Contactors - Best strategy for control?

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cloudy
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Contactors - Best strategy for control?

Post by cloudy »

Designing the basic HV layout for a car using a Tesla Small Drive unit, 96S battery (simpBMS) with outlander charger/DCDC with possible DC fast charging/CCS in future.

A start of the layout is below (its not complete), I'm wondering how people approached the control of HV contactors - especially as several common systems expect to be wired to them, and also which parts of the system you energise when charging.

Tesla SDU - Has precharge and contactor control
SimpBMS - Has precharge and contactor control
DC Charge - will need separate contactors


Should simpBMS be given sole control of the HV pack contactors?
Or perhaps should the SDU and the simpBMS be wired with AND logic to require both?
As the DCDC can be controlled separately to the charger could I just energise the whole system even when charging using main pack contactors - the DCDC in the charger will want power whenever the drive is powered (obviously interlock the drive enable with the charge)


Grateful for any feedback or discussion around a sensible approach - I'd rather use the minimum number of contactors to do the job safely....
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Re: Contactors - Best strategy for control?

Post by ZooKeeper »

Not that anything I say should be taken as wise, authoritative and certainly NOT gospel...

I am using the VCU to handle the DC side HV controls and the charger to handle the AC side relay(s). Not having all the components, this plan has not yet been physically validated.
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Re: Contactors - Best strategy for control?

Post by tom91 »

Largest Issue I found with BMS contactor control is that if drive units are harmed with HV drop outs, best to have the drive unit control main contactors or not have them controlled by BMS or Driveunit.

Ways would recommend running it is a logic that allows both BMS or DU to allow turning on of contactors, but contactors only dropping out on ignition cycling. The BMS would pull drive enable when issues occur and not drop out the HV.
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cloudy
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Re: Contactors - Best strategy for control?

Post by cloudy »

That was a consideration, as the Tesla SDU is rumoured to be sensitive to HV dropouts. It would seem both recommendations call for a separate VCU that "owns" contactor control and either reads BMS/DU stats via CAN and does software logic - or I could build some hardware logic from the digital contactor outputs from DU and BMS...

Any downside I wonder to just having one set of contactors at the battery for AC charge and drive modes? Means the DU is powered during charge - any downsides (assuming hardware interlock during charge)?
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Re: Contactors - Best strategy for control?

Post by johu »

tom91 wrote: Mon May 03, 2021 10:21 pm Ways would recommend running it is a logic that allows both BMS or DU to allow turning on of contactors, but contactors only dropping out on ignition cycling. The BMS would pull drive enable when issues occur and not drop out the HV.
That is pretty much exactly what I did in Touran. VCU owns the positive contactor and closes it once key is in start position and various other conditions are met. After that it is NEVER opened again until complete car shutdown.
Negative and precharge are always on when car is on.
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Re: Contactors - Best strategy for control?

Post by arber333 »

tom91 wrote: Mon May 03, 2021 10:21 pm Largest Issue I found with BMS contactor control is that if drive units are harmed with HV drop outs, best to have the drive unit control main contactors or not have them controlled by BMS or Driveunit.

Ways would recommend running it is a logic that allows both BMS or DU to allow turning on of contactors, but contactors only dropping out on ignition cycling. The BMS would pull drive enable when issues occur and not drop out the HV.
I have both Openinverter and Lebowski systems. And i trigger DC contactor only at deliberate start or stop.
My BMS even though it only has 2 outputs pulls them down to GND which in turn shows GND to a relay which then activates MPROT pin on the Openinverter and reset pin on the Lebowski. This only shuts down the pwm and as soon as reset signal returns inverter connects itself back.
Contactor goes out only when i remove 12V power to inverter completely.
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Re: Contactors - Best strategy for control?

Post by celeron55 »

I think the other important consideration is having enough ways for charging to stop before overcharge occurs, as that's the main reason the car could burn down unattended.

Usually the charger measures total pack voltage by itself, which is one way, but doesn't take individual cells into account. That's one failsafe, but not perfect if a single cell fails.

Then there's the BMS, which will generally have a "stop charging" output to the charger. That will protect the pack on a cell level if the charger is listening.

Then you're left with the case of the charger not listening to the BMS when a single cell is at overvoltage. I think it is important to make sure the BMS can force the charging to stop even in this case. In my system the BMS controls the contactors and precharge, but it's not recommended to rely on that when driving as the inverter may not like a HV dropout. But you can enforce this logic at many levels, for example using a BMS controlled contactor at the charging port or charger output, or using a VCU or even just relays as final logic for contactor control.
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Re: Contactors - Best strategy for control?

Post by LRBen »

I was planning to use my OI control board to control the contactors via the contactor and precharge ground signal pins. I did wonder if I should use automotive relays in between as I thought the contactor closing currents might be too high to go through the board.

But thinking about it now. Maybe it would be smarter to have the teensy control the contactors, as they could draw in allot more information from the inverter and BMS and it would allow for a tighter control of when the contactors close.
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Re: Contactors - Best strategy for control?

Post by cloudy »

This is really helpful - thankyou... To paraphrase the competing requirements seem to be:

On
  • Something needs to control the precharge, precharge success check and positive contactor for drive mode startup
  • Something needs to bring the DC- contactor online (could just be ignition switch, but ign would need to be on during charge)
  • Something needs to contact at least battery > charger during charge mode startup
Off
  • BMS needs to at least be able to pull a charge or pack contactor for charge safety
  • DU may need to pull contactor on overcurrent? BMS could also handle this with main pack fuse as a last control
  • Something needs to be able to pull the battery contactors once the vehicle is stopped to switch off
  • HV isolation check (if installed) needs to be able to pull both contactors
Any considerations I've missed?
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Re: Contactors - Best strategy for control?

Post by arber333 »

cloudy wrote: Wed May 05, 2021 9:50 am This is really helpful - thankyou... To paraphrase the competing requirements seem to be:

On
  • Something needs to control the precharge, precharge success check and positive contactor for drive mode startup
  • Something needs to bring the DC- contactor online (could just be ignition switch, but ign would need to be on during charge)
  • Something needs to contact at least battery > charger during charge mode startup
Off
  • BMS needs to at least be able to pull a charge or pack contactor for charge safety
  • DU may need to pull contactor on overcurrent? BMS could also handle this with main pack fuse as a last control
  • Something needs to be able to pull the battery contactors once the vehicle is stopped to switch off
  • HV isolation check (if installed) needs to be able to pull both contactors
Any considerations I've missed?
Ok i can provide further examples:
  • Something needs to control the precharge, precharge success check and positive contactor for drive mode startup
Openinverter has integral output for precharge relay which comes online when 12V is applied to inverter. It goes offline the moment when DC contactor is active.
  • Something needs to bring the DC- contactor online (could just be ignition switch, but ign would need to be on during charge)

Openinverter has integral output to control DC contactor. It is interlocked with DC link voltage a threshold you can set in interface.
DC contactor will go offline:
a) when DC link is lower than precharge setting
b) when you disconnect power to inverter
c) when conditions are met for safety disconnect, a setting which i rather set at "allways" so that inverter tries to reset under power in case of fault condition.
  • Something needs to contact at least battery > charger during charge mode startup
I keep AC charger permanently connected to DC side in front of the contactor and via 20A fuse. My BMS disconnects AC power by AC relay.
I will probably replace the fuse when i incorporate chademo, but that will also require i connect 2x contactors separately.
  • BMS needs to at least be able to pull a charge or pack contactor for charge safety
Not really, i have a fuse and AC contactor which is much easier to control. .... well to be honest, i have both AC and DC ciontactors part of my EMW charger, not for safety, but to reduce energy surge in case i would suddenly pull the AC cable.
  • DU may need to pull contactor on overcurrent? BMS could also handle this with main pack fuse as a last control
No! i rather use safety disconnect switch (notaus) to pull down PWM and keep DC link connected untill i come to a stop.
I explained my circuit to TUV inspector and when i demonstrated notaus switch he was content it is safe enough.
I use a relay wired across notaus switch which is controlled by BMS. This is how i disable my car when charging and in case of overcurrent it would pull down PWM and car will stop.
Also BMS controls charger CAN bus and AC relay with addition of EVSE CP relay.
  • Something needs to be able to pull the battery contactors once the vehicle is stopped to switch off
Yes that is the function of DC contactor.
You may also have a quick fused disconnect on the other side. It comes realy handy when you need to service your charger or BMS. Just break the negative line and you can work on DC link safely.
  • HV isolation check (if installed) needs to be able to pull both contactors
I would rather use the circuit that would wait for the next inverter start and NOT allow charging or start then. Safer that way.
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Re: Contactors - Best strategy for control?

Post by mackoffgrid »

In my Solar Ute project, I didn't know where the contactors going to placed so I made a CAN based contactor controller - may seem over the top, but it includes the pre-charge circuit, and detection of full pre-charge circuits . https://github.com/mackelec/CAN-tactorR

What is relevant to this discussion I think is, one of the CAN commands will lock the contactors ON using hardware and will only release by removing 12v power. I don't have to use the LOCK feature - but I CAN :-)
https://github.com/mackelec/SolarUte
meFDCAN Arduino Library 3 FDCAN port stm32G4xx
meCAN Arduino Library 2023 version 2/3 CAN port stm32F0xx, stm32F1xx, stm32F4xx, stm32L4xx
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