Bit of electronics for a change, circuits, chips! yummy jummy! (2023 Update)

If a hot water heat pump is pulling heat from a heated space, don't you have to pay to reheat that space? Draw hot water, which often goes down the drain, and the furnace has to come on to warm up the house. That's an improvement?

On Thursday, 1 September 2022 at 06:29:02 UTC-7, Jan Panteltje wrote: ...

No it doesn't.

There is nothing intrinsically better running the motor at 800v vs 400V.

If the volume of copper in the windings is the same for the two voltages the copper losses are identical.

You can imagine having the 800v winding split into 2 halves.

If you run them in series it takes 800V with a certain current density and resistive loss.

If the two halves are put in parallel it would take half the voltage but twice the current. The losses are identical.

The improvements can be in the external circuitry and wiring.

If the active devices can be made with improved figure of merit in breakdown voltage vs on-resistance there is an advantage for higher voltage. Large band-gap devices such as Silicon carbide have an advantage here.

Wiring can get improvements at higher voltage as insulation tends to be lighter, cheaper and smaller than copper so going to a higher voltage can help.

With modern EVs the active devices IIGBT typically) in the motor driver were first available with breakdown voltages of the order of 1000V and so were only good for system voltage about half of that - 400V tended to be used. With SIC that has increased so 800V (that can go up to ~950V when fully charged) are practical.

There is a limit to the usefulness of increasing the system voltage as some switching losses increase with voltage.

For small motors such as window winders, yes ...

Not really as weight and space are important and can influence efficiency throughout the cars life.

kw

On Thursday, 1 September 2022 at 21:52:49 UTC-7, Jan Panteltje wrote: ...

Modern car headlights tend to be LED and so do run on a regulated supply as well as dramatically reducing power consumption.

kw

On Saturday, 3 September 2022 at 16:08:38 UTC-7, Ricky wrote: ...

The water heaters in California are typically in an unheated space so it is not an problem, but that would be an issue if it wasn't.

A friend remodeled his house and put in a heat-pump water heater and he did have problems with the basement getting too cold. It was solved by improving the ventilation.

kw

On a sunny day (Sat, 3 Sep 2022 16:15:27 -0700 (PDT)) it happened " snipped-for-privacy@kjwdesigns.com" snipped-for-privacy@kjwdesigns.com wrote in snipped-for-privacy@googlegroups.com:

The question now is when we get motors with high temperature super-conducting windings and zero volts accoss the windings. Very cold weather starts would be better :-) Zero volt batteries needed! Only a small normal battery needed for a bit of cooling.... fishsicks

High voltage needs thick insulation on the wire, and skinny wire windings lose window area to insulation more than fat wires. And insulation doesn't conduct heat as well as copper. Triple whammy.

On Saturday, September 3, 2022 at 4:15:31 PM UTC-7, snipped-for-privacy@kjwdesigns.com wrote: ...

If that's the case, we should go with 1200V. These IGBTs are amazing with 1200V 40A 500W (huge heat sink) in TO-257.

I didn't read this carefully. But why half system voltage?

1600V 30A IGBT:

On Sunday, 4 September 2022 at 07:32:10 UTC-7, snipped-for-privacy@highlandsniptechnology.com wrote: ...

I agree for low power motors with small gauge wire this means it is a disadvantage to go to higher voltages.

However for the traction motors where the wire has to be able to handle hundreds of amps it is of such a large cross-section that the insulation area occupied is much less of an issue.

kw

..

There needs to be some voltage margin and the highest voltage rating device will be more expensive than mid-range ones from the same family, there may be tradeoffs in other parameters such as ON resistance and speed. A 400V system may be close to 500V when the battery is fully charged.

Also don't forget that the 400V decision was made something like 15-20 years ago - the devices were not so capable.

These days the trend is to use silicon carbide FETs rather than IGBT devices as the latter is very limited in switching speed.

kw

That's what clamping diode is for, to provide enough margin for less cost. I don't know about other EVs, but my Leaf never go much higher than 390V when full. 1600V should be enough for 800V to 1kV system.

But FETs can't beat IGBT in current capability, and how fast do we need for driving motors?

I didn't say it wasn't.

Was it cheaply available 20 years ago?

Around 10kHz is typical for modern ones. Your leaf is ~5kHz (presumably IGBT). The Prius that also uses IGBTs runs at 2.5kHz according to this web site:

kw

The ihw30n160r5 (1600V 30A) can switch up to 60kHz, most IGBTs are fast enough for motors.

On Sunday, 4 September 2022 at 16:18:33 UTC-7, Ed Lee wrote: ...

Maybe, but you can't avoid the 2 volt drop of IGBTs.

At 100 Amps that's 200W dissipation.

kw

I believe you can parallel IGBTs, just like FETs.

Doesn't help much.

An IGBT has a minimum of a volt or on-voltage so even at low current..

kw

I thought the Teslas ran up to 30 kHz in their motors.

400 Vdc is sufficient to drive a 120/208 V three phase motor with a sine wave. 800 Vdc is sufficient for 230/400V motors. The insulation thickness is not an issue for normal 230/400 V motors in kW size motors.

The preference for 800 Vdc battery voltage is in the inverter. 1200 V semiconductors are cheaply available and they should survive in a well designed 800 Vdc system.

Using a higher voltage will reduce the current. The cost of a transistor is usually proportional to the chip area which depends on the current rating. Reducing the current (by using higher voltage) requires smaller chips and may reduce total cost, if the higher voltage doesn't significantly increase costs. Now that 1200 V devices are cheaply available, why not go for 800 Vdc ?.

Going for 1500 Vdc would require 2 kV devices, which today is expensive.

I agree, it's all about the trade-offs.

The higher voltage is also useful to keep the conductor size and weight down for wiring both in the vehicle and especially the charging cable. Human ability to handle the cable can be a limiting factor on charging rate.

At these higher charging currents of several hundred amps liquid cooling for the cable and connector may be required:

kw