Start bank fuse size?

[daddle]

Would seem rather foolish to put all those breakers and fuses on the dinky 5 and 10 amp circuits and none at all on the 1000A starter circuit. "Yea, make sure you have a little glass fuse on the VHF so you don't get a lille smoke in the cabin if something goes wrong. But don't worry about that several thousand amp explosion in the engine room when the starter wiring fails."

[F51]

Originally Posted by ocean40

Ford lehman manual specifies a locked starter draw of 1070A and a running starter draw of 650A.

I looked and finally found this in the manual. So, now I want to find a fuse and fuse holder of about 700a. This should allow the starter to run, but blow on a locked rotor starter. Can you say "Hydrolocked"?

[CarlF]

A good reminder to check:

1: Is the always "hot" red starter wire insulation chafing on some vibrating piece of the engine such as a mount?

2: Is the nut holding it to the starter truly tight with a locknut.

[dugout]

It will help to do a little studying. Most the fuses used for this purpose are designed with a blow delay. They blow at the published rating but only after X time. Trip time of starter in rush is a short duration. The short term rating is much higher than the labeled rating. It can be confusing.

https://bluesea.com/productline/specs/135

The trip time of the BS ANL 300A fuse is 900A, (300%) up to a full sec.

[RUSTYNAIL]

Not fusing your starter would make as much sense as deciding not to have a circuit breaker for one of your big appliances, like a dryer at home because it was just too much current. The regulations are old, but there is a push to add an inline fuse in the starter circuit regulations. If you have ever seen what happens when a starter solenoid locks up, it isn't pretty, and the starter continues to heat up along with the battery cables and batteries until the weakest link melts, and sometimes across something that will burn. Go ahead and put a good size fuse in line. It's best to contact the engine manufacture and find out what the correct fuse would be. Buy the fuse with the most surface area to bolt to so there isn't much resistance at the connections. You can buy circuit breakers, but they are expensive. Mount the fuse with a cover so there is no chance of hitting it with a wrench to ground.

[CarlF]

When the ABYC wrote its rules, boats had simple color coded wiring and maybe a single flooded battery. I think it’s a dangerous to not fuse everything on today’s complicated boats with large high amperage battery banks.

My boat was built by Shannon with a 300 amp ANL fuses on the start circuit. There’s a smaller fuse on the alternator circuit. The engine is a Yanmar 4JH4 HTE (110hp). The fuse has never blown even when there was as a bit of air in a fuel line and I cranked for 30 seconds.

If you do fuse the alternator be sure to install zap stopper across the alternator terminals so if the fuse does blow it doesn’t burn out the alternator diodes.

[Wotname]

Originally Posted by ocean40

Ford lehman manual specifies a locked starter draw of 1070A and a running starter draw of 650A.

I realise this is an 8 year old thread but....

I seriously doubt a running starter draw of 650A. Maybe that is a peak current or an initial inrush current but it can hardly be an average current surely???? That equates to about 10 hp which would be a seriously big starter motor.

Maybe it's right but it doesn't seem so. I will make a note of checking a mate's Ford Lehman next time I can!

[Jim Cate]

I seriously doubt a running starter draw of 650A. Maybe that is a peak current or an initial inrush current but it can hardly be an average current surely???? That equates to about 10 hp which would be a seriously big starter motor.

Good point, Wottie. I suspect that what they mean is that peak w/locked rotor is 1070 A and peak with a free to turn rotor is 650, ie normal inrush current. Those numbers seem feasible to me.

Jim

[YANDINA]

The REASON for not having fuses or breakers in the starter circuit is that not infrequently the starter will draw the CCA from the battery. CCA is the maximum amps the battery can produce. If you install a fuse rated higher that the battery can produce it can never be blown making it useless.

[Sailmonkey]

Originally Posted by YANDINA

The REASON for not having fuses or breakers in the starter circuit is that not infrequently the starter will draw the CCA from the battery. CCA is the maximum amps the battery can produce. If you install a fuse rated higher that the battery can produce it can never be blown making it useless.

I’ve got what I consider a fairly normal engine. A three cylinder Kubota.

With a 1000 watt starter, there’s no way the load (starter) with a locked rotor can pull the rated CCA from the battery. If the starter seizes, burns and shorts, the fuse will protect the cables and batteries.

[Bycrick]

Once upon a time, I bought a few new starters for our Yanmar 3GM30 engines. They came with what was purported to be a "quality inspection test" report. Given the Chinese source, I decided to verify it. Specs were: 80 amps no-load, 250 amps starting, 450 amps stalled (locked rotor). I checked only the first two, with a newly calibrated Fluke meter, and they were within reasonable variance. They’re fused with 200 amp MRBF fuses which have never blown.

If anything, the fuse is too big because the Blue Sea trip specs are for 200% of rating for about 10 seconds.

[Wotname]

Originally Posted by YANDINA

The REASON for not having fuses or breakers in the starter circuit is that not infrequently the starter will draw the CCA from the battery. CCA is the maximum amps the battery can produce. If you install a fuse rated higher that the battery can produce it can never be blown making it useless.

With respect, this is incorrect and potentially dangerously incorrect.

Any fully charged battery can deliver way more current than it's rated CCA. A quick look at a battery specification will show the MCA, HCA and if given, the PCA will be well above the CCA.

Example - Odyssey PC1200 has a CCA of 540A, a MCA of 725A, a HCA of 860A and a PCA of 1200A.

FWIW, the definition of CCA - The Cold Cranking Ampere (CCA) rating refers to the number of amperes a battery can deliver for 30 seconds at a temperature of 0°F (-18°C) before the voltage drops to 1.20 volts per cell, or 7.20 volts for a 12V battery. A 12V battery that has a rating of 550 CCA means that the battery will provide 550 amps for 30 seconds at 0°F (-18°C) before the voltage falls to 7.20V.

Clearly a battery at engine room temperature will deliver more short term current than a battery at 0F.