openinverter forum

Hi everyone, I have a chance of getting a 30kw CHAdeMO evse module at a good price. It has PFC, adjustable Voltage and Current outputs, CAN and over current/voltage protection etc. Can anybody see a good reason why this module can't be used as OBC (with a few safeguards or mods) ? It seems too good to be true. Thanks ..... Steve

Should be doable, but likely to be 3-phase supply only, and assuming that's the case, you'd need to prevent it trying to work if plugged in to a single-phase chargepoint. This may be less than trivial as the chargepoint won't tell you if it's single or 3 phase - you only know when the power is turned on. A decent 3-phase device ought to detect lack of phases, cheapo Chinese one maybe not so much. You can get relays designed to detect loss of phases for protecting motors etc.

You'll also need to make it limit its current draw based on the incoming J1772 PWM signal. Again that may be less than trivial as you need to limit the input current, not the output.

Hi Mike, yes, it's 3ph + PE, which is fine for me as this is for "travelling charge" (eg motorways). Domestic charge is via the inverter/motor.
The module has a phase-present check, also short-circuit, voltage in/out current in/out protection. It did seem to good to be true, as it's lighter and smaller than 3x 6.6kw chargers - cheaper too.
Current draw should be ok, as I'm using 400v dc and the module draw is around 80A max (about 0.44C of my 180Ah batteries)
It looks like I'll need to build suitable sensors between the batt pack and module and maybe some sort of soft-start if needed. I'm not sure what CAN protocol is used. I understand from Electrocity, that all 3 phases are live on their public evse - maybe I'll check with ZapMap too.
Thanks for your interesting comments....Steve

Any chargepoint listed as 11, 22 or 43kW will be 3-phase, you just need to limit your current draw accordingly

That's just what I need to know - many thanks

Hi again, Just to clarify (please bear with me - I'm old and very new to this ). If my car identifies itself as being, say, 30kw capable, the evse will supply 11kw its max, at a 11kw unit or 22kw, its max, at a 22kw unit or 30kw at a 43kw unit ?? Or do I need to select the appropriate resistor (switched) to suit the particular evse pwm ? S

The EVSE capability is communicated via a PWM on one of the control pins (CP). If your charger can process that directly, it will limit its input current accordingly. If not, it will try to pull 30 kW from an 11 kW station. Then you'd need to process the CP signal in a separate unit (e.g. your vehicle control unit, if existent) and only command as much DC power as there is AC power available. Perhaps minus 5-10% heat loss.

Esbro wrote: ↑Sat Jun 19, 2021 9:27 pm Hi again, Just to clarify (please bear with me - I'm old and very new to this ). If my car identifies itself as being, say, 30kw capable, the evse will supply 11kw its max, at a 11kw unit or 22kw, its max, at a 22kw unit or 30kw at a 43kw unit ?? Or do I need to select the appropriate resistor (switched) to suit the particular evse pwm ? S

It's the other way round - the car does not tell the EVSE what it's capable of. The EVSE tells the car how much it's allowed to draw, via the PWM duty cycle ( note this can potentially change dynamically during charging, e.g. if load balancing with other chargers) . The car's onboard charger must limit its input current accordingly.
There is an additonal control - a resistor on PP that indicates the cable capacity ( for a non-tethered cable) , so if you use a 16A cable on an EVSE/car combination that would otherwise pull 32A, the car limits the current to 16A.

As the Chademo module probably doesn't have a way to limit input current, you'll need to read the PWM signal and set a limit on output based on output power, likely input supply voltage (input current increases at lower supply voltage), and measured efficiency to get a reasonable estimate of what input current will be under those conditions. In practice, unless you're trying to squeeze every last drop, you may be able to just apply a safety margin and scale the output current once you've measured how the module behaves. a 16A EVSE is not going to trip or burn up at 17A.

Ah. now I understand. Thank you both for your answers . It seems that this module may not be the way to go. I thought it was too good to be true - otherwise everyone would want one .......Steve

It strikes me that there is a system design problem with evse. Wouldn't it be sensible to limit current at the source, to avoid potential overloads ? - or is it just me . ..... Steve

Esbro wrote: ↑Sun Jun 20, 2021 8:51 am It strikes me that there is a system design problem with evse. Wouldn't it be sensible to limit current at the source, to avoid potential overloads ? - or is it just me . ..... Steve

No, because it would be very difficult (read expensive and inefficient) to limit at source.
The car's onboard charger already needs to be able to control output power (and hence input power) to regulate the charge process, so to have it be able to limit input power based on information from the EVSE is trivially simple and cheap to do.

Overloads would only happen as a result of faults with the OBC or cable damage, and are dealt with like any other overcurrent situation, with a circuit breaker.
It may be the case that some EVSEs monitor current themselves and shut off if the car draws more than it's been told, to avoid tripping a breaker, but I have no idea if any actually do this in practice. The EVSE doesn't actually need to monitor current at all, though many do, to provide user feedback/remote status etc.

OK thanks - that's a good argument - I consider myself corrected. Like many others, I'm on a very steep learning curve and I'm most grateful for any input. Thanks again..... Steve

I have "tripped out" a 22kW EVSE with my 3 kW charger because I pulled more than the communicated cable limit. Seems to be a safety feature in some. A few minutes after removing the cable it reset and could be used again. They also measure current for billing kWh delivered, a legal requirement here in Germany.

Wow - definitely need to get that right !