Dual Battery Select Charge & Use Control Switch System Modification

[OverEasy]

Hi All!

I was asked if I could make a new topic thread on some of the modifications/ improvements we have made on Over Easy.

This is for our “DUAL BATTERY SELECT CHARGE & USE CONTROL SWITCH SYSTEM” Modification.

BACKGROUND:

Batteries are all slightly (and sometimes more than) different from each other depending upon prior usage, discharge cycles, recharge process, age, chemistry and type category. Some get used a lot just for a quick start while others are long laborious drawn out affairs that each affect a battery differently over time. Some are drawn down just a little, others a lot. Some get recharged with regular usage and others sit idle for weeks on end. Some are brand sparky new and others are examples of geriatric wonder.

Some batteries are START batteries, some are STORAGE DEEP CYCLE batteries, some are DUAL PURPOSE START/STORAGE batteries.
Some are basic lead acid types, some nickel-cadmium and then there others are ‘exotic’ Lithium-carbon-hyroxigenated-*gawdonlyknowswhatkindastuff chemistries.

Some a liquid, some are gel, some have meshes, some have plates and some I really don’t want to know constructions (‘cause I might not sleep again ).

All these examples are to explain that no two batteries are quite the same and they generally like to be charged “independently” of each other. The easiest example pair most are familiar with are START and DEEP CYCLE batteries. Most modern commercially available battery chargers worth owning have a selector switch for each of these types. (NOTE: As was explained to us the DUAL PURPOSE START/STORAGE battery is actually more like a DEEP CYCLE than a START battery and should be charged as a DEEP CYCLE.

This system is identical to a system we have utilized for over a decade and a half on a 30 foot RV trailer to replace the factory charge/use controller that repeatedly failed/replaced/failed and repeatedly ruined multiple expensive RV Deep Cycle batteries prematurely. The factory system insisted on and was only capable of charging both batteries at the same time while at the same time was only capable of drawing from both batteries at the same time whether charging or not. What this did was set up the batteries to compete with each other for charge which caused more amperage to be delivered to the more fully charged battery than it needed leading to over heating of that battery, electrolyte boil off and internal damage. In a related manner when drawing from both batteries the weaker battery ‘robbed’ charge from the stronger battery which drew down the system faster than they would have separately.

The fix to this was to use all those years as a design/development/analysis applied engineer and chuck the factory battery system (and the very nice rep), actually use what people paid me for and make a system that put us back in control of the process while not having to physically fuss with the batteries clipping/unclipping charger leads etc...

Once we implemented this we no longer had any charger failures or premature damage or wear out of our RV Deep Cycle batteries.
After the change over our battery life improved to over 6+ years (often 8 yrs).
This system allows for the charging of different battery types and constructions by being able to change the shore power charger setting to match the battery type.

Our experience was and is based upon lead acid type chemistry batteries.

CRITICAL NOTE:
I personally WOULD NEVER EVER ATTEMPT to use either the CHARGE or USE selector switch in the Both Or ALL positions when working with batteries of conventional lead acid AND exotic chemistries. Some exotic batteries have differing charge/output voltages that can cause serious problems. Some exotic batteries can/have experienced substantial exothermic and/or catastrophic failure due to internal current/voltage issues. Past experience in equipment/system design has taught me to NEVER MIX conventional lead acid batteries with any other chemistry (ESPECIALLY EXOTIC LITHIUM BASED). The potential risk of injury/damage to personnel, property or equipment just isn’t worth it after having to deal with the aftermaths of other individuals attempts.

WHAT THIS SWITCHING SYSTEM ACCOMPLISHES:
A) This system described here is a ‘clean’ means to manually address isolating an individual battery of a dual battery system for charging from a shore power charger while the other battery is available to run the ‘house’ or boat 12 volt DC systems.
B) This system also allows you to swap which battery is charging and which one is being used to run the ‘house’ or boat 12 VDC systems.
C) It also allows one to charge and or use both batteries concurrently if necessary (though my personal choice is to never be USING the battery BEING CHARGED from the shore powered charger.)
D) Allows one or the other or both batteries to be charged from the engine when it is in operation (if it has that capability through the engine start leads).

WHAT WE CHOSE TO DO:

Using a pair of standard off the shelf Perko 8501DP Marine use Dual Battery Switches and a quality Automatic current limiting charger (which means that once the battery is charged the charger converts automatically to a trickle charger to maintain the battery over protracted periods of time without damage) along with a 1/4 sheet of Lexan polycarbonate sheet we fabricated the following:


Please pardon the in process photo and blue tape labels as we haven’t yet unpacked the LABEL MAKER (such a wonderful device ).

The switch on the left (Aft) controls which battery(s) is/are getting charged from the shore powered charger.
The switch on the right (Forwardj controls which battery(s) is/are getting used by the ‘House’ or boat and engine systems.

A hand sketch of the wiring schematic is below:


We used Marine Grade Use #6 AWG ELECTRICAL CABLES THROUGH OUT this design.
All lines are makes at both ends.
There is a HARDWIRED COMMON GROUND leads to appropriately sized Marine Grade Buss Bars for both Positive and Negative functions.


BASIC SWITCH OPERATION:
Begin with everything turned off including the shore power battery charger.
A) Set the CHARGE & USE SWITCHES to the “OFF” position
B) Set the CHARGE switch to the battery to be charged
C) Turn on the shore powered battery charger which has been set to the proper battery type and chemistry.
—-> Allow the battery to come fully up to charge as indicated on the gauges of the shore powered charger.
As needed:
——-> Turn off the shore powered charger
———-> Set the shore powered charger for the proper type and chemistry of the next battery
—————-> Change the CHARGE Selector switch to the next battery and turn on shore powered charger
D) Set the USE switch to the battery NOT BEING CHARGED to enable electrical power to be distributed to the vessel.
As needed:
——> Change the USE switch select to OFF to isolate both batteries from the vessel systems.
——> When the current in use battery has been depleted change over to the alternate battery AFTER making sure that that battery is not being charged from the shore power charger.

E) IF ONE DESIRES one can still choose to charge both batteries at the same time simply by changing the CHARGE selector switch to ALL
F) IF ONE DESIRES one can still choose to draw off both batteries at the same time simply by changing the USE selector switch to ALL

G) FOR ENGINE STARTING battery selection is accomplished from the USE selector switch
Options are Battery 1/Battery 2/Both(ALL)

H) ENGINE CHARGING OF THE BATTERIES is accomplished by setting the CHARGE selector switch to OFF and setting the USE selector switch to either Battery 1/ Battery 2/Both(ALL)

BASELINE UNDERSTANDING:
As with anything that anyone does it is the full responsibility of the person doing the work and using the system to do it properly with the appropriate parts and connections taking care to ensure and check there are no miswires, mistakes or errors. That each wire is appropriately sized, terminated and insulated. All qualified technicians utilize the proper tools (proper crimpers, terminals, heat-shrink, wrenches, etc...) and circuit integrity checks BEFORE applying ANY power to ANY ELECTRICAL CIRCUIT.

SPECIAL CAUTIONARY NOTE:
ELECTRICIANS TAPE IS NEVER TO BE USED AS ELECTRICAL INSULATION WHEN THERE IS ANY RISK OF HARM TO PERSONNEL, PROPERTY OR EQUIPMENT. EVER.

This is what we chose to do, have used in the past and are comfortable with.

Hope this helps.
Best Regards from Over Easy!

[chipveres]

Second to OverEasy's don't use lead-acid and lithium batteries in parallel. The voltage and charge curves are utterly different. And the lithiums are prone to explosive disassembly. You can do this experiment if you want, but you may not live long enough to regret it.

Chip V.
s/v Sand Dollar

[Inquisitor]

Second to OverEasy's don't use lead-acid and lithium batteries in parallel. The voltage and charge curves are utterly different. And the lithiums are prone to explosive disassembly. You can do this experiment if you want, but you may not live long enough to regret it.

Chip V.
s/v Sand Dollar

You might want to read some material on the subject. Although Li-Ion can explosively disassemble if not charged and discharged correctly, LiFePO4 can not. In fact, the chemistry was popularized by an EU requirement to be able to drive a metal spike through all the plates and it do nothing dangerous. Can that be done with a lead-acid chemistry battery?

And yes, the LIFePO4 and lead-acid do have utterly different curves. And again papers on the subject (in use on boats) show a quite complimentary coexistence where each's strengths mesh with the other's weaknesses. The design is quite compelling in a purely "house" type battery system for large boats having equally large and mixed battery banks. I am still very interested in OverEasy's battery switch methodology as I'd always want to keep from discharging the lead-acid battery below being able to start the motor. However, I might want to charge the LiFePO4 battery from the alternator. His switching system would easily support that. (Caveat - There are other issues to charging LiFePO4 from an outboard alternator that must be observed).

I think I would have to disagree on charging and using the electricity at the same time. Although I would be interested in why you might considered this a problem. Lead-acid batteries have relatively poor power-out versus power-in efficiencies (80% to 90% depending on age and type of lead-acid). This gets even worse once you're in the trickle charge range. You may only be getting 50% of the power you put into the battery. If you are simultaneously using the power, that power going to your electrical load, is being pulled directly and used at 100% efficiency. Only excess is charging the battery. If you restrict to only using from "the chemistry", that 10%, 20%, 50% inefficiency is being wasted. This might not be such a concern when connected to shore power at a flat rate, but when your primarily charging is solar/wind, wasting that electricity is not very wise. IMO.

Inq

[OverEasy]

Hi All

Thank you for the comment and information.
I’m sure of all the different chemistries for sure.
That would be a whole career in itself to be sure.

My, how would you say, poor experiences were with early Lithium Ion batteries (as in automotive type) and relative rapid discharge rates from the Litium Ion battery into what was a well below 50% lead acid which generated a substantial amount of heat which caused structural damage. Fortunately there was not a larger event. There were multiple issues at play and the resolutions were involved.

Inquisitor is very correct in that LiFePO4 batteries ARE DIFFERENT and can take substantial external physical damage including penetrations without destructive shorting of the internal plates. I am the first to admit that I have a lot to learn about them and look forward to doing so.

We have to run to get our shots right now but look forward to continuing this informative discussion.

[Inquisitor]

Hi All

Thank you for the comment and information.
I’m sure of all the different chemistries for sure.
That would be a whole career in itself to be sure.

My, how would you say, poor experiences were with early Lithium Ion batteries (as in automotive type) and relative rapid discharge rates from the Litium Ion battery into what was a well below 50% lead acid which generated a substantial amount of heat which caused structural damage. Fortunately there was not a larger event. There were multiple issues at play and the resolutions were involved.

Inquisitor is very correct in that LiFePO4 batteries ARE DIFFERENT and can take substantial external physical damage including penetrations without destructive shorting of the internal plates. I am the first to admit that I have a lot to learn about them and look forward to doing so.

We have to run to get our shots right now but look forward to continuing this informative discussion.

Now that is a great point. All the forum topics, YouTube videos and papers I've read so far do caution in the initial hook up that all batteries need to be fully charged. I know a LiFePO4 battery is not for everyone, but it certainly is not a danger as the ole Lithium phone, and laptop fires might lead someone to believe. It is certainly not a safety issue of the level of gasoline versus diesel engines or propane versus alcohol based stoves... or for that matter a lead-acid battery off-gassing. Having a 3.6 kWhr battery for the less money and about 10% of the weight of a Trojan quality battery bank, I am willing to deal with the differences.

Shots Congratulations. I was able to get my first round last week. I'm sure ready for some trend toward the old normal.

[OverEasy]

Hi!

Back from our shots and everything is good!
Right now we’re at the Sands Beach in Port Royal SC enjoying the BEAUTIFUL day!

[OverEasy]

Hi All!

Regarding the aspect of choosing to not using the battery being charged...

It is based upon the aspect that house loads on a charging battery can/does change the shoreline battery charger current control circuit amusing it to potentially apply more current to the battery than it (the battery) needs in its charge cycle. Not so much of an issue with START batteries but more of an issue with DEEP CYCLE and DUAL PURPOSE batteries.

Leaving the charging battery alone decreases the time to charge, minimizes battery heating and by my years of use has dramatically increased DEEP CYCLE battery useful life. Drawing on the charged battery is also a constant flat line DC voltage without the voltage & current fluctuations from the charger.

Whereas drawing on a charging battery can introduce a pulsating DC voltage to the house use circuits as many shore power chargers utilize a single phase pulsating DC rectification. There is also the voltage variation that a shore power charger introduces to the house use circuit side that can affect items in use, sometimes with negative or undesirable consequences.

Again we are referring primarily to utilization of a AC shore power or AC generator supplied battery charger to charge one battery at a time which is how batteries tend to like to be charged.

When utilizing the outboard engine generated charging capability it is accessing the battery(s) via the USE selector switch setting. This is a practical functionality compromise given that the start circuit to the engine is also the charge circuit from the engine once it is running it still allowing the opportunity to charge one battery at a time (or both if that is needed or desired.

Functionality over the decade and a half utilizing this system on a 30 ft RV our experiences have shown us that drawing on one battery at a time while leaving the other battery alone to charge has resulted in shorter charge times, better battery utilization and substantially increases in actual useful battery longevity. This is in direct repeated contrast to having both batteries being charged concurrently, being used concurrently and being simultaneously being charged and used concurrently.

For lead acid type batteries the current cost of a new small frame DUAL PURPOSE battery is about the vicinity of $130-170 each. A similar frame size purely DEEP CYCLE is similar to or slightly more expensive. A similar purely START type battery is slightly less.

Extending the useful functional life of our batteries has functionally and practically paid off several times over when we converted over to our dual battery select charge & use control switch system.

Being able to select what type of charging process to utilize on what type of battery without having to open up the battery compartment and change charger leads around has been enormously convienent and beneficial for us.

Best Regards,
Over Easy

[Inquisitor]

Obviously you are very experienced and you oversee the batteries cycling far more than the average boater/RV'r. What do you do for the time to charge criteria? Most everyone specifies no more than 50% SOC. The 6 volt Titan deep cycle cells that seem to be the gold standard even specifies 50% on their charts to get their 1200 cycles life. I'm curious where the best battery life would come occur under low utilization:

• Charge every night even if you only got down to 80-85% SOC.
• Wait till you get to 50% SOC - But you only put one cycle on it instead of 3 cycles.

[OverEasy]

Hi Inquisitor!

What we have done is very much like what MK Batteries has recommended.
https://www.mkbattery.com/blog/how-exte ... ttery-life

Let me share their very good well written article:

HOW TO EXTEND DEEP CYCLE BATTERY LIFE
You’ve probably heard all of the perks of using a sealed deep cycle battery for your power scooter, solar array or battery backup system. One of the biggest reasons that these batteries have grown in popularity is that they require very little maintenance to have a long life. Nevertheless, even the tiniest bit of maintenance could extend your battery life significantly and save you money in the long run. Let’s look at a few ways that you can add months (and maybe even years) to the life of your battery.

FULL CYCLE CHARGING VS OPPORTUNITY CHARGING
One of the easiest ways to extend your battery’s life is simply by making sure that you are giving your battery a chance to fully charge in a complete cycle each day. This allows your battery to go through a conditioning phase which prevents sulfaction damage to the plates. Opportunity charging is when you plug your battery in sporadically throughout the day, and then unplug it as you need it, without ever completing a full cycle. This does not give your battery the time needed to condition itself properly, and will ultimately deteriorate your battery life.

UNDERSTANDING DEPTH OF DISCHARGE
Another thing you can do to protect your battery is to learn about the depth of discharge specifications of your battery. Most deep cycle batteries are built to handle a 50% depth of discharge, but some can handle up to 80% discharge. If you are always recharging your battery in a complete cycle, you could expect to get just over 220 complete cycles when you drain the battery 80% each day, whereas you would get almost 750 complete cycles if you only discharge 50%. On the other hand, you also don’t want to constantly charge your battery when it has been discharged less than 10%. Like opportunity charging mentioned above, this will prevent your battery from ever completing a full cycle, and will cause damage.

PROPER STORAGE
When not in use, your deep cycle battery should always be fully charged. These batteries are designed with longevity in mind, and they do not tend to lose a lot of charge when sitting idle. Thus, charging them fully before you place them in storage, and then checking them periodically to top them off if they discharge to 20% DoD will allow you to keep them in good shape without having to constantly keep a charger plugged in. While we’re talking about storage, temperature is another key factor. Batteries stored in freezing temperatures or extreme heat will break down faster than other batteries. It is always best to bring your deep cycle batteries inside and store them in a cool dry place to prevent damage.

SLOW CHARGING
Finally, the best way to extend your battery life is by making sure to charge your battery as slowly as possible. For instance, slow charging overnight is much kinder to your battery’s internal components than using a rapid charger for only a few hours. This is because rapid charging increases the internal temperature of the battery.

With these four quick tips, you can give your battery the lifespan it deserves. Most deep cycle batteries can last up to six years with proper care and charging (depending on the frequency of use). It’s up to you to make sure that your battery isn’t being damaged by your charging routine. To learn more, contact MK Battery today and speak with our sales team about proper charging equipment and techniques.

Using this approach we have actually exceeded 6 years (some past 8 to 9 years).

Our process is a little bit different in that we choose to charge one battery at a time and GENERALLY discharge one battery at a time. (There are the odd situations where one may have a known specific situation where one may choose to want both batteries available for concurrent use. For those specific situations we would need to have a much more pressing immediate need that we are concerned with rather than on extending our battery life cycle, but for us those situations are rare.)

The automatic control chargers that fully drop out when the battery is charged are the type we would use and recommend. Some varieties (fewer today than in the past) had a constant 2 amp trickle charge being supplied to the battery whether it needed it or not.... WHY?...

ASIDE: There actually seems there may have been a semi rational reason... it had to do with the old philosophy of keeping the battery topped up to its absolute maximum possible. This came from the older START battery construction/chemistry technology perspective where it was expected that batteries are consumables and should only last maybe 12 or 24 months before being replaced. In fact, many older plug-in chargers didn’t even have a trickle function...they stayed on at max charge current rate and happily and quite literally boiled away a battery’s electrolyte until someone remembered to physically turn it off.

Unfortunately there are still some of those plug-in chargers on the market and legacy designs that still have no trickle charge or have a 2 amp constant trickle charge aspect.

Fortunately there are now a few more grown-ups in the room who have designed chargers that drop out completely and then monitors the holding voltage level of the battery and wait until it declines sufficiently until it makes sense to add charge. The monitoring is done digitally and does not deplete the battery in doing so.

Hope this helps.
Best Regards, Over Easy

[Inquisitor]

I think most of the people on the forum are in the lead-acid group and this is definitely some very good information for them and that was a great reference and read. Thanks.

[Starscream]

I am sooo impressed with the level of expertise and knowledge, and the willingness to share.

My personal preference for batteries is set-it-and-forget-it. I don't want to take batteries out for the winter, I don't want to heat them, I don't want to figure out which one I'm charging, I don't want to think about which battery I have to start the motor with etc. On a typical 5-day trip, I turn the battery selector to 1 and leave it there for the duration. The next time out I'll try to remember to use battery 2.

I use two 55Ah(rated) AGM dual-purpose, group 34, Optima blue-top batteries. A single-bank charger is connected to one battery, and a 100W solar array is connected to the other, and I use an ACR to share the charge. That means that both batteries are automatically charging when the motor is running, or when the sun is shining, or when I have shore power, without any input from me and that's the way I like it, for now. Our house loads have never been able to run a single battery down to the point that it can't start the motor. If I had refrigeration, the system would be insufficient though. The batteries are about 5 years old now, but the system is still going strong and meeting our needs...knock on wood!

Total weight is 89 lbs of batteries, and along with 150 lbs of fresh water on the port side they create a noticeable list. So I am totally ready to put down some boat-cash for a super-light LiFePo4 battery bank that can: crank my engine, be stored in the cold, fit 2 in the battery compartment, and be combination-charged from any source with an ACR. I'm sure the technology will get there soon, hopefully before I have to replace the Optimas.

[Inquisitor]

... So I am totally ready to put down some boat-cash for a super-light LiFePo4 battery bank that can: crank my engine, be stored in the cold, fit 2 in the battery compartment, and be combination-charged from any source with an ACR. I'm sure the technology will get there soon, hopefully before I have to replace the Optimas.

Even though I'm a proponent of the LiFePO4 batteries, they're not there yet for a fire and forget system. As you pointed out, they would require heating to handle your locale. Some pre-built ones (very expensive) already have that ability and they are self maintaining. And a DIY'r could add that functionality fairly inexpensively. I haven't studied it as I just don't need it down here. The second issue, you pointed out was cranking the engine. That one is a little more difficult and I haven't seen anything yet that claims to have the cold cranking amps of even the most basic starter battery. The LiFePO4 cells can easily handle it. My battery cells are rated at 540 amps continuous and far higher for short durations. The problem is the electronic BMS that handles all the other duties is not rated over 120 amps. This might be enough to start a typical Mac outboard... but it doesn't leave near the wiggle room that even a deep-cycle battery can provide.

Once I get my system installed, I'll see if I can start my engine with it. I know in an emergency, I'd just by-pass the BMS, but that is because in a DIY solution, I have access to those inner connections. Even if a solution existed, I think I'd still keep the segregated... lead-acid to start the engine and charged by the engine. And separately a house-only battery charged by solar/wind/shore power or with the engine's alternator with safeguards for the motor.

[C Buchs]

I'm installing a 2015 etec 90hp and was just researching its cold-cranking amps (CCA) requirements. I was thinking that instead of spending money on 20' of new 1 AWG battery cables ($160), I could install a smaller lead-acid battery somewhere in the cockpit and prepare for a LiFePO4 house system in the future. Unfortunately, my outboard manual says that 600 CCA is required and I need a full-sized lead-acid battery.

Jeff

[Sheppie62]

I would like to copy your beautiful electrical system best I can. Where is this hatch in the picture located? My shore power inlet is on left side near the switch panels, and batteries are left of gallery. I am considering putting 2 large AGM batteries toward front to get some weight forward, offset heavier motor.

[Sheppie62]

I think I figured it out, must be side of galley.