LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[Cottontop]

Seems Tesla will have to deal with the overcharging problem from always connected solar, and they will certainly have to deal with the runaway fire possibility, two of the big problems mentioned in this thread.

I need a good system, in about a year. I'm going to keep wishing, really, really, hard.

[OceanSeaSpray]

It is not hard to make a good system for a given usage. It just depends on how you define "good" and then how you use it.
Keeping it simple helps. Before you buy any charging gizmo, ask:

- Can it be configured for a suitably low voltage?
- Can it be configured so it essentially stops charging (i.e. 13.3V or lower, or off) automatically?
- Can it be disconnected without any problems?

If any of the three is no, move on.

[CGirvan]

Just wondering if using a hot water heating element as a load dump instead of trying to turn charging sources off would be easier/safer. Additional bonus would be a hot shower at the end of the day.

[Jd1]

Originally Posted by CGirvan

Just wondering if using a hot water heating element as a load dump instead of trying to turn charging sources off would be easier/safer. Additional bonus would be a hot shower at the end of the day.

No ..... what would you do if you already have the tank at set temp?

[transmitterdan]

Originally Posted by CGirvan

Just wondering if using a hot water heating element as a load dump instead of trying to turn charging sources off would be easier/safer. Additional bonus would be a hot shower at the end of the day.

It's not a stupid idea. If you have a 6 gallon hot water tank it would take a 100 watt load dump more than 30 minutes to raise the temperature 10 degrees C (18F). A fairly simple mechanical thermostat could be used to shut off the charging sources once the water was hot enough.

[Dod42]

I read through the many pages that some are using Victron BMV-702 monitors to monitor their LifePO4 banks. Other than the peukert number what other setting did you change to suit. There is the most obvious ones like bank size and voltage but what about CEF % and the settings that basically say I'm full. I can see the alarm voltages but how well does it work out SOC and TTG etc

[Jd1]

Originally Posted by Dod42

I read through the many pages that some are using Victron BMV-702 monitors to monitor their LifePO4 banks. Other than the peukert number what other setting did you change to suit. There is the most obvious ones like bank size and voltage but what about CEF % and the settings that basically say I'm full. I can see the alarm voltages but how well does it work out SOC and TTG etc

I use the SOC parameter to control the internal relay and that relay is controlling my battery charging bus. Basically I use the circuitry that cuts off charging based on the BMS control signal but use the internal relay to trigger the circuitry early. Only if the SOC control is disabled (or defective) will the BMS charge control shut things down.
As an example, I might set it so that charging is disconnected at 90% SOC and resumes at 60% SOC.

[Dod42]

Originally Posted by Jd1

I use the SOC parameter to control the internal relay and that relay is controlling my battery charging bus. Basically I use the circuitry that cuts off charging based on the BMS control signal but use the internal relay to trigger the circuitry early. Only if the SOC control is disabled (or defective) will the BMS charge control shut things down.
As an example, I might set it so that charging is disconnected at 90% SOC and resumes at 60% SOC.

Yes I'm thinking of doing something similar, I'm just unsure how accurate the SOC calculations are on the 700. I know on my previous BMV600 (AGM Bank) it took a lot of trial and error to get the settings so I was confident with the SOC even then I would regularly sync it.

I was also able to set Voltage alarms on the 600 and I will also on the 700, It just seems the voltage line is very flat on LifePO4 between 80% and 30% so not sure other than another backup if its a good guide.

So is the consensus that these are accurate enough once the settings are configured to trust SOC and where there any settings like Mid point? that seemed to be advantageous?

[Jd1]

Originally Posted by Dod42

Yes I'm thinking of doing something similar, I'm just unsure how accurate the SOC calculations are on the 700. I know on my previous BMV600 (AGM Bank) it took a lot of trial and error to get the settings so I was confident with the SOC even then I would regularly sync it.

I was also able to set Voltage alarms on the 600 and I will also on the 700, It just seems the voltage line is very flat on LifePO4 between 80% and 30% so not sure other than another backup if its a good guide.

So is the consensus that these are accurate enough once the settings are configured to trust SOC and where there any settings like Mid point? that seemed to be advantageous?

I am completely unconcerened about accuracy. The batteries are protected by the BMS (two levels of protection) and the SOC control is on top of that.
In practice my SOC is averaging around 70% and if anything it is a bit low. I have a bypass switch for the SOC control and when out for more than a day or two I end up bypassing in order to maximise SOC while motoring (alternator is my only source of charge when not on shore power).
I have a cell voltage monitor that is checked easily enough if/when I want to re-sync or balance the cells or whatever (not required so far).
The batteries are oversized for my needs so even if the SOC figure is out by 200 aH it isn't critical for me.
I have the 700 - no mid point setting as far as I know.

[offpist]

Some pictures of my setup.

1000AH Winston, Masscombi Ultra 3500W/150A, plus Charge Master 100A.
Total 250A charging power when using the generator or shore power.


Lifepo4 start/thruster/windlass battery.


Lifepo4 for the dingy!


48V, 115AH for the dingy.


Two Balmar 120A combined with two Mastervolt Alpha Pro MB regulators gives me plenty of power, and good safety as I can adjust the 3 charging stages as I want. Everything is connected together with masterbus.

I am currently installing the Masterbus->Nmea2000 converter, should give me battery information for both service and start on the helm.

Video of the dingy.. I have about on hour if power at top speed. (22 km/h).
If i run slowly, at 6 km/h, I can run about 10 hour.

https://www.youtube.com/watch?v=KvG-csJMMEM

[deckofficer]

offpist, your dinghy really gets with the program on the Torqeedo 4.0. Is that the stock V19 prop? If so your squeezing 3 km per hour more than the pitch would dictate. Using 3.25 volt LiFePO4 cells, are you running a bit more voltage than the Torqeedo lithium battery? My guess is 0.2 volts more.

[offpist]

I changes the prop to the "high speed" one.
It gives me slightly more top speed, but not as much as I had hoped for.


Battery is steady at about 50V-52V under load.

Actually, I have double set of batteries onboard, but i found this to be unnecessary. The cells are harvested from an electric car that was wrecked.

I am using an piktronik 48V/9A charger, fully programmable for Lifepo4.

[deckofficer]

Did you try it with the stock V19 prop before going with the V30? The V30 is good for 30 km per hour if hull weight and drag allows full rpm. The V19 would give a better hole shot but tops out at 19 km per hour.

[offpist]

Originally Posted by deckofficer

Did you try it with the stock V19 prop before going with the V30? The V30 is good for 30 km per hour if hull weight and drag allows full rpm.

Yes, the original propeller gives me about 16km/h top speed.
My dingy is probably not the easiest one to pull, it has glass fiber V-bottom with wheels and stuff.. But its very good in ruff sea so i don't want to change it for a flat bottom.

Being just 18.3KG, the motor is very easy to handle.
Batteries are 30Kg each so they are heavy, but also easy with the handles and all. (those are Harley Davidson saddle bags).

I can pull my boat (42 feet) with the dingy quite easily also.
At this the original propeller is better, as it has more torque.

[OceanPlanet]

Originally Posted by woodenboats

SuperB, Victron Energy and Mastervolt have done it, and I could come up with more.
Not everyone will like the price tag, but then - what is the price of an replacement battery for a Volt vor Tesla?


Sent from my Lenovo B8080-H using Cruisers Sailing Forum mobile app

No mention of Genasun? I'm truly hurt...

Have been doing Li systems since 2006...