starter, more or less, 5 seconds worst case, total load 10 kilowatt-seconds. Divide by 12 volts, yeieds 833 amp-seconds. Divide by 360 to convert to amp-hours, 2.3 amp hours of drain for a worst-case scenario, more like half for the well-behaved engine in warm wx. No big deal.

As long as it starts, and doesn't start playing "Oh, I'm a diesel engine, I'm merciless about air in my fuel" or one of those other traditional tunes.[g]

[GordMay]

Thanks for the nice presentation, Acoustic.

A general rule of thumb is that the starter current will be about 1 A - 1.5 Amps, per cubic inch of engine displacement.

Since the Westerbeke 44B is specified at 107.0 cu. in. displacement, we’d expect to see somewhere between 107A to 160.5 Amps ~ Acoustic’s starter measured right in the middle of the “expected” range at 132.5 A.