Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rating: Thread Rating: 39 votes, 4.85 average. Display Modes
Old 20-12-2012, 07:02   #781
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 257
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by CharlieJ View Post
OK. Your opinion; my opinion.
It's not an opinion---8 watts vs zero is a fact. By mentioning the shunt trip breaker, I am pointing out the existence of different, possibly superior disconnect technology. Let's leave it at that.
diugo is offline   Reply With Quote
Old 20-12-2012, 07:02   #782
Nearly an old salt
 
goboatingnow's Avatar

Join Date: Jun 2009
Location: Lefkas Marina ,Greece
Boat: Bavaria 36
Posts: 22,801
Images: 3
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
#777
Dave-In fact the overcurrent protection device (OCPD), fuse or circuit breaker, has an ampere interrupt capacity (AIC) rating that is based on the short circuit current of the source.

The AIC is the maximum current that can be:
> interrupted by a circuit breaker that will leave the circuit breaker functional or
> interrupted by a fuse with the fuse and fuse holder remaining physically intact; i.e., not blown to bits!
ogh I understand all you are saying,

But what I am saying , is that if there is a fuse & breaker combination , then there is no need to rate the breaker at the interrupt capacity. The primary purpose of a BMS driven breaker is to disconnect normal loads from the battery in the event of a LVE. A suitablely rated fuse ( with a very high interrupt capability) should always be installed in any Li battery system given the potential short circuit currents. The breaker in this case is not there to perform an emergency short circuit disconnect. ( Ie its not acting as a "overcurrent protection device " device) This removes the need for a very heavy duty breaker.

Dave
__________________
Interested in smart boat technology, networking and all things tech
goboatingnow is offline   Reply With Quote
Old 20-12-2012, 07:21   #783
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 257
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

All circuit breakers have a high interrupt capability already built in, to handle a direct short circuit situation. To be specific, the 100A shunt trip breaker I'm looking at is rated at something like 10,000 amps. Now, that may seem adequate---except that 10kA is only 14C to a 700Ah bank, and LFPs have been known to produce 20C or even more, when shorted. Therefore a "catastrophe fuse"---one with an interrupt rating much higher than 10kA---would also be prudent. The nominal fuse rating should be based on the ampacity of the interconnects and main lines (300A in my case).
diugo is offline   Reply With Quote
Old 20-12-2012, 07:28   #784
Nearly an old salt
 
goboatingnow's Avatar

Join Date: Jun 2009
Location: Lefkas Marina ,Greece
Boat: Bavaria 36
Posts: 22,801
Images: 3
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Again, I think there is a fundemental question about the purpose of LVE monitoring. IN my technical opinion ( and I have designed a couple of special purpose BMSs in the past), is that the disconnect device is purely to disconnect normal loads. The breaker ( relay) should be rated conservatively for this option.

That is very different from short circuit protection. for Li a fuse is the only practical method and one with as high an interrupt capacity as possible.

to put in in reverse, I don't believe LVE monitoring was EVER intended to act as short circuit protection.

Dave
__________________
Interested in smart boat technology, networking and all things tech
goboatingnow is offline   Reply With Quote
Old 20-12-2012, 08:09   #785
Commercial Member
 
CharlieJ's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: St. Petersburg, FL
Boat: Gulfstar Long Range Trawler; 53'; BearBoat
Posts: 1,524
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
to put in in reverse, I don't believe LVE monitoring was EVER intended to act as short circuit protection.
My thought, exactly.
__________________
Charlie Johnson
ABYC Master Technician
JTB Marine Corporation
"The Devil is in the details and so is salvation."
CharlieJ is offline   Reply With Quote
Old 20-12-2012, 08:20   #786
Commercial Member
 
CharlieJ's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: St. Petersburg, FL
Boat: Gulfstar Long Range Trawler; 53'; BearBoat
Posts: 1,524
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
But what I am saying , is that if there is a fuse & breaker combination , then there is no need to rate the breaker at the interrupt capacity. The primary purpose of a BMS driven breaker is to disconnect normal loads from the battery in the event of a LVE. A suitablely rated fuse ( with a very high interrupt capability) should always be installed in any Li battery system given the potential short circuit currents. The breaker in this case is not there to perform an emergency short circuit disconnect. ( Ie its not acting as a "overcurrent protection device " device) This removes the need for a very heavy duty breaker.
Got it. In my designs, I have chosen a high continuous current contactor, as mentioned above, as the control element. It is easy to interface with the output from the BMS. Short circuit protection is provided by a Class T fuse with a 20,000A AIC.

Unfortunately, ABYC Standard E-11 has this requirement:

Quote:
11.10.1.2.3 For batteries or battery banks with a CCA rating greater than 2200 CCA, or 500 amp hours, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating at least as great as the battery
manufacturer’s short circuit rating or 100 times the battery’s nominal amp hour (Ah) rating.
It is unfortunate because many battery manufacturers do not provide the short circuit information so I am forced to the "100 x" requirement and the Class T fuse would only be "legal" for a 200Ahr bank!!
__________________
Charlie Johnson
ABYC Master Technician
JTB Marine Corporation
"The Devil is in the details and so is salvation."
CharlieJ is offline   Reply With Quote
Old 20-12-2012, 08:34   #787
Registered User

Join Date: Dec 2012
Posts: 508
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by CharlieJ View Post
It is unfortunate because many battery manufacturers do not provide the short circuit information so I am forced to the "100 x" requirement and the Class T fuse would only be "legal" for a 200Ahr bank!!
Has anyone found the short circuit rating for Winston LFP batteries?

Does the 11.10.1.2.3 requirement even make sense for batteries wired in series? What is the probability that four or more batteries wired in series could short circuit? I guess a lot lower than the probability of the boat being hit by a meteor.
mcarling is offline   Reply With Quote
Old 20-12-2012, 08:40   #788
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 257
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Littlefuse LDC fuses are interrupt rated for 50,000 amps DC. This should be adequate for banks up to 500Ah. For larger banks, one way to comply with the reg might be to limit the maximum cell size to 500Ah---and then use parallel strings of cells in series, each string with its own LDC fuse.
diugo is offline   Reply With Quote
Old 20-12-2012, 09:22   #789
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 3,731
Images: 4
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

All this high amp stuff has me confused. On my next pack I was going to fuse for short circuit protection a series string. I was going to pick a rating around 50% higher than peak combined loads. The 48 volt bank will be used for propulsion and inverter. Max propulsion loads around 25KW, inverter 9KW, so I had planned to use a 1,000 amp fuse. Am I wrong?
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
https://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 20-12-2012, 09:31   #790
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 257
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Bob, for simple overload protection, the nominal size of the fuse (1000A in your case) should really be based on the ampacity (currently handling capability) of the conductors you plan to use---which in turn should be chosen to supply your maximum expected loads without significant voltage drop.

For true short circuit protection, the interrupt rating of the fuse (much higher than its nominal size) comes into play. It is a function only of the battery voltage divided by the resistance of all of the conductors and connections completing the short circuit.
diugo is offline   Reply With Quote
Old 20-12-2012, 09:47   #791
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 3,731
Images: 4
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Doug,

I will size all wire and connections for the loads. The main bank will be (16) 1000 a-hr cells in series. The most the inverter could draw at its surge rating is 8800 watts or 173 amps. (2) propulsion 12 Kw motors, 24000 watts or 470 amps and a DC-DC converter for 12 volts at 600 watts or 12 amps, for a total max amp draw (would probably never happen) of 655 amps.

What should I fuse the bank for? This isn't BMS, just safety fuse for short circuit protection.
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
https://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 20-12-2012, 10:15   #792
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 257
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Bob, your 48V 1000Ah bank is a major powerhouse that has the potential to liquify wiring if the wiring isn't sized appropriately. The good news is, your 655 amps of load requires thick wires simply to operate at all. The bad news is, those thick wires have very little resistance---probably well under a millohm (0.001 ohm).

Divide 48 volts by 0.001 and you get 48,000---which is already very close to the DC interrupt rating of the newest Class LDC fuses (50,000A).

In other words, even this fuse may explode or melt before simply "blowing", because your bank is so powerful. From an underwriter's standpoint, that's not acceptable. From a practical standpoint, you'll need to take extra measures that ensure that your vessel and passengers do not suffer if the fuse explodes or melts.

As far as the fuse's nominal rating goes, if you use a 1000A fuse, then the wiring needs to be properly sized to carry 1000A. So it may be more practical to size the wiring for 700A and then use a 700A Class LDC fuse.
diugo is offline   Reply With Quote
Old 20-12-2012, 10:29   #793
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 3,731
Images: 4
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Thanks Doug. Only the series buss bars will ever see that load. Each system will have its own dedicated cabling off of the bank, all very short runs, as both motor controllers and inverter will share the same space.
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
https://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 20-12-2012, 10:47   #794
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 257
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Meanwhile, back at the ranch, I noticed that Balqon's $99 160Ah clearance specials have been "out of stock" for a couple of days now. I didn't want them shipped during the pre-Christmas crunch, so I held off on ordering them!

What do you suppose the likelihood is of them finding some more?
diugo is offline   Reply With Quote
Old 20-12-2012, 10:53   #795
Registered User

Join Date: Dec 2012
Posts: 508
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by diugo View Post
What do you suppose the likelihood is of them finding some more?
Somewhere between slim and none.

My wildly speculative guess is that this clearance sale is consequence of deckofficer having noticed that they had shipped him old product.
mcarling is offline   Reply With Quote
Reply

Tags
battery, grass, lifepo4, LiFePO4 Batteries, sailing

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Advertise Here


All times are GMT -7. The time now is 04:03.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.