Starting battery - need your input

When I bought the boat, it came with 2 deepcycle 4D batteries that were used as house bank and starting. It worked fine but I'm doing things the right way this year and rewiring the system. I'll have 2 banks made up of 2 deepcycle 4D batteries and a starting battery. I was going to buy another 4D for starting but I'm starting to question the need to install such a big and heavy battery to start the engine. Would a regular car-sized battery do the job? What do you use?

Just as in our Ram/Cummins truck, we use a pair of small (group 34) AGM starter batts wired in parallel.* Tons of cranking amps, only ~ 80 lb total.* Optimas in the truck (9 years old and counting) and Deka Intimidators for the boat's VP KAD44 diesel.

"Just as in our Ram/Cummins truck, we use a pair of small (group 34) AGM starter batts wired in parallel"

Heck I only had one optima in my Dodge/Cummins truck*and it was plenty of cranking power even in below zero weather.

But in my boat (with 120 Lehman) I have two grp 31 starting batteries in parallel for some piece of mind.

A pair of 31's will start a 600 hp 18 wheeler in the cold.

Should work for you.

Fotoman

You didnt say what engine you are trying to start. That can make a difference.

For a Lehman 120, the manual says "140 amp/hr minimum" but does not mention COLD CRANKING AMPS, which is how you normally measure a start battery.

*

For my Lehman 120, I use about a 1000 CCA battery. No need for a big bulky 4D.

And, if you think you might ever need MORE POWER (as Tim the Toolman says), then be sure you have a way to use jumper cables to reach your house bank (or a battery switch).

Next you need to pay attention to your charging system.

R.

When I bought the boat it had three 8 Ds, which I replaced with a set of six golf cart batteries for the house, and a single group 31 to start my 420hp Cat. Works great.*

Thanks, this confirms what I was thinking. I'll get a single 31 I think (is this the biggest before a 4D?). I have a Lehman 120.

The Optima Blue Top (Group 31) provides 900CCA.

Lots of starting power for the 210 Cummins, should work good for the FL.

(10) 6volt cart batteries for the house (1100AH)

2 group 24 low maintenance for start (1 per engine)

Group 24 for the gennys

Twin Lehman 120 and 12.5KW Kohler genny and 7.7KW Westerbeke

Works perfect


-- Edited by Daddyo on Friday 23rd of September 2011 09:53:38 PM

In modest weather it is fairly easy to NOT have a dedicated start batt.

The plate surface area of a good sized house bank will easily start most diesels to about freezing.

With a SOC monitor , if the batts were only dragged down to 50% , no second start is required.

Makes using a 3 or 4 stage Voltage regulator and robust alt for re charging really EZ.

With a noisemaker with its own start batt , and a 100A charger or far better, its own belted 135A alt , you have "belt and suspenders" if you are the nervous type.

Fotoman my boat is just like yours and same engine. I replaced the 2 wet call 100amp-hr house batts, which used to also double (paralleled) as start batts, when they died, with 2 AGMs 100amp-hr for house, (paralleled - I have no AC on board, and have solar panels and AirBreeze wind turbine for charging on the pick, so no need for more capacity), and a separate, low maintenence truck batt, dedicated, but capable of being linked, for starting, (sounds a bit like this 31 people have mentioned), and it works great. At the dock I have C-Tek 15 amp smart marine charger on the house batts, (as they don't like us using the wind genny in the marina), and a small matching C-Tek trickle charger for the start batt, and they keep them up to scratch perfectly.

I suppose it depends on your system and the engine requirements.
In my own paticular case the engine start is 24 V so I have 2 x 120 AMP/Hr 12 V start batteries for the main engine 1 x 90 amp/hr 12 volt gen set start , 1 x 90 amp/hr 12 V as radio battery, (this is installed in the wheelhouse) and the house batteries are 8 x 6V Trojan 105s.
Managed by a Victron 2000 W 50 Amp 24 V Inverter Charger
A small smart charger keeps the radio and gen start batteries toped up in the marina.

The house and engine start can be switched over to swap use or be combined.

Benn

Our boat is like any sailboat of yesteryear , 2 batts and a rotary switch.

Our RV has a 300A -24V alt and (2) -ser31 batts for start and engine /tranny brain boxes..

A Trace 24V 4000W sine wave inverter will run both air cond while the engine is operating from the alt.

A Vannier 60A unit provides 60A of 12V to a 4-6V golf cart batt set .

Everything aboard is 12V (water pump, fridge , lighting,) for ease of replacement.

The power hose or noisemaker charge thru the Trace to keep everything operating with 120 or 240 .

Load shedding is used underway for the HW heater , if both air cond are required.

on my boat i have 2 x 8d agm's for starting, way overkill right?
engines are 3208 cats (they have always started within 1.5 sec of cranking)

Per wrote:
on my boat i have 2 x 8d agm's for starting, way overkill right?

Click to expand...

*Right!

We have a small (1100CCA) Optima but we only have a 107 cu in engine.

Before I repowered, I had two 8D gels for both house and starting, and a rotary selector switch. This meant that I had to keep an entire 8D in reserve. With the new engine, I added a new, smaller battery for starting, and tied the 8D's together as a single house bank -- doubling my house capacity.

What no one has mentioned yet are charging considerations. The gel's aren't the best for starting, so I ended up mixing batteries; the new starting battery is an AGM starting battery. The AGM's are supposed to be a bit tougher, and are better suited for high-current. That said, I'm still using the house batteries for the bow thruster.

The cool thing about the new system is the Blue-Sea automatic charge relay (ACR) that replaced the rotary switch. The ACR will automatically connect the house and start batteries together if the house charger is on, or if the engine is running. It disconnects when nothing's charging the batteries. The ACR can be manually controlled from a switch at the helm. I can disconnect the batteries, or, for starting purposes, I can force the house batteries to be tied to the start battery.

By adding a small start battery and an ACR, I've doubled my house capacity, and I no longer have to decide which battery to use for house and starting.

"By adding a small start battery and an ACR, I've doubled my house capacity, and I no longer have to decide which battery to use for house and starting."

...and no more forgetting to select the house only at anchor after selecting 'All' for charging while on the engine(s).*


-- Edited by FlyWright on Saturday 24th of September 2011 10:42:36 PM

"and no more forgetting to select the house only at anchor after selecting 'All' for charging while on the engine(s). "

This seamless operation can be has with an $18.00 RV solenoid,

My Monk 36, Cummins 210 HP, has the OEM set up of 2 - 8D which run the house needs, including bow thruster and windlass, and start the main.
The genset has it's own 12V with no external charging. I really have had no problem at all with this system
When it come time to replace the 8Ds I plan to do like several Monk owners have and replace the 8Ds with six 6V AGMs which will fit in the same box the 8Ds are in now. Maybe adding a separate 12v Optima, or similar AGM, to start the main.
When I bought the boat it did not have a "smart charger" I had to add water to the 8 Ds often, since then I installed a Magnum inverter/charger which has worked very well and I very seldom have to add water to the 8Ds.
Steve W.

FF wrote:
"and no more forgetting to select the house only at anchor after selecting 'All' for charging while on the engine(s). "

This seamless operation can be has with an $18.00 RV solenoid,

Click to expand...

Can RV solenoids handle the current required to start an engine, or is it just for charging?* The BlueSea ACRs are rated at 120A or 500A.* I have the 500A version ($150), which should be enough to handle both the starting current, and the current into the starting battery if I'm using the house batteries to deal with a dead (or cold) starting battery.

bobc wrote:* The BlueSea ACRs are rated at 120A or 500A.* I have the 500A version ($150), which should be enough to handle both the starting current, and the current into the starting battery if I'm using the house batteries to deal with a dead (or cold) starting battery.

Click to expand...

*The 120A is continoius use rating. Its higher for temp use such as cranking or pulling up a hook.

we have the 120A version and its worked fine, however i would really have liked it much better had it had the manual override option, local and remotely.

"Can RV solenoids handle the current required to start an engine, or is it just for charging?"

No merge unit , except high quality rotaries can handle START currents. at times 2000Amps

The Engine system is seperate from the house system .

ONLY when the engine is operating is the merge solenoid closed to allow the engine system to charge the house side.

IF an emergency start is required from dead engine batts , either the std rotary switch in parallel (with key lock to keep guests from "helping") or a set of jumper cables connect the house to the engine , and will handle 700+ amps of a diesel start - if its warm.

Many more amps required for cold weather cranking.

comment to FF:

thats the (almost) entire point of using and ACR or solenoid, exactly that to ONLY combine the two batts DURING charging and possible some light house loads.
never was intention of blue sea to merge/combine for cranking.

thats the (almost) entire point of using and ACR or solenoid

My point on the RV unit is you get the same result for $18. bucks ( per 75A) with a really robust method,,

instead of big bucks and transistor brain that can not be repaired.

The recommended start battery size for my JD 4045TFM engine is 640CCA. My guess is that actual starting currents are far less than that. Surge currents may be higher.

Here are the BlueSea ratings. I think I'm safe trying to start the engine through the ACR.

Cranking Rating: 10 sec. 2,500 Amps*
Cranking Rating: 1 min. 1,100 Amps*
Intermittent Rating: 5 min. 700 Amps*
Continuous Rating 500 Amps*

FF wrote:


ONLY when the engine is operating is the merge solenoid closed to allow the engine system to charge the house side.

Click to expand...

*if you use the startkey to energize the solenoid then in fact the current is going thru the solenoid when cranking, but if you use something like an oilpressure switch then obviously the engine is running already.

how is yours wired?

bobc wrote:FF wrote:
"and no more forgetting to select the house only at anchor after selecting 'All' for charging while on the engine(s). "

Click to expand...

*I have set mine up with 3 on off switches. One always on for house bank. One always on for start battery. One always off for combining the two.**A combiner charges both.

So I don't have to switch anything.**If the start ever runs low I can manually combine the two banks.

SD

skipperdude wrote:bobc wrote:FF wrote:
"and no more forgetting to select the house only at anchor after selecting 'All' for charging while on the engine(s). "

Click to expand...

*I have set mine up with 3 on off switches. One always on for house bank. One always on for start battery. One always off for combining the two.**A combiner charges both.

So I don't have to switch anything.**If the start ever runs low I can manually combine the two banks.

SD

*i think that was discussed also, however its an awful lot of heavy cabeling.

" if you use the startkey to energize the solenoid then in fact the current is going thru the solenoid when cranking,"

No the acc terminal is NOT powered as the fear of a stuck starter being spun by the engine (hundreds off volts) is too great.