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  #1  
Old 01-17-2009
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Summary of AC/DC, RF, Galvonic, Lightning grounds

OK sailnet community, first; this is a great site full of information. Well, my project, (of many) to gut and rewire my 1979 Starratt45. I have removed the salon floor and old fuel/water tanks. Another story. But now I have a clean pallet to start from. I intend to move the battery bank from the engine room to the salon floor. three things; more weight towards the center and lower in the boat. Plus easier to service. I narrowed it down to 8 6v trojan T105's or T125's or equivelant GC2 batteries, plus 2 each 12v batteries dedicated to windlass and starter, switched accordingly. The majority of threads around here favor the T105's. Also, in the EV (electric vehicle) circles. But I still have to research life cycles of this battery family. Such as; Crown, Trojan, Deka, Interstate, US Battery, Rolls-Surrette...I have a cross reference chart to work from. I'll take any inputs from battery experiences, such as; easy to source outside of USA, easy to maintain, longest life cycles and best Ah per dollar value. I have steered away from AGM, GelCel and big 8D wets for many reasons. Although, If there was a 30 year battery, I would consider it. Since we change out wets every 5 years, a battery 6 times the price with a 30 year life would justify the cost. You see, I am after easy low maintenance. That leads me to the topic of this thread. I have search and read many articles about grounding topics, here and in marine books. I have understood most of it have drawn up a plan for each system.
However, my question is a theory about DC grounding. Does our boat DC system have to be grounded thru to water (earth) or can the DC system be capacitve isolated as in an automobile? I had a plan to put a lovejoy coupler between the propshaft flange and tranny to isolate the engine. These flexible couplers do a few things; isolate current, vibrations and account for slight missalignments. I want to use the engine as my DC - ground. I think the AC ground would go thru to seawater since seawater is earth. I came up with this from reading threads about corrosion, stray voltages, shorts, and such. Also, could I use my 12,000# lead keel for any type of grounding (DC, AC, RF)? I have fabricated a non cunductive spacer for the mast and step to isolate the keel (encapsulated keel) from lightning strikes and will bond the foward and mid chainplates to the mast tying them to a solid copper plate sandwich thru the hull. I figured the rear stays will have RF isolators and be bonded to the SSB tuner and thru to a Dynaplate via copper foil. (Gordon West reading). Next, should the Zinc galvonic system bonded to the thruhulls be stand alone or bonded to the AC ground. I think isolating the Direct Current system , boats DC system would suffer less damage from surges, lightning, corrosion and stray draws.
Could some one could simplify the 5 grounding systems in the title. Is there a master One All code manual for marine wiring? Homes, autos, airplanes have codes. Seems that boats are flavor of the day techniques. ABYC has standards but others have written different and don't all agree with ABYC. so lets figure it out once and for all. Thank you
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Old 01-17-2009
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An excellent place to start to find the answers you seek:
Grounding

Bill
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Old 01-17-2009
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Talisman...Pls. say a bit about how you will be using the batteries and charging them. (i.e. daily living on the hook, charging at the dock, etc.)
You are looking at roughly a 1000ah house bank...you must have some big plans.
Why would you have 2 batteries for your starter? Understand the two for the windlass.
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Old 01-18-2009
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Cam...I figured a rough 1000Ah bank because consuming 33% of that bank would be 333Ah in 24hrs. Most say to triple your anticipated daily usage because you don't want to run your batteries down much below 33%. So I used semarine.com Ah worksheet and figured it for on the hook, and undersail. My boat is narrow beam and space is limited so I don't have room for a genset and genset spare parts. I will recharge once perday for roughly 1 hour with a 300 amp 12v dual fan brushless alternator with TAD diesel serentine belt conversion (Perkins 4-108, coming out in spring for O.H. since the tanks are out.) via Balmar MC612 and a digital duo charger for the 12v starter and windlass batteries. If you have better hardware recommendations I'll take it into consideration. Also, I figured 3 or 4 130watt solar panels and wind gen. But we know those "green" methods are limited. maybe even a tow behind water gen undersail. The 2 additional 12v batteries are wired to the starter and windlass seperately but switched to select or combine if needed. I need all the input I can get. I am curious about isolating my ground circuts. What do you think of keeping the battery power circuts capacitive? And letting the AC circuts go to seawater(earth)? I'm starting with a clean sheet and want to only do this once and do it right. With all your experiences if you had to do it over again what would you consider the best simple low maint. solution for enjoyable cruising. Not bluewater band-aid repairs on the fly. I have a "honey-do" list full of that junk at home. Nice boat by the way, I wish I had seen it earlier...Dave
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Old 01-18-2009
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Umm... 300 Amp-hours daily usage is a lot of electricity for a boat, regardless of size. Just curious as to what you're doing that requires that much juice.
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Old 01-18-2009
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Well...first...the general rule is 50% discharge...not 33. You will get more cycles at 33 but most feel the $$ tradeoff in batteries and weight and space is not worth it.
300 amps will NOT be accepted by a 1000 amp hour bank. Maximum 200amps...more likely 150. Unless you go to AGM's or Odysseys.

You'll need not only dual pulleys but a pillow block as well to divide the sideloading of the engine bearings. Even at that I would worry about the long term impact of that "150amp" load on the small Perkins.

Where are you gonna put 400 watts of panels on that boat?

Frankly...I don't like your plan at all and have never seen anyone attempt anything quite like it. But it sounds like you've done a lot of reading and thought about it a lot....so don't let me stop you.
***************
What would I do?
I'd have 600ah's of AGM's and a 110a Balmar on a single belt. I'd have a 4 winds wind generator and as many solar panels as I could fit without shading...say 200 watts (and an Mppt controller)...count on them for at LEAST half of my daily amphour needs and make up the rest with the engine or a honda generator if you can't fit a real one.
Alternatively...I'd try the Odyssey batteries in a 400ah bank.
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Old 01-18-2009
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Talisman66,

Cudos for doing the reading and thinking and planning for your new system. However, it would appear that you need to do a bit more on the research and planning side.

First, as others have said, 300AH per day on average is a very large draw for a 40-45 footer. You might want to do a careful recalc of what your actual draw is likely to be. You should be able to get it below 200AH without much trouble, even if you have electric refrigeration and run a laptop (these are generally the biggest amp hogs aboard). Lighting draw can be reduced with LEDs, refrigeration draw can be reduced with good insulation and/or a better compressor setup, etc., etc.

Next, I agree that trying to run a 300amp alternator on a 4-108 is troublesome and unrealistic. On re-examining your likely daily usage you may find that an alternator which averages 90-100amps --- the largest single-belt alternator suitable for a 4-108 --- PLUS some input from solar panels may well be enough for your needs.

Note that from what you describe your house bank consists of six T-105s. That's 675AH capacity, not 1,000. Presumably, the windlass and start batteries are independent.

BTW, I have 8 T-105s on my 42' sloop. Six are for the house bank (675AH), two for the windlass (225AH). They are set up independently...no need to switch them, in my case. Additionally, I have a 100AH 12V Group 31 starting battery. While T-105s may be used for starting, they're not designed to deliver a lot of amps fast and, IMHO, a starting battery is better. The start battery on my boat is maintained via a Xantrex EchoCharge. The windlass battery bank, located in the forward cabin, is charged with it's own dedicated 110V 55A Iota charger, which is powered either from shore or from my onboard generator (or even by my onboard inverter if ever required).

Re: your grounding question, the cardinal rule is that there should be ONE and only one grounding point for both AC and DC. All ground wires should be run, via appropriate busses, to this one point....usually the engine.

RF grounding, by contrast, should be separate from the DC/AC ground system.

I think if you sit down with a pencil and a calculator and do some rethinking, you'll be able to solve your electrical puzzles fairly quickly, and you'll save a LOT of money and angst along the way :-)

Bill

Last edited by btrayfors; 01-19-2009 at 09:45 AM.
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Old 01-18-2009
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xort has a spectacular aura about xort has a spectacular aura about xort has a spectacular aura about
the 33% number is USABLE capacity of a house bank in cruising use.
draw the bank down to 50% but only charge up to about 80%. topping off to 100% is slow when out cruising due to slow acceptance rate as the battery tops off with a charger.
Plugged in at the dock overnight you can top off to 100% which is needed about once a month to prevent sulfation.

Seems like 150 to 200 is about the biggest draw to plan for on a loaded cruising boat. using 200 per day and recharging every day would run: 800a bank drawn down to 400a and then recharged to about 600a (75%).
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Old 01-19-2009
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Bill, one small correction:

Six T105s are 675 amp-hours, since each is 225 amp-hours at the 20 hour rating. If you've somehow managed to get T105s that have 290 amp-hours in them, let me know where you bought them.

Xort's point about cruising use on batteries is a good one...most cruisers don't try re-charging to 100% of bank capacity on a regular basis, so the 35% rule is generally what they use.... so his bank sizing isn't that crazy.
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Old 01-19-2009
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dog,

Absolutely right! A senior moment -- or, maybe, just wishful thinking! :-)

Thanks, I've corrected it.

Bill
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