Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rating: Thread Rating: 34 votes, 4.82 average. Display Modes
Old 24-01-2013, 15:07   #1426
Registered User
 
NahanniV's Avatar

Join Date: Mar 2011
Location: On the Boat
Boat: Finnsailer 38
Posts: 1,027
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by downunder View Post
What did you do the chart with? Thanks
I used a program called Logview: LogView Startseite

Connected to a PowerLog 6S (similar to CellLog 8S).
__________________

__________________
NahanniV is offline   Reply With Quote
Old 24-01-2013, 17:15   #1427
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 261
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by deckofficer View Post
I'm just letting voltage differential determine charging current when the cells are in parallel for balancing. I set the PS at 3.7 volts on a 80~90% DOD cells and it starts out charging at about 4.5 amps. 3 days later as cell voltage is coming up, it now is only putting 1.8 amps into the cells.
Now I see your situation---0.03C @ 400Ah is 12 amps. So technically you should have stopped charging before you began!

What is the parallel cell voltage right now at 1.8A?
__________________

__________________
diugo is offline   Reply With Quote
Old 24-01-2013, 17:18   #1428
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 4,197
Images: 4
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by diugo View Post
Now I see your situation---0.03C @ 400Ah is 12 amps. So technically you should have stopped charging before you began!

What is the parallel cell voltage right now at 1.8A?
It has dropped to 1.6 amps and cells are 3.46, 3.46, 3.46, 3.47
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 24-01-2013, 17:22   #1429
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 261
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by deckofficer View Post
It has dropped to 1.6 amps and cells are 3.46, 3.46, 3.46, 3.47
Are you conducting a test with them right now? If not, could you take one cell out of the parallel pack, put just it on your 3.7V PS, and report the cell's voltage and current?
__________________
diugo is offline   Reply With Quote
Old 24-01-2013, 17:23   #1430
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Isn't C/30 regarded as the cutoff point ?


Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 24-01-2013, 17:30   #1431
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 261
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by goboatingnow View Post
Isn't C/30 regarded as the cutoff point ?
In standard CCCV charging, yes. But Bob is using only CV. That's why I am intrigued. Bob, if you turn off the charger, what does the parallel voltage fall back to?
__________________
diugo is offline   Reply With Quote
Old 24-01-2013, 17:36   #1432
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 4,197
Images: 4
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

The charge current is determined by voltage differential, so one cell or 4 in parallel, the PS at this voltage will only push 1.6 amps. This is why my 50 amp charger programmed for LiFePO4 charges at 14.8 volts, as this is the fastest way to charge with a delayed taper, than that of a lower voltage. If you have errant cells, then having the charger cut out at a lower voltage would insure no cell jumps above 4.0 volts, but the voltage taper would start sooner and the time to fully charge would be longer. That is why I balanced so many times because in the beginning one cell would jump above 4.0 volts before the others even reached 3.4 volts and on discharge a different cell dropped to 2.5 volts before the others had dropped to 3.3 volts. Now this bank discharges and charges with very tight voltages among the cells, taking out the worry of using the 50 amp charger.
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 24-01-2013, 17:41   #1433
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 4,197
Images: 4
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by diugo View Post
In standard CCCV charging, yes. But Bob is using only CV. That's why I am intrigued. Bob, if you turn off the charger, what does the parallel voltage fall back to?
It doesn't fall back, stayed at 3.46 volts.
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 24-01-2013, 17:43   #1434
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 261
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Bob, I think the mistake is the 3.7V. You're charging along the asymptote, so I would set the PS no higher than 3.45V.

I think you are done charging. Especially if you consider that the PS has already returned 220Ah to the cells---(4.5+1.6)/2 * 24 * 3.
__________________
diugo is offline   Reply With Quote
Old 24-01-2013, 17:54   #1435
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Fundementally this isn't a good way to charge Li. There must be active cutoff , then you can charge CV followed by CV. I would have thought that using CV unless you set the voltage quite high , ( and Li can handle that once you have fast cutoff. ) nothing would really flow into the cells., ie the charging currents would turn put to be very low

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 24-01-2013, 18:06   #1436
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 4,197
Images: 4
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

This is the last balancing cycle for this pack. The last cycle I did the same, and after it the voltages were tight to each other. They are even tighter this time.
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 24-01-2013, 18:12   #1437
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 261
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by goboatingnow View Post
Fundementally this isn't a good way to charge Li. There must be active cutoff , then you can charge CV followed by CV. I would have thought that using CV unless you set the voltage quite high , ( and Li can handle that once you have fast cutoff. ) nothing would really flow into the cells., ie the charging currents would turn put to be very low
Obviously there is flow, 1.6 amps' worth. I think it comes down to a question of energy. Energy removed and returned. If you know you took 100Ah out of a battery, CV can be used to return it---but only if you keep good track of the amp-hours in. Adjusted for Peukert for good measure. Probably why CV isn't generally used!
__________________
diugo is offline   Reply With Quote
Old 24-01-2013, 21:00   #1438
Registered User
 
deckofficer's Avatar

Join Date: Feb 2011
Location: Northern and Southern California
Boat: too many
Posts: 4,197
Images: 4
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

The reason I picked 3.7 volts is that is what each cell would be (balanced) at the end of the fast 50 amp charge.
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 24-01-2013, 21:36   #1439
Registered User
 
diugo's Avatar

Join Date: Dec 2012
Location: Yuma, AZ
Boat: USS Asymptote
Posts: 261
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

3.7V is a good educated guess for 50 amps. The correct value is the sum of the cell's fully charged voltage (3.45V) and the product of the cell's internal resistance (3 millohms) and the charge current: 3.45 + (0.003 * 50) = 3.60V. Things are quite different with your PS charging four cells in parallel. First, the internal resistance is divided by four. Second, the charge current is much less. The correct voltage here is 3.45 + (0.0075 * 1.6) = 3.462V.
__________________
diugo is offline   Reply With Quote
Old 24-01-2013, 21:43   #1440
Registered User
 
NahanniV's Avatar

Join Date: Mar 2011
Location: On the Boat
Boat: Finnsailer 38
Posts: 1,027
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by diugo View Post
...the cell's fully charged voltage (3.45V)
Where did you get 3.45V from ?
__________________

__________________
NahanniV is offline   Reply With Quote
Reply

Tags
battery, lifepo4, LiFePO4 Batteries, sailing

Thread Tools
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


Similar Threads
Thread Thread Starter Forum Replies Last Post
LiFePO4 Batteries - Okay Tear Me Apart ;-) jallum Electrical: Batteries, Generators & Solar 395 03-12-2015 13:19
Voltage drop under load, amps read 99% ?? VVD Electrical: Batteries, Generators & Solar 25 28-06-2011 16:25


Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 04:49.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.