Newb Asks: Is There A Clever Way To Connect A Charger To The Safety Box

[Gregski]

first apologies I don't know where to post this question, as I feel it is brand specific (aka BMW Safety Box) but I am using a first gen Chevy Volt battery charger, so here is my question, I am a minimalist, obsessed with repurposing OEM hardware (though I aint skierd to roll my own) the goal here is to use as little components as possible to SAFELY use the same safety box (if possible) to supply power to the [Lexus GS450h] Inverter as well as allowing the charger to interface with the battery but only when charging. I believe these events need to be mutually exclusive, please put me in the right place if I am mistaken. I hope to use Damien's VCU ver 2 (pre ZombieVerter) to control all three components with an Arduino sketch if possible: the Inverter, the Safety Box, and the Charger.

• Can we connect the charger directly to the same safety box?

• If so how can we connect the charger to the safety box?
  • more specifically which contactors do we use and what side of them do we tap into?

• do we have to use both contactors, can we use only one and do some tricky VooDoo stuff that connects the charger to the pack but does not turn on the Inverer

I do not plan on using a Level 2 J1772 chord thingie at first, just a standard 120v 15a wall plug, so aside from not driving off with the charger still plugged in to the wall socket:

• can we damage the charger if we inadvertently power up the Inverter?

• and more importantly can we damage the Inverter if we accidentally turn on the charger?

I blow up the BMW Safety Box into smithereens here: I went after the Safety Box next it was before I had the ballz to post something on this forum, and knew better, mea culpa

forgive me for picture overlap and redundancy with some of my other posts I do not intend to clutter the forum I just like for each thread to stand on it's own

[johu]

Putting inverter, charger, dcdc etc. all in parallel is common practice (e.g. Nissan Leaf stack). Don't see a need to dedicate a relay to just the charger.

[Gregski]

Putting inverter, charger, dcdc etc. all in parallel is common practice (e.g. Nissan Leaf stack). Don't see a need to dedicate a relay to just the charger.

Thank you so much so let me repeat that in Gregski speak (pretend I am typing this very slowly, lol) and request one point of clarification which I will highlight .

So when I "start" my car, obviously the VCU will command the Safety Box to pre charge and then close both the contactors, this will supply "big power" to all three components the Inverter, the DC-DC converter, and the onboard charger, and we are good with that, other than the orange leads to the charger being hot (not warm but full of zappy electricity) we don't care it aint gonna hurt noffin'. This part I can live with.

Now I plan on doing some sort of tricky Ricky thing with my 1971 ignition switch in the truck so that instead of "starting" the vehicle I only enable charging [by using the ACC aka accessory position so turn the key counter clock wise (to the left you young iWatch owning Padawans instead clock wise to the ON position) so in this case the VCU again will command the Safety Box to pre charge and then close both the contactors, this will supply "big power" to all three components the Inverter, the DC-DC converter, and the onboard charger, however the Inverter will be powered off.

This is the part that I was hesitant about, since I don't understand the internals of the Inverter, when the Inverter is OFF (no low voltage provided) does it still need to be pre charged? Why would you pre charge a powered off Inverter? Well cause it's all physically connected in parallel. So do I still need to follow the same pre charge first than close both contactors routine so that the inrush of full power from the battery pack to it won't blow up it's capacitor(s)? Or is there some sort of internal protection that disables that link/path when it is powered off? So that if I only want to charge I can just enable both the negative and positive contactors and skip the precharge? I ask because I believe the Volt charger does not require a pre charge. This is more of a satisfy my curiosity question than anything else.

so just connect it directly to the Safety Box just like what I did below for the DC-DC convert with the onboard charger:
(that safety box is stripped just for demonstration purposes, the actual one is loaded with all sorts of OEM gizmotron goodies)

[Zieg]

I think the capacitor in the inverter is going to need to be precharged whether the low voltage side is active or not. Don't think the inverter being inactive would affect that.

[Gregski]

I think the capacitor in the inverter is going to need to be precharged whether the low voltage side is active or not. Don't think the inverter being inactive would affect that.

[Gregski]

Putting inverter, charger, dcdc etc. all in parallel is common practice (e.g. Nissan Leaf stack). Don't see a need to dedicate a relay to just the charger.

The Nissan Leaf must be a different animal, since as it turns out (having welded stuck 4 contactors, lol) this may not work with the Lexus GS450h inverter due to what we think is an internal discharge circuit, let me explain

In what I call Charge Mode, I am supposed to turn on the VCU, the BMW Safety Box, and the Charger automatically (also the Tesla water pump and an Arduino UNO to PWM it) the Inverter stays OFF

so the Arduino sketch aka the VCU program straight away closes the Negative contactor and the Pre Charge relay in the BMW Safety Box, then it waits for the Output voltage to exceed my pre set voltage (say 270 volts) well this never happens because with the Inverter OFF the voltage is bleed off and I have watched the S-Box output voltage only go up by 1 volt like every 30 seconds so that would take 9 minutes before the VCU would command the Positive contactor to close in the S-Box for the charging to begin

[arber333]

....
This is the part that I was hesitant about, since I don't understand the internals of the Inverter, when the Inverter is OFF (no low voltage provided) does it still need to be pre charged? Why would you pre charge a powered off Inverter? Well cause it's all physically connected in parallel. So do I still need to follow the same pre charge first than close both contactors routine so that the inrush of full power from the battery pack to it won't blow up it's capacitor(s)? Or is there some sort of internal protection that disables that link/path when it is powered off? So that if I only want to charge I can just enable both the negative and positive contactors and skip the precharge? I ask because I believe the Volt charger does not require a pre charge. This is more of a satisfy my curiosity question than anything else.
....

Inverter normally has additional large power rated, cca. 160R resistor which is wired across the main cap. This one is for safety so when DC link dissapears the remaining voltage is consumed. Normally in operation resistor is cooled by internal cooling plate as for the IGBTs. If you would keep your inverter under precharge you could damage this resistor if cooling wouldnt work. Also this resistor sinks some small current and it would decrease your SOC in the long run or require your charger to push more capacity into battery.

My way is to connect charger by a 6mm2 line in front of the DC contactor and fuse that line. In this case your charger does the job when car is stationary and there is no other HV system connected to it with possible strange outcomes...
If you already have a contactor box from OEM then just figure out how relays worked to open the charge line. OEMs do not want to leave charger connected if there is no charging going on.
Chargers today normally have inrush limiters which will protect caps during precharge so you can also connect them by DC relay directly.

[celeron55]

I've never seen a charger have its own relay into the main battery. It's always paralleled with the inverter and DC-DC and subject to the same precharge process. What OEMs are you talking about @arber333?

[arber333]

I've never seen a charger have its own relay into the main battery. It's always paralleled with the inverter and DC-DC and subject to the same precharge process. What OEMs are you talking about @arber333?

Chevrolet Volt

[EV_Builder]

Why not use a second box for the charger? Maybe it's the inverter which should have an extra relais connecting HV when low voltage is applied. Then the box stays the box and the inverter bleed is countered.