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Discussion Starter #1
I am getting concerned about power the car consumes just sitting, because our electric rate is 25 cents per kwh. (Electric company just discontinued off-peak rates.:() I have only begun measuring and keeping notes so I can't say anything definitive yet. I notice the car does not stay at 100% if you disconnect the charger, so we are using power for the privilege of having the car in the garage even if we don't drive it.

I just got a kill-a-watt meter and started keeping notes on kwh use after the battery reaches 100%. When I get the email the car has reached 100%, if I'm still awake I go down to the garage and note the time and the kwh reading on my kill-a-watt meter, then note it again in the morning. There was one instance of using about a full kwh in less than a day of just sitting at 100%. But last night it only used .06 kwh after reaching 100% for a 12-hour period.

Has anyone made a thorough study of their ED's parasitic losses?

Would it help to minimize parasitic losses/passive discharge to stop charging at 90%? (In other words, is the battery more able to hold 90% than 100% while off charger?)

Car is a 2015 with 2000 miles on it (bought new a few months ago) and is garaged every night. I am in Massachusetts, so temps are cold.
 

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Don't worry about it

Here's a six month summary for our ED.

It typically gets charged on the following pattern:
  • Workday week 10am - 4pm - L1
  • Evenings 7pm until 100% - L2

We leave the car plugged in most of the time. It does about 12,000 km in 6 months.

You can see there is no measurable power usage after charging is finished (e.g. 5am). It is possible that if the car was plugged in and the temperature was -10C or lower it would engage the battery heater. However that's rare.





 

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Per the J1772 standard, the car manipulates a "pilot" signal from the EVSE ("charger") to disconnect the power once it is fully charged - only reconnecting if it needs power for pre-heating/cooling or battery pack heating. So the only quiescent draw would be from the EVSE to generate the low voltage signal (a 12V square wave) but it should be tiny. There could be additional draw of course from the EVSE's power supply for it's electronics, but that should only be a couple watts.

But at any rate, aside from very cold (0F/-18C)or very hot 100F conditions, and to pre-heat the car cabin before departure, there is no reason at all to leave the car plugged in anyway. Leaving it sit unplugged at 70% SOC is better for the battery pack anyway.

In your area, follow the weather forecast, and assuming the garage is unheated, only plug it in if a strong cold spell is forecast.
 

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Discussion Starter #4
Well, it used close to a kwh last night after reaching 100% and I got a second email that "your car is fully charged" hours after the first one, with no driving in between.

The other way to get at this question is to leave it not plugged in and see how much charge it loses just sitting there. I'll try that tonight.

Thanks for the responses.
 

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Indeed. I have seen similar behaviour if the temperature drops overnight and the heater may come on. Or for that matter if the temperature rises and then the battery capacity increases and the charger is turned on again.

Horrible shame about the discontinuation of the low tariff rate! I would protest - or install some solar panels and a wind generator...
 

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Discussion Starter #6
Oh I have the solar panels -- sufficient to cover all my family's usage and that of my son's family too. But, I still value a kwh at its market price. Any kwhs I generate and don't use get carried forward as a cash credit and will turn into cash (or cash expense avoided) at a future time. I can transfer credit to any other customer of the same utility so I could always get a friend or another family member to buy my credit balance.

Yes, the end of time-of-use rates is a tragedy. It meant I got 28 cents during the day when I was earning credits to my bill from the solar power and then used energy at night at 15 cents. I had a bill in winter that was positive in dollar terms even though it was negative in pure kwh terms.

If the case is that the temp went up and battery capacity therefore went up and that's where the kwh are going after reaching 100% that would be no loss.

The car is in the garage, which is insulated, so I don't think the battery heaters are coming on. It stays above freezing. One reason I got a Smart is the Smart and my wife's Prius can share one side of the garage end to end, leaving room for my van in the other bay, making our 2-car garage into a 3-car garage.
 

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Well, it used close to a kwh last night after reaching 100% and I got a second email that "your car is fully charged" hours after the first one, with no driving in between.

The other way to get at this question is to leave it not plugged in and see how much charge it loses just sitting there. I'll try that tonight.

Thanks for the responses.
Charging of lithium (and for that matter even lead acid) cells in a battery pack is done using three steps.

1. A constant current step, where the pack is fed full charge current - about 10 amps for 240 volt charging, or half of that for 120 volt charging. This continues until the first cell hits the "full" voltage of (for Li-Mn-Co type chemistries) 4.2 volts then:

2. a "cell balancing" step - where the voltage of each cell is not allowed to exceed 4.2 volts, by reducing the charging current and shunting the current past the cells that have hit 4.2 volts, until all cells have reached 4.2 volts, then,

3. A "constant current" step where the voltage of all the cells is held at 4.2 volts by tapering the charging current down, until all the cell can only accept a few tenths of an amp of current at the constant 4.2 volts - then charging shuts off.

In a pack in theoretical "perfect" health, step 2 is very brief, with all cells hitting 4.2 volts at the same time - and step 3 will be brief, becasue the cells charging resistance is low, so the cells fill full without lot of current tapering needed. But more typically, Steps 2 and 3 might take a half hour or so (my car typically takes 20 minutes) but it might be longer with level 1 (120v) charging particularly in colder weather.

I suspect that the reason that one get two "fully charged" messages is that the first one is when step 1 is completed, and, at this point the pack really is nearly full. But another kW can easily be used going to step 3 - and this (due to not-so good engineering) results in a second message being sent.

You should be able to see the progress through step 2 and 3 on your kill-a-watt meter by looking at the amperage reading - you will see the amperage continuously going down - then it should shut off altogether aside from a very small draw.

If you unplug it upon being fully charged. Then plug it in later, it typically won't charge. The charger is programmed to not start charging unless the pack is a couple percent below full. At least that is how my Smart ED works.

And also, you probably pay a pretty good efficiency penalty charging the car with the 120 volt EVSE adapter instead of a 240 volt EVSE. You might think about getting a level 2 EVSE if you have a available 240 volt circuit in your house.
 

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Well, it used close to a kwh last night after reaching 100% and I got a second email that "your car is fully charged" hours after the first one, with no driving in between.

The other way to get at this question is to leave it not plugged in and see how much charge it loses just sitting there. I'll try that tonight.

Thanks for the responses.
Two points about what you observed
1) The email comes from an external monitoring system which isn't all that reliable.
2) We've left our 451ED unplugged for two weeks and the car still read 100% charge. So there's very little self discharge, at least over that kind of period.
 

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Discussion Starter #9
Thanks Blaine. That's the kind of information I need. I could not say that about my car. Are their more people out there willing to report how much they lose on their SOC meter when the car is just sitting? I would greatly appreciate responses of that type.

My car has been sitting for 12 hours, disconnected from the charger. SOC has gone from 100% to 94% over that 12 hours of just sitting. About a kwh, in other words. None of the above explanations/observations from others would seem to fit this observation, and I very much appreciate them. What I am seeing seems to be pure parasitic loss. Either my batteries cannot hold a charge fully for long, due to some flaw in the batteries, or something in the car is using about a kwh per 12 hours when the key is off. When connected to the charger, I see this as power drawn from the grid after reaching 100% charge just to keep the batteries full. When disconnected from charger and not driven, I see this as a diminishing reading on the SOC meter.

I need a few more statement's like Blaine's above. If I take it to the dealer and ask for this parasitic loss tendency to be corrected under the warranty, I fear they are going to claim it is normal. If it isn't, I need data to back me up. I would like to be able to point to posts on this thread as evidence this is not normal -- meaning people who testify they see no significant loss on their SOC meter when the car is sitting overnight or longer.
 

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I haven’t had my 451 ed too long yet and the longest I’ve left it unplugged was for 2 or 3 days. In that time I’ve seen no drop in SOC on the gauge. It’s possible it could have dropped 1%, but that’s not very easy to see on gauge.

It too stays garaged and my battery tests have come out pretty uniform.

We also squeezed 3 cars into our 2 car garage.

 

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My car has been sitting for 12 hours, disconnected from the charger. SOC has gone from 100% to 94% over that 12 hours of just sitting. About a kwh, in other words. None of the above explanations/observations from others would seem to fit this observation, and I very much appreciate them. What I am seeing seems to be pure parasitic loss. Either my batteries cannot hold a charge fully for long, due to some flaw in the batteries, or something in the car is using about a kwh per 12 hours when the key is off. When connected to the charger, I see this as power drawn from the grid after reaching 100% charge just to keep the batteries full. When disconnected from charger and not driven, I see this as a diminishing reading on the SOC meter.
That level of discharge is pretty high, and the power must be going somewhere. You might want to poke around the motor bay with a non-contact thermometer and see if anything is above ambient temperature. That could give you a clue.

I'd also want to check the battery temperature. If for some reason the car thinks the battery is very cold it might activate the heating element and "coolant" circuit. Which would suck power.

Maybe you can put together one of these battery diagnostic tools, or get a friend to do it.

https://github.com/MyLab-odyssey/ED_BMSdiag

That will allow you to read the internal battery temperature sensors. There are three, one for each cell stack in the battery compartment.


hth.
 

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Several data points from my experience.

I started getting two emails stating that charging had completed, commencing when the weather got cold. It did not happen before overnight temperatures dropped into the 40 degree Fahrenheit range. A couple of days when the overnight temperatures were warmer, I only got one email stating that charge had completed.

A typical drive I take after the car is fully charged is about 2 miles in distance. I often will get there with the state of charge showing at 98%. A couple of hours later, the state of charge is a percent or two lower. This also seems to have started when the weather became colder.

We have left our car sitting for 3 weeks or more at a time. When we know we are going to do this, I leave it at about 70% charge, and the charge does not decrease when we return home. I also have let it sit, unplugged, at 100% for a day or two, and the state of charge also remains at 100%.
 

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The only time I saw parasitic discharge was when sitting outside in <10 degree F temps at a low battery charge level, which is about when you'd expect the pack heater to kick in.

Otherwise it can sit for days at a charge level with no loss and no apparent efficiency hit when driving off.
 

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Discussion Starter #14
Thanks folks. Given what you are telling me, it's clear my car is malfunctioning. More responses would nevertheless be helpful.

I'll be taking it to the dealer. I'll post an account of that visit.
 

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Thanks Blaine. That's the kind of information I need. I could not say that about my car. Are their more people out there willing to report how much they lose on their SOC meter when the car is just sitting? I would greatly appreciate responses of that type.

My car has been sitting for 12 hours, disconnected from the charger. SOC has gone from 100% to 94% over that 12 hours of just sitting.
(bold mine)

No, The SOC should absolutely _not_ be doing that. Something is drawing current from the main pack that shouldn't be. This is a dumb question, but you are turning the keyswitch off and removing the key aren't you? Normally when the key switch is off, the traction battery voltage completely isolated by relays in the pack and even the external pack terminals are not hot. Even if you leave the running or dome lights on, it will flatten the 12 volt accessory battery (I've done it), not the traction pack.

You might want to get a battery pack scan unit from Len Sokoloff and run a battery pack test. Go here:

http://www.smartcarofamerica.com/forums/f170/more-battery-test-units-ready-go-146729/

Is the warranty still in force? Becasue unfortunately, if anything is internally wrong with the battery pack - even a $50 relay or a $0 bad connection - the only recourse made available to the dealer is to replace the whole traction pack.
 

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Discussion Starter #16
Fair question, Yinzer. Yes, I am turning it off and removing the key each time. Thanks for info about protections that are supposed to prevent parasitic drainage.

I have made an appointment with the dealer for Wednesday. I don't want to spend my time on this doing tests (nor my money buying more instruments) so I am hoping the dealer will find and fix the problem -- but I appreciate the suggestion. Meanwhile, I will be driving a Mercedes loaner car! It's 11 miles to the nearest dealer, so good thing they give free loaners!

I hope you are right that something is connected to power that should not be and it is draining the battery. That should be easily isolated and fixed by the repair person. The other possibility that occurs to me is that the battery pack is defective and cannot hold a charge even in perfect isolation. The warranty should cover that, since it's a defect, but would they make good on it given that a battery pack is worth more than the car?

This is a 2015 that was not sold until late 2017 and not driven all that time. I bought it new in December 2017 and have put just over 2000 miles on it in the 4+ months it has been in service. I got it from an out-of-state dealer (Ray Catena in NJ). My buddy bought one at the same time. I have asked him to perform these same experiments on his, but he's a super busy guy and may not get to it for a while.

It lost more like 4 or 5 percentage points from 10 pm to 10 am last night. First time I have measured it from a lower state of charge than 100%. This was going from a shade under 85% charge to about 80%.
 

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I am at a loss at to what could be draining the pack with the key off. It is a required safety feature in all 4-wheel EV's that the battery power be isolated in the impact-resistant battery pack case when the car is switched off (or in a crash strong enough to actuate a air bag) so any such abnormal parasitic drain would have to come from inside the battery pack case (like a high resistance short) necessitating replacing the whole pack.

The only other possibility is that the key switch is not actually switching the car pack power off? When you switch the car off, do you hear the "doo-doonk!" of a relay underneath you about a second after turning the key?

At any rate the warranty is in force. A battery pack costs about $20,000 by the way, so basically a Smart ED is a write-off if anything happens to the batter pack off-warranty. But fortunately, like most electronic things, if it gets though the warranty period, the battery pack is very unlikely to fail save for the slow degradation in capacity.
 

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Discussion Starter #18
Yes, I hear that noise when turning off the key.

The P remains lighted indicating the car is in Park. Just noticed that now, and it has been almost two hours since I last used the car and key is not in ignition.
 

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Yes, I hear that noise when turning off the key.



The P remains lighted indicating the car is in Park. Just noticed that now, and it has been almost two hours since I last used the car and key is not in ignition.


With the dash indicator not shutting off, it makes me curious if the SAM is going to sleep. Looks like somethings stay running on your smart that should go off shortly after key being removed. Mine will go off after about a minute unless I open the door.
 

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Curious, the SOC meter goes to zero when the key switch is off - right?

I recall that the "P" will remain lit for a while after shutting off in my car.

Johannesl, what is "SAM"? Not to be snarky, but on my (government) job, I always have to spell out an acronym the first time it is used in any kind of memo or report.
 
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