how much battery is actualy needed

[67hat34c]

I helped my dock neighbor on Friday. He had been out of the country for a few months and now could only get one engine to crank. his boat is a bout 2 yrs old, Regal 42 with 330B's. Showed him how to use the parallel switch and got the other motor to start. I then proceeded to inspect his batteries. turns out he has one small starting battery for each engine and a separate house bank for everything else. Start batteries were of unkown size but appeared to be basic automotive size and type. Found one was fried so I sent him out to get 2 new ones which we insalled and the thing runs fine.

My question: Is there a real need for larger batteries if it is only to start it and you have a good parallel switch? I would have thought 4d starting batteries would be a better choice but they wont fit in the factory battery compartment.

 

[thoward]

There are some good marine batteries out there that push close to 1000cca and that should be more than enough with 2 dedicated batteries.

 

[Genesis]

An Optima Starting Battery (AGM Group 27!) can push 1000 CCAs. Two of those will roll over a 6V92 or 8V92 easily! ONE can start a 330b.

I like a configuration that has a starting bank comprised of these and wired to BOTH main engines, a big house bank of deep-cycle batteries for the house, and a parallel switch to bridge them when necessary. The latter's primary use is NOT to start the mains "raw", but rather to frist start the Genset, THEN start the mains once you know you have a charging source operating.

 

[SKYCHENEY]

With trucks we sometimes can just jump them with a car battery, but that is only in warm weather. You can get by with smaller batteries if the conditions are optimal, but if it gets cold or you have a weak starter or an older battery, you are asking for trouble. You need the bigger batteries for extra cranking amps in those unforseen times. I would not downsize simply to conserve weight or save a couple of bucks. Get the recommended amp output for the engines you have. This may or may not let you use a smaller battery but as long as the minimum output starting amps are met, you should be okay.

 

[WK2CRUZ]

The whole idea behind the parallel switch is in the case one bank is to low to do the job that is needed. It should not be something that you have to use on a regular basis. That said there are options out there to change what was originally installed some 20 or 30 years ago. I recently changed my 2 8d batteries out with 2 grp 31's from Optima. Plenty of cranking power and 150 pounds lighter. Bad thing had to build my own battery boxes. Nothing on the market that holds two grp 31. Suppose to have much longer life than old lead acid batteries.

Wk2CRUZ

 

[fixin-to-cruise]

Starting is one mission for the batteries, usually accomplished at the dock with lines attached. The real need is when you are trying to restart an engine after a tank runs dry or to keep an engine going with a dead alternator. The batteries will also supply power for all those motors that have higher peak currents than your battery charger can supply.

When in doubt go with what Hatteras put in your boat (size of battery), but go with an upgrade to a 3 or 4 stage smart charger that will double the life of your batteries. I bought and sold a boat with the same 8D's and ran them for 6+ years by having them hooked up to a Hart Freedom 25 inverter-charger that babied them. I've seen some "ferroresonant" chargers boil out the electrolyte and destroy batteries in 2 years - stay away from them!

 

[Genesis]

With Detroits, there is no issue with keeping an engine running with a dead alternator - they will run just fine with ZERO electrical system. Yes, I've done it - made a 60nm run with a dead electrical system - and not by choice.

The big deal with any diesel (including mechanical ones) is getting ONE charging source running. Offshore or away from the dock where AC power is not available, the WISE person starts the GENERATOR first, because (1) its the easiest to start, and (2) it provides both alternator charging AND a feed for the AC charger.

If you have no genny, well, then you need to make darn sure your starting batteries are PROTECTED for the mains! And this means no house loads - ever - can be on the engine starting battery bank.

With diesels you absolutely want priming pumps. Its simply STUPID to use limited engine cranking batteries and the starter to try to re-prime the fuel system if you suck air for any reason. $100 fixes this (a Walbro pump with a check-valve bypass) and you're insane not to install them on any diesel boat. Its NOT just the batteries - if you burn up a starter trying to reprime an engine away from the dock you're screwed.

Personally I prefer a dual-bank engine starting system with both engines tied to the same bank, so the 1/2/ALL/OFF switch has BOTH engine positive feeds off the common on the switch, and bank 1 and 2 connected to the appropriate place. This gives you TWO protected starting energy sources - remember, you only need to get ONE main going to be "safe" - and you then use a combiner between 1 and 2 to make certain you always have one protected starting bank. NO house loads are on that bank.

House is then on its own bank.

House is charged by the AC charger and the generator's alternator (assuming it does not have its own dedicated starting battery, which is a good idea, as you can usually use a small battery for that purpose) - and a combiner to the engine start bank.

So when you have engines up, ALL charging sources restore their priority first, then restore the others. This means an engine restores its own starting capability before it worries about the house, and the genset/AC charger restores the house first, then worries about the mains.

Anyway, this may not make sense - I can draw a picture if that would help...

 

[(Nobody You Know)]

Nothing on the market that holds two grp 31. Suppose to have much longer life than old lead acid batteries. Wk2CRUZ

I thought so too until I saw this recently:

http://www.defender.com/productsearchresult.jsp

I have not purchased anything from these people but Perhaps soon when I convert to AGMs.

Capt'n Bill

 

[bateau beau]

Defender is a good outfit to do business with. Fortunately, I live near their outlet store in Connecticut, and I give them all my business..

 

[rufus mathews]

Karl,

I am interested in your diagram.

Thanks

Rufus