Universal M-25/XP starter amperage?

[KWKloeber]

Has anyone confirmed (i.e., measured) their starter draw?

I know 80 or so is the rule of thumb but Rodd indicates that the max would be MUCH higher (which says to me more than 2x, maybe 3x?) 
Unfortunately, Rodd hadn't put actual numbers to an M-25; only to a larger 4-cylinder Westerbeke.

Thx!

[Carbon]

I put a Victron Smart shunt on my battery bank. It should see all the current going to the starter while cranking. It shows about 150 Amps. I can't see the inrush, it's too quick and over too fast for the Victron to pick it up.

The glow plugs draw about 50 amps.

The engine is a Universal  M-25XP.

[Kyle Ewing]

Not a direct answer but another data point: I have a 150 amp breaker on my M25xp start battery. It hasn't tripped once in many years.  I sized it based on feedback from this forum and online research.

[High Current]

Sorry I'm late to the party.  It just so happens I measured mine with an oscilloscope shortly after I bought the boat a year and a half ago     Summary answer is peaks ~220A, but the battery was a little tired so give it some margin.

Here's the capture.  CH1 (yellow) is voltage, CH2 (blue) is current.  My current probe is 10mV/A, so 2.22V is 222A and 1.14V is 114A.  The large ripple is caused by the compression strokes.

[KWKloeber]

Ben

Is she an XP?

[Carbon]

Sorry I'm late to the party.  It just so happens I measured mine with an oscilloscope shortly after I bought the boat a year and a half ago     Summary answer is peaks ~220A, but the battery was a little tired so give it some margin.

Here's the capture.  CH1 (yellow) is voltage, CH2 (blue) is current.  My current probe is 10mV/A, so 2.22V is 222A and 1.14V is 114A.  The large ripple is caused by the compression strokes.

That's interesting. I've played around with an oscilloscope a bit but I don't own one.

If you were sizing wire & fuses would you size it for the peaks at 220 Amps or the average at 167 Amps? The average is close to what my Victron Smart Shut reports (150 amps). I tend to think the average is what you would use, but I'm prepared to learn something.

Thanks

Jack 

[Stu Jackson]

Ben

Is she an XP?

Ken, with that hull # it is most likely an M25XP.  Unless someone changed it out, it came from the factory with an XP.

If you were sizing wire & fuses would you size it for the peaks at 220 Amps or the average at 167 Amps? The average is close to what my Victron Smart Shut reports (150 amps). I tend to think the average is what you would use, but I'm prepared to learn something.

Thanks

Jack 

Jack, don't overthink this.  From the earliest Catalina 34 boats, the wiring from the batteries to the starter was #4.  Some would argue that this is now considered "horribly undersized."  But for years. Maine Sail has been making the point that while the current may be high it is for an extremely short duration.  My #4 wiring is still in place and I have had no trouble starting my engine (it's an M25, but essentially the same electrical load as an XP's starter).  Catalina has increased the wire size in later models, although I do not know specifically what it is.

[KWKloeber]

Thank you to all who posted their data points!!
A prior reply questioned where I got the 90A average - it wormed into my brain a long time ago, and was also on Jon's spreadsheet for his rewiring (techwiki site.)  Perhaps I misunderstood his spreadsheet.

If you were sizing wire & fuses would you size it for the peaks at 220 Amps or the average at 167 Amps? The average is close to what my Victron Smart Shut reports (150 amps). I tend to think the average is what you would use, but I'm prepared to learn something.

@Jack,
Sizing new cables for someone else was exactly my reason for the question. 

ABYC E-11 says to size all critical circuits (starter, nav lights, bilge pump, and the like) for no more than 3% voltage loss round-trip. 
ChatGPT returned:
ABYC standards specify that the maximum voltage drop for starter cables should be less than 3% of the system voltage, and this calculation is based on the peak starter current.  This ensures that the engine receives sufficient voltage during cranking, which is critical for reliable starting performance.

But I see nothing in ABYC E-11 re: peak vs avg.  Perhaps that was clarified in a later "Interpretation Letter," but based on peak makes sense to me.  One would not want to starve the starter of full voltage at the point where it pulls the greatest current.  Unlike a fuse not blowing when amperage exceeds its rating for a brief time, the V drop will occur regardless of how short the time period (the 3% sizing is for performance not safety.)

I found Rod Collins adds three other data points:
...a 1987 Universal M-25 draws roughly 225A +/- depending upon temp and other factors. This is the in-rush load though.
and:
the starter [on a Westerbeke 4-cyl] drew slightly over 640A during the peak inrush. [no mention of the avg draw] and later  the "average" starting load [presumably the same engine] was 286A. on a 20F day with the bank/bilge at 32F.

And also from Rod:
Universal / Westerbeke BATTERY CABLE REQUIREMENTS (wire length round trip)
2GA = 8'
1GA = 10'
1/0 = 14'
2/0 = 18'
3/0 = 22'
4/0 = 28'

Everyone should agree that proper-size cables equal easier starting compared to OEM #4 (perhaps that's why some need to add the (IMO) dumb preheat solenoid "fix".)

Jack,
Rod discusses sizing battery fuses and the 150% rule here:
https://pbase.com/mainecruising/battery_fusing


Cheers,
Ken

[KWKloeber]

Here's the capture.  CH1 (yellow) is voltage, CH2 (blue) is current.  My current probe is 10mV/A, so 2.22V is 222A and 1.14V is 114A. 

@Ben

Could you provide a quick lesson how to understand what the screen is telling us?

i.e., the left scale points (circled) and is 114A the AVG or the MIN?
But I'm interpreting 1.14v curve A (voltage, yellow) as the V at the starter B terminal (not starter amperage.)
I'm obviously misunderstanding what the scope is displaying.

Am I correct that it took 2 secs (circled) to start your XP?

Thx
Ken

[Stu Jackson]

Thank you to all who posted their data points!!

>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>

I found Rod Collins adds three other data points:
...a 1987 Universal M-25 draws roughly 225A +/- depending upon temp and other factors. This is the in-rush load though.
and:
the starter [on a Westerbeke 4-cyl] drew slightly over 640A during the peak inrush. [no mention of the avg draw] and later  the "average" starting load [presumably the same engine] was 286A. on a 20F day with the bank/bilge at 32F.

And also from Rod:
Universal / Westerbeke BATTERY CABLE REQUIREMENTS (wire length round trip)
2GA = 8'
1GA = 10'
1/0 = 14'
2/0 = 18'
3/0 = 22'
4/0 = 28'

Everyone should agree that proper-size cables equal easier starting compared to OEM #4 (perhaps that's why some need to add the (IMO) dumb preheat solenoid "fix".)

Jack,
Rod discusses sizing battery fuses and the 150% rule here:
https://pbase.com/mainecruising/battery_fusing

Cheers,
Ken

Thanks, Ken.

1.  For some of you who are new to our Forum, Rod Collins IS MAINE SAIL, who we refer to often in the Forum.  His pbase website is the original version of much of his work, and his marinehowto 'site has his newer material.  Ken and others and I often urge you to spend valuable time there, since Rod discusses interesting boat electrical issues, some specific to our Catalina series of mid-size boats as well as other  issues, like programming Balmar regulators and choosing & wiring battery chargers.  Many of his contributions are linked in our Electrical 101 Topic thread.

2.  Pre-heat solenoid - I do not believe this feature has anything to do with starting wiring sizing, and also don't think it is a "dumb fix."  [I assume you mean the glow plug solenoid --- https://www.c34.org/wiki/index.php?title=Faster%2C_More_Efficient_Glow_Plug_Heating_with_a_Solenoid] Based on your comment, Ken, I'd ask what you mean by: "Fix for what?"  All it does is reduce dependency on large current through small wires to the cockpit panel and back.  IIRC, these solenoids were actually added right to the engines in later models.  Those of us old geezers with M25s added the relays ourselves.  Why do you think it is dumb?

[KWKloeber]

[Rod Collins' aka MAINE SAIL's pbase website is the original version of much of his work, and his marinehowto 'site has his newer material.

Newbies, be sure to bookmark both sites!
Rod duplicated most of (but not all) his content on the Pbase website on the MarineHowTo website (his article that I referenced is an example that wasn't.)

Rod also has good content on SailboatOwners.com that is not on his web pages (I believe that some SBO is referenced in the 101 Topics, but in the past there had been an issue when SBO modified its URLs and our links were dead. That may have been corrected(?) but be aware that one might need to search SBO directly if a Rod link comes back "not located."

[High Current]

Could you provide a quick lesson how to understand what the screen is telling us?

Hi Ken,

Sure!  There are two traces showing, respectively, current and voltage (Y axis) as a function of time (X axis).  Across the bottom is the scale per division of the grid:  2V/div for CH1, 500mV=50A/div on CH2, and 500ms/div (0.5s) for time.

The arrows labeled "1" and "2" on the left side indicate the zero point for each channel.  So at the top left, yellow is 6.2 divisions above the "1" arrow, meaning the battery starts at 12.4V. and dips to approximately 11V (with some ripple) while cranking.  Current meanwhile starts at zero, spikes briefly to about 225A, then oscillates between 220A and 114A at about 5 cycles per second.

The horizontal dashed lines (yellow and white) are "cursors" used for making quantitative measurements.  On the right side you see the "source" is CH2 = current.  So I'm just measuring the peaks and valleys of the blue waveform.  These numbers are displayed in the box at top right:  222A peak, 114A valley, 222-114=108A between the lines.

Finally, the vertical orange "T" marker indicates the "Trigger," i.e. the event that caused the oscilloscope to capture the data - in this case, the rising current signal.

Yes, it is an M25XP.  No, it did not start in 2 seconds.  As I later found out, the key switch was broken and the glow plugs were not getting power.

I would definitely defer to ABYC, but absent guidance I would size the wire for the average current, not the peak.  Even then the tables may be overly conservative because you don't crank long enough for the wire to really heat up.  Voltage droop (3%) should be the deciding / limiting factor, and that depends on wire length.

You gain little if anything by exceeding the standard.  You can see my battery droops to 11V, which is -11% or so.  MCA is spec'd all the way down at 7.2V!  But 4 AWG is 0.25 mOhms per ft.  If the cable is 20 ft (round trip) that translates to an average droop of 0.84V, which is definitely more than 3%.  I guess I'm adding that to my list of winter projects...

[Carbon]

I've got a winter project in mind to upgrade the boat's electrical system, including installing LiFePo4 for the house bank and a dedicated lead-acid battery for starting. The plan includes the installation of the Victron Orion XS DC to DC charger so that the alternator will be attached to Lead Acid and the charger will handle the different chemistries. Also, a Victron Inverter/Charge is in the mix.

The boat already has a third battery installed in front of the starboard water tank under the settee. That's where I intend to install the starter battery. The LiFePo4 battery will go where the factory batteries were installed.

The only problem I see is that the location in front of the starboard water tank is a long way from the engine. Just eyeballing it, I'd estimate it to be at least 10 feet, probably a bit more. That would be at least 20 feet round trip.

Looking around at online wire size calculators, it looks like for a 20-foot round trip, 1/O wire would be the right size with a 2.5% voltage drop. If it turns out to be closer to 30 feet the voltage drop would go to 3.5%, still pretty good. My current thinking is to use 1/O wire unless it turns out to be longer than my best guess. If that's the case, I'll probably start looking for another place for the battery. 2/O and bigger wire is expensive and hard to work with.

I'd like to hear anyone's thoughts on this.

Jack

[Noah]

I would reconsider battery placement. My group 24 reserve/starter battery is located under the aft bunk.

[Carbon]

I would reconsider battery placement. My group 24 reserve/starter battery is located under the aft bunk.

I've been looking back there, and it makes more sense than the placement in front of the starboard water tank. But, someone has put in a battery box with tie-downs, etc. in front of the tank. It would be easy to reuse it. The downside is the length of the wire run. If it needs more than 1/O wire, then I'll probably move it.