Starting/reserve battery size

[dfloeter]

I am adding a reserve battery to our 1996 C34 with the M35A.    Our Kobota dealer recommends a 500CCA battery for a 30hp diesel but that is also presuming winter cold weather usage.   Can I use a U1 size battery with half the CCAs and still reliably start the diesel when I goof and let the fridge drag the house bank to nothing?

Dietrich Floeter
#1317 1996

[Stu Jackson]

Dietrich,

There is a lot of helpful information in the "101 Tpoics," "Electrical 101" ---

Engine Starting Loads - Amp Draw Data (by Maine Sail)

http://forums.catalina.sailboatowners.com/showthread.php?t=102027

[dfloeter]

Thanks Stu.  I have gone through the 101 topics and maybe missed this specific item.   Mainesail does mention having started his 44hp on a smaller battery and I was hoping somebody with a 30hp might also have some experience with a smaller battery that will fit in a tighter space than a Group 24 would.

[Roc]

I have an M35B engine and it starts with no problem using a Group 24.  That's what I have as a reserve battery.....

[Ralph Masters]

When I installed my start battery I went overkill and put in a group 27 "start" battery. Stbd side just aft of the tranny.  Battery on/off switch in the bulkhead right by the aft berth, can't miss it.

Ralph

[karista]

I had installed a group 34 AGM deep cycle battery due to its smaller size on its own switch! It died after 1 1/2 years! I then installed a maintenance free group 34 Battery with a 3 year replacement warranty and a 8 year pro-rated warranty from Sams club at less than 1/2 half the price of the AGM.
It has a much higher CCA rating than the AGM had! This battery does not, in my opinion need to be a deep cycle as it hardly ever gets used.
The group 34 is a smaller size and fits easily close to the engine on the starboard side, it is maintenance free so no need to check the wet cells.

[dfloeter]

Thanks for the thoughts.   I see I need some testing on this one.   My 300 amp jump start battery pack will be tried first and I will see how quickly the engine will turn over without starting of course.    If it will spin a cold engine with cold oil I can be satisfied, if not well off to a bigger battery.

thanks

[Ron Hill]

Dietrich : Even though I had a separate Gp24 starting battery I engaged all (starting battery and 3 GP 31 house batteries) when I started the engine.  

There was no holding back power from the starter!! 
However, I did charge the house bank directly from the duel output alternator.  So the "B" was used for starting and left in that position after the engine started.   

A thought

[Stu Jackson]

Using B to start a battery is probably the last thing to do.  And it all depends on how it's wired.  If the switch is a use switch or a charging switch. 

Here's why (added to the "Electrical 101" Topics just the other day, this thread:  Basic Battery Wiring Diagrams  This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html )

If your wiring, connections and basic system design are sound, a single small battery of any type, or your house bank, should be more than adequate to start our small diesels.  A separate "reserve" bank, compared to a "start" bank is an issue of either or both 'management' of the use of your banks and your choice of wiring and switching your electrical battery system, also covered in that link.

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USING THE 1-2-B SWITCH  added 1/6/2015

This is another good explanation from Maine Sail:

Question:  is there really a need for an emergency parallel circuit when you have a 1 ..both..2 switch installed?


Not unless you use it as a charge directing switch..

With a dead bank your best option is to simply switch to the good bank and not to combine them, before starting the motor..

When you combine a bad battery with a good one all it does is make the good battery work harder trying to both start the motor and to charge the bad battery. It is kind of like saying I can easily run a 100 yard dash and you are then asked to give someone a piggy back for the 100 yards. Think you'll perform the same...?

What if the dead bank has suffered an internal short, this happened just two days ago to member Capta on his generator starting battery. Your bad bank could now be a 10V battery as opposed to a 12V battery. Ouch!!

This is NOT a good time to be using BOTH as the battery voltages will never equalize and the shorted bank will continue to heat up and suck the good bank dead too..

Best practice with a 1/2/BOTH is to simply switch entirely to the good bank until you have a charge source on-line.

The BOTH portion was really intended for charge directing but is most often misunderstood because boat builders used to supply very small batteries and grossly undersize the wiring. With two batteries the boat started better so the myth that you need to use BOTH to start got a foot hold. If you need to use BOTH to start a motor there is something DRASTICALLY wrong with the batteries, system or wiring.

__________________
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-Maine Sail / CS-36T

[Ron Hill]

Guys :

"Using B to start the engine is probably the last thing to do"

Tis amazing that I wired my C34 some 10-15 years before "Electrical 101" was published and that wiring operated flawlessly for over 25 years and is still working with out any problems!!
 
I started the engine in the "B" position and let it there until the engine was shut down.  I did have a battery monitor and knew the battery status at all times.

A thought

[sailaway]

I installed a starting batt aft. I installed a new  red switch aft that has 4 positions 1,2,both, off. That way if I have a dead batt I don't have to go threw the both position. 1 is the old house bank , 2 is the new starting batt   Charlie

[Mike and Joanne Stimmler]

At least for me, the biggest reason for having a dedicated starting battery that can be isolated from the main bank and also be charged when the engine is running is so that while sailing, I can use all my electronic gadgets on board without worrying about not being able to start the engine when necessary.

[Ron Hill]

Guys : If you have good connections at the batteries and starter, it doesn't take that much power to start your little 21 or 23 or 30 or 35 hp engine. 

Now if you are going to sail for 8 hours, it's hot with the fridge ON and you are using radar constantly with 2 Grp 24 house batteries - you might consider a starting battery.

My thought

[Randy and Mary Davison]

I use a U1 AGM as my starting battery on Gorbash.  It's located just under the small compartment cover in the aft cabin where I can reach it easily.  It has a high current in-line switch installed so I can connect it or disconnect it easily by feel.  It's been maybe a dozen years since I installed it so I'd have to take a look to remind myself of the details but basically it's wired to the starter with a short run of very heavy wire.  It's connected to my house bank of 4 golf cart batteries through an automatic combiner.

The boat is in western Washington so we never have to deal with extreme cold but I always use the small battery to start the engine and it has always started easily with the exception discussed below. 

The reason I used an AGM battery was so I could mount the U1 on it's side to fit comfortably below the wooden cover including being strapped down inside a standard plastic battery box.  This, of course presents the issue of what battery type settings to use on the TruPower charger and Balmer regulator for my mixed battery type situation.  I can't remember here sitting at home whether I chose AGM or flooded but I know it was whichever one was least likely to overcharge the AGM.  I think I remember that this left the house bank floating at a slightly lower voltage than ideal but it was by only a small amount. The current house bank batteries are about six years old and are due for a capacity check but last summer on a month long trip they seemed to take about the normal amount of time to get down to 50% - so it seems this slight undercharge is not hurting anything.

The problem that has occurred is that charging regime for the house bank appears to be unduly hard on the much smaller AGM even though all the stage voltages on the chargers are optimized for the AGM.  Early on I left the AGM connected to the combiner all the time and found that the first U1 AGM failed to hold a charge after three years.  Another died the same way about four years later.  The third AGM U1 is still going strong after another four or five years.  I now manually disconnect the U1 when we leave the boat for long periods or when the house bank is being recharged after a deep discharge.

I thought about replacing my four flooded house bank batteries with AGMs with all their associated advantages (and expense) but concluded that the source of the U1 failures was more likely from being charged in a mixed SIZE environment than from a mixed TYPE environment.  This conclusion came from watching my Link type battery monitor and noticing the large amount of time the U1 was facing unduly high voltages while the house bank was being charged from a deep discharge.  Of course this occurs at the end of the charging cycle for the house bank but still, the U1 is seeing 14 volts for what I think is way too long given that it is hardly used in starting the engine and so is almost fully charged during the entire house bank charging cycle.  Thus my habit of disconnecting the U1 except when needed.

This theory may in fact by haybag but the system works well enough that it hasn't been worth it to me to rework it.  I have fiddled with trying to get the smart combiner to use it's overvoltage protection circuit to cut off the "combine" when the voltage rises beyond 13.8 volts or so but that induced other problems.  As we're planning multiple month trips up the BC coast now, I will probably replace the house bank "just cause" and may consider AGMs for other reasons.  I would still be leery of the capacity mismatch and would probably still disconnect the U1 much of the time.

Your inputs are welcome!

Randy

[mark_53]

The problem that has occurred is that charging regime for the house bank appears to be unduly hard on the much smaller AGM even though all the stage voltages on the chargers are optimized for the AGM.  Early on I left the AGM connected to the combiner all the time and found that the first U1 AGM failed to hold a charge after three years.  Another died the same way about four years later.  The third AGM U1 is still going strong after another four or five years.  I now manually disconnect the U1 when we leave the boat for long periods or when the house bank is being recharged after a deep discharge...


Randy

This is one reason I decided to just carry one of those inexpensive auto jump start batteries you can buy at harbor Freight for about $50.  On the rare occasion the batteries are to low to start the engine, I pull out the jump start battery, connect to the battery terminals and I'm going again.  I plan on adding some small cables I can connect directly to the starter so I can start in the event something else, (fuse, start button, cable) goes out and I don't have a spare.  Very inexpensive direct solution to backup starting.  Only issue is it may take a couple of minuets to pull out the backup battery and hook up.  Could be an issue if drifting towards rocks with no wind.