Adding battery bank

K

Kahuna

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I have an old boat. I've redone about everything on it including complete repower, now it's time for updating the DC system.
I currently have a starting battery for each engine, and 1 for the genset. I'd like to add 4 golf cart batteries as a dedicated housebank. Should I use isolaters, or automatic charging relays to keep them charged? The house load is divided between the 2 engine start batteries now.
I just don't want to wind up with dead batteries.
Any design input would be appreciated.
 
I think I'd use the "automatic charging relays" also known as "battery combiners" between each starting battery and the house bank. Once the starting bank is charged (priority) the house bank will get charged. Either engine (or both) will charge the house bank.

My boat has an isolator, and it works fine, but some alternators don't work properly with isolators.
The more I read/hear about "combiners" the better they sounds to me. Also a combiner is easier to hook up.
 
Mine is original Sea Ray setup, but it seems to work well and is pretty efficient.

It's a variation on Scheme F in George's How To with the addition of a converter/charger. The difference is mine does not have a separate DC house bank. Instead, the Port engine bank has parallel batteries for increased capacity. All the batts are dual purpose AGM's. In addition, there is an emergency start solenoid that allows both port and starboard sides to be connected in parallel should one be weak for starting. Both banks have separate on/off switches. From the batt side of the switches the port side feeds the main (lower) bilge pump plus stereo memory and sump pump. The load side of the same switch feeds the electronics, control station and the other house DC circuits. The starboard batt side feeds the emergency (high) bilge pump. The only added circuit on the load side of from starboard is the windlass. A three-bank AC convertor/charger feeds both banks on the batt side of the respective switches. The third leg from the charger is used for a genset cranking battery, that is dedicated for nothing else.

The parallel solenoid for starting is a good addition - if one bank is weak, then the other side can be used as a built-in jumper.
 
I redid my twin engine Bayliner last winter and used the voltage sensitive diodes. They are sweet.

I have on/off switches for both starting batteries and one on/off for the house bank. I have an on/off which will combine the starting batteries in case a battery or alternator croaks. This also helps because my charger only has two leads, so one goes to house bank and one to Port start battery, I can link the two starting batteries to take advantage of the shore power charging.

Once the starters are fully charged the relays open and begin charging the house bank.

Some electrical engineers have dumped on this because the diodes cause a bit of voltage drop, but the ease and reliability of this way of "captainproofing" my electrical system is worth it to me.

I love it.
 
Thanks everyone for your input. As I get into it more I know I'll have more questions.
 
I am facing the same challenge with my 1986 Bluewater Coastal. I also need to separate the starting and house DC.

I suppose AGM batteries might solve the deep cycling problem and also handle the starting duties. But I would appreciate it if you would share your opinion with me in the matter.

Please email me direct if that is convenient.

Thanks, Tom Cheairs

Tcheairs**aol.com
 
The four golf cart batteries will give you a great cabin battery. You might want to consider having the generator and one of the main engines share a starting battery. You shouldn't need a separate battery for every engine and it will just be a hassle and a lot more wiring to have the shore power battery charger keep four battery systems charged.

As for the system to combine the batteries, let me ask you a question first.

How often do you move from one anchorage to another that involves a runtime of at least an hour? I don't mean the time from your dock to the anchorage, or the anchorage back to the dock, but from one spot to another.

If the answer is never or "very rare" then I wouldn't worry about "recharging" the cabin batteries from the engines. It would be nice to have at least one engine provide power to the cabin while underway so that you didn't drain the cabin system while on a long cruise but you shouldn't need much for recharging purposes.

Here is the reasoning:

When you leave the dock the cabin batteries should be full. On the cruise out to the anchorage you want to keep the batteries from discharging, but since they are already full you won't need much current from an alternator.

When you up anchor and head back to the dock you don't need to be concerned about charging the batteries becasue as soon as you get to the dock you will plug in and the batteries can charge during the next few days.

If you need to charge the batteries while you are anchored out you would be much better off to start the generator and use the battery charger than to run an engine.

If you do cruise from one anchorage to another you would need several hours of cruise time in order to significantlt recharge the house battery. Unless you have a "smart" regulator on the engine's alternators they are going to cut back to a fairly small charge rate fairly quickly, and combinging two engine's alternators is not going in significantly increase the charge rate. With the standard voltage regulator you may not get more than 20 amps of charge into the battery or less. I am guessing that you would consume over 100 amp-hours a day, so it would take 5 hours of cruise time to replace what you use in a day.

Therefore, my recommendation is to have each engine connected via a battery on/off switch to its own battery and another switch that will connect the two engine batteries together for emergency starting (this could also be accomplished by having one of the switches be a A-BOTH-B switch).

Use a battery combiner to connect the house battery to an engine battery.

Rod
 
BEP Marine has an interesting setup for adding a battery bank: http://www.bepmarine.com/showcategory.cfm?categoryid=4
It includes three switches AND a charging relay, and it appears everything is already connected. It should be a LOT easier to install than building the system from separate components. I think they have a twin-engine version as well.

Les might be able to get you one...
 
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