Over Current Protection On Pos Battery Connection - Page 3 - SailNet Community
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post #21 of 38 Old 02-28-2012 Thread Starter
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Concerning fusing solar panels, I am a little confused.

I have about 80 watts of solar power coming into a charge controller. The charge contoller then feeds to the battery to charge it. I will have a fuse on the + lead at the battery connection, but say there is a short on the wire that feeds from the charge contoller to the pv panel? Without fuse protection could not the wire heat up and start the insulation on fire? But you would not want to say fuse the panel with a 7 amp fuse becuase under normal conditions the fuse would blow. It does not seem possible to protect the output of a solar panel. I have searched many wiring diagrams and they typically show no fuse between the charge controller and the solar panel.
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post #22 of 38 Old 02-28-2012
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Looks like you've gotten great advice. One more piece. While ABYC addresses overcurrent protection rarely if ever is the starting power to the engine fused. The reason is that for engines, especially diesels, the starting current surge will likely exceed fues capacity.

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post #23 of 38 Old 02-28-2012
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Looks like you've gotten great advice. One more piece. While ABYC addresses overcurrent protection rarely if ever is the starting power to the engine fused. The reason is that for engines, especially diesels, the starting current surge will likely exceed fues capacity.

This is just not true. There are lots and lots of boats that have both banks fused. The ABYC allows an "exception" for starting circuits IF other criteria are met. It is still wise to fuse the start bank especially on small AUX diesel engines that draw soooo little current. I have been starting on fused circuits for over 20 years. Even had my old Cummins on our Downeast style boat fused. Never in 20 years have I blown a bank fuse unless I shorted the wire or fuse with a wrench. This is thousands and thousands of starts on small and fairly large diesels (Cummins)

In-rush can largely be ignored as the duration is far to short, less than 0.20 seconds, to pop an ANL, Class T or MRBF...

I have well over 40 boats I know off off the top of my head that have engine starting circuits fused. I don't know a single one who's blown a fuse in a "nuisance" blow. I do have customers who have shorted them with wrenches while working on things and popped them but not a properly sized fuse.. Most of these are fused at 300A or less and are sailboats.

I do however know of many boats that have burned to the waterline due to electrical fires because there was not adequate OCP. I also know of at least one Sabre that is still floating because it had the starting circuit fused (see pic below).

The wording for this exemption is one area where I strongly disagree with the ABYC. Even Ed S, the ABYC education director, would like to see the wording changed and the "exception" be only for engines that can't be adequately fuse protected or where the cost would be prohibitive.


These are just some of the reasons I fuse...
Vibration Video

Starter wire that WAS fused. This one saved a Sabre from burning to the waterline......:



Starter wire that was not fused (just two minutes before this fire erupted there were a number of 8 & 9 year old junior sailors on this boat):


No fusing on the battery cables, deemed electrical fire:


It is important to remember that the ABYC does not say to NOT fuse starting circuits, they give an "exemption" IF the "starting circuit" wires are protected.

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Last edited by Maine Sail; 02-28-2012 at 04:30 PM.
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post #24 of 38 Old 02-28-2012 Thread Starter
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Those pics are a wake-up call. Thanks Maine Sail
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post #25 of 38 Old 02-28-2012 Thread Starter
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Concerning fusing solar panels, I am a little confused.

I have about 80 watts of solar power coming into a charge controller. The charge contoller then feeds to the battery to charge it. I will have a fuse on the + lead at the battery connection, but say there is a short on the wire that feeds from the charge contoller to the pv panel? Without fuse protection could not the wire heat up and start the insulation on fire? But you would not want to say fuse the panel with a 7 amp fuse becuase under normal conditions the fuse would blow. It does not seem possible to protect the output of a solar panel. I have searched many wiring diagrams and they typically show no fuse between the charge controller and the solar panel.
Regards
Maine Sail,
Could you provide a reply on the PV panel overcurrent protection? I think a direct short on a PV panel will make the output go to zero power. But what it the short is not zero resistance, say a high resistance short, I could see the panel still putting out power that may lead to the conductor insulation cathing fire.
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post #26 of 38 Old 02-28-2012
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Casey, in theory the output wiring from a solar panel has been sized so it can safely and continuously carry the full output of the panel. Therefore a short circuit of any kind, i.e. a short where those wires go into the solar controller, can't cause any damage to the wires because they are already sized to safely carry that full power load.

The other concern might be the panels themselves, i.e. will a dead short on the panel output cause any damage to the panel? That one I don't know yet, I suspect part of the answer would involve whether there are additional panel diodes and whether the short caused any localized overheating in any components on the panel. I've never seen fusing suggested for this in low power (i.e. not trying to replace grid power at 100+ volts) installations.
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post #27 of 38 Old 02-28-2012
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Maine sail has it exactly right. As I mentioned above, I installed a 300a ANL on the start leg of my Yanmar G3GM30 and have not had a problem. Just see what your starter draws and fuse it accordingly. The key idea here is that a fuse WILL blow on a dead short whereas a wire will very possibly burn. Not only that but ANY wire, such as a light gauge solar panel wire that is not fused can short and if touching the batteries, burn through and cause an explosion of battery gasses. I've seen this happen. So, all the + wires leading from batteries need to be fused close. I guess that's why the CG specs are as they are. SOME regulations and guidelines actually make a lot of sense.

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Maine Sail,
Could you provide a reply on the PV panel overcurrent protection? I think a direct short on a PV panel will make the output go to zero power. But what it the short is not zero resistance, say a high resistance short, I could see the panel still putting out power that may lead to the conductor insulation cathing fire.
Regards
Solar panels are by design self limiting in that if shorted they can't produce more than their rating.

The wire you use will usually be well in excess of the panels current and wires ampacity rating will be significantly larger than what the panel could produce because you're trying to keep the voltage drop low. Keeping the voltage drop low requires larger wire that will almost always exceed the panels rating in current.

Even in a dead short the wire should remain below its melt point. You can fuse the panel side of the controller but it is not as critical as the battery side..

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post #29 of 38 Old 02-29-2012
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There are lots and lots of boats that have both banks fused. The ABYC allows an "exception" for starting circuits IF other criteria are met.
Quite right. The ABYC standard was written back when the types of fuses available could not handle the surge (I was on the committee). But over the years fuses have become available that can handle the surge without blowing. It requires a "slow Blow" fuse. Today, more and more boats are being fitted with Over Current Protection for the starter circuit.

I too can show you some pics of serious electrical fires. It can ruin your whole day.

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post #30 of 38 Old 02-29-2012
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Quite right. The ABYC standard was written back when the types of fuses available could not handle the surge (I was on the committee). But over the years fuses have become available that can handle the surge without blowing. It requires a "slow Blow" fuse. Today, more and more boats are being fitted with Over Current Protection for the starter circuit.

I too can show you some pics of serious electrical fires. It can ruin your whole day.
The BlueSea website has a little graph showing the time delays built into their ANL fuses. I actually lowered the amperage for the starter leg when I looked at these specs. There is a large time delay in all the ANLs before they will open. The main point is that with a dead short, they will blow whereas an unfused 2/0 wire will burn off the insulation, sometimes along its entire length, getting red hot and possibly igniting anything it touches.

Another thing I did on the long runs to the motor was to shield the wire with some 1/2" flexible plastic conduit; the blue stuff you can get in Home Depot, etc. This worked out really well and is inexpensive. I suppose you could use something like Etcoflex if you wanted to spend more money.

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