Vampire Drain? Simple way of checking it ...

[TomLee]

Hi folks

I'm pretty new to all the EV things as I own my SR+ for only four months. I was since bothered by the car not reaching its EPA range. I understood that no car can reach its EPA rated range in real life, but I didn't expect they can be off by that much (one extreme example is that 17km of driving cost me over 53km of range). Instead of close my eyes and switch the display to %, I decided to read and record my own numbers. First post I have related to this topic is Overall M3+ Efficiency w/ Detailed Data. I got a lot of help, especially from @AlanSubie4Life and @darth_vad3r, in that thread. After that, I realized that measure the loss over the rated range as vampire drain is not scientific. Vampire drain strictly speaking is the drain while not driving. Since it's not driving, you can't measure that by distance or range.

Recently, I started a new method, not new to a lot of members here, of recording to determine the drain. I recorded a lot of numbers, even switch between % and kms, to minimize the error. As a side product of this method, I found a simple way to determine the vampire drain. Here's how: charge your car to a certain percentage every time, read out the difference between the kWh used from last charging and kWh Added, that's the vampire drain in between your two charges.

For the pic below, I charged my car two days ago to 80% SoC. I drove 140.4km and used 21kWh of power. Theoretically if no vampire drain, I would have added 21kWh juice to top up to the same 80% SoC. However, added kWh suggested that I used 27kWh. That difference of 27kWh - 21kWh = 6kWh is the vampire drain for that two days.

It's not the most accurate way of doing it, but simple enough to understand and measure. Thoughts and recommendations?

Thanks!

 

[TimothyHW3]

Not sure what those two told you, but they confused the hell out of you

The rated distance can be used to measure the vampire drain. The reason it is not scientific is not "because you are not moving", but due to deviations in the temperature and rounding errors. Yes, switching to km will give you better results.

To explain what is going on - the rated range is nothing more than a representation of your capacity (think of gas thank capacity). It is basically your total battery capacity (77 roughly when new) divided by an arbitrary constant used by the EPA called "typical" which is 153Wh/km on AWD and a bit lower on SR+(you can find it in the energy tab)

So whenever the capacity of your battery pack decreases, being due to weather or electronics in the car, the rated miles/km are affected. Regardless wether you drive or not.

Your method has even more flaws as it doesn't take degredation between charges nor heat loss when driving into consideration.

Just switch to KMs and mark the state when you leave the car and when you get back - this is the vampire drain.

 

[rrolsbe]

What I am not sure about is whether the 27kwh is the estimated amount of energy added to the traction battery or the amount of energy drawn from the wall socket your UMC is plugged into. During the warmer months either case may be close to the same number; however, charging during temps at or below about 47F will use shore power to heat the traction battery (via the traction motor). If the battery temp is considerably below 47F, there could be a fair amount of KW usage just to heat the battery to allow charging and that usage may not be reflected in the 27KWH number in your example. If I had to quess, the 27KWH ONLY includes energy added to the traction battery??? If true, your method would not be very accurate during charging sessions at temps considerably colder that 47F. What you need is a way to measure the amount of energy drawn from at the wall socket, which would not include the energy dissipated as heat in the circuit wiring (ie... if the unloaded open circuit voltage was 240V and the voltage during the charging session was 230V @ 32A, then the loss in the wiring would be 10V * 32A or 0.32KWH. So in the winter time your 21KWH butt time driving usage number will go up (less regen, heater usage, etc..) as will your power usage drawn from the power company. Also you may want to do your test over say six days for a more accurate number. That said, I have seen 3KWH of phantom/vampire drawn per day on several occasions in the past year. 3KW may not seem like a lot but I have read that some areas of the country pay over 50 cents/KWH during peak time or in upper tiers.

 

[TomLee]

Not sure what those two told you, but they confused the hell out of you

The rated distance can be used to measure the vampire drain. The reason it is not scientific is not "because you are not moving", but due to deviations in the temperature and rounding errors. Yes, switching to km will give you better results.

To explain what is going on - the rated range is nothing more than a representation of your capacity (think of gas thank capacity). It is basically your total battery capacity (77 roughly when new) divided by an arbitrary constant used by the EPA called "typical" which is 153Wh/km on AWD and a bit lower on SR+(you can find it in the energy tab)

So whenever the capacity of your battery pack decreases, being due to weather or electronics in the car, the rated miles/km are affected. Regardless wether you drive or not.

Your method has even more flaws as it doesn't take degredation between charges nor heat loss when driving into consideration.

Just switch to KMs and mark the state when you leave the car and when you get back - this is the vampire drain.

I wouldn't be here in the first place if I'm not confused! You agreed with me that the vampire drain should be the drain when you are not moving, however, you insist to take driving condition into consideration when measuring vampire drain. Isn't that confusing? I was on the same boat to record everything in kms, but eventually felt the vampire drain confusing. How about if I drive more efficient? Should that drain less significant? How about the other way around? Anyway, back to the topic, degradation is not in the formula that's for sure. That's because I don't believe degradation is happening within one or two days and that's why it's not in here. However, I do believe, all losses, be it heat loss or the driving habit losses, happened in the driving were included in the "kWh Used" screen. That's the base of using the difference to determine the vampire drain. I'm happy to be educated that my base was wrong.

As I stated in the OP, this method is not the most accurate, but easy to understand: you repeat your charge to the same point, then the kWh used should equal to the kWh you added.

 

[TomLee]

What I am not sure about is whether the 27kwh is the estimated amount of energy added to the traction battery or the amount of energy drawn from the wall socket your UMC is plugged into. During the warmer months either case may be close to the same number; however, charging during temps at or below about 47F will use shore power to heat the traction battery (via the traction motor). If the battery temp is considerably below 47F, there could be a fair amount of KW usage just to heat the battery to allow charging and that usage may not be reflected in the 27KWH number in your example. If I had to quess, the 27KWH ONLY includes energy added to the traction battery??? If true, your method would not be very accurate during charging sessions at temps considerably colder that 47F. What you need is a way to measure the amount of energy drawn from at the wall socket, which would not include the energy dissipated as heat in the circuit wiring (ie... if the unloaded open circuit voltage was 240V and the voltage during the charging session was 230V @ 32A, then the loss in the wiring would be 10V * 32A or 0.32KWH. So in the winter time your 21KWH butt time driving usage number will go up (less regen, heater usage, etc..) as will your power usage drawn from the power company. Also you may want to do your test over say six days for a more accurate number. That said, I have seen 3KWH of phantom/vampire drawn per day on several occasions in the past year. 3KW may not seem like a lot but I have read that some areas of the country pay over 50 cents/KWH during peak time or in upper tiers.

Thanks for your advice on testing it on a wider span of days. I started to log these on my computer. The example I have here is a bit extreme and probably caused by YouTube and Netflix from V10. Normal numbers were anywhere from 0.5 to 3.5 kWh/day loss.

For the charging losses, this particular charge happened on Supercharge so I assume minimum losses compare to the home charging. And I didn't record these numbers directly from the screen, I used the Stats app so have more decimals. The purpose of posting the screen is to qualify for "SIMPLE way of checking it"

 

[ewoodrick]

Vampire drain is easy to test and there really is only one way to do it. Let the car sit for a day or more.
Most everything else that you seem to be testing has all sorts of other factors that can cause it.

And it is quite easy to hit the EPA numbers, Go drive a route at 55 mph and you'll beat the numbers.

If you try to measure range in short trips, like 17 km, many other factors such as car conditioning come into play. The same thing happens on ICE vehicles.

 

[darth_vad3r]

@TimothyHW3 he doesn't sound confused at all.

@TomLee, what you are 'measuring' here with that technique is all losses -- which is vampire drain PLUS losses going in/out of the battery (any drivetrain inefficiency or regen inefficiency) while driving.

With this method you would get more "vampire drain" per hour of not driving than if the car just sat parked for the same number of hours (because just sitting there you don't have the partly inefficient power consumption for driving, and recharge events from regen).

Now I say 'measuring' because we are relying on the dashboard numbers from the car which are rounded and also potentially not showing us what we think they should be showing us. We think it is DC kWh added to the battery, and we think it is DC kWh out of the battery, but who knows if we are right

But in the end, a loss is a loss ... so the number is useful. It's just not accurate to call it "vampire drain" though.

 

[AlanSubie4Life]

As I stated in the OP, this method is not the most accurate, but easy to understand: you repeat your charge to the same point, then the kWh used should equal to the kWh you added.

Unfortunately this is not the case.

For the AWD, each mile decrement takes 230Wh on the trip meter, and each mile added during charging takes 245Wh.

The numbers are different on the SR, but the percent difference is about the same.

The result is that with your proposed method you are overestimating vampire drain.

I took a road trip of 1200 miles over the last few days, and the data makes this discrepancy very clear. The reason for it I am not sure, but it certainly exists!

 

[TomLee]

@TimothyHW3 he doesn't sound confused at all.

@TomLee, what you are 'measuring' here with that technique is all losses -- which is vampire drain PLUS losses going in/out of the battery (any drivetrain inefficiency or regen inefficiency) while driving.

With this method you would get more "vampire drain" per hour of not driving than if the car just sat parked for the same number of hours (because just sitting there you don't have the partly inefficient power consumption for driving, and recharge events from regen).

Now I say 'measuring' because we are relying on the dashboard numbers from the car which are rounded and also potentially not showing us what we think they should be showing us. We think it is DC kWh added to the battery, and we think it is DC kWh out of the battery, but who knows if we are right

But in the end, a loss is a loss ... so the number is useful. It's just not accurate to call it "vampire drain" though.

I fully understood the lack of accuracy on the screen will cause the inaccuracy of the results, and I also ignored a lot of things here, regen, charging losses, and etc., so that’s why I’m saying “a simple way” of checking, instead of “measuring” it. I also believe the battery in/out and the regen inefficiency were small enough to be cancelled out by the reading errors. That’s also why I’m logging all my charging event now trying to figure few constants to calculate/make sense/cross check other numbers. Just one thing, I don’t quite understand why you are saying I may have more vampire drain calculated using this method? I don’t know where Tesla put that regen energy to, but most likely kWh used. So basically kWh used on the screen display came from the battery capacity part and the regen part as well. We will need to charge to a higher level if no regen present. Isn’t that means I measured less vampire drain?

Anyway, the whole purpose of this post is to provide a easy way to check the losses, be it “vampire” drain only or not. It’s more of make sense your own numbers than scientific methodology. But, any scientific discussion on the topic is welcome as I’m trying to discover the whole myth underneath it!

 

[TomLee]

Unfortunately this is not the case.

For the AWD, each mile decrement takes 230Wh on the trip meter, and each mile added during charging takes 245Wh.

The numbers are different on the SR, but the percent difference is about the same.

The result is that with your proposed method you are overestimating vampire drain.

Thanks for replying! No where in your quoted words I mentioned miles or range. I purposely not to introduce range back in the calculation to avoid adding more complicities(driving habit, wether, etc) here. All I’m saying is kWh for kWh.

 

[AlanSubie4Life]

I also believe the battery in/out and the regen inefficiency were small enough to be cancelled out by the reading errors.

It actually has nothing to do with this as far as I can tell.

On my trip the way out was over 8000 feet of elevation gain. On the way back, 8000 feet of loss. The discrepancy of 245/230 was exactly the same. To first order, it is independent of regen losses and such. The number displayed on the trip meter simply is a scaled (down) version of the added kWh. So that is where your error comes from with your method.

 

[AlanSubie4Life]

Thanks for replying! No where in your quoted words I mentioned miles or range. I purposely not to introduce range back in the calculation to avoid adding more complicities(driving habit, wether, etc) here. All I’m saying is kWh for kWh.

I know. I am just saying the kWh on the trip meter are not equivalent to the kWh added on the charging display. I can post pictures proving this - since I was on a road trip with continuous driving, there was effectively zero vampire drain. Yet the discrepancy exists (245/230 ratio, roughly).

 

[TomLee]

I know. I am just saying the kWh on the trip meter are not equivalent to the kWh added on the charging display. I can post pictures proving this - since I was on a road trip with continuous driving, there was effectively zero vampire drain. Yet the discrepancy exists (245/230 ratio, roughly).

I’d like to be educated. Seriously, thanks!

 

[TomLee]

It actually has nothing to do with this as far as I can tell.

On my trip the way out was over 8000 feet of elevation gain. On the way back, 8000 feet of loss. The discrepancy of 245/230 was exactly the same. To first order, it is independent of regen losses and such. The number displayed on the trip meter simply is a scaled (down) version of the added kWh. So that is where your error comes from with your method.

I don’t quite understand the in/out concept here. My little brain tells me that 10kWh added on the screen actually translate to 11kWh or more, depend on voltage and ac/dc etc, output from the charging station. But if I only used the numbers shows on the screen (assuming it’s added to the battery), isn’t that the loss being taken care of already?

 

[TomLee]

BTW, if I compute Wh added over the km added, I get a constant of 136Wh/km (219Wh/mile) which I believe is what Tesla uses to convert Wh into range.

 

[AlanSubie4Life]

BTW, if I compute Wh added over the km added, I get a constant of 136Wh/km (219Wh/mile) which I believe is what Tesla uses to convert Wh into range.

That is correct for the SR+.

For the “out” kWh, it is about 5% smaller.

For example, if you drive and use 20kWh on the trip meter, you will find that to recharge to your original miles, you will need to add about 21kWh. (5% difference).

In other words, it is about 209Wh per rated mile for consumption for the SR+ (I have no way to measure this myself on an SR+, so I do not know the actual exact value. I can only do that test with the AWD.

 

[darth_vad3r]

It actually has nothing to do with this as far as I can tell.

On my trip the way out was over 8000 feet of elevation gain. On the way back, 8000 feet of loss. The discrepancy of 245/230 was exactly the same. To first order, it is independent of regen losses and such. The number displayed on the trip meter simply is a scaled (down) version of the added kWh. So that is where your error comes from with your method.

Ya my assumption here is I that one (the?) reason the meter reading is using a smaller constant than the charge screen is to account for average losses on the output side (which includes regen coming back in and being inefficient, as well as general battery in/out inefficiency). Much like it’s an EPA estimate, I think this lower number may be an estimate by Tesla to discount the energy losses. In a way, it’s more like the input number is the estimate. The 245 Wh required to tick up 1 km is factoring in the expected losses from DC charging side to final energy count on the output side.

But ... who knows

 

[darth_vad3r]

BTW, if I compute Wh added over the km added, I get a constant of 136Wh/km (219Wh/mile) which I believe is what Tesla uses to convert Wh into range.

Ya, that’s 136.08 DC iWh/km. It’s a smaller number for oWh/km though, which is what the trip meter presumably is ‘measuring’.

i = in
o = out

 

[darth_vad3r]

I don’t quite understand the in/out concept here. My little brain tells me that 10kWh added on the screen actually translate to 11kWh or more, depend on voltage and ac/dc etc, output from the charging station. But if I only used the numbers shows on the screen (assuming it’s added to the battery), isn’t that the loss being taken care of already?

If you add ~10.5 kWh to the battery (according to the charge screen) and then immediately use all of that energy, the trip meter will show ~10kWh used. This 5% loss is automatic. Nothing to do with vampire drain, just how the car works.
It will then take you another 10.5kWh (according to the charge screen) to get you back to where you started.

Put another way, trip meter counts koWh. But charge screen shows you kiWh.

If you want to convert trip meter koWh to charge screen units you have to multiply by ~1.05.

 

[AlanSubie4Life]

Ya my assumption here is I that one (the?) reason the meter reading is using a smaller constant than the charge screen is to account for average losses on the output side (which includes regen coming back in and being inefficient, as well as general battery in/out inefficiency). Much like it’s an EPA estimate, I think this lower number may be an estimate by Tesla to discount the energy losses. In a way, it’s more like the input number is the estimate. The 245 Wh required to tick up 1 km is factoring in the expected losses from DC charging side to final energy count on the output side.

But ... who knows

I have no idea why either, I just know the difference, which is important for interpreting the trip meter and drawing conclusions about how far you can go...which I found to be slightly helpful on my trip (though mostly I just went with the car estimates - which were ok as long as I selected the appropriate wheels. . )

Two issues with your hypothesis: 1) for Supercharging, I kind of feel like people might expect that they are paying for the energy delivered and stored as “available” energy in their battery. And 2) the 245Wh/rmi number is the only value you can use and get close to the EPA document total measured discharge (78+ kWh). (As discussed elsewhere, the reserve adds to that and you arrive at the ~78kWh number.)

So I think that 245Wh per rated mile number really does represent the actual energy available. Because messing with the EPA is not a good idea...best to not lie about things (VW!!!)...and they require that the energy measured in the test be available to the consumer, from what I understand.