Starter Protection.

[Manateeman]

Seeking the latest opinions on protecting the starter and avoiding fire on a Diesel engine. I’ve read previous posts but technology is always changing.
The engine is 170 hp Yanmar turbo after-cool. 12 volt electrical system.
Starter is Hitachi 2.5 kw
Starting batteries ...Two, 12 volt Lifeline AGM 105ah 880 CCA @68, 750 @ 32
The batteries can be combined or used individually. They are not in the engine room and the run is about 6 feet one way.
Relay on engine. Battery disconnect switch outside engine room. There are no batteries in the engine room and nothing to burn in the room.
The house system is 24 volt and not connected to any starter.
Yanmar recommends a 660 CCA battery and one of the current batteries lights the engine within seconds. Never had any issues just looking for the safest and most reliable system. Spare starter and additional engine parts on board.
The question is not wire size but rather what fuse, where and why or why not.
Thanks in advance for posts.
Mark.

[Dockhead]

Originally Posted by Manateeman

Seeking the latest opinions on protecting the starter and avoiding fire on a Diesel engine. I’ve read previous posts but technology is always changing.
The engine is 170 hp Yanmar turbo after-cool. 12 volt electrical system.
Starter is Hitachi 2.5 kw
Starting batteries ...Two, 12 volt Lifeline AGM 105ah 880 CCA @68, 750 @ 32
The batteries can be combined or used individually. They are not in the engine room and the run is about 6 feet one way.
Relay on engine. Battery disconnect switch outside engine room. There are no batteries in the engine room and nothing to burn in the room.
The house system is 24 volt and not connected to any starter.
Yanmar recommends a 660 CCA battery and one of the current batteries lights the engine within seconds. Never had any issues just looking for the safest and most reliable system. Spare starter and additional engine parts on board.
The question is not wire size but rather what fuse, where and why or why not.
Thanks in advance for posts.
Mark.

My system is similar, except I have a solenoid isolater in the circuit.


I don't have a fuse, but I think one of the Blue Seas battery terminal mounted "cube" fuses is a good idea. MaineSail also thinks so:

https://www.sailnet.com/threads/fusi...-option.64546/

See here: https://www.12voltplanet.co.uk/batte...s-50-300a.html

Don't know however if 300 amps is enough for the surge loads of a 2.5kW starter.


Definitely mount AT THE TERMINAL. That's the only way to protect against all possible faults.

[tkeithlu]

Safe bet that most starter battery set-ups are not fused. That said, it's a bunch of amps just waiting to do some free hand welding in your engine room. My approach is to put the starter battery very close to the starter, so a very short run, and insulate everything possible. A 300 amp fues might do it, but then, a 299 amp short could do a pretty good fourth of July in your engine compartment.

Another approach, which I use on our house bank but not on the starter (maybe I should) is a knife switch and wire up to the panel - pull the wire and disconnect the battery.

[smac999]

You would probably be fine with a 250 or 300a mrbf fuse. They will handle 200% briefly

Trial and error for sizes and carry spares... worst case if blows while cranking. Just move battery cable back onto battery and you are back to stock to get home.

If you are blowing 300a ones you will need a bigger anl. Instead.

Peak amps from a amp meter doesn’t really help. As it’s only a mirco sec of peak. You really need more of an avg

[Spot]

Is it still V times A equals W ?

300 A @ 12.8V =3.84 kW
250 A @ 12.8V =3.2 kW
starter is 2.5 kW so 195A @ 12.8V
but is 2.5 kW the starter's max or average draw?

Tell those manatees to stop throwing wrenches around the engine room!

[smac999]

Starter will be around 10v while cranking not 12.8. Which would be 250a.

[Dockhead]

Originally Posted by Spot

Is it still V times A equals W ?

300 A @ 12.8V =3.84 kW
250 A @ 12.8V =3.2 kW
starter is 2.5 kW so 195A @ 12.8V
but is 2.5 kW the starter's max or average draw?

Tell those manatees to stop throwing wrenches around the engine room!
[emoji3]

Problem is the inrush current, which can be several times the nominal power of the motor. Fuses can take some multiple of their nominal rating for some brief period, but what multiple and how brief? I don't know.

To make matters worse, with a big load like that, voltage won't be 12.8v so current will be even higher.

Unless someone has concrete experience, I think only experimentation will lead to any knowledge. I would start with 300 amps.

[GordMay]

Yes, you can select a fuse with a time/current curve that will offer short cct protection, and still allow the starting current.

Blue Seas MRBF fuse curves ➥ https://www.bluesea.com/products/518...al_Fuse_-_200A

[Paul L]

Good and pretty complete writeup on fusing starter batteries on a boat here
https://pbase.com/mainecruising/battery_fusing

[tkeithlu]

Core notion in here - a 300 amp fuse does not blow at a peak 300 amps, because fuses blow from generated heat - they melt. A transient 300 amps, that is, a few milliseconds of current, will not heat up the fuse. Ergo, the time/current curve Gord May displays.

[Onebadlarry]

Originally Posted by Manateeman

The question is not wire size but rather what fuse, where and why or why not.
Thanks in advance for posts.
Mark.

Thus is the question my man.... what is the cable size?

I for one am all for fusing starter circuits.

A 300amp MRBF will most likely suit your setup if on a budget, but I would like to know the cable size before committing to my statement.

[Frankly]

Keep in mind that fusing the starter circuit is most typically to protect against a short circuit (lots of vibration/ chafing and grounded surfaces). Large wire short run so the current is likely to be quite high (often 1,000 + amps). 300 or 400 amp fuses are going to clear the fault pretty quickly. ANL fuses are pretty slow to blow near their ratings so a good selection for this application.

I am using a 200 Amp for my 3GM and in 15 years it has never blown. I still double insulate the wire.

Frankly

[GordMay]

The Prestolite / Leece-Neeville Electrical Training Manual provides a step by step, easy to understand, outline of the procedures for maintaining and diagnosing a heavy-duty vehicle's electrical system.
Lo-res ➥ https://www.prestolite.com/literatur...nual_lores.pdf
Hi-res ➥ https://www.prestolite.com/literatur...ningManual.pdf
Including:
Section 4: “The Starting System” ➥ https://www.prestolite.com/pgs_training/training_4.php

[Manateeman]

Greetings. Thank you all for the replies. Paul L reminded me to look again at the Marine How To article which answers a lot of my questions. Thanks also to Gordo
because I never saw the Prestolite article before.
I did not mention my cable size because I was not sure I wanted to change them.
I’m probable just fire paranoid. I’m thinking a nice big T fuse rather than MRBF or ANL. I have a way to disconnect the starting batteries now from outside the engine room, and outside the battery area. I frequently clean all the connection points and check the cables. We shut off the starting battery/ engine connection unless needed. The feed cables from the seperate 12 volt solar and gen set powered charger are all on circuit breakers. Where the starting batteries are located there are dedicated smoke / fire alarms.
I’ll run the fuse choice calculations again.
My manatee crew has been known not to count tools after finishing work as the scent of cookies from the galley results in a work stoppage. Manatee union rules.
Well again, the technical gurus have come to the rescue . Thanks to all.
Mark and his unionized manatee crew.

[smac999]

the class t blows every fast and is designed to protect electronics. I would rather have a slow blowing one to handle the high inrush current.