LifePO4 batteries for use with Midnite Classic 150?

[karrak]

No I wont sell the design to you I will give it away, github.com/simat/BatteryMonitor.

Would you buy a car with no warning gauges or lights that tell you when something really bad is going to happen unless you stop and fix the problem, or how about an electric appliance that could burn your house down without extra fault monitoring circuitry built into it?

[karrak]

Currently in my position I have over 200 Lithium battery's in various forms. 150 or so for RC planes. dozen or so in cell phones and cyber toys. 30 large format cells installed in a racing golf cart Another 8 large format in my ham shack on solar. and a new set for the golf cart waiting to go in.

What, no beloved Lead Acid batteries that you recommend to everyone else?

[vast]

Hello to all from Romania!

I came here because I need your help. I buy this month an Midnite Classic 150 and I want to know which are the best setup for parameters in every submenu.

My system is:
- panels: 20 x 185W Sharp mono
- charger: Midnite Classic 150 + Shunt (50mV 500A) + Whizbang jr.
- inverter-charger: PIP 4048MS (made by Voltronic Power and rebranded by MPP Solar)
- battery: 16s 48V 100Ah Sinopoly

Till now I used internal solar charger from PIP inverter, but it has few options (manual). For PIP inverter-charger I can setup Bulk and Float, but no option for Absorb.

Midnite has a lot of options and I don't know how to setup properly. Now I have this settings on Midnite:
- Absorb = 56V, time = 2Hr
- Float = 54V (I was inspired by Victron settings)
- End Amps = 5A (0.05C)
- Battery efficiency = 94%
- Rebulk = 51.2V
- No EQ
I can't find Bulk in menu.



Thank you in advance for help.

[jflorey2]

[edit - old post]

[karrak]

Midnite has a lot of options and I don't know how to setup properly. Now I have this settings on Midnite:
- Absorb = 56V, time = 2Hr
- Float = 54V (I was inspired by Victron settings)
- End Amps = 5A (0.05C)
- Battery efficiency = 94%
- Rebulk = 51.2V
- No EQ
I can't find Bulk in menu..

Your settings for the Midnite look good for an off grid system where there are intermittent loads like fridges etc. turning on and off all the time. These settings will charge your battery up to around 99% full and keep it there until the sun goes down. Dropping the Float voltage to 53.6V will still keep your battery full and may increase its lifespan. The coulomb (current) efficiency of LFP batteries is around 99.5%. I am not sure if the battery voltage has to drop below the Rebulk voltage at night for the Midnite to start charging the battery the next morning. If this is the case I would set the rebulk voltage to 52.8V.

From the Midnite manual

Bulk MPPT
This stage of the Classic means that the Classic will be putting out as much current as it can to raise the
battery voltage to the absorb voltage set point. This is also known as Constant Current Mode.
Absorb
This stage means that the Classic will maintain the Absorb set point voltage until the batteries are charged.
This stage is terminated at the end of the Absorb time or the End Amps set point, whichever is reached
first. At this stage the Classic is not putting out maximum current, as that would increase the battery
voltage over the Absorb set point. This is also referred to as Constant Voltage Mode.
The absorb time is proportional to the bulk time (i.e. the time bulk takes to reach the absorb voltage). The
battery is considered full at the end of the absorb charge cycle.

From this I take it that Midnite's term "Absorb set point voltage" is the same as bulk/absorb voltage.

Till now I used internal solar charger from PIP inverter, but it has few options (manual). For PIP inverter-charger I can setup Bulk and Float, but no option for Absorb.

The PIP inverter-charger should work with your LFP battery. I know of at least one person in Australia who is using one to charge an LFP battrery. There are mixed reviews about this inverter. Do a search for PIP 4048 on the Australian Energy Matters Forum for more information.

I am interested to know what other people are doing to monitor, protect and balance their LFP batteries. Would you mind posting information on what sort of battery management you are using.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

[vast]

Hi Karrak,

Thanks for answers. I don't have any kind of BMS because I can't find a BMS properly for renewable energy (PV, wind or hydro). All the BMS on market are for EV's. I have a friend in Romania who build a prototipe for our use, but I don't testing yet.

I find a forum in AUS for PIP4048, but they testing some modified software. As inverter is very good, but as charger it's not so good even for Pb. As you see in manual which I posted, you can set only Bulk and Float, but nothing for Absorb (voltage and time). There are many others who buy from Voltronic, like Giant (AUS) or Effekta (Germany).

These days I find something interesting: in a cloudy day my batteries was charged with small current and batts was very eguals in voltage (3.37V/cell x 16 = 53.9V). But if it was a sunny day I find batts from 3.35V, 3.37V, 3.4V and 3.43V (all pack at 53.9V).


P.S. Please excuse and correct me if I made grammar mistake.

[karrak]

It is difficult finding a suitable BMS for off grid systems, that is why I designed my own. I have made it an open source project which you can find here github.com/simat/BatteryMonitor. There are some commercial systems out there but they all have their problems, IMO probably the best is called 123smartbms and comes from the Netherlands, battrium which comes from Australia and the Orion Jr BMS from the USA. The venerable Cellog8 is also useful and cheap but will unbalance a battery if it is not modified. Sorry about not posting links, this forum doesn't like links.

When you measure the cell voltages also makes a big difference as to how spread out they are. As you can see at the start of the absorb phase the voltages are close together. They are at the most out of balance when the solar controller goes from the absorb phase to float at around 130 minutes. During the absorb phase some of the cell voltages go down while some go up!


GeoffAbosrbVolts.jpg
Your English is very good, much better than my Romanian!

Simon

[Sunking]

Karrak is a fraud and should be banned permanently. Extremely dangerous with very little knowledge. Now is a SPAMMER.

[jflorey2]

When you measure the cell voltages also makes a big difference as to how spread out they are. As you can see at the start of the absorb phase the voltages are close together. They are at the most out of balance when the solar controller goes from the absorb phase to float at around 130 minutes. During the absorb phase some of the cell voltages go down while some go up!

The cell voltages diverge until they are about .25V different. That's a lot for a chemistry with such a flat voltage profile during charge/discharge. How do you account for that? Are you sure it's not instrumentation error?

[Sunking]

The cell voltages diverge until they are about .25V different. That's a lot for a chemistry with such a flat voltage profile during charge/discharge. How do you account for that? Are you sure it's not instrumentation error?

Jeff, Karrrak cannot answer the question, he is a fraud, dangerous, and a spammer. That is why he has been banned so many times. 0.25 vpc on a LFP battery is roughly 75% difference in SOC. Karrak does not know WTF he is talking about and giving very dangerous advice. The kind that makes battery fires.

OP you have been warned by two engineers to ignore Karrak.

[vast]

Before I write my first post here I read many threads in this forum. This is my rule: not write a new post in thread before I read all posts. Also, I respect all opinions. Maybe someone say something "wrong" - for me it is not wrong, it is a thing which must be avoid, like in brainstorming.

So, Sunking I respect your opinions about LFP. Can you help me with settings? There is something which I can improve in my system?

[Sunking]

Before I write my first post here I read many threads in this forum. This is my rule: not write a new post in thread before I read all posts. Also, I respect all opinions. Maybe someone say something "wrong" - for me it is not wrong, it is a thing which must be avoid, like in brainstorming.

So, Sunking I respect your opinions about LFP. Can you help me with settings? There is something which I can improve in my system?

You need a CC that allows you to set Bulk = Absorb = Float = 54.4 volts. What you DO NOT WANT to do is fully charge LFP batteries. No reason to go above 90%. You will double to cycle life staying under 90%. Under no circumstances over discharge them as that is instant death. You want to limit charge voltage to about 3.4 to 3.45 volts, Never let them go below 3 volts. That gives you an operating range of 48 to 54.4 volts. With Sinopoly old Thenderturd cells you can go up to 55.2 volts, but I advise against it.

Most important thing you do is how you intend to do the Bulk or Initial Balance. Do not use a BMS to regulate charge. They require you to Over Charge the cells, and the number 1 cause of premature failures and fires.

[karrak]

The cell voltages diverge until they are about .25V different. That's a lot for a chemistry with such a flat voltage profile during charge/discharge. How do you account for that? Are you sure it's not instrumentation error?

Sorry, I should have stated the charge rates with that graph that I posted. At the start of the absorb phase at 0 minutes the charge rate was ~0.16C dropping down to ~0C at the end of the absorb phase at ~130 minutes. I agree with you that if you were charging at rates greater than ~0.5C that the 3.45V charge voltage would be in the flat portion of the curve. All the manufacturers charge curves that I have seen are at charge and discharge rates of 0.5C or higher. The graph below shows the charge curves at charge rates that are more applicable to off grid use. As you can see at charge rates of 0.05C (C/20) which is a common absorb termination current the SOC of the cell is ~99% and in the very steep section of the curve.

ChargeDischargeCurves.jpg
Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

[Sunking]

Would some mod please make Karraks ban permanent. Get rid of this fraud and liar.

[jflorey2]

Sorry, I should have stated the charge rates with that graph that I posted. At the start of the absorb phase at 0 minutes the charge rate was ~0.16C dropping down to ~0C at the end of the absorb phase at ~130 minutes. I agree with you that if you were charging at rates greater than ~0.5C that the 3.45V charge voltage would be in the flat portion of the curve.

That seems backwards.

When a bank is first commissioned, the cells are equalized; their voltages are matched at some SOC. This is not perfect of course but you can come very close, within millivolts. They tend to keep that matched voltage at least at first, which is why it's possible to run without a BMS under some conditions.

However, their internal resistances may not be the same. Thus during HEAVY discharges and charges, their apparent voltage may differ more, since V=IR (and R in this case is the somewhat variable internal resistance of the cell.) But when the charge/discharge rate is decreased, they should return to close to their original balanced state.

Your diagram shows the opposite - a widening divergence in cell voltage as charge rates (and thus currents) drop.

All the manufacturers charge curves that I have seen are at charge and discharge rates of 0.5C or higher. The graph below shows the charge curves at charge rates that are more applicable to off grid use. As you can see at charge rates of 0.05C (C/20) which is a common absorb termination current the SOC of the cell is ~99% and in the very steep section of the curve.

That's for a single cell, and it shows ~.025V difference between 30% and 70% charge. Yet your curves show a difference of .25 volts between cells. What accounts for the DIFFERENCE in your cell voltages, and why does the difference increase as the charge current drops?