HV DC power supply for inverter testing

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davefiddes
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HV DC power supply for inverter testing

Post by davefiddes »

I'm trying to figure out a simple low-cost way of getting a high voltage DC supply for testing my work on the Tesla Model 3 inverter. We need over 60V to get the inverter to wake up which is beyond common bench PSUs. Don't need much current to start with but would like to be eventually get the motor turning. A degree of portability is desirable, I'm working inside as it's winter but the motor is a garage.

Was contemplating hooking a beefy bridge rectifier to the output of a cheap variac with a incandescent lightbulb to act as a current limiter. This would rely on the bus capacitors in the inverter to turn into DC. Obviously potentially lethal but with the HV DC positive and negative isolated from everything else in the inverter not too bad.

Is this mad? Is there a better way?
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mjc506
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Re: HV DC power supply for inverter testing

Post by mjc506 »

One of these and a laptop PSU?
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celeron55
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Re: HV DC power supply for inverter testing

Post by celeron55 »

I used the rectifier + light bulb method for my Leaf inverter testing. I did use a 500W isolation transformer at least some of the time. I also replaced the light bulb with a 10A ceramic fuse when I needed more current, but kept the light bulb as a precharge resistor.

Beware of regen.
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celeron55
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Re: HV DC power supply for inverter testing

Post by celeron55 »

Let me still elaborate on the regen part: Openinverter and the Tesla units (both separately and with each other) are known to destroy themselves if the HV feed is cut by anything, be it a contactor, a fuse or a switch, when the motor is turning at speed.

I got away with my testing of the Leaf OEM stuff because I didn't burn my fuse, and possibly because the Leaf OEM control is smart and fast enough to handle a cut contactor/fuse situation. Not sure about the latter, definitely no promises.

A HV feed created by a rectifier immediately turns into the "cut HV feed" type thing when regen happens.

Damien is known to never recommend anything other than a real battery for the HV feed.
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Re: HV DC power supply for inverter testing

Post by arber333 »

celeron55 wrote: Thu Feb 10, 2022 9:24 pm A HV feed created by a rectifier immediately turns into the "cut HV feed" type thing when regen happens.

Damien is known to never recommend anything other than a real battery for the HV feed.
Maybe you would get away with 60Vdc power supply i am sure 230Vdc would blow IGBT if contactor would drop.
If you really need to spend money for testing equipment then i recommend to buy one of Kia or Hyundai mild hybrid battery. Its some 1.5kWh and 240Vdc. It is capable of reasonable current and can handle regen. All contactors and fuses you will ever need come with it.
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Re: HV DC power supply for inverter testing

Post by MattsAwesomeStuff »

1 - Variac

2 - 3 cheap laptop power supplies in series.

3 - A few tool batteries in series.

4 - 15-20 18650s from tool batteries wired in series (~$20). Good for 30A. SecondLifeStorage resellers could probably hook you up with a pack.

5 - 4-5 old car batteries in series, for $20 each, from an autoparts store that will sell you old ones taken in for their core charge.

Lots of terrible ways to do this.
davefiddes
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Re: HV DC power supply for inverter testing

Post by davefiddes »

MattsAwesomeStuff wrote: Fri Feb 11, 2022 2:57 am Lots of terrible ways to do this.
:D

Thanks for the summary. Initially it's just volts I'm after so don't need to worry about regen. The hope is that will progress to hooking up a motor. Tesla M3 does appear to have HV DC gate drive interlocks that should reduce the likelyhood of abrupt HV loss causing problems (I think). Working under/over voltage/current protection is probably also important...
fbo
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Re: HV DC power supply for inverter testing

Post by fbo »

I doubt regen is an issue here. The rotor is not even turning yet, it is not even connected and even further away from being pushed down a hill by 2t of metal around.

I tested with a AC/DC charger at 66.7V max 2.5A. There is still something preventing the gate drivers to work. Either we need more than that or HVIL or any other gatekeeper is still in play.
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Re: HV DC power supply for inverter testing

Post by anguicito »

you have tried an inverter welder · MMA? it's crazy?
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Re: HV DC power supply for inverter testing

Post by Romale »

fbo wrote: Fri Feb 11, 2022 12:00 pm There is still something preventing the gate drivers to work. Either we need more than that or HVIL or any other gatekeeper is still in play.
look for the driver's problem elsewhere. high voltage is not a problem. I conducted an experiment: I powered the brain of the inverter and the driver with a 12 volt battery,- I applied ONE 18650 cell to the high voltage input and the motor rotated when the gas pedal was pressed. awfully slow but spinning!! the power module or mosfets do not care what voltage they commute. in different modules, I was looking for gate control channels in general without high voltage, just by feeding 12 volts of power to the driver board and going through the inputs from one 18650 relative to the input of +5 volts.
evil neodymium :twisted:
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