Replacing Flooded Battery With AGM

Capt J, you raise some very valuable and logical issues with my approach. I hope you will find my answers equally as logical for my particular needs. I will take each observation one at a time. Thanks for helping.

"then why not use the same battery type for both the house and starting?"
I must admit, I am still struggling with this one. The primary reason is cost. The Deka SM8A8DM AGM battery is $488 while the Deka (NAPA 7271) Wet battery is $183. The second reason is functionality. The Wet is better at cranking and the AGM is better at cycling. If I were going to use only one battery type, I would have to go to all AGMs, as the Wet will fail in a short time period if cycled. I already have both battery chargers. The ProMariner ProTech-4 (the one that came on the boat) does not have a separate charging cycle for AGMs, so if I used it, I would be mixing charging profiles. If I don't use it I am losing 50 AMPs of charging power. The new smart ProMariner ProNautic has 2 AGM charging profiles to choose from.

If charged & maintained properly, the life expectancies of 2 8D AGM batteries and 2 HD Wet/Flooded batteries are close. The 2 AGMs are $600 more. . . . . I am still struggling with this one.

"or mount another alternator on one engine that only charges the house?"
That is a good suggestion and I will think more about it in detail. I had initially run from the amount of work involved in setting up the mounting hardware and pulley configuration to run a second alternator. I have built a few cars in my lifetime (www.BullockCars.com), so I will rethink it again.

"or just let the house batteries charge from the generator and have a battery switch where you can combine both one engine and the house in an emergency situation........"
This is my current plan, now that I have discovered that my Hitachi alternators will not work with a battery isolator. I have a Kohler 8-32EOZD generator that provides AC power for the battery chargers. I think the switched solenoid, to combine the crank and house batteries makes since.

"why not leave the generator running while fishing?"
When I fish overnight, I have not turned it off, nor will I. When I fish for an afternoon and anchor up, it is nice to not smell the diesel and to be able to hear the ocean sounds. On one of these afternoon fishing excursions, a dead cranking battery is what led me to discover how the 36 Luhrs' batteries are wired. My redesign is to allow me to fish and still be able to crank and come home on time.

I would love to read more of your thoughts and ideas. Thank you!

Charlie J

Fascinating read! Thanks for taking the time.

The location currently planned for my 2 8D House batteries is under a port bench seat on the bridge. Your # 9 & 10 points above, caused me to think about using a voltage sensitive relay to power a muffin fan to ventillate the contained space under the cushion. It would only work when the batteries were being charged and should dissapate the heat. So, thanks for that!
Carl

Thanks for all of your inputs thus far. I have reached some preliminary direction with the charging system, but I need more help.

I plan on connecting the port alternator directly to the port cranking battery and using a Voltage Sensitive Relay to connect it with the starboard cranking battery. These Yanmar diesels are electronically controlled and I was told today by the factory that they use between 25-30 amps to run. Now that I have had time to study a lot of variables, I can see some major disadvantages to running the port alternator through a battery isolator. What are your opinions?

I am still up in the air about how to connect the starboard alternator. I do have a large load draw on the house/electronic battery bank and a 2 hour run to the fishing grounds. I sure would not want to start with drained batteries. Connecting the port alternator directly to the house/electronics battery bank will replace the amps being used, but I am not sure if the charging rate will be too high for the AGMs. What do you think about sending that charge through one half of a high output battery isolator and dead ending the other half? Would the diode reduce amperage transferred? I know it will charge at, let's say a .7 volts lower rate, but will the amperage be less? I am attaching my alternator specifications page for the electronics experts out there to analyze.

My backup for the alternators is the on board Kohler 8-32EOZD generator. The generator will power a ProMariner proTech-4 1250 battery charger (50 amp) for the 2 8D wet cranking batteries and a ProMariner ProNautic 1260 C3 (60 amp) battery charger for the 2 8D AGM house/electronics batteries. I do run my generator when I am running the main engines.

Need help with this charging phase. Help by getting all of the different options out there, along with the Pros & Cons.
Thanks,
Carl

I am almost to that conclusion too, just need to understand the charge voltage needs of an AGM better. My ProNautic battery charger manual indicates that it charges an AGM to 14.3 volts during the absorption phase, while charging a Flooded to 14.8 volts. Since the diode of the isolator reduces the charging voltage by .7 volts, wouldn't that more close approximate the requirements of the AGM battery type? My alternator's regulated voltage is 14.5 volts and its output current for 13.5 volts is 75 amps (from the previously posted schematic).

This is the remaining part of the charging algorithm that is not clear to me. If the 14.5 volts is reduced to 13.8 volts through the diode, would it provide the stated 75 amps reflected in the schematic, or would the diode reduce the amperage too?

My only fear is that my alternators will charge the AGMs to a voltage that is higher than recommended and it appears from my battery charging manual that the AGM voltage is .5 volts lower than the Flooded. Since my Hitachi alternators were setup from Yanmar to charge Flooded batteries, wouldn't it be better to reduce the regulated rate by .5 volt? Since I can't very easily do this because my regulators are internally regulated, would the diode do this? I would appreciate any and all help with confusion.

You may be right, but like you said, we probably won't know until we do a trial and error. I did ask that question of Ian, a technician from ProMarina, and here is a copy of his email.
From: xxxxxxxxxxx.com
To: carl@xxxxxxxx.com
Sent: 12/15/2009 9:26:39 A.M. Eastern Standard Time
Subj: RE: Professional Mariner


Hi Carl
If the charger and alt are running at the same time.
The alt will over power the charger.
So the charger powers back.
Because the alt has a higher amperage output.
Give me a call will talk shop.
My direct line is 603-xxx-xxxx.
Ian

I never thought about that. Henning, that is very creative! Thank you.

Do you know what the approximate losses would be going through that process?

Thanks,

Carl

This information is for Deka AGM batteries and came from their web site.

DEKA AGM Battery Charge Voltage​

Temp F --- Optimum Charge --- Maximum Charge
> 120 ----------- 13.6 ----------------- 13.9
110-120 --------- 13.8 ----------------- 14.1
100-110 --------- 13.9 ----------------- 14.2
90-100 ---------- 14.0 ----------------- 14.3
80-90 ------------14.1 ----------------- 14.4
70-80 ----------- 14.3 ----------------- 14.6
60-70 ----------- 14.45 ---------------- 14.75
50-60 ----------- 14.6 ----------------- 14.9
40-50 ----------- 14.8 ----------------- 15.1
<50 ------------- 15.1 ----------------- 15.4

Details
How critical is recharge voltage?
Why are all VRLA batteries so charge
sensitive?
All lead-acid batteries give off hydrogen from the negative plate
and oxygen from the positive plate during charging.
VRLA batteries have pressure-sensitive valves. Without the ability
to retain pressure within the cells, hydrogen and oxygen would be
lost to the atmosphere, eventually drying out the electrolyte and
separators.
Voltage is electrical pressure. Charge (ampere-hours) is a quantity
of electricity. Current (amperes) is electrical flow (charging speed).
A battery can only store a certain quantity of electricity. The closer
it gets to being fully charged, the slower it must be charged.
Temperature also affects charging.
If the right pressure (voltage) is used for the temperature, a battery
will accept charge at its ideal rate. If too much pressure is used,
charge will be forced through the battery faster than it can be
stored. Reactions other than the charging reaction occur to
transport this current through the battery—mainly gassing.
Hydrogen and oxygen are given off faster than the recombination
reaction. This raises the pressure until the pressure relief valve
opens. The gas lost cannot be replaced. Any VRLA battery will dry
out and fail prematurely if it experiences excessive overcharge.
Note: It is the pressure (voltage) that initiates this problem—
a battery can be “over-charged” (damaged by too much voltage)
even though it is not fully “charged.”
This is why charging voltage must be carefully regulated and
temperature compensated to the values on the chart above.

Battery Isolators May Be The Answer For Charging AGMs With Alternators

I have pasted below an email with answers to some battery isolator questions that should be of interest to all of us boaters with alternator charging questions. These answers are very revealing about the unique qualities of battery isolators and how they may be the optimum solution to charging AGM type batteries with alternators (when external regulators are not an option). This email came from an engineer that was involved with the development of fiber optics in the telecommunications industry. I have feedback from equally qualified sources (just received in the last 2 days) and all have provided similar responses. This email was graciously written for ease of understanding, so I have posted it as it was written.


"First the long answer. Then below that the short answer to Carl Bullock's questions with my comments added in Red.
--------------------
These are silicon diodes being discussed if they are said to have 0.7 volts drop. Current flows thru them in only one direction. They will have a voltage drop across them of a nominal ).7 volts dc. That drop will vary slightly from almost no current up to the maximum rating of the diode. The actual drop will depend a little bit on the amount of current and on the temperature, But in general it will be less than plus or minus ).05 volt, i.e. 0.65 to 0.75 over the extreme worst cases.


So yes, putting a diode between the charger and the battery will reduce the maximum voltage that the battery gets charged up to with that particular charger. However when ever the battery voltage is less than that maximum, the battery will soak up the same amount of charge current as the charger would normally supply.


Chargers are set up to work in the current limited mode when the battery voltage is low. The current limit is set small for trickle chargers. So the charger can be smaller and cheaper. Also it will not cause much temperature rise of the battery and therefore not boil out any water. High power chargers will have the maximum charging current set to a limit that does not overheat/overload the charger. That will charge the battery faster but also cause the battery to get hotter.


During the charge cycle as the battery voltage builds up, the charge current will eventually drop off as the battery approaches its fully charged voltage level. The final charged voltage will be 0.7 volts less if a diode it used.


My guess is that if the charger voltage was correct in the first place for the particular battery type, then yes putting a diode in the circuit will cause charging to stop a little sooner. However in terms of the total amount of charge put into the battery, that it will probably be only a few percent less than if no diode was used. The difference is probably no greater than the amount of charge a battery can hold when it is charged on a summer day versus a winter day. So the whole argument is probably about a small percentage of charge difference and also about only a small difference in time to do a full charge."
--------------------------------------


On Jan 11, 2010, at 6:55 AM, xxxxxxx@xxx.com wrote:


"Questions from Carl Bullock:
A battery isolator reduces the charging voltage by .7 volts and because of this, some say that it undercharges batteries. I am thinking about purchasing AGM batteries for my boat, that will be damaged if charged at too high of voltage. The battery manufacturer is suggesting that the maximum AGM charge voltage should be .5 volts lower than for their Flooded (Wet) batteries.

I immediately thought that a battery isolator would be the solution, since my alternator is internally regulated and not easily changed. Some on those posting on the boat forums came back and said that isolators undercharge batteries. I would agree, if one was charging Wet batteries.

This has led me to try and understand how current is passed though the heavy duty split charge diode. From the literature that I have read, it sounds that once the "electrons and holes are pushed towards the junction, the distance between them decreases. This lowers the barrier in potential. With increasing forward-bias voltage, the depletion zone eventually becomes thin enough that the zone's electric field can't counteract charge carrier motion across the p–n junction, consequently reducing electrical resistance".

From this, I am getting the impression that the diode junction results in a .7 volt lower passing voltage, but the current flow will be barely change. CORRECT


So my question is; Will my alternator transfer close to the same 75 amps (maximum alternator output, assuming a drained batter) going through the battery isolator at a reduced charging voltage of 13.8 volts as it does going directly to the battery, without using an isolator and charging at a rate of 14.5 volts? YES


In other words, does a battery isolator reduce the amperage in the same way that it reduces the charging voltage rate by .7 volts? NO

I am trying to compensate for the .5 volt lower charging needs of the AGM battery type by using a battery isolator. I don't want to over heat the batteries during the charging process but I want to charge them as fast as practical. I will be able to finish off any incomplete charges with an AGM specific on board AC battery charger after the main engine's alternators have been shut down. The small amount of additional charge obtained may not be worth the effort.

Thanks in advance for your help,

Carl Bullock"

I am creating a stand alone House/Electronics battery bank. I am thinking about using a 150 Amp Blue Sea 185-Series circuit breaker for my house/electronics battery bank cable thermal protection. From what I have read (Interrupt Rating of 3,000 Amperes), I am also thinking that this circuit breaker will meet the American Boat and Yacht Council (ABYC) requirements for battery switches. If this is the case, I can eliminate the purchase/installation of an additional On/OFF battery switch for this bank.

Would like to hear others' opinions on this.



http://bluesea.com/category/3/10/pro...ne/overview/13

185-Series Thermal Circuit Breaker Panel Mount
Product Overview Detailed Specifications
•Ignition protected - Safe for installation aboard gasoline powered boats
•Meets SAE J1171 external ignition protection requirements
•Weather Resistant
•Combines switching and circuit breaker function into one unit
•"Trip Free" - cannot be held closed after trip
SpecificationsInterrupt Rating 3,000 Amperes
Maximum Voltage Rating 42 Volts DC
Operating Temperature Range -25°C to +82°C
Circuit Breaker Type Thermally responsive bi-metal blade
Circuit Breaker Class Type III - Switchable/Manual Reset - Trip Free
Terminal Stud Size 1/4"-28
Terminal Stud Torque 50 in-lb
Mounting Holes Accept 1/4" (M6) Screw
Weight Lb (Kg) 0.25 (0.11)
Case Material Phenolic

Charlie, thanks for the reply and helpful information.

My battery bank is comprised of 2 8D Deka AGM batteries with 1450 CCA each, making a total of 2900 CCA. The Table IVA in E-11 reflects a need for 5,000 AMPs. I assume that table is referring to Ampere Interrupt Capacity.

Since the Blue Sea 185-Series thermal circuit breaker only has an Interrupt Rating of 3,000 Amperes, It will not work. It appears that I will need to use a fuse like the Blue Sea ANL series which has 6,000 Ampere Interrupt Capacity (AIC) and Blue Sea states that it satisfies ABYC requirements for main DC circuit protection on large battery banks.

That would also mean that I would need to install a stand alone ABYC compliant On/Off switch rated at over 5,000 amp interrupt capacity.

Would you agree?

I have not been able to find a thermal circuit breaker (panel mount) rated at 150 AMPs that has higher than the 3,000 AMP interrupt capacity. Do you know of any that meet the 5,000 AMP ABYC requirement?

Thanks

http://bluesea.com/category/5/22/productline/overview/135