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Old 03-10-2008, 13:42   #1
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Engine Starting Video / Real World Amp Load Data

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..

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Old 03-10-2008, 14:34   #2
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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]
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Old 03-10-2008, 14:36   #3
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Originally Posted by hellosailor View Post
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!
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Old 03-10-2008, 14:57   #4
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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
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Old 03-10-2008, 15:09   #5
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I can't believe I enjoyed that video. It was interesting. Thanks for sharing Acoustic.
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Old 03-10-2008, 15:28   #6
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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]
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Old 04-10-2008, 11:33   #7
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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.
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Old 18-11-2010, 18:19   #8
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Quote:
Originally Posted by hellosailor View Post
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]

Not to be nitpicky..... well maybe.... There are 3600 seconds in an hour. By your figures that'd be 0.23 amp hours drain.

Jason
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Old 18-11-2010, 20:25   #9
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And it took you THIS LONG to catch that mistake?

This is why you should never, ever, believe any numbers you find on the internet, unless they've been put there by a federally licensed mathematician. Which I never will claim to be.

Next you'll be wanting to know what "yeieds " means, I suppose? <G>
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Old 19-11-2010, 02:06   #10
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I know this an old thread, but its likely to show up in searches.
I hesitate to criticize Maine Sail as you do some fantastic articles, but in this case I think the equipment you are using is not suitable. You really need to use an oscilloscope to measure the short time of the initial inrush current.
Results I have seen like:
Blue Sea Systems Engine Starting Standards - Resources - Blue Sea Systems
Show the inrush current is about 1000A or so.
This is for a very short duration, but needs to be taken into account when selecting a battery for starting a diesel.
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Old 19-11-2010, 08:16   #11
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I have and did test that with a meter capable of measuring "in-rush". The peak loads captured are all between 130 to 180 amps in-rush. The 180 range is with ambient air temps in the low 40's not somehhing the average sailor will encounter very often.

Also keep in mind that my batt voltage never even drops low enough to drop out any of my electronics even at a 50% state of charge so for my engine deep cycles are providing much more MCA than is necessary. Each one of my batts produces over 1000 CA at 68 degrees even at four years old as tested with a Midtronics EXP 800. This means my engine can possibly see upwards of 3000 CA off my deep cycle house bank or a LOT more than Westerbeke wants per specs. I also used to start my big Cummins on my downeaster off two 6v GC batts just fine.. Using my batt monitor was much easier than using my AC/DC in-rush capable clamp meter for the video.
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Old 19-11-2010, 10:40   #12
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Quote:
Originally Posted by Maine Sail View Post
I have and did test that with a meter capable of measuring "in-rush". The peak loads captured are all between 130 to 180 amps in-rush. The 180 range is with ambient air temps in the low 40's not somehhing the average sailor will encounter very often.

Also keep in mind that my batt voltage never even drops low enough to drop out any of my electronics even at a 50% state of charge so for my engine deep cycles are providing much more MCA than is necessary. Each one of my batts produces over 1000 CA at 68 degrees even at four years old as tested with a Midtronics EXP 800. This means my engine can possibly see upwards of 3000 CA off my deep cycle house bank or a LOT more than Westerbeke wants per specs. I also used to start my big Cummins on my downeaster off two 6v GC batts just fine.. Using my batt monitor was much easier than using my AC/DC in-rush capable clamp meter for the video.
The equipment you used is not capable of measuring the inrush current. The time frame is too small. In the kink I posted you can see after the initial 1200A inrush current a much lower current, consistent with your results, is measured.
I agree many large deep cycle batteries are capable of producing this capacity. Your batteries, if capable of producing 3000A, are of course easily capable of supplying this stating current.
However I caution cruisers with a smaller house bank from assuming the batteries will need to supply only 130-190A. For at least for short time the batteries need to supply current nearly an order of magnitude higher than this.
Yacht owners need to select a battery bank that is capable of delivering this current on a consistent basis, without significant damage, when starting a diesel..

Most electronics are protected from the voltage drop associated with starting.(some Raymarine plotters seem to have skimped on this) so I do not believe that functioning electronics during the start sequence can be used as a reliable guide that the batteries used for starting are suppling an adequate voltage/current.



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Old 19-11-2010, 12:22   #13
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I have two data points on this subject:

1. I tried to measure the starting current on a 27 hp Yanmar using a clamp on DC ammeter. The current exceeded the 200 amp maximum scale of the meter.

2. Once (by mistake!) I started a 5.3 liter, 370 hp Yanmar using a 440 amphour house battery bank and not the 4D starting battery. It started right up.

So I agree with the conclusion, but not the numbers.

David
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Old 19-11-2010, 12:44   #14
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Quote:
Originally Posted by noelex 77 View Post
The equipment you used is not capable of measuring the inrush current. The time frame is too small. In the kink I posted you can see after the initial 1200A inrush current a much lower current, consistent with your results, is measured.


.
And you know this how?

From the owners manual:

"Peak Hold
The Peak Hold function captures the peak AC or DC voltage or current. The meter can capture negative or positive peaks as fast as 1 millisecond in duration."

There are a fair number of meters out there that can capture DC in-rush but you need to read the lit to be sure. The Fluke's, like the 337 or 376, are 100ms which is still plenty fast enough, and the Extech's are 1 ms (1/1000th of a second) capture speed.

Quote:
Originally Posted by Blue Seas
When starting the engine there is a large current spike of approximately ¼ second duration required to begin the rotation of the engine. This phase of engine starting is called the Inrush Period. Once the engine is rotating, but before it starts there is another period averaging 9-3/4 seconds, called the Cranking Period. These two Periods combine to make the Engine Cranking Cycle.
If you are concerned about the speed of the instrument I used I would simply argue, IMO, it just does not really matter if it spikes over my measured reading of 120-180 amps for anything less than 1/1000th of a second. Considering Blue Seas states .25 seconds and my meter captures to .001 seconds then I suspect it is capturing in-rush well, unless I have been mislead by the manufacturer..

We also do not know what engine Blue Seas used to get that data. In all likely hood, to make their point about battery switches, it was a very large diesel on a Sport Fisher not a 44HP diesel with a stated CCA draw of just 160 amps. My video obviously does not apply to an 800 HP Man or Caterpillar as it is a small 44 HP diesel.

The 44B Four engine has a stated cold cranking amp draw of 160 amps @ 79 degrees. Here's a link that shows it: LINK

Westerbeke wants to see a battery for my engine with at least a 600 CCA rating. This is not a large CCA rating for a 44 HP diesel.

Just one single group 27 West Marine/Deka deep cycle has 575 CCA and a Group 27/SCS200 Trojan Deep Cycle has 620 CCA. Who really has a single battery bank for house loads of just one group 27 that also has a diesel engine and actually cruises their boat?? Just two WM grp 27's can supply 1150 CCA & 1430 MCA.

Even two Sea Volt/WM/Deka 6V batteries in series will give you 975 MCA or well over the necessary 600 CCA for our 44 HP.

CCA ratings for a more popular engine such as the Universal M-25, M-35 or M-40 are for at least a 400 CCA rated battery. Most any good group 24 deep cycle battery will easily exceed 400 CCA. Heck they make personal watercraft batteries with 500 CCA these days. The WM/Deka group 24 Deep Cycle is 500 CCA for just a single battery and is actually 100 CCA over what is necessary for an M-25 - M-40 per the manufacturers specs.

On our 44 HP engine I have measured it as high as 180 and as low as 120 peak/in-rush and this is a meter than can do 1/1000 of a second captures.

Considering I have been starting small sailboat aux engines, and mid sized diesels on deep cycle batts for well over 20 years, and never once had an issue, and have measured the starting loads as best I can with products designed to do so, I suspect these "peaks" of .25 seconds or less really don't matter much in the whole scheme of things.

When you parallel banks, and they get bigger, you combine the amps, which includes the cranking amps. Most small boat sailors (sub 45 feet), even with deep cycle batts, have a lot more CA available in the house bank than the single small group 24 or 27 starter battery they have they just have not yet figured that out.

If you compare the WM pure starting battery ratings to the WM deep cycle batt you get:

WM Grp 27 Deep Cycle = 715 MCA

vs.

WM Grp 27 Starter = 925 MCA

This is only a 210 CA difference from a true deep cycle to a starter battery.

Combine the two deep cycle batts into one house bank and you now have approx 1430 MCA vs. 925 MCA for the single starter bank....

All engines are slightly different and the peak draws will be too, some higher and some possibly lower. But most house banks, even when deep cycle, will start a small marine aux diesel with no issues. My point is still the same that a sufficient house bank of deep cycle batts should easily start most any small aux diesel engine the bank has been properly cared for.
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Old 19-11-2010, 12:55   #15
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Quote:
Originally Posted by djmarchand View Post
I have two data points on this subject:

1. I tried to measure the starting current on a 27 hp Yanmar using a clamp on DC ammeter. The current exceeded the 200 amp maximum scale of the meter.

2. Once (by mistake!) I started a 5.3 liter, 370 hp Yanmar using a 440 amphour house battery bank and not the 4D starting battery. It started right up.

So I agree with the conclusion, but not the numbers.

David
David,

I don't have the manual handy for the Yanmar 27 but I do have the 3YM 30 and the LOADED MAXIMUM CURRENT spec for the 1.4 kw starter motor on the 3YM 30 engine is 250A. This is Yanmar's loaded maximum current rating. Still, 250A is a small load for most any deep cycle house battery bank.
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