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

[Lagoon4us]

LMAO yep i'm head down checking what i've got now, is it better to connect at the cell end more towards the terminal post for the loggers sensor wire or is the middle of the connection acceptable?

Cheers

[T1 Terry]

Under the terminal bolt is fine, in a long parallel string I usually connect the wire some where around the middle, just looks neater that way, only 1 wire for each parallel connection, either the negative of a cell in each parallel group and the last one on the positive, easiest way, or the other way around, a wire on a positive terminal of each parallel group and the last one on the negative. Even if you have 50 cells connected in parallel, the logger sees them as one cell because all the voltages will be the same in a parallel connected string (as long as the connections are good part of Kirchhoff's 2nd law I think)
Remember, cell 1 on the logger starts at the negative end, cell 4 is the positive end.

T1 Terry

[Lagoon4us]

Cell logger is now connected and running, thanks for the help Terry & Rolf. After watching the loggers minute size digits i'm happy i've ordered a 50mm voltage readout that i can flick momentary off on switches to read individual cells, the logger can just switch the latched relays (through a smaller relay of course) and handle alarms.

Cheers Frank

[roetter]

Originally Posted by Lagoon4us

Cell logger is now connected and running, thanks for the help Terry & Rolf. After watching the loggers minute size digits i'm happy i've ordered a 50mm voltage readout that i can flick momentary off on switches to read individual cells, the logger can just switch the latched relays (through a smaller relay of course) and handle alarms.

Cheers Frank

You might want to order from Amazon a 4-channel 12V relay module. It costs a whopping $3.47, has transistors at the front end (uses 5mA to drive the relays). The relays are good for 30V 10A DC or 250V 10A AC. Each relay has a little LED on the board so you see if it is on or off. I use it to drive a Blue Sea 450A contactor relay.

Amazon.com: 12V 4 Channel Relay Shield Module Expansion board For Arduino ARM PIC AVR DSP: Home Improvement
Attachment 62634

[Lagoon4us]

That's the go , thanks

[Lagoon4us]

For over voltage charge disconnect are you considering putting a 'reset' timer in circuit to bring the charge back on so you don't eventually go into a low voltage situation from house draw?

[goboatingnow]

Originally Posted by Lagoon4us

For over voltage charge disconnect are you considering putting a 'reset' timer in circuit to bring the charge back on so you don't eventually go into a low voltage situation from house draw?

I suggest that is a bad idea. Overvoltage should not happen in a correctly designed system, either you have a cell badly out of balance or something has failed in the charging system. These should be investigated, rather then relying on automatic reconnects.

Dave

[Lagoon4us]

Once a load is put on the cells the voltages fall in line very quickly, normally in real practice as charge reaches peak a cell will pop 12 to 20 thousandths of a volt, wherever you set your logger just one of those thousandths will put it into alarm.

Frank

[roetter]

Originally Posted by Lagoon4us

For over voltage charge disconnect are you considering putting a 'reset' timer in circuit to bring the charge back on so you don't eventually go into a low voltage situation from house draw?

That will be part of my testing. But in reality I only want to guard against one of the many charge system failing. I am also talking four different boats. I convinced some friends to go LiFePo.

On my cat there will be:
Two Hitachi internally controlled 125A alternators - I may go to external controllers if I have to - only running when I am on board
Two Cristec shore power chargers (one 60A, one 40A) - unless I replace them,
- only running when I am on board, will probably be used very rarely, as we are not marina people.
2 Outback 60 solar controllers - when I am not on the boat I will likely keep one of them on to deal with the regular consumption. I am not sure what I need to do to deal with humidity when we leave the boat during the summer in the Bahamas on a mooring buoy in a hurricane hole.

I am considering using an Arduino micro controller to send me a message if there is an alarm while I am not there fro the summer. Then I can send a local friend to investigate.

[T1 Terry]

Our set ups use the alarm port of the logger to trigger a timer circuit that drives a relay. We use 3.6v and 2 mins.
when the timer is triggered it opens the relay, this cuts one of the legs to a solid state relay switching side, this stops any charge current going in the batteries or the system for 2 mins, the natural loads pull the high cell down.
This is a secondary back up system to the main charge controller, if all cells are in reasonable balance this circuit is never activated, but it gives you peace of mind if something goes astray while you are not looking. Some sort of ratcheting relay to hold a light on could be added to tell you there has been a safety circuit function so you can start a logging run for the next charging period, then you can look to see which cell has caused the alarm. Don't draw down the high cell, just charge the lowest cell, this will bring the pack closer in balance so the normal charge controller reaches battery cut off voltage before any cell reaches HVC. Far better to do it this way, when things are going wrong and staying alive is your main priority, an automated safety system seems like a sensible way to go, when the emergency is over and you have a bit of spare time, then rebalance the battery bank if needed.
The act of discharging a cell above 3.4v the same amount as discharging a cell under 3.4v will tend to pull the high cell back into line, an Ah below 3.4v is just an Ah of capacity, an Ah above 3.4v drags the surface voltage off very quickly, then takes an Ah out of that cell. You can't have an Li cell 110% charged, that apparent extra 10% blows away like dust, but it still requires charging amps to get it up there, each time it's blown away, the other 3 cells catch up that little bit. It is a little hard to get your head around but think of it as the reverse of an equalising charge on lead acid batteries, there they waste energy boiling electrolyte, here we use the energy to power a load that had to be powered anyway.

T1 Terry

[Lagoon4us]

Agree from what i've watched as the cells reach their end of charge is a flutter in the cell voltages (20 or so thousandths of a volt) if i cut the charge and allow the almost constant 7 to 10 amp draw from the boat take some amps out the difference between cell charge levels go to 4 or 5 thousandths.

More so for solar if the logger detected an over charging cell i want to cut the charge and bring it back on in say thirty minutes which should allow the fridges to level the cells somewhat and then the timer brings the charge back on even if in 30 mins it repeats i don't care theoretically.

I'm fairly sure my BEP Monitor has a bilge pump use function that in my absence records if the pumps activated, maybe i could use this to read any connect/dis-connects or alarm signals ex the Logger???

Dave we are talking small differences i was using my 'quite nice' multimeter that reads to 100ths of a volt until i got the Junsie wired in and now with being able to see the miniscule constant fluctuations in the three decimal point range a whole new world of panic has opened up!!! LOL.
Thanks Terry and Rolf.

Cheers Frank

[T1 Terry]

now with being able to see the miniscule constant fluctuations in the three decimal point range a whole new world of panic has opened up!!! LOL.

:lol: that one takes a little while to adjust the thinking and realise those numbers are hundredths and thousandths of a volt, if we even read a tenth of a volt before we thought that was reasonably close.
This is the reasoning for creating a log file, to see just what is happening when a cell hits 3.6v, it could be that the other 3 were at 3.599v, something has gone astray in the charging circuit, or one cell has hit 3.6v and the others are down around the 3.3v, yet as soon as the charging stopped and the load hits, the run away cell dropped back to 3.3v or lower, a bad conection in a parallel string so the effective capacity of that string is reduced, quicker to reach 100% SOC and then have a voltage run away, yet the reduced capacity doesn't have the staying power under load that the other cells have. Lots can be read and diagnosed from a cell logged chart once you understand what it's telling you, for $28 it's a really handy tool to have.

T1 Terry

[Lagoon4us]

We are cycling the charge by mainly using Solar, if a day's cloudy or the boat is shielding the sun simply by us sailing or the prevailing winds holding the boat at a totally wrong heading.

So charge in by day and out by night, if the cells are down we boost if running the engines motoring from place to place but we only boost to within 10% of full charge, i have a BEP Moniter with fuel gauge read out, i set the Peaukerts to .09 from memory and the 400 amps seem to top up just as the voltages sharply rise and the GSL Lithium controller throttles back so i think the fuel gauge is close to correct which is very handy.

We consume on average 70 amps by night and a fairly constant 10 amps/hour by day so i normally see a positive flow of around 20 amps going into storage.

I have a 80 amp latched relay on the solar and auxilliary charge circuits that i can actuate from the helm to either bring on or cut off charge should i see fit.

The one thousandth volt range is very active but as you say going to two decimal points unless you are on the brink of a decimal point change you wouldn't know but for the Junsie accuracy.

It's my intention to have a larger read out at the helm with two momentry switches allowing me to check individual cell voltages and leaving the Junsies to log and alarm undisturbed.

The physical structure of a Junsie requires reading glasses to see the small readout and the wiring isn't conducive to being easily panel mounted.

Cheers Frank

[Lagoon4us]

An interesting part of the Junsie readout is in top righthand of screen the fluctuations are shown,, load or charge those numbers constantly flicker in the 7thousandths of a volt range.

A bit like market fluctuations at the track, maybe not as quick!!!!

[roetter]

Originally Posted by Lagoon4us

We are cycling the charge by mainly using Solar, if a day's cloudy or the boat is shielding the sun simply by us sailing or the prevailing winds holding the boat at a totally wrong heading.

So charge in by day and out by night, if the cells are down we boost if running the engines motoring from place to place but we only boost to within 10% of full charge, i have a BEP Moniter with fuel gauge read out, i set the Peaukerts to .09 from memory and the 400 amps seem to top up just as the voltages sharply rise and the GSL Lithium controller throttles back so i think the fuel gauge is close to correct which is very handy.

We consume on average 70 amps by night and a fairly constant 10 amps/hour by day so i normally see a positive flow of around 20 amps going into storage.

I have a 80 amp latched relay on the solar and auxilliary charge circuits that i can actuate from the helm to either bring on or cut off charge should i see fit.

The one thousandth volt range is very active but as you say going to two decimal points unless you are on the brink of a decimal point change you wouldn't know but for the Junsie accuracy.

It's my intention to have a larger read out at the helm with two momentry switches allowing me to check individual cell voltages and leaving the Junsies to log and alarm undisturbed.

The physical structure of a Junsie requires reading glasses to see the small readout and the wiring isn't conducive to being easily panel mounted.

Cheers Frank

Frank

I contacted Junsi with regards to changing the software such that one can set a hysteresis for the alarm port. That way you would not need latching relays or any other complication to use the Junsi alarm port for driving the LVC and HVC. However, Junsi said the software development for the CellLog is finished. He also declined to let me have the source code and instructions on how to download the change code to the Junsi CellLog. I understand his position for his company. But I thought I would ask.

I opened a Junsi and found it to use an ATMega micro controller. I have just recently started to play with the Arduino micro controller development kit. It uses the same micro controller. I have already run a test reading the cell voltages with the Arduino and it works fine. I have ordered several different LCD displays to test as well. They should arrive later this week.

For the problem with the small numbers to read and some missing function in the JunsiI am going down this way now.

This is what I plan to do.
- Assemble and Arduino micro controller with a large LCD display either 2 lines 16 character, 4 lines 20 characters or a 3.2 inch graphic screen. These are much larger than the Junsi small display.
- write the code such that it will display voltages of 4 cells, pack voltage, min and max voltage as well as voltage difference.
- the code will raise separate alarms on low and high voltage. the alarms can drive the relay boards
- the hysteresis (voltages at which the alarms will cancel) can be set. I will also put in the option of a timed delay for the alarm.

There will also be an option to record measurements onto a SD card, which will give several GB of data and can be easily taken out for analysis on the computer.