I blew a fuse!

Tally Ho

Tally Ho

.
Jan 7, 2011
5,263
Oday 322 East Chicago, IN
So, I will freely admit that boat electricity is not my strong suit.

But last year, I (finally) replaced my (2) Group 31 batteries with (2) 6-volt GC batteries. The delay was, in part, because I wasn't sure how to wire them for 12 volts.…I said boat electricity is not my thing.

My boat had no fuse at the battery bank, so over the winter, I installed a fuse at the battery…

B80EB146-53D2-4147-BC67-041F59F50D78.png

I worked on the boat over the winter, and no issues with the DC power (but no real loads in it…just some lights on).

Today, I launched Tally Ho in 45 F temps.
A44DA14A-CF5D-4A69-9AD9-6DB6C4F118BF.jpeg
Once in the water, but still in the slings, I tried to fire up the trusty Yanmar 2GM20F. She turned over, but didn’t fire right off the bat. I stopped pushing the button after 20 seconds, took a beat or 2, and them pushed the start button again…she turned over, but then stopped. And no alarm from the control panel…:mad: Went below, and my battery monitor was not reading any voltage, analog VM in the panel didn’t move…

Then it dawned on me…I bet that “+%€¥£€^[ fuse blew. Sure enough, I removed the fuse and connected battery cable direct to the battery, went back to the helm, turned the key on, got an alarm tone, hit the start button, fired up the Yanny and moved her to my slip.

So, my question is what size fuse should I use ? The one that blew was 100 amps. I have (I think) 2 AWG wire from the battery bank to the battery switch.

So was my fuse too small (200 and 300 amp fuses were also an option, but I ordered with the 100 amp fuse)…or do I have thing else (worse) wrong in my engine starting system that killed a fuse that should have been OK for this small system?

Give me a quick education so I can order a new (correctly sized fuse)!

Thanks,

Greg
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
22,904
Catalina 34 224 Maple Bay, BC, Canada
Greg,

Assuming your wire is sized properly, given what you've shared with us we can't know.

This may be helpful, too:

Battery Fuse Sizing - How?

Lately there have been a number of questions, on this and other forums, about battery bank fuse sizing and I wanted to give a brief explanation of how I size these fuses. Simply put you size the fuse to the wire provided your wire is sufficiently sized. #1 The standard. The ABYC requirement...
forums.sailboatowners.com
 
Siamese

Siamese

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Aug 2, 2009
651
Catalina 315 Muskegon
Hopefully, I'm misunderstanding what you said in your post about pushing the starter button for "20 seconds". Continuously? o_O Serious danger of filling your exhaust system with water and that water entering the combustion chamber via the exhaust valve, and destroying your engine. I'd provide addition information, but maybe I took you too literally?
 
heritage

heritage

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Apr 22, 2011
903
Hunter 27 Pecan Grove, Oriental, NC
I have been using a 175 amp MRBF on the battery that starts my 2gm20f for about a year with no issues.
 
Tally Ho

Tally Ho

.
Jan 7, 2011
5,263
Oday 322 East Chicago, IN
Siamese said:
Hopefully, I'm misunderstanding what you said in your post about pushing the starter button for "20 seconds". Continuously? o_O Serious danger of filling your exhaust system with water and that water entering the combustion chamber via the exhaust valve, and destroying your engine. I'd provide addition information, but maybe I took you too literally?
Click to expand
I didn’t time it, but I am aware that cranking too long can lead to hydrolock and some really bad news. I didn’t crank that long. Maybe it only felt like 20 seconds because she didn’t fire Up.

But thanks for the reminder that cranking away can lead to some real problems.

Greg
 
Tally Ho

Tally Ho

.
Jan 7, 2011
5,263
Oday 322 East Chicago, IN
heritage said:
I have been using a 175 amp MRBF on the battery that starts my 2gm20f for about a year with no issues.
Click to expand
Good to know.
I just ordered a 200 amp, so will see how that goes.

Greg
 
Scott T-Bird

Scott T-Bird

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Oct 26, 2008
6,216
Catalina 320 Barnegat, NJ
Well, if you are blowing a 100 amp fuse on a 20' roundtrip run with 2 AWG, I'd suggest that your cable size is too small and so is your fuse but you don't want to use a much larger fuse with that cable. My rec would be to increase the size to 1/0 minimum (that would be "0" on the chart Stu posted) and use a 250 amp fuse. I actually put a 300 amp fuses (allowing for the 150% rule) on my batt terminals with MRBF holders with 1/0 for both House & Start. I use 1/0 because the boat has it installed and the runs are in conduit, not to be changed.
 
Tally Ho

Tally Ho

.
Jan 7, 2011
5,263
Oday 322 East Chicago, IN
I
Scott T-Bird said:
Well, if you are blowing a 100 amp fuse on a 20' roundtrip run with 2 AWG, I'd suggest that your cable size is too small and so is your fuse but you don't want to use a much larger fuse with that cable. My rec would be to increase the size to 1/0 minimum (that would be "0" on the chart Stu posted) and use a 250 amp fuse. I actually put a 300 amp fuses (allowing for the 150% rule) on my batt terminals with MRBF holders with 1/0 for both House & Start. I use 1/0 because the boat has it installed and the runs are in conduit, not to be changed.
Click to expand
If the recommended fuse for 2AWG wire is 200 amps, why change wires because I blew a 100 amp fuse?

The boat is 30 years old, and was never fused. I am trying to protect the wires, but I don’t want to replace them.

If I decide to replace wiring, yes, maybe I would go up a size or 2…but she was worked fine for 30 years.

Greg
 
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Scott T-Bird

Scott T-Bird

.
Oct 26, 2008
6,216
Catalina 320 Barnegat, NJ
Tally Ho said:
I

If the recommended fuse for 2AWG wire is 200 amps, why change wires because I blew a 100 amp fuse?

The boat is 30 years old, and was never fused. I am trying to protect the wires, but I don’t want to replace them.

If I decide to replace wiring, yes, maybe I would go up a size or 2…but she was worked fine for 30 years.

Greg
Click to expand
Stu provided charts that show for 3% voltage drop at a 20' run the 2 AWG size pretty much runs out at 100 amp current. You blew a 100 amp fuse, so I'm assuming the current was greater (perhaps significantly). The next chart down shows 150 amp and 125 amp fuses for 2 AWG for bundled runs (maybe yours are not). In any case, your application appears to be on the edge with 2 AWG cable. Maine Sail wrote an article that suggests that boat builders basically learned that they undersized their cables when they produced boats with 2 AWG cable and subsequently increased cable sizes to 1/0 or 2/0.

My Starwind had 2 AWG cables and I used 200 amp fuses with no problems, but I'm not going to rec to you to be on the under-sized side of the edge. YBYC.
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,693
Canadian Sailcraft 36T Casco Bay, ME
Guy's I have said this before, many times. For any bank that may ever be called upon to start a motor 250A is the bare minimum but 300A is better..


Funny you bring this up now because Nigel and I were just discussing this on Monday and he just posted this video yesterday!!.


Here is one of my own videos where you can witness a tiny 1kW starter motor on a bench, not even connected to a motor,pulling 365+A for in-rush...''
 
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Stu Jackson

Stu Jackson

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Feb 26, 2004
22,904
Catalina 34 224 Maple Bay, BC, Canada
Tally Ho said:
Stu, the circled link doesn’t work for me…does it work for you?
Click to expand
Greg, thx for noting that, I removed it. But the information it used to contain is also in the other links. Thx again.
 
Tally Ho

Tally Ho

.
Jan 7, 2011
5,263
Oday 322 East Chicago, IN
So, what heard in the Nigel Calder video is that:
1) starting circuit is one place you may not want a fuse
2) if you do, oversize it so you don’t blow it (300 or more amp fuse)

So what are you supposed to do if you use your house bank to start the engine?

Could a person run 2 positive wires from the battery bank to:
1) the starter (unfused)
2) the selector switch / panel (fused)

Greg
 
B

Benny17441

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May 24, 2004
7,141
CC 30 South Florida
Siamese said:
Hopefully, I'm misunderstanding what you said in your post about pushing the starter button for "20 seconds". Continuously? o_O Serious danger of filling your exhaust system with water and that water entering the combustion chamber via the exhaust valve, and destroying your engine. I'd provide addition information, but maybe I took you too literally?
Click to expand
That is true, but only if the exhaust port is under the waterline. I believe, not sure, the 80s Oday 322 had the exhaust above the waterline.
 
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