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gavin avatar image
gavin asked

Is anyboby using Byd LV Flex5 lithium batteries. Problem with charge derating.

The system consists of 6.6Kw of solar connected to froinus 5Kw grid inverter which is on the output of a Multi Plus II GX. The batteries are 2x Byd LV Flex5 and 1x BMU. The system is off-grid.

The problem is that the CCL(charge current limit) is set to 26.8 amps when the battery temperature is 15degC or below. The manual states charge derating occurs between -10 and +5degC. The firmware verisons for the battery are BMU 1.22, BMS 1.13 and parameter table 1.4. Does anybody have LV Flex5 batteries with this issue?

BYD
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gavin avatar image
gavin answered ·

Spoke with ALPS Power (Byd distributor in Australia) and was told, charge derating would happen between -10degC and +15degC and the data sheet version 1.5 reflects this. Anybody thinking of using this battery, be aware charge derating happens when the battery temperature drops below +16degC.

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Alexandra avatar image Alexandra ♦ commented ·
FYI not limited to BYD. Pylontec also do the same.

It is common for lithium charging.

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom#my_system_isn_t_charging_at_the_rated_capacity_or_my_pv_is_shutting_down


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gavin avatar image gavin Alexandra ♦ commented ·
I'm sorry but you are missing the point, The LV Flex5 battery is advertised as having a Charge Current de-rating between -10degC and +5degC. So if the battery temperature is +5degC and below, the max charge current would be reduced and if the battery was warmer than that, you would have maximum charge current. But Byd have changed the specifications to Charge Current de-rating between -10degC and +15degC and this is not reflected in there operating manual. Also Victron did a webinar with Byd that has outdated information in it and I wanted everyone to be aware of this.
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Alexandra avatar image
Alexandra answered ·

@Gavin

They show what more they can take. Not so much the total.

You will see the same on discharge. The DCL will drop according to hiw much more you can pull. When you see if drop to zero than you are pulling max out.

I have also noticed when they are at lower SOC they like to gently bring up the SOC to over 50% before letting and ramping up to the full charging amps in.

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Alexandra avatar image Alexandra ♦ commented ·
Trying to make the explanation clearer 2 units can take 120A of charge.

If you are putting 83A in already you will see 37A on the CCL.


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gavin avatar image gavin Alexandra ♦ commented ·
With the LV Flex5 battery that we have, DCL has not changed from 120A and CCL only changes with battery temperature or at 99% state of charge. so far the SOC has ranged from 21% to 100% with use and recharge. CCL changes from 26.8A to 89.6A when battery temperature increases to 17degC and will drop from 89.6A to 26.8A when the battery drop to 15degC.
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Alexandra avatar image Alexandra ♦ gavin commented ·

We are also off grid- but no AC PV - Maybe that is the difference. Also on this instance we had only one on the system to see how it behaved.

This was the result - temps also 17degC untill it was charging.

byd.jpg


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