12 V system in trouble

We had a short ride yesterday / yesteryear and have been charging a little bit today. Looking how much range I noticed the 12V system misbehaved. Lights dimmed and the fake motor sound sounded like the 12V dropped rapidly. Display looked somewhat darker than usual, indicators missing.

Charging with a 12V charger improved things. End of the year problem or just a mishap?

I had no problem "starting the engine".

My 3A arithmetic, 5A eff charger delivered 3A that dropped below 2A after a little time. In position "Ready" it still delivered some 0.4A and I remember it used to be almost zero. The car is some 3 years old and I guess so is the battery.

Peter, if I understand you correctly you put your external charger directly onto the 12v battery, and it started out at 3A and eventually dropped into float but was 0.4 and still charging. Doesn't sound bad and I would expect that 0.4A to continue dropping over 24 hours. What is its voltage and what does it drop to a couple of minutes after you've removed the charger?

It sounds as though your dc-dc converter is not charging your 12v battery, because your small external charger seems to be doing fine. I started digging into the manual but still have not spent the time trying to figure it out so I'm no help for now. Maybe someone?

The external charger dropped to 2A. Only when I "started the engine" and the DC-DC converter was running, did it come down to 0.4A.

My dealer has got a new battery tester and wants to test both of them. I'll tell you later what happened.

peterdambier said:

The external charger dropped to 2A. Only when I "started the engine" and the DC-DC converter was running, did it come down to 0.4A.

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Ah, that sounds like the dc-dc is working and the 12v battery is perhaps the problem. If the test shows it to be bad, I'd be inclined to replace the stock battery with an AGM if the regulated voltage out of the dc-dc is below 14.4v.

Everything is fine.

The tester, an EXP-830 from Mitsu, said it is 13.21V at 8 Celsius and 100% charged. Ok, that is 9 km from home and half an hour of driving.

Most likely charging 330V was finished but the 12V system was reconditioning the battery. So I caught it just at the right moment.

I am charging again right now. Should be some 4 hours at 230V/16A and it should be dark again when finished.

peterdambier said:

Most likely charging 330V was finished but the 12V system was reconditioning the battery. So I caught it just at the right moment.

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Peter, glad to hear everything is fine, but since you opened up the discussion, this doesn't make sense.

The 12v battery stays fully charged when driving and gets the dc-dc converter charging output as soon as the key is turned ON (if the 12v battery has sufficient voltage to activate the system). I don't know how much of the dc-dc output is dedicated to battery charging and how much goes to the other loads.

When you are charging the traction battery the car is OFF, and I don't believe the dc-dc converter is active and thus I don't think the 12v battery is charged at the same time.

EDIT 3 January 2013: This statement is incorrect, as pointed out by alohart in a subsequent post http://myimiev.com/forum/viewtopic.php?p=6474#p6474. The remaining question is the 12v battery charge rate from the dc-dc.

When traction battery charging stops, there is nothing to tell the dc-dc to charge the 12v battery. You can have a dead 12v battery yet still have a fully-charged traction pack.

The battery voltage of 13.21volts - was that no-load open circuit or is that with the key ON and the dc-dc operational?

Had you perhaps run your stereo or other 12v battery load with the key turned to the accessory setting but the car OFF, thus depleting the battery ... and the dc-dc converter simply didn't subsequently have time to catch up and charge the 12v battery?

Enquiring minds want to know...

JoeS said:

When you are charging the traction battery the car is OFF, and I don't believe the dc-dc converter is active and thus I don't think the 12v battery is charged at the same time. When traction battery charging stops, there is nothing to tell the dc-dc to charge the 12v battery. You can have a dead 12v battery yet still have a fully-charged traction pack.

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That's right. The 12V battery is not charged when the traction battery is being charged.
Once I wanted to record the charge of the main battery using the MUT-3 and a notebook. The notebook was connected to the 12V socket. After about 5 hours the 12V battery only had about 8V. That's not enough for the Battery Management Unit. The loading operation was stopped.

By the way, the power consumption in stand (all OFF) is 12mA.

This time everthing went right after charging. Even when the lights switched on (not ready) 12V was fine.

The tester was connected directly to the 12V battery with everything switched off and all doors closed.

I suspect I must have something forgotten to switch off.

Toying with a 12V charger and reading current I have found the DC-DC converter does run when charging and stops when finished.

So while charging say 6 hours EVMOTO did have enough power but the next 6 hours would drain the 12V battery. That is why I have modified a 12V charger to plug into the 12V socket and run my laptop from the charger with the battery as a buffer. I'll run it from another battery, not from the i-MiEV.

Oh, dont forget, when running down to 2 bars everything, DC-DC, heater, A/C gets disabled and that is what I did the day before.

EVMOTO said:

...By the way, the power consumption in stand (all OFF) is 12mA.

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EVMOTO, thank you for this - very good information. Now, does locking the doors and enabling the alarm system cause this standby current to go up? I haven't had a chance to dig in and make the measurements myself.

peterdambier said:

Oh, dont forget, when running down to 2 bars everything, DC-DC, heater, A/C gets disabled and that is what I did the day before..

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Peter, this points out that when describing a possible problem it is best to fully describe all the symptoms, conditions, and pre-conditions associated with the issue. It appears to me that in your situation the 12v battery had simply been heavily discharged and insufficient time was allowed for it to recover.

peterdambier said:

Toying with a 12V charger and reading current I have found the DC-DC converter does run when charging and stops when finished.

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I thought so. My observation isn't very scientific, but i noticed that when the vehicle is off and I've either got a door open or have just recently exited the vehicle, when I then plug in the car, the dome lights and every other light, get slightly brighter.

This is what led me to believe that the 12V was indeed getting charged up right along with the traction battery.

As a new I owner who's still reading through the thick owner's manual, I noticed that the first note on page 1-17 of the General Information/Charging section states:

"The 12V starter battery will be automatically charged during charging and also while the ready indicator is illuminated."

alohart, thank you for pointing this out and I've edited/corrected my previous post to reflect this. The remaining question is the amount of current and if there is a controlled charging curve feeding the 12v battery from the dc-dc converter.

The DC to DC converter is built into the on-board charger. Takes the 330v and brings it down to 14.x volts to charge the 12v battery like a alternator does for a gas car. A volt meter at the 12v battery posts will confirm this with the ign key in the READY mode or while the 330v battery is being charged.

Precautions when using a 12v battery charger. IF used improperly, damage may occur to the on-board charger. On some 12v battery chargers, there is a 50 amp jump start feature for gas cars. This amperage surge may be too high for the circuitry inside the OBC (onboard charger). Fast charging of the 12v battery with industrial grade chargers may have similar results. Best practice is to disconnect the 12v battery from the vehicle when charging.

Dome lights causing the 12v battery to discharge. The imiev has a auto shut off feature for the dome/map lights when they are set in the door mode They should shut off in about 30 min. The dome / map lights will not shut off if they are manually set to the ON position. Thus possibly draining the 12v battery below the threshold to power certian ECUs (sometimes SRS DTCS will be generated).