Dedicated starting power

Stu Jackson · Aug 2, 2011

Good idea, no reason not to.

Don S/V ILLusion · Aug 2, 2011

opinions differ but my advice would be to put both new batteries together as one bank so you will not draw them down as quickly or as much as you would if they were separate. The bank on ! and the third start battery on 2 or simply direct connect to the engine and have a cross-over switch.

alexco38 · Aug 2, 2011

This is what you needed. It switch both circuits at the same time but keep them separate. Optionally you can combine them if needed but prevent mistakes.

http://bluesea.com/products/5511e

tkanzler · Aug 2, 2011

That's exactly what I did on my H340. Two deep-cycles in parallel on one, and a single start battery on the other. Charger was a 3-channel, with two combined for the two deep-cycles (per the charger instructions), and the third channel on the back-up battery.

I never used the back-up battery, but kept it charged with the shore power charger. The engine's alternator would only charge which ever bank was in use, so it never charged from the engine, but I'd keep it charged manually. Other systems are more sophisticated, but this was good enough for me.

The two group 24's would run all systems, including cold-plate refrigeration, autohelm, instruments, some minor water use, and my notebook computer with nav. software running and gps antenna, all day long (14 hours on one trip) and still had plenty to start the engine at the other end.

I never needed the backup battery, but I was glad it was there.

Stu Jackson · Aug 2, 2011

alexco38 said:
This is what you needed. It switch both circuits at the same time but keep them separate. Optionally you can combine them if needed but prevent mistakes.

http://bluesea.com/products/5511e

It's actually the last thing you need or want. The concept is ridiculous. If either of the battery banks is not working, the last thing you want to do is to combine them.

Get a simple 1-2-B switch.

I've gathered a lot of links if you'd like to read more. http://c34.org/bbs/index.php/topic,5977.0.html

Scott T-Bird · Aug 2, 2011

Agreeing with Alexco ...

The switch he references is perfect for simplicity. You turn it "ON" and all batteries are available for use as you want them. The combined is no different than B on the 1-2-B switch so any argument against using the "combined" is the same as arguing against using "B". If that is what you are saying than so be it. I've never had a need to use "combined" anyway.

Put the 2 house batteries on one circuit and put the start battery on the other. Simply turn it "ON" and the alternator charges both circuits when the engine (or shore power or generator or solar) is charging.

With 1-2-B, don't you have to have it on B to charge the 2 circuits concurrently?

1-2-B is useful but the archaic system. When switched to 1, 2 is not available and vice versa. The switch that Alexco references is the better way to go because switch it "ON" and both circuits are available but separate.

tkanzler · Aug 2, 2011

ancientmariner said:
That's a thought, tkanzler. I've been thinking that my 10amp charger isn't up to the job.
If I replace it, I would certainly go for a 3 channel.

I don't remember what brand it was, but I think it was a 30A, with 10A on each channel, and they could be combined or left separate, any way you like. I think that concept is pretty common, though - shouldn't be hard to find what you want. Must have had diodes or other separation techniques employed, as low house batts didn't draw down the separate stand-by start battery.

jviss · Aug 2, 2011

Echo charger

My plan, which I haven't yet implemented, 'though I have most of the parts, is two house banks on 1 and 2 of the 1/2/B switch, and a dedicated starting battery that is charged using an echo charger. I also want to put a time delay in the field current wire of the alternator to keep the charging load off the engine until the engine is started and running well. Finally, I'd like to be able to start from the house bank in case the starting battery fails, but I can probably just keep jumper cables around for this purpose.

Questions are, what size battery is necessary for starting? I imagine a "lawn and garden" size battery is adequate.

Also, where to get the time delay relay?

Scott T-Bird · Aug 2, 2011

Why have 2 house batteries on separate circuits? There doesn't appear to be a purpose for doing that. Is there a reason you want to switch from one battery to another for a house circuit? They serve one function, just put them on one circuit. Use the second circuit for a start battery or a back-up bank, whatever your desires.

tkanzler · Aug 2, 2011

AFAIK, the typical alternator found on small engines puts out next to nothing at idle, and I would imagine nothing at all at cranking speeds. Once the engine lights, gas or diesel, I can't imagine the alternator putting any kind of significant load on the engine until it's running at speed, but by that time, it doesn't matter.

Don S/V ILLusion · Aug 2, 2011

ancientmariner said:
"simply direct connect to the engine and have a cross-over switch"

How would the cross-over switch work, Don? I suppose the starting battery wouldn't normally need to connect to the house batteries. Should both banks be connected to my charger, or would the starting battery be happy with a short charge from the alternator after starting?

Interesting reading some of the suggestions. Obviously, there are a number of ways to do it and each has it's proponents.
In answer to your question, the cross-over is a simple A/B or in the vernacular, a 1 or 2 switch which allows the engine to be started from either bank. Essentially, you would have two options to start the engine if the other fails or becomes discharged.
Neither bank would be interconnected which, as Stu pointed out, is useless in most cases and detrimental in some. Unless you have some reason I don't understand, both sets of batteries should be connected to separately to the charger (assuming your charger has multiple outputs).

Stu Jackson · Aug 2, 2011

The B on the 1-2-B switch was originally used when the AO went to the C post of the switch, so both banks could be charged when running the engine. When the engine was shut off, the switch should have been moved to the house bank. In "ye olden daze" the general design was to have two equal house banks, and switch daily. with the growth of electrical-hungry accessories on boats, the preferred method is to have as large a house bank as possible to support said loads, with a separate reserve bank. Some folks prefer to have a separate start bank so they don't drop anything that's connected to the house bank, like electronics, out when their engine starts.

The AO now is recommended to go directly to the house bank, NOT the switch. This avoids damaging the alternator diodes if the switch is touched during engine run.

The house bank is connected to the reserve bank with a separate relay of some sort, like an echo charger, combiner, oil pressure switch. The simplicity afforded is easy: get on boat, turn to house bank, use your boat, turn off at end of day.

The ONLY time B would ever be used is when the engine is running and the relay fails. It's a backup, B for backup.

The significant advantage of the 1-2-B switch over the dual circuit switch is two fold: one, since you're smart, you don't put it on B when the originally selected battery doesn't start your engine, you switch to the other battery (the dual circuit switch simply cannot do this, it combines them at the worst possible time!); two, you can actually use the reserve bank to run your house loads, albeit limited because of the smaller ah capacity of the reserve bank.

1-2-B is useful but the archaic system.

That's simply not true. The switch was (incorrectly) wired for convenience of the builders by combining the starter feed with the AO wire to the C post. Besides, the switch is not a system. An understanding of the proper application of the 1-2-B switch and electrical systems will show that the dual circuit switch has a an illogical position when used in real life - combining batteries as Blue Seas discusses in their literature for that switch will only hurt the folks it's meant to help. The only advantage that switch has is to separate the house and start functions, but many of us do not have issues with the 1-2-B switch, nor electrical items "dropping out" as Maine Sail has repeatedly mentioned.

Much of this, like all of it, is covered in the links I provided.

Here's a good summary from that link, with other links for you to read: http://c34.org/bbs/index.php/topic,5977.msg38552.html#msg38552

As always, your boat, your choice.

Scott T-Bird · Aug 2, 2011

Detrimental or useless ...

I understand that normal use in the "B" or "Combined" mode is not recommended and can be detrimental if you have a weak bank combined with a strong bank. But if used, say, when you have a dead battery for starting, how is it useless or detrimental. The charged battery will certainly start the engine even if it is combined with a dead battery. The alternator will be charging the banks no differently than otherwise while the engine is running. How is it useless or detrimental to use that switch position under that circumstance? What circumstance would you use the "B" position (or the "Combined" position)? Or in other words, why does the manufacturer give you that option by making the switch that way?

Scott T-Bird · Aug 2, 2011

I see the difference and its a good point. I installed mine with a house bank on one circuit and a small starter battery on the other circuit. No issues since installation so I've never found a reason to do anything other than simly turn it "ON" or "OFF"

jviss · Aug 2, 2011

Scott T-Bird said:
Why have 2 house batteries on separate circuits? There doesn't appear to be a purpose for doing that. Is there a reason you want to switch from one battery to another for a house circuit? They serve one function, just put them on one circuit. Use the second circuit for a start battery or a back-up bank, whatever your desires.

I'm talking about two house banks on two circuits. You shouldn't parallel batteries unless they are the same exact make/model, and connected together when new (i.e., subjected to the same loads over their life). With two banks, if one shorts or is otherwise damaged or destroyed, you can use the other. An automatic circuit connects them together when a charging source is present (I use a "Pathmaker).

Bill Roosa · Aug 2, 2011

Well T-bird when you combine the dead and fresh battery the fresh one begins to charge the dead one and at a fairly high rate (~0.30 the AH of the dead battery). So my 410 AH dead house bank is being charged by my 100 AH fresh start battery at 410*.3= 123 amps. This represents a significant portion of the cold cranking amps on my start battery and also a will significantly lower the voltage avalable for powering the starter. If you switch the batteries it is not that significant however but still a pretty high current.

Questions to the group; how long will this high current last? what size cable would be required to safely handle that size current?

I'd stick with the old school 1-2-both-off switch and then you get to choose what is going on. Just switch to the house bank for overnighters or a very long daysail. Otherwise leave it on BOTH to have the largest size bank to draw from. My personal history suggests that you don't need to take it off BOTH unless you know you would be drawing down the entire system to a low SOC.