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Old 05-02-2013, 16:41   #1936
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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How about as an option using a Genasun Lithium controller (price $599) for your put together battery pack.


GLi-CP-1 | Genasun

Looks as if Genasun sell them seperatly. Certainly more expensive but nothing like buying the full genasun 360AMP pack for $6,399.

Paul who owns Sulaire a St Francis 50 recently fitted the Genasun batteries.

Cheers
Genasun stopped selling those a few months ago. Was a very nice product and would have been my first choice...
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Old 05-02-2013, 16:49   #1937
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Genasun stopped selling those a few months ago. Was a very nice product and would have been my first choice...
You would have paid $1.21 per watt vs the $0.20 per watt you paid for your 400 a-hr cells?
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Old 05-02-2013, 16:57   #1938
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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You would have paid $1.21 per watt vs the $0.20 per watt you paid for your 400 a-hr cells?
No, but I have installed them and they are beautifully executed...

I was referring to the BMS system Genasun used to sell so you could build your own pack. They discontinued it about 4-5 months ago. It was a very sweet set up for the $599.00 they sold it for....
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Old 05-02-2013, 17:37   #1939
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Got a chance late this afternoon to start work on my BMS box. The alarm buzzer, reset button, BMS board and two HVC relays are installed but not all of it wired up yet. I added a terminal strip to make wiring into to the vessel easier. The box is a simple Velleman job box...

The two 70A Cole Herse SPST relays will cut the Balmar reg and the MPPT controller in the event of a HVE. The house loads will be on an external EV200 contactor.

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Old 05-02-2013, 20:42   #1940
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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She is compressed with 1/4" aluminum plate which is then drawn together with 5/16" threaded rod and precisely spaced with 1/2" aluminum square tube to fit into the slots on the cells.
Nice thoughtful work. Thanks for posting that.

Why 1/4" aluminum plates? Experience, guessing, or did you find a technical reference on the expected pressure?

What brand/model are those BMS units?
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Old 05-02-2013, 21:48   #1941
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Nice! I vote purple. Or actually violet, 2 parts blue 1 part red.
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Old 06-02-2013, 03:09   #1942
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I'll vote for Black, stand out nice against the yellow cells. You could also probably polish them and spray them with 2 pk clear

T1 Terry
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Old 06-02-2013, 06:34   #1943
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by Maine Sail View Post
Got a chance late this afternoon to start work on my BMS box. The alarm buzzer, reset button, BMS board and two HVC relays are installed but not all of it wired up yet. I added a terminal strip to make wiring into to the vessel easier. The box is a simple Velleman job box...

The two 70A Cole Herse SPST relays will cut the Balmar reg and the MPPT controller in the event of a HVE. The house loads will be on an external EV200 contactor.

Another option with the Cell Boards inside a waterproof (splash/drip proof) enclosure.
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Old 06-02-2013, 15:40   #1944
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Nice thoughtful work. Thanks for posting that.

Why 1/4" aluminum plates? Experience, guessing, or did you find a technical reference on the expected pressure?

What brand/model are those BMS units?
"Why 1/4"?....Why not? No really, I had some around that I use for mounting Espar heaters and such and I prefer to work with 1/4" aluminum anyway as anything thinner is pretty flimsy..... I don't ever expect to get my batteries to the point of bulging so it is more for mounting...

The BMS board (House BMS) and cell modules are from Dimitri at Clean Power Auto in Florida.
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Old 06-02-2013, 17:56   #1945
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Genasun stopped selling those a few months ago. Was a very nice product and would have been my first choice...

That is unfortunate. Genasun does understant Li as much as anyone and has more experience marine wise.
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Old 06-02-2013, 18:02   #1946
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Moving the boards away from the battery is not a bad idea, but remember that there will be voltage drop on the cables when that 5w resistor kicks in so if the board is relying on the cable to sense voltage you will end up with rapid switching of the resistor, as the voltage drops under load and then returns to the higher voltage when the load switches off. the other thing to keep in mind, each of those 5 w resistors are producing 5w of heat, that has to go somewhere, you have no air circulation in that box, it will get very hot very quickly inside there if all 4 resistor start burning off current.

T1 Terry
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Old 06-02-2013, 18:44   #1947
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Terry,

You raise a good point about the heat but your last sentence puzzled me. Why would a BMS ever turn on all 4 cell balancing shunts? Correct me if I'm wrong here, but it seems that if 3 shunts are on and the 4th cell gets up to voltage, you would just stop charging.

Maybe that's not how some of these systems work, but it seems like it would make sense.

Charlie
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Old 06-02-2013, 20:18   #1948
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I have one of these units and Terry is right.
Normally there's no discernable heat, but all four can be shunting for a time before actual HVC disconnect occurs.
The heat dissipation needs to be accounted for under that condition.
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Old 06-02-2013, 22:43   #1949
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Terry,

You raise a good point about the heat but your last sentence puzzled me. Why would a BMS ever turn on all 4 cell balancing shunts? Correct me if I'm wrong here, but it seems that if 3 shunts are on and the 4th cell gets up to voltage, you would just stop charging.

Maybe that's not how some of these systems work, but it seems like it would make sense.

Charlie
Mine start shunting at 3.55V, but does not hit HVC until one cell reaches 3.61V. So all can be on above 14.2V if the cells are balanced, and the HVC disconnect would not happen until >14.4V. In practice, my chargers are all set to remain below the shunting voltage.

Some BMS systems may handle this different, but this is typical.
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Old 06-02-2013, 23:03   #1950
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Not singling any one active BMS system out here, this goes for all of them in general, some are better than others. The theory is, the cell reaches 3.6v so a shunt load is activated across a resistor to burn off some of the capacity, it the cell voltage reaches 3.8v or some such figure the board sends a signal to a central unit that switches off the charger. Sounds great, but the associated bits are completely ignored.
(1) When the cell goes over 3.45v the electrolyte starts to heat up, a few millivolts creates a few miiliwatts and the cell can dissipate that, much more and things start to heat up. The bit that conducts the most heat is the lump of copper and the lump of aluminium attached to the anodes and cathodes within the cell. The mini BMS board is attached across here, is it dissipating the heat? No, it's generating more heat through the resistor so this is adding to the problem, not assisting it.
(2) When the load from the resistor is applied to the circuit the voltage within the circuit drops, not enough to turn the resistor off but enough to effect the complete shut down the charger voltage point, so the shut down point moves up from 3.8v to around 4v, now lots of heat is being generated inside the cell as well as by the board itself

Add these two things together and then bear in mind, the transistors that switch the resistor on and off are sensitive to heat, if they get too hot they punch through, now the resistor is on full time and full tilt. The voltage finally climbs high enough for the shut down alarm to trigger, hopefully the type of charger integrates with this shut down and the charging stops, the cell has suffered from an over voltage charge but now there is a resistor across the terminals dragging power out, and it won't turn off. After a while an imbalance between this cell and the other cells creates a bigger over charge on the other cells, the cut off voltage is the combined total of all the cells remember, and one cell has been discharged more than the others because the resistor is active full time. It doesn't take long before real damage is done, the operator is oblivious to what's happening, they trust the $$ they spent on the BMS is keeping them safe.

Wouldn't a better system be to simply turn the charger off for a while when a cell reaches 3.6v and give the operator a display of the voltages in each cell so they can decide if it's a major issue or not?

T1 Terry
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