openinverter forum

I'm looking into ways of charging a 24kWh battery within one or two hours on locations where's no AC/grid power ?

When using for example two Tesla Gen2 chargers fed by a 30kVA generator, would that work ?

Or is it possible to 'carry along' a second pre-charged battery pack of 24-30kWh and use that for some sort of DC-DC charging ?

The first idea would work as long as the battery is happy with being charged at that rate (it should be).

Pack to pack charging is nasty, skip it; a buck/boost converter is required which is a lot of electronics.

Is this a Leaf?
-Isaac

The battery is from a Nissan Leaf and going to be used in an electo racing car.
Between (training and race)sessions the battery needs recharging but I need to care of that myself (no grid connection provided).
At this time I'm looking at a 35kW pto driven generator and using (2 or 3) Tesla chargers or (8) Brusa NLG5 chargers in parallel to provide enough charging power to recharge upto 80-90% SOC within an hour.

prensel wrote: ↑Wed Feb 03, 2021 7:53 am The battery is from a Nissan Leaf and going to be used in an electo racing car.
Between (training and race)sessions the battery needs recharging but I need to care of that myself (no grid connection provided).
At this time I'm looking at a 35kW pto driven generator and using (2 or 3) Tesla chargers or (8) Brusa NLG5 chargers in parallel to provide enough charging power to recharge upto 80-90% SOC within an hour.

Wouldnt you be better off with making a CHADEMO type interface directly to battery? 35kW is not so large. I am sure you couold make a stabilised buck charger from 600Vdc rectified down to 360Vdc. AND implement usual precautions when handling non isolated circuits, or make them isolated by default!

I am sure you could convince Prius gen3 inverter to accept 3phase from the generator and rectify and buck it down to usable power. Remember that it is liquid cooled!

arber333 wrote: ↑Wed Feb 03, 2021 8:43 am Wouldnt you be better off with making a CHADEMO type interface directly to battery? 35kW is not so large. I am sure you couold make a stabilised buck charger from 600Vdc rectified down to 360Vdc. AND implement usual precautions when handling non isolated circuits, or make them isolated by default!

I am sure you could convince Prius gen3 inverter to accept 3phase from the generator and rectify and buck it down to usable power. Remember that it is liquid cooled!

Yes I'm installing a Chademo port on it anyway and make the chargers an external box or something to plug in.
Using a Prius inverter to use as a 'charger' is an interesting option. Would any Prius inverter be usable for that ?

The poor mans charger would lent itself to charging a higher voltage battery from a lower voltage battery. If you're handy with power electronics it's not that hard to do and you can use a V2 or V3 mainboard for current regulation with stm32-charger software.

The Leaf batteries are not the best cooled batteries, and you will certainly generate a lot of heat in them while racing, subsequently fast charging and racing again. Would it be an option to make two batteryboxes and a smart solution to easily swap them ?

if your intent is racing then temp management is going to be a big factor. The chemistry in leaf cells is great, the pack construction is poor. No good active cooling/heating.
introduced some liquid cool plates, and your cells will maintain a much longer life and be more suited for rapid draw and charge cycles.

This is why Chevy volt packs are popular with Folks pushing big numbers out of Tesla LDU. very similar chemistry, but the temp management on the cell level is very well done.

We've been charging our race car with two Tesla Chargers and a 35kW diesel genset. Using this setup we charge at 18kW/hr which meets your criteria. As others have pointed out, temperature management is going to be an issue. When we used an air cooled Kia Soul pack, it would take us 3+ of hours to cool down the pack (from 65 degC to 45 degC) using blowers before we could use it again.

dougyip wrote: ↑Thu Feb 04, 2021 5:42 pm We've been charging our race car with two Tesla Chargers and a 35kW diesel genset. Using this setup we charge at 18kW/hr which meets your criteria. As others have pointed out, temperature management is going to be an issue. When we used an air cooled Kia Soul pack, it would take us 3+ of hours to cool down the pack (from 65 degC to 45 degC) using blowers before we could use it again.

This is what I have/had in mind until someone mentioned using a modded Prius inverter as charger.
I'm currently considering a 38kVA PTO generator which I want to drive/power with my Land Rover that tows the racing trailer anyway.
Temp mgmt has my attention and since the pack is bolted under the car in a seperate space I could create some naturally air flo when driving, enhanced with extra fans if needed.

Does your Land Rover actually have a PTO take-off? I've also thought of using a PTO generator and building an adapter so I can drive it off a wheel with the tow vehicle sitting on jacks. We also looked at the DC-DC charge, but our application is road racing, so we need multiple charges/day and couldn't get by without a generator. What is your racing application?

Slightly off topic but;
how much losses are we seeing from a generator—> charger —>battery pack? Would a custom/modded generator be worth it in this case? Likes of a open inverter power stage rectifying and regulating straight from the generators coils to the battery pack.

You mean just a motor on regen? Should be a few % more efficient because you don't need the extra boost or buck stage.

If you would like to have maximum efficiency & compactness and are in for a challenge, and BMW i3 REX generator could be an option. 650cc 2-cyl petrol motor with an integrated 25kW starter/generator. Weight including the matching inverter is around 100Kg.

BMW W20 engine According to the technical training documentation, the RDME (petrol engine DME) and the REME (inverter) are coupled to the PT-CAN & PT-CAN2. No FleyRay connection. With a CAN-log of a charging vehicle and some rainy weekends you might get the set running & charging outside of the vehicle.

FJ3422 wrote: ↑Sat Feb 06, 2021 8:07 pm If you would like to have maximum efficiency & compactness and are in for a challenge, and BMW i3 REX generator could be an option. 650cc 2-cyl petrol motor with an integrated 25kW starter/generator. Weight including the matching inverter is around 100Kg.

Heh... i just got a crazy idea... You could take the REX and inverter unit and put it in a house/basement. Then you would take coolant hoses and loop them in a water container for some 800L. You could wire the inverter output to some solar inverter and make electricity and hot water.
Additionaly you could make the REX run on LPG instead of petrol... Cogeneration at its best.

Do you think heat output would be too much for a 2 family building?
Gas engine efficiency is about 25%. So if motor would produce only 10kW, then its heat output should be 40kW!!!? Too much?

FJ3422 wrote: ↑Sat Feb 06, 2021 8:07 pm If you would like to have maximum efficiency & compactness and are in for a challenge, and BMW i3 REX generator could be an option. 650cc 2-cyl petrol motor with an integrated 25kW starter/generator. Weight including the matching inverter is around 100Kg.

BMW W20 engine

108943_12_W20-Engine.pdf

According to the technical training documentation, the RDME (petrol engine DME) and the REME (inverter) are coupled to the PT-CAN & PT-CAN2. No FleyRay connection. With a CAN-log of a charging vehicle and some rainy weekends you might get the set running & charging outside of the vehicle.

BMW i3 RDME-REME.pdf

Very cool. Definitely thinking on much smaller scale. 5kwh would be ideal.

johu wrote: ↑Sat Feb 06, 2021 8:52 am You mean just a motor on regen? Should be a few % more efficient because you don't need the extra boost or buck stage.

Yes. The scale I’m thinking of is 2.5-5kw generator. so a 10% gain would warrant the work implement your brain (or a lebowski). I guess it’s time to run some test to actually see conversion losses across each step

dougyip wrote: ↑Fri Feb 05, 2021 12:35 am Does your Land Rover actually have a PTO take-off? I've also thought of using a PTO generator and building an adapter so I can drive it off a wheel with the tow vehicle sitting on jacks. We also looked at the DC-DC charge, but our application is road racing, so we need multiple charges/day and couldn't get by without a generator. What is your racing application?

Yes it's a 109 Series 2A with centre PTO.
Last friday i've looked at a Lister powered 20kVA generator and next week i'll be looking into a PTO-driven generator of 38kVA.
The Lister looked okay and I could probably install stationary in the front of trailer but carrying an extra 3 cylinder diesel engine with me while the Landy has the PTO didnt appear as the smartest move to me. Total weight was about 600ish kg also.

The PTO generator weighs about 200kg but thats including the tractor PTO connector and steel sled construction.
Maybe I can install the generator inside the chassis on the Land Rover and have it easy available when needed.


The 'racing application' is currently a modded 60kW Think City but will be a to EV converted Mini Cooper S (86kW, work in progress).

arber333 wrote: ↑Sat Feb 06, 2021 9:18 pm Heh... i just got a crazy idea... You could take the REX and inverter unit and put it in a house/basement. Then you would take coolant hoses and loop them in a water container for some 800L. You could wire the inverter output to some solar inverter and make electricity and hot water.
Additionaly you could make the REX run on LPG instead of petrol... Cogeneration at its best.

Do you think heat output would be too much for a 2 family building?
Gas engine efficiency is about 25%. So if motor would produce only 10kW, then its heat output should be 40kW!!!? Too much?

That is a good idea, if LPG is cheaper that electricity, is it?
Don't know you could calculate that, but it's probably possible.

Instead of using a PTO driven generator that supplies a 3-fase 380V AC output that powers a Tesla Gen2 charger would it be possible to use an EV motor controlled by the OpenInverter v3 board and have it set in regen mode to provide a DC charging capability when connecting to the battery pack ? The EV motor is powered by the PTO shaft of the Land Rover.

prensel wrote: ↑Sat Feb 20, 2021 12:47 pm Instead of using a PTO driven generator that supplies a 3-fase 380V AC output that powers a Tesla Gen2 charger would it be possible to use an EV motor controlled by the OpenInverter v3 board and have it set in regen mode to provide a DC charging capability when connecting to the battery pack ? The EV motor is powered by the PTO shaft of the Land Rover.

Nice idea. You put a cheap pmsm motor like Outlander on a trolley and connect PTO shaft to it. Actually you could just as well use one 3phase bridge since pmsm motor is internaly excited...
Above motor you mount your bridge or prius inverter and use another cable to supply 12V...

arber333 wrote: ↑Sat Feb 20, 2021 2:50 pm Nice idea. You put a cheap pmsm motor like Outlander on a trolley and connect PTO shaft to it. Actually you could just as well use one 3phase bridge since pmsm motor is internaly excited...
Above motor you mount your bridge or prius inverter and use another cable to supply 12V...

I have a small 24kW AC motor which would fit underneath the floor.
The PTO connection is directly on the transfer gearbox so I could either drive the PTO output from the diesel engine or power the gearbox by the PTO as input using the AC motor. When using the diesel in stationary mode I could put the AC motor in regen and charge a batterypack.

arber333 wrote: ↑Sat Feb 06, 2021 9:18 pm

FJ3422 wrote: ↑Sat Feb 06, 2021 8:07 pm If you would like to have maximum efficiency & compactness and are in for a challenge, and BMW i3 REX generator could be an option. 650cc 2-cyl petrol motor with an integrated 25kW starter/generator. Weight including the matching inverter is around 100Kg.

Heh... i just got a crazy idea... You could take the REX and inverter unit and put it in a house/basement. Then you would take coolant hoses and loop them in a water container for some 800L. You could wire the inverter output to some solar inverter and make electricity and hot water.
Additionaly you could make the REX run on LPG instead of petrol... Cogeneration at its best.

Do you think heat output would be too much for a 2 family building?
Gas engine efficiency is about 25%. So if motor would produce only 10kW, then its heat output should be 40kW!!!? Too much?

what you describe is a CHP (Combined Heat & Power) plant. Had one at my old company (MG Rover) They had a gas turbine and generator to make power and used the excess heat for site heating - can be very efficient use of the fuel (not needing fuel for heating) - BUT only if you make use of the waste heat!

prensel wrote: ↑Sat Feb 20, 2021 12:47 pm Instead of using a PTO driven generator that supplies a 3-fase 380V AC output that powers a Tesla Gen2 charger would it be possible to use an EV motor controlled by the OpenInverter v3 board and have it set in regen mode to provide a DC charging capability when connecting to the battery pack ? The EV motor is powered by the PTO shaft of the Land Rover.

Yes and you can use the DC current limit (idcmin) to set charge current.

johu wrote: ↑Wed Apr 07, 2021 11:36 am Yes and you can use the DC current limit (idcmin) to set charge current.

Hello Johu,
I would like to operate the BMW i3 REX without a car, to charge the battery.
I tried to find some information but I didn't find that anyone had succeeded.
I see problem 2:
1. how to start and drive the REX, I assume that there is an immobilizer in the ECU and that cannot be bypassed. The idea is to use another control unit.

2. how to solve the charger from the generator (and therefore also start with a motor generator)
At this point I was interested in the possibility of using an open inverter.
And that is my question, can I connect an Openinverter to the i3 generator and use it so that I will start as a motor and then change the mode to recuperation and charge the battery?
I am quite new to this, what do I need besides the generator, the Openinverter board?
Thanks for the guidance.