Battery Isolator or Combiner?

I'm refurbishing and repowering my 32' FB Sedan and is used for week long outings. I have twin engines/altanators and will be using a three bank battery system. I've read that some voltage is lost through battery isolators. Are battery combiners a better choice? My new Mercruisers suggest a separate battery for each engine and I think with the combiners I would also eliminate the battery switches. I've seen little information on wiring diagrams for use of combiners.

 

Looking at the safety side, it's not a good idea to combine the batteries.
With separate batteries you have a back-up, if you combine the batteries and the battery bank is dead, you're out of options

 

Battery combiners work out to be a better option than isolators for sure. But if you are an attentive user and don't mind a little work involved in your boating routine, the best option yet is to mechanically switch them yourself. This comes with the risk of being absent minded and draining your back-up bank.
There are many choices in setting up a battery and charging system...to design a system (and for me to help you) you must make some decisions about how the boat will be used. Runabout, day boat afternoon fishing, the occasional overnighter, at anchor or at the marina, long cruises with much power usage? These questions must be settled to optimise a power system. Otherwise you could waste a lot of money on unnecessary equipment.

 

Sorry...didn't see the part about week long cruises.
Two starting banks and a house bank is a good option for what you are doing...or a simpler method is two banks. One is a totally isolated starting bank that will get you going. The other bank serves (a larger bank) as starting and house. This allows you to size the alternators to the individual demands. (I'm assuming alternators will be your primary charging source.)

 

Dutch Peter is right. NEVER - NEVER put batteries together . The older the battery, the higher the full charged voltage of it. If you have 3 different age batteries and completly charged each one. Ran a battery test on each. Then jumpered all 3 together. Came back the next day, ran a battery test again, you would NEVER NEVER leave any 2 or more batteries jumpered together again. The newest battery should have the lowest full charge voltage. It WILL - WILL discharge the other batteries DOWN to it's voltage. You have effectively reduced your reserves to the one NEW battery, only. Does not sound right- but that is what happens every time. Buy ALL 3 NEW batteries at the same time, if you must do that combine junk. If 3 NEW are combined and 1 of the batteries shorts out 1 cell inside. All HELL is going to happen in that battery bank. The shorted battery very likely will overheat and explode from the other 2 batteries trying to bring it up to their voltage.----- Have a battery selector switch that can select ANY 1 battery to be the starting one, BY IT SELF. Hopefully you will then change the too slow cranking battery when you you hear the different speed. Or have it checked out if you are not sure of the reason for the slow cranking. Plan ahead or stay behind. I have found if I have all the equipment in good working order, I have no problems. ---------3 seperate batteries eliminates the dangerous condition of the GOOD batteries blowing up the one with a shorted cell .

 

Thanks for the response. I have been considering part of your suggestion. I think I will use a seprate starting battery for each engine and a West Marine battery combiner connected to a deep cycle bank. This gives me two deep cycle banks for the house and I can use a selector switch for the house banks. This method gives me a starting battery for each engine as required by the manufacture due to engine electronics. And each 65 amp alt will be charging equal amount of batteries. This should help keep the battries recharged faster. The deep cycle banks will each be twin 6 vt. golf cart battries. This should give me enough capicity with minum recharging during outings.

 

Hey drs3317.
Please let me know what you ended up doing. I have a similar situation, except that my two batteries are divided between house and engine. That is battery 1 service 1 engine and part house. Battery 2 service the other engine and part house. I have a switch at the helm labelled "para" which allow me to use both batteries to start the engines. Crazy setup I'm told. But other than buying batteries every 2 years, it ...whatever. lol Anyway, I'm evaluating what benefits I will get with a combiner under my current setup.
Anyway, are you saying that you plan to have one (1) battery for the engines and 2 for the house? Just curious.

 

A piece of battery advice. You CAN and SHOULD only use a deep cycle battery on a boat. Why ? It can take a complete cranking down to a crawl with little damage. You do that to a starting battery and you are killing it. The plates are very thin. Deep cycle, size # 27 I believe cranks anything that is a V 8. Mine go for years in freezing areas.

 

wow,you guys seem to know what your are talking about.Perhaps you could guide me through a theory or two? I always use two batt isolators one neg and one pos. I just feel that its better to be all off. Some books that i have seen encourage bonding through the boat-ie all skin fittings, tanks,you name it, to the neg of the batt.they even say ground the ac system to it. Whoa are you sure?
My house system is all separate exept when egines are running then i switch them into the eng batts for charging. All works very well Eng batts coming up for 30 months( normal lead acid) 44 foot cat that sits in a marina.
I have 2 Yanmar 6LP and at present I change engine zincs at about 6 months with 60% 70% corrosion .Is that normal and if it isnt do you think that this could be the consiquence of my engines being not normaly negative.