fusing a 450 Ah bank

[mariner36bob]

laying on new T105's. (4) of them for a 450Ah bank.

Is fusing the new bank as simple as a 450 amp fuse or am I missing it?

thanks.

[roetter]

Originally Posted by mariner36bob

laying on new T105's. (4) of them for a 450Ah bank. Is fusing the new bank as simple as a 450 amp fuse or am I missing it? thanks.

Your fuse should be not much larger than what you expect to put on as a load. Your batteries do not support 450A except for a few seconds. What kind of inverter do you have, that would likely be the biggest load. Navigation, fridges and the like are minimal. Any electric winches? How about your windlass?

[skipmac]

Originally Posted by roetter

Your fuse should be not much larger than what you expect to put on as a load. Your batteries do not support 450A except for a few seconds. What kind of inverter do you have, that would likely be the biggest load. Navigation, fridges and the like are minimal. Any electric winches? How about your windlass?

Exactly. The size of the fuse should be based on the size of the load but don't forget to also take into account the size of the wiring from the battery bank to the loads.

The fuse should be of a size to keep the smallest wire from overheating and creating a fire hazard in case of a short.

[BambooSailor]

As roetter wrote, you do not fuse battery bank, you fuse your wiring which you size based on max expected load.

[Maine Sail]

The fuse is sized for the wire you are protecting. If that bank may ever be called on or be used to start the motor then it should be sized to account for starter loads. On a Mariner 36 a 300A fuse would cover you, if the wire can handle it. Would need to know the size of your heavy gauge battery cables for that..

[mariner36bob]

Good morning and thank you. I misspoke, and do understand the fuse is protecting wire and loads from the battery, not battery itself thank you. Our inverter is small, 1000 watt used for charging a cell phone or two. We do have electronics, no fridge (yet), no windlass (yet) and no electric winches (never happen). The manufacturer installed battery cables are 2/0 I believe, but I will have to go verify that. Been several months since I've been on board, winter in New England. Yes the house bank will be used to start the diesel under normal operations. I'm installing a start battery that will only be used as a fall back in case of house bank failure. There are no other small gauge wires attached directly to the battery posts, but there will soon be battery monitor wires attached which will be individually fused at a much smaller amperage.

[djmarchand]

bob:

Your expected practice of only using the start battery to start is contrary to normal practice. What you propose doesn't let you exercise the start battery and it may be dead when you need it. The other way around insures that both are exercised routinely.

But in any case, ABYC doesn't require and it isn't really a good idea to fuse the starting circuit. If you could separate the house and starting load and fuse only the house load it will mean a smaller fuse. A 1000 watt inverter will pull about 100 amps at full output. So you could use smaller, say #2 wire and put a 100 amp fuse in that circuit.

David

[mariner36bob]

Thanks fellas. It was cold but I did climb on board today.
I was way off, the battery cables are #1. New boat.
Wires are just under 30 ft round trip.
Would that then make the load it's currently wired for 150 amps?
Would a 150 amp fuse cause problems with that banks start capability? I’m sorry I don’t know what the starter load would be.
I’m hoping If I solar charge both banks and exercise that start battery manually then I shouldn’t ever find a dead starter battery. Hell, our season is only about 28 days long as it is!

[Stu Jackson]

Blue Sea website have a great fuse and fusing set of tables.

http://assets.bluesea.com/files/reso...ence/20010.pdf

[mariner36bob]

Thanks Stu!

[btrayfors]

MaineSail already answered your question:

If you are going to use the house bank to routinely start the engine, you'll need a 300A or larger fuse in the start circuit. Starter in-rush current can be several hundred amperes.

I don't agree with the earlier comment about not fusing the start circuit. Yes, it's true that ABYC doesn't require it. But it's a VERY good idea to avoid possible fires in the event of a short circuit. Nigel Calder agrees with this, as do many ABYC-certified electricians.

My boat has had the starter circuit fused for several years (4-108 Perkins).

Not sure what you mean by "manually exercising" the start battery. I much prefer to use the start battery for starting the engine routinely, and to maintain that battery automatically with a voltage follower device like the EchoCharge or the DuoCharge. No switching necessary :-)

Bill

[Jim Cate]

Originally Posted by djmarchand

bob:

Your expected practice of only using the start battery to start is contrary to normal practice. What you propose doesn't let you exercise the start battery and it may be dead when you need it. The other way around insures that both are exercised routinely.


David

I disagree with this statement: a dedicated start battery, used solely for engine starting, is both common practice and an excellent one to boot.

Charging via a "follower" system like the Echo charger keeps the battery topped up, and normal starting "exercises" the battery plenty.

Cheers,

Jim

[goboatingnow]

Originally Posted by BambooSailor

As roetter wrote, you do not fuse battery bank, you fuse your wiring which you size based on max expected load.

To be a little pedantic , engineers use fuses for many things , source protection, load protection, and wiring protection included.

Dave


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[evm1024]

Trojan t-105s have a short circuit current capability of around 4000 amps. With a bank of 4 at 12 volts you might see 8000 amps. This will blow a 400 amp ANL fuse in around 0.02 seconds.

That same 400 amp ANL will blow in about 3 seconds at 1000 amps and it could take over 100 seconds for a 500 amp load.

(http://www.cooperindustries.com/cont...S_2024_ANL.pdf)

Thus I fuse my starter on my perkins 4-236. I tried a 250 amp ANL inthe starter circuit and had no problems starting the engine. It is speced to take 10 seconds to blow with a 1000 amp load.

Setting the fuse to match the wiring is the way to go for normal operations.

The only fire I had onboard (well, melted insulation and discolored copper) was due to an under sized engine to negative cable in the (unfused) starter circuit on that perkins. A dead stall on the started otor can really draw the current.

Regards

[mariner36bob]

That's some damn fine knowledge right there.

It's going to be a 300 anl on both banks. I appreciate the idea of protection and i don't want melted wires for sure.

My start battery as a back up idea was ridiculous i see. It has to be a dedicated start. And why shouldn't it be, that's why they call it a start battery.

I dont want to have to go below to switch after starting. I'd like to turn the key and have start batt. start the boat. But at same time have bank 1 power the house. A combiner can charge the start I understand.

To do this i have to remove bank 2 from the 1/2/both switch and make it's own starter loop with it's own switch, right?

Could this be accomplished and maintain capability of house bank (not in the aforementioned starter loop) to also start the boat (as a back up)?