Dedicated start battery

[tmh]

I am exploring the use of a Dedicated start battery but will not integrate it in to the current house system at this time. I just posted a query on an external jump starter but they do not seem to work yet.
So on the short term I think I just want to buy a battery and place it on the boat. Peace of mind for me. I currently have 2 new 4-D AGM’s for the house But after two nights on the hook they are almost completely discharged. I can start the diesel but it takes 3+ hour to charge them back up at about 8-10 Amps
I am seeking advice about what size battery I will need to start the M35B.

[wolfe10]

Mike,

10-12 amp charge rate for a deeply discharged battery bank is WRONG-- it should be at least several times that.

What alternator do you have?

What engine RPM are you running to charge?

Also, many of us have installed an "emergency battery". An AGM battery can easily be fit in the compartment just forward of the battery compartment. Wiring can be as simple as jumper cables or through an ON-OFF marine battery switch. Most elegant is to permanently wire the emergency battery negative terminal to the main battery bank negative. Then new ON-OFF switch from the positive of the new battery. Out from the switch to the C (Common) terminal of the original OFF-1-BOTH-2 switch. If the original batteries are dead/too low to start the engine, turn OFF the main battery switch and turn ON the emergency battery switch. Now you have full emergency battery amps directly to the starter rather than "diluting" amperage by it trying to bring up main battery bank voltage. Once engine has started, turn on main battery switch to charge main bank. Remember to NEVER turn off all battery switches/disconnect batteries with the engine running. That would "let the smoke" out of the alternator.

If you want, private message me your phone number and we can visit about this.

Brett

[SeaBreeze]

Mike
Wolfe’s suggestions are excellent. Allow me to suggest another option just to give you something to think about. I have my house batteries wired in parallel to battery switch #1 and an emergency start battery wIred to battery switch #2. Normally I have my switch on position #1 all the time and hold the start battery for emergency only. The start battery I chose is a Group 27 size with 840 CCA at 0 degrees F. Overkill. It’s located at the aft end of the locker under the settee on the port side as wolfe explains. The reason for your post raises some questions. How do you know the batteries are deeply discharged after two nights on the hook and how do you know the alternator is charging at a 10 amp or less rate? I use a Victron battery monitor and even in the summer my 450 ah house bank will only be about 25–30% discharged after two nights on the hook and 50% discharged after 3 nights. It still starts my M35B. Also, my 40 amp output OEM not so smart alternator will pump out 35 amps after engine start and begin to decline after about 45 minutes and still be above 10 amp output after about 3 hours of motoring to the next anchorage. So you may have something going on that needs some investigation.
Rick

[wolfe10]

Yes, Rick''s way is also excellent. Makes the original two batteries into ONE large battery bank. It would make Mr Peukert happier (yes, look up Peukert's law written in 1897).

But (OK, large BUT) it requires that the operator be more electrically savvy, as you are really back to two battery banks instead of two plus an emergency battery.

Again, a very viable alternative for those who are electrically savvy, particularly in conjunction with a good electrical monitor system.

[Olivia Mae]

I also installed our emergency start battery as Rick mentioned above, with a paralleled larger house bank. One last piece of the puzzle I added, was a Victron battery combiner, so both the house bank and the emergency start battery will both be charged no matter how the battery switch is selected.

[wolfe10]

And with that configuration (two original batteries combined and on one lug of battery switch and new battery on other lug) to charge both batteries merely put the battery switch to ALL.

[tmh]

Brett and Rick,
Thank you so much. To start I am a novice sailor and have even less knowledge about 12V DC current!
I have 2 new 4-D West Marine house batteries. The previous owner ran them together and left the battery switch on BOTH. I asked why and he was 'unsure' and I left them that way.
I have two meters aboard.
One is analog [needle] at the Nav Station The other is a Xantrex Link 20 [digital] at the nav station, with 4 read-outs; Volts, amps, amp-hours, and time to complete discharge. They agree on the voltage.
I will leave the Marina fully charged [12.8v] in the afternoon sail for a few hours and then drop the hook. The only big draw is the fridge at 4-6 amps when the compressor turns on. I do need a new compressor and wonder if this is causing it to cycle on too often [???] Mostly LED lights.
In the morning of night one, I am down to 12.2-12.25v. Morning of day two 11.8v
The motor starts, and I charge at idle around 900-1000 rpm. The Xantrex reads 8-10v at this time. Takes 3+ hours
My alternator is aftermarket and I think 85 amp, but I will have to double-check that. It was an upgrade from the standard stock alternator. My 350 is a 2005 model year
I do have wind power but do not think it is working.
No solar power.

[Olivia Mae]

And with that configuration (two original batteries combined and on one lug of battery switch and new battery on other lug) to charge both batteries merely put the battery switch to ALL.

Yes, that will also charge both. For normal use, we only run on the house bank. If I want to ensure that the emergency start battery is always charged and ready, I would have to leave the switch on both much of the time, which defeats the purpose of keeping them separate. Putting in a combiner takes the human element out of it, and believe me, I'd be the one to leave the switch in both and manage to run both banks down. I have all charging sources (alternator, solar, and shore power charger) run to the house bank, and the combiner keeps the emergency start battery topped off from there.

[wolfe10]

Yes, suspect there will always be the choices between KISS (Keep It Simple Stupid)-- simple marine battery switch

AND

Totally automatic devices.

No right or wrong answers-- weigh YOUR priorities and abilities.

For me, the further from home you cruise, the more you tend toward KISS.

[Olivia Mae]

I have 2 new 4-D West Marine house batteries. The previous owner ran them together and left the battery switch on BOTH. I asked why and he was 'unsure' and I left them that way.

In the morning of night one, I am down to 12.2-12.25v. Morning of day two 11.8v

Mike,

Not Brett or Rick here, but I'll throw in a couple of thoughts. To find out what the previous owner did, you're gonna have to do some wire tracing from the batteries up to the battery switch. Take a look at the link below. It has a good discussion of how a 1, 2, Both battery switch works and various ways it could be wired. This may be all too much information for you, but if you read it over several times and understand the diagrams, you should be able to figure out how your own boat was set up by the previous owner. I can tell you that ours was wired from the factory like his first diagram, until I made some changes. The only addition to that first diagram is the shore power charger. On our boat, it had 2 outputs, one of each wired to each battery.

Concerning your battery state of charge, if you continue to run them down to 11.8 v, you will kill those new batteries in pretty short order. They shouldn't be discharged more than about 50% in order to get the best life out of them. I would plan on finding a way to get them recharged after day 1 and not wait til day 2.

https://forums.sailboatowners.com/threa ... gs.137615/

[Captain Kirk]

Hello all,
I have a similar setup to others, with the house bank paralleled (4 golf carts - 450aHr) and a separate "no" maintenance Group 27 starter battery. I normally stay on the house bank and use the starter battery occasionally to make sure it actually works (it always does).
Since I have the optional 3rd water tank under the port settee, there was no room for the Group 27 there but it fits very nicely located aft of the engine under the berth. The Victron battery monitor is a key piece for us as is the solar charging system I installed 2 seasons ago. With these additions I'm on top of the DC system and find the solar panels keep the batteries well charged. We cruise for up to 8 weeks at a time and rarely need to charge with shore power or with the engine.

I agree with input from Scott on tracing wires, its key to help in understanding the boats systems. Documenting your findings means you don't need to rely on your memory.

After buying Sand Dollar 3 years ago I needed to know what the PO had done with the various systems to understand what I would need/want to change. I went through all the systems on the boat and documented them in the form of schematic drawings. I did the DC wiring schematic first which I have attached here. I keep it updated as I make upgrades/changes etc. Also did a plumbing drawing for the Hydronic heating system (its needed in the Pacific NW for any shoulder season cruising).

Most recently I did the navigation instrument schematic which includes the network backbone I installed in order to upgrade the chart plotter and other instruments to meet the NMEA 2000 (Seatalk-ng) requirements of the newer instruments. Some work on this is still in progress/pending so I can refer to the drawings as I tackle new projects. Drawing is attached here.

Documenting as many of the systems as you can really pays offs when you have a memory as poor as mine.

Love this forum!

[Olivia Mae]

NIce drawings! What program are you using for that?

[S/V Tavish B.]

Hello,

I ditched the original battery switch for some new technology...

Our vessel came with three batteries total, the two 4D's wired in parallel as the the house bank and a Group 27 start battery in a battery box in the port side compartment just forward of the house bank as others have mentioned here.

I struggled, A LOT, with remembering to switch between the "1-2-Both-Off" original battery switch and was elated to find that Blue Seas Systems made an "Add-A-Battery" Kit, with a new battery switch that fits in the same hole as the original, but isolates my two battery banks. The kit includes an automatic charge relay, can detect a draw or charge on either bank, and will open or close the circuit between the two banks to facilitate charging when there is a source, but isolate the batteries when there is a draw. I haven't needed it yet, but the switch also comes with a "combine" option, helpful should maybe both banks independently be too low to start the engine, but combined maybe provide enough juice.

This is not a paid advertisement, it's just been one of those widgets that has GREATLY improved my boating experience by removing my requirement to think or remember, "what position did I leave the battery switch in?"

Here's a link to the manufacturer's website, I bought mine at West Marine and from what I can recall, it didn't take much effort to swap out from the old one, just some additional battery cables and fuses to wire up the charge relay.

https://www.bluesea.com/products/7650/A ... Kit_-_120A

Also, here's a link to a video I posted, more about my solar charger, but a brief description about the switch and charger:
https://www.youtube.com/watch?v=ANr3Y8jqPOs

Safe Travels,
Nick C.
S/V Tavish B.
Hull #26

[wolfe10]

Kirk,

Yes, very nice drawing.

A minor suggestion:
On your four 6 VDC main battery bank, have the house positive and negative come off different pairs so electrons flow equally through both battery pairs.

So, either positive from A2, negative from B1 OR positive from B2, negative from A1.

I also agree that any new buyer should not ASSUME how a previous owner wired their boat, but to VERIFY so they know how to maximize 12 VDC performance.

[tmh]

Thank you, everyone, for this valuable and informative discussion!
Brett, could we talk tomorrow? Sunday?
What would be a good time for you?
I am CDT here.

Mike

[Captain Kirk]

Scott:

My wife produces the drawings from my hand sketches, she a retired drafter. With no access now to the high-end CAD software, she used Microsoft Publisher to do these drawings.

Brett

Thanks for the input, I've heard/read somewhere about wiring them that way. Its on my list now.

[knitchie]

I recently rewired the two switches that control the flow from the batteries to the aux and house panel. Our boat came with 2 4D house batteries wired as a single 12 v bank, and a start battery. The house was wired to position one and the start battery to position two of the 1-2-both switch on the left side under the nav table. The output of that switch ran to the house panel and the switch on the right which needed to be on in order to start the aux. So, two switches needed to be on to start the aux, and if the first switch was on position two, the house was running off the start battery. And, if I forgot to switch back to one after turning off the aux, the start battery would drain unnecessarily. Dumb and dumber.

I moved the wires around so that the start battery runs to the right side switch and can start the aux when that switch is on, regardless of the left side switch. The output of the right side switch also goes to position two of the left side switch.

Now, I can run the house on the house battery and start the aux with the start battery independently.
But, if I need more juice to start the aux than the start battery provides, I can switch the left side switch to all.
Or, if I need more juice to run the house than the house battery provides, I can switch to two or all to pass power from the start battery to the house panel.

This is working very well and I am far more comfortable with the arrangement now.

Fair winds,
Ken
Reverie, #447

[tmh]

All,
I want to thank everyone for their valuable thoughts, ideas, and suggestions.
A special "shout-out" to Brett Wolfe who called me on the phone to discuss my issue(s).
I wanted to now "finish" the story ...
My first issue was poor charging of my house batteries after a night or two on the hook and that got me thinking about a dedicated start battery, but I still needed to figure out why I was only getting 8-10 amps back into a 50-75% discharged battery. And it taking 2-3 hours to charge back up.
Things I did along the way;

Removed and bench-tested the aftermarket Balmar alternator [it was good],
2-new 4-D batties $$$$ [others were 4 years old],
Cleaned all alternator contacts [was certainly needed, but did not solve the poor charging]
Replaced the Balmar MC-612 regulator [not made anymore] with a Balmar ARS-5 regulator and BINGO!!!!

Now is was recharging a 75% discharged battery with 20-30 amps in 30-60 minutes!!

Lesson for me was that the regulator should 'scroll" through its functions when the key is on but engine not yet started. The old MC-612 was not doing this. The new ARS-5 does and everything is now back to normal.
Again THANK YOU everyone for your help and support along the way.
Hope this might be helpful for someone sailing a C-350