Tesla Model 3

[hayden55]

Originally Posted by redpoint5

It's not the higher voltage that is mostly responsible for reducing the charging losses, it's completing the charge sooner.

i would need to see a further explanation on this. I could blast something with energy to charge it faster but it will overheat. Theres a reason why wires are rated for amps and temps not voltages. (*to a certain point, the HV stuff just gets into safety issues around people and arcs, not dealing with the energy and heat side)

[aerohead]

I've been told that, as line-voltage approaches closer to the final pre-rectified DC charging-voltage, that step-up transformer heat losses are reduced, thereby structurally improving charging efficiency, by default.

[redpoint5]

Originally Posted by hayden55

i would need to see a further explanation on this. I could blast something with energy to charge it faster but it will overheat. Theres a reason why wires are rated for amps and temps not voltages. (*to a certain point, the HV stuff just gets into safety issues around people and arcs, not dealing with the energy and heat side)

https://ecomodder.com/forum/showthre...tml#post677696

[hayden55]

Originally Posted by redpoint5

https://ecomodder.com/forum/showthre...tml#post677696

Isn't there a report some where that listed the amps they charged at with each voltage and recorded the power required at the panel? That would tell us. L1 vs L2 doesn't say much.
A standard test of L1 vs L2 charging at 3 different amp rates would show a lot.

[redpoint5]

Originally Posted by hayden55

Isn't there a report some where that listed the amps they charged at with each voltage and recorded the power required at the panel? That would tell us. L1 vs L2 doesn't say much.
A standard test of L1 vs L2 charging at 3 different amp rates would show a lot.

I don't quite follow your question.

Let me give an anecdote though;

I went from charging my Prius at 120v (L1) and 12 amps to charging at 240v (L2) and 12 amps (same EVSE modified to accept the higher voltage). Doubling either the voltage or the amps doubles the wattage. That means it takes half as long to charge the Prius. The line losses (which are fairly negligible) remain exactly the same because I'm charging at the same amperage.

The only explanation for that resulting in cutting losses in half is that the vehicle spent half the time running pumps and fans and relays and computers during the charging process. It spent half the time charging because it charged at twice the power.

Furthermore, 100% of line losses exhibit as heat, so if there was major line loss, the cables themselves would get quite hot. If someone was charging at 10 kW, and there was 10% line loss, that would be 1,000 watts of heat generated in the cable, which is a huge amount of heat. The cable would burn up, because it wasn't designed to be used as a space heater.

[JSH]

Originally Posted by hayden55

i would need to see a further explanation on this. I could blast something with energy to charge it faster but it will overheat. Theres a reason why wires are rated for amps and temps not voltages. (*to a certain point, the HV stuff just gets into safety issues around people and arcs, not dealing with the energy and heat side)

Faster charging makes a big difference when charging in cold weather.

If the battery is cold the car will run the heater and circulate coolant to warm the battery so it can be charged safely. On a typical 120V / 12 amp circuit you can use the majority of the electricity provided just to keep the battery warm enough. If you are using 1 kW to heat the battery that only leaves 0.4 kW to charge. The charge takes forever and wastes a lot of electricity. Jump to 11 kW and 1 kW to heat is a small fraction of the energy and the charge time is near normal.

[aerohead]

Originally Posted by redpoint5

I don't quite follow your question.

Let me give an anecdote though;

I went from charging my Prius at 120v (L1) and 12 amps to charging at 240v (L2) and 12 amps (same EVSE modified to accept the higher voltage). Doubling either the voltage or the amps doubles the wattage. That means it takes half as long to charge the Prius. The line losses (which are fairly negligible) remain exactly the same because I'm charging at the same amperage.

The only explanation for that resulting in cutting losses in half is that the vehicle spent half the time running pumps and fans and relays and computers during the charging process. It spent half the time charging because it charged at twice the power.

Furthermore, 100% of line losses exhibit as heat, so if there was major line loss, the cables themselves would get quite hot. If someone was charging at 10 kW, and there was 10% line loss, that would be 1,000 watts of heat generated in the cable, which is a huge amount of heat. The cable would burn up, because it wasn't designed to be used as a space heater.

The charger will only draw a fraction of what the conductors are rated for. It's a passive safety factor built in to all of them.
You cannot have line losses, as it's structurally impossible develop a voltage drop, which would affect the current draw.
The losses occur within the voltage step-up transformer windings.( You may have seen utility linemen pointing infrared scanners at pole-mounted trans-formers ).
A transformer converting 120-VAC into 400-VAC, then rectifying it into 400-VDC will have more heat loss than a 240-VAC transformer stepping up to 400-VAC, then 400-VDC.

[hayden55]

Originally Posted by redpoint5

I don't quite follow your question.

Let me give an anecdote though;

I went from charging my Prius at 120v (L1) and 12 amps to charging at 240v (L2) and 12 amps (same EVSE modified to accept the higher voltage). Doubling either the voltage or the amps doubles the wattage. That means it takes half as long to charge the Prius. The line losses (which are fairly negligible) remain exactly the same because I'm charging at the same amperage.

The only explanation for that resulting in cutting losses in half is that the vehicle spent half the time running pumps and fans and relays and computers during the charging process. It spent half the time charging because it charged at twice the power.

Furthermore, 100% of line losses exhibit as heat, so if there was major line loss, the cables themselves would get quite hot. If someone was charging at 10 kW, and there was 10% line loss, that would be 1,000 watts of heat generated in the cable, which is a huge amount of heat. The cable would burn up, because it wasn't designed to be used as a space heater.

Yeah i forgot to add that the transformer and DC-DC converter that converts the 120 AC or 240 AC to the nominal DC voltage that the battery is adds to the inefficiency as well. The efficiency will be greater with the 240v charge as it is closer to the nominal battery voltage as well. This could explain the efficiency gain with the equal amperages. But typically yes less amps will be more efficient if ambient temp being too cold is not a factor. (same road block as wanting to use 48v electrical systems over 12v electrical systems in a car, but for a plug in prius i assume the nominal voltage is around the mid 200s and the optimal would be like the 800v system that they use on some hypercars)

My original comment was more about an entirely theoretical instance where if the whole system was 1000v ac and dc there would be a lot less losses from high current heating up the system for the same kW/h charging rate. Not entirely applicable.

But yeah somebody try differing your amps on your 240v charger and note the efficiency change. The longer charge should be more efficient and it is better for battery longevity. Fast charging reduces cycle lifes available a lot more.

*when i say losses and heat i mean in the whole system not just the wire. We would just measure at the panel to record the overall loss. The heat is loss in the batteries, the onboard charging system components, the wire, each connection etc...

[hayden55]

Originally Posted by JSH

Faster charging makes a big difference when charging in cold weather.

If the battery is cold the car will run the heater and circulate coolant to warm the battery so it can be charged safely. On a typical 120V / 12 amp circuit you can use the majority of the electricity provided just to keep the battery warm enough. If you are using 1 kW to heat the battery that only leaves 0.4 kW to charge. The charge takes forever and wastes a lot of electricity. Jump to 11 kW and 1 kW to heat is a small fraction of the energy and the charge time is near normal.

More of a situational instance, but this is true so definitely one of the first things to consider on a cold day. Charging lithium batteries below 39F and especially at 32F and below is a challenge. You would need to heat them. But in these instances i'm not factoring in outside temps. But yeah that makes the testing harder right now for a lot of us as the optimal won't always be the same lol.

[JSH]

Originally Posted by hayden55

automotive engineers hate 12v systems but we are stuck with them over going to higher voltages because of pita factor.

Yes, 12V systems are long out of date. We should have switched to 24 and then 48v decades ago. It looks like the rise of 48V hybrids and EVs might finally move accessories like power steering, A/C, and water pumps to 48V.

Originally Posted by hayden55

But yeah somebody try differing your amps on your 240v charger and note the efficiency change. The longer charge should be more efficient and it is better for battery longevity. Fast charging reduces cycle lifes available a lot more.

In the summer when it is 70F overnight - yes lower amps will be more efficient (to a point). Right now when overnight temperatures are at or below freezing the car will run the heater all night.

EDIT: I decided to test this and plugged in my car to charge. With the ambient temperature at 41F and my charger set to 24 amps the charger is delivering 5.8 kW to the car and the car is using 2.0 kW of that to run the battery heater.