Why Primary/Reserve vs House/Starter

Jan 7, 2017
92
beneteau 36 new london
Branched off MS's thread here http://forums.sailboatowners.com/in...-thoughts-musings.137615/page-10#post-1346551

"Primary" is the (much) bigger bank, used for both House loads and cranking the starter in normal circumstances.

The other battery is "Reserve", large enough to run (for a while, a subset of) House Loads if necessary, but top priority is to ensure its capacity is kept preserved to crank the starter, in the event something goes wrong with Primary.

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Maine Sail> This is fine, if that is how you want it, but why do you want it that way?

First of all, why not? Seems overall more logical & consistent with my overall perception of best practices in many other components, sub-systems and design factors.

Given minimized running of engines or gensets, can prioritise immediate smart charging Primary (house), maximizing Bulk high currents getting where it's needed, rather than waiting for a barely depleted starter to be topped up before the more important job starts.

Best scenario for backup reliability, battery health & longevity of the reserve (critical for safety) is maximised by being discharged as little and as infrequently as possible.

Keeps potentially "abusive" cycling patterns, when required, to be isolated to Primary.

Simplifies and gives widest range of choice in isolating/combining technologies, all charge sources directly connected to the one bank, all other batteries/banks clearly subsidiary to Primary. Limits or eliminates relay cycling, or use more intelligent echo/combi charging, enables transitioning to newer more expensive chemistry type.

Possibility exists of building up the "next Primary" bank, over say the first year of service, without a big difference between bank members in number of dis/re-charge cycles, only less critical calendar months "in float on the shelf". When Primary needs to be retired, maybe suddenly when funds are short, if Reserve is large enough can take over as Primary, and a relatively cheap consumer cranking battery can serve as Backup Starter for a while.

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I imagine there may well be other good reasons, as well as counter-arguments.

Those, as well as discussion on some of the less settled ideas above, would be most welcome, from anyone.

Please ignore the original context, any specific switching design or combining tech, let's try to discuss the Primary/Reserve design principle on its own generalized merit, as opposed to the more usual Starter/House dichotomy.
 
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Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
Why?:banghead:

You already listed the reasons to do so.

Isn't it like saying: "We know how useful fire and the wheel are. Can we please regurgitate those reasons?":deadhorse:

Folks (for the past twenty years) have been suggesting this approach. Because larger, non-split house banks simply last longer. 20 years ago (and even now!) manufacturers have been delivering boats with two equal house banks. Calder summed it up best (see below). Once that FACT was established, split and equal house banks made little sense in terms of the amount of lead you hauled around, so a largest house bank with a small AND SEPARATE "backup", reserve, start bank made more sense: same amount of lead to schlep, greater longevity.

Thousands of folks have done it. Haven't heard any complaints. :poke::laugh:

Here's Calder: (yet again, must have been posted two thousand times)


IS IT BETTER TO HAVE ONE OR TWO BATTERY BANKS FOR HOUSE USE?
(By Nigel Calder - I DIDN’T write this!!!)

The popular arrangement of having two house banks alternated in use needs scrutiny before I go any further.

LIFE CYCLES: As we have seen, the life expectancy of a battery in cycling service is directly related to the depth to which it is discharged at each cycle - the greater the depth of discharge, the shorter the battery’s life.

This relationship between depth of discharge and battery life is NOT linear. As the depth of discharge increases, a battery’s life expectancy is disproportionately shortened. A given battery may cycle through 10% of its capacity 2,000 times, 50% of its capacity 300 times and 100% of its capacity around 100 times.

Let’s say, for arguments sake, that a boat has two 200-ah battery banks, alternated from day to day, with a daily load of 80 Ah. Each bank will be discharged by 40% (80 Ah of one of the two 200 Ah banks) of its capacity before being recharged. The batteries will fail after 380 cycles, which is 760 days (since each is used every other day). If the two banks had been wired in parallel, to make a single 400 Ah battery bank, this bank would have been discharged by 20% of capacity every day, with a life expectancy of 800 days, a 5% increase in life expectancy using exactly the same batteries!

But now let’s double the capacity of the batteries, so that the boat has either two 400 Ah banks, or a single 800 Ah bank, but with the same 80 Ah daily load. The two separate banks will be cycling through 20% of capacity every other day, resulting in a total life expectancy of 1,600 days. Doubling the size of the battery banks in relation to the load has produced a 210% increase in life expectancy. The single 800 Ah bank will be cycling through 10% of capacity every day, resulting in a life expectancy of 2,000 days - a 25% increase in life expectancy over the two (400 Ah) banks, and a 250% increase in life expectancy over the single 400 Ah battery bank!

There are two immediate conclusions to be drawn from these figures:

1. For a given total battery capacity, wiring the (house) batteries into a single high capacity bank, rather than having them divided into two alternating banks, will result in a longer overall life expectancy for the batteries.

2. All other things being equal, any increase in the overall capacity of a battery bank will produce a disproportionate increase in its life expectancy (through reducing the depth of discharge at each cycle).

FOR BATTERY LONGEVITY, A SINGLE LARGE (HOUSE) BANK, THE LARGER THE BETTER, IS PREFERABLE TO DIVIDED (HOUSE) BANKS.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
Quote: Maine Sail> This is fine, if that is how you want it, but why do you want it that way?

First of all, why not? Seems overall more logical & consistent with my overall perception of best practices in many other components, sub-systems and design factors.
The whole premise of the "PRIMARY/RESERVE" use switch is for those who already had or have a 1/2/BOTH switch installed and reconfiguration to another switching system is too costly or cumbersome..

This 1/2/BOTH as a use switch with house-primary/reserve-start just really simplifies things, with a 1/2/BOTH, works adequately well and is inexpensive.. If starting from scratch, with essentially unlimited switching choices, and you can do other switching scenarios, it is never a bad idea to create a dedicated starting bank and a house bank.

Given minimized running of engines or gensets, can prioritise immediate smart charging Primary (house), maximizing Bulk high currents getting where it's needed, rather than waiting for a barely depleted starter to be topped up before the more important job starts.
The house gets priority charging in both wiring scenarios if that is how you desire it or wire it. Best practice for charging performance is to feed all charge sources direct to the house bank then use *charge management devices (*ACR/VSR's/Combiners, Echo Chargers, Duo Chargers, B2B chargers etc.) to feed charge current over to a reserve or starting battery from the house bank.. There is no edge here for house/primary & reserve/start over house/start when it comes to charging performance.

Best scenario for backup reliability, battery health & longevity of the reserve (critical for safety) is maximised by being discharged as little and as infrequently as possible.
Batteries calendar age too and are murdered much more rapidly by heat than folks often assume. I've seen no real world evidence that a battery used as reserve only lives a measurably longer life than one used for starting only. When wired properly both last a good long while. I have many dedicated starting batteries (usually "deep cycle" on sailboats) that last 6-12 years or more where the house/cycling bank has been replaced one, two or three times. When cheap auto-type starting batteries are used for starting or reserve applications the average life I see is about 3-7 years regardless of starting or reserve use. Whether used as a dedicated starting or reserve battery really seems to make little difference in longevity though battery type does.

Starting an engine really does not "discharge" a start battery like folks incorrectly assume it does. The average starter duration I measure is just about .9 seconds, loaded to unloaded starter motor cranking duration. Some are as short as 0.62 seconds and some as long as 2 seconds. When you do the math you are looking at tenths to hundredths of Ah's per engine start.

If we look at an average cranking amp load over the starter motors loaded cranking duration of 286A (high for many sailboat engines)

286A X 0.00021h (0.75 seconds) = -0.06Ah's Consumed to start

Even if we bump that to 400A and greatly extend cranking times:

400 X 0.00416h (15 seconds) = -1.66 Ah

or

400 X 0.00055h (2 seconds) = -0.2 Ah


Heck a Toyota Prius starts as many as 100X plus per day, in average driving, with a puny little battery of about 30 Ah's in capacity. The typical start/reserve battery I install on most sailboats in on the order of 100Ah's or more so it can serve as a back up to House/Primary. It is not sized this way for cranking requirements but for "reserve capacity" in the odd event that you may need it.

Keeps potentially "abusive" cycling patterns, when required, to be isolated to Primary.
In either a reserve or starting scenario there is no abusive cycling until your house bank fails. Again no edge here for reserve over starting.

Simplifies and gives widest range of choice in isolating/combining technologies, all charge sources directly connected to the one bank, all other batteries/banks clearly subsidiary to Primary. Limits or eliminates relay cycling, or use more intelligent echo/combi charging, enables transitioning to newer more expensive chemistry type.
Is suspect you may be reading what you "want to read" to justify some assumptions you've made? Again there is no difference between a properly wired dedicated starting battery and a reserve battery for the items you just mentioned.

Possibility exists of building up the "next Primary" bank, over say the first year of service, without a big difference between bank members in number of dis/re-charge cycles, only less critical calendar months "in float on the shelf".
Regardless of the start or reserve bank, a primary or house bank should be installed as a contiguously wired bank with batteries of the same age, date codes and *similar internal impedance (*if you have access to this equipment). Adding batteries to an already used bank leads to intra-bank imbalances. Beyond that batteries should ideally be commission charged and balanced if they will be series or series>parallel wired.


When Primary needs to be retired, maybe suddenly when funds are short, if Reserve is large enough can take over as Primary, and a relatively cheap consumer cranking battery can serve as Backup Starter for a while.
A house bank, if kept in good health, maintained and charged properly and tested annually should not yield any surprises. A sudden failure means you're simply not paying attention to the banks overall condition and Ah capacity degradation.. Sure internal shorts/failures can happen on occasion, even in healthy banks, but this is extremely rare compared to abused banks. Again, same answer in that this makes no difference if you use your second battery as a reserve or dedicated starting/reserve. The only caveat I would make, no matter whether you use a dedicated starting battery or a reserve, is to size it for emergency consumption and to choose a deep cycle battery over a starter or dual purpose battery.

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I imagine there may well be other good reasons, as well as counter-arguments.
With a dedicated starting battery you will always know the rough condition of the battery by how it is physically cranking the motor. With this information you can make an educated decision as to when to replace it. With a reserve battery you will still want to regularly test it for cranking capability upwards of multiple times per year. In hot climates, battery temps regularly above 80F, a dedicated starting battery is going to give you much better information on a regular basis than a reserve only battery will.

With a dedicated starting battery you can avoid transients events caused by the starter motor and this wiring is more forgiving of bad wiring practices for electronics. This does not eliminate transients caused by the many other on-board systems but does eliminate one potential source.

Depending upon house bank size, a dedicated starter also eliminates "brown outs" during starting regardless of how deeply you discharge the house bank. If your house bank is well sized, 300+ Ah, wiring is large enough, connections well made, and the system is properly wired then brown outs should not occur on a house bank if you are not discharging below 50% SOC. If brown outs start occurring when using a "primary/reserve" protocol the bank is getting long in the tooth..

Bottom Line: When I have a choice, and am not locked into a 1/2/BOTH, that choice will usually be for a dedicated starting battery and a three-switch or similar switching configuration.
 
Jan 7, 2017
92
beneteau 36 new london
Why?

You already listed the reasons to do so.

Isn't it like saying: "We know how useful fire and the wheel are. Can we please regurgitate those reasons?"
MS asked me for my reasons, and they did see to have raised valid issues for me to (re)consider.


> split and equal house banks made little sense in terms of the amount of lead you hauled around, so a largest house bank with a small AND SEPARATE "backup", reserve, start bank made more sense: same amount of lead to schlep, greater longevity.

That was what I was thinking.

as MS put it

> If you're going to have a reserve battery there is really no sense in not having one that could run house loads. We are talking about 15-20 pounds difference...

Sorry to have annoyed you, I am (as you can likely tell) a noob. Never heard of any Calder other than the sculptor, family friend "Sandy" lived up the road in Roxbury. Helped him with his tractor once visiting the Millers next door.

Thanks much for providing that, and the only time I'd end up with equal sized banks would be if my old in-use Primary/house was likely on its way out, and my unused Reserve (or now perhaps becoming barely-used Starter), was growing over time as I could afford to add to it with new cells over time.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
Sorry to have annoyed you, I am (as you can likely tell) a noob.
You did not annoy me, but Stu can occasionally come across as a bit terse with folks who he feels have not adequately researched a bit first.


From where I sit I think you are asking good questions but perhaps just a bit prematurely. Keep reading, researching, understanding and it will come to you. You'll still have questions though...
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
Folks (for the past twenty years) have been suggesting this approach. Because larger, non-split house banks simply last longer.
Stu,

He never asked about using split house banks (read the post again) he was asking about using a reserve only (only used in emergencies) vs. a dedicated starting battery (used for everyday starting) as the secondary bank on-board.
 
Jan 7, 2017
92
beneteau 36 new london
never a bad idea to create a dedicated starting bank and a house bank.
...
When I have a choice, and am not locked into a 1/2/BOTH, that choice will usually be for a dedicated starting battery
OK, pretty much sold, fact that the starting load hardly counts as use anyway, better familiarity with its condition, plus the isolation gained from noise/ brownouts.


> Best practice for charging performance is to feed all charge sources direct to the house bank then use *charge management devices (*ACR/VSR's/Combiners, Echo Chargers, Duo Chargers, B2B chargers etc.) to feed charge current over to a reserve or starting battery from the house bank.

That's the plan, and your way means cranking current doesn't need to pass through the combiner or require a manual switch be used, a design like Dual Circuit Plus where "normal stays on" would suffice.


> murdered much more rapidly by heat than folks often assume.

plan to keep them cool, just means some more copper to the engine right? But if LiFePO4 one day, then less true than lead, correct?

> Batteries calendar age too...
> I've seen no real world evidence that a battery used as reserve only lives a measurably longer life than one used for starting only.

The telecoms I bought at auction for off-grid use in early '80's outback Oz held up pretty well; I was told they were 10+ years old at the time. Huge 2v FLA monsters they were.


> cheap auto-type starting batteries

not under consideration here except for emergencies or poverty.


> I suspect you may be reading what you "want to read" to justify some assumptions you've made?

likely, most common fallacy innit.

> bank should be installed as a contiguously wired bank with batteries of the same age, date codes and *similar internal impedance (*if you have access to this equipment). Adding batteries to an already used bank leads to intra-bank imbalances.

I agree in an ideal world. But my finances are such that it is more likely I could buy a new cell when I get a bit of extra income in a given month, than have enough in the bank at the time were the Primary to fail. This might even let me get started with LiFePO4, get away from the PSOC damage done by my anticipated unavoidable circumstances (long cruising, mostly short motor/alt, little solar).

But if it really is the case that the whole bank will in effect be in the SoH as the oldest cell obviously would be a stupid strategy, need to find a "trustee" vendor to lock away my "bank deposits" :cool:

> Beyond that batteries should ideally be commission charged

Sorry what's that? hard to google. . .
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
You did not annoy me, but Stu can occasionally come across as a bit terse with folks who he feels have not adequately researched a bit first.


From where I sit I think you are asking good questions but perhaps just a bit prematurely. Keep reading, researching, understanding and it will come to you. You'll still have questions though...
I apologize.

However, I often provide a lot of information, too, many of them include links to Maine Sail's excellent information.

Like this one:

Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html
http://c34.org/bbs/index.php/topic,5977.0.html
Have fun reading, John.
 
Jan 7, 2017
92
beneteau 36 new london
No offense taken, all good stuff and par for the noob course, greatly appreciate all feedback.
 
Jan 7, 2017
92
beneteau 36 new london
Just an addendum, with something like the standard three-switch layout, or my "non-KISS" setup under discussion here: http://forums.sailboatowners.com/in...y-switches-layouts.182986/page-2#post-1347024

The whole question of which bank you're cranking your engine starter from becomes a matter of flipping a switch or two.

As MS pointed out, it's a decent seat-of-the-pants state of health check and worth routinely switching over from the usual battery to "the other bank" once in a while just for that reason, if you have a switch layout that makes that easy.

Assuming you don't have (or avoid while testing) a "sensitive electronics affected by cranking" issue.

The actual battery load of cranking being so minor, should not be an issue on any healthy bank, whatever you call it.

And footnote, still hoping to learn what "commission charged" means, from MS or anyone? googling doesn't help. . .
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
still hoping to learn what "commission charged" means, from MS or anyone?
OKie Dokey, Johnny, one more time: have you read the Electrical Systems 101 topic I've sent you a few times?

This one is right there:

Breaking in New Wet Cell Batteries: http://c34.org/bbs/index.php/topic,6353.0.html
You might wanna consider spending a day reading through it.
 
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Jan 7, 2017
92
beneteau 36 new london
Thanks Stu, that is a very valuable but also large collection of links, some of which are each leading to a graduate course's worth of reading.

I will be slowly working my way through it, at least four hours a week I promise.

That Ample primer is a good start, thanks, and do please feel free to keep reminding me, my ADHD does lead me down tangent rabbit holes.