Mystery electrical system problem - not sure how to proceed.

thataway · Posted: Fri Oct 18, 2013 11:14 pm Post subject:

Looks like you are "OK" for now, and should be fine getting home. I have read and re-read the above posts, and most likely have missed somethings.
As I recollect you added up all of the amps a few days ago in a tablet form.
You have the Victron monitor/ ammeter, so can determine loads.
We also have to all keep in mind that Sunbeam is currently on Lake Powell--not at some place where tools and supplies are all available.

I share your question about a 30 amp fuse for a modern boat. From what you describe on the boat it would be easy to exceed 30 amps. You have the relay trim tabs at 20 amps, and the auto pilot at 15 amps--just there you are over 30 amps. Are these going to draw 35 amps at the same time?You are close to the limit with 30 amps. The Chart plotter / depth sounder are fairly low draws--the radio can be more; 5 to 6 amps on transmit. Stereo? Lights can be a large draw. A cigarette lighter is alway a big question. There are all sorts of things which plug into them, and can have a short, loose connection or high current draw (such as a spotlight or 300 watt inverter!) Conclusion from this is that 30 amps is not enough.

I have found that most of the C Dorys are not adequately wired. I usually double the size of the wires to the console bus bars (both positive and negative!). I also go with a 60 amp breaker for the main breaker at the battery. I then put in more fuses at the console. With the current C Dory we utilized the one 6 fuse present and added a second 12 fuse block.

I am not familiar with a "Blue Seas 30 amp Safety hub". There are 100 to 250 amp safety hubs (with a AMI large fuse), with up to six ATO or ATC fuses up to 30 amps each. When Sunbeam gets back on land, she can clarify if this is one of the 100 amp safety hubs with a single 30 amp ATC fuse in it; (most safety hubs are more designed for a center console boat which does not have a fuse block.)

Although this may not apply here, but when you start the engine, since the starting battery and house battery are always combined (I believe you said), you can drop the voltage at the console, and thus increase amperage draw.

For now--stay away from the cigarette lighter. Have a good rest of the trip--and sort out the electrical later. Are you using a VSR?

AK Angler · Posted: Fri Oct 18, 2013 11:34 pm Post subject:

Regarding the size of the main fuse, it may - or may not - be undersized. Just remember... fuses are there to protect the wire. If needed, electronics or other components will have dedicated fuses in - or very near - the unit itself. As such, trunk and branch circuit fuses should be sized relative to the size of the wire between the fuse and the load. If there's too much load for the wire, upgrade the wire and then increase the fuse size accordingly. Never just bump up the size of a fuse because there's more load present than it can handle. The latter is a recipe for disaster.

Sunbeam - What size wire do you have connected to that 30A fuse? Is it tinned marine wire, or non-tinned copper?

AK Angler · Posted: Fri Oct 18, 2013 11:40 pm Post subject:

Sunbeam · Posted: Sat Oct 19, 2013 1:12 am Post subject:

Everyone:
You are definitely helping! I was baffled and lost when this happened (again) today. Now I am feeling a bit more confident. As I mentioned, this is not my strong suit, so this is a learning experience. I'll try to answer some of your questions - and maybe that will lead to something (plus, it's polite to answer anyway).

AK Angler · Posted: Sat Oct 19, 2013 2:14 am Post subject:

Sorry for the confusion, Sunbeam. Let's see if I can clear things up a bit...

Your 30A fuse protects the main wire that runs from the SafetyHub, up to the fuse/distribution block at helm. And, if both legs of that circuit are made up of 10ga wire (both the positive, and the ground wire), the 30A fuse is correct, and a larger fuse would not offer adequate protection for that circuit. If EITHER of those wires are smaller than 10ga, you need a smaller fuse. If BOTH of the wires are larger than 10ga, you MAY use a larger fuse.

Regardless, the 10ga wire in your house trunk circuit (and subsequently, the fuse) may be too small (marginal at best) to actually run all the house branch loads. That's how my boat was wired, and I was getting low voltage issues cropping up, so I upgraded to 6ga for that run and haven't had any problems since.

And, if you're wondering what protects the wires connected directly to the battery and switches (on the battery side of the SafetyHub) the answer is... nothing. If they are short runs made of large wire (I don't have the specifics sitting in front of me at at the moment), the ABYC says that they can be unprotected without raising red flags, or causing any safety issues.

AstoriaDave · Posted: Sat Oct 19, 2013 2:22 am Post subject:

Sunbeam wrote:
Okay, so if all the wiring on the "other" side of my equation is #6… that seems like it is plenty good for a larger-than-30-amp fuse. But….I only have 10 gauge running from the positive bus up to the helm panel (and that is wire that came with the boat, so probably nothing special in the quality department). However now I'm getting confused Embarassed I now think I know that all the individual fuses (mentioned in my list) protect the "small" wires running from the components to the fuse block (behind the helm), or the switches (by the helm). But does the 30 amp main fuse protect the "other" wires "behind" it (house battery/ACR/Safety Hub/main switch in lazarette, all #6 wire), OR does it protect that "supply" wire running from the positive bus to the helm area? I should be able to figure this out but…. maybe my brain has too small a fuse tonight

Diagram this all out and it will make more sense. Sounds like the fuse should protect just the run from the battery TO the buss bar/fuse block behind the helm, #6 all the way, yes? Other runs off the same battery terminal, perhaps passing through a switch, should have their own fuses, if that is what you are describing. I don't know what loads you can expect to those other items, so wire size and fuse will need to be selected accordingly.

hardee · Posted: Sat Oct 19, 2013 2:24 am Post subject:

Hi Sunbeam,

Sorry to hear about the electrical challenges. I am not boating electrician like some of the respondents are but, I would bet on the 12v cigar lighter plug. It is not uncommon for them to do a direct short when plugging or unplugging a device. I have seen them heat up to the point of melting things around -- and found that due to the smell of hot plastic.

These plugs do come in 2 (that I know of) different diameters. Some plugs are too large to insert, if it is the smaller size, but if it is the larger one, they will all fit, just not snug, as you have found.

That was a pretty cool full moon rise. I watched it come up over Whidbey and light across the PT bay and the forming fog.

Sounds like you have your electrical outage in hand.

Harvey
SleepyC Moon

AK Angler · Posted: Sat Oct 19, 2013 4:24 am Post subject:

OK, Sunbeam (and others following this thread)... I've got a correction to make to my earlier posts regarding wire/fuse size amperage limits. (I DID say I was digging those numbers out of my memory... Embarassed

)

According to this wire/fuse sizing chart available on the BlueSeas website, 10ga wire (that's bundled with other wires) can be adequately protected by a 40A MIDI/AMI fuse. So, if you find the fuse is popping because you simply have too much load for the 30A MIDI/AMI fuse, according to Blue Seas you can safely bump it up to a 40A MIDI/AMI fuse with your 10ga wire.

However (and not really related to your current fuse blowing problem), that same chart indicates that a 30-foot run of 10ga wire (positive and negative combined length) can only handle a 10-amp load before getting voltage drops greater than 3% (can screw with electronics), and up to 30-amp loads before getting voltage drops greater than 10% (bad for even "non-critical" loads). To handle 40 amps of current without voltage drop issues, you might be able to get away with 8ga wire, but 6ga would definitely be better. This may be why your installer opted for a 30A fuse, instead of the max-capacity 40A unit.

That being said, at some point you should add up any/all loads that may ever be used at the same time and see what your actual maximum load on that circuit is. You can use the fuse sizes in the distribution block at the helm, but that will over estimate the actual numbers. For instance, the wire to a wiper motor that draws 2 amps may be protected by a 5-amp fuse. So, it would be better to use the actual loads of your devices - if you can find them. Don't include any combinations that you know you will never use - like maybe the washdown pump and the trim tabs, or the autopilot and a windlass.

Then, when you're confident that you have a realistic upper end for the load, you can take a look at the wire/fuse size chart and make a determination if you need to upgrade. And, I would use the 3% voltage drop chart, because some electronic components are voltage sensitive, and we're talking about the main house feed. Besides, at some point you may want to add another gizmo or gadget, and it'll be nice to have a bit of "extra" electrical capacity.

jerry97230 · Posted: Sat Oct 19, 2013 11:36 am Post subject:

Fuse holders can be bad, not making a solid ocnnection with the fuse and there for heating the fuse and causing it to blow.
If everything is fused, the little fuse should blow first. So either the total load is to large or there is a short in the ciruit before the smaller fuses, or there is something wrong with the main fuse holder.
Jerry C Nile C22

Sunbeam · Posted: Sat Oct 19, 2013 12:48 pm Post subject:

Good morning all,

Your new posts have clarified about which wires are being protected, by what - thanks!

So we did some thinking and figuring this morning (before logging in here).

I found a West Marine chart for both 10% and 3% voltage drop. From what I (now) understand, 10% voltage drop is adequate for protecting some wires (i.e. so they won't catch on fire). 3% is best for equipment functioning (and also recommended for some important "smaller" loads such as running lights, etc.)

So, I figured my up & back run to be about 28'. Based on that, 10 gauge wire (which I have at the moment) is fine with a 30 amp fuse. So therefore (if my new and tenuous understanding holds here), the current wire running up to the helm and back, and the 30 amp main fuse are compatible. Perhaps this is why the 30 amp main fuse was chosen in the first place (not by me then, but now I am learning Thumbs Up

).

Then I wrote down loads for the current equipment, plus added some things I may install. To figure out what wire size would be best to upgrade to (after which I could see what size main fuse would safely protect it). Here is what I came up with (some equipment didn't list a draw, so I had to go by what fuse size they recommended - realizing draw is probably less).

Basic instrumentation now, all on = 2.5 amps

Future radar = 3.0 amps

Two (one future) 12 volt outlets = 18 amps (yes they are rated for more, but I'm trying to be somewhat "real world" and, for example, my computer charging and in use with full screen brightness and inverter is 5.0).

Future Autopilot 0.0 (would be mounted in laz); (current autopilot not listed in specs, and I'm not even sure it's working, so not counting for now).

Future wipers, two AFI 1000 5.0 for both, estimated.

Cockpit spotlight = 3.0 amps

VHF transmit = 5.0 amps

Fan (plus future second fan) = .5 total for both

Washdown pump (if have switch forward) = 6 amps

Cabin lights = would use LED so not counting for now (current two draw 3 amps total, but I don't use them).

Bilge pump manual switches, if both running via those switches = 2.2

Nav lights = .37 (although would be more if LED lights stopped functioning and I had to put in spare incandescent bulbs; but I'm ignoring that for now because if that happened I could consciously reduce other draws).

Horn = 5.0

Scenario #1 All together (including equipment I don't have yet) is around 50 amps

Scenario #2 Removing 18 amps somewhat arbitrarily (say VHF and washdown pump and bilge pump manual switches and horn not used together, etc.) = 32 amps.

Other draws on boat don't run through helm area (e.g. trim tabs). Future windlass would have its own wiring.

So:

28' run, 10% drop, 50 amps = 8 gauge wire.

28' run, 3% drop, 50 amps = Just on border between 4 gauge and 2 gauge.

Scenario #2, for 32 amps (probably more realistic, I'm thinking, given my overall use and system size):

28' run, 10% drop, 32 amps = 10 gauge
28' run, 3% drop, 32 amps = 6 gauge.

I chose 32 amps for two reasons: One is I realistically don't think I would be drawing more than that at a time in the real world. Two is that it was the amount that let me slip into the 6 gauge wire range for 3% voltage drop and it sounds like that is what people who have upgraded consciously have found to work. And it's still very high. 4 gauge or 2 gauge just seem like overkill. Even 6 gauge is probably ample (right?)

I now don't think the wire size is what got me into trouble over the past week, as I have not been drawing even remotely that much, especially when the fuse blew both times (we have been watching draws on battery monitor). And the 10 gauge wire I have looks to be sized properly for both what I have been drawing and for the main fuse. However, that doesn't cover a short or something like that, so I will keep looking (unless the problem never recurs, in which case I'm going to think it was the unfused cigar lighter).

Unless I read here something I didn't think of about why it would be wrong, I think I will rewire that "helm feed wire" with 6 gauge wire up and back, and increase my fuse block slots with a new block(s), just so I can have a fuse in the block for each thing (and get rid of some inline fuses).

They say that something good comes of even bad things.... well, here I am learning a lot more about electricals on the boat, and I will be making some good upgrades. So that's a plus Thumbs Up

Sunbeam

Just to clarify: The Safety Hub is wired between the house battery and the main switch. From the main switch, a wire goes to a positive bus, and from there is where the "helm feed wire" runs forward. That wire is the 10 gauge one (now). Everything "behind" that is #6.

AstoriaDave · Posted: Sat Oct 19, 2013 1:27 pm Post subject:

Rewiring with 6 ga and replacing inline fuses with fuse block is a very good idea. Much easier to chase a dead fuse if they are all in one place.

Looking ahead, you may want to run a separately fused 6 or 10 from that positive buss for the heavy current draw items, radar etc., to keep the voltage drop down below 3%. Your total run (both legs) is more than I expected.

If you are using split loom to contain the wires, might pay to put in a size which has room for more wires than you currently have.

Sunbeam · Posted: Sat Oct 19, 2013 1:39 pm Post subject:

AstoriaDave · Posted: Sat Oct 19, 2013 2:31 pm Post subject:

Sunbeam,

No, your estimate of the runs seems OK. I had been guessing shorter, not knowing your layout. No issue there.

My main concern is that you may need to run a lot of amps in a worst case emergency or similar. Suppose rough conditions, heavy rain, occasional spotlight use, obscured visibility or darkness. I figured you might be using all of these, not continually, but at some point all might be on: instruments, radar, wipers, spotlight, VHF TX, bilge pumps, nav lights, and horn. That came to 26.1 Amps. No need for the washdown, interior lights or the fan, most likely. But what about those 12V outlets? Would you need one of those to run a navigation app on a laptop? If so, then I think you will be over the 32.1 Amps that slid in under the 3% voltage drop requirement for 6 ga wire to serve your needs.

It might be that the 12 V outlets will have uses you can not imagine yet. If you run a 10 ga circuit dedicated to those, separately fused, then the 18 Amps they might draw does not burden the main circuit to the helm.

Sounds like you are in a good position to work through this and sort out the best wiring and fusing choices for your use now, so you won't have to come back and run another wire later.

thataway · Posted: Sat Oct 19, 2013 3:35 pm Post subject:

The 14 foot each way/28 foot is a good estimate; I use 30 to 32 feet because of the twists and turns along the way. Agree with Dave about there may need to be higher current draw, with less voltage drop in the future.

ABYC requires fusing within 7" of the battery. I choose a 60 amp breaker for the main bus feed, with wire sized to handle the 60 amps. None of our C Dory loads are critical to the 3% range--but 5 to 6% is more realistic-number-and that is why I go doubling the wire capacity from the factory wiring.

The person who Sunbeam had help wire her boat, used a 100 Safety hub (which can really handle a total of 7 circuits) for just a single expensive and hard to obtain, 30 amp AMI fuse. . If this is the case, a single circuit breaker would do the same, at less price and then you would not be stuck trying to find the AMI fuse on Lake Powell. As Sunbeam found, the loss of this fuse disabled most of the boat's electric functions, except the outboard motor.

The moral here seems to be understand what you have, and why you have it, in the circuit breaker/fuse protection on the boat.

AK Angler · Posted: Sat Oct 19, 2013 3:43 pm Post subject:

Sunbeam - It sounds like you've got a pretty good handle on your electrical situations at this point. That's good to hear.

In regard to upgrading your existing 10ga house feed, AstoriaDave has a good suggestion. There are two basic scenarios to consider.

Scenario #1) Remove 10ga wire and replace with larger capacity wire (in this case, 6ga wire). Also, remove existing fuse block, and replace with larger capacity unit to ensure all new and existing circuits are fused. In this case, you may be banging up against the carrying capacity of the wire in certain (although infrequent) circumstances.

Scenario #2) Leave existing 10ga wire and fuse block in place to run critical systems (maximum 3% voltage drop), and add another wire from a MIDI fuse at the SafetyHub to a new fuse block at the helm for the remaining systems.

After running the numbers on Scenario #2, you may find that with some systems running off of the existing 10ga circuit, you might be able to save a couple of bucks by dropping to 8- or even 10ga wire for the new 10% voltage drop systems circuit. Or (and this is what I would do), you could decide to run the 6ga wire in addition to the existing 10ga for no additional cost over Scenario #1.

In the latter case, you will have moved away from the minimums you calculated to get to the 6ga wire in the first place, and your electrical system will have a bit of extra headroom - it will essentially be "future-proofed". And, this would still leave one MIDI fuse available in the SafetyHub to protect a heavy draw circuit added later - like a future windlass!

So, options:
0) do nothing (must always be considered)[cheapest option - least capacity - most risk for problems]
1) replace 10ga wire with 6ga wire to meet minimum capacity from voltage drop calculations, and replace fuse block with bigger unit [more expensive than 2a, but similar capacity]
2a) as a cost saving measure, install additional 'calculated minimum' house trunk circuit (including additional fuse block), and keep existing 10ga circuit to seperate electronics from other systems [less expensive than 1 with similar capacity; less expensive and less capacity than 2b]
2b) install additional 6ga house trunk circuit and new fuse block, and keep the 10ga wire and fuse block in place for a dedicated critical systems circuit [same cost as 1, more expensive than 2a, but greater capacity than both - overall least risk option]