PV1
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Investigation - fast 12v depletion while stored

Tue Apr 03, 2018 10:49 am

On both of my I-MiEVs, I've noticed a trend that, in my case, usually results in rapid discharge of the 12 volt battery (rapid being a few days).

The Symptoms
While the car is parked longer term and not being driven, there is understandably some drain on the 12 volt battery. Usually, each I-MiEV can last quite a while and successfully start without a boost. Sometimes, the car will run the battery dead over a 3-4 day weekend and need a manual 12 volt charge to start.

Possible Cause
Lately, since I drive my Chevy Bolt most days, both I-MiEVs sit parked for extended periods of time. I've noticed that both will maintain their charge over several weeks. However, if I unlock the doors (I always lock the doors when I park the cars), open a door, close it, and then re-lock the car, I notice afterwards that the battery dies pretty quickly. I don't manually toggle any dome lights or touch anything electrical in the car, and all lights go out after locking. Both I-MiEVs exhibit this behavior.

Now, several days ago, I did the same procedure of unlocking, opening, closing, and re-locking the doors, but the difference here is that I started the car and moved it a few feet before shutting it off and locking it back up. Last weekend, the car started right up.

Latest Test
This morning, I had to grab my phone charger out of the car. I unlocked and opened the passenger door, started the car, shut it off, closed and locked the doors. We'll see if it can start this weekend. If it can, then next Tuesday, I'll do the same but skip the step of starting the car.

Question
Has anyone else noticed behavior like this?
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
Solar-powered since 10/10/2013

"Koorz" - 2012 Cool Silver Metallic ES with QC - 1/5/2015

2017 Bolt EV LT in Orange with QC - 7/31/2017

Driving electric since 2-21-2013.

kiev
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Location: The Heart o' Dixie
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Re: Investigation - fast 12v depletion while stored

Tue Apr 03, 2018 9:27 pm

When you "lock" up the car, are you using the key remote to turn on the security system, or

just doing it manually?

The security system current draw is my guess to the culprit. For long term if i lock one up i go the manual route--the aux battery seems to hold much longer that way.
kiev = kenny's innovative electric vehicle

PV1
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Re: Investigation - fast 12v depletion while stored

Wed Apr 04, 2018 4:59 am

I always lock using the fob button, pressing twice to get a horn chirp. This is a constant.

The difference is whether or not I start the car. I'm trying to see if something in the car doesn't go back to sleep mode if READY isn't invoked.
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
Solar-powered since 10/10/2013

"Koorz" - 2012 Cool Silver Metallic ES with QC - 1/5/2015

2017 Bolt EV LT in Orange with QC - 7/31/2017

Driving electric since 2-21-2013.

jray3
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Location: Tacoma area, WA
Contact: Website

Re: Investigation - fast 12v depletion while stored

Mon Apr 09, 2018 9:05 am

Here's a data point. After two weeks of unplugged storage at 40% SOC during our recent vacaton, MR BEAN snapped back to life and the first reading I saw on my cigarette lighter plug-in meter was 14.38 Volts. That indicates to me a plenty healthy house battery that had not been depleted in the least by 2 weeks of inactivity. This is the original battery. I've only topped off the cells' water twice, the second time this winter was unnecessary. I think that the charging algorithm for our 'starting battery' is excellent for long service life of a flooded lead acid.
2012 i-SE "MR BEAN" 89,000 miles
2012 i-ES traded at 21,648 miles
1983 Grumman Kurbwatt,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

DBMandrake
Posts: 54
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Investigation - fast 12v depletion while stored

Mon Apr 09, 2018 11:20 am

jray3 wrote:Here's a data point. After two weeks of unplugged storage at 40% SOC during our recent vacaton, MR BEAN snapped back to life and the first reading I saw on my cigarette lighter plug-in meter was 14.38 Volts. That indicates to me a plenty healthy house battery that had not been depleted in the least by 2 weeks of inactivity. This is the original battery. I've only topped off the cells' water twice, the second time this winter was unnecessary. I think that the charging algorithm for our 'starting battery' is excellent for long service life of a flooded lead acid.

14.38 volts means the DC-DC inverter must have been running (car in ready mode) when you took the reading - the open circuit terminal voltage of a fully charged 12v lead acid battery is only 12.6 volts, so assuming it hadn't been charged in the last 30 minutes or so (not holding a surface charge) any voltage above about 12.6 volts indicates the DC-DC inverter is active.

You needed to get a reading of the terminal voltage with no significant load and no charging to get a true picture of the state of the battery after 2 weeks sitting. With the DC-DC inverter running you'll get about 14.4 volts pretty much regardless of the state of charge of the battery.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

jray3
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Re: Investigation - fast 12v depletion while stored

Mon Apr 09, 2018 11:42 am

Yes Mandrake, you are correct. However, the battery snapping back up to 14.38 V immediately upon the first start in 2 weeks indicates that it was not significantly discharged, as it would have shown some voltage sag EVen with the dc-dc running. In my EV conversions with standby loads and equally powerful DC-DC converters, the house battery needs some recovery time after a hibernation like that before it will show such a high voltage. I went to take a direct reading from the posts before startup, but our positive post is so well protected that I couldn't get a probe to make contact without investing too much time in removal and reinstallation of the covers. Time to install that Anderson SB175 pigtail that most of my vehicles receive for fast and low resistance hookup of battery chargers or jumper cables.

DBMandrake wrote:14.38 volts means the DC-DC inverter must have been running (car in ready mode) when you took the reading - the open circuit terminal voltage of a fully charged 12v lead acid battery is only 12.6 volts, so assuming it hadn't been charged in the last 30 minutes or so (not holding a surface charge) any voltage above about 12.6 volts indicates the DC-DC inverter is active.

You needed to get a reading of the terminal voltage with no significant load and no charging to get a true picture of the state of the battery after 2 weeks sitting. With the DC-DC inverter running you'll get about 14.4 volts pretty much regardless of the state of charge of the battery.
2012 i-SE "MR BEAN" 89,000 miles
2012 i-ES traded at 21,648 miles
1983 Grumman Kurbwatt,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

DBMandrake
Posts: 54
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Investigation - fast 12v depletion while stored

Mon Apr 09, 2018 12:42 pm

You can measure the non-charging voltage at the cigarette lighter socket without putting the car in ready mode - just turn the key to ACC or ON without entering ready mode, and the cigarette lighter socket will have power without the DC-DC inverter running.

As long as you have the headlights, seat heater, blower fan, radio etc all turned off there will be very little load on the battery so the reading should be valid.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

jray3
Posts: 1512
Joined: Tue Dec 06, 2011 1:05 am
Location: Tacoma area, WA
Contact: Website

Re: Investigation - fast 12v depletion while stored

Mon Apr 09, 2018 1:46 pm

DBMandrake wrote:You can measure the non-charging voltage at the cigarette lighter socket without putting the car in ready mode - just turn the key to ACC or ON without entering ready mode, and the cigarette lighter socket will have power without the DC-DC inverter running.

Good to know, and wow- that's a curious design decision. Likely a carryover from ICE design, but why stress the house battery by leaving the DC-DC converter off during accessory operation?
2012 i-SE "MR BEAN" 89,000 miles
2012 i-ES traded at 21,648 miles
1983 Grumman Kurbwatt,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

DBMandrake
Posts: 54
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Investigation - fast 12v depletion while stored

Tue Apr 10, 2018 2:50 am

jray3 wrote:
DBMandrake wrote:You can measure the non-charging voltage at the cigarette lighter socket without putting the car in ready mode - just turn the key to ACC or ON without entering ready mode, and the cigarette lighter socket will have power without the DC-DC inverter running.

Good to know, and wow- that's a curious design decision. Likely a carryover from ICE design, but why stress the house battery by leaving the DC-DC converter off during accessory operation?

By "house battery" I assume you're referring to the 12v auxiliary battery ? (I've never heard it called that before...)

On these cars the DC-DC inverter that charges the 12v battery is outside of the main traction battery enclosure, so for it to operate the high voltage contactors in the pack have to be energised. This consumes power running the contactors, and also means that the high voltage system around the car is now live, as is all the electronics involved in driving like the drive inverter etc. Also the DC-DC inverter will consume some power even if the 12v battery is fully charged.

You wouldn't want this happening when the car is just set to ACC so you can sit in the car and listen to the radio, both from the safety reason of the whole high voltage system being energised unnecessarily, and also the power losses caused by having the contactors energised, the drive inverter powered up, and the DC-DC inverter running when it isn't needed.

(By the way the contactors are also energised and the DC-DC inverter active when the car is charging with the key off)

The battery is about 33Ah so you can use the radio for many hours without discharging the battery. In fact it takes quite a bit to run it down, which I found out the hard way recently. I have two heated seat covers that plug into the cigarette lighter socket - both of them turned on is about 50 watts or just over 4 amps.

While I was replacing the front brake discs I had the key in ACC so that the steering lock was disengaged so I could turn the steering back and forth. Unfortunately I forgot to turn off the heated seat covers...

The key was probably on for about 6 hours in total including a lunch break - by the time I tried to start the car the 12v battery was discharged enough that I could neither start it or Level 2 charge... I ended up having to connect a 12v battery charger to "jump start" it, and then plugged it into the Level 2 charger to charge up the main traction pack. (Which was at about 40% due to driving earlier in the day) As the main charging process charges the 12v battery as well I didn't need to leave the 12v charger on once the car itself was charging.

If the traction battery had already been nearly fully charged I would have had to just leave the 12v battery charger on to do the job as the car only charges the 12v battery until the traction battery has finished charging.

So running a high accessory load for a long time without the car in ready mode can potentially drain the 12v battery.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

jray3
Posts: 1512
Joined: Tue Dec 06, 2011 1:05 am
Location: Tacoma area, WA
Contact: Website

Re: Investigation - fast 12v depletion while stored

Tue Apr 10, 2018 8:02 am

Thanks Mandrake- I confirmed that the ACC position does not bring in the dc-dc, as my house battery (a yachting term) is resting at a measly 12.1V even after an overnight charge plus an hour of driving. :o
With temperature correction for 50 degrees F, that's only 25% state of charge, and turning on the headlights and radio pulls it down to 11.5 V within a minute.
So some close monitoring is in order, as this little battery may be closer to end of life than I hoped. I've been carrying a LiPo jump starter box since fall just in case...

In EV conversions, it is common to leave the DC-DC energized at all times, but that does run the risk of depleting the house battery, which I did a number of times to my NiCad pack. However, discharging to zero is a regular maintenance step for balancing NiCads (and nicads only!). When I put the Karmann Eclectric back into regular service, I'll have to add a relay to the DC-DC input.

In my EVen older RX-7 conversion (still flooded lead-acid), the Vicor dc-dc puts off enough waste heat just floating the house battery to prevent snow or frost accumulation on that section of the hood. It needs a top-up charge every few weeks.

Teslas are notorious for a short service life on their 12V batteries due to the standby loads and continuous wireless connectivity.
2012 i-SE "MR BEAN" 89,000 miles
2012 i-ES traded at 21,648 miles
1983 Grumman Kurbwatt,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

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