Mystery major short circuit

[Captain Lee]

Originally Posted by Scrimshaw4

You might want to check around your boat to see if you took a lightning strike. otherwise check your ac and charging circuits. Good luck

That would be an excellent answer, Scrimshaw, but no lightning in San Diego.

Thanks for the ideas!

[Captain Lee]

Sounds like a good answer for many. Fortunately, we have no lightning in San Diego

[Captain Lee]

Originally Posted by Maine Sail

You'll want 250-300A MRBF if you are starting that engine, 200A on the very low end.

Responding 7 weeks after initial post. Very rude to post a question, then disappear, especially with all these good suggestions. Other things in life unexpectedly got in the way. However, I am now back at boat, have studied and thought for 2 days before posting now.

Btrayfors, Maine Sail, and Stu Jackson: I know some or all of you are very experienced, and I understand the conventional wisdom of your answer re: fuses too small. However, I lean away from this explanation for these reasons:
a. I think the current draw with starter has to be at the very low end of possible range. This engine, in warm San Diego, has started within 2 seconds for the last 4 years without any fuse or wire overheating issues. True, I have only had fuses at the battery terminals for the last year, but no prior problems with engine start and fuses during that year.
b. I always use only battery 1, never both batteries, to start the engine. I would have had to make a still unrecognized error with the battery switch setting to have both batteries exposed to the starter current.
c. If both batteries were simultaneously in the circuit, I would have had 100+100=200 amps of fuse protection overall, greater than the 190 CCA of the engine specs.
d. In contrast to my several years of no-drama engine starts, this problem occurred after months of intermittent major electrical work (new AC panel, new DC panel, new AC shore receptacle, new battery switch, new AC and DC ground wires to engine.) I have had a lifelong interest in electrical projects, but still consider myself a novice at real life boat electrical problems. I think the highest probability lies with: I did something really dumb, didn't notice it at the time, and still can't figure out what I did.


Will post more!

[Captain Lee]

Originally Posted by W3GAC

100a is a BIG load/ short. As said, hard for normal 16-14ga branch circuits/ wiring to pull 100a w/o melting in half... and that would happen only once.

I would attack two ways:

Using Ohm Meter
- Disconnect batteries
- Turn off all battery switches & panel
breakers
- Connect ohm meter across the
now pigtailed + & - battery wires
- Should read infinity (no meter
deflection)
- Starting with each battery SW if
more than one... Slowly cycle
through each position while
watching for short (full meter
deflection)
- If all OK, leave on and move on to
panel & flip breakers one by one
watching Ohm meter for short

If a short still exists this should reveal which circuit has issue

If you don't have Ohm meter or if this hadn't revealed any issues, connect the negative battery lead to the negative battery terminal on only one battery. And temporary wire a 12v filament type light bulb between the position battery lead and the positive battery post. The higher wattage the 12v bulb, the better... like a spare 55w 12v spreader light. If you trigger a short/ high load the bulb (now in series will glow dim to bright depending on load/ full short circuit. This will save blowing a costly $17 fuse as you progress through finding
the short with the boat's 12v system softly energized.

- With the 12v system now being activated, but with limited current availability because of the series 12v bulb, repeat the above sequence. I wouldn't expect any difference, but if you have to do some/ all this working alone... it's a good technique to be at two places at the same time because you can position the bulb to be seen as you go to other location on the boat.

Assuming you haven't found the short yet, now go back to your most recent projects (statistically new problems are usually triggered by new work... directly/ or indirectly by misplaced pliers left behind fallen and shorting something unrelated to the project at hand) and shake, rattle, roll the wiring/ new device you just installed. It won't be the first time a new light fixture came with shorted bulb base, or a wire got pinched, hidden wire got drilled through,... doing an otherwise simple project. Stop, look, listen, smell around each job site for any clues. While it's more likely that your project somehow triggered the current issue, it's possible that long term chaffing of wiring just picked this time/ or so slight nudged and failed. So grab and tug on any/ all wiring harnesses/ bundles whether you were around them or not.

As part of this process, pay particular attention to/ trace (every inch) of each of your high current battery cables to their destinations.

While further down the list of probable cause, if your batteries are wired in parallel or the battery SW was left in the Both position and one battery developed an end of life shorted cell it could possibly trigger a catastrophic event leading to a battery-to-battery high amp short through your fuses, which is one reason why they are there! So while the batteries are separated check their standing voltages (no charger/ loads) to see that both are in the range of 12-13v'ish.

Many boats, despite ABYC guidelines run their bilge pump wiring directly to a battery to ensure it never accidentally gets flipped off with the rest of the breakers on the panel. Of course, even wired this way there is usually a 'twist & lock' glass cartridge fuse next to the ubiquitous ''Auto-Off-Run Bilge SW to protect the boat from direct shorts that might cause a fire/ dead batteries. But it is possible that the bilge pump wire from the battery somehow got pinched/ shorted before it got to that protective fuse. Again, I doubt that the typical bilge wiring gauge could cause a 100a fuse to blow... but if you haven't found the issue by now, it's worth tracing that bilge wire from the battery to its destination. We should all do these checks once in a while anyway, including the shake, rattle, roll of wiring harnesses. Better to find issues at the dock than coming into a marina chased by a storm and the lights all go out.

Circling back... I'd really especially check all the big cables from the battery... and really check the ones to to the starter and the electrical panel... because generally they are the only big red wires that end up going to places where there is a clues by negative terminal/ metal that could cause such a significant 100a short if it got loose/ came off its stud.

Most boats now used switching technology based chargers... lighter because no big heavy iron transformer. But w/I that isolation transformer, when switching power supplies fail it can result in the 120v AC it's connected to at least temporarily connected to your battery. Again, I sorta doubt that this could fry a 100a fuse, but if you have exhausted other options, it's worth disconnecting the charger wires and checking it's output voltage.

I saved this last one for last because it's very unlikely, and I hope it isn't the cause, and because if it caused a 100a fuse to blow, there could be a serious safety issue. Our boat are all usually 'grounded' to the salt water via shaft/ prop mechanically connected to the engine which in turn almost always has a big negative battery cable bolted to it to complete the starter circuit. Also many boats have their safety green ground wire from their shore power cord eventually also finds itself connected to the shop's 'ground.' If your dock ground (green) or neutral (white) wiring has lost its continuity your boat may have temporary taken the dock's return path to ground when you re-plugged in your boat. Again, this is highly unlikely, as by now many boats would be suffering some all kinds of low voltage, hum in electronic audio circuits, erratic operation of most electronics equipment. But if this has occurred, you should disconnect your shore cord until the issue is resolved by a professional.

Give us a status update/ what you found, or if you need more ideas.


Sent from my iPhone using Cruisers Sailing Forum

Really appreciated post by W3GAC. Very thorough and logical.

[Captain Lee]

Originally Posted by Cadence

I would have to agree it is nothing you did wiring with 16 awg.. Blowing 100
A fuses would have probably crisped 16s. Do you not have fusing for the lighting circuit that would have gone first?

yes, I do.

[Captain Lee]

Originally Posted by geoffr

Lee,

If I understand your set-up correctly you have:
2 batteries:
#1 - AWG4 to battery selector (position #1)
- AWG6 to battery charger
#2 - AWG4 to battery selector (position #2)
- AWG6 to battery charger
- AWG? to bilge pump
On both batteries the wires are connected to the battery via a 100A terminal fuse.

You found that both 100A fuses (battery #1 and #2) were blown.

Questions:

1- The only way I can see that the both fuses were blown is that you had the battery selector in the combine/both position - can you confirm this?

2- Where is your engine starter connected? (battery selector or direct to battery?)

3- Where is the alternator connected?

4- I assume as jeepbluetj noted you have a wire from the battery selector to a fuse/breaker panel - were any of these fuses/breakers blown?

Responses to Geoffr:

You have described my setup and event accurately. I will post photos soon. Bilge pump wires are 16 ga and I have 5 amp fuses on pos and neg wires where they attach to battery #2.

Questions-
1. I do not think I had battery selector switch on to COMBINED, but human error always possible.
2. Cable to starter looks like 2 ga and runs 10 feet from batt switch to starter motor.
3. I do not know where alternator is connected. Have not tackled that chapter yet. All its wires look normal, undamaged.
4. As I am doing major rewire, the running lights are the only DC circuit I have at this point. They have a circuit breaker at DC distrib panel, not tripped.

[Captain Lee]

Originally Posted by DeepFrz

One other situation to consider is that maybe your start cct. energized with the fuel shutoff in stop mode. That could have caused the engine start system to run long enough to blow the fuses. Have you ever had that situation occur. It is often corrosion in the start cct. somewhere. That could have blown both fuses if the switch was left in the both position. Just a thought.

Thanks, deepfrzz. Good advice. In this case, engine started in 1-2 sec.

[Captain Lee]

Originally Posted by hellosailor

If, as the OP states, he only starts from B1 and both battery fuses were blown, one might ask "How and when is the system set to "Both", so that both fuses could blow?


Are the batteries only combined (in this time frame) when the charger/inverter/shore power is running?


Is there some chance a cable has been chafed in or near that equipment, so that it only rarely shorts out as it hits a metal bulkhead or equipment case?

Thanks HelloSailor. When I am charging, both batteries are being charged via cables direct from charger, and batt selector switch is OFF.

I keep getting drawn to battery charger as somehow being involved-see post to follow soon.

[Captain Lee]

Originally Posted by Cadence

I kind of blew this off until remembering my pickup getting fried by lightening. I hope that is not it, It had hi,pot shorts in everything, It did take out the battery fuse link/

Thanks, Cadence. No lightning in San Diego, part of our current drought issue!

[Captain Lee]

Originally Posted by hellosailor

If, as the OP states, he only starts from B1 and both battery fuses were blown, one might ask "How and when is the system set to "Both", so that both fuses could blow?


Are the batteries only combined (in this time frame) when the charger/inverter/shore power is running?


Is there some chance a cable has been chafed in or near that equipment, so that it only rarely shorts out as it hits a metal bulkhead or equipment case?

No chafes. Cables new in 2011, still look new.

[Captain Lee]

Originally Posted by Brian Russell

While others have correctly suggested "checking the cables", I think it is important to state that one should also check the torque on the nuts on battery posts and starter studs, as well as any other screw terminals in the circuit, such as at fuse blocks, terminal strips, etc. Are the terminals properly made up, tinned, with heat shrink and are they free of corrosion? A loose connection , or corrosion, can seriously cause a voltage drop, which in turn will cause amperage to increase. Never place a stainless steel washer between a terminal and the contact surface below the stud, as stainless has very poor conductivity and will also cause a voltage drop. Regularly checking these connections should be on the semi annual maintenance list, in my opinion. Good luck tracing the problem, detective!

To Brian Russell-I think this answer has real possibilities. I found that I had placed a washer BELOW the fuses, as well as above. I do not know whether that was stainless steel (and can't check anymore), but I do use stainless fasteners liberally, and this point had not occurred to me. The answer is attractive because it might help explain why two fuses are fried but every other electrical component looks fine and works fine.

[Captain Lee]

I am attaching photos of the major components of my electrical system. Several important comments:

1. I see that there are labels on each battery case, and that these are mislabeled. The battery on the left is battery 1, and on the right, battery 2.

2. You will notice that one large cable from the positive terminal of battery 2 is black. I inherited this from PO. Although the color is wrong and dangerous, it seems to carry electricity fine in the correct direction. On the "to-do" list to replace.

3. On the back of the battery switch, the large red cable on the lowest post loops out of the photo to the right, then U-turns back in, supplying DC from battery 2 to the DC distribution panel immediately below.

4. On battery 2, you can see the ground wire from the bilge pump with its yellow fuse cover. Similar positive cable not connected in this photo.

5. For readers who, like me a little while ago, may not understand what these terminal fuses look like, here is my new 150A fuse and its box. In the photo next to it is one of the blown 100A fuses

[Captain Lee]

2 more photos. I mistakenly said I have a Xantrex charger. Actually, it is a ProMariner ProTech 1240iPlus.

I have the "common ground" for both AC and DC on the bolts of the engine exhaust flange. Plenty of room for improvement here re: not ideal place for ground, rust, corrosion on old cable, but resistance between any element of this ground connection and the negative battery terminal is 0 ohms.

I do not have any common bonding for any of my through-hulls or shaft. All well zinc'd, with minimal loss of zinc material over a year.

[Captain Lee]

2 more photos. I mistakenly said I have a Xantrex charger. Actually, it is a ProMariner ProTech 1240iPlus.

I have the "common ground" for both AC and DC on the bolts of the engine exhaust flange. Plenty of room for improvement here re: not ideal place for ground, rust, corrosion on old cable, but resistance between any element of this ground connection and the negative battery terminal is 0 ohms.

I do not have any common bonding for any of my through-hulls or shaft. All well zinc'd, with minimal loss of zinc material over a year.

[Captain Lee]

So I decided to conquer this major mystery yesterday. I used the following tools:
1. Night before, printed out, read, and re-read all of your responses. This community can collectively provide a pretty comprehensive list of good ideas.
2. Night before, I read, then re-read Nigel Calder, "Boatowner's Mechanical and Electrical manual, 3rd ed., 2005, International Marine, chapters 4,5,6.
3. Full night's sleep
4. Good coffee
5. Notebook to record observations step-by step.
6. Clear mind.

7. I went down to the boat, opened the battery compartment, and took all the photos I have posted today.
8. Next, I just sat and looked and thought for a little while.
9. Next, I followed the "Comprehensive Grounding and Corrosion Test Procedure" on pp 234-235 )of Nigel Calder's book. (Without a silver/silver chloride half cell, I did not do the galvanic current tests). I combined this testing with combined with his troubleshooting on pp 125-134 of chapter 4, and the excellent comments of W3GAC.

Results:

A. I did a hydrometer test on all 6 cells in each of 2 batteries. As might be expected after 7 weeks off the charger, Sp.Gr was down somewhat, but not bad, ranging from 1255-1260 on battery 1, 1240-1245 on batt 2, with one cell down at 1205. Fluid level low in all cells. Filled with distilled H2O, and charged apparently normally, over 3-4 hours. Have not rechecked Sp.Gr. yet but do not expect surprises.

B. Using combination of detailed volt, ohm, and amp testing over a number of hours, I could not find even a small instance of ground leak or unwanted resistance in any element of the DC, AC, or shore power electrical system.

C. Probably worth saying that I am at a well run salt water marina, completely re-done with new docks, wiring,, etc 4 years ago. I assume there are some boats, maybe near me, that do not have ideal electrical configurations.

D. All wires look to be in good shape, no evidence of melt or missing insulation.

E. One odd observation: I took all wiring off before I started checking battery condition in detail. To reconnect wires, I (incorrectly) connected the ground wires first: Battery charger ground, common ground cable from engine block, joint ground cable between batts 1 & 2, all to neg terminals of both batteries. As I started to place the positive cable from the battery charger on the pos terminal of battery 2, there was a small spark. With the cable detached, I was able to measure a 12 volt differential between the charger cable and the positive battery 2 terminal. This was with battery charger connected to AC, but charger AC circuit breaker OFF at the AC panel.

I was able to repeat the observation in a different way: starting over from scratch, I made all positive connections first, then last stared to connect the ground cable from charge to neg terminal of battery. Again, a small spark. Again, a 12 V potential measured from loose end of negative cable and negative terminal of battery.

I did not understand this. The observations suggested that there would be a continuous DC current flowing from positive batt terminal, through charger DC side, to neg battery terminal, even with charger off.

I did an additional test. Using voltmeter, I turned charger on and again measured voltage between charger + terminal and batt + terminal. I found a 2.4V potential, as I would expect from a charger in its initial phase and a partially discharged battery.

Confusingly, later when I tried to measure resistance across these same charger cables to find another way to show continuity between charger + and ground cables, I found infinite resistance. I was also unable to reproduce the spark and voltage observations.

Contacting support at ProMariner was unhelpful.

My tentative conclusions from this whole saga:
1. I did not fry fuses with starting engine.
2. Of all the answers, I like Brian Russell's the best: my extra washers at the terminal, different from the configuration specified by Blue Sea, may somehow have caused the problem.
3, I do not understand why I saw sparks and voltage at the charger cable terminals.
4. Writing down your observations as you go is really important. I need to do better and be even more detailed to crack a difficult problem.
5. I should just forget it and sail at this point, and wait till something else happens. If it does, I promise to post an update.

Thanks to all,
Captain Lee