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Old 02-07-2013, 07:31   #2791
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by T1 Terry View Post
It looks like you are trying to develop a problem so you can build a solution :lol:
T1 Terry
T1 Terry, with all due respect but... it is much easier to critisize everything. Please be (more) constructive.

The goal is to make the fully automatic BMS with cell monitoring function for the unlimited number of cells and at the affordable cost.
So it could be your piece of mind to protect the investment (lifepo4 are not cheap) and manage the charge/discharge. And give you the detailed voltage of every cell, warn about low/high voltage or over-hearing.

Looks like a good system to have. And Arduino is well-setup for the job. And cost nothing
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Old 02-07-2013, 11:16   #2792
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Terry our 4 400 amp cells are faultless no BMS just watch them and life is good. we consume 50 amps average per night and the banks full by mid afternoon.
Life is sweet and not complicated!!!!

We agree .....
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Old 02-07-2013, 11:22   #2793
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Terry our 4 400 amp cells
Lagoon4us, how is your lifepo4 producer? what is your base single cell - is your 400ah 3.2v single cell or multiple?
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Old 02-07-2013, 11:27   #2794
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

4 x 400 amp cells only with a GSL SOLAR Regulator MPPT
with 750 watt 36volt converting to 14.1 average...

Cheers
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Old 02-07-2013, 11:30   #2795
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

How made/sold the cells?
I was of the opinion that it is impossible to make a single 400ah cell, that they are batteries (made of smaller cells in parallel)...
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Old 02-07-2013, 11:33   #2796
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They come in single cell sizes to at least 1000Ah. See the Balqon store.
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Old 02-07-2013, 11:34   #2797
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

4x400 amp 3.6 volt cells make up one battery read back through the posts :-)
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Old 02-07-2013, 11:37   #2798
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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They come in single cell sizes to at least 1000Ah. See the Balqon store.
Yeah, really? why would then a Balqon 1000ah battery will have 3 (+) and 3 (-) contacts? )
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Old 02-07-2013, 12:40   #2799
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Yeah, really? why would then a Balqon 1000ah battery will have 3 (+) and 3 (-) contacts? )
Why do *you* think a 1000 AMP hour cell would have multiple contacts per side?
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Old 02-07-2013, 13:19   #2800
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I do not know what is "a conventional wisdom"

....
Also, it is possible to install 30A current sensor and add Amp/h counting function.
Here is a link to a +/- 75A current sensor Pololu - ACS709 Current Sensor Carrier -75A to +75A. They have many more. I am planning to use smaller versions to monitor the consumption of my fridges with the Arduino.

Here I have it installed on a Blue Seas busbar that I cut up in the middle and added small bolts for the señor. Works great.

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Old 02-07-2013, 22:00   #2801
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by SVI View Post
T1 Terry, with all due respect but... it is much easier to critisize everything. Please be (more) constructive.
Quote:
Originally Posted by SVI View Post

The goal is to make the fully automatic BMS with cell monitoring function for the unlimited number of cells and at the affordable cost.
So it could be your piece of mind to protect the investment (lifepo4 are not cheap) and manage the charge/discharge. And give you the detailed voltage of every cell, warn about low/high voltage or over-hearing.

Looks like a good system to have. And Arduino is well-setup for the job. And cost nothing

The difference between building a 4 x 100Ah cell in parallel x 4 units in series or building a 4 x 400Ah cell in series is that the connections are on the outside, not inside the plastic cover. If one of the 4 x 100Ah cells was to have a problem it could be isolated and there would still be an operational 300Ah battery till the problem cell could be replaced, you can't do that with a single 400Ah cell. Another difference is that due to mass production, no 2 cells will be identical, you could have one cell with a percentage higher capacity or higher internal resistance for what ever reason, if 4 of the high ones were in one group and 4 of the low ones were in another group, a mix and match would produce 2 400Ah groups that have very similar characteristics, you can't do that if all the cell connectors are inside the plastic case.
But that is the only difference, the connectors are on the outside not the inside, both produce a 400Ah cell, so why would you want to monitor individual cell voltages, it would just produce angst that is meaningless, but paralleling 4 x 100Ah batteries would require a lot of monitoring equipment and load/charge balancing, with zero gain.
Prismatic Li cells don't suddenly go dead short or open circuit, the way they are constructed doesn't allow that to happen, so building a monitoring system to protect against an event that can't happen doesn't make sense.
It's like an automated cell balancing system for a 4 cell in series battery, they are not powerful enough to do the initial balance and once the initial balance of the cells is done it's highly unlikely the cells will go out of balance unless a cell develops and internal short, then the balancer module couldn't get the cells back in balance anyway, a partial solution for a problem that isn't really there but another weak link added as they themselves can fail and cause the cell to discharge and imbalance, creating a problem that wasn’t there.
KISS is the key, the more systems you add, the more potential from a problem, why add problems to a system that didn't have them to start with?

T1 Terry
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Old 02-07-2013, 22:03   #2802
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Why do *you* think a 1000 AMP hour cell would have multiple contacts per side?
I hate guessing - asked Balqon. Hopefully they will reply.
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Old 02-07-2013, 22:08   #2803
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

SVI,

Make things easy on yourself. What ever a-hr pack you want to put together, do it as a single series string. As to the three terminals on the 1000 a-hr cell, it has no problems and very little voltage sag cranking out 3000 amps, so does that explain the 3 terminals?
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Old 03-07-2013, 00:16   #2804
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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SVI,

Make things easy on yourself. What ever a-hr pack you want to put together, do it as a single series string. As to the three terminals on the 1000 a-hr cell, it has no problems and very little voltage sag cranking out 3000 amps, so does that explain the 3 terminals?
Maybe it is made of 3 (or more) separate cells. Then one can buy 2 1000ah batt to make a nice 500ah 12.8v one. I have asked Balqon if this can be done - the price is bloody nice!
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Old 04-07-2013, 17:49   #2805
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Quote:
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Maybe it is made of 3 (or more) separate cells. Then one can buy 2 1000ah batt to make a nice 500ah 12.8v one. I have asked Balqon if this can be done - the price is bloody nice!
I don't know for sure, but my guess is there are many pouch cells inside. Nothing you can cut in half. Buy the size you need?

Something like this, but obviously larger and perhaps more pouches.

http://liionbms.com/php/prismatic_cells.php

I suggest you go to page 1 of this thread and spend a few hours reading forward.

Bob
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