Parallel Onboard Charging?

[nubster]

If I had a 100kWh Tesla battery pack powering two Openinverter Tesla SDUs, could I simultaneously use both units' onboard 5kW charging capability to charge the battery at ~10kW?

The idea is to have two separate 5kW solar setups, each feeding a separate SDU connected to the same battery. So, each SDU only sees 5kW, but the battery receives 10kW total. Is this possible, and if so, what are the limitations/considerations?

[arber333]

If I had a 100kWh Tesla battery pack powering two Openinverter Tesla SDUs, could I simultaneously use both units' onboard 5kW charging capability to charge the battery at ~10kW?

Did you mean AC charge via the motors? I am not sure the circuit would see this any different than AC charging in paralell. You would need to assure the same connection for L and N allways!
SDU is a drive unit which can feed batery mechanicaly via regen. Did you mean PCS? Each PCS is 11kW charger so if you used 2 then you would have 22kW charging system.

[johu]

I've never tried paralleling these booster converters but I find it pretty cool that you're using the facility in the first place

You could run them off a common rectifier pre-empt any phase troubles

[nubster]

Did you mean AC charge via the motors? I am not sure the circuit would see this any different than AC charging in paralell. You would need to assure the same connection for L and N allways!
SDU is a drive unit which can feed batery mechanicaly via regen. Did you mean PCS? Each PCS is 11kW charger so if you used 2 then you would have 22kW charging system.

I'm referring to the onboard charging capability that Openinverter boards feature, per this wiki article:
https://openinverter.org/wiki/Battery_Charging

Per the article, you need to feed it a DC input voltage, wire it up for Step-Up or Step-Down (depending on input voltage vs. battery voltage), and then set the FORWARD and REVERSE pins to high at inverter startup. I understood this to be a direct DC charging solution. So, I wonder if I could double the charge rate if I had two motors/boards running in this mode.

I've never tried paralleling these booster converters but I find it pretty cool that you're using the facility in the first place

You could run them off a common rectifier pre-empt any phase troubles

I want to try it out, but decided it was probably best to ask first just to be safe!

The idea was to use two separate 5kW solar setups as the DC inputs (one to each motor). I assumed this would avoid needing any rectification, but let me know if I am mistaken.

[johu]

Ah, no solar doesn't need rectification
So then both input voltages are floating anyway. Not sure about regulation. It is a current controller so it will keep increasing PWM until current is reached. No MPP

[nubster]

Naturally, the next question is: does it scale? Could you do 3, 4, or even 6 motors in parallel?

I recently had a long conversation with my neighbor. He wants to build a large mobile platform for Burning Man to crawl across the playa, potentially with up to six motors. His idea is to use a full Tesla battery pack that he can solar charge during the day, and roam around at night for a few hours using tank steering. This sounded like a wildly awesome project, so I told him I would look into it for him.

[arber333]

Naturally, the next question is: does it scale? Could you do 3, 4, or even 6 motors in parallel?

I recently had a long conversation with my neighbor. He wants to build a large mobile platform for Burning Man to crawl across the playa, potentially with up to six motors. His idea is to use a full Tesla battery pack that he can solar charge during the day, and roam around at night for a few hours using tank steering. This sounded like a wildly awesome project, so I told him I would look into it for him.

That seems a lot of HV DC contactors built in just to go for a ride when not needed.
Maybe you could actually build a dedicated boost charger in the way EMW charger was built. Design is online.
Rectification is not needed so no smearing on the AC network... just pure DC chopper. There is even Wifi module for control...
https://github.com/arber333/3phase-EMW-kind-of-charger
https://github.com/dimecho/ESP8266-EMW-Charger
I sucessfully used Prius inductor to charge 18kW buck from 3phase EVSE station. Cooled by air!!!

[nubster]

That seems a lot of HV DC contactors built in just to go for a ride when not needed.
Maybe you could actually build a dedicated boost charger in the way EMW charger was built. Design is online.
Rectification is not needed so no smearing on the AC network... just pure DC chopper. There is even Wifi module for control...
https://github.com/arber333/3phase-EMW-kind-of-charger
https://github.com/dimecho/ESP8266-EMW-Charger
I sucessfully used Prius inductor to charge 18kW buck from 3phase EVSE station. Cooled by air!!!

The scaling question was just more out of curiosity.

Burning Man gets an average of 6-7 hours of solar insolation per day. 10kW of panels should be enough to keep the battery charged, as long as he doesn't consume more than ~60kWh per day. So if we can get two Openinverter boards working in parallel, it could be a very cost-effective and simple solution, considering the Openinverter boards will already be present.

Building an EMW-style boost charger is an interesting option, however... I will read up on it. Thanks for the idea and links!

[arber333]

Building an EMW-style boost charger is an interesting option, however... I will read up on it. Thanks for the idea and links!

There is a lot of that online. My design was for the buck charger as i had to downplay 600Vdc from rectified 3phase mains. i also got more kW from bucking 600V than i could get from boosting 300V single phase... and i have a phase limit of 3.5kW here in EU!!!

Vallerys design was for boost - buck single phase to smooth the networks out. It was made on base of Arduino nano or mini with isolated opamp voltage - current control and a nice display. There was even a version which could run as a household Chademo charger.
https://www.diyelectriccar.com/threads/ ... 0/#replies
Not sure how legal is that here in EU but it did run at about 75% efficient in most cases. His version was more efficient because of the PFC stage, but his inductor was awfull. For my most succesful version i simply took Toyota Prius gen 2 inductor and use it in buck mode. That is the version that gave me 18kW from 22kW EVSE if i was really in a hurry.