Fuse for solar?

[David Morton]

I'm in the middle of installing a new panel and Genasun controller. The old controller had a fuse wired to the battery. Genasun install instructions, however, make no mention of wiring a fuse. Wondering what to do? General feeling is that a fuse can't hurt. Being an electrical moron, I submit to the smart guys on this erudite board.

[Russell]

I'm in the middle of installing a new panel and Genasun controller. The old controller had a fuse wired to the battery. Genasun install instructions, however, make no mention of wiring a fuse. Wondering what to do? General feeling is that a fuse can't hurt. Being an electrical moron, I submit to the smart guys on this erudite board.

Yes, fuse it between the controller and battery.

[David Morton]

That was easy! Thanks, Russell.

[Russell]

Generally, if you think you might need a fuse, you probably do. 90% of boats are not properly fused, here in Panama I am doing a lot of charging systems for cruisers and most boats just have one large primary fuse and nothing else. I actually got into an argument with another guy here about fuses, I was ordering a pile fuse bars for a boat, and he asked me why. I told him ABYC specifies it, he was once a boatyard manager somewhere thus an "expert" and disagreed specifically on a fuse for the alternator, when I told him ABYC not only specifies a fuse, but they specify two fuses if the alternator is wired in line with the starter (which is the norm, even if not the best way to do it), he said no one fuses alternators and its not right. Glad I never had a boat in his yard!

Anywhere there is current, you need a fuse or breaker, preferably both. On light house loads like lights you rarely bother, but on heavy loads you always should! Its easy to have a mess of inline fuses all over the place, causing one to hunt them down when needed. Centralizing them can often mean a major rewire on an older boat. Even after a major rewire on my CD36 it is not properly fused to ABYC (but I bet its the best protected CD36 out there anyway).

Oh, and why do you need two fuses on the typical alternator/starter setup? Current goes two ways here, and you always want to fuse close to the source. Alternator sends current to the battery, vica versa battery sends current to the starter. Though when I did my first DC overhaul 10 years ago, I split those, independent wires for charging and starting (and both fused).

[David Morton]

So I'm curious about the statement that the fuse should be close to the source of the current. My reading implies that the fuse between the Pos battery and controller should be placed within 7" of the battery, yet, the current should be from the controller to the battery. Is the fuse actually to protect the controller in the case of a reverse in current from the battery to the controller? And under what circumstances might that happen? A grounded short in the controller? And while we are at it, what size fuse would be appropriate for my 10 amp controller ? 15 amp fuse? Pardon my newbie-ness to all things electrical!!

David

[Maine Sail]

Generally, if you think you might need a fuse, you probably do. 90% of boats are not properly fused, here in Panama I am doing a lot of charging systems for cruisers and most boats just have one large primary fuse and nothing else. I actually got into an argument with another guy here about fuses, I was ordering a pile fuse bars for a boat, and he asked me why. I told him ABYC specifies it, he was once a boatyard manager somewhere thus an "expert" and disagreed specifically on a fuse for the alternator, when I told him ABYC not only specifies a fuse, but they specify two fuses if the alternator is wired in line with the starter (which is the norm, even if not the best way to do it), he said no one fuses alternators and its not right. Glad I never had a boat in his yard!

Anywhere there is current, you need a fuse or breaker, preferably both. On light house loads like lights you rarely bother, but on heavy loads you always should! Its easy to have a mess of inline fuses all over the place, causing one to hunt them down when needed. Centralizing them can often mean a major rewire on an older boat. Even after a major rewire on my CD36 it is not properly fused to ABYC (but I bet its the best protected CD36 out there anyway).

Oh, and why do you need two fuses on the typical alternator/starter setup? Current goes two ways here, and you always want to fuse close to the source. Alternator sends current to the battery, vica versa battery sends current to the starter. Though when I did my first DC overhaul 10 years ago, I split those, independent wires for charging and starting (and both fused).

Russell,

There is not an ABYC requirement to have a fuse the the device end of a current limited source, which alternators are. The fuse is placed at the battery end, if direct wired to the battery. If jumpered to the starter, the jumper wire between starter lug and alt gets a fuse at the starter lug end, if the wire is smaller than the cranking conductor, which it usually is.

An alternator can't dump a higher failure mode current than its rating. It can't fail beyond what the wire is already sized for, but the battery bank can supply massive currents into a short. If the alt wire is sized properly for voltage drop then the alt can run at max output all day long and never melt the wire.

Solar is also considered a current limited source and should not ever be able to ignite the wire, if properly sized. There is no failure mode of an alternator or PV panel than can cause it to deliver more than its output.

The wire should already be comfortably sized to handle solar or alternator max output for hours on end. Even if the alternator developed a dead short internally the battery bank is driving the dangerous current into that short, not the alternator, this is why the fuse goes as close to the battery as possible..

The battery bank, especially a large house bank, can provide in excess of 20,000A into a dead short. A single Odyssey Group 31 battery can deliver 5000A of short circuit current. This is why OCP is installed at the battery end or whenever a drop in wire gauge occurs. The battery bank is the dangerous current source that needs the OCP not the alternator end, solar system end of the system.

The upside of all this is you can save a bunch of money on fuses and terminals...!

The Genasun should be fused as close to the battery as possible in the positive conductor.

ABYC E-11
"11.10.1.1.1 Overcurrent Protection Device Location

Ungrounded conductors shall be provided with overcurrent protection within a distance of seven inches (178mm) of the point at which the conductor is connected to the source of power measured along the conductor. (See FIGURE 15.)


EXCEPTION: Self-limiting devices."

This is further clarified in the upcoming E-11 which is in consensus ballot right now. If you are an ABYC member, and on the Electrical committee, you can view the clarifications on this under EZ-PTC then click on My Committees.

[Klem]

Okay, this got me thinking and maybe Maine or someone else can answer my question. If I remember right, the Genasun controllers have fuses inside them. Am I correct in assuming that you don't need an additional fuse then? Thanks.

[Maine Sail]

Okay, this got me thinking and maybe Maine or someone else can answer my question. If I remember right, the Genasun controllers have fuses inside them. Am I correct in assuming that you don't need an additional fuse then? Thanks.

The fuse is to protect the wire not the controller. Anything connected to the battery should be fuse protected in a safe ampacity rating for the wire... If that wire were to short the battery bank can throw thousands of amps into that short circuit....

In most instances the fuse or breakers are there to protect the WIRE.

The exceptions would be bilge pumps, macerators, bilge blowers, shower sumps etc.. or any DC motor that could develop a "stalled rotor". In these cases there should be a fuse no larger than what the pump manufacturer recommends so that it trips when the rotor is stalled and prevents the motor from melting down... These fuses are really not intended to protect the pump, though they can, but rather they are there to protect the boat from a fire..

This little 15' foot Boston Whaler was destroyed by nothing more than a single group 24 battery with no fuse.

[Klem]

Maine, thanks for the response. Unfortunately, what I was thinking and what I wrote were 2 different things. I guess I am not fully awake yet. What I meant to say was that if you mounted the controller right next to the battery so that the internal fuse was within the appropriate distance. You make a good point on wire size which would need to be appropriate for that internal fuse as well.