Is anyone using the Classic 150 to charge Simpliphi LFP batteries?

[Gordon]

Hi Folks,

I just switched from FLA batteries to the Simpliphi 3.8 M LFP batteries. I'll describe my observations and would like to see if anyone has any comments or can answer some of my lingering questions.

My rig consists of 1800 W of panels running though a Classic 150 (CL150) into a 24 VDC bank of two PHI 3.8 M batteries for a total of 302 AH of storage. Simpliphi (SP) states that you should charge up to 28 VDC and that there is no need for an absorption phase. Yes, I know that their integration guide states to set absorption to .1 Hr (6 min.); per phone conversation they say that is just because most controllers won't go any lower than this. So I did exactly what the guide says; bulk/abs 28.0, float 27.0, EQ and T-comp disabled.

Now, in addition to this when you get really picky you see that there is a slight voltage drop from what the charger sees and what the batteries are getting especially at high current flow. Even with only a .005 ohm resistance you will get a .2 VDC drop at 40 amps and a .3 VDC drop at 60 amps. This seems unavoidable even with 4 AWG coming out of the controller and 00 AWG from the DC disconnect to the batteries just because you have multiple connections/crimp-lugs etc. in the disconnect. In my case there is the wire from the CL150 to the breaker, the wire from the breaker to the DC positive buss bar and from there to the positive terminal on the main inverter breaker where the DC battery positive cable is. On the negative side there are not as many connections, but you add it all up and you get a slight resistance, resulting in the voltage drop.

Third issue, when you set the bulk/abs voltage to 28.0 V the CL150 will actually start the absorption timer when you get the 27.7 V. So now your 6 minute countdown has started at 27.7 and you're flowing at least 40 amps at this point so your batteries are only seeing 27.5. I've watched this happen now and when the 6 minutes is up it goes strait from a 40 amp charge at 27.7 to the float mode, never getting up to 28 at the CL150 or at the batteries. I had a case yesterday where it was cloudy all morning and the charge rate was very slow and the sun only came out in the last couple minute of absorption and the charge rate shot up to 60 amps, the timer ran out and it went right to float.

So I called and told the rep at SP all this stuff and he said that it sounds OK since my batteries come to rest at 26.7 after the charge with no current applied, and that they don't really need to see the full 28.0 to get a full charge. That all sounds good but it still has me asking why they specify the 28.0 and if it doesn't need to see that voltage why was there a 60 amp charge going into batteries that were supposedly fully charged already?

Work-around #1 that I tried was to put the absorption time down to zero in hopes that if there is no absorption specified that it won't actually go into float until it reached the 28.0. That doesn't work because the CL150 won't go lower than 3 minutes. I didn't want to make voltage offsets in the Tweaks menu because the voltage drops are current dependent and they would still apply when there is very little current flowing and no corresponding voltage drop. My next step is to increase the absorption time to see if I can get the CL150 voltage time to come up to 28.0 and get a little reduction in total current flow. Even with that there will still be the voltage drop between the CL150 and the batteries so I'm quite certain that this is safe since the batteries still won't see the full 28.0.

Just wondering what you folks may think. My intention is to get the longest/best service life out of these batteries and not have them go bad from undercharging if that is possible. The final option is to simply forget about all this stuff and go with what SP says and ignore all the details. That's perfectly fine with me too if you folks think that's the way to go.

Thanks,

Gordon

[ClassicCrazy]

Lithium are not like lead acid - so undercharging them slightly isn't going to be an issue. If you look at the charging curve of lithium you see that it most of the charge capacity is already in the batteries well below what you are probably talking about seeing. That few percentage capacity in the final stage of charging isn't going to make a big difference . The issue with lithium is not being undercharged - it is if the cells get way out of balance. The built in bms in your batteries should hopefully do the job to prevent against that - keeping any individual cell from going over voltage. There are some who say that the lithium are going to last longer being undercharged .
The other point you make about the ending point of charge - are you using ending amps ?  Lithium have such a different way they act in that there is little to no curve from charging to full so it isn't unusual for them to just shoot from absorb to float quickly.
These are some of my observations and from what I have read up about lithium.
Yes it would be nice if Classic had voltage sense wires instead of just using the battery cable voltage . That is something Vic has talked about in the past .

Larry

[Gordon]

Hey Larry, thanks very much for the reply. It's good news that they don't need to be fully topped-off in order to remain healthy. No, I didn't have any end amps setting; two reasons, 1) I don't use the Whizbang Jr. so it would be a controller out amps instead of a battery in amps and 2) the current never got even close to being as low as 2% of the capacity which would be 6 amps in my case.

If full charge isn't needed for equalization of cells then there is no reason for me to do anything any differently from what I have on there and that's great news. The only thing that was making my system flip from absorb to float was the timer set to six minutes per the SP integration guide. My concern was that that was going to be much too soon based on what I was seeing during the process, ie. voltage never even getting to the desired 28.0 at the CL150 let alone at the batteries.

Thanks again very much. Right now all I did was bump up the absorb time to 12 minutes just out of curiosity to see what a few more minutes at the end of the charge do and I think I will not bother over thinking this issue any more.

Thanks Again,

Gordon

[Steve_S]

I have familiarity with SimpliPhi, they are a tad optimistic with their profiles but their BMS' are setup to manage it quite well.

Couple of quick things. 
LFP full Volatge Range is 2.500-3.650 per cell.
LFP Working Voltage Range is 3.000-3.400 with Nominal Voltage @ 3.200V per cell.
SimpliPhi is using A+ ESS Grade Cells.  They can discharge up to 1C for 1 Hour and take charge at 0.5C for 2 hours (from empty).
These cells have an actual Working Range of 2.900 to 3.475.
FYI:  ALL LPF regardless of class Settles !   You can charge the cells to 3.650 until they take less than 1A Charge for Full Saturation, within One hour of Charge Stop, the cells will be settled close to 3.500.

The Quick Math:
Working Voltage for 24V System: 24.0V to 27.2V /  A+: 23.2 to 27.8V
From 2.500-2.900 & 3.450-3.650 only actually represents 5% of Gross Capacity.  (SimpliPhi will say it's a 100AH Battery Pack but it will have 105A or 110A cells) which they derate to ensure Full Service & Longevity.   BattleBorn & Relion do the same.

I migrated from Heavy Lead (Rolls Surettes) to LFP and now run with 2x24V/280AH (Bulk Cells) 1x24V280AH (Matched & Batched) and 2x175AH used EV-Class LFP, in one LFP Bank for 1190AH/30.4kWh.  This broad section has allowed for some intense testing including Hard Thrashing to the performance edges. 

I do FLOAT the battery packs because that allows the Full Cells to level up and the balancers enough to bring everything nicely up within a short period of time. NB: I use Chargery BMS8T 300A with 300A DCC's (Solid State Contactors) and 1 QNBBM-8S Active Balancer on Every Production Pack in the bank.

Midnite Classic 200 LFP Charge Profile With WizBangJr
All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT).
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
NB: Victron Forum discussion says EndAmps = TailCurrent
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.

** Coulumbic Efficiency for LFP is 99%

Hope it helps, Good Luck.
Steve

[Gordon]

Wow Steve, thanks very much for the info!

You say that SP are a bit optimistic with their profiles. I have to assume that you are saying that they are optimistic that their charge specs will result in a full charge. With the inevitable voltage drop in the system between the CL150 and the batteries, the absorb timer starting its countdown at absorb-.3 VDC and the very short absorb time I will never have the batteries reach their specified end amps of 2% in that short 6 minute absorption (constant current time). The timer will always time out before that.

Based on your analysis I feel very comfortable in extending that absorb time a bit like I was going to and even bumping up the bulk/absorb voltage to 28.2, since the batteries will never even see more than 28 before the timer switches to float.

It appears that you are using a 1% end amps figure and adjusting for five batteries, the highest of which are the three at 280 AH. If that is the case, do you ever see your end amps setting curtail the absorb phase before your 15 minute timer times out? Just wondering because that seems to be the only time that that would come into play.

Thanks very much,

Gordon

[Steve_S]

SimpliPhimakes a darn good product.  When I say optimistic, is they "know" the packs can take the higher charge point "but" the reality is, that LFP is LFP, it will do what the chemistry says it will, simply put.  The A+ Grade cells they use of course will "make spec" but pushing cells to the edge all the time... not such a good idea no matter how you look at it.  The likelyhood of stuff coming up later as they age a bit too, imbalances etc...  I do not believe they have any form of Active Balancing or even Passive for that matter.

Because of the configuration, the process is kind of "peculiar".  I'll try to explain with an example.
Assuming Bank is at 75% SOC and Solar comes in to charge and ramps up to 75A and reaches the 28.2V.

At this point looking at the different packs (I can monitor each pack, cells and all pertinent info):
- the 175AH packs will be at their 100% Voltage wise, the cells will be deviating roughly 80mv and increasing with resistance, the BMS' will usually start to alert for limits and eventually trigger for cell differential and cutoff charge.  My own settings for these.

- the 280 Bulk packs will be taking the balance of the released amperage and will also quickly top up and similar to the 175AH, the differential MV will increase with resistance & the packs reduce the Amps taken.  The differential can reach 120mv at the top but it settles very quickly due to the Active Balancers.  The matched pack will only be 35mv differential at this point.

The 0.05C Rate to calculate EndAmps is derived from LFP Specs & Docs for ESS grade cells, EVE, CATL, LISHEN & BYD. 

Now as I said, I use the WizBang and it's set for 14A End Amps based on the 280AH (largest AH pack size in bank) and when the packs reach low amps being taken, it does flip to float and happily does the job.  TBH, I tried with absorb set to 1 hour as a  test and it lasted 20 minutes but the SCC was only pushing out 20A.   THAT's the rub too, it depends on how many amps are going into the battery packs.  More Amps at the top = More Deviation between cells, Faster increase in resistance and quicker charge completion.

Couple of things though... again my setup is quite different and the BMS' also have Passive Balancing and other functions, I'm able to tweak the "behaviours" at that level and tinker.  Nature of being a DIY kinda guy.

One thing for darn sure, LFP charges weird in a way but a heck of a lot faster than any Lead or AGM I've seen.

[Gordon]

Thanks very much for the additional insights. I really appreciate it. I think what I'll do is just make a simple adjustment for the voltage drops that are happening and go with the SP recommendations. Easiest thing to do and it sounds like there will be no harm. Nothing will be getting pushed to the limits and these batteries should have a long life. I think I'll probably see a lower current flow at the end of the absorb time and that should solve the issue that started this whole thing over here.