Battery Replacement/Rewire

[Dale Tanski]

Yes...

For the most part the article was nothing more than a well written marketing piece directing the reader to the Smart Gauge.  It did contain factual information, much of which were stand alone facts unrelated to the stated conclusion that the Smart Gauge was the end all answer. 

Such as... It is well accepted that the sun is a truly 93 million miles away.  Experts agree that the surface temperature of the sun is 5000 deg C. Given these two facts, the only intelligent conclusion is you should be using the ACME air conditioner which offers superior comfort.

The lengthy sales pitch lists every conceivable short fall or negative possibility of every other system out there, of which most have been in reliable service for 30 years, while stating only the positive benefits of its own configuration.  The "article" focuses completely on why the smart gauge is better and Peukert conclusions are superior giving specific examples that don't necessarily state such.

Just because 100% of all people drink water each day and there 150,000 people that die each day, does not mean drinking water will kill you.

The Smart Gauge and Perkert may indeed be correct, but ignoring the issues associated with connecting large banks of batteries in parallel situations and ignoring how batteries fail is short sighted.

Dale

[Della and Dave]

Hi:  I did read it, but I'll let Pete and Dale give you advice because they know more than I do. I did come across a discussion and some testing on the compass marine site that might be of interest.  http://www.pbase.com/mainecruising/smart_gauge. He also has some other info on electrical stuff. 

[PeteW]

I don't know if I'd give Peukert a Noble prize for his work. But nice job curve fitting the charge/discharge inefficiency of a storage devices to that of a simple first order non-linearity, if indeed that's all that is actually going on in the physics of battery chemistry. As an Engineer I don't think I'd be so vain as to name the equation  after myself. Looks a lot like Euler's equation and we call that plagiarism.  

What the basic equation says is the efficiency of a battery can be gauged by the exponent K. In a perfect lossless battery K=1. In an AGM battery K=1.05. In a new flooded battery K is about 1.1. In an older sulphated flooded battery K gets up to 1.5 or more.

So in a conventional flooded battery, as K increases over time more energy is lost during discharge and the battery discharges faster. And to make matters worse, as the rate of discharge increases (current draw) so does the inefficiency. So even more energy is lost as heat. The battery goes non-linear or what is called a snowball effect. (exponential increase in inefficiency with current)

In regards to running banks in parallel or not it can make an insignificant difference in total capacity (AH) or it can make a huge difference depending upon the value of the exponent K. In an AGM battery where K=1.05. Discharging 2 banks connected in parallel gives you a 5% improvement in capacity. You will be able to go 45 minutes longer in 16 hours. Not much.

But if you have flooded batteries that are more than 1 year old, K can get up to 1.5 In this case, you can expect to get 40%less capacity by not running the batteries in parallel. Notice that I did not say 40% more capacity. There is nothing to be gained, your losses which are already high are simply lowered by running in parallel.

You can calculate all this for yourselves as I did using this online calculator.

http://www.batterystuff.com/kb/tools/calculator-for-load-specific-run-time.html

By entering the 20 and 100 hour AH rating from the manufacture it will calculate Peukerts value for K. You can also enter empirical values that you get from your own batteries. Then based on load it calculates AH capacity and run time.

Using this calculator, Two 100 AH AGMs running at 10 amps (5 A each) the total capacity is 210 AH. Individually there capacity would only be 100 AH each (200 AH total or 5% less)

Running the same simulation on two degraded 100 AH capacity flooded batteries (k=1.5) in parallel, my total combined capacity was only 117 AH (way down from the 210 AH out of the same sized AGMs) Individually it was a pitiful 41 AH (82 AH) combined by not running in parallel. Nothing to gain but plenty to loose. A wopping 143% loss in capacity from good batteries.

In summary, If your batteries are good (AGMs preferably) discharging in parallel makes little difference in capacity. If your batteries are old, running them in parallel will buy you some time before they go completely dead.

If I could buy into the theory, it says on good battery banks  where(k=1.05) you save 5% capacity each time you double the number of banks in parallel or each time you half the current. So 2 banks saves 5%, 4 banks save 10%, 8 banks in parallel saves 15%. A pretty silly  and expensive diminishing return.

My take away from this is, that there is a charge discharge non-linearity in batteries and one can benefit in various degrees by switching them in parallel during use (not during storage) and mostly that AGM batteries are superior to flooded . AGMs are 80-90% efficient in charge and discharge. Flooded only 40-60%. AGM will self discharge at 1-3%/mo, whereas flooded batteries self discharge at 20-40%/mo. AGM can be brought back from stone dead , flooded will be permanently degraded in a single deep discharge (K will be much greater than 1).


Good thread, I learned a lot. Thanks to all. Pete

[P69]

I finally finished replacing the batteries, thanks to all on this group who offered their advice.
I ended up with the following system using four 6 volt golf cart batteries (US Battery US2200XC for $100 from local golf cart modification shop). The start battery is an existing 2 year old generic group 27 wet cell, ~800 CCA.

Key points:

• All charging sources go to the house bus bar
• If start battery dies, I put 1,2,both switch on both and on/off to off for starting the engine/generator
• If house battery dies, I move 1,2,both to 2 and leave on/off at on to use start battery for house, sparingly
• All house batteries are in same spot, bottom fwd of port cockpit locker

Thanks again. Now let's see what else breaks!!

[Jim S]

I like your system.  It places a lot of amps in the house bank and reserves a separate, appropriate, battery for starting purposes.  My system is identical...great minds, etc.

Jim

[barrylab]

I've been watching this thread trying to bite my tongue and not comment, but everything I know and think I know screams for me to say something.
I design circuits to test circuits that charge and monitor batteries of all kinds. I do this for a living, so I know that everyone appears to be ignoring a vital parameter called self discharge.

Peukert did his tests when batteries and specifically lead-acid batteries were just a few decades old.
The real control factor in Peukert's formula is the series resistance caused the physics of lead, and the heat developed by drawing current through that resistance. Self discharge is partially the resistance of the electrolyte. Lead's bulk resistivity goes up as temp does, the electrolyte's bulk resistivity goes down as temp goes up. As you draw more current from the battery, more power is wasted in the series resistance of the lead, heating up the electrolyte, causing more self discharge.
One big reason it's not a good idea to permanently connect two banks in parallel is you are doubling the self discharge rate and wasting energy heating up the batteries: Both battery banks are effectively discharging through half the leakage resistance (they are now in parallel too).
It is done in the solar industry for the same reason it's done in the UPS industry. The batteries spend far more time charging than discharging, so self discharge isn't a problem.

In a new lead-acid cell self discharge is about 5% per month at room temperature. This rate goes up to about 20% at 40 degrees Celsius, and both the room temp discharge rate and the effect of temp increase with age until it becomes so excessive you believe the battery won't hold a charge, and replace it.

In older technology flooded cell lead-acids, the lead plates flake, fall in to the wells between plates, and reduce the distance through the electrolyte reducing resistance and increasing self discharge. In AGM and Gel cells, dendrites form with the same effect. As batteries age, series resistance and internal leakage go up. Accelerating this phenomenon is what you avoid by not paralleling your banks needlessly.

There, I feel better now.

[slokat]

Barry, does the fact that my batteries are topped up by the solar panels almost daily mitigate any of the self discharging effects?

And, what do you think about my shore charger mode that is is supposed to vibrate the scale off the lead (or whatever it actually does)?

Don't have the manual with me but there is a set interval that they recommend using that mode for one charge cycle, then it reverts to it's normal setting.

I too use (4) 6v golf cart batteries, with a separate dedicated starter battery.

[barrylab]

The solar cells do reduce the effects of self discharge in newer batteries, but there is another issue I didn't go in to. The internal resistance from + to - goes down with both age and heat as I mentioned. Heat causes aging, and with one battery in worse condition than the other, the aging of the better battery is accelerated. Where that battery would have a negligible amount of self heating due to leakage currents, it is now feeding the weaker battery, developing more heat in the series resistance of both. Many high end UPS supplies have a load balancing circuit to keep this from happening. Some even sacrifice a few hundred millivolts to an isolator that keeps them from exchanging current. Newer isolator technology uses MOSFET transistors and a control circuit that has far less drop, so it will probably become a standard, but that industry tends to move slowly.
As for the shore charger, I don't think it vibrates the scale off the plates, that would only accelerate the process. It probably de-sulfates the battery. Lead-acid battery charges by creating ions within the sulfuric acid electrolyte. This causes sulfur ions to slowly become trapped in the surface of the lead plate, reducing the effective surface area, increasing the series resistance. De-sulfating actually increases battery life by reducing that series resistance I mentioned.

I think we'll soon be seeing Super/Ultra capacitor banks replacing some applications (Super Capacitor is trademarked, so Ultra is the generic term). I'm considering a bank for a starting battery. They are used in the railroad industry (charged by big diesel gensets) and some tractor-trailer rigs have them to be switched in parallel to a small starting battery before starting.
The benefit is that although they have much more ESR (effective series resistance) than a smaller capacitor, they have much less than a battery. Maxwell have an Ultra-capacitor block that fits in about a quarter the standard Series 31 battery space, has 2.1m Ohms of ESR and is 500 Farads with a 16V rating. 500 Farads That means if you charge it up to 14.5V (typical lead acid full charge) you can pull 160 Amps for about 3 seconds before it drops to 13.5V, and it can produce 2000A for a full second without damage. Their self discharge is around 170mA continuous not dependent on charge state. That sounds like a better alternative to a second battery in parallel, although at about $600.00 they are a little cost prohibitive today. 
By the way, they won't be completely replacing lead-acid, as this is only a 2 Amp-Hour solution (500 Farads X 14.5V/ 3600 Seconds), but in parallel with a lead-acid it takes all the surge currents that can cause heating.

[PeteW]

Barrylab,

I kind of feel like you and I and Dale are arguing that smoking is bad for you to the tobacco industry. But I think you very effectively explain:

1. Why connecting batteries in parallel is simply bad for the life of your batteries.  You nailed this discussion and I recommend that we all  need to read it a few times for full comprehension.

2. How technology has moved us away from this (above) practice with very low on resistance high current power MOSFET smart battery isolators.

3. And that technology is addressing the need for better electrical storage cells beyond the lead-acid types. Super Capacitors and might I say Lithium-ion  have superb power densities and  charge-discharge performance approaching that of the super cap.

Thanks for chiming in.    Pete

[barrylab]

Thanks for the kind words Pete, I wasn't sure if I came off as arrogant. When I don't know who I'm explaining something to, I have trouble with how deep to dive to explain something. Being an engineer by training and profession I have a sometimes violent reaction to marketing/sales belief systems that seem unsupported by physics, and need to scale it back a little. My friends know this button, and love to push it.

As for the lithium based batteries, they do have some very impressive characteristics, but still scare me some. I have a friend who is a dive instructor using them in a dive light. A few years ago he had a leak, and molten lithium (still burning) exited the bottom of his dive light at 70 feet. Hydrogen gas from Lead-Acid is dangerous, but molten lithium knows no bounds, and would go right through fiberglass. The charging circuits are pretty cool with all the safety features (current control & temp sensors) though, and some lithium technologies are 3 Volt cells instead of 1.4-1.6 like most other battery technologies. Fewer cells means less complexity and lower series resistance. I'm very risk averse (again the engineer thing), but I can see how they might have a future in the marine industry. (My friend still uses them in his new dive light!)
If you change the electrolyte, you have a super capacitor. Not a s much storage, 2.5V cells, but much safer aand still very low series resistance.

[PeteW]

Here's a schematic that shows how I've wired my battery banks. I think this scheme incorporates all of the feedback presented by everyone in this thread. No battery banks are permanently connected in parallel, while all batteries receive charge and float via the smart battery isolator. Any or all banks can be selected to run the house or if need be the start bank can be paralleled up with the house to start the engine the engine.



Not shown is the external smart regulator that controls the alternator field current. There is a sense wire from that device that goes to the pro-split-r. I also have a 3 way voltmeter select to monitor each bank.

I will next experiment with moving the Zantrex charge cable over to B+ input to the smart isolator. I will have to Diode Or the +12V to power the isolator from either the alternator or charger. I will also need to install a SPDT switch on this charge cable so I can select "Invert" and draw current from the House when in that mode or "Charge" when connected to shore power. In "Charge "mode all three batteries will receive charge and float current regardless of which battery bank(s) is supplying house current. Exactly what I think you need when the boat is unattended. Typically I will only leave one battery bank selected to run the bilge pump.

When I add a Solar Switching Regulator/charger I will also run that through the smart isolator in a similar manner as the Zantrex Charger/Inverter.

Pete

[Della and Dave]

I could use some advice on charging systems.  One of this springs first projects is putting in a new 200AH AGM slimline battery from Mastervolt. We have our system split similar to Pete's with two golf cart batteries as our house bank, that are dead/dying and they are the ones that are getting replaced by the single 200 AH AGM.  (Got a screaming deal on one that was slightly damaged in shipping). It also may let us clean up the port locker some and get better engine access to change belts etc.

Unfortunately, our charger is probably original equipment, so wasn't designed with AGM batteries in mind and of course doesn't have a float feature.  It's probably part of why the existing bank is almost dead.  It also hums loud and doesn't have any state of charge info. 

I'm considering the Mastervolt power charger (http://www.westmarine.com/buy/mastervolt--power-charger-battery-chargers--P010976165)  in a 40 amp size, but there are obviously other options out there.  Three  questions:

1). If I set the charger for AGM will it overcharge our 12v flooded lead acid start battery?  ( the battery type setting on the Mastervolt is a dip switch for all three banks, same battery type).

2) Is 40 amp overkill, or is 20 enough?  We are in sort of binge sailing mode, curse of having a regular job, s o we plan on a week put away from the dock at an time with long periods of inactivity between. 
3) Is that a good charger, or are there better ones out there in the same basic price range? I mainly thought of it because it's the same brand as the battery, and they are available, but I don't have any other reason to choose this one over any other.   

[Dale Tanski]

I do not know of a battery charger that allows the user to select the type of battery for individual battery banks.  What this means is if you select the traditional wet lead acid battery and it was a 3 bank charger all three outputs would have the charge profile and voltage output curve.  In your case with your new AGM and your non AGM battery, one will receive the correct charge characteristics and the other will not.  Charles Industries at one time did make such an animal but I called them and they no longer produce that unit.

20 vrs 40 amps is a question of draw.  Because you state you are away from the dock for a week at a time, and then stay tied and on shore power for a few weeks, a small 10 or so amp would be just fine.  You have hundreds of hours to recharge before you shove off again.  Large amperage chargers are desirable when you sail all day and half the night using your precious power, tie up and plug in until morning and head out with the next tide.  Here you need to top off as fast as you can because your charging time is limited. 

As far as manufactures go there are many excellent choices out there.  Mastervolt is typically only known through West Marine. They are not a private label but damn near. 

I would like to suggest the following...

Purchase a quality charger that will satisfy the requirements of your new house AGM battery and dedicate that charger for that battery. Leave your old buzz box for your start battery.  Typically the start battery never gets that depleted as after the engine starts the alternator recharges the start battery on its own. 

When your start battery dies, replace that with an AGM and then tie both to the new charger and heave ho your old buzz box.

Have you considered an inverter/charger?  An inverter takes your ships 12 volt DC power and converts it to 120 volt AC power just like you have at home.  This means that you can operate a coffee pot, microwave or even plug in power tools while away from the dock.  Our favorite thing is making microwave popcorn while out sailing and watching the other boats reaction when they get a sniff. 

An inverter/charger goes the other way so to speak when you plug into shore power and the inverter then recharges the batteries power that it used.  You can purchase a nice Xantrex Freedom HF inverter/charger that will make 1000 watts at 120 VAC for $416 and a 1800 watt unit for $550.  They both feature three stage charging curves and charge at a rate of 20 & 40 amps accordingly.  These chargers are only single bank but you could add a cheap battery isolator and charge both banks at the same time. 

E-Mail me or call me with any questions or needed clarifications.  Here is the link to the Xantrex - http://www.xantrex.com/power-products/inverter-chargers/freedom-hf.aspx

Dale Tanski

[PeteW]

My boat came with an older model of Xantrex Freedom Inverter Charger. Its a standard old style 60Hz transformer rectifier design, meaning its heavy, has laminations that make a humming noise and is bulletproof compared to the modern designs  rely on high frequency AC line switchers and smaller lighter ferrite core transformers.

The other features I like is the built-in inverter and transfer switch. I recommend getting the remote front panel and installing that in the cabin. I relocated the actual unit to the starboard sail locker behind the water heater so I could not hear it humming. From the remote panel you can select invert to switch your AC outlets over to pure sine wave 60 Hz. Press invert again and they switch back to shore power. I wired all the circuits with the exception of the water heater to the AC output side of the Xantrex. The water heater remained on the AC input side. Very simple to wire up You will need a breaker for the AC output in addition the shore power AC input breaker.

If you scroll up to the 3 bank battery schematic you will see that I can select all or 1 or 2 banks for charging with the SPST bank switches. When I'm not at the boat I leave only one bank on. As far as mixed chemistry goes, I don't advise it. My start battery is AGM like the house batteries and my external smart regulator on the alternator is also set for AGM.

Pete

[Dale Tanski]

I installed a Xantrex Freedom Inverter/Charger when I got the boat.  It is a 2000 watt unit that runs our microwave and my wife's coffee maker nicely.  It weighs about 50 pounds.  In the charge mode it puts out 100 amps and has the selectors for wet/gel/AGM batteries.  I installed the basic remote which give you a nice insight into the battery condition, allows you control over the inverter function and you can limit your shore power amp draw.  I also installed a battery temperature sensor which throttles back the charge circuit if the battery temperature becomes too elevated.  One of the worst things you can do is over temp your batteries while charging.

It is indeed a workhorse.  Mine does not hum at all.  I also installed it where the factory hot water heater was located in the starboard locker.  The only noise it makes is when it is charging hard and the cooling fan runs.  I wired mine in to cover all of the AC circuits which includes the water heater.  I have on occasion, while motoring, run the HW heater which has a 1500 watt element.  My HW heater does not currently have the engine heat hooked up.  We have on occasion run a household box fan sitting in the companion way to ventilate the boat on a hot night while at anchor, or not on the shore power plug.  It has run the fan all night with minimal battery loss.

The auto shore power transfer switch works perfectly however there is a several second delay which is no big deal except the microwave clock is seldom correct.  I do not leave the inverter in the on mode when I leave the boat because if the shore power were to die, the inverter uses a small amount of battery power internally even in the idle mode. 

An inverter is like refrigeration, once you have that little item you don't want to live without one.  All of my batteries are AGM but I can understand due to the high cost, changing one bank over at a time. 

Dale