LiFePO4 for House bank final designs

[Anjin]

Originally Posted by exMaggieDrum

I charged both cells to 3.6v and let them sit. They both went down to 3.33v +/-. I'm not sure if I need to give them a slower charge or not but I expected them to accept this .17C current and keep the voltage up.

When you say you charged them to 3.6 an "let them sit" was that still connected to the charger?

If you set the supply to 3.6 and charge them and let them stay connected at 3.6 for some time (with 2 CA100 it should not be long - maybe an hour) you should see the current flow tail down to an amp or less. Then when you disconnect they will probably hold something closer to 3.45. This is the "absorption" phase which Lithium needs as much as LA.

I'd suggest you look closely at the charge/discharge curves for the CA100's. I studied them for the CA180 and began to realize what I should expect and it all started to make sense.

The experts on the forum can probably offer a better explanation and better advice.

- Art

[exMaggieDrum]

Originally Posted by Anjin

When you say you charged them to 3.6 an "let them sit" was that still connected to the charger?

If you set the supply to 3.6 and charge them and let them stay connected at 3.6 for some time (with 2 CA100 it should not be long - maybe an hour) you should see the current flow tail down to an amp or less. Then when you disconnect they will probably hold something closer to 3.45. This is the "absorption" phase which Lithium needs as much as LA.

I'd suggest you look closely at the charge/discharge curves for the CA100's. I studied them for the CA180 and began to realize what I should expect and it all started to make sense.

The experts on the forum can probably offer a better explanation and better advice.

- Art

When I let them sit it was with the charger removed, overnight. I never saw a taper. It stayed at 17 amps right up to 3.61v when I took it off. I suspect I need to adjust the power supply overvoltage limit differently than I have. I will play around with it. I also attempted to contact Mastech/Volteq about it and will see if they get back to me. I feel confident I'll get it sorted out. Obviously, as I expected, the cells will not push back and limit the current themselves, even at the high knee and even at a low voltage setting with a 17A current.

Once I get the voltage setting worked out I will leave them on charge for a couple of hours at a tapering charge while carefully monitoring them. I was seeing a 10mV change every 1-3 minutes while coming up with the way it was set up yesterday. At rest (overnight), the cell was at 3.33v and went to 3.50v immediately when I put the charger on. It took less than 15 minutes to go from 3.50 to 3.61 which is when I took it off.

The voltage does indeed rise very fast towards the end. All cautions given by others are entirely accurate as to the need to be there watching.

[Anjin]

Originally Posted by exMaggieDrum

I never saw a taper. It stayed at 17 amps right up to 3.61v when I took it off. I suspect I need to adjust the power supply overvoltage limit differently than I have. I will play around with it. I also attempted to contact Mastech/Volteq about it and will see if they get back to me. I feel confident I'll get it sorted out. Obviously, as I expected, the cells will not push back and limit the current themselves, even at the high knee and even at a low voltage setting with a 17A current.

Joe, we need to back up a bit. I doubt if there is anything wrong with your charger. The charger won't taper because it has some smart controller in it. It tapers simply because there is less potential difference between the charge voltage and the battery voltage. To prove it, set your charger to 3.4 volts (again measure with your multimeter) then connect it to one of your batteries that are at 3.3 or so volts). Do not adjust the current flow - you must leave it in constant voltage mode. Make sure the connections are solid. You will see some current flow and it will gradually diminish. If you see no current flow, set it to 3.5 volts instead and try again.

When your batteries reach 3.6 volts and the current didn't taper you probably did what I first did when that happened - pulled them off to avoid overcharge. But if the supply is set to 3.6 volts (again, Constant Voltage mode) it simply can't push the battery any higher than that. If it were me, I'd set it to 3.55 (I'm conservative) and just leave it on, even at 17 Amps and yes, it may go to 3.56 or 3.57 because that may be the actual output of the supply but it will taper. It's getting full current at first simply because it's at the start of the absorption phase.

I'm sure one of the experts here can do better job of explaining - I'm just speaking from my limited experience over the past 6 months.

[gpeacock]

Hey Joe
Ive been following your discussion with Art closely as I am almost ready to pull the trigger on my cells.
Im surprised you are working with just two of the cells. I understand your hesitance to put all the cells in danger when you are still figuring out your new power supply but if thats the case grab a cheap 12 V auto battery from your car and practice on that.
Now that you've played with the two cells you've undone all the hard work the guys at the shop did for you when they got you a matched balanced set.
Once you are comfortable with how the power supply works I would strongly recommend you only work with the remainder of the cells as a whole batch. You will save your self a tonne of work trying to get everything in balance at the end. As you've seen, the voltages change very quickly at the top so you can't just pick a voltage and charge each cell individually to that and expect them to be balanced. You really need to work with the cells together at a pack level.
Gary

[gpeacock]

Originally Posted by exMaggieDrum

Once I get the voltage setting worked out I will leave them on charge for a couple of hours at a tapering charge while carefully monitoring them. I was seeing a 10mV change every 1-3 minutes while coming up with the way it was set up yesterday. At rest (overnight), the cell was at 3.33v and went to 3.50v immediately when I put the charger on. It took less than 15 minutes to go from 3.50 to 3.61 which is when I took it off.

The voltage does indeed rise very fast towards the end. All cautions given by others are entirely accurate as to the need to be there watching.

This info on the rate of voltage change was really helpful for me. Lots have said "fast" but I think you are the first I've seen that quantified what "fast" meant.
Keep up with the reporting! I'm about a month behind you.
Thanks
Gary

[Anjin]

Originally Posted by gpeacock

Now that you've played with the two cells you've undone all the hard work the guys at the shop did for you when they got you a matched balanced set.
Once you are comfortable with how the power supply works I would strongly recommend you only work with the remainder of the cells as a whole batch. You will save your self a tonne of work trying to get everything in balance at the end. As you've seen, the voltages change very quickly at the top so you can't just pick a voltage and charge each cell individually to that and expect them to be balanced. You really need to work with the cells together at a pack level.

Gary, just from my experience, you're right that you "can't just pick a voltage and charge each cell individually to that and expect them to be balanced" and you're also mostly right in that the final balancing should be done with all cells wired in parallel. But Joe didn't "undo" anything because the "shop" probably didn't provide a "matched balanced set." Yes, my cells showed up at pretty much the same voltage but that doesn't tell you much about state of charge and I would never have relied on that.

It's fine to play with single cells or groups of cells as long as you don't push them far into the knees and as long as you have a means to discharge them. Just remember that when charging, voltage changes come quickly after 3.4 volts but VERY SLOWLY before that - and 16 times slower if you do them all in parallel.

When you're ready to top balance try to get most of the cells near 3.4, wire them together in parallel for a couple hours ahead of time to let any differences flow out. Then hook the charger/supply up with positive at one end of the 16 cell pack and negative at the other end. Set the supply to whatever you think is appropriate (I used 3.55 but mostly 3.65 is recommended by the experts) and let the whole pack get to that voltage and absorb at that voltage. When the current has tailed off to (in this case) a couple of amps or less (the lower the better), you can disconnect them and just let them sit for a few days wired together. Now they're balanced.

Maine Sail offers a more complete description at his website.

Cheers -

- Art

[exMaggieDrum]

Art and Gary,
Thanks for both of your comments. I just got a reply from Mastek and they gave me a slightly, but importantly, different way to adjust the output of the power supply. I will try that later this morning. I believe it will work.

Just to recap though. I received my cells and they were all exactly 3.29v as best as I can measure with my DVM. They had been in transit for at least two months so I would think they were as "balanced" at that level as I could ever achieve. But they need to be top balanced higher.

I am starting with two cells, one at a time, only so I can work out the process of doing it in a reasonable amount of time. To bring up 4 cells at one time would take days let alone hours if done in a carefully observed manner. I won't leave this first set of cells on the charger for longer than 10-15 minutes at a time. I make a note of voltages (power supply display and my DVM on the cell) and the amperages (power supply display and my Fluke clamp-on on the charging wires). I am trying to get to a reliable and repeatable process to make the remaining cells easier, faster and still safe.

I intend to bring each individual cell up to close to 3.60v, intending to go to 3.65v with 4 cells in parallel. After that I will put all 16 cells in parallel. If the total set is still at 3.65v I will just leave them hooked up for a few weeks while I do more prep work on the boat. I believe this follows what Maine Sail and what you have said basically.

Yesterday afternoon, I reset the power supply so that it was doing more of what I wanted to see. It was still not operating the way I expected as it was still putting out 6 amps at a displayed 3.7v. Per the manual, it should have already reached the overvoltage limit and stopped charging completely and it did not. I had set the overvoltage limit at 3.7v and the charging voltage at 3.6. I have verified that the amp readings on the power supply are reasonably accurate compared to my DVM but that the voltage readings are not necessarily so.

With the setup and adjustments I had, I got the one cell up to 3.65v with about 5-6 amps still flowing. I did not want to go to 3.7v so I disconnected at that point. Ideally, I want to get to 0.1-1.0 amp at 3.6v for an extended time for each cell. And then I will put all cells together and let them sit as noted above.

My issues seem to be mostly with getting used to the power supply. It is not what I would call a precision instrument and is awkward to adjust for the overvoltage limit in particular. It only displays and is set to 0.1 volt increments which is not very precise for what I am doing, especially for one cell. It will be better for four or more cells provided I watch it carefully. The reason I say that is because a low amperage will not quickly change the cell pack voltage and I will be able to react if there is a problem at the knees.

Based on what I have seen so far I believe the real exponential voltage increase (upper knee) is 3.7v or higher. The Sinopoly specs call for 3.7v as a maximum charge. If that is correct that should be well below the actual knee but I don't want to experiment with that on my own cells.

I will know more today as I continue to fine tune the operation of the power supply. I think I was putting too much credence as to how manageable the power supply is. I take all voltage measurements only at the tops of the cells (not the stainless bolts). I am using a couple of my copper cell straps which I lightly sanded and put on the lightly sanded cell terminals. I hook up m charging terminals to those straps rather than connecting them to the bolts in the terminals.

Short of putting ring terminals under the bolts to the terminals I can't get a better connection. I don't want to use rings under the bolts since I may have to quickly disconnect the power supply and you can't just turn off the power supply before disconnecting the load (per manual).

I think today I will get to where I need to be. In a couple of days I should have my first set of four cells done. I don't have 8 hour stretches to be at the operation so it will just be several days before I get done.

Again, I appreciate your comments. I am trying to implement your thoughts using the new adjustment process I just got from the vendor, living with the imprecision of the controls even with that. I can see why Maine Sail prefers a fancier power supply.

[Anjin]

Joe, sounds like a good plan. I recommend one small change that will make it easier and probably achieve better balance. Once you bring all the cells to 3.6, skip the "4 cells at a time" to 3.65. Just wire all 16 together and charge them up to 3.65 together. It will go quickly even with 16 cells in parallel and will ensure balance. Just wiring them together without raising the voltage may look like balance but it might not be.

- Art

PS, what model charger are you using?

[exMaggieDrum]

Originally Posted by Anjin

Joe, sounds like a good plan. I recommend one small change that will make it easier and probably achieve better balance. Once you bring all the cells to 3.6, skip the "4 cells at a time" to 3.65. Just wire all 16 together and charge them up to 3.65 together. It will go quickly even with 16 cells in parallel and will ensure balance. Just wiring them together without raising the voltage may look like balance but it might not be.

- Art

PS, what model charger are you using?

Hi Art,
I'll try your suggestion. It would save a lot of time. I got the charging sorted out I think after using the procedure I was sent. It is a bit different than the manual. The manual was brief and a bit hard to understand all the options so it may have just been a user error. I got the one cell to 3.61v and down to 0.0 to 0.1 amps. So I left it on for three hours while I did other things. I will go on to the next cell and so on and then put all 16 in parallel and bring them up to 3.65 (or 3.64 or 3.66). The adjustments to the power supply are not too fine.

My power supply is the Volteq HY3020EX sold by Mastek. This is the brand recommended by Maine Sail. I bought it direct for around $220. I think that is a very reasonable price and I am happy I got it. The customer support was quick and helpful although no one joined my chat. They followed up with an email which got the job done.

Thanks,
Joe

[ColdEH]

Originally Posted by exMaggieDrum

Hi Art,
I'll try your suggestion. It would save a lot of time. I got the charging sorted out I think after using the procedure I was sent. It is a bit different than the manual. The manual was brief and a bit hard to understand all the options so it may have just been a user error. I got the one cell to 3.61v and down to 0.0 to 0.1 amps. So I left it on for three hours while I did other things. I will go on to the next cell and so on and then put all 16 in parallel and bring them up to 3.65 (or 3.64 or 3.66). The adjustments to the power supply are not too fine.

My power supply is the Volteq HY3020EX sold by Mastek. This is the brand recommended by Maine Sail. I bought it direct for around $220. I think that is a very reasonable price and I am happy I got it. The customer support was quick and helpful although no one joined my chat. They followed up with an email which got the job done.

Thanks,
Joe

I have the same power supply, Be patient , it took me almost two weeks to get my cells all up and charged .

Its been two years now and they are still within an average of 4mv apart from each other . So you will probably not be doing this again .

Regards

[exMaggieDrum]

Originally Posted by typhoon

I have the same power supply, Be patient , it took me almost two weeks to get my cells all up and charged .

Its been two years now and they are still within an average of 4mv apart from each other . So you will probably not be doing this again .

Regards

It's going well now. I'll be patient. I don't have a reason to rush and every reason to do it the right way. I'm multi-tasking on so many projects my head is spinning. So far all are progressing well. No cells before their time.

Two weeks sounds about right for the time it will take. I'm tearing out the old battery cabling now and putting in new AC and DC panels. I'll be pretty happy when it is all done. I do have to restart the battery management pieces soon though. I got it all sorted out, designed, got most all parts, but will have to go back and re-educate my brain on all of it after a few months with it all in boxes.

Thanks,
Joe

[JBPohle]

It has been 6 months playing with these batteries and final put together the entire bank. It is 16 ea CALB CA180's in a 2P8S 24 Volt bank. 360 Ah at 24V. The batteries are strapped or compressed between 3/8" AL plate with 5/16" dia tie rods compressing the batteries. The hold downs are fabricated out of 1"x1"x1/8" fiberglass angles. Skin still itches from cutting it. I used ATO style fuse blocks to fuse the BMS and Cell Log S voltage sense wires. I'll also take off of these for the voltage monitoring by the Inverter and BMV702. What you don't see yet is the 4/0 wiring off of the + and - terminals, 400amp T style fuse, etc. That's the next part of the project.

[Maine Sail]

Originally Posted by exMaggieDrum

It's going well now. I'll be patient. I don't have a reason to rush and every reason to do it the right way. I'm multi-tasking on so many projects my head is spinning. So far all are progressing well. No cells before their time.

Two weeks sounds about right for the time it will take. I'm tearing out the old battery cabling now and putting in new AC and DC panels. I'll be pretty happy when it is all done. I do have to restart the battery management pieces soon though. I got it all sorted out, designed, got most all parts, but will have to go back and re-educate my brain on all of it after a few months with it all in boxes.

Thanks,
Joe

Joe,

With the Mastech do not run it at full bore. Redice to about 15A and set your voltage into a fixed mA load before connecting to the batteries.

[ColdEH]

Originally Posted by Maine Sail

Joe,

With the Mastech do not run it at full bore. Redice to about 15A and set your voltage into a fixed mA load before connecting to the batteries.

I printed off Mainsail's LifePo4 Musings and used it as a manual to install and setup my system as I am sure many of us has . I reference it often .

Regards

[SV THIRD DAY]

Originally Posted by Anjin

Joe, we need to back up a bit. I doubt if there is anything wrong with your charger. The charger won't taper because it has some smart controller in it. It tapers simply because there is less potential difference between the charge voltage and the battery voltage. To prove it, set your charger to 3.4 volts (again measure with your multimeter) then connect it to one of your batteries that are at 3.3 or so volts). Do not adjust the current flow - you must leave it in constant voltage mode. Make sure the connections are solid. You will see some current flow and it will gradually diminish. If you see no current flow, set it to 3.5 volts instead and try again.

When your batteries reach 3.6 volts and the current didn't taper you probably did what I first did when that happened - pulled them off to avoid overcharge. But if the supply is set to 3.6 volts (again, Constant Voltage mode) it simply can't push the battery any higher than that. If it were me, I'd set it to 3.55 (I'm conservative) and just leave it on, even at 17 Amps and yes, it may go to 3.56 or 3.57 because that may be the actual output of the supply but it will taper. It's getting full current at first simply because it's at the start of the absorption phase.

I'm sure one of the experts here can do better job of explaining - I'm just speaking from my limited experience over the past 6 months.

Bingo....
You just described why a simple LiFePO4 battery set-up doesn't really need any top end controls or cut outs if you simple set the charge voltage output of your various chargers to your Max save voltage. Been doing it for over 2yrs now and it works like a KISS dream. Is the goal to have a dependable good battery bank or a science project...that seems to be where so much of the hupla costly controls come into play.