Does “shore power” go through the battery?

[darth_vad3r]

Can the car route “shore power” directly to accessories? (well not directly directly, but after AC to DC conversion.

e.g. If you have 6 kW AC input power and then turn ~1 kW of accessories on (AC + high fan?) is the car (a) sending all 6 kW to the battery and taking 1 kW out of the battery, or (b) sending only 5 kW to the battery and 1 kW to accessories?

The charge screen display certainly shows a drop in the charge speed (lower mi/hr rate) but this itself doesn’t prove anything, but it did make me think originally that only X% of the input power was being sent to the battery, and the rest was diverted to accessories — I didn’t think it meant it was showing me the net add amount after first all power went to the battery and then some came out for accessories, but it certainly could mean that I suppose.

Anyone know?

 

[theredviper]

I'm no electrician and can only guess wildly, but wouldn't that require multiple AC-DC rectifiers? and possibly more DC-DC voltage converters to get from 375V to 12V?

My guess is that it all runs through the HV battery.

 

[Saghost]

The charger converts it all into high voltage DC, and pushes it onto the circuit. The battery sits on that circuit, in parallel with all the other HVDC items. They all get fed together, so if you're pulling power for the A/C compressor, it goes from the charger straight there.

To do it any other way would require a bunch of additional complexity with circuits separated by diodes and wouldn't gain anything useful.

 

[darth_vad3r]

I'm no electrician and can only guess wildly, but wouldn't that require multiple AC-DC rectifiers? and possibly more DC-DC voltage converters to get from 375V to 12V?

My guess is that it all runs through the HV battery.

I guess I asked the question wrong, based on an answer in another thread. I’m just wondering if the input DC power must necessarily all charge the battery, or if some can bypass the battery. Whether that’s directed actively by the car or just passively by virtue of the loads being in parallel and how electricity works.

 

[darth_vad3r]

The charger converts it all into high voltage DC, and pushes it onto the circuit. The battery sits on that circuit, in parallel with all the other HVDC items. They all get fed together, so if you're pulling power for the A/C compressor, it goes from the charger straight there.

To do it any other way would require a bunch of additional complexity with circuits separated by diodes and wouldn't gain anything useful.

Ok so this seems like another vote for bypassing the battery, and me asking the question slightly wrong in the post by implying the car “directs it” actively

 

[theredviper]

Great, so I can and should run all accessories and HVAC while on a free charger?

 

[darth_vad3r]

Great, so I can and should run all accessories and HVAC while on a free charger?

Might as well? Pre-cool that car down to 15C!

EDIT: As long as you’ve added enough range and don’t mind the charge rate slowing down

 

[AlanSubie4Life]

Ok so this seems like another vote for bypassing the battery, and me asking the question slightly wrong in the post by implying the car “directs it” actively

It's not really bypassing it. It just isn't charging it. The battery is sitting there on the output of the AC-DC converter, and the AC-DC converter is supplying just the right amount of voltage such that zero current flows into that battery (assuming you have the charge limit set below the current battery charge level), but sufficient current can flow from the AC-DC converter into anything else that needs it that runs on the HV rail. Anything that uses 12V is running off the 12V, which has its own converter (DC-DC from HV to 12V) to supply it as needed (this DC-DC converter is one of the loads on the HV rail).

At least that's my understanding; there may be small errors in the above as I haven't studied the wiring diagram. Sounds like it matches what @Saghost describes though.

(This is why I think leaving the car plugged in likely messed with my latest failed vampire drain test - though it was intentional on my part to leave it plugged in - figure it's marginally better for the car over time if there is less drain from the battery.)

I can't answer your poll because I don't think it's bypassing the battery (if you hypothetically removed the battery from the car you'd probably have an open circuit...there's probably current flow across the main terminals) and I don't think it's drawing from the battery either.

 

[Saghost]

Great, so I can and should run all accessories and HVAC while on a free charger?

All the accessories that'll help you right then, yes - assuming you'll reach your desired SoC before you want to leave with them on.

No reason to be wasteful just because someone else is footing the bill, and running them will extend your charge session if you're charging to a specific value.

 

[Big Earl]

Great, so I can and should run all accessories and HVAC while on a free charger?

You can, but it will take longer to charge because some of the energy that would be going to the battery is now going to the accessories. Depending on the size of the charging station, the energy required to run the climate control might be more than the station can provide (example: cabin heat on a 16 amp charging station).

You shouldn't unless you need to because it's wasteful.

 

[jdw]

The chargers, battery and inverters all come together in the high voltage junction box .The contactors close when the chargers or heater are working, so it would seem that they are all connected together in parallel. I've never heard of any other switching circuit, other than the BMS system, which is likely what determines whether the battery is actively charging or not. But I see no method by which the battery is switched in or out of the circuit at the HV junction box. This makes sense also, as if your heaters are maxxed and your shore power/charger isn't able to supply the needed power, the battery will.

I would like to see a real schematic of what is going on, rather than speculate.

 

[darth_vad3r]

It's not really bypassing it. It just isn't charging it. The battery is sitting there on the output of the AC-DC converter, and the AC-DC converter is supplying just the right amount of voltage such that zero current flows into that battery (assuming you have the charge limit set below the current battery charge level), but sufficient current can flow from the AC-DC converter into anything else that needs it that runs on the HV rail. Anything that uses 12V is running off the 12V, which has its own converter (DC-DC from HV to 12V) to supply it as needed (this DC-DC converter is one of the loads on the HV rail).

At least that's my understanding; there may be small errors in the above as I haven't studied the wiring diagram. Sounds like it matches what @Saghost describes though.

(This is why I think leaving the car plugged in likely messed with my latest failed vampire drain test - though it was intentional on my part to leave it plugged in - figure it's marginally better for the car over time if there is less drain from the battery.)

I can't answer your poll because I don't think it's bypassing the battery and I don't think it's drawing from the battery either.

I don’t see how “not charging it” isn’t bypassing it. If the power (current) doesn’t flow through the battery (for whatever reason), then it has bypassed the battery, no? And the question in the poll is if the “shore power” (for accessories, not charging power) goes “through” the battery or not. Answer that question.

 

[miimura]

As said above, it's a passive "nature of electricity flow" kind of thing. The charger (rectifiers) is putting current into the system "at the junction box" as said above. Any consumption by accessories is siphoned off and whatever current remains goes into the battery, mostly because it has nowhere else to go. If you want to call that "bypassing", sure it's doing that.

 

[darth_vad3r]

The chargers, battery and inverters all come together in the high voltage junction box .The contactors close when the chargers or heater are working, so it would seem that they are all connected together in parallel. I've never heard of any other switching circuit, other than the BMS system, which is likely what determines whether the battery is actively charging or not. But I see no method by which the battery is switched in or out of the circuit at the HV junction box. This makes sense also, as if your heaters are maxxed and your shore power/charger isn't able to supply the needed power, the battery will.

I would like to see a real schematic of what is going on, rather than speculate.

Note though that I asked if it bypasses the battery, I meant the cells, not the BMS. Since the BMS can do switching, it could also theoretically actively send less power to the cells if it knew the accessories wanted that power, right?

Also, c’mon. Speculate! I gave you that option in the poll!

 

[AlanSubie4Life]

I don’t see how “not charging it” isn’t bypassing it. If the power (current) doesn’t flow through the battery (for whatever reason), then it has bypassed the battery, no? And the question in the poll is if the “shore power” (for accessories, not charging power) goes “through” the battery or not. Answer that question.

I updated my post concurrent with this response to clarify what I mean. It's kind of an arbitrary distinction. If you treat the battery as a ideal black box with zero size terminals, yes, it's bypassed since there is minimal current flow into or out of those terminals.

 

[jdw]

As said above, it's a passive "nature of electricity flow" kind of thing. The charger (rectifiers) is putting current into the system "at the junction box" as said above. Any consumption by accessories is siphoned off and whatever current remains goes into the battery, mostly because it has nowhere else to go. If you want to call that "bypassing", sure it's doing that.

I think it is more that if the BMS is not asking for power to charge the batteries, and if the load is not such that it requires power from the batteries, then the batteries are effectively bypassed.

It's not a serial Charger->Battery->Load (heaters, BMS whatever), it's a parallel Charger+Battery->HV Junction Box->Load as far as I can tell.

 

[darth_vad3r]

Please note that I asked about power, which is voltage x current.
If the battery “sees” the voltage but the current doesn’t flow through it, then the power isn’t going through it.
Whether we want to call this a “bypass” or not is up for debate, but the question is if the “shore power” (the power that’s coming indirectly from AC plug to power the accessories) goes through the battery or not.

 

[miimura]

I think it is more that if the BMS is not asking for power to charge the batteries, and if the load is not such that it requires power from the batteries, then the batteries are effectively bypassed.

That's not how it works. The BMS is monitoring the batteries and can only take extreme measures to open the contactors to protect the battery from over current or over/under voltage situations. The on-board charger is responsible to regulate the power taken from the wall and pushed into the HVDC bus. It looks at the BMS data and obeys the charging profile programmed for the battery based on the user settings like charge level and amperage. If there is accessory load, it will naturally be taken from the HVDC bus and whatever extra power remains will naturally flow into the battery.

 

[Saghost]

That's not how it works. The BMS is monitoring the batteries and can only take extreme measures to open the contactors to protect the battery from over current or over/under voltage situations. The on-board charger is responsible to regulate the power taken from the wall and pushed into the HVDC bus. It looks at the BMS data and obeys the charging profile programmed for the battery based on the user settings like charge level and amperage. If there is accessory load, it will naturally be taken from the HVDC bus and whatever extra power remains will naturally flow into the battery.

This. The exact voltage of the bus fluctuates up and down slightly, which will determine whether the pack charges or discharges as the charger loads it and accessories pull power out.

 

[jdw]

That's not how it works. The BMS is monitoring the batteries and can only take extreme measures to open the contactors to protect the battery from over current or over/under voltage situations. The on-board charger is responsible to regulate the power taken from the wall and pushed into the HVDC bus. It looks at the BMS data and obeys the charging profile programmed for the battery based on the user settings like charge level and amperage. If there is accessory load, it will naturally be taken from the HVDC bus and whatever extra power remains will naturally flow into the battery.

I thought that was kind of what I said, (guess not), but what I said was assuming that the car was not charging, merely plugged into shore power to run the heater(s). I think the OP was asking whether that situation charged the battery and *then* took power from the battery for the load or whether the battery was just a bystander in all this if the charger could supply all the required power.