[!CAUTION] Working with high voltage is dangerous. Always follow local laws and regulations regarding high voltage work. If you are unsure about the rules in your country, consult a licensed electrician for more information.

Compatible BYD batteries

The code supports a variety of BYD vehicle batteries. Check the product code sticker, and verify that the battery has already been tested with the Battery-Emulator, indicated by the ✅-mark that contactor closing works and the pack has been confirmed working

To get contactor closing to function, start BYD battery first, and Battery-Emulator afterwards. If you start Battery-Emulator before the battery, it wont close contactors before you restart the emulator. Also make sure no FAULT events are active when trying to start, this will open contactors.

Product Type	Byd Model	Energy	Capacity	Nominal voltage	Status
PV2	?	40 kWh	150Ah	300.8V	✅
PE4	Seal	61.66kWh	150Ah	409.6V	✅
???	Atto 3	50kWh	?	?	✅
P48	Atto 3	60.48kWh	150Ah	403.2V	✅
VD6	Seal U DM-i	18,32kWh	54Ah	339.2V	:x: (Type B LV connector)
PA4	Tang	86.4kWh	135Ah	640V	:x: (Type B LV connector)
PE5	Seal	82.56kWh	150Ah	550.4V	✅
PE6	Seal	82.56kWh	150Ah	550.4V	✅
PK3	Dolphin	49.92kWh	150Ah	332.8V	-
P07	T3	50.37kWh	115Ah	438V	-
P94	Dolphin	44.928kWh	135Ah	332.8V	✅
P99	?	44.928kWh	135Ah	320.0V	-
PC5B	Dolphin mini	38.8kWh	135Ah	288V	:x: (Type B LV connector)
?	Song Plus	82.56kWh	150Ah	550.4V	✅
PM6	Song Plus	87.04 kWh	170Ah	512.0V	✅
PM7	Seal U	71.80 kWh	170Ah	422.4V	✅
VM7	Sealion 8 (AU)	?kWh	78.4Ah	454.4V	:x: (Type B LV connector)
PW4	Seal 7	91.392 kWh	170Ah	537.6V	✅

Confirmed working BYD Seal 60kWh battery example sticker:

[!NOTE]
If you intend to run two BYD batteries in parallel, make sure they are both the same model!

Example battery install, Atto 3 P48 battery

The extended range nominal 60.48 kWh BYD Atto 3 blade battery pack is 1.2m wide by 2.1m long and 120mm high, weighing 402kg. The battery chemistry is LFP (LiFePO4). The battery configuration is 126s1p, estimated capacity of fully charged pack is 126 cells at nominal 3.2V x 150Ah connected in series = 60.48 kWh. Fully charged the pack produces total voltage of 441V max (3.5V/cell) and at 10% SOC, about 403V (3.2V/cell), as measured and monitored by OBD2 CarScanner during charging.

Viewed from the front, left is the low voltage connector, central is two refrigerant lines and right is the HV connector, with +ve on RHS.

The front connectors end of the battery also includes the contactor block. There is a well-hidden 800V/350A fuse near the positive contactor(coil:12VDC/contactor:250A) on the RHS of the block, along with a mini pre-charge contactor (coil:12VDC/contactor:10A) and a pre-charge resistor, which is underneath the HV connector. There is no Tesla-like pyro fuse that blows when airbags are deployed; the system just opens the contactors.

Software configuration

For this battery type, use the option called "BYD Atto 3/Seal/Dolphin" under the "Battery Protocol" setting

Video example

Here is a great video made by "Flying Tools" showcasing how to connect the BYD Atto 3 battery

https://www.youtube.com/watch?v=YBYWBapnnyM

Battery specifications

LV Connector Type A

The connection diagram is derived from reverse engineering the pins. The following pinout is valid for, but not limited to, PE4, PE5, PE6 and P48 battery. It can be identified easily by seeing that there are 4 rows of pins, and three thicker pins on the side

LV Connector Type B

This connector appears on newer battery types, such as the PA4. The software does NOT have support for TypeB batteries yet :x:

PA4:

PC5B (upside down compared to PA4):

PC5B pinout from manual:

• 4 - Constant 12V power
• 5 - Ignition 12V power
• 8 - Charging Subnet CAN-L
• 10 - Energy Subnet CAN-L
• 12 - DC charging pos/neg power supply (12V in)
• 13 - HV interlock signal 1
• 14 - DC+ temp sensor signal
• 15 - Charging Subnet CAN-H
• 16 - GND
• 17 - Energy Subnet CAN-H
• 18 - HV interlock signal 2
• 20 - DC- temp sensor signal
• 21 - DC charging port temp sensor GND
• 22 - Collision signal
• 23 - GND
• 24 - DC charging pos contactor control signal
• 25 - Charging connection confirmation CC
• 26 - DC charging aux power supply wakeup A+
• 29 - Ignition 12V power
• 30 - On board charging connection signal
• 31 - DC charging negative contactor control signal
• 32 - DC charging sensor signal
• 33 - Charging connection confirmation CC2

HV Connectors

High voltage connectors vary a bit between the different BYD variants. Due to this, it is best to try and source the high voltage cable from the same type of vehicle that the battery came from.

Contactor Block Modification

In the event of the battery being locked, the pre-charge and two contactors can be wired to manually switch on, or preferably to automatically activate via 3 SSRs with the GPIO pins on the Lilygo board (see https://github.com/dalathegreat/Battery-Emulator/wiki/Contactor-Control-via-GPIO-pins). When accessing the internals of the battery, wear the appropriate safety gloves and follow safe procedures to avoid shorting across HV terminals. To access the contactor block, first remove the top cover, which fortunately is not sealed down; ~ 76 screws and 2 central top bolts require removal. In the pictorial description that follows, details of the full removal of the contactor block is shown, to identify the various parts. With connection points identified, it is now not necessary to remove the block as these 12V connection points are accessible from the top of the block. This current protocol involved connecting 3 circuits individually to the precharge and two contactor relays. This was achieved merely by wiring in extra lines on top of existing wiring connector points. With hindsight, a more effective alternative is included in the discussion below (Unlocking a crashed battery). https://github.com/juancruz1953/Images/blob/main/Atto3ContactorBlockRewire.pdf

Contactor control over CAN (software — no teardown)

As an alternative to wiring the contactor block to GPIO via SSRs, Battery-Emulator can open and close the pack's own contactors over CAN. For a healthy (non-crashed) pack this means you don't need to open the battery or fit any relays.

Requires firmware [10.11.0]+

Behaviour

• Closing is automatic — Battery-Emulator closes the contactors once the inverter signals it is ready and there is no active fault.
• Opening is sequenced like the car — power is commanded to zero first, BE waits for current to fall to a safe level (with a timeout), then runs shutdown → open-request → standby. The pack is never dropped under load.
• Manual open/close is available from the More Battery Info page. [confirm exact button labels]

Safety interlocks

Contactors are commanded open automatically whenever:

• the equipment-stop is active,
• the inverter withdraws permission to close (e.g. Solax / SMA not yet ready), or
• the system enters a FAULT state — including loss of CAN communication with the battery or inverter (faults after ~60 s).

Notes

• Keep the original startup order: power the BYD battery first, then Battery-Emulator.
• There is no remote dead-man on the control link — if you lose the web UI / VPN, the contactors stay in their current state. For unattended installs, rely on the fault / e-stop / inverter interlocks above and treat manual control as on-site only.

Parts list

Here are some of the part numbers and purchase links, incase your battery came without them

Part	Product Link	Notes
LV connector	AliExpress	19pin 1192800MB 1192800FB BYD
LV connecor Pre-wired	https://a.aliexpress.com/_EHMKS3i
HV cable	----	OEM numbers: 1364774600 & SC2EM215300A or SC2EM-2105300
HV cable PE5/PE6	----	OEM numbers: EKEA2105300Y / 13568667-00

Example, high voltage cable for P48 Pack # 1364774600

Example, high voltage cable for PE5/PE6 Pack # EKEA2105300Y / 13568667-00

Note on reusing HV cable :zap:

If you are using the HV cable that came with the battery, and plan to cut off the ends to crimp on new terminals, be aware that the cables contain an outer shield layer. It is very important to properly insulate this, so you do not short high voltage to protective earth accidentally.

When preparing the cable, special attention must be taken the cable's shielding:

First make sure to leave at least 8mm space:

Then apply hot glue or other insulation adhesive:

Final insulation layer applied:

It is recommended to check your handiwork, by performing an insulation test on the cable after completing the work

How do I know if I have a crashed&locked battery?

If the contactors do not engage when sending CAN towards the battery, the pack is most likely locked.

Another way to check is to inspect the "More battery info" on the webserver. This page contains the SOC% value sent by battery (SOC Highprec). If this value stays the same when charging, discharging, the battery is locked.

SOC Drift overtime

All users will experience a phenomenon where the battery’s SOC appears to drift when using SOC measured by BMS, causing the charging process to stop before the SOC reaches 100%. This drift will gradually increase over time, reducing the available capacity of the battery. Typical value is 1-2% SOC underreported drift per day.

[!NOTE] As of firmware 10.10.1+ there is an Auto-calibration function to counteract this but the following manual method can still be used for SOC and capacity manipulation if required.

• Go to the "Calibrate SOC" option. From version 10.3.0 this can be done from the "More Battery info" page.
• Set the "Calibration target SOC:" option to the desired SOC% you want.
• Set the "Calibration target capacity:" option to the desired AH capacity (this value will be copied by default from the BMS and will effect your SOH (State Of Health) values!
• Finally, press the "Calibrate SOC" button

Automatic SOC calibration

Rather than running the manual Calibrate SOC procedure periodically, Battery-Emulator can recalibrate SOC to 100% automatically whenever it detects the pack is genuinely full — correcting the BMS's gradual coulomb-count drift on its own.

Requires firmware [10.10.1]+. (on by default).

What it does

When enabled, BE watches for the pack sitting at a true, settled top-of-charge and then performs the same calibration write as the manual button — a security-access write into the BMS — so the correction persists across reboots. It then starts a cooldown so it won't repeat unnecessarily.

When it triggers

A calibration is performed only when all of these are true at once (whose status is visible in the more batt info page):

• Automatic calibration is enabled.
• The pack is at the top of charge — the charge taper has reached its critical stage (cells near full and current capped to the ~1 A tail).
• The main contactors are closed (the pack itself reports closed).
• Current is essentially at rest — roughly between 0.5 A discharge and 3 A charge.
• That settled, full condition has held continuously for ≥10 minutes (a brief current excursion of up to 60 s is tolerated without resetting the timer).
• Reported SOC has drifted below 100 % by more than your configured threshold (so it only acts when there's meaningful drift to correct).
• At least 1 hour has passed since the last calibration (cooldown).

If any condition isn't met — for example your setup never quite reaches a sustained full charge — it simply won't fire, and you can still calibrate manually.

Configuration

On the More Battery Info page:

• Auto-calibrate SOC to 100% when full — the on/off toggle.
• Auto-calibrate trigger drift (%) — how far below 100 % SOC must drift before an automatic recalibration is allowed (higher = less frequent corrections).
• A live status panel shows each trigger condition (taper reached, current in-window, dwell timer, drift %, cooldown ready, contactors closed) so you can see exactly why a calibration has or hasn't happened.

Notes

• It is deliberately conservative: it requires a genuine, sustained full charge and real drift and the cooldown, so it won't spam writes to the BMS.
• It writes to the BMS exactly like the manual procedure, so the same persistence and caveats apply.

How do I unlock a crashed battery?

There are two methods to try and unlock the battery. The methods are via More Battery Info page (easy), and alternatively via CAN Replay (harder)

[!IMPORTANT] To be able to unlock, you need separate control over B+ and IGN pin going towards battery (The two 12V pins on the battery). These need to be powered on/off in a specific sequence

• Pin 4 12v+ BMS
• Pin 5 12v+ ignition
• Also make sure 12V supply has atleast 12.8V and 2A available before starting the unlock procedure

More Battery Info Unlock

There is a button in the "More Battery Info" page in the webserver, that when pressed will attempt to unlock the crashed battery.

CAN replay

One user reported success by manually sending the CAN log file while the battery

resetLockedBYD_v1.txt

User 1: About the power cycle and how I did it..

• Battery-Emulator compiled with only TEST_FAKE_BATTERY and no inverter selected
• Started with no power to either 12V constant or 12V ignition. I have separate switches for them though.
• So first Battery-Emulator hardware is powered on.
• Then 12V constant switch on, wait a few seconds and ignition on.
• At this point no communication is present on CAN, complete radio silence.
• Run unlock commands, upload resetLockedBYD_v1.txt in the CAN replay page in Battery-Emulator, and transmit it towards the battery
• Once again radio silence.
• Switch off 12V ignition.
• Wait a few seconds and then switch off 12V constant.

User 2 success story:

• I have B+ and the 2 ignition wires on seperate switches.
• I turn on B+ first then ignition.
• Software was setup for BYD ATTO 3, v8.13.0
• Then I ran unlock procedure via "More Battery Info" page
• After the unlock I turned off ignition then B+ and the Liligo together then reverse process turning back on.
• Contactors closed after.