Energy management on a sailboat

opampca

Sailboats are like other mobile homes, (Motorboats, RV,) but somehow different.

- Sailboats do not generate energy from a running motor, or at least very seldom.

So care has to be taken to save energy and harvest differently.

- Sailboats spend some time at the dock, where grid energy is available to charge batteries and run devices. The rest of the time, it has to be autonomous.

I am trying to design a system that is easy to operate, reliable and efficient, here is the diagram.

To be efficient and save weight, I would like to use LiFePO4 batteries.
I am trying to avoid multiple sources to charge the batteries, so all the sources go thru the CC.

Sources are conbined to the CC via diodes to isolates them from each other.


When I arrive to the dock, the AC source trigger a relay to switch the 117v AC outlets from the inverter to the shore power.
Also there is a power supply that is turned on to supply power to the utilities, and charge the batteries.

There is always a load on the batteries (fridge, instruments, etc..), and always a charge when at dock.

I have a question: There will be a constant voltage from the CC to the batteries since there is always a load on it. How will that affect the batteries ? Will the LiFePO4 batteries suffer from this ?

dennis461

I just started reading about 'smart' chargers for LiFePO4 batteries.  It looks like your setup will always provide current to the batteries. The 'smart' chargers stop charging when LiFePO4 battery is at full voltage/charge.  

I also see you have 120VAC outlets connected to an inverter.  Your sailboat already has ALL outlets connected to the shore power plug and breaker panel, correct? Are you going to re-wire a small number of the outlets to the inverter, or all of them?

and

Let's see a picture of your 'hole in the water' 

westbranch

Unless that fridge is DC and the CC can handle a large load (guessing ~30 Amps)  you will have to move it to the battery or inverter if 120VAC...

opampca

@ Dennis... the problem is that I always have load on the battery, so the CC or charger would always think battery needs charge...
All the outlets are together on inverter, but switched to shore when shore is energised (relay)
@ westbranch... the fridge is 12vdc and can be handled by CC no problem.
I just don't like to see the battery always getting voltage from CC when at dock... :-(

Raj174

Hi Opampca,
With LFP, it's not so much that there is voltage on the battery, it's what that voltage is. LFP's don't mind sitting around for months at 60% SOC, but sitting for long periods of time at 90% SOC will shorten their lives. So if the boat is going to be sitting in dock for long periods of time then the float voltage would need to be around 13.1 volts, close to 50% SOC. Since there is a constant 36 volt PV input, the CC would remain in float and the batteries would be fine. If the CC is not that finely adjustable or does not have that preset then I would not recommend LFP. However, there are CC's available that have individual absorb and float adjustments to the 10th of a volt, but they are not cheap. Midnite Solar Kid marine version for example.

mike95490

For Li batteries, you need a charger that will bulk the batteries to their 90% full voltage, and then drop back to FLOAT, so you don't overcharge them, AND the PV can still provide power to the loads, without being shut off.

The wind generator needs it's own charge controller with a DUMP load or a brake to stop it from spinning when the battery is full. I've never seen wind and solar combined successfully on a single controller.

opampca

Hi Raj, The CC is fully ajustable, and compatible with LiFePO4 batteries. What I do non know is if it sees the load apart from the battery and knows it has to supply current to the load independently from the battery. I sent an email to techsupport at Epever to know about it. If it sees that the battery is at high SOC, it should stay at float voltage. Here is the control parameter.... 
Hi Mike, Thanks for the advice for the wind generator. I plan to get one, and will definitly install a protection device at the output.

I should receive the CC before next week, I will set up a lab for it and try few things, and keep you posted....

Thank you !

westbranch

Not being familiar with your CC ,,,  I have MidNite Solar products...  AFAIK electrons do not know where they are going nor does the CC, yours will see the battery and if it is accepting electrons (ie Volts) or sending electrons, this is determined by the internal resistance or acceptance of the battery to power presented to it.  The power going towards the battery goes to the place of lowest resistance, so if both the fridge and inverter were wired at the same spot on your diagram the item(s) that had lower resistance than the battery would get the flow from the panels, not the battery..  hope this makes sense.
to know exactly how many Amps went into your battery you need something like this, the Whiz Bang jr http://www.midnitesolar.com/productPhoto.php?product_ID=519&productCatName=Charge Controllers - Classics&productCat_ID=21&sortOrder=9&act=pc

opampca

This makes sense for sure....  I wonder if the CC will be able to discriminate between the battery and the load to decide in what mode it gets, bulk, constant, or float. If it sees that the battery is at high SOC without being influenced by the load, It should stay in float mode ?

westbranch

If it sees that the battery is at high SOC without being influenced by the load, It should stay in float mode ?

That is what it should do but changes in PV output also affect that as well as loads.

opampca

It should stay in float, if the CC is well designed, that is what I will see... it is not an expensive unit, but it's probably the largest chinese CC maker, and they have been around for quite a while. There were good reports about it.
For the PV out, it should remain constant while at the dock. When I leave the dock, it is another story, load will be powered by the battery with the help of the PV when there is sun. This case is more like normal behaviour.

mike95490

I do not like the settings I see. Li batteries do not have an Absorb time or Eq time, Zero those out, unless the battery mfg instructs you otherwise.

And you have Boost & Float so, set your float at the long term float voltage (about 85-90% full charge)  The higher the float voltage, the shorter battery life you get.

In short, follow the battery Mfg spec, don't trust the charger vendor to have done it right.

opampca

Mike, these are some default settings that make no sense to me either. EQ is absurd on Li batteries. I will definitly review all these settings for sure. Thanks for the head up !!

Raj174

Good that it's adjustable. These settings are for a battery pack that has been professionally designed, configured and balanced along with a BMS (Battery Management System) to prevent overcharging. It will charge to 100% SOC (3.65 volts per cell) and drop to 14.4 volts which is float. In my opinion 14.4 is too high and my shorten battery life. I would recommend setting float to 13.6 (90% SOC as there is not a lot of capacity to be gained by keeping the voltage much higher) before you set sail.
When docked and connected to shore power and you set float to 13.1 volts, the battery pack will supply the loads until it reaches 13.1volts and then the CC will be pretty much be supplying the loads and keep the battery at that voltage. Keep in mind, these settings are not for a DIY battery bank. i.e. 4 LiFePO4 prismatic cells wired in series.   

Rick

Dave Angelini

This seems to me as risky and the reward is not worth the risk when there are so many safer solutions. I would use a deep cycle lead acid and a marine rating gives you a vibration spec on good makes of batteries. All of the Li-Ions I have seen have pretty numerous warnings on vibration and shock. Good Luck!

Estragon

Where are the solar panels going? I don't see a bimini or dingy davits.

Cute headsail.

opampca

@ Rick.. what is special about the diy battery bank ? this is what I was gonna get... CALB or Winston...
@ Dave... it is for sure a risk, but they will be smaller and lighter... also I like to go forward... my boat is called "Fast Forward".. :-)
@ Estragon... I will build a support on the back, 2x 120watts that will serve also as bimini

I received the CC yesterday... I am impressed with the construction.... very sturdy.. 
I started to do tests.... For MPPT, it will react in about 1.5 minutes from 24v to 34v in simulated PV.
The CC will stay in float mode with a 10 amp load. The PV input will supply the load fast (20 secs) after turning on PV (dock situation with 36vdc supply) and leave the battery in float mode after. I will keep doing tests for few days and more. The CC has a modbus rs485 connection to a wifi server (smail dongle) so I can remotely monitor and change parameters.... keep you posted !!

westbranch

Have to assume you are using FLA s for the testing.... Have you checked the sgs to confirm they are giving a 'full' charge?

Dave Angelini

Smaller and lighter is always great on a sailboat. I am very biased because I cruised for 10 years to places where you could never get a deep cycle battery unless you waited a month and prayed for DHL nightly.

Most of us are all land based and can walk away from a fire. There is nothing worse than a fire at sea. Carry a good life raft or a dinghy and Good Luck!

Raj174

Let me ask a question first. Will you be using a BMS on the proposed DIY battery bank? If yes, the settings already discussed will work. If no, the absorb setting (boost?) would need to be set to 13.8 volts. The reason for this is that, in either scenario the individual cells will need to be fully charged with a 3.65 volt LFP charger. Then connected in parallel for 8 hours. This is called top balancing and is necessary to keep all the cells balanced at full charge. At this point wire the batteries in series and if you have a BMS, it can be installed now.

The BMS serves 3 functions,
1. It has bleeder boards that are connected between the + and  - post of each cell. When the charging voltage reaches 3.65 volts the bleeder board circuitry will activate and bleed off power through a resister until all the boards are activated and the cells are rebalanced at 100% SOC.
2. Battery monitoring, either to a digital display or a communications port.
3. It can activate a high and low voltage disconnect relay

In the case on no BMS, setting absorb (boost?) to 13.8 is necessary because of the nature of the LFP charging curve. At the top of the charge curve, between 80 and 90% the curve starts to go from almost flat to vertical at 100 % SOC. Here the voltage rises very quickly and can cause cell damage if it goes too high, so without a BMS it's best not to go there. Setting absorb and float lower keeps the state of charge from ever getting near the vertical aspect of the upper knee in the charge curve. The margin of safety at the top and bottom of the charge and discharge curves costs about 30% of battery capacity.

So there is also something else to consider. A high and low voltage disconnect if you don't use a BMS. But there are solutions for this also.
I use a digital amp hour meter and DC contactors on my system for this purpose.
Later,
Rick        

Raj174

This is a link to MarineHowTo.com. Here you will find an interesting and informative read on LiFePO4 batteries from a marine perspective. I'm sure you will find it very helpful.

http://www.pbase.com/mainecruising/lifepo4_on_boats

Rick

karrak

All the research I have done and my own personal experience tells me that keeping an LFP (LiFePO4) battery at around 99% full will not significantly reduce its lifespan. I think the idea that charging LFP batteries to 90% rather than 100% will double their lifespan comes about because you can roughly double the life of lithium cobalt cells (the ones in phones, Laptops ect.) that have a fully charged voltage of 4.2V/cell if you only charge them to 90%.

The daily charge regime for my offgrid battery is to charge to 3.45V/cell if there is enough sun and terminate the charge and shift to float when the charge current reduces to C/50. This results in a battery SOC of >99% (battery >99% full). A float voltage of 3.35V/cell will keep the battery at around 99%SOC. At night we run off the battery. After nearly four years I haven't noticed any change in the performance of our battery.

One change I would would make would be to have your shore battery charger set to 3.35V/cell (13.4V for 12V battery) and connect it via a fuse straight to the battery. The wind turbine will probably have its own charge controller which could connect directly to the battery.

What are you doing with regards to a BMS?

Here is some more light bedtime reading, http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html

Simon

karrak

I haven't read the cruiserforum discussion for a while and was surprised to find this statement from user Maine Sail who is well respected on that forum
"After 12 1/2 months of doing nothing but sitting there, at 100% SOC, the cells had lost -11.6% of their previous rigorously confirmed Ah capacity. Remember this is just sitting there at full charge with no float...."
in this post
http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-367.html#post2312168
This has left me scratching my head as the experience of myself and a number of others who post on the Australian Energy Matters forum and user SteveG who has an LFP based system that is over 6 years old and occasionally posts on what I would call the "alternate facts" forum  is somewhat different.

None of us have had anything like that level of loss of capacity. The big difference as far as I can see is that although we are charging to and floating at ~100%SOC during the day  we are cycling our batteries on a daily basis.

With this in mind I would change the charge voltage from your shore charger to 3.27V/cell which corresponds to around 50%SOC and disconnect the solar panels from the solar controller if your boat is going to be docked for a period of time.

If you are using solar and wind to charge the battery when cruising I would still keep charging to and floating at ~100% as you need as much reserve as possible to get you through cloudy weather.

For those that want some recently published technical information on capacity loss of lithium batteries during storage it can be found here http://jes.ecsdl.org/content/163/9/A1872.full.pdf . Thanks to user OceanSeaSpray from the cruiser forum for finding this.

Simon

mike95490

Raj174 said:

This is a link to MarineHowTo.com. Here you will find an interesting and informative read on LiFePO4 batteries from a marine perspective. I'm sure you will find it very helpful.

http://www.pbase.com/mainecruising/lifepo4_on_boats

Rick

That's a very meaty and technical post, I'm halfway through the 1st part.  Thanks
 Like Dr. House says : Everyone lies.   Especially when they can sell you something


At 375 pages, and starting in 2011, the http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html   was way too chatty to try to bother with.