Correct Settings for LiFePo4 40AH

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SimonH
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Joined: 02/25/2017
Points: 20

Hi Everybody,
I drive my Vectrix VX1 LI with a LiFePo4 40AH Batterypack since end of September. Not long after I had to learn, that this kind of Battery has it's problems with temperatures below 20° Celsius.
Now I'm looking for a way to optimize my VX1 a bit. I realized that my vectrix is starting to have problems with accelarating when low voltage is below 2.75V and hi voltage is below 2.8V
Since the LiFePo4 Cells have discharge minimum voltage of 2.0-2.3V I wonder if maybe there is something missconfigured.
From what I have read in this forum I guess 2.7V is the usual discharge minimum voltage for 18650 Cells.

I'm I right?

Thanks for your answers
regards
Simon

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Heavendenied
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Joined: 02/01/2015
Points: 79
Re: Correct Settings for LiFePo4 40AH

No, the configuration is OK. The Cells should never bei discharged to 2.0V. That would not be very good for the cells.
What Kind of "problems" do you have with your scooter when cell volategs are at 2.75V? Normaly its like that:
•When the Scooter is in GO mode you can ride without any power limitation till lowest cell get 2,4 V ( Overdischarge protection – Voltage read from BMS )
•Battery Red tale will appear when the lowest cell voltage is below 2,65V with current load below 25AH for 6 second (about less than 3% power available at lowest cell)
What is the Range of your VX-1 till you get 2.75V? Do you have the CAN-BUS Cable and Diag soft?

SimonH
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Points: 20
Re: Correct Settings for LiFePo4 40AH

Hi Heavendenied,
Many thanks for your reply.
OK, let me try to explain my overall problem
I have my bike in a shed during night. It's not heated so during winter there is a good chance that the temperature is dropping below 0°C, That doesn't matter to me because in those temperatures I do not drive with the bike anyway.
But as soon as the daily temperature goes above 10°C I'd like to drive to work with my bike, if the weather allows. This actually means the shed is still around 3-5° in the morning. So I started to heat up the shed in the early morning hours to bring the batteries to at least 14°C.
The distance to work one way is 22km so both ways 44km. There are some little slopes along the way and one which is really though (10% for 1.5km).
When the temperature is above 25°C I'm able to drive with about 85km/h top speed both ways with a bit of a drop before I'm back home. I don't know what the Battery voltage was at this time, because I didn't care then. But the last view weeks I started to check Voltage and Current while driving just because it was getting annoying to drive with maximum 65km/h to be able to get home with a somewhat reasonable speed.

I start with a fully charged battery in the morning:
Outside Temperature: 10°C
Temperature: 14°C
Cell Voltage low: 3.28V
Cell Voltage high: 3.32V
Voltage Battery: 133V

After 22km the battery shows something like this:
Outside Temperature: 11°C
Temperature: 17 - 18°C
Cell Voltage low: 2.9V
Cell Voltage high: 3.04V
Voltage Battery: 124V

When I finished work and drive home the battery displays:
Outside Temperature: 17°C
Temperature: 17 - 18°C
Cell Voltage low: 3.04V
Cell Voltage high: 3.06V
Voltage Battery: 126V

After 2km the Hill comes and on top of it the battery shows something like this (speed up hill: 50km/h max)
Outside Temperature: 17°C
Temperature: 18°C
Cell Voltage low: 2.78V
Cell Voltage high: 2.9V
Voltage Battery: 117V

First the road now goes downhill quickly so the battery is able to regenerate a bit. After that the road is going upward steadily. Luckily there are some villages where you can't go faster then 60km/h by law. But after about 30km You could drive 80km/h if your vehicle does it. Unfortunately mine is not going faster then 70km/h at this time and the pace is decreasing the further I get.

At 37Km the display shows:
Outside Temperature: 16°C
Temperature: 20°C
Cell Voltage low: 2.74V
Cell Voltage high: 2.8V
Voltage Battery: 112V

Every little upward slope is a pain. Sometimes I do not even get over 50km/h.
At least the last 2km are going downhill where I manage some 75km/h

Because of this the battery shows the following in the end:
Outside Temperature: 16°C
Temperature: 22°C
Cell Voltage low: 3.02V
Cell Voltage high: 3.1V
Voltage Battery: 126V

The highest current displayed I've seen was 80A. Usually it is around 25 to 35A
The charging meter shows half/half when I'm back home. And I really think this could be true.

My dealer told me everything is fine with the bike. I can't belief that. But why is the pace dropping so quick even though I don't get the battery light?
I'm not that heavy though, just about 70Kg.

I always read how happy everyone is with the LiFePo4 batteries and never heard about problems with max speed. So why me? buhu...
So now you have a lot of text to read. I'm just unsure if there is something wrong that would explain the drop in speed and power. So everything that could be a hint would be very much appreciated.

Heavendenied
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Points: 79
Re: Correct Settings for LiFePo4 40AH

Sorry, but i think there are very few people who are really happy with the GP LiFePo4 cells ;-) They have very bad quality and most of them have very fast decrease of capacity.
What is very curious with your Vectrix is, that the cells seems to be very well balanced because the voltages even on load doesn't drift very much.
The fact that voltages go down on load is OK and totaly normal but what is not normal is the reduced power. I can drive my Li+ with full power even if the cells are nearly empty. Even with voltages of about 2.5V under Load...
The second thing thats very curious is the relativly low cell voltages without load after only 44kms and showing half full battery. I think the cells have decreased capacity but the vectrix still "thinks" it has full 42aH...
Did you ever drive it till it shows empty? What range did you get? Did you ever messure how much kWh you can charge into your vectrix with a normal electricity meter?
Do you have the CAN-BUS cable to check firmware? How old is the scooter and how many kms does it have on odometer?

MEroller
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Points: 812
Re: Correct Settings for LiFePo4 40AH

To me that pack sounds like it has developed a very high internal resistance, which causes great voltage drops at high current draw, thus reducing the maximum speed. No matter if fully charged or almost empty. High internal resistance seems to be the main aging factor in LiFePO4 chemistry - actual capacity drop comes in second place only.

__________________

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E-Sprit Fury (basis is the Erider Thunder 5000) since May 03, 2011. Highly moded - but now in active retirement

Heavendenied
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Points: 79
Re: Correct Settings for LiFePo4 40AH

That voltage drop on high current is normal with these GP cells. I have the same voltage drops, but the Vectrix can still be driven with full power! Maybe this is because of high internal resistance but if than all of my cells have this too.

SimonH
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Points: 20
Re: Correct Settings for LiFePo4 40AH

Hi again,
thanks for your quick reply. Also thank you MEroller, you see I try to get into it.. ;-)
So then you think, the power drop is not only because of low temperature? So do I!
Unfortunately I do not have a CAN-Bus Adapter Cable but I guess it's time to get one.
I bought the scooter last September. And short after that I startet to realize those strange behaviours. So I took it to a reseller to have it checked. But they tell me everything is fine with the bike.
The bike is a 2008 Vectrix originaly with NiMH battery pack that was modified to LiFePo4 in 2015. The Odometer now shows ~40200km, the battery age though is around 2.5 years. It comes from a showroom bike and may have around 10'000km on it now. Maybe the conversion was not done properly.
When I drove with it to the reseller it was about 60km the battery light did not turn on but the top speed when I arrived was 25km/h. I believe to remember that it showed arround 2.5V low or high cell voltage. Unfortunately I can't remember the overall voltage.
I did not meassure how much kWh I can charge. I have to get an electricity meter as well then. :-(

Heavendenied
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Points: 79
Re: Correct Settings for LiFePo4 40AH

That really sounds very strange.... The range and voltage drop is OK for an Li+. For sure, the voltage drop on high current is lower on higher temperatures, but it still is very high in comparison to good cells (as mentioned the GP Cells are not good even if they are new). But what is really strange is that reduced power and speed. I can remember that was something the NiMh bikes did, but not the original Li+ ones. Maybe the bike still has an old firmware from the NiMh version? Don't nknow if that is possible, but i can't imagine any other reaseon for this behaviour.
For sure the only way to find this out is the usage of the Can Cable and Vectrix Diag.

PJD
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Points: 1383
Re: Correct Settings for LiFePo4 40AH

Not a Vectrix, but my scooter with 24, 60AH, 7-year old GBS cells (LiMnFePO4) used almost daily for 3/4 of the year, has some performance degradation but will still maintain 75 kph up a moderate hill at a temperature of 0C or a little below. I don't know what their voltages are going down to under load - presumably 2.5 or lower for the worst cells but going back to at least 3.2V at rest and 30-50% SOC. So, you can count me in that minority that is happy with Chinese LiFePO4 performance. I'm not looking for blazing speed.

With what I know now (don't charge to full unless you absolutely need the range or to balance the cells a few times a year!) I can probably extend the life of a new pack with the same cells indefinitely.

The main problem has been the charging resistance has gotten very high with age when charging below 10C (poorly heated garage), causing premature switching from high CC charging mode to low current "balance" mode and very long charging times. And the hoped-for price decline (in the USA) has never happened. Replacing the 4.4kWH pack is still about $2200!

SimonH
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Points: 20
Re: Correct Settings for LiFePo4 40AH

Hi PJD,
With 75km/h uphill I would be happy!
On my way home on Friday I could not drive faster then 75km/h on a flat road.

@Heavendenied
I ordered now an electricity meter. It should arrive on Thuesday. Then I will see how much Energy it charges. I also will buy the PCAN-BUS Adapter but it has to wait until next month.
When I took my Vectrix to the garage end of Novemeber, I drove 62km one way. At the end I was driving with 20km/h on flat road but the battery lights did not display.
Anyway... I will update as soon as I got results from electricity meter and later from the informations I get from the Firmware.

Thanks to all for the feedbacks.
Simon

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