Isolated starting battery for Isuzu 6BD1

[Jay Knoll]

Hi everyone.

I've got (I think) a 150 hp Isuzu in my 27FC. I'm planning on cleaning up the electrical system and setting up a house bank and an isolated starter battery. Right now I've got 2 4Ds with a 1/2/all switch.

I can't find any recommendations for the size of a dedicated starting battery. I really don't want to use another 4D just for starting.

What are others of you with this engine using?

Thanks for the assistance

Jay

[jleonard]

A regular group 31 will have no trouble starting that engine.

[Jay Knoll]

Thanks so much! I just went to a battery/starter shop and asked them the question, they don't know boats but they know engines. That was their recommendation as well.

Jay

[jleonard]

If you wanted to go really sick you could install a premium group 31 like an Optima Red Top for example. I ran my Dodge Cummins pickup for 7 years on a single Red Top. It never came close to failing even in some below zero starts.

[Jay Knoll]

that's an idea, but I'm not going to take this boat anywhere where the temp drops below 50!

[don123]

Based more on my sailboat experience than anything else, I'm using four 210 AH golf cart batteries. One pair for House Bank #1 and the other pair for House Bank #2 - I can start the engine from either pair. I've found that deep cycle golf cart batteries are the biggest bang for the buck in 'boat batteries'. I usually get 6 to 8 years of service from them

My alternator charges both banks through a Blue Sea ACR (Automatic Charging Relay)

Don

[Binford]

A regular automobile battery is designed for short bursts of high-ampere draws, such as you'd need for starting an engine.

The deep cycle batteries, such as the golf cart batteries, are designed for slow, low-ampere draws that draw the battery way down over a longer period.

Using an automobile battery for a house battery on a boat (drawing it down as with a deep cycle battery) will destroy it in short order because the plates are much thinner, but more plentiful.

Conversely, using a deep cycle battery to start an engine is fine, but you may find it just doesn't have the "oomph" enough to do it sometimes if you have a hard-starting engine. That's because the plates are much thicker and fewer in number, thus the surface area of the plates (where the electrical energy conversion is taking place) is lower and can't keep up with the sudden high-amp demand.

So in the case of an engine-starting battery, you're better off with a regular automobile battery with the thinner plates and more surface area to provide the high-amp power. Your best bet is to have a regular automobile battery for engine starting and an isolated house battery (or several of them) for meeting your electrical needs when the engine (and thus alternator) is off.

[don123]

True, deep cycle batteries have fewer cranking amps than a starting battery of equal size, so most experts recommend oversizing them if you intend to use them for starting purposes - 20 to 25% larger than a dedicated starting battery

http://www.solar-electric.com/deep-cycl ... html#Using a deep cycle battery as a starting battery

There is generally no problem with this, providing that allowance is made for the lower cranking amps compared to a similar size starting battery. As a general rule, if you are going to use a true deep cycle battery also as a starting battery, it should be oversized about 20% compared to the existing or recommended starting battery group size to get the same cranking amps. That is about the same as replacing a group 24 with a group 31

But, a pair of golf cart batteries in series is about 200% oversized when compared to a 55 AH group 24 starting battery and about 100% oversized when compared to a group 31 battery (220AH vs 105AH) so even when 50% discharged, they should have no trouble starting your engine

I've just never been a big fan of carrying a dedicated starter when I already two much larger banks already onboard, but opinions will vary on this strategy - If you don't monitor your usage, you could conceivably run both banks so low you cannot start the engine

If you only want one house bank, a pair of golf carts would be an excellent choice and then a dedicated starting battery separate from the house system would be the way to go. Keep them both charged using an ACR

Don