General electronics

[Sanguinius]

Well I've been going through the boat I recently acquired. I don't quite understand the electrical systems on these thing. I know that my boat has both AC and DC but I'm trying to figure out how it all works together. I will be likely rewiring the ENTIRE boat ('65 Owens 36' Cabin Cruiser) and the better the understanding I have of the workings the better I can re-wire it for proper inspection.

I tried searching through the forum it seems most posts are fairly application specific so hopefully this will get some good info. Thanks.

 

[Silvertip]

Re: General electronics

Electrical systems vary significantly between manufacturers and improvements have certainly been made in equipment over the years but basically here's how it works in a nutshell.

When the boat is moored, shore power (117 volts AC) may be available at the dock. If your boat has an AC system, you plug into shore power which feeds AC power to the service panel on your boat. From the service panel, various AC circuits feed the outlets, air conditioning, microwave and any other devices that require 117 volt AC power. Another device similar to a battery charger converts 117 volts AC to 12 volts DC to charge the house battery bank. These batteries power 12 volt accessories when under way. The boat may also have an inverter that does the opposite of the charger. It converts 12 volts DC to 117 volts AC to power those circuits. Keep in mind however, that when running an inverter, the electrical demands may quickly run down the house batteries. Depending on the size of the charging system on the propulsion engines, those generators can also charge the house battery bank as well as the starting batteries. Bad 117 Vac wiring can kill so make sure you know what you are doing when rewiring the boat.

 

[Sanguinius]

Re: General electronics

I'm sure it can. So what does an inverter look like and where are common places to hide them? I'm assuming this boat has one since I've seen all sorts of 112 outlets (Badly wired BTW) all over. I'm fairly good with electronics and am a bit of a perfectionist (Just kept making my increasingly angry thanks to the fact that the previous owner didn't bother to use marine grade wire to wire what he did).

Also I'm assuming that the twin 318's would have plenty of power to recharge the battery. But with this setup would it be recommendable to put in a second battery?

 

[Zero Balance]

Re: General electronics

Here are some links that were very helpful to me when I re-wired a couple seasons ago. Theres nothing more rewarding that performing this task and knowing your system. Good luck and happy wiring.

http://www.crowbarelectricalparts.com/Specifications.htm#Gauge

http://www.floridasportsman.com/HowTo/051068/#cont

http://www.cncphotoalbum.com/doityourself/wiring/wiring.htm

http://www.islandnet.com/robb/marine.html

http://www.bepmarine.com/

 

[Silvertip]

Re: General electronics

If all your boat has is a starting battery for each engine, you very likely do not have an inverter. You should not use the starting battery to power house loads as you run the risk of discharging them thus leaving you stranded. My thoughts are, depending on accessory loading, is to have a separate starting battery for each engine. For house batteries, a minimum of one very large deep cycle and better yet, two deep cycle batteries are needed. Power of the engines has nothing to do with charging output. Thats a function of the alternator on each engine. As for the location of the inverter, look near the service entrance panel or near the house battery bank. If it's an inverter only, it will have 12V input and 117V output. If it's a combination inverter/charger, it serves both as a battery charger when operating on shore power, and an inverter while under way.

 

[Sanguinius]

Re: General electronics

So then the 117V items will only be able to be used in port if there is no inverter? So far (I haven't pulled the outter panel to trace the wires yet will do that next week as well as removing the deckplates to get at those wires as well) I haven't seen anything in the battery well other than the hanging starting wires. I also have not seen any other battery locations. Also I found a battery charger on the boat but not hooked up to anything (New?). I don't believe I saw anything on it about being an inverter but I didn't really examine too hard. Was too busy ripping the ramshackle woodwork the previous owner stuck in the boat haphazardly.

If it doesn't have an inverter, what will I need to do to install one? Obviously rewiring is necessary so putting it in now would be easier than waiting till I've already got her floating and figure I need one then.

Thanks again. Especially for the links I'll be pouring through those all week so I know what to hunt for when I get back to the boat this weekend.

 

[Silvertip]

Re: General electronics

To add an inverter, one must first make a list of each and every device that will require 117V to operate. (TV, fridge, microwave, lights, etc are just a few). Then you need to determine the current draw for each of those items. You then add the total current draw and if you were to run all of them at the same time, that total represents the MINIMUM output current rating of the inverter you need. Since you will not likely run everything at one time, you could get by with a little less power but again, there is no free lunch when it comes to batteries and inverters. A marine inverter would wire to the house batteries (not the starting batteries). The output of the inverter would connect through a breaker to the service panel. Do not confuse a battery charger with an inverter -- they are direct opposites of each other. Marine/RV inverters may include a battery charging feature but battery chargers are not inverters. Without an inverter you have no way to power 117V circuits -- because you have no place from which to obtain 117V from. To avoid the hassle, you might even consider a small Honda generator to meet the 117V power needs.

 

[Sanguinius]

Re: General electronics

Now something else to think about is that the boat has a range top, microwave/toaster oven, and fridge. I would imagine it would have an inverter and that those would be available to run out to sea. Just a thought but I could be wrong there. The previos owner was none too bright...

 

[Silvertip]

Re: General electronics

The devices you just named are all very high current draw devices and running them off an inverter means you would need a verrrrrry large battery bank to run them. A single battery would likely last a matter of minutes. Remember, as I said, batteries can only supply so much power and heating applicances are the worst offenders. I really suspect this boat does not have an inverter, and the only time those devices were used is when connected to shore power or if there was a small generator on board.

 

[Sanguinius]

Re: General electronics

Well then I guess I'll be looking for a generator... What about the AC unit? Would that have been an AC or DC item? All I know is it is a Sea Breeze unit.

 

[Silvertip]

Re: General electronics

A/C is another high current draw item and it's likely an AC unit. Just so you know, an inverter big enough to run all this stuff is going to be expensive -- and that does not include the very large bank of very big batteries you'll need. I suggest you Google "Marine Inverters" to get an idea of the costs associated with high capacity inverters. If you feel a generator makes a better solution to the power issue, PM me. I can put you in touch with someone that can probably supply you with a marine genset. Here are some wattage figures for various devices. Add them up and add 15% to determine the size inverter you need. Most units have a tag on them that indicates wattage or amperage.

? Stackable Washer/Dryer: 2500 Watts? Heavy Duty 7 1/4" Circular Saw: 1800 Watts
? 12" Compound Miter Saw: 1800 Watts? Electric Chain Saw: 1700 Watts? 10" Bench Saw: 1560 Watts
? Full Size Microwave: 1400-1750 Watts? 42" Fan: 1235 Watts? Chest Freezer: 1200 Watts
? Mini Microwave: 1000 Watts? 1/3 HP Submersible Pump: 920 Watts? Reciprocating Saw: 720 Watts
? 1/2" Reversible Drill: 620 Watts? Coffee Maker: 600 Watts? Portable Vacuum: 525 Watts
? Computer and Monitor: 450 Watts? Blender: 450 Watts? Orbital Sander: 420 Watts
? Refrigerator: 360 Watts? Home Stereo: 350 Watts? 3/8" Drill - 320 Watts
? 20" TV-VRC Combo: 300 Watts? Quartz Halogen Spotlight: 250 Watts
? 12" Three-Speed Fan: 130 Watts? Computer/Printer/Fax - 150 Watts? Laptop Computer - 90 Watts

 

[wire2]

Re: General electronics

A little Ohm's law goes a long way. Amps x volts = watts.

A 1200 watt load at 120 volts = 10 amps.
A 1200 watt load at 12 volts = 100 amps.

You get the idea.