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Old 30-12-2012, 10:33   #871

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

"All circuit breakers have a high interrupt capability already built in,"

Not true. Conventional breakers found in marine panels have about a 3000A rating (3300? 3500?) at which point may will arc over and fuse. They are expressly not suitable for use on batteries as even a Group24 SLI can throw higher amperage into a crowbar short.

The next step up are rated around 5000 amps and may cost you $75-100 per breaker to get that extra protection.

I don't know what a "shunt breaker" is or where you find 10kA ratings, but conventional "circuit breakers" are simply not rated that high. That's why batteries are normally fused, not put on breakers.
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Old 30-12-2012, 10:36   #872
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

"Bob" as a promotional code, I like it.

As to banding, I'm only going by what I've been told and that is if your charge and discharges are in the 1~3 C range it will help keep the cells from bulging. Since I charge at 0.5C (50 amp) and discharge at 0.3C, I didn't need banding for use on the kayak but since these are so lite I will probably use them for portable power on a 2000 watt inverter, and at full load would be 1.6C.
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Old 30-12-2012, 10:37   #873
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Mind that the breaker interrupt rating is for DC. Often much lower due to the continuous arcing.
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Old 30-12-2012, 10:39   #874
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Can you point me to the Shunt Trip Circuit breaker you are considering ?
The particular one I'm looking at is a Square D QOU21001042. It has two 100A breakers which come ganged, but could be easily separated to control two independent circuits (eg loads and charge sources). I also like that it has standalone mounting tabs, which eliminates the need for a box. And, most importantly, its shunt trip works with 12VDC@5A---a lot of other shunt trips seem to require 120VAC (which is not acceptable).

An RV friend wants to sell me his used one for $35, which is a great price IMHO.
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Old 30-12-2012, 10:48   #875
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by hellosailor View Post
"All circuit breakers have a high interrupt capability already built in,"

Not true. Conventional breakers found in marine panels have about a 3000A rating (3300? 3500?) at which point may will arc over and fuse. They are expressly not suitable for use on batteries as even a Group24 SLI can throw higher amperage into a crowbar short.

The next step up are rated around 5000 amps and may cost you $75-100 per breaker to get that extra protection.

I don't know what a "shunt breaker" is or where you find 10kA ratings, but conventional "circuit breakers" are simply not rated that high.
I said "all breakers have a HIGH interrupt capability", which certainly IS true---as I meant "high" in comparison to the nominal breaker rating. I never suggested that all breakers have a 10kA AIR.

I also later said that a fuse should be employed with LFPs, as clearly even 10kA would be inadequate in the event of a direct short.

So gimme a break!

PS. Upon further research you were right about one thing---the particular 10kA breaker I was referring to, is only rated to 5kA at 60VDC.
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Old 30-12-2012, 11:01   #876

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

OK, take a break. Coffee's on me.<G>

That breaker you mention does have a high rating--also a retail price over $450. Folks are offering them at $250 "out of stock" or $100 "used, refurbished" which really is not the way I'd want to buy a breaker, unless I knew more detailed information about how it was "refurbished".

I'm also curious as to why LiFePo cells need banding to prevent bulging in normal use. If bulging is an issue, why aren't the cases strong enough to deal with it? Or, is banding really not "optional" but something that's just not talked abut a lot up front?
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Old 30-12-2012, 11:13   #877
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Another question is: Might it be better to let them bulge if they need to? Since the quantity of chemicals inside is fixed, preventing the batteries from bulging would result in higher internal temperatures.
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Old 30-12-2012, 11:13   #878
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Thanks, good coffee

Re used breakers, I figure if I'm buying used batteries from Balqon, might as well get matching used breakers to go with 'em---the series fuse will be new, however. And I will be thoroughly testing the shunt trip functionality.

Re banding, the case is designed for the manufacturer's "standard charge" current of 0.5C, but many users---EVers in particular---like to push it to 3C.
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Old 30-12-2012, 11:14   #879
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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If your objective is just to hold them together, cable ties would be easier and cleaner. I've seen them up to 1.5 meters (about 60 inches) in length. If you're concerned about the possibility of bulging, then neither strapping tape nor cable ties will help.
I plan to use aluminum end caps, 1/4" thick, and drilled & tapped aluminum round stock to hold the cells together. It will be similar to the cell laying on its side in this pic. Sorry I did not have a better one..

Should cost me about $15.00 - $20.00 in materials...
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Old 30-12-2012, 11:18   #880
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Normal use for a lead acid would be 0.1C charge, <1.0 C discharge, and the Winston cells would not need banding for the same parameters. If you plan to flex the muscles (pun intended) and charge at 1.0C and discharge at 3.0C, then the experts recommend banding.
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Old 30-12-2012, 11:18   #881
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by hellosailor View Post
OK, take a break. Coffee's on me.<G>

That breaker you mention does have a high rating--also a retail price over $450. Folks are offering them at $250 "out of stock" or $100 "used, refurbished" which really is not the way I'd want to buy a breaker, unless I knew more detailed information about how it was "refurbished".

I'm also curious as to why LiFePo cells need banding to prevent bulging in normal use. If bulging is an issue, why aren't the cases strong enough to deal with it? Or, is banding really not "optional" but something that's just not talked abut a lot up front?
Industrial cells (for forklifts etc.) have flimsy cases as well, they are fit tightly into metal boxes and often need to be lubricated to get them in.

Why waste space and material on a hefty case if the cells will be packed together anyway ?
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Old 30-12-2012, 12:14   #882
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I get the feeling that the banding is not needed for the typical boat' house bank usage. It is designed to keep the cells from bulging in high charge-discharge applications. But of many of us, we won't ever be charging or discharging them enough to introduce bulging.


Now if you have a charging source that can do 1C+ continuous, then by all means band them up. The banding also would make them easier to secure on the boat. Mine are un-banded, but are in boxes with secured tops, and rubber blocks to take up the extra space (originally made for other battery sizes).
If I am wrong, please contradict, as I said this is a conclusion I have come to, I have never read it anywhere that I remember.

Chris
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Old 30-12-2012, 12:28   #883
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

To me, swelling is indicative of a bad charging condition---either excessive current, or overvoltage---and banding hides this. The swelling occurs as a result of the electrolyte breaking down and generating gas that obviously wants to expand rapidly---and banding prevents this.

So the only banding I'll be doing will be with cable ties---simply to prevent excessive motion of the cells during transit. I'll be using flexible braid for the interconnects, and it might get torn if the cells aren't secured relative to each other.
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Old 30-12-2012, 13:01   #884
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I get the feeling that the banding is not needed for the typical boat' house bank usage. It is designed to keep the cells from bulging in high charge-discharge applications. But of many of us, we won't ever be charging or discharging them enough to introduce bulging.


Now if you have a charging source that can do 1C+ continuous, then by all means band them up. The banding also would make them easier to secure on the boat. Mine are un-banded, but are in boxes with secured tops, and rubber blocks to take up the extra space (originally made for other battery sizes).
If I am wrong, please contradict, as I said this is a conclusion I have come to, I have never read it anywhere that I remember.

Chris
I believe you are correct. Still, I want a professional looking pack and the end caps of aluminum will also support a polycarbonate cover to protect against shorting etc.. The aluminum will also act as a heat sink to move heat away from the end cells. Not that this is necessary on a sailboat but it certainly can't hurt. I have also thought of using G10, which I have a lot of kicking around the shop.. I am using 1/4" aluminum stock for the end caps so I can drill and tap into it for L brackets for mounting to the vessel. It is more to hold my cells together, create a mounting method, and mount for the polycarb cover than to prevent bulging....

I am still waiting on the ABYC to see whether or not they want to see these batteries in all metal cases. There was talk of this in PTC from what I understand but the standard remains un-changed from July 2011.

It is still possible I guess for a cell to get out of whack and over charge if not paying attention to BMS alarms, and if not installed with and HVE disconnect you could potentially run the risk of bulging a cell...?
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Old 30-12-2012, 13:10   #885
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I really like the idea of a plastic cover over the battery terminals, but why polycarbonate? Why not a softer plastic such as PVC or HDPE?
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