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bestfriend 11-02-2007 03:25 AM

Electrical upgrade
The time has come. I have three-three year old group 27s, two house, one starter, and they are washed up. I also have a Mariner 35amp charger. The whole system is kind of rinky dink with no way to monitor anything. Basically set up for a daysailor that didn't use the boat much. Lets say in the near future I plan to do some short term cruising, maybe a week at the longest, and some weekends. Not much time on the hook, probably lots of time wired at the dock. I don't have a lot of electronics, yet. I've got the fridge, water heater, and electrosan as the biggest draw. Lets say in the near future I will add a gps chartplotter, radar, TV, laptop, maybe some other small electronics.
What I would like is new batteries(maybe another house battery), a better charger, possibly inverter, and a way to monitor it all. Go ahead, have at it. Give me your recs on the top of the line down to the miser brand, sizes, and best place to buy them.
I am not electronically inclined(I can work on my own house wiring) and will have someone else do it, but I want to know what it all means and how to use and install properly in case I need to work on it.

sailingdog 11-02-2007 09:11 AM


If you can work on your house wiring, you can do this installation yourself. It isn't any more complex.

Given that you have a water heater ( is it 12VDC ??? ), refrigerator ( is it 12 VDC ??? ) and electrosan head... and want to add a chartplotter, radar, tv and laptop, you really need to do an electrical budget to figure out what your average daily usage is going to be, based on what you will be using and how long on average per day you will be using it. You then have to figure out how many days on average you will be going between recharging the batteries. This will give you a base number... double it to get the size of the battery bank you'll need.

For instance, if your daily electrical budget is 120 amp-hours, and you want to go two days between re-charging the batteries, you would probably want a 500-600 amp-hour battery bank.

As for equipment.... I would highly recommend getting a Xantrex inverter/charger, like the Freedom 20, which would give you 2000 Watts of AC power as well as a three-stage intelligent 100 amp battery charger IIRC. I would also add a Blue Sea Dual Circuit Plus Battery switch with the battery combiner. This would automatically combine the house and starting banks while charging dockside or under power and isolate the starting bank from the house bank, yet allow you to combine the house and starting banks to start the engine. It also would protect the electronics from the voltage drop caused by starting the engine unless you have the banks combined.

For batteries, I would recommend going with AGM batteries. This is mainly due to their higher charge acceptance rate and lower maintenance. Provided you keep the charged on a regular basis, they'll probably last as long as wet cells, if not a bit longer.

If you have any specific questions, let me know.

camaraderie 11-02-2007 09:44 AM

OK...first, lets theroze that you might need up to 150A/H's a day once you get all your toys installed. That would mean you need a house bank of 300 A/H's for a day on the hook before recharging. So 3 group 27's will give you that if you have room for a 3 battery house bank. 3 group 31's will give you about 400 AH, 2 group 4D's will give you about 300 and a single 8D will provide around 260. So...first step is to evaluate how much room you have and what will fit there that will give the capacity you need.
Standard dimensions for different battery types can be found here: under section 7.81
I would recommend good wet cells given your intended use. Trojans would be a good choice.

Next you will need to be able to effectively charge this bank at the dock as you visit marinas which means a 60AMP range charger with three stage charging routine AND an Equalization setting so you can occasionally EQ your bank to de-sulphate.
Since you are thinking about an inverter as well, you might as well combine the charger with the inverter for wiring simplicity. The Xantrex Freedom15 will give you 1500watts AC and 75 amp charging along with echo charging for your starter battery. Other sizes are available if your needs differ appreciably from this.
The nice thing about the Freedom 15 is that you can hook in a Link 1000 to both control your Freedom15 and give you a complete rundown on battery use and status. All the Xantrex stuf can be had for less than $1000 here at the sailnet store. This is a "high road" solution, hopefully others will chime in with different thoughts about cheaper, less integrated approaches.
Note...I am specifically disagreeing with Dawg on AGM's vs. Wet cells. AGM's are NOT a cost effective solution compared with good wet cells EXCEPT in the circumstance of living aboard where they DO stand up better to constant daily cycling. Wet Cells are more cost effective for dockside use and occasional weekend/weeklong trips. His recommendation of the freedom20 and a bigger bank is fine if you want to go a bit longer without recharging and have the room.

deniseO30 11-02-2007 11:34 AM

I guess I'll join in with bestfriend. My boat has 4 bats.. 2-12 volt and 2-6 volt golf cart Trojans. Original alternator. volt meter is shot, the battery charger works. big switch with "1, both, all"

OH! what does "group" mean about batteries? like "group 27" I have the sailboat electrics book but still get somewhat confused on battery stuff. I have lots of help in my boat club.

My hopes are to eventually get 2 -15 watt solar panels, a solar controller, new alternator. (I think the one inboard is 70 amp) Battery monitor and meters. Also diodes, and all that stuff to protect things make it more reliable.

I'll get the batteries checked. (every one says "you only need 2!" I say: "it has 4!" they say.. and it goes on. sheese..

oh I just read some of the FAq's..

forgot to say that I should make sure what I have is working right! I will replace/solder all battery terminals and or cables first!

bestfriend 11-02-2007 11:41 AM

Excellent info guys. I keep the fridge on all the time, I think thats what did these wet cells in. I do plan on spending a lot of time on her dockside, in between weekend trips, probably several days a week, so maybe AGM would be the way to go. I have the reevaluate the battery location. I have room for three, bigger than the 27s that are in there now, in the engine compartment. I may be able to find room for the starter in a separate cubby about two feet away out of the engine compartment. I will post a picture of the aft space. Maybe just less of the bigger batteries will work. Fridge and water heater are 12v.

sailingdog 11-02-2007 11:41 AM


You'll probably want more than two 15 watt solar panels. More like two 50 or 100 watt solar panels. Two 15 watt solar panels are probably just enough to keep your batteries topped off, but not much more than that.


Might be worthwhile to see if you can cram six 6V golf cart batteries in that space. That'd give you about 540-675 Amp-hours of battery bank.

camaraderie 11-02-2007 12:20 PM

BF... I do plan on spending a lot of time on her dockside, in between weekend trips, probably several days a week, so maybe AGM would be the way to go.
I think you misunderstood me...AGM's are NOT cost effective for mostly dockside use. The only other reason for YOU to get AGM's is because they are sealed requiring no maintenance or if you need to install them on their sides for space reasons.

Denise...if you like, suggest you start a separate thread so we can keep our answers specific and not hijack BF's thread. "Group" is simply the physical size of the batteries like a width of a shoe being A,B,C,D or Sailing Dogs pants being extra-large!! (g)

HoffaLives 11-02-2007 12:48 PM

If you are looking at 300AMp-hr capacity you should look at a 100 amp alternator to make sure they are topped up. These batteries are expensive if your system sulfates them due to incomplete charging. Equalizing charging will not undo this kind of chronic damage. You have to count on anywhere up to 30% loss in charging system efficiency, so beware of absolute numbers.
Also get rid of the power switch on the output of the alternator and instead use an isolating diode setup. Rewire the system so that you have minimal connections in the loop: alternator, diodes, batteries, alternator.

The problem with cheaper solutions is that they are not. How much does a set of deep-cycle batteries cost? If you don't build in adequate charging capacity, if you don't use a proper three-stage regulator, if you don't have adequate battery capacity to keep above the 50% discharge level, you will be replacing batteries more often than you need to be.

bestfriend 11-02-2007 01:46 PM

Cam - I reread, got it.

Hoff - you're speaking Greek to me with the diodes and the rewire, thats why I need a pro to come look at it, or you, is your shaft tube fixed yet?:D

SD - Is there an advantage to the golf cart batteries or is it just getting more amps out of a limited space?

sailingdog 11-02-2007 02:21 PM


Basically, it is easier to haul, move, and work with 70 lb. batteries than it is with 130 lb. batteries. :D And they do seem to pack a bit more punch for the given space used.

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