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orientalnc2010 12-04-2010 08:42 PM

ANL fuse size at battery
 
Winter is near :( and I've been looking over my wiring etc to get familiar with the systems. I have 2 group 31 AGM batteries(105 amp/hrs) as the house bank, these are connected in parallel with 2 AWG tinned copper. 2 AWG is also used to connect this bank to my battery switch and house panel aprox 10' away. What concerns me is the ANL fuse within 7" from the battery is 250 amps. Since the blow point of the ANL fuse so high at 400 amps and 2AWG is rated for 210 amps outside an engine space, is the fuse to big? How do I calculate the size needed?

Maine Sail 12-04-2010 09:38 PM

1- You are not protecting the "load" with battery fuses you are protecting the wires in the event of a short so you are on the right track.

2- The allowable amperage for a single 2 GA conductor per ABYC E-11 Table VI is 210 amps outside engine spaces, and 178.5 amps inside engine spaces. This is for marine battery cable with a 105C jacket temp rating. You can safely rate this fuse at 150% of the above ampacity ratings, if you absolutely need to, and the fuse blow specs are already considered into this 150% number. I always prefer to run bigger wire and size my fuses at 100% or less but have on occasion gone to 150% with boats like Catalina's where the owner did not want to spend the $$ on new battery cable. Our fuse on the current boat is sized at less than 100% and is a 250 ANL on 2/0 wire.

Start Battery Fusing?

The ABYC does not specifically require fuses on dedicated start batteries but this is because on big engines they just don't make typical fuses big enough to handle both cable protection and starter loads, but we are talking BIG engines. I have fused up to 330HP with zero issues and no nuisance blows. It has nothing to do with the in-rush loads as the fuses will not trip on those short durations anyway unless their is something drastically wrong and the in-rush lasts longer than it should..

I have spoken at length with both John Adey and Eric Johnson (who recently left the ABYC) regarding this matter. They both feel personally that fusing smaller engines is a good practice, and many ABYC techs already do this. The standard was written around start batteries being close to the engine and short wire runs. They do require a batt switch as a safety mechanism but this is a poor safety mechanism in the locations many of them are installed in IMHO. We know short wires runs to the start battery are just not the case in MANY installations these days so I almost always fuse them on small aux engines.

It is very hard to write a standard to meet all applications thus the starter battery exemption, which I tend to disagree with, even though I understand the difficulty in applying this to all motors. They are working on changing this but we don't yet know what it will look like and it may then only apply to certain battery types such as LiIon. This subject, fusing starter batteries, is discussed in nearly every E-11 PTC meeting..

The ABYC also specifically do not address starter cable sizing because the industry is using rather outdated meausres for rating starting current loads. In-rush is also not a good measure because it would be extremely difficult to size either wire or most fuses for that. You basically want it sized for average cold cranking starter load and some manufacturers provide this and some don't. We have chuckled many times over how some builders, Catalina is one example, size starter cables. Unfortunately they can do this because it is not specifically addressed in E-11. I can assure you though that every time I convert an owners boat from 4 AWG to 2/0 the motor starts and cranks like a bat out of hell compared to the original factory wiring.

3- Proper marine rated ignition protected fuses, such as ANL fuses from Blue Seas, will not blow on in-rush current if sized correctly for your small motor. I personally ran a 200 amp ANL on our 2005 Catalina. Our current boat runs a 250 amp ANL on a 44HP Westebeke 4 cyl diesel. I have installed LOTS of start battery and house battery fuses and never had one "nuisance blow". Most folks I know start off the house bank anyway and house banks are required to have fuses, at least on new boats.

ANL's will handle up to roughly 150% of their rating for approximately 500 seconds. For a 200 amp ANL this is 300 amps for up to 500 seconds, or about 8 minutes. For in-rush they can handle up to 600% of their rating for about .5 seconds. This is substantially longer than in-rush currents generally last, which is usually under .2 seconds. For a 200 amp ANL this is 1200 amps for half a second. They can also do 300% for up to 1 full second which is 600 amps for a 200 ANL. In-rush currents are usually measured in milliseconds and rarely last any longer than .2 seconds.

I can't count the number of bank fuses that I have installed but I have never once had one "nuisance blow". Depending upon your engine you may be just fine with a 200 amp ANL but 250 is not an unsafe fuse size based on the ABYC ampacity tables.

orientalnc2010 12-05-2010 10:59 AM

1 Attachment(s)
Thanks Maine Sail for the insightful and clear response.
The inspection of battery wiring was necessary to become familiar with my factory install as I am adding a windlass. I believe that this is relevant to my thread in that;
I have run 2/0 cables from the windlass directly to the house bank, with a 110 amp breaker in the feed. The windlass is 1000watts and draws 85 amps according to the manufacturer. The total length of the run is 52' round trip.
My question concerns using my emergency cross over connector that is in my blue seas panel. My blue seas panel has a rotary switch for engine battery, on or off. There is a switch for my house battery, actually it is a 100 amp breaker.
Then there is an emergency crossover switch, looks like a windup key and has two positions, on and off. ( I have auto combiner, ACR or echo charger by choice at this time)
Simple and easy to follow but what happens if my house bank has some sort of catastrophic event and I have to use my emergency crossover.
Lets say it I start dragging anchor at 2AM because a strong front moved in. The house bank is completely useless for some unknown reason at this time, so I start the engine. I'm now operating all systems on my start battery. Group 27 100 AH
I need to use the windlass to reset the anchor. I have my running lights on but that's it. When I start the windlass all of the current will be going through 2AWG from my aux battery to my emergency crossover switch then back down 2AWG to my house battery, aprox 20' (the panel is 10' one way from the batteries). The current then has to travel the 2/0 cable to the windlass, 50' round trip. Would 2 AWG stand up to this temp situation?
I would think that 10% voltage drop may be OK for this "not likely" circumstance.

Am I over thinking this? I like to prepare for the worst case because this is what happens when you are least expecting it.

orientalnc2010 12-05-2010 01:50 PM

I just made my own case for a dedicated windlass battery. Since the house bank is dead using the emergency crossover would not be a good idea.

Maine Sail 12-05-2010 03:01 PM

Quote:

Originally Posted by orientalnc2010 (Post 673693)
I just made my own case for a dedicated windlass battery. Since the house bank is dead using the emergency crossover would not be a good idea.

Good choice now you just need to figure out how you will charge it..

hellosailor 12-05-2010 03:24 PM

Oriental-
"I have run 2/0 cables from the windlass directly to the house bank, with a 110 amp breaker in the feed."
You might want to doublecheck that. If you were to have a crowbar short at the winch (i.e. drop a crowbar across the power cables) and full battery power were to run in the cables through a dead short, it might weld the breaker shut instead of tripping it. Most common 12V breakers will weld shut and fail at something like 3300 amps, which even a common "automobile" battery can put into a dead short on a heavy battery cable. The breakers designed for higher loads (for direct use in battery cables) are often over $100 each. If you're already using one of those "nevermind". Otherwise, you might want to use an ANL fuse in that line as well.

Maine Sail 12-05-2010 04:49 PM

Quote:

Originally Posted by hellosailor (Post 673705)
Oriental-
"I have run 2/0 cables from the windlass directly to the house bank, with a 110 amp breaker in the feed."
You might want to doublecheck that. If you were to have a crowbar short at the winch (i.e. drop a crowbar across the power cables) and full battery power were to run in the cables through a dead short, it might weld the breaker shut instead of tripping it. Most common 12V breakers will weld shut and fail at something like 3300 amps, which even a common "automobile" battery can put into a dead short on a heavy battery cable. The breakers designed for higher loads (for direct use in battery cables) are often over $100 each. If you're already using one of those "nevermind". Otherwise, you might want to use an ANL fuse in that line as well.

This is good info and one reason to use ANL's, MRBF's or Class T fuses rather than breakers. I rearely if ever install thermal breakers in large loaded items directly connected to a large house bank.

The amperage interrupt rating (AIC) of the fuse or breaker used should exceed the banks cranking amp capacity. For instance three group 31 12V deep cycle batts can easily supply over 3000 CA at 70F. Many cheap breakers are a 3000 AIC rated product. You have to spend more money to get breakers that have a 5000 AIC rating. ANL's are 6000 AIC, MRBF's are 10,000 AIC and Class T fuses are 20,000 AIC rated.

orientalnc2010 12-05-2010 05:36 PM

[QUOTE=hellosailor;673705]Oriental-
"I have run 2/0 cables from the windlass directly to the house bank, with a 110 amp breaker in the feed."

Thanks for pointing this out,I should have been more specific. Since the circuit breaker would be 4-5' away from the battery I would put a fuse, such as terminal fuse by blue seas, within 7" of the battery. A welded shut breaker would be a nightmare.

orientalnc2010 12-05-2010 05:58 PM

Quote:

Originally Posted by Maine Sail (Post 673733)
I rearely if ever install thermal breakers in large loaded items directly connected to a large house bank.

You have to spend more money to get breakers that have a 5000 AIC rating. ANL's are 6000 AIC, MRBF's are 10,000 AIC and Class T fuses are 20,000 AIC rated.

The breaker came from Lewmar with the H3 windlass so I hope it is up for the task. No specs came with it. I will call Lewmar to verify the 5000 AIC rating. My bad on explaining the breaker directly to battery, there will be a fuse within 7" of the battery.
As far a charging I have decided to use an echo charger from the house bank.
The alternator goes to the house bank so I figure the windlass battery will always get a charge. The start battery can only be charged by using the crosssover switch at the moment. Since the house batteries are within 5' of the start battery would an ACR make more sense than another echo charger off the house to the start? Does the start battery really need 30 amps that the ACR can supply or would the 15 amps from the echo do the trick?

Maine Sail 12-05-2010 06:15 PM

Quote:

Originally Posted by orientalnc2010 (Post 673755)
The breaker came from Lewmar with the H3 windlass so I hope it is up for the task. No specs came with it. I will call Lewmar to verify the 5000 AIC rating. My bad on explaining the breaker directly to battery, there will be a fuse within 7" of the battery.
As far a charging I have decided to use an echo charger from the house bank.
The alternator goes to the house bank so I figure the windlass battery will always get a charge. The start battery can only be charged by using the crosssover switch at the moment. Since the house batteries are within 5' of the start battery would an ACR make more sense than another echo charger off the house to the start? Does the start battery really need 30 amps that the ACR can supply or would the 15 amps from the echo do the trick?

If that windlass wire is already fused at or near the battery bank then you don't need to worry about the AIC of the breaker as it will be redundant at that point for protecting the wire..


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