3-phase charging on supported public EVSEs (charging stations)

[dazzleworth]

Hi all,

This is my first post, so bear with me. Has anyone tried this config before either in terms of knowledge theory or practice? The idea is to utilize all 3-pins (L1 - L3) to separately power 3 AC e-bike chargers simultaneously for parallel battery charging. The chargers are off-the-shelf 220 - 250 VAC but high current (8 - 12 Amps) that will not be modified internally in any way.



This design is compatible with both 1-ph (which make up the majority of chargers in my area) and 3-phase EVSE if available. Charger 1 will always be running by default.

My questions

1) Is there an issue with 3 chargers sharing the same neutral line? 3- phase lines from the grid at 480 V will have 250 VAC when connected in phase-to-neutral, but EVSE output may implement higher safety tolerance as stated in the internal spec. In most other vehicles OBC, based on my research simply rectify all the Lines to DC and have its own GND without ever returning to neutral. However, this is 3 separate single phase systems.

2) On the DC side output that will feed the battery, how will the chargers on the network know when the battery is full to turn itself on standby mode? Will it happen together? Which charger will shutdown first? Given that compatible charger with battery selection and that all 3 chargers are of same volts DC output 48/60/72/84/96 VDC, are there safety or fire risk issues that I need to take note of with using 3 chargers?


Control circuit

On the website Proximity Pilot and Control Pilot overview - PhilipMcGaw.com , there are 2 versions of the control circuit that can be used to initiate charging. The 1st one is a legacy circuit that can draw max 10 amps from the EVSE. Presumably, that also means 1-ph charging only



The 2nd image is a more updated circuit that allows "fast charging". 3 phase charging is generally considered "fast charging" due to the more power it provides. So I'll have to implement the new control circuit:



What are your thoughts?

 

[dominik h]

I have already done three phase charging my scooter, but only from a normal three phase CEE Socket.
They also share the same neutral.
This works without any problems.

The chargers will end charging every one by itself, when the charger thinks the battery is full.

The Screenshot is from charging with two Huawei R4875G5 (each set to 43,5V = 87V) in series connected on two phase and neutral and two Vertiv R48-2000E3 (set to 87,5V) in series connected on the third phase.

 

[dazzleworth]

Yup, doing my own wiring isn't a option because I don't have access to my home's distribution board (it's an apartment), but I have charging stations near by. But my bike is used for work

 

[amberwolf]

1) Is there an issue with 3 chargers sharing the same neutral line? 3- phase lines from the grid at 480 V will have 250 VAC when connected in phase-to-neutral, but EVSE output may implement higher safety tolerance as stated in the internal spec. In most other vehicles OBC, based on my research simply rectify all the Lines to DC and have its own GND without ever returning to neutral. However, this is 3 separate single phase systems.

As long as the chargers are internally electrically isolated, so that none of the DC side connects to any of the AC side, you can connect them however you need to, as far as they are concerned.

If they are not isolated, you cannot parallel them unless the input side wires that are shared with the output side wires are also paralleled; if they're connected in a way that shorts across anything then the chargers (and battery!) are shorted as well.


For the EVSE side I don't know if it makes any difference, but since home wiring shares the neutral on two phases I would expect the same to be true with EVSE.

AFAICR, in multiphase AC the neutral doesn't carry current; that's all done on the phase lines. You can verify if this is correct or not at AC electrical wiring learning sites. The only relevant one I saw in a few seconds of searching was this Three Phase Electrical Wiring Installation in Home - NEC & IEC if it's helpful.

2) On the DC side output that will feed the battery, how will the chargers on the network know when the battery is full to turn itself on standby mode? Will it happen together? Which charger will shutdown first?

If you mean the chargers you are using, then the charger with the lowest votlage output will shutdown first. (they are never exactly perfectly identical). This is because chargers are normally designed to shut off when their output current drops below a threshold (usually a few mA). If all the voltages are very very close, then they will all shutoff very close to each other.

Given that compatible charger with battery selection and that all 3 chargers are of same volts DC output 48/60/72/84/96 VDC, are there safety or fire risk issues that I need to take note of with using 3 chargers?

In addition to using isolated chargers, I'd fuse each one individually on it's input and output side, just in case anything goes wrong with any part of the system. Use fusing designed to protect the wiring itself, as that's where fires usually start, so sized for the current normally used in each part of the system, and sized to blow before current that could damage the wiring is reached. Fuses all have a chart from their manufacturer showing time to blow vs current flwoing thru the fuse. Major brands (eaton/bussman, etc) often have "how to size (or pick) a fuse" documentation as well.

 

[dazzleworth]

As long as the chargers are internally electrically isolated, so that none of the DC side connects to any of the AC side, you can connect them however you need to, as far as they are concerned.

If they are not isolated, you cannot parallel them unless the input side wires that are shared with the output side wires are also paralleled; if they're connected in a way that shorts across anything then the chargers (and battery!) are shorted as well.

How can we tell?



This is my charger

 

[amberwolf]

With the chargers disconnected from everything, use a multimeter on continuity or lowest ohms range, and measure from each DC side connector pin to each AC side connector pin.

You should read open circuit (usually OL or --) for every test. Anything that reads lower ohms is a non-isolated connection.

The most common non-isolated connection is AC ground to DC negative (ground). Second most common is AC neutral to DC negative (when there is no AC ground pin).

 

[amberwolf]

Oh, another consideration: What rate can your battery be safely charged at? Most ebike batteries have a safe charging limit of a few amps or less. If fed higher currents the cells and/or BMS can be damaged, or even start a fire.

Unless you're charging a huge battery (like a car or other large EV) or one made from cells that accept high charge rates (Lithium Titanate, for instance) therels not much point to even paralleling normal small chargers on a regular AC outlet.


Example: An old 8Ah 18650 Luna pack I have could safely be charged at maybe 3-4A, and heats up at that rate, so it's higher than it should be charged at; 2A is all I'd use for that.

The 40Ah EIG pack I use in the SB Cruiser has cells that like many safely accept only a low rate of 0.5C to 1C, but because it's a large pack it can be charged at a relatively high current; I regularly use 12A charging for it. I have used 24A charging for it in testing and it works fine; I have not tried 40A charging but it should accept that too).

 

[RoninMiles]

Great technical discussion! It’s fascinating to see how people are optimizing 3-phase charging. I’m still learning, but threads like this really help deepen my understanding of EV setups. Thanks to everyone who shares their builds and data—it’s super valuable for DIY enthusiasts. Academized’s buy expository essay service saved me when I was struggling with a complex topic. They helped me explain the subject in a clear and concise manner. If you need help with an expository essay, visit Academized. Their expert team will help you deliver an informative and well-structured essay.

 

[dazzleworth]

Oh, another consideration: What rate can your battery be safely charged at? Most ebike batteries have a safe charging limit of a few amps or less. If fed higher currents the cells and/or BMS can be damaged, or even start a fire.

Unless you're charging a huge battery (like a car or other large EV) or one made from cells that accept high charge rates (Lithium Titanate, for instance) therels not much point to even paralleling normal small chargers on a regular AC outlet.


Example: An old 8Ah 18650 Luna pack I have could safely be charged at maybe 3-4A, and heats up at that rate, so it's higher than it should be charged at; 2A is all I'd use for that.

The 40Ah EIG pack I use in the SB Cruiser has cells that like many safely accept only a low rate of 0.5C to 1C, but because it's a large pack it can be charged at a relatively high current; I regularly use 12A charging for it. I have used 24A charging for it in testing and it works fine; I have not tried 40A charging but it should accept that too).

That's where the Control Circuit comes in. Battery is about 50 Ah. Looking at another thread, it seems we can control the charging process via signals to the charging station's control pilot with another device and the charging states by opening/shutting relays when the voltage is over. See more here. In DC charging stations, there is a high level communication protocol that the station and the vehicle use to communicate charging states. Not sure if it applies to 3 phase AC charging as well

 

[amberwolf]

That's where the Control Circuit comes in. Battery is about 50 Ah. Looking at another thread, it seems we can control the charging process via signals to the charging station's control pilot with another device and the charging states by opening/shutting relays when the voltage is over. See more here. In DC charging stations, there is a high level communication protocol that the station and the vehicle use to communicate charging states. Not sure if it applies to 3 phase AC charging as well

Regardless of the source of power for the chargers, the voltage will never go "over" unless you are using the wrong charger for the battery, and if your'e doing that then you need as many safety cutoffs as you can get, because if they fail and you overcharge the battery, it's then damaged (in ways you cannot see from outside the cells) and has the potential for future fireworks at any moment.

If you use chargers whose terminal votlage matches that of the pack, you don't have to worry about that (unless a charger fails in a way that causes excessive voltage, which is rare; a BMS on the pack should prevent problems in that event).


If you're not using a BMS on the pack**** then the charger's voltage limit is your only real safety against overcharge, and the controller's LVC is your primary safety against overdischarge.

If you are using a BMS on the pack, then if it's correctly specified and designed for the cells you're using, it will be a secondary layer of protection...but you should still use a charger that is correctly set for the pack.


You can use either the pack voltage or the charger current or the BMS FET state to determine end of primary charge (not including balancing) and terminate charge at the station interface. You can even use multiple detections and logic to require any or all of them before charge termination.


If you were using the station's DC output, and programming it to a specific voltage and current, then communication with the station would be required to prevent damage or destruction of the cells.

With AC all you need is the ability to turn the AC power on. You don't even need to be able to turn it off when charge is complete because your chargers, if they are real chargers and not just CC/CV sources, will cease DC output once charge current drops below some point (whateve they're designed for).





****I don't because my EIG cells are well-matched and stay balanced, so a system-level LVC and HVC are sufficient to prevent overdischarge or overcharge. The charger is set to well below the total full voltage of the pack, less than 90% full IIRC, and the system LVC is set well above the pack empty point. Every so often I check the cell balance in static at full, empty, and under load.

 

[amberwolf]

Anyway, none of that has anything to do with what I was trying to point out in the post you'd quoted: that unless your pack is designed to be charged at the rate three chargers put out (36A total if they are 12A each), you'll damage the cells by charging them at too high a rate.

Many cells are only designed for 0.5C (or less) charging rate. If it's a 50A pack, that could mean a max of 25A or less charging. If the chargers are adjustable down to 8A (as in the "8-12A" in the OP), then you could get down to 24A which is a hair less than 0.5C for a 50Ah pack.

So, if you have not already done so, you'll need to find out what your cells can safely be charged at before deciding on a charge setup.