Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rating: Thread Rating: 34 votes, 4.82 average. Display Modes
Old 06-02-2013, 23:26   #1951
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

That is why I'm going naked and no BMS. Just a cell logger/alarm, and when needed, I'll balance the cells.
__________________

__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 07-02-2013, 00:28   #1952
Registered User

Join Date: Jul 2011
Location: Australia NSW south coast
Posts: 616
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

It's one of those catch 22 things, if you don't over charge the cells by selecting a cut off voltage close to the cell full voltage, then the active BMS will never function as cell drift is unlikely to occur, so you don't need the activeBMS in the first place. If you select a high cut off voltage relying on the active BMS to save the day, then you are flirting with danger and I can see no gain by doing it, there is no more capacity to be had after 3.4v, full is full, they can't be charged to 110% capacity, so why try to?

T1 Terry
__________________

__________________
T1 Terry is offline   Reply With Quote
Old 07-02-2013, 00:41   #1953
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

Terry,

My usage is different than house bank use, and I want fast charging. The only way I know to fast charge is with the highest acceptable voltage differential, so I charge at 14.8 volts. If the cells are balanced, I'm OK, but if not balanced well, it would be easy to get a high cell voltage alarm.
__________________
Bob
USCG Unlimited Tonnage Open Ocean (CMA)
http://tbuckets.lefora.com/
deckofficer is offline   Reply With Quote
Old 07-02-2013, 04:15   #1954
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Has anyone looked at unit cell chargers. I have a nice digitally controlled SMPS on the CAD system. wondering if it would make a nice multi cell Li charger, with in effect a built in BMS, no wasted balancing energy either. The SMPS, can be paralleled ( it has active current steering), so in theory I can put several together,

The outputs are floating so that handles one aspect.


anyone see any issues here , interested in feedback.

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 07-02-2013, 04:26   #1955
Registered User

Join Date: Jul 2011
Location: Australia NSW south coast
Posts: 616
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by deckofficer View Post
Terry,

My usage is different than house bank use, and I want fast charging. The only way I know to fast charge is with the highest acceptable voltage differential, so I charge at 14.8 volts. If the cells are balanced, I'm OK, but if not balanced well, it would be easy to get a high cell voltage alarm.
Hi Bob,
Have you tried different charging voltages to see just what te difference is? might be different with mains chargers, but the solar regulator doesn't back off till my 720Ah bank reaches 98%, it takes another 20 mins or so for the last 2 percent. witha 100Ah battery, that's only 2 Ah, would that be critical?

T1 Terry
__________________
T1 Terry is offline   Reply With Quote
Old 07-02-2013, 05:12   #1956
Registered User
 
ebaugh's Avatar

Join Date: Dec 2011
Location: On the boat
Boat: DeFever 44
Posts: 525
Quote:
Originally Posted by goboatingnow View Post
Has anyone looked at unit cell chargers. I have a nice digitally controlled SMPS on the CAD system. wondering if it would make a nice multi cell Li charger, with in effect a built in BMS, no wasted balancing energy either. The SMPS, can be paralleled ( it has active current steering), so in theory I can put several together,

The outputs are floating so that handles one aspect.

anyone see any issues here , interested in feedback.

Dave
I'm assuming you are thinking of 1 cell per charger, only paralleled for additional charging current if needed. It would work fine.

But it would need to be the only charging source to solve the high voltage cutoff function of a BMS, and would not cover the low voltage side.

Unless you had very precise outputs, I don't think it would handle balancing nearly as well as a series connected for partial charges. Or if there was firmware to vary the output of each charger keeping the voltages balanced, at least for the last 20% of charge.
__________________
ebaugh is offline   Reply With Quote
Old 07-02-2013, 05:18   #1957
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by ebaugh View Post
I'm assuming you are thinking of 1 cell per charger, only paralleled for additional charging current if needed. It would work fine.

But it would need to be the only charging source to solve the high voltage cutoff function of a BMS, and would not cover the low voltage side.

Unless you had very precise outputs, I don't think it would handle balancing nearly as well as a series connected for partial charges. Or if there was firmware to vary the output of each charger keeping the voltages balanced, at least for the last 20% of charge.

Yes thats the building block approach. I was thinking its easy to add in LVC and HVC disconnect circuitry, really only MOSFets relay drivers as all the rest is onboard anyway.

I dont understand your comments re balancing, Each charger would stop at the predetermined voltage point. Since the voltage set points are the same each cell would automatically be balanced ( well balanced in the same way that in circuit BMS balance them). Only with this method there is no need to have shunt resistors, Shunt resistors are only there in BMS systems becuase the BMS cannot regulate the charger.
__________________
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 07-02-2013, 05:24   #1958
Registered User

Join Date: Jul 2011
Location: Australia NSW south coast
Posts: 616
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

On the EV DIY forum there was a member who developed a single cell charging system for his 48v pulling tractor. It was not a great sucess, the mini boards he used were moisture sensitive and he had many failures. His co worker/builder went a different way and developed boards to hold 4 Junsi cell loggers that could be coupled to another board and so on to accomidate large series string battery packs, this idea seems to have been much more successful but I haven't been following it for a while now, there is a limit to how many forums you can stay active on and still get any work done :lol:
Another EV person developed a charging system using mini wallwarts with circuitry to limit max voltage to 3.7v and he was using this to finish off the cell charging on his EV ute, but he pulled it all out for some reason, he didn't explain why though.

T1 Terry
__________________
T1 Terry is offline   Reply With Quote
Old 07-02-2013, 05:33   #1959
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by T1 Terry View Post
On the EV DIY forum there was a member who developed a single cell charging system for his 48v pulling tractor. It was not a great sucess, the mini boards he used were moisture sensitive and he had many failures. His co worker/builder went a different way and developed boards to hold 4 Junsi cell loggers that could be coupled to another board and so on to accomidate large series string battery packs, this idea seems to have been much more successful but I haven't been following it for a while now, there is a limit to how many forums you can stay active on and still get any work done :lol:
Another EV person developed a charging system using mini wallwarts with circuitry to limit max voltage to 3.7v and he was using this to finish off the cell charging on his EV ute, but he pulled it all out for some reason, he didn't explain why though.

T1 Terry
I agree that home brew solutions have problems. But redundant parallel charging sources is a far better way technically to achieve high current solutions. Its not done in comsumer electronics because its more expensive ( all that redundant parallel control electronics for example). Its quite common in larger telecoms setups where long life and graduated failure is required

Leaving aside designing the environmental to suit the environment. ( some of my older gear is in rock crushers!!), I was interested in the pros and cons and any technical gotchas. To me it seems a far more elegant idea Then in effect putting in monitoring systems to cope with the problems of large single charger systems.

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 07-02-2013, 05:34   #1960
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
there is a limit to how many forums you can stay active on and still get any work done :lol
aint that the truth.

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 07-02-2013, 06:19   #1961
Registered User
 
ebaugh's Avatar

Join Date: Dec 2011
Location: On the boat
Boat: DeFever 44
Posts: 525
Quote:
Originally Posted by goboatingnow View Post

Yes thats the building block approach. I was thinking its easy to add in LVC and HVC disconnect circuitry, really only MOSFets relay drivers as all the rest is onboard anyway.

I dont understand your comments re balancing, Each charger would stop at the predetermined voltage point. Since the voltage set points are the same each cell would automatically be balanced ( well balanced in the same way that in circuit BMS balance them). Only with this method there is no need to have shunt resistors, Shunt resistors are only there in BMS systems becuase the BMS cannot regulate the charger.
If you fully charge every time, it would be balanced. But if you stop charging before reaching the end of charge, the balance is only as good as the current regulation of each charger. If one puts out 5 amps and the one next to it 6 amps, then stop charge early, it's no longer balanced. So long as you don't do this every cycle, it won't hurt anything. Or have very precise charge control, but I suspect that would require fancy current measurement for every cell. At low current charging, not a big deal, but at 100A it gets a bit harder to be precise. It's a small point. But compounds on multiple partial charges, which is almost all I do. I charge until the admiral is done in the galley and I can turn off the generator.

BMS is a broad term, fully implemented it means HVC, LVC, Balancing, Charger Control, and Temperature cutoff. Maybe some stuff I forgot. But for what we are doing its basically HVC and LVC.

The biggest point related to balancing is its not required beyond the initial charge and perhaps occasionally as a maintenance item. Even with large serially connected banks > 200V, the EV guys are not finding the cells drifting out of the initial balance after installation with no balancing in their chargers.

Im not sure what your envisioned application is, but for marine there are almost always multiple charging sources. Properly configured and installed, no charging source should ever hit HVC, but the BMS is a fail safe device. It means there must be multiple failures to cause overcharge since both the charging source and the BMS must both fail to reach that condition. So for marine, I like the separation of function.

However your concept would greatly assist installation since there would be no need to balance prior to install. Just hook up and run with it. So one charger like this would greatly simplify installation.
__________________
ebaugh is offline   Reply With Quote
Old 07-02-2013, 06:31   #1962
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
If you fully charge every time, it would be balanced. But if you stop charging before reaching the end of charge, the balance is only as good as the current regulation of each charger. If one puts out 5 amps and the one next to it 6 amps, then stop charge early, it's no longer balanced. So long as you don't do this every cycle, it won't hurt anything. Or have very precise charge control, but I suspect that would require fancy current measurement for every cell. At low current charging, not a big deal, but at 100A it gets a bit harder to be precise. It's a small point. But compounds on multiple partial charges, which is almost all I do. I charge until the admiral is done in the galley and I can turn off the generator.

Maybe Im being dense here, It can happen staring at a CAD screen. ( its not been a productive morning). All Li chargers user a voltage cutoff, you really dont have anything else. If you set that voltage at or below the knee, then the current is zero at the cutoff voltage , if you set it above the knee, you fast charge the cell potentially to destruction since there no charge acceptance rate like LA.

If you dont complete the charge cycle, you are just in the same position as a series charger, each cell maybe at a different SOC, who cares.

I dont see what the current has to do with balancing. When we balance cells , what we are trying to do is SOC balance, what in practice we are doing is voltage balance. All that current shunt top balancers do is shunt charging current when the cell terminal voltage reaches the set point, In reality all its doing is trying to prevent the whole pack charger from continuing to charge that cell by diverting charge current. It only really works if the assumption is your not fast charging above the knee, other wise potentially the BMS could have to divert large currents into a resistor!. There have been lots of BMS failures using this method where the set point was set to high and high current chargers pumped way too much charging current into the shunt resistors.

In fact I cant see how you could use small scale shunt resistors in a potentially 40-100 amp charging situation , too easy to fry the BMS.

Mine is just a "gedanken" at the moment , I think it has far more advantages over the single charger and separate BMS, but its a good bit more expensive. ( not to me I'll just build them all, 10 SMPS arnt much more expensive then one).

Thanks so far

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 07-02-2013, 06:40   #1963
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
I dont see what the current has to do with balancing. When we balance cells , what we are trying to do is SOC balance, what in practice we are doing is voltage balance. All that current shunt top balancers do is shunt charging current when the cell terminal voltage reaches the set point, In reality all its doing is trying to prevent the whole pack charger from continuing to charge that cell by diverting charge current. It only really works if the assumption is your not fast charging above the knee, other wise potentially the BMS could have to divert large currents into a resistor!. There have been lots of BMS failures using this method where the set point was set to high and high current chargers pumped way too much charging current into the shunt resistors.
Maybe some BMSs do it differently of course, I havent studied the literature extensively

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 07-02-2013, 06:56   #1964
Registered User
 
mbianka's Avatar

Join Date: Mar 2008
Posts: 2,125
Images: 1
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by goboatingnow View Post
Has anyone looked at unit cell chargers. I have a nice digitally controlled SMPS on the CAD system. wondering if it would make a nice multi cell Li charger, with in effect a built in BMS, no wasted balancing energy either. The SMPS, can be paralleled ( it has active current steering), so in theory I can put several together,

The outputs are floating so that handles one aspect.


anyone see any issues here , interested in feedback.

Dave
Dave:

This is how I charge my 48 volt AGM propulsion bank with a Dual Pro Quad charger. It works very well in keeping my AGM LA bank balanced. I start with a series bulk charge using my 48 volt Zivan NG-1 and before it reaches full charge I switch to the Dual pro quad which tops off each of the individual four batteries separately. Don't know see why such a system would not work with Lith's. Except if I had my 48 volt bank made up of lith's that would be a lot of individual chargers. Maybe a hefty main power supply with individual charge regulators for each cell might be the way to go. From what I'm seeing the BMS units can not shunt that much current but, individual chargers on each cell could provide more to each cell resulting in a faster charge for each cell and the battery bank as a whole. Unless I am missing something?
__________________
Capt. Mike
mbianka is offline   Reply With Quote
Old 07-02-2013, 07:13   #1965
Registered User

Join Date: Mar 2010
Location: Tampa FL
Posts: 111
Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by T1 Terry View Post
Sounds great, but the associated bits are completely ignored.
(1) When the cell goes over 3.45v the electrolyte starts to heat up...
(2) When the load from the resistor is applied to the circuit the voltage within the circuit drops, not enough to turn the resistor off but enough to effect the complete shut down the charger voltage point, so the shut down point moves up from 3.8v to around 4v, now lots of heat is being generated inside the cell as well as by the board itself

Add these two things together and then bear in mind, the transistors that switch the resistor on and off are sensitive to heat, if they get too hot they punch through, now the resistor is on full time and full tilt. The voltage finally climbs high enough for the shut down alarm to trigger...

Wouldn't a better system be to simply turn the charger off for a while when a cell reaches 3.6v and give the operator a display of the voltages in each cell so they can decide if it's a major issue or not?

T1 Terry
Oh boy, you really turning this into "science" fiction Terry. Both points are completely baseless, in both theory and practice. None of this stuff actually happens in real world in real scenarios. I suggest to go back to EE 101, thermodynamics 101, etc. before you continue to fill this forum with "information".

I have 100s of customers using our BMS over past 3 years and NONE of the things you so passionately describe actually happen in real life. How do you explain that?
__________________

__________________
electric1 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 04:54.


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.