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Old 26-01-2013, 11:41   #1516
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Bob, you know I like LFP. Wouldn't have spent $850 on it if I didn't.


But if the lead acid battery in your car or truck died tomorrow, would you really put a $500 LFP in its place, along with all the proper charging, monitoring, and disconnect circuitry it would require?
No, but for a house bank lead is dead to me. A cranking battery sees such a different life, thin plates for a lot of surface area, a short duration high amp draw, then quickly replenished. Not cycled.
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Old 26-01-2013, 11:45   #1517
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Otherwise, I'd just buy 40Ah cells.
Right, but then the cells might not be as well matched, and might require manual balancing, and you'd need interconnects and banding and all that jazz---which is not everyone's cup of tea. The 4-cell battery is a lot more plug-and-play---and many would happily pay extra for that.
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Old 26-01-2013, 11:59   #1518
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Originally Posted by ebaugh
I think you need at least automated cell level monitoring with a disconnect for house bank sized cell groups. In order to make my point, I attached 2 graphs from a Sandia Labs presentation to support the conclusion.

First, one shows that LiFePO4 is intrinsically safe. This graph shows several Li chemistries that if a cell is simply heated beyond a certain point, start to self generate more heat, adding fuel to the fire so to speak. Since we use LiFePO4, no additional heat is ever generated. But other chemistries could generate over 2 million calories on their own in a house bank sized group of cells. I'm not a chemist, but that sounds like a lot....ie. Boeing. This is a good thing thing for LiFePO4....and why there are so many of us willing to adopt.

Second, there is a graph that shows heat generated by overcharging LiFePO4 cells. This is a real risk and must be managed. The heat starts to be generated the first second a cell is overcharged, and can eventually reach near 180 degrees C based on the graph. I don't want to go there...do you? Are you always aboard to respond to an alarm? The problem that can be inferred with other chemistries, called a runaway, is the overcharging can generate enough heat to lead us back to the first graph where the chemical reaction itself leads to even more heat and more potential bad things.

But LiFePO4 simply slowly rises to its max potential at an attempted 140% SOC, by which time the cell has simply self destructed. I believe these charging tests were done on small round low capacity cells, so the results could be different, better or worse, for large format rectangular cells. But since I have a working disconnect, Im never gonna find out!
This is a great post , I've been searching for these gens for a while.

We should really summarise the. Charging experiences to arrive at a consensus. My experience is with smaller c,hinder cells. While I have a large cell to test , I've not done too much with it yet. My current project is LiCo ( hence all my friends making explosion noises. !!!). The shelf life issue is a bummer for LiCo.

Dave
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Old 26-01-2013, 12:04   #1519
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by diugo View Post
Right, but then the cells might not be as well matched, and might require manual balancing, and you'd need interconnects and banding and all that jazz---which is not everyone's cup of tea. The 4-cell battery is a lot more plug-and-play---and many would happily pay extra for that.
For his app of powering the SSB radio, you don't get as soft a "start" load as that. Receive about 18 watts, key to transmit and current corresponds with voice peaks. Even at 50% efficiency of an AB amp, for 100 watts RF out is only 200 watts DC in / 13.3 volts of this battery would only be 15 amps on a ramping basis. With this type of service, if care was exercised in cell selection for the 12 volt battery (which the manufacturer states they do) , and it was never over charged or allowed to run flat, there will be no balance issues.
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Old 26-01-2013, 12:14   #1520
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

"Allowed to run flat"---Bob, I never pegged you as a Brit or Aussie!
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Old 26-01-2013, 12:30   #1521
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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For his app of powering the SSB radio, you don't get as soft a "start" load as that. Receive about 18 watts, key to transmit and current corresponds with voice peaks. Even at 50% efficiency of an AB amp, for 100 watts RF out is only 200 watts DC in / 13.3 volts of this battery would only be 15 amps on a ramping basis. With this type of service, if care was exercised in cell selection for the 12 volt battery (which the manufacturer states they do) , and it was never over charged or allowed to run flat, there will be no balance issues.
Is there a simple BMS system, maybe not at a cell level, which will prevent the overcharging, over discharging, or running flat? This will be the fourth battery bank on board; I don't want to devote any thought to managing it. I need it to just work.
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Old 26-01-2013, 12:37   #1522
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Originally Posted by goboatingnow View Post

This is a great post , I've been searching for these gens for a while.

We should really summarise the. Charging experiences to arrive at a consensus. My experience is with smaller c,hinder cells. While I have a large cell to test , I've not done too much with it yet. My current project is LiCo ( hence all my friends making explosion noises. !!!). The shelf life issue is a bummer for LiCo.

Dave
Dave,

This is a great point...I cringe every time I hear someone routinely charging over 3.5V per cell. The recommended charging profiles quoting a specific voltage cutoff are usually based on higher rates than we would see in a marine house bank. The cutoff voltage varies somewhat significantly with rate. See my attached charging curves and hold a piece of paper up at 100% SOC position to see the difference. Like Terry said, the cup is full at 100%. Anything over that is potentially causing damage. Even 3.5V or 14V held on the bank long enough will eventually destroy my cells, or CALBS or anything other than maybe, and only maybe Winston/Sinopoly.

I can't find this same data for Winston/Sinopoly, maybe someone else can. But from everything I've read, those cells are sufficiently similar to suffer the same long term issues using higher voltages. The capacity gained is simply not worth the risk until conclusive data exists.

The only two published float voltage specs I've seen are for USA made cylindrical cells. A 2006 dated A123 spec shows float at 3.45 and a current 2013 Valence spec at 3.4V. My supplier quoted 3.35 for GBS, but it's not written anywhere.

Everyone can debate the point...and will...but bulk charging to 3.45 then immediately switching to float at some number below 3.4 per cell is safe on a balanced pack. Regardless of the charging current. Very high rate charging may call for slightly higher bulk voltage, but not until > .5C charge, or 200A on a 400Ah bank.

Bob
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Old 26-01-2013, 13:02   #1523
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Is that you, Mitt?
Huh?

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I would take you up on your generous offer---but you'll need the dough when you turn your current set of LFPs into boat anchors.
I knew you wouldn't bet. It's too obvious that you'd lose.
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Old 26-01-2013, 13:24   #1524
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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"Allowed to run flat"---Bob, I never pegged you as a Brit or Aussie!
I am watching the Australian Open mate. lol
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Old 26-01-2013, 13:52   #1525
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by Dockhead View Post
Is there a simple BMS system, maybe not at a cell level, which will prevent the overcharging, over discharging, or running flat? This will be the fourth battery bank on board; I don't want to devote any thought to managing it. I need it to just work.
I don't think it is needed. One small solar panel and a charge controller set at 14.2 volts, and you have a stand alone power for you radio.

Here is a 7 amp 14.2 volt charge controller for $17.
Sunforce 7 Amp Charge Controller : Amazon.com : Automotive

Any solar panel that puts out 16 to 18 volts and 15 to 20 watts will be fine, total investment for panel and the above controller should be under $75 and with the 12 volt 40 a-hr LiFePO4, you will have a stand alone, no hassle power supply for your SSB that is always ready to use no matter what has happened to your boat's other systems.


Or you could just use a regulated power supply rated at 25 amps, 13.8 VDC and plug it in and have your inverter power it like I did many years ago on my Cal 40. If you remember I told you I had a 30 amp switching power supply for the radio and a heavy transformer type PS @ 75 amps for the solid state amp.

This one is more than you need, I'm sure if you search you can find a 13.8 volt 25 amp for just under $100. Problem solved, other than the inefficiencies of running your inverter to take your 24 volt battery bank to 120 VAC just to reduce it to 13.8 VDC.
http://www.amazon.com/Pyramid-PS46KX...+for+ham+radio
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Old 26-01-2013, 14:06   #1526
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I don't think it is needed. One small solar panel and a charge controller set at 14.2 volts, and you have a stand alone power for you radio.

Here is a 7 amp 14.2 volt charge controller for $17.
Sunforce 7 Amp Charge Controller : Amazon.com : Automotive

Any solar panel that puts out 16 to 18 volts and 15 to 20 watts will be fine, total investment for panel and the above controller should be under $75 and with the 12 volt 40 a-hr LiFePO4, you will have a stand alone, no hassle power supply for your SSB that is always ready to use no matter what has happened to your boat's other systems.
This looks like a perfect solution to me.

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Or you could just used a regulated power supply rated at 25 amps, 13.8 VDC and plug it in and have your inverter power it like I did many years ago on my Cal 40. If you remember I told you I had a 30 amp switching power supply for the radio and a heavy transformer type PS @ 75 amps for the solid state amp.

This one is more than you need, I'm sure if you search you can find a 13.8 volt 25 amp for just under $100. Problem solved, other than the inefficiencies of running your inverter to take you 24 volt battery bank to 120 VAC just to reduce it to 13.8 VDC.
Amazon.com: Pyramid PS46KX 35 Amp Power Supply: Electronics
Why go from DC -> AC -> DC? Why not just use a DC-DC converter configured as a LiFePO4 charger?
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Old 26-01-2013, 14:29   #1527
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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This looks like a perfect solution to me.


Why go from DC -> AC -> DC? Why not just use a DC-DC converter configured as a LiFePO4 charger?
Because of RFI that DC to DC converters are prone to produce. But like you, I like my top solution, as it reminds me of the stand alone DC bridge power I always had on the ships I sailed on, but in this case scaled down a lot.


Back to my cells. On pack #2 that I had such an imbalance, I'm pleased to report after the last bottom to top balancing that I preformed in parallel at low current for around 200 hours, these suckers are balanced. Been off the PS for a day and pack voltage is stable as a rock at 14.08 volts and all cells at 3.52 volts. Now pack #1 that was fine, looks shabby in comparison to how tight pack #2 is.
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Old 26-01-2013, 14:30   #1528
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

These 'stand alone's' are available from the supplier of our gear.
EV-Power | LiFePO4 Battery Pack (12V/17Ah PCM)
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Old 26-01-2013, 14:44   #1529
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

BMS only there as 'protection of last resort' below is what EV-Power state:-

FAQ: SBM questions
It is possible to change the voltage levels (thresholds) for the SBM settings?
No, it is not possible. The SBM boards are sold as they are. There is no way for users to change the voltage level settings. (For large quantity orders - 100 pcs and more - it may be possible to design a custom setting version of the SBM boards.)
Is it possible to use the SBM for 12 cells with less cells (e.g. only 8 cells or 9 cells)?
No, it is not possible. The board must be used with the exact number of cells. All cells must be connected; otherwise the board does not work properly. (For large quantity orders - 100 pcs and more - it may be possible to design a SBM with a customer number of cells.)
After deep discharge, how to restore the function of the battery pack?
First of all the SBM should be used only as a „last resort“ protection measure. This means you should monitor the battery pack and stop discharging before the voltage goes too much down. The SBM should not be used to replace such monitoring.
Secondly, if the pack gets discharged deeply and the SBM makes the protection, we suggest recharging the battery pack as soon as possible.
In order to restore the function of the SBM, you need to disconnect the load. After the disconnection, the voltage of the cells may go up and the SBM function should get released.
In some cases, the voltage may get too deep or the cells maybe misbalanced – in such cases you may need to recharge the cells first to restore the function of the SBM.
What about overcharge?
The same rules apply to the overcharge protection. You should stop charging before the SBM cuts-off the battery pack. In case the overcharge protection disconnects the pack, you may need to wait for some time until the voltage of the cells drops down to allow the SBM to reconnect.
Does the SBM monitor the temperature?
Some SBM models monitor the temperature of the high-current component to detect the high current over-discharge. However the SBM boards do not have any temperature sensors to monitor the temperature of the battery pack.
Warning: Please note that that the lithium cells need to be charged regularly if protective electronics like SBM are connected to the cells. The lithium cells need be charged to full before letting them stay unused for longer periods of time.
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Old 26-01-2013, 14:52   #1530
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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These 'stand alone's' are available from the supplier of our gear.
EV-Power | LiFePO4 Battery Pack (12V/17Ah PCM)
How active are you on HF? If you average two hours per day, split 50/50 transmit to receive, a 17 a-hr battery will have the capacity you need. Receive for 1 hour = 18 w-hr, transmit at the duty cycle off SSB will be 100 w-hr, total 118 w-hr / 13.8 = 8.5 a-hr. 17 a-hr X .8 (80% DOD) = 13.6 a-hr used. If your active for more than 2 hours per day, then the 40 a-hr battery.

You have to make sure the amps at your voice peak do not exceed what that small built-in bms can handle. A voice peak could draw 200 watts (if it is a 100 watt RF output radio) / 13.8 = 14.5 amps, so under 1C for the 17 a-hr battery and OK, but not a lot of margin. I would still go with the 40 a-hr, but that is just me, a like to over engineer things.

But one thing will be clear, no voltage sag with the LiFePO4, and no ripple of a power supply, you will have the cleanest SSB signal on the air.
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