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Old 02-14-2018, 12:45 PM   #1
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Backup Battery Power in Pilothouse

When I bought my boat the PO had put a battery in the pilothouse which I think ran the radio. I pulled it out as it was an odd setup but now that Ive completely redone the electronics I am starting to think about it again, specifically what are the critical systems if you have a complete power failure at sea, for instance in the event of a fire.

The setup I am thinking about is a single large 12v battery in the pilot house hooked up to charge from the main system.

That battery would then power the following:
NMEA2000 Network
Furuno GP33 GPS (through N2K)
Icom M506 w/ DSC (GPS through N2K)
Icom M806 w/ DSC (SSB) (GPS through 0183 from GP33)

Has anyone else done something like this and if so what were the critical systems you put on the secondary power source?

Thanks
AC
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Old 02-14-2018, 12:55 PM   #2
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When I bought my boat the PO had put a battery in the pilothouse which I think ran the radio. I pulled it out as it was an odd setup but now that Ive completely redone the electronics I am starting to think about it again, specifically what are the critical systems if you have a complete power failure at sea, for instance in the event of a fire.

The setup I am thinking about is a single large 12v battery in the pilot house hooked up to charge from the main system.

That battery would then power the following:
NMEA2000 Network
Furuno GP33 GPS (through N2K)
Icom M506 w/ DSC (GPS through N2K)
Icom M806 w/ DSC (SSB) (GPS through 0183 from GP33)

Has anyone else done something like this and if so what were the critical systems you put on the secondary power source?

Thanks
AC
AC

A dedicated 12v system for instruments is not uncommon. My instrument guy says space availability for a battery is a plus and overly complicated initial setups seems the determining factors.

After your rewiring efforts you may be fine, but try it without first especially when operating other onboard systems such as microwaves, toasters, hair dryers etc that may cause voltage surges.

Battery backup in industrial applications is not uncommon either.
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Old 02-14-2018, 01:20 PM   #3
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Thanks, I also think that a separate battery system could eliminate some of the noise in my power which I think is affecting the performance of my M802.
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Old 02-14-2018, 01:51 PM   #4
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There are lots of things that might happen at sea and a total power failure is only one and probably pretty rare.

The real problem with your proposed setup is keeping the backup or electronics battery charged. Remember, power can flow both ways in a pair of wires so if you just connect your emergency battery to the other batteries, when they fail, power will flow from your emergency battery to the failed batteries and this will drain your emergency battery.

A simple diode would seem to be the solution because it would allow charging current but block current from your emergency battery from flowing "backwards" to the other batteries. The problem with this solution is, there would be a voltage drop across the diode and the emergency battery would never fully charge.

A "battery combiner" or "automatic charging relay" would probably solve the problem.

Again though, what you are thinking about is pretty rare so unless you have some special circumstances, I wouldn't be overly concerned about it.

Also, if you connect the batteries for charging purposes, they are no longer separate and any noise in the system will be transferred to your new battery. A better plan is to find and eliminate the electrical noise.
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Old 02-14-2018, 01:56 PM   #5
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I thought about getting one of those "jump start" portable batteries. Some of them have USB charging ports and cigarette-lighter plugs. Assuming you have a cigarette lighter outlet on the helm somewhere, it might be possible to just plug it in if the rest of the electrical system is lost, such as dead batteries or even a fire in the ER or in some of the wiring in between.

Plus, it could be used for a jump start of your own boat, or even a car shoreside.

One problem with old boats is that the electrical system usually "evolves' a lot over time. Things are added to existing circuits until a new circuit needs to be run, so there may be several circuits that feed critical equipment, and that equipment may share a circuit with other, less critical things.
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Old 02-14-2018, 01:58 PM   #6
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I think a good installation, regular checks, and regular maintenance of a central main battery bank would have a very, VERY low probability of failure.

I wouldn't think the solution is to add more connections, batteries, and failure points to a vessel.

But I might not be seeing your whole picture.
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Old 02-14-2018, 02:15 PM   #7
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All valid points, I have gone through the electrical system and its pretty much what you would expect out of a 30 year old boat. That said battery bank is new, charger and alternator/inverter are all high end and pretty new. Good isolation between starter batteries for Engine, Genset, House and Stern Thruster.

I just worry that all those systems are below sea level, in other words in a situation where water starts entering the boat they are in danger of failure, feels like some system to still operate the radios is a plus. Not to mention if I can isolate the noise for the M802 thats likely a heck of a lot less work than figuring out where its coming from after 30 years of upgrades, enhancements and creative solutions by the PO

The other easy option is a 12V battery on a selector switch to power the above electronics and simply charged by a battery tended connected to 120v.

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Old 02-14-2018, 02:27 PM   #8
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The need for emergency power, separate from the engine starting battery and the house battery system would be a very rare event. Something would have to fail like a sulfate shorted battery taking down the other house batteries. Even in that case you just start your propulsion engine, switch the house systems over to the start battery and keep going.

Or your propulsion engine's alternator can fail, but then that should immediately trigger a warning light and power adjustments can be made to keep going.

We can postulate all sorts of scenarios, but it will be extremely rare if it disables your boat, navigation or communications for long.

FWIW offshore sailboat racing rules do require an entirely separate battery system, nav lights, and nav radio, but because it applies to sailboats there is nothing about an emergency engine starting battery.

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Old 02-14-2018, 03:54 PM   #9
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Depending on how isolated your cruising area is.....keeping a charged handheld, with the ability to plug it into your main antennae might be a much simpler goal, that would provide emergency comms if your batteries were underwater. It wouldn't give you all the capability of the system you describe, but it is uncomplicated enough to be reliable and easy to set up.
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Old 02-14-2018, 03:55 PM   #10
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Large commercial fishing vessels (>20m) in Canada are required to have an emergency battery supplying power to a vhf , GPS and wheelhouse light. Can't remember if one of the SSB's was also required to be connected. I had a 4d battery for this purpose. For emergency lights we had to have kerosene lamps with colored lenses (or clear for white light). I'm sure there were other alternatives for portable emergency nav lights too.
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Old 02-14-2018, 04:02 PM   #11
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wow....I can't imagine trying to ( or wanting to!!) light a kerosene lamp when the shit is hitting the fan !!! I don't even like lighting candles in my house !!
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Old 02-14-2018, 04:41 PM   #12
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Passed along to me, but I used to tend to quite a few backup systems on commercial fishing boats when working for a marine electronics firm....even put one on my sportfish to eliminate flybridge voltage drop on engine starts....

"All inspected towing vessels, and GMDSS equipped vessels are required to have a battery backup system.

https://www.law.cornell.edu/cfr/text/46/143.555

https://www.navcen.uscg.gov/?pageName=gmdssReservePower

This does not apply to recreational vessels, it is not required for (smaller recreational) boats but it shows that such systems are far from rare or exotic. The systems are simple and effective and easily fitted to a recreational trawler if that makes the owner feel better. "
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Old 02-14-2018, 05:50 PM   #13
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Has anyone else done something like this and if so what were the critical systems you put on the secondary power source?
AC
I have a separate above deck battery bank for the HF SSB & Vhf radios only.

The cranking batteries are also separate, and while I don't see other assorted electronics as necessarily "critical" I do have extra hand held units.

My boat was once in commercial survey, so the above deck batteries were mandated, along with high capacity firefighting pumps and bilge pump manifolds.

While I mightn't install any of this stuff myself, it certainly doesn't hurt to have them.
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Old 02-14-2018, 08:00 PM   #14
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My boat has an 8d in the pilot house that runs a few emergency lights, radios, nav appliances and can be used to power the bilge pumps. There's a relay that turns on the emergency lights with a power failure. The boat used to carry eco-tourists in 5 double cabins along the NW inland passage and emergency lighting was required.
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Old 02-15-2018, 06:52 AM   #15
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Some times the PH battery is to keep the electronic items from dropping out from low voltage during engine start.
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Old 02-15-2018, 07:30 AM   #16
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Has anyone else done something like this and if so what were the critical systems you put on the secondary power source.
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Old 02-15-2018, 10:30 AM   #17
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Some times the PH battery is to keep the electronic items from dropping out from low voltage during engine start.
Powering the electronics from the house bank eliminates that problem but if the boat doesn't have a house bank, that is one solution.

Of course, the additional battery pretty much becomes a "house bank".
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Old 02-15-2018, 10:56 AM   #18
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Like EAGLE419 said , I didn't install the equipment but it is nice to have.
Our bridge helm has a separate 12V battery that powers the bridge electronics. The battery has its own 20amp charger that is powered by an inverter. The inverter is supplied with power from the engine batteries. The bridge 12v system has a separate volt meter and battery monitor.
The reasoning here is that if the boat is going down you would still have communications until the bridge was awash.
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Old 02-15-2018, 10:57 AM   #19
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[QUOTE=aboatman;636580]Powering the electronics from the house bank eliminates that problem QUOTE]

I can tell you first hand that the house bank does not necessarily eliminate voltage surges that instruments may see. That is why I suggested to AC to run all his 110 appliances with instruments and inverter on and no shore power to insure no issues.

Each vessel's wiring setup, grounding system, inverter, battery and instrument layout is different. That is the purpose of the instrument only battery, to isolate the instruments from the sporadic other loads, voltage or frequency spikes that may (or may not) weasel their way through.
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Old 02-15-2018, 11:22 AM   #20
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Adding a separate battery for critical electronics is not a bad idea.

From your house battery bank run a ACR to the “nav battery”.

This setup does present risks though. Big risk is that you then have a single point of failure in your “nav battery”. It also presents a risk when on the hook as nav loads represent a significant power drain even at anchor. This would require sizing the nav battery accordingly, and it would have replacement lifecycle to consider as well.

What we do is to provide separate circuits to our crtical nav equipment (which is 100% redundant). These come from a dedicated house battery that we monitor all the time, and have more than one charging source for.

We also have the house circuits on a switch that can choose between the house battery and one of the dedicated engine batteries, providing throw of the switch redundancy.

We do have a risk of fire or flooding though as all the batteries are in the same general vicinty in the lazarette.

In the case of fire we protect using an auto fire system, with networked smoke detectors.

In the case of flooding we have a high bilge water alarm and a real 60 gpm dewatering pump (not some 12V unit that claims high volumes and does not deliver in real life).

The key to mitigating flooding and fire in my opinion is early detection.

I have carefully considered a dedicated nav battery (or in our case two of them) and have not seen a convincing case that with our setup that we have any real gains in system reliability to be realized.

We boat in one of the remotest areas of North America, and because of this I am a huge fan of redundancy. People in our situation should carefully plan their systems taking into account and mitigating single points of failure.

Do you have fully redundant navigation systems?
Redundant propulsion?
Redundant dewatering?
Redundancy against inverter failure?
Redundant battery charging?

Look at your boat and imagine if a particular piece of equipment was to malfunction. Would you be safe to continue your voyage? Woud you be so inconvinced that you need to cut your trip short?

Those are the things that people that boat in remote areas need to think about. It’s not just life health safety. It’s ruining a long planned trip because a piece of gear malfunctions.
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