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Old 16-11-2012, 16:47   #1
F51
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Start bank fuse size?

I have no fuse in the start battery bank (2 parallel 12v lead acid group 31s).
The cables from the battery to starter and eng ground are 2/0. However, the cable from the start solenoid to the starter is a 1/0. I believe this is the cable that I must protect. 1/0 has an ampacity of 242a @ 122 deg F. If I put a 250a fuse at the battery, what is the chance the starter inrush will blow this fuse? The engine is a 120hp Ford Lehman. Thanks.
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Old 16-11-2012, 17:08   #2
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Re: Start bank fuse size?

Using an accurate ohm meter and clean connections measure the resistance across the start motor. It will be around 0.1 ohms. Using Ohm's Law or I=E/R calculate the maximum current draw of the motor - i.e. when it is stalled with good batteries:

Stall Current of Motor in Amps = 12 / Terminal Resistance in Ohms

Or use a value from the motor datasheet ... which is probably silent on the subject.

The fuse should be maybe 20% bigger than that to avoid false blows. Examine how that max current relates to the wire size of 1/0.

That said, a 250A fuse is probably fine.
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Old 17-11-2012, 21:12   #3
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Re: Start bank fuse size?

Ford lehman manual specifies a locked starter draw of 1070A and a running starter draw of 650A.
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Old 17-11-2012, 21:56   #4
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Re: Start bank fuse size?

Engine starters do not usually have a fuse
The regs call for conduit for protection if over a certain length
(I don't remeber the specs)
But they are not required to have a fuse
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Old 18-11-2012, 06:54   #5
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Re: Start bank fuse size?

What if you use a Blue Sea ACR 9112 between 2 banks as a paralleling switch.
Look at their schematic.
It requires fusing.
Jus' sayin'
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Old 18-11-2012, 07:13   #6
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Re: Start bank fuse size?

Quote:
Originally Posted by Blue Stocking View Post
Look at their schematic.
It requires fusing.
Jus' sayin'
Only the combining relay has a fuse
Look again , follow the + from the battery to the starter
Note that only a switch is in that circuit, there is no fuse between the starter and battery
https://bluesea.com/files/resources/...tions/6693.pdf
Starters are not fused

Back to the OP
Second question
You have concern over having a smaller gauge wire between starter and solenoid
You should be fine as long as that wire is short < 1ft
I have seen where a smaller wire was used to reduce strain on connections or due to a tight radius
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Old 18-11-2012, 07:31   #7
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Re: Start bank fuse size?

There was a lengthy thread last year on a couple who lost their boat due to a short in starter circuit. Extinguishers put out flame but it ws reignighted by the shorted wire. It got me to put a fuse in the circuit.

I blew the fuse when I wrapped the prop and then tried to restart in gear. Can't recall size I used but will look at it next time I go to the boat, need to get a spare anyway.

It's a good idea. In this case you want a fuse not too much greater than needed for starter, you are less protecting the wire than tring to defeat a short. West Marine sells holders that fit on battery terminal with an adequate size range. Worst case get one of these with a smallish fuse, see if it holds. Get two spares, one one size bigger. May not be mathematically perfect but a whole lot better than nutten.
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Old 18-11-2012, 07:56   #8
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Re: Start bank fuse size?

I've got a 300 amp fuse on the starter line with my Perkins 4.236. It's never blown, but my engine also starts nearly instantly--if it doesn't, I know something is wrong. (OT, but I learned the hard way not to "try" the starter to see if it is OK when I'm checking out the boat before launch--even after sitting all winter it just takes a touch on the starter and it goes.)
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Old 18-11-2012, 08:58   #9
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Re: Start bank fuse size?

I fuse every circuit on the boat. It's crazy not to. Fire on a boat is no fun.

Most large fuses are designed to carry substantial extra current for a short amount of time. The Blue Sea ANL fuse won't trip at 300% of it's rating for a full second - over 600% for 1/10th of a second. This is plenty of time to get a starter past any normal high current "locked" draw. If the starter can't turn (wrapped line), I'd much rather burn out a fuse than the starter.

Here's the blue sea spec:

Detailed Specifications for ANL Fuses*&mdash;*Blue Sea Systems

I use a 250amp on a 110hp Yanmar and never had it blow. Maybe Yanmars have much lower draw starters but I'd be surprised. I do carry a spare.

Carl
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Old 18-11-2012, 09:37   #10
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Re: Start bank fuse size?

Quote:
Originally Posted by hpeer View Post
There was a lengthy thread last year on a couple who lost their boat due to a short in starter circuit. Extinguishers put out flame but it ws reignighted by the shorted wire. It got me to put a fuse in the circuit.

I blew the fuse when I wrapped the prop and then tried to restart in gear. Can't recall size I used but will look at it next time I go to the boat, need to get a spare anyway.

First point

This may have been preventable
An insurance surveyor could of caught that there was no battery disconect on the starter circuit (most tend to be critical towards electrical)

All of my boats have had them, my current boat has them in an inconvenient location next to the battery in the engine room
This requires removing a floorboard to reach..not the best if there is a fire

My previous boat had 4 Cole hersee Emergency Cutoff switches located in the wheelhouse away from the engine room installed by the builder
For the main engine,aux engine,and 1 each for the 2 gensets
That boat was an inspected boat over 100ton,built to the highest standards ,and inspected every 5 years through steamship in Canada as required under regulations under the Canada Shipping Act
No fuses on batterys other than house system

Second point

I don't see any reason not to add a fuse if you want other than a worry on a nuisance trip as you noted
Just make sure that there is some form of disconect (battery select with an off position, or single shutoff switch),
I am sure that is required even on new pleasure boats these days
One trick that I have been doing for a while is to nylon tie a replacement fuse on the wire right next to the fuse block or holder
I do that for all electronics, so that you don't have to hunt for the correct size
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Old 18-11-2012, 09:48   #11
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Re: Start bank fuse size?

I would have a cutoff switch of some sort in addition to a fuse. I have a 1,2,Both switch set up so that it selects which battery is used to start the engine. Normally I use position 1 for a dedicated starting battery, 2 connects to the house battery bank. When I leave the boat for a long time I turn it to off. It is useful to have the off switch when doing routine maintenance on the engine in order to prevent shorting something out--for example, replacing the impellor on my water pump has me working with metal tools right next to the starter.
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Old 18-11-2012, 09:49   #12
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Re: Start bank fuse size?

Here is what ABYC has to say, in part, about DC systems.

Quote:
Originally Posted by ABYC E-11
11.12. OVERCURRENT PROTECTION
11.12.1. FOR DC SYSTEMS
11.12.1.1. Battery Charging Sources
11.12.1.1.1. Each ungrounded conductor
connected to a battery charger, alternator, or other
charging source, shall be provided with overcurrent
protection within a distance of seven inches (175mm)
of the point of connection to the DC electrical system
or to the battery.
EXCEPTIONS: 1. If the conductor is connected
directly to the battery terminal and is contained
throughout its entire distance in a sheath or
enclosure such as a conduit, junction box, control
box or enclosed panel, the overcurrent protection
shall be placed as close as practicable to the battery,
but not to exceed 72 inches (1.83m).
2. If the conductor is connected to a source of power
other than a battery terminal and is contained
throughout its entire distance in a sheath or
enclosure such as a conduit, junction box, control
box or enclosed panel, the overcurrent protection
shall be placed as close as practicable to the point of
connection to the source of power, but not to exceed
40 inches (1.02m). Overcurrent protection is not
required in conductors from self-limiting alternators
with integral regulators if the conductor is less than
40 inches (1.02m), is connected to a source of power
other than the battery, and is contained throughout
its entire distance in a sheath or enclosure.

11.12.1.1.2. In addition to the provisions of E-
11.12.1.1.1, the ungrounded conductor shall be
provided with overcurrent protection within the
charging source, or within seven inches (175mm) of
the charging source, based on the maximum output of
the device.
EXCEPTION: Self-limiting devices.
11.12.1.2. Overcurrent Protection Device
Location - Ungrounded conductors shall be provided
with overcurrent protection within a distance of seven
inches (175mm) of the point at which the conductor is
connected to the source of power measured along the
conductor. (See FIGURE 15.)
EXCEPTIONS: 1. Cranking motor conductors.
2. If the conductor is connected directly to the
battery terminal and is contained throughout its
entire distance in a sheath or enclosure such as a
conduit, junction box, control box or enclosed panel,
the overcurrent protection shall be placed as close as
practicable to the battery, but not to exceed 72 inches
(1.83m).
3. If the conductor is connected to a source of power
other than a battery terminal and is contained
throughout its entire distance in a sheath or
enclosure such as a conduit, junction box, control
box or enclosed panel, the overcurrent protection
shall be placed as close as practicable to the point of
connection to the source of power, but not to exceed
40 inches (1.02m).
NOTE: The United States Coast Guard has
promulgated mandatory requirements for electrical
systems in Title 33, CFR 183 Subpart I, Section 183.
Refer to the CFR for complete, current federal
requirements.

If one has a fire, especially in the engine compartment, the first thing that should be done is to shut off the main switch. If it happens to be an electrical short then it stops the feed to the fire and can be extinguished. If the power is allowed to continue the fire will just increase until the batteries or wiring is gone.
As well one should have a fuel shut off to the engine compartment.
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Old 18-11-2012, 09:56   #13
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Re: Start bank fuse size?

BTW I have 2/0 cables to each battery bank of 1200 CCA each and I'm running the recommended 250A breaker to each within 18" of the battery.
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Old 18-11-2012, 10:07   #14
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Re: Start bank fuse size?

delmarrey

Could you clarify that for me,as it relates to a starter
Quote:
EXCEPTIONS: 1. Cranking motor conductors.
Do I read this correctly does this mean starter wires are not included ?
Regs are confusing

And good point on fuel shutoffs
On my inspected boat there were 3 tanks all with shutoff extensions in the main cabin
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Old 18-11-2012, 11:15   #15
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Re: Start bank fuse size?

Quote:
Originally Posted by Stray-Cat View Post
delmarrey

Could you clarify that for me,as it relates to a starter

Do I read this correctly does this mean starter wires are not included ?
Regs are confusing

And good point on fuel shutoffs
On my inspected boat there were 3 tanks all with shutoff extensions in the main cabin
I've been searching the web for the proper diagram but hard to find something simple. So, I've gone directly to the USCG source.

Down load this pdf and goto page 70. http://www.uscgboating.org/assets/pd...ELECTRICAL.pdf

This shows the proper installation. The starter link does not require a fuse but should have a switch to shut it off. Although, mine is fused. I prefer preventive maintenance vs repair work.
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