Alternating Battery Banks (Odd/Even, or?)

[Frank C]

Spinning this thread as distinct from Harrison's concurrent thread on Starter vs. House batteries, since it is an entirely different approach to servicing DC demands. I'm surely an electricity novice (*), but I'm sharing here what I learned at ASA Sail School, and the logic described by that Instructor. Comments invited from all our resident EEEs (electrical engineers or experts).

The sail school uses the ODD/EVEN methodology of battery service and maintenance, for their entire fleet. In this approach, Batt#1 is used on Odd dates and Batt#2 on Even dates. The logic in this scenario is to always have one battery "resting" in reserve, while also assuring that BOTH batteries get "regular exercise". Odd-even is a convenient approach for a fleet shared among many different Skippers, but it's not the only approach.

The alternate mgmt scenario requires an Either or Both switch, like from Perko, and works best if a Combiner can permit the Alternator to service both batteries when surplus engine current is available.

IMO, this approach is particularly well-suited to Macgregor powersailers, where we tend to have pretty strong DC demands, pretty regular recharging by the outboard, with fairly light engine starting loads.

The Honda 50 is smaller than many motorcycle engines, which are amply serviced by a battery weighing less than 10 pounds. It seems wasteful to dedicate 50 pounds of Starter battery to that demand, and then allow that battery to spend it's life in waiting.

Using the ODD/EVEN approach, "today's battery" will service both house and starting demands, good exercise for the entire day. If it happens to get too low, the "resting battery" is available to start the motor. If it gets low too frequently, it's time to consider retirement.

(*) Electricity novice = one meager step beyond Total Electricity Dunce~!

(Edited: to clarify title, alternating, odd vs. even, etc)

[Frank C]

Implementing Odd/Even
After learning of this potential approach I altered my battery management plan. I finally replaced my very weak factory starter battery with a Deep-cycle from Walmart, nearly matching my original Wally-Deep. They are either a Group 29 or Gp 31, not sure, but I do know the newest has 115 amphrs. I had planned to use them in a simple parallel bank of ~200 ah. I also carry a PowerPak jumpstarter, religiously, just in case.

However, 200 ah is way-more capacity than I ever need in a given day. My internet reading reveals that too much capacity can be a disadvantage also. If the bank is typically drawn only 10%, then topped again, it's not a good way to life-cycle the batteries. They will have much better life-cycle with regular deeper exercise (20+ percent), followed by recharging. It's sorta improved "cardio-cizing" for the batts. Later on I'll seek out some of the weblinks that prompted this new approach.

So, I decided that it will be better to cycle these two big boys, Odd/Even. Another advantage ... my older Deep (Batt#1) is clearly weaker than the newbie. This permits me to monitor #1 performance, with #2 serving as benchmark and backup. Most importantly, #2 CANNOT serve as a hidden crutch, masking the demise of #1, since he must pull his own weight on assigned dates.

Either battery can start my Suzuki DF-60 without any sweat. It's still a relatively small, 1100cc EFI motor that fires every time on the first or second rotation. As mentioned earlier, this scenario simply requires the correct style of Perko (I actually have two switches instead), plus a Battery combiner to make recharging easier & automatic.

[Frank C]

Implementing Odd/Even with different battery types

We have deep cycle/standard batteries on the boat we recently purchased. Is there any harm in putting the Perko on combined once the motor is running so we can charge both at the same time? We've basically been running of the deep cycle all the time, starting or otherwise, and now the standard is starting to run out of juice (we don't have a way to charge it without removing it and taking it home with us). Wasn't sure if it would harm one or the other if we used the combine setting.

Great question, I'd like to know the answer as well. ---Harrison

BTW ... I see no reason to delay implementing the Odd/Even scenario, even if using 2 different battery types, Starter & Deep-cycle. Your existing Starter-Batt can receive 'regular exercise' for the remainder of it's useful life, being finally replaced to end up with a pair of matching Deep-cycles ... AND, there's no requirement that they match, in size. If your current Deep is only 65 Ah, no reason to limit your next one to that size. However, mixing Wetcells with Gels or AGMs .... that's not ideal and deserves close study.

So ... Odd/Even scenario works well for two batteries of dissimilar ages, as well as dissimilar capacity. If Battery#1 is the older Starter, you still choose that one for the Odd dates. If it happens to go flat on its assigned day, just switch to Batt#2 without paralleling them (which would just weaken #2 unnecessarily). If Odd fails on several different dates, you'll know its time has expired. Meanwhile, you'll be alternating with Even, helping to judge Odd's performance, and always have #2 as backup.

[Frank C]

System Weaknesses

• As Odd approaches his end-life, he's a less reliable backup for Even. After a failure or two by Odd, eventually you'll elect to retire him.
• On an extended cruise, you need to be using the engine pretty regularly to top "today's battery" hopefully tomorrow, at latest. This isn't terribly different, though, than related issues of the Starter plus House approach.
• One way to side-step this "extended cruise" issue is using a Link monitor for both batteries ... always better to see what's happening and adjust consumption where necessary.
• And during an extended cruise, knowing my approx capacity and usage, I might choose to run the initial battery deeper, beyond his "assigned day" holding the other battery in a longer reserve cycle.

All good reasons to carry a PowerPak, at least for a long cruise, or when we know one battery is aging rapidly.

[DLT]

If you treat them as odd/even day batteries, then there would be little issue with vastly different batteries. After all, they are pretty much kept separate, except when charging.

Of course, a starting battery just isn't designed to pull amps for a long period. But, if all you are doing to running electronics and such, you're probably not pulling enough to be a problem.

On the other hand, a deep cycle isn't designed to pull really big amps, even for a short period. But, if your engine doesn't pull too much, then maybe that's not an issue either.

In my case, the motor dealer/installer actually had to install a bigger starting battery saying the stock one wasn't rated for the ETEC starting requirements. I don't know if that was just an excuse to sell me a battery and I haven't tried to start the motor with the stock battery.

At any rate, I use that starter battery as pretty much just that, and a backup for the house bank. The house bank is 3 group 24 dual purpose AGMs. Its probably about on par with both of your group ~30 deep cycles, but they are smaller, and lighter. One fits next to the starter battery under the companionway steps in the stock "battery box" and the other two are nestled up right next to the dagger board under the forward dinette seat.

[Frank C]

Thanks ... Understand completely. The fact that most outboards are just motorcycle engines means they just don't have a big amperage demand for starting. IMO, we get trapped into the mind-set of a Starter vs. House by the boating industry, which manytimes is trying to service a big V-8 inboard, or a diesel with gonzo compression, hence massive amp-draw. The Mac simply doesn't match that industry template.

I think it's my advantage that the 26X fits both big batteries under the same galley seat. Makes this 2-way scenario easy to physically manage, visualize & remember. It also makes for very short runs of the mega-wiring.

I forgot that the M would require different battery placement, perhaps smaller batteries. If your daily consumption was amenable, sounds like you could arrange them in two similar-sized banks, each with 2 batteries .. total of 4 batts. Doesn't really matter where they physically reside.

[Scott]

I have 2 batteries.

1 a deep cycle monster marine jobby (Technical jargon) this battery runs the house

2 the original battery that came with my boat over 10 years ago. this is starter only

I have a 2 bank guest charger that is used when slipped at all times. It does the float charging thing (more tech jargon) When the motor is running the starter battery is the only on that charges from the motor.

I have a neither /nor switch or in other words none at all. I have yet to kill my starting battery since I separated the 2 circuits. When both circuits were run from 1 battery I used a pull cord the couple times I drained it.

After sitting all winter in the dry yard off the charger both batteries were reading near full charge.

[aya16]

I use the optima batteries. They are the deep cycle blue battery (also the most expensive. They make great house batteries and never have to smell fumes when being charged. Now I have only had them a year or so. but so far they charge fast and stay charged for long long time.

as house batteries go My motorhome used to have 4 batteries 3 house and 1 starting. This was charged by a 30 amp smart charger (very expensive) that I bought from Cabellas. It will charge all batteries at what ever they need and do it from completely dead to full charge in 3 hours.

But every two years the batteries had to replaced because they would not last very long. Now I use two house batteries and a starting battery for the motorhome. And bought a 1000 watt generator to give the power I need without hearing it run.

What does that have to do with the Mac??? well the optima batteries last longer and will start the motor. But as in the motorhome I do not use the house batterys for extended use at a mooring or slip. I use 110 hook ups at the slip and I will run my suz 50 four stroke for extended power use. Like dvd's or hours of lights to read by. The motor is quiet and will charge the batteries as I use the lights or what ever.

Now of course you dont want to run the engine all night, although you can because its so silent, so I make sure Im drunk and pass out long before it gets to dark...

[Harrison]

Great information guys. Thanks.

---Harrison

[50/50]

I have implemented a similiar system on my 26X.

I have a small 50amp starting battery mounted at the pedastool which is wired to an isolator switch there. this is then connected to a Voltage sensitive relay.

http://www.bepmarine.com/showproduct.cfm?productid=12

The VSR ensures the starting battery receives the charge until fully charged and then changes to the house battery.

The house battery is constantly monitered by a Nasa battery monitor.

http://www.yachtbits.com/nasa/nasa_clip ... system.php

The house battery is only 75amp capacity. I have just returned from a 300 mile 8 day cruise of the Scottish West Coast and although we used quite a lot of power (laptop charger, 300w inverter, stereo, lighting etc) the system coped amply with the usage and never need shore power.

[tangentair]

OK, I am way behind in reading - but while reading this thread two issues did stand out. For the novice who might not fully impliment all the practices

1 - mixing battery types (wet/gell/agm) in circuits that allow cross connections and charging them at the same rate or from the same source such as the engine alternator and
2 - using deep cells for rapid discharge/high current uses like starting even for short periods

And I suppose that mounting them is not so much an issue because it would be difficult to get them overheated if they are in the bilges, but extended usage in temps over 80 I have heard are a factor in the newer type batteries' lifespans.

and while I do not keep a jumper battery on board, I have wired the stationary vhf with a double throw switch and a 12 volt dry cell mounted up under the cabin roof, so if I am ever swamped and the main batteries are flooded out, I can switch over and still get off a Mayday.

[Frank C]

The general principle that I'm advocating (learned in an ASA Sailing Class) is that
Alternating Battery Management is better than Functional Battery Mgmt (Starter vs House).
(Double-posted here and in another battery thread.)

We are indoctrinated to "functional battery mgmt" by the traditions of cruising boats ... but that "cruising boat paradigm" has been notably crushed by Roger Macgregor~! Functional Battery mgmt is based upon needing a dedicated automotive battery to spin a heavy-amperage starter motor for automotive or a high-compression diesel inboard engine. By contrast, all Macs are powered with motorcycle engines, which are easily served by a "little brick" of a battery, weighing about that much too.

The logic path for Alternating Battery Management is based on several factors:

• 1. Our dedicated Starter Batteries (50 lbs. of Sears DieHard) receive way too low a duty cycle to be used effectively;
  2. Starting amps of our little motors are easily met by the House bank 'du-jour';
  3. The "Alternate" battery is always available as a backup;
  4. Managing demands across 2 alternating banks more effectively "life-cycles" both banks;
  5. Alternate banks need not have matched capacities, as long as each bank meets the daily demands.

Finally, Alternating Batteries need not necessarily be used solely in an Odd-Even scenario. That's a good way to manage batteries among a fleet that's shared by many Skippers. However, we are our own masters. It's just as fine to record which battery is used at the start of each weekend, and then use the Ship's Log to manage the swapping of duty-cycles.

[Chip Hindes]

I have been using a different methocd of alternating two identical deep cycle batteries, charged through the now relatively standard three switch system using a voltgage sensitive relay.

I switch the batteries from house to starting duty each year.

[Frank C]

That makes lots of sense too, less to remember w/only one change per year.
I guess alternating each weekend is just busy-work ... just seems Salty!

[Boblee]

I guess everybodies situation is a bit different due to the versatility of these boats. I agree with Frank and others we do not need a dedicated battery for motor starting and also agree that all batteries whatever type SHOULD be the same type but not necessarily the same size.

As to the alternating idea it probably is a good idea, if the boats and power are used during the day and charged at night or used with limited load and charged with reasonable motor use to charge them fully. Personally I think the best all round type of battery is a good quality marine battery as depending on the quality they will give a good compromise between deeper discharge and good cranking even when down in voltage.

The problem is that one manufacturers marine battery is anothers car battery. No battery, deep cycle or otherwise benefits from heavy discharge 11v would not be desirable, the modern car and 4wd cranking batteries are considered flat at 11.8v. The (some/most) calcium type batteries once below 11.2 need charging at 16.2 v to bring them back, this is not desirable if you don't have a special charger.

At present I am using the standard mac marine battery with two wet cell batteries with removable caps, definitely NOT desirable but manageable, one of the two wet cells will be replaced prior to heading off with another marine battery but kept separate when not charging. The other wet cell is portable but strapped in under the front berth and it won't be replaced until it dies.

In mine and many situations the alternate arrangment will not work as they can drop below the desirable voltage quickly thus shortening their life, besides I have other things to do without fiddling with batteries, if I could remember. I would not think of going from dark to daylight with only one 90amp hour battery as by morning it could be well below the danger point even if fully charged unless of course we were on shore power.

With some Calcium super 4wd batteries of 70amp hour rating I tested from fully charged, I could only take 42 amp hours out before the sight glass went white, from this point the alternator could not bring them back and they needed extended charging at a higher voltage to reservice them according to the MANUFACTURER, as far as I was concerned they were as useful as tits on a bull for my purposes. I think I told him what I thought after losing a fridge full of fish fillets a 1000klm's from anywhere.