Phev charger - does it need precharge

[FFMan]

I'm reworking my HV layout as i add another pack, and in my design the main contractors are connected directly to the 12v feeds that get livened up when the key is turned. i.e. pre charged occurs on position 1, full connect when the ignition is switch on i.e. position 2. this requires the driver to pause, but it time to put your seatbelt on and wait for the arduino to start etc.

The phev charger needs connection to the HV when the key is off so is conencted 'before' the main precharge setup.

Do i need to precharge the connection to the charger if i need to disconnect/reconnect it, or is precharge only really required on devices with big caps etc

[tom91]

You should not have any live cables outside the battery packs when the car is not key on or charging.

Also relying on a driver to do the precharge is quite a dangerous thing, that can lead to major damage.

[Bigpie]

The gen3 prius logic board can take care of your pre-charge for you. When charging I have the inverter in neutral and use it's start function so it will not drive.

My setup isn't ideal, I'd want to have the BMS decide if it's good to parallel the packs, but at the moment they just get paralleled when powered up, but stays behind the main/pre-charge setup. My main contactors are the beefy gigavacs. I've also got a fuse for each pack, but not shown on my diagram.

Idea is that the orange wires outside of the batteries are disconnected from both poles when the car is off.

[FFMan]

thanks for that.

I was intending leave my packs joined most of the time. I was concerned that being different ages and capacities they would settle back at different rates when idle, and whilst it should only be a few mv, i had a concern that rejoining them with a voltage difference wouldn't be advised.

The plan to join them, was charge them separately to the same voltage and then join them and leave them. Each pack will have a 400a fuse built into the service disconnect.

Not sure which is the better idea really. I like the idea of absolutely no current flow when disconnected, but on the other hand, i don't fancy joining the packs if they've sat disconnected from each other for a week - or am i worrying unnecessarily ?

[janosch]

...
I was intending leave my packs joined most of the time. I was concerned that being different ages and capacities they would settle back at different rates when idle, and whilst it should only be a few mv, i had a concern that rejoining them with a voltage difference wouldn't be advised.
...

Not sure which is the better idea really. I like the idea of absolutely no current flow when disconnected, but on the other hand, i don't fancy joining the packs if they've sat disconnected from each other for a week - or am i worrying unnecessarily ?

I also wondered about this when elaborating to connect packs manually, I always thought you could connect them via a resistor first, maybe put an Amp clamp meter around and see how much is actually flowing.

Anyone with good EE care to elaborate? I assume the answer is in Ohms law: If you have 100mV diff (quite lot, and unlikely after a week I would have thought), then connect it with a 1 Ohm resistor, you are limiting the current to 100mA, is that right?

There is a video of muxsan balancing in his range extender into a Leaf, I wonder what the maximum diff is for which you don't need to worry about inrush current.

[Alibro]

I'm reworking my HV layout as i add another pack, and in my design the main contractors are connected directly to the 12v feeds that get livened up when the key is turned. i.e. pre charged occurs on position 1, full connect when the ignition is switch on i.e. position 2. this requires the driver to pause, but it time to put your seatbelt on and wait for the arduino to start etc.

The phev charger needs connection to the HV when the key is off so is conencted 'before' the main precharge setup.

Do i need to precharge the connection to the charger if i need to disconnect/reconnect it, or is precharge only really required on devices with big caps etc

Some time last year I got good advice NOT to wire the contactors this way as sooner or later you will end up with welded contactors and a dangerous situation.
When rebuilding my HV junction box I discovered both contactors were welded shut and I had no idea when or how it had happened.

I'm using a BMWEV Nissan Leaf Gen 1 VCU which has outputs for this purpose so I now use them to control the precharge and main contactors. The VCU will not enable the main contactor until the inverter has more than 300V through the precharge.

[FFMan]

Some time last year I got good advice NOT to wire the contactors this way as sooner or later you will end up with welded contactors and a dangerous situation.
When rebuilding my HV junction box I discovered both contactors were welded shut and I had no idea it had happened.

I'm using a BMWEV Nissan Leaf Gen 1 VCU which has outputs for this purpose so I now use them to control the precharge and main contactors. The VCU will not enable the main contactor until the inverter has more than 300V through the precharge.

I guess it could happen and therefore will at some stage especially if my wife drives it and in a lapse misses the precharge step.

So i'm reworking this to have two timed relays, one precharges for a few secs and then the main cuts in, and the precharge drops out. I'm not sure i get the need for waiting for the voltage, if the batteries are connected it's gonna happen, and if they're not then it doesn't matter. I've been running my prototype setup with first stage precharge controlled by my fair hand, counting to two and then cutting in the main.

[Alibro]

I guess it could happen and therefore will at some stage especially if my wife drives it and in a lapse misses the precharge step.

So i'm reworking this to have two timed relays, one precharges for a few secs and then the main cuts in, and the precharge drops out. I'm not sure i get the need for waiting for the voltage, if the batteries are connected it's gonna happen, and if they're not then it doesn't matter. I've been running my prototype setup with first stage precharge controlled by my fair hand, counting to two and then cutting in the main.

That's pretty much how I had mine connected using little timers with relays built in but somehow I still managed to weld my contactors.
In my case it may have been incompetence or a bad connection but there are other scenarios where, if the precharge fails to happen you'll have welded contactors and possibly a damaged inverter. One that springs to mind is the timing part of those timer modules are very unreliable as I have found in the past.
I have just rewired my HV junction box and am still using the timer modules but only because the VCU output is a switched Neg and it doesn't like driving relays or contactors directly. The Neg from the VCU seems happy driving the modules so I'm not relying on the timer aspect of them.

[arber333]

I think this was discussed here a lot of times.
To summarize; modern chargers are made with current limiters in circuit so connecting them directly to DC does no harm.

I use direct charger connection BEFORE main contactor and a DC fuse on the line. Put the blow fuse near the charger as it is more likely for the shor tho happen inside charger than battery. Fuse is essential as it is needed to protect the wiring from fire, not charger circuit from electrical overload. Keep this in mind if using permanent connection to DCDC as well.

One thing this kind of circuit will absolutely require is HV battery disconnect. Not just a fuse inline. This will greatly help you to service any part of your HV connection.

[FFMan]

I think this was discussed here a lot of times.
To summarize; modern chargers are made with current limiters in circuit so connecting them directly to DC does no harm.

I use direct charger connection BEFORE main contactor and a DC fuse on the line. Put the blow fuse near the charger as it is more likely for the shor tho happen inside charger than battery. Fuse is essential as it is needed to protect the wiring from fire, not charger circuit from electrical overload. Keep this in mind if using permanent connection to DCDC as well.

One thing this kind of circuit will absolutely require is HV battery disconnect. Not just a fuse inline. This will greatly help you to service any part of your HV connection.

> To summarize; modern chargers are made with current limiter

ok i wasn't aware of that. But i need precharge anyway for the inverter and the cabin heater. Since i first wrote the post i've changed the wiring layout.

for protection each pack has a 'master service disconnect' from cintini with a 400amp fuse in it located as close to the pack as possible. Pulling both MSD isolates the car entirely. For safety i have an 'HV live' neon on the contactor box so ii'll see if the contactors weld shut hopefully.