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Old 01-28-2011
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Best way to fuse Battery

This question is mostly for Maine Sail but there are several others that frequent this forum who also have very very valued knowledge and experience.

After reading the thread Maine Sail wrote on installing the Victron Battery monitor I have started to think that I need to learn more about the best way to "fuse" the hot side of my DC system. I liked the look of the what Maine Sail had (blue seas fuse) in the pictures in that thread but I'm not sure just exactly how that works. Looking at the Blue Seas web site, I found what I thought were the same parts but I couldn't figure out exactly how it works. (a metal bar with a threaded post thing that a square donut like thing that sits over and is a fuse ? Huh?).

So I'm coming out and openly saying.... I'm an idiot.

Would some one please tell me the best way (or even just a very good way) my electrical system hot side should be fused? I have a very simple electrical system. No fridg., no radar, no microwave, not even a lot of interior lights. Basically I run an auto pilot, depth sounder, Chartplotter, Marine Radio, nav lights, anchor light, a few inside lights, a couple of fans, a car stereo, bilge pump (direct wired) and the CO and propane detectors.

My battery bank now is a couple of 5+ year old group 24 batteries but I'd like to upgrade in the near future to a couple of Golf cart batteries (to get about 220 amp hr).

I've gotten by the past years with an inline 15 amp fuse on the cable that runs from my battery switch to the electrical panel. Each circuit in the electical panel also has a fuse. But, the fuse is just downstream from the battery switch. I don't even remember why I ended up putting it there. I know it would be better if the fuse was between the battery and the battery switch. Are the blue seas fuses shown in the Battery monitor thread beter?

If possible: Give me part names, part numbers, links to vendors, even recommended amperage fuses for a "small" system like mine.

Anyone who cares to help.... thank you very much.

Last edited by Tree; 01-28-2011 at 02:13 AM. Reason: grammer
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One of the simpler ways is to use a battery post-mounted fuse, which Maine Sail has posted photos of recently. However, these do require that your battery box or space have enough height to accommodate them.



As an alternative, you can mount one of these on a buss bar with the cable going to the main battery switch, and have all the batteries connected to the buss bar instead, but the buss bar would have to be located very close to the batteries for that setup to be considered safe. IIRC, Btrayfors posted a photo of that very setup in another thread.
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Last edited by sailingdog; 01-28-2011 at 06:13 AM.
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Yes, that's a very good way to do it. These fuses have a high ampere interrupt rating (AIC) and are one of only three types which are acceptable under current ABYC E-11 recommendations for direct connection to a battery bank (the others are the Class-T and ANC types). Note that most breakers are NOT suitable, as they don't have a high enough AIC, except for the new Blue Sea System breakers which are specifically designed for such service.

And, you're right to be concerned about the placement of the fuse: it should be within 7" or so...if possible...of the battery bank, NOT after the main cutoff switch.

Bill
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BTW, the BlueSea part numbers for those are seen in the photos. The fuse blocks and fuses are available here.
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Quote:
Originally Posted by sailingdog View Post
One of the simpler ways is to use a battery post-mounted fuse, which Maine Sail has posted photos of recently. However, these do require that your battery box or space have enough height to accommodate them.


The red insulator cap shown in the photo protects the fused terminal, but the way I see it....it does not protect the battery post. ?? What am I missing since a tool or something else could come into direct contact with the battery post and create a short.
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Quote:
Originally Posted by lancelot9898 View Post
The red insulator cap shown in the photo protects the fused terminal, but the way I see it....it does not protect the battery post. ?? What am I missing since a tool or something else could come into direct contact with the battery post and create a short.
It is supposed to be in a battery box with the battery, so that isn't an issue. If you're dropping or storing tools in your battery box, you have other issues to deal with first.

You can also add battery terminal covers to your battery posts, like these:

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Quote:
Originally Posted by btrayfors View Post
Yes, that's a very good way to do it. These fuses have a high ampere interrupt rating (AIC) and are one of only three types which are acceptable under current ABYC E-11 recommendations for direct connection to a battery bank (the others are the Class-T and ANC types). Note that most breakers are NOT suitable, as they don't have a high enough AIC, except for the new Blue Sea System breakers which are specifically designed for such service.

And, you're right to be concerned about the placement of the fuse: it should be within 7" or so...if possible...of the battery bank, NOT after the main cutoff switch.

Bill
Bill (or others) - could you elaborate a bit more on the need for AIC rating, with respect to battery banks. What Im really asking is - then how EXACTLY should such a battery fuse be sized/selected with respect to AIS ratings, etc. etc. etc. Thanx
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Originally Posted by RichH View Post
Bill (or others) - could you elaborate a bit more on the need for AIC rating, with respect to battery banks. What Im really asking is - then how EXACTLY should such a battery fuse be sized/selected with respect to AIS ratings, etc. etc. etc. Thanx
Sure. The needed AIC is a function of the size of the battery bank, specifically, it's total cold cranking amps (CCA) rating. For banks larger than 1100CCA -- which means most house battery banks on cruising boats -- a circuit protection device (CPD) with an AIC rating of at least 5,000 amps is required. The purpose of the high rating is to avoid disaster in the event of a catastrophic short-circuit. The potential amperage flow is a function of CCA. CPDs with less that the indicated rating could themselves arc over, short out, and fail to interrupt the circuit, leading to overheating and fires.

Blue Sea Systems has a nice little primer on DC circuit protection here:
DC Circuit Protection - Resources - Blue Sea Systems

Normally, CPDs are sized to protect the wire, not the connected devices. Branch circuit breakers and fuses are designed to protect the (smaller wires) and, often, the attached devices.

I'm a conservative kinda guy with regard to CPDs. If I KNOW that there will never be a demand greater than, e.g., 80 amps on a wire connected to the battery -- even a very large wire capable of carrying much more than that load -- then I'll use a CPD of, say, 100 amps on that wire, providing that it has an AIC of at least 5,000 amps.

Example: I use AWG6 or AWG4 battery cable direct to the house batteries to provide power to HF/SSB radios. I fuse them near the house batteries on both positive and negative cables with 30-40 amp fuses (normally, terminal-type or ANL fuses), since I know the load will never exceed that amount, even though the AWG6 or AWG4 cables are capable of carrying a lot more amperage than that.

Bill

Last edited by btrayfors; 01-28-2011 at 12:19 PM.
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Thanks - good info.
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Fuse Muse

Thanks for all the replies.

I'm ordering the blue seas terminal fuse block. Now: What size fuse?

(look at my original post for specifics on my electrical needs) 30 amp sound about right?
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