[corbin]

Hi all,
I've read various places of people doing an initial charge of their batteries in parallel before wiring them up in series. I have 48 cells that I will be running in series for a total of 154 (48*3.2) nominal volts.

I have the Manzanita Micro PFC30 and will be using an Elithium BMS.

My questions are:

Is an initial charge in parallel necessary?
Or will, a initial charge with a BMS attached also properly balance the cells?

If I have to do an initial charge, can I use the PFC30, or will I need another charger? If I need another charger, any recommendations? What wiring to people use for this initial charge? (i.e.: 10 or 12 gauge common automotive wire?)

Any pointers to external documentation or websites are greatly appreciated. Thanks!

corbin

 

[frodus]

Is an initial charge in parallel necessary?
Or will, a initial charge with a BMS attached also properly balance the cells?

Always equalize the pack before you install. This ensures that the batteries are all at the same voltage before you install. If you install and then let the balancers work, it'l take quite a few charges to get all of the batteries completely balanced. Yes it'l work, but it'l take a long time to become balanced. If you start balanced, the BMS won't have to work as hard, if at all, to keep the batteries in balance.

If I have to do an initial charge, can I use the PFC30, or will I need another charger? If I need another charger, any recommendations? What wiring to people use for this initial charge? (i.e.: 10 or 12 gauge common automotive wire?)

no you cannot use the manzanita charger. If you parallel all batteries, the voltage will go between 3 and 4V or so. The PFC 30 goes 12 to 450VDC output. You will need a single cell charger. This can be a very low current charger. Batteryspace.com has several:
http://www.batteryspace.com/smartchargerforlifepo4batterypacks.aspx

This one is on sale for $20:
http://www.batteryspace.com/Smart-C...1-Cell-LiFePO4-Rechargeable-Battery-Pack.aspx

Just parallel all batteries together (or in groups) and plug this in to charge. Might want to let them sit. Then after the charger is done, let the batteries sit for a night or two to let the charges equalize.

Any pointers to external documentation or websites are greatly appreciated. Thanks!

www.manzanitamicro.com
www.elithion.com

 

[corbin]

Thanks Travis -- this is helpful, but still leaves me with questions.

You will need a single cell charger. This can be a very low current charger. Batteryspace.com has several:
http://www.batteryspace.com/smartchargerforlifepo4batterypacks.aspx

Those chargers are 3.2v chargers with 3.0v nominal; if I understand right, that isn't correct for Thundersky batteries, which are 3.2v nominal, and 3.8max (recommended). They also have a range up to 163ah; I have the 200ah cells. Will that be a problem?

www.manzanitamicro.com
www.elithion.com

[/QUOTE]
Thanks -- I obviously have seen those sites; I'm curious about some specific pages or documentation that recommends where and how to do an initial charge.

corbin

 

[frodus]

Those chargers are 3.2v chargers with 3.0v nominal; if I understand right, that isn't correct for Thundersky batteries, which are 3.2v nominal, and 3.8max (recommended). They also have a range up to 163ah; I have the 200ah cells. Will that be a problem?

read the description of the charger:

Cut-Off voltage = 3.65 +/- 0.05V

Nominal doesn't really matter, its the charge current and the cutoff voltage. The cutoff voltage can be lower than the max voltage of the TS cell, as long as its above the nominal voltage of the cell (in this case, TS is 3.2Cut-Off voltage = 3.65 +/- 0.05V), it will charge. The charger tries to PULL the voltage up to 3.65V, but no more.

You just want every one of the cells to be at the same exact voltage. Leave a parallel bank on the group until its charged, take it off, put another group on and charge them. Before you install, make sure all of the groups are at the same voltage. Then take out of parallel and install in your desired pack configuration.

The charger will be fine for equalizing cells, but I wouldn't try to use one of these to charge a cell from completely dead to a full charge. A single cell charger, IMHO, is required for lithium builds. It should be in every toolbox. If the BMS fails, or one becomes too out of balance for some reason, you'll need this to help bring it back up.


[/quote]
Thanks -- I obviously have seen those sites; I'm curious about some specific pages or documentation that recommends where and how to do an initial charge.

corbin[/quote]

Although it has been discussed on a few other threads, you can just use this thread. I'll help you figure out what you need to know, just ask. If I don't know it, I'll know where to find the information. I work as a consultant for both ManzanitaMicro and Elithion and previously with EVComponents.

 

[corbin]

Thanks Travis! This is great information. I'll order one of those cheap chargers to do my initial balance.

--corbin

 

[frodus]

No problem Corbin!

I'd say get a small (0.7A) charger, but you never know when you can use the higher amperage one. It'l equalize quicker for ya.

 

[Tesseract]

Thanks -- I obviously have seen those sites; I'm curious about some specific pages or documentation that recommends where and how to do an initial charge.

corbin

The implication in the above quote is that you would like some evidence to any assertions made herein. A reasonable, and prudent, demand when dealing with internet advice. This 75 minute long video will tell you all you need to know about the care and feeding of LFP packs for EVs and if you truly value your expensive investment then you will watch every minute of it and take good notes along the way:

http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387

Connecting all of your cells in parallel first then charging to a specific voltage somewhere along the knee of the upper end of the charge curve is top balancing. That's fine as long as you understand that it shifts discrepancies in cell capacity to the end of the charge curve. Conversely, discharging all of those cells to a voltage somewhere along the knee of the lower end of the charge curve results in bottom balancing the pack, and you will then need to use a BMS with a cell-level high voltage cutoff to terminate charging as soon as the first cell just enters the upper knee of the charge curve (say, 3.50-3.55V). Even better would be to terminate charging when a specific number of Ah have been returned to the pack (ie - the charger has a Coloumb counter).

 

[frodus]

Top balancing and bottom balancing is always going to be a debate.

Due to the fact that Corbin mentioned Manzanita and Elithion.... I chose to give him the prep for the Elithion system, which is a Top Balancing BMS.

 

[Tesseract]

Top balancing and bottom balancing is always going to be a huge debate. Everyone has an opinion.

It's not really a matter of having an opinion (ie - like Jack Rickard), rather, it's understanding how you need to change your "care and feeding" strategy depending on which method you use.

Your advice was product specific, mine was more along the lines of "get to know your battery pack".

 

[revhead]

An initial parallel charge can get the cells perfectly balanced if you can be bothered going to all the trouble of connecting them up.
If you are using a balancing BMS then it is not necessary as the BMS will prevent any cell going over-voltage and will bring them all into line eventually. It may take a few charge/discharge cycles though.

 

[Lordwacky]

I'm in the same boat as Corbin. In fact we have virtualy exactly the same hardware. I have a PFC 30/ elithion / sky energy 180 ahr. EVcomponents speacial (when they were actualy delivering).

After watching the video above I think have decided to parallel my batteries first and charge to ~ 3.5V / cell then series them and let the manzanita/elithion top off the cells to 3.8V (closely monitored) I want to do this to test the HVC of the system. 3.5V should get me high enough on the knee of the curve so all the batteries are at roughly the same SOC so when the manzanita starts to top it off balancing with the Elithion with be faster/easier. The elithion only has a shunting capasity of 200mA if I remember right, which just isn't enough for an initial balancing if the batteries are far out of balance.

I just bought an old surplus HP DC power supply that I plan on using for this (HP 6286A)
0-10V @ 10 amps has both CC and CV modes which is nice.

I don’t know if I would recommend the charger Frodus recommended (though it will certainly do the job) simply because the out amperage is really low.

If you do a little math. Time to charge the battery (in hours) will be given by the (Estimated SOC* Ahr rating)/amperage of the charger.

So for your case if you assume a 50% SOC, using the charger recommended 0.5(200 ahr)/.7a = 143 hours for one battery. If you have all 48 of your batteries in parallel it will take you 143 hrs (48) = 6864 hrs to charge your pack, which is like 9 ½ months sooo….. that’s a long time.

There is a 6 A charger on the site I would recommend getting that one if you are going to get any of them. You can buy 3 of those for what I paid for my power supply after you figure in the cost of S and H plus they have automatic cut off which is nice and they are a plug in and go which is also nice.

I chose my HP because I have been wanting a low voltage adjustable power supply that was capable of highish amps for a while for other projects that I tinker with from time to time so this was a good excuse to buy one.

If you find your batteries are really low you can always charge them at high current with your Manzanita then top them off with the single cell charger, that will significantly reduce the balancing time, but you run the risk of overcharging a cell or cells if you neglect the process.

I hope this helps

 

[Lordwacky]

Oh sorry forgot to answer the wire guage question.

in a parallel configuration the max current in each battery will be the max current of the charger/n where n in the number of cells you have in parallel.

so for your case if you get the 6A charger and parallel all 48 of your batteries then each battery will get 6/48 = 1/8 of an amp, which is really small, pretty much any wire you have laying around can carry that current.

12 guage can carry up 9ish amps. 18 guage can carry 2-2.5 amps and 24 guage can carry ~0.6 amps, so you can kinda hunt an peck around for whatever configuration you want.


Good luck

 

[frodus]

If you are using a balancing BMS then it is not necessary as the BMS will prevent any cell going over-voltage and will bring them all into line eventually. It may take a few charge/discharge cycles though.

I think I already said that.....

If you install and then let the balancers work, it'l take quite a few charges to get all of the batteries completely balanced. Yes it'l work, but it'l take a long time to become balanced. If you start balanced, the BMS won't have to work as hard, if at all, to keep the batteries in balance.

 

[frodus]

The elithion only has a shunting capasity of 200mA if I remember right, which just isn't enough for an initial balancing if the batteries are far out of balance.

Yeah, its fairly low current. One more reason you should equalize before.

So for your case if you assume a 50% SOC, using the charger recommended 0.5(200 ahr)/.7a = 143 hours for one battery. If you have all 48 of your batteries in parallel it will take you 143 hrs (48) = 6864 hrs to charge your pack, which is like 9 ½ months sooo….. that’s a long time.

I didn't recommend the 0.7A, I said get the 6A charger. And you need to realize, this is an equalization charge, not a charge from EMPTY to FULL. It won't take but a night to equalize.

There is a 6 A charger on the site I would recommend getting that one if you are going to get any of them.

repeat

This one is on sale for $20:
http://www.batteryspace.com/Smart-Charger-6.0A-for-3.2V-1-Cell-LiFePO4-Rechargeable-Battery-Pack.aspx

 

[frodus]

12 guage can carry up 9ish amps. 18 guage can carry 2-2.5 amps and 24 guage can carry ~0.6 amps, so you can kinda hunt an peck around for whatever configuration you want.

really?

Last time I checked, 12Gauge can carry 25A. 18 can do over 10A, and 24 can do 2-3A.

http://en.wikipedia.org/wiki/American_wire_gauge
http://wiki.xtronics.com/index.php/Wire-Gauge_Ampacity
http://wiki.xtronics.com/index.php/Wire-Gauge_Ampacity

 

[Lordwacky]

really?

Last time I checked, 12Gauge can carry 25A. 18 can do over 10A, and 24 can do 2-3A.

http://en.wikipedia.org/wiki/American_wire_gauge
http://wiki.xtronics.com/index.php/Wire-Gauge_Ampacity

this is the website I refered to http://www.powerstream.com/Wire_Size.htm
I quoted the power transmission limits as they are the most conservative. Since this will be a continious load for a long period of time so I felt those numbers were the most appropriate to use. I maybe wrong as I am frequently.

The fact of the matter is that the current will be so low even with a 6A charger virtually anything he has laying around will work, even cat 5 cable (24ish guage).

I didn't recommend the 0.7A, I said get the 6A charger.

repeat

I'd say get a small (0.7A) charger, but you never know when you can use the higher amperage one. It'l equalize quicker for ya.

I’m sorry I must have misunderstood the later comment as recommending the 0.7A charger

And you need to realize, this is an equalization charge, not a charge from EMPTY to FULL. It won't take but a night to equalize.

repeat

this is not the behavior that is reported by dtbaker in this thread.

http://www.diyelectriccar.com/forums/showthread.php/normal-initial-charge-li-52341.html

I don’t know what SOC the batteries ship out with nor do I know how long the batteries were sitting since they were charged last. My batteries have been sitting for nearly a year an and half at this point so I anticipate significant balancing time.

even if the batteries are at 90% SOC the time to charge one cell with the 6A charger is (1-0.9)(200 ahr)/6A = 3 1/3 hrs , for all 48 in parallel it is 3 1/3 * 48 = 160 or so hours.... I'm thinking it will likely take at least a couple of days. But you are the consultant and I'm sure you have done this before so I would probably tust you more then me.

 

[frodus]

The fact of the matter is that the current will be so low even with a 6A charger virtually anything he has laying around will work, even cat 5 cable (24ish guage).

Agreed.... although 6A is a little much for 24gauge , but anything larger than that will work great.

this is not the behavior that is reported by dtbaker in this thread.

http://www.diyelectriccar.com/forums/showthread.php/normal-initial-charge-li-52341.html

just read that. That is a little surprising that they are shipped not fully charged. Sorry I assumed.

I don’t know what SOC the batteries ship out with nor do I know how long the batteries were sitting since they were charged last. My batteries have been sitting for nearly a year an and half at this point so I anticipate significant balancing time.

Yeah, if they've been sitting, they probably self discharged a little bit. It'l take a while to equalize.

even if the batteries are at 90% SOC the time to charge one cell with the 6A charger is (1-0.9)(200 ahr)/6A = 3 1/3 hrs , for all 48 in parallel it is 3 1/3 * 48 = 160 or so hours.... I'm thinking it will likely take at least a couple of days. But you are the consultant and I'm sure you have done this before so I would probably tust you more then me.

Yeah, it'l take a little while, but if he wants it to equalize quickly, it'l cost a bit. Large single cell chargers are not easy to find nor are they cheap. You could use a large power supply, but for $20, a 6A doesn't sound that bad. Thats what, a week? Maybe get two or three and do multiple banks.

The long and the short of it is that you want to get your batteries to the same resting voltage.

 

[Lordwacky]

Agreed.... although 6A is a little much for 24gauge , but anything larger than that will work great.

.

correct if I am wrong here, but if all the batteries are in parallel the current through each battery is = Charger current/n where n is the number of batteries in the chain.

so if he used the 6A charger and had all 48 of the batteries in parallel then the current in each wire would be 6/48 = 1/8 of an amp, 24 guage can carry that with out much issue.

this of course assumes some considerations in the wiring configuration. that I don't really want to get into because its kinda beating a dead horse at this point. But suffice it to say each battery will only be seeing a faction of the 6A output.

 

[dtbaker]

I bought a Mastech 0-30v power supply that outputs a max of 10a per specs. I wired my pack of 100ah cells in parallel, and it output about 8a to start with CV set to 3.70. Early on, I cranked it up and let it chug at 4.0v/8amps.

I wired with 16ga stereo wire, which did not even get warm. I DID wire per suggestion with most + at one end of string and most - at other end.

It took DAYS... and kill-a-watt meter at wall read 11kWhr when I got impatient, re-wired in series and threw the series charger at it and spent a couple days attempting manual balancing on the fly. Big mistake, should have just left it parallel. I suspect cells were 'about 50% DOD, and at such low current the power supply was probably only 50% efficient in getting juice into the cells.

Finished charge in parallel with v=3.80 till amps dropped to 0

It has been sitting for a couple days now still wired in parallel, I haven't had time to do anything....

 

[frodus]

correct if I am wrong here, but if all the batteries are in parallel the current through each battery is = Charger current/n where n is the number of batteries in the chain.

so if he used the 6A charger and had all 48 of the batteries in parallel then the current in each wire would be 6/48 = 1/8 of an amp, 24 guage can carry that with out much issue.

this of course assumes some considerations in the wiring configuration. that I don't really want to get into because its kinda beating a dead horse at this point. But suffice it to say each battery will only be seeing a faction of the 6A output.

Sorta wrong..... lemme explain. If they're really out of balance, when you parallel them, there are amps going through the wires as they self-equalize. There is nothing on each battery to control the current. it goes where it wants to go. Now, when you hook up the charger, the maximum amps that COULD go through that wire is the limit of the charger (6A) + whatever current is flowing between batteries, could be much higher than the 1/8A. Always design for worst case and then derate. It keeps people safe and keeps things from burning down the house. Another thing, is if he connects the charger to the first battery, and then parallels each from there, the current going to the first battery is 6A, then the current to the next is 5.875A, then 4.75A and so on. How you connect also has an effect on how much current the wire carries.

Just because you parallel everything, doesn't mean current is equally split, thats a risky assumtion to make.