Multiple onboard chargers

Kohler Controller said:

Val,
Do you normally charge each pack separately, or did you just do it this time to capture individual pack recharge capacities?

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only this time - for that very reason, yes ;-).

We have just built a power distribution unit to manage battery connections - see photo at https://docs.google.com/a/emotorwerks.com/file/d/0B8zi8eqgqJWod05tcEhKSG1DQ0k/edit.

It will also handle our special battery arrangement for mobile CHAdeMO charger we will be doing a public demo on in ~2 weeks.

V

I like that the RAV4EV used the AUX pack more than the main pack during its bulk discharge, thus always leaving the main pack for the bottom end where you need more accurate range estimation. I'm wondering when you bump up the AUX pack to 111 cells, if the packs will start to share more evenly, thus losing this benefit?

Kohler Controller said:

I like that the RAV4EV used the AUX pack more than the main pack during its bulk discharge, thus always leaving the main pack for the bottom end where you need more accurate range estimation. I'm wondering when you bump up the AUX pack to 111 cells, if the packs will start to share more evenly, thus losing this benefit?

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this will always happen due to particular shapes of discharge curves for the involved chemistries. AUX pack (LFP) has a much flatter curve relative to the Tesla pack. So almost no matter how many cells you have, you will always fully discharge the AUX before you fully discharge the Vehicle pack. With 108 cells, we have AUX discharging when 50% of the main pack is left. Moving to 111 cells would cause this to happen sooner - say, when 70% of the main pack is left.

PS. We have decided not to go to 111 cells after all. Doing so would result in difficulty to top-balance the AUX pack as no cell would reach the balancing voltage of 3.5V (CV of LFP cells we are using is 3.6V - 111 cells will have combined CV of almost 400V which is too high - we need to match native pack's CV of 382-386V). We will deal with equalizing currents through a PDU (power distribution unit) that I have shown in my previous post - it will connect the AUX pack when main pack voltage falls to AUX level and will disconnect when AUX gets discharged (based on cell-level BMS signal).

Val,
I have an idea for another product that needs to be produced that will require your 20kW charger.

I have plans to drive from Austin to College Station this month to see a baseball game with my father, brother, and son. It is 120 miles away. I've made this trip several times in the fall (football season), so I know I have the range. I simply use one of the many public charging stations in the university's parking garage to fill up overnight. But for the baseball game, we won't be spending the night, which means I'll only be parked for 2-3 hours. This is where (perhaps next year when my vehicle has both your 20kW charger and Tony's CHAdeMo connection on board) I could use a faster charge than what's available with their 6kW J1772 public EVSE systems. Since there are no QC's there, nor planned, what I would need is a device that could take in three J1772 connectors from three public charging stations, and output a single 208VAC/90A supply into your charger. The three 208VAC should all come from the same source so we wouldn't have to worry about synchronicity, right?

If I were to park near three charging stations (they have 8 in a row there), I could plug in each connector into a box that housed three J1772 receptacles that supplied the correct charging resistor to each acting as a car requesting 30A. The output could be a cable system going to the input of your charger. Now I could recharge from empty to full in 2.5-3 hours instead of the 8-9 hours it normally takes on a single public EVSE.

This is just a technical request to see if it is feasible. I don't want to go into the moral decision of whether it is right using one EV parking space, but three EVSEs, at this time.

If this gets built, rather than royalties, can you call it the Kohler Connector?

Kohler,

What makes you think the three adjacent chargers would be on the same phase? I would expect some round-robin arrangement if it is on 3-phase service. If the breakers went straight down the panel they would probably be L1/L2, L3/L1 and L2/L3. Those all just look like 208VAC single phase.

miimura said:

Kohler,

What makes you think the three adjacent chargers would be on the same phase? I would expect some round-robin arrangement if it is on 3-phase service. If the breakers went straight down the panel they would probably be L1/L2, L3/L1 and L2/L3. Those all just look like 208VAC single phase.

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True, I guess I was thinking of 3 EVSEs hooked up to the same rails in the breaker box. This is why I posed the idea, to judge it's practicality (usefulness) as well as technical (syncing up EVSEs that may not be on the same circuit).

Kohler Controller said:

miimura said:

Kohler,

What makes you think the three adjacent chargers would be on the same phase? I would expect some round-robin arrangement if it is on 3-phase service. If the breakers went straight down the panel they would probably be L1/L2, L3/L1 and L2/L3. Those all just look like 208VAC single phase.

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True, I guess I was thinking of 3 EVSEs hooked up to the same rails in the breaker box. This is why I posed the idea, to judge it's practicality (usefulness) as well as technical (syncing up EVSEs that may not be on the same circuit).

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The way we would do it would be a 3-phase Boost topology PFC rectifier. This topology is immune to loss of one phase and hence is intrinsically suitable for ambiguous power source you are describing. It would also work off one, two, or three J inputs without any change in hardware. You plug in however many you have and it just works. Pre-power stage commutation may require some thinking. The typical problem of such 3-phase units on a single-phase supply is that 2/3rds of the hardware are unused and you end up paying for 3x the power hardware giving you 1x the output. One could figure out commutation of inputs so this does not happen, though.

Could be an interesting project for an enterprising EE. Anyone here? We could fund it ;-)

Or arrive a couple hours early and start an EV tailgate group.

If you just had 3 separate chargers, each with their own J-connector (the basic idea of this thread), then your idea would work fine.

valerun said:

The way we would do it would be a 3-phase Boost topology PFC rectifier. This topology is immune to loss of one phase and hence is intrinsically suitable for ambiguous power source you are describing. It would also work off one, two, or three J inputs without any change in hardware. You plug in however many you have and it just works. Pre-power stage commutation may require some thinking. The typical problem of such 3-phase units on a single-phase supply is that 2/3rds of the hardware are unused and you end up paying for 3x the power hardware giving you 1x the output. One could figure out commutation of inputs so this does not happen, though.

Could be an interesting project for an enterprising EE. Anyone here? We could fund it ;-)

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Most chargers can accept DC input as well as AC input. If your 20kW charger can accept DC input, could we put 3 full wave rectifiers in the box converting each 208VAC (regardless of phase) into DC source?

fooljoe said:

If you just had 3 separate chargers, each with their own J-connector (the basic idea of this thread), then your idea would work fine.

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True, but Val's big charger is less expensive than two additional Brusas.

Kohler Controller said:

valerun said:

The way we would do it would be a 3-phase Boost topology PFC rectifier. This topology is immune to loss of one phase and hence is intrinsically suitable for ambiguous power source you are describing. It would also work off one, two, or three J inputs without any change in hardware. You plug in however many you have and it just works. Pre-power stage commutation may require some thinking. The typical problem of such 3-phase units on a single-phase supply is that 2/3rds of the hardware are unused and you end up paying for 3x the power hardware giving you 1x the output. One could figure out commutation of inputs so this does not happen, though.

Could be an interesting project for an enterprising EE. Anyone here? We could fund it ;-)

Click to expand...

Most chargers can accept DC input as well as AC input. If your 20kW charger can accept DC input, could we put 3 full wave rectifiers in the box converting each 208VAC (regardless of phase) into DC source?

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Oh yes, you can absolutely do that. Power factor will be pretty bad but it will work. A number of our charger customers do just that.

Any news on the multiple charger front? Reading about Devin's trip to Utah has me thinking about how silly it is to be waiting 5 hours for a charge while a 2nd (and maybe 3rd) J1772 sits right next to you.

I'll bet almost every time you find an available public charging station (or RV outlet) there's at least one more close by just sitting unused. Cutting charge time in half would go a long way to making road trips doable, and would maybe even be as good or better than adding CHAdeMO, since it's so much easier to find J1772 stations and RV parks than CHAdeMO stations.

It is actively being explored.

fooljoe said:

I'll bet almost every time you find an available public charging station (or RV outlet) there's at least one more close by just sitting unused.

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I've done this with my Leaf.. added dual LQ Brusa's and put them up front. Thing is, it's the only way to do it with the Leaf as air cooled is not an option as..
1.They are too big to fit 2 under the hood
2. Cooling is barely enough with 1 during the summer.

That was always my biggest argument when I added the Brusa.. always another L2 plug sitting around not doing anything, and I don't have CHAdeMO on my Leaf so there's a spare port waiting..

I sold Allen my AC Brusa setup and got 2 LQ units directly from them and set them up. They are beautiful pieces of work, small and compact and 2 will just squeeze under the hood of the Leaf.

I've been thinking about a way to inject more power into the Rav.. but 3.3kw just isn't enough..

JasonA said:

I've been thinking about a way to inject more power into the Rav.. but 3.3kw just isn't enough..

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It's not worth doing if the new charger can't take all 30 amps from a public station.

miimura said:

JasonA said:

I've been thinking about a way to inject more power into the Rav.. but 3.3kw just isn't enough..

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It's not worth doing if the new charger can't take all 30 amps from a public station.

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I agree.. I wish Brusa or a commercial vendor would make atleast a 7.2kw unit for 240v single phase. You can just stack 2 LQ Brusa's together.. but then it starts to become kinda large compared to the Tesla unit.

Run them in AUTO off 1 J-plug.. but that'll never happen.. I'll just wait for Tony's CHAdeMO

I'd love to add another 10kw Tesla unit... but the CAN hacking is ugh... :?

A second Tesla unit would of course be nice, if you could get one... What about one of the EMW 12kw units? I envision just adding a connector to plug it in under the hood and taking the charger with you to plug in externally when needed, so you don't have to worry about finding a place to permanently install it and the possible cooling constraints that entails.

fooljoe said:

A second Tesla unit would of course be nice, if you could get one... What about one of the EMW 12kw units? I envision just adding a connector to plug it in under the hood and taking the charger with you to plug in externally when needed, so you don't have to worry about finding a place to permanently install it and the possible cooling constraints that entails.

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Thanks for considering us. We are using one of our units on RAV4EV now. You can see some videos in our YouTube Channel. Let us know if you have any questions. Thanks, Valery

valerun said:

Thanks for considering us. We are using one of our units on RAV4EV now. You can see some videos in our YouTube Channel. Let us know if you have any questions. Thanks, Valery

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I've seen your videos - the one where you charge the Rav at ~22kw is great! That's basically where I got the idea. It looks like you tapped into the DC lines at the inverter, and added an HV DC connector to attach the output of your charger. This seems like a good way to go - then you can carry the charger in the back and plug it in when needed. Plus if the connector is appropriately-sized perhaps it could double for connection of a CHAdeMO inlet when that's ready or a range-extending trailer if that ever becomes a reality.

So my questions to you would be: How close to marketability is this? What exactly would we need to use your charger with the Rav? I assume charger (PFC, water cooled?), J1772 inlet, and cable/connectors - anything else? Can we charge using it and the built-in charger at the same time - for example from two (or more) public J1772 stations or 2+ 50amp RV outlets? As I recall from your video the car was on when charging, while the on-board charger requires the car to be off - can we work around that? How difficult would installation of the HV DC connectors be? Would you be able to provide an installation service in both NorCal and SoCal? And of course - how much?!