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Discussion Starter · #1 ·
ED battery failures, the expensive $15,000 kind, happen because the 12 volt battery weakens or dies during periods of neglect ie not being driven on a more or less daily basis. So the high voltage battery tries very hard to keep the 12v battery fully charged but failing to do that it ends up killing itself. Same as if you left the headlights on etc.

The solution is to disconnect the negative post of the 12 volt battery and connect a 'float charger' to this battery to keep it fresh during your absence. So even if the 12 volt battery does die somehow on its own this will have no effect on that $15,000 high voltage battery. The hv battery will slowly discharge when connected but this can be estimated from experience. After 10 weeks my 2016 ED3 traction battery went from 85% down to 45% during temperatures ranging from 20*F > 35*F. If much colder is expected do NOT expect similar results.

See: "Case Studies Needed - ED Long Term Storage" in the "smart fortwo Electric Drive" forum for prior reporting.
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The hv battery will slowly discharge when connected but this can be estimated from experience. After 10 weeks my 2016 ED3 traction battery went from 85% down to 45% during temperatures ranging from 20*F > 35*F. If much colder is expected do NOT expect similar results.

See: "Case Studies Needed - ED Long Term Storage" in the "smart fortwo Electric Drive" forum for prior reporting.
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I'm surprised that the battery self-discharged that much. Lithium batteries don't self-discharge, so the "supervisory" BMS boards must be doing the discharging - or maybe it is jsut an error that accumulated on the SOC gauge and the pack did not actually discharge.

Another tip that is needed is to verify that the the 12V battery is not in an active charging cycle (DC-DC converter turned on if the battery voltage goes below 12.0 volts or so) when you disconnect the 12V battery. There are some reports of this casusing problems and even brickings.
 

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Discussion Starter · #3 ·
This post was written as a STICKY which I requested from 'administrator' so more people can see this issue.

I also posted an update in "Case Studies Needed . . ."

You are correct, I have a house full of LiMC/LiNC/etc batteries that sit unused for the time being and keep 99% of their voltage from 6 months prior. So the ED3 must have something else going on. But 10 weeks is a good bit longer than I've ever abandoned the ED3 before so I'm relieved once again that it survived. Btw with a fully charged battery I went for a completely normal round trip yesterday so the BMS has proven/reset itself.

Anyway, you raise a new point re checking the voltage before disconnecting 12v battery. So you suspect the DC-DC might stay latched in 'charge mode' even after the main contactors click off. Hmmm makes no sense BWDIK. :)
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Discussion Starter · #5 ·
If your 12 volt battery is over 4 years old, lets say, then it might make sense to:

1. Disconnect negative post (the easy one to get to) and tuck safely away from contacting terminal.
2. Hook up one of those tiny 'float chargers' to 12v battery. No need to use a normal charger, could be a hazard.
3. You could get stuck away from home and a few weeks turns into 10.

EV has no 'battery test' like starting an ICE, so you have no constant reminder how good your battery is.
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With the negative cable of the 12V disconnected from the 12V, it goes against all I've learned from Physics and EE that it was being charged...

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Anyway, you raise a new point re checking the voltage before disconnecting 12v battery. So you suspect the DC-DC might stay latched in 'charge mode' even after the main contactors click off. Hmmm makes no sense BWDIK. :)
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The contactors will not be clicked off. If the car is parked, keyswitch off, and12V battery falls below a certain voltage (below 12V? or 11.5V?) the contactors will close and the DC-DC converter turned on until the 12V battery charges back up. I heard the contactors close on my smart once in this situation.

This can be checked with a voltmeter - if the battery voltage is above 13.5 volts or so, assume the DC-DC converter is on and wait for the voltage to drop back down to resting voltage (13 V or lower).

As JMK2020 explained it, there is a programmed logic of the car doing these recharge cycles a set number of cycles over a period that the car is parked, then it "gives up" and lets the 12V battery voltage discharge all the way down. It is during the "brownout" condition when the 12V system voltage falls down below 10 volts, the DC-DC converter goes haywire, damaging hardware (BMS and current sensor) and triggers the permanent P18051C code, bricking the HV pack.
 

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Discussion Starter · #10 ·
Au contraire, once you disconnect the 12 volt negative terminal from the SmartEV battery there is NO energy available to activate or close the contactors. So the car is now safe from direct destruction as in "bricking" of the high voltage (traction) battery. This is a genuine relief for owners to appreciate.

However, as my recent episode indicates, there is a slight limitation to how many MONTHs this protective procedure can be effective. My maximum of 10 weeks (so far) of disconnection has indicated that the BMS remains connected and is ever so slowly discharging the traction battery. In my case this discharge brought the battery down from 85% to 45%, so we still have room to experiment here. Anyone disconnecting their ED3/451 for more than 10 weeks PLEASE reply here with your findings.

As this is now an official STICKY with hopefully more eyeball exposure please limit responses, if that is the rule with stickies (?), to additions to this specific topic.

Seriously, if you plan to abandon your beloved ED3/451 for a longer period seriously consider having someone come to give it an interim plug-in charge session. Or just loan them the car!
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Maybe some experience and background again. For sure the physics is valid also for the Smart 451 ED3.
BUT:
as told by Yinzer, an active contactor powering a 12V bord net will stay active it the condition for charged battery is not reached.
Means 12V battery is below 11,7V, the internal charging process is started and even you disconnect the negative pole of the 12V Battery the DC/DC will power it self.
Like a self holding/powering relay circuit.

In my view it is not necessary to disconnect the 12V Battery you only need to pay attention the discharge is refilled by connecting a 'float charger' to this battery to keep it fresh and healthy.

But again a big BUT:
In this situation pay attention your charger is working always correct. For me the last weekend run in a emergency case. By a circumstance the 12V charger stops to work and i could see the healthy 12V battery get discharged slowly as expected by a young 12V battery over 3-4 days. The SoC of the HV battery was about 83,5%.
Yesterday night i rechecked it and the 12V was loaded by internal DC/DC charger and the Soc of the HV battery was only 67%!!!!!

Also you need to pay attention if you want disconnect the 12V battery the car is really in standby state and not just ignition switched off.
Otherwise the 3 CSE on stacks / battery packs could not fall in standby and will just load the local the 3 battery packs.
This explain the case of Vincent losing charge even the HV battery was not at all active.
If you do the right sequencing there is no issue to lose any charge even after month of no usage.
 

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Discussion Starter · #12 ·
No, I will NOT abandon my ED3 without first disconnecting the 12 volt battery! My years of success, so far, back me up on this. Usually I repark the car to a different position in the garage at the last minute so that gives me a sense of the voltage/charge in the 12v battery: bright dash lights and normal shifting response etc. If the 12v battery was in an '11 volt state' in need of a proper charge then I would notice this. But the suggestion to first check the voltage, using a handy cigar-lighter voltmeter thingy, before making the final disconnection IS a good idea. I will do this in future and record: 1. % Charge on meter 2. Voltage of 12v battery - on a paper kept in glove box.

Please someone publish a schematic diagram of the ED3 hv battery/BMS ie the entire hv battery box.

The BMS runs off the hv battery NOT off the 12v buss. So this slowly draws down the hv battery over time. True or false :)
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@Vincent Rapide It may be good to note the mileage on your ED when you left it for 10 weeks. The reason being that depending mileage, roughly proportional to health, how long the charge will last.

(Thank you for sharing)!

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Discussion Starter · #15 ·
LOL, I thought you were going to say someone snuck into my garage and was joyriding my ED3 all over the island while I was away !!

The car is a 2016 with [head scratching] either 16k (or 27k miles), can't be sure from this remote location (no Tesla App for the Smartie). And it is always the same car, my only running SmartED which I have abandoned these dozen +/- times.

Yinzer is correct saying Li-Ion batteries do NOT lose charge while sitting UNconnected. I have several Ford LNMPO2 batts sitting for years in their shipping boxes that I open up every year or so to measure voltage of each module & cell and the loss per year is invariably less than one tenth of a volt. So miniscule that I've never bothered to think about charging them back up to the ~3.50v the seller sets them at before shipping. So, to repeat, it must be the connected BMS that is leaking the charge down during the 10 week period or whatever else remains connected. But certainly the contactors are OFF so the 12v buss is also OFF.
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So nice he posted it twice !! :giggle::p
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Solved, sorry but to be honest it is already posted in other threads several time already.

And as you asked i will not hide public available information, even i have some more and detailed pinouts which are under NDA, sorry.

By the way why you tell there is no Tesla App for Smart 451 ED3.

By OVMS i can tell you always about the latest status of any cell of my smarts all over the world via WWW. :) so even much more detail as available on Tesla.
Ok i am just waiting for my MYP.
Time to get some more EV for my collection. Soon i can compare.
 

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Please post link/s.

Is OVMS a phone app? That would be nice.
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Check it out Dimitrie78, a German guy, did a really brilliant job on the Smart 451 ED3 port of the OVMS software.

Only issue the connected system pulls or drain addition energy of the 12V system in standby. But it overs emergency triggers if something is going wrong.

You even can have pre condiioning with the unit again. Also you could emulate the paddles for the Different recuperation modes, which could be activated by coding. And also you could take benefit of the 4th Ds Mode in Brabus configuration.
Real nice feature which also could changed by tuning.
No need for external boxes. :)
 

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My 2013 is stored inside over the NJ salt season each year with a SOC of 65/70%. The 12 volt battery is NOT disconnected but is being monitored by a BatteryMinder Model 2012 smart charger. From the first snow until roads are salt free (usually Mid- March) it just sits. I have never seen a SOC less than 50% at the end of any hibernation season. I replaced the 12 volt battery after 5 years (thanks for the suggestion, Len) but that, desiccant cartridges and the software update are the only service since new. I regularly get 70+ miles per charge and 4.3 miles/Kwh as measured by total mileage divided by total Kilowatts as measured by a Kil-A-Watt in line with the charge cable. My experience indicates it is unnecessary to disconnect the 12 volt battery for extended storage as long as a smart charger is being used.
 
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