12v charging when plugged in but not in “ready”

[tewharaunz]

I’ve been having 12v battery problems and (I think) I have read every post in this topic area and haven’t found anyone with the same issue.

Replaced 12v (aux) battery with Lifepo4 (drop-in replacement with BMS).
Had no problems for a week of daily type 2 charging (commute is 80kms)

After long weekend (4 days without charging), aux battery battery stopped (low voltage protection).
I put a 12v charger on it for 15 minutes, and that was enough to “wake it” but it cut out again at work and I had to pull it and charge it in my office.

During a type 2 charge, the aux was ~14v and after it was 13.3v.
When I got home (turned off) it was 13.07v, and when I turned it back on (ready), it was 12.9v.

Does anyone have any experience with their aux battery not charging in ready mode, but charging fine when plugged in?

I’ve looked through the service manual for likely fuses, but nothing has jumped out.

 

[Boffingham]

Don't know much about this but why would you install a 12 volt battery with a BMS? This seems like overkill and maybe the i-miev cannot communicate properly with the 12 volt?

 

[tewharaunz]

Good question. I have been having issues with the 12v battery running flat, which significantly shortens the life of lead acid batteries. The lithium 12v replacement only $50 more than lead acid and has a built in protection circuit.

I’ve tracked the problem down to a lack of 12v charging when driving, so if I don’t use any accessories, I can get to work and back (~80kms).
Also, if I overstress the power steering, that seems to use up 12v power in a hurry.

When I plug in the car, the 12v battery charges fine, so I don’t think the Battery is acting up.

I’m hoping it’s just a fuse or fusible link, and someone here knows which one to check/replace. I’m usually good with manuals, but the miev service manual has me stumped.

Cheers, David

 

[kiev]

Howdy David, sorry to hear of your issue with the 12V charging.

There is a thread that has lots of detailed technical information and schematics for the DC/DC converter that creates the 12V to recharge the starter battery.
http://myimiev.com/forum/viewtopic.php?f=23&t=4737&p41793

But your issue is quite an interesting and unusual puzzle, because the DCDC is not broken, but has an intermittent problem. The control for the DCDC comes from the EV-ECU located under the rear seat.

First thing to do would be check the continuity of the wiring from the EV-ECU to the CN101 connector on the OBC. Maybe a loose or corroded contact terminal in a connector, or a rodent may have chewed insulation off some wires.

Do you have any error lights or DTCs show up on the OBDII Can buss?

 

[JoeS]

tewharaunz, interesting problem you've posed, with kiev providing a great start for your troubleshooting.

...Does anyone have any experience with their aux battery not charging in ready mode, but charging fine when plugged in?...

I never checked, but had always understood that the path from the dc-dc to the 12v battery was the same, irrespective of whether the car was in READY or charging.

..and when I turned it back on (ready), it was 12.9v.

Yes, a key clue that the dc-dc is not feeding that battery.

My own suspicion would be that LiFePO4 battery, as my first (crude) inclination would be to slap any old 12v lead-acid battery in there and see if the same problem occurs.

At that relatively low price, what is the Ah capacity of the 12v LiFePO4 battery? Could you provide a link to its specs, especially upper and lower voltage protection? What happens at the terminals when the input upper voltage limit is exceeded? Conversely, same question at the lower end - does a relay inside the 12v BMS open up the circuit? Also, is there any way you can check to see if the cells are balanced?

Four days of inactivity being enough to bring the voltage level down so the i-MiEV won't go into READY ... the next time that happens, could you measure that 12v, exactly? Be sure to check the calibration of your voltmeter.

One more thing - if I understand correctly, the car did not die on you on the road but just wouldn't go into READY when you tried to restart it. Is that right? Your commute must now be a nailbiter. :roll: :shock:

Wish you all the best and please do stay in touch to let us know of your progress.

 

[tewharaunz]

Thanks for the ideas, Kiev and JoeS,

I'll try to answer both your questions...

Kiev:

I will check the wires this weekend. I'm wondering if there is a separate circuit path for activating the DC-DC converter when plugged in and when running.

No OBD codes because the OBD port stopped connecting to Hobdrive a few months ago (around the same time the 12v charger stopped while ready.

JoeS:

Yes, it was happening before I changed the lead acid battery for a ithium one. The differences was the usable AmpHours were so much less, so I couldn't go as far before getting a 3 beep warning and shut down. The Lithium battery has 18 AmpHours but 17 of them are "usable" so it is comparable if not a bit larger capacity than the lead acid one.

These are the specs:
Capacity: 18Ah
Cut-Off Voltage: 10V approx.
Discharge Current: 18A
Max Continuous Current: ≤30A (≤5 sec)
Charge Voltage: 14.6V
Internal Cells: 32650 LiFePO4
Operating Temperature: 0-45°C (60°C max discharging)

To clarify, the 4 days included a short trip to deliver daughter to dance class. Without the DC-DC charger, I think the 12v has to power a lot of things (I'm guessing the power steering) so every trip takes its toll. It has died several times, but I've been at work or at home, usually because I have to parallel park.

I know should just park it up until I fix it, but it does add an element of excitement to an otherwise uneventful commute...

Thanks for the comments/suggestions and I'll report back soon.

Cheers, David

 

[Don]

I'm inclined to believe the problem has something to do with the LiFePO4 battery as well - We have so little experience here with anything other than lead acid 12 volt batteries. My thought would be to put a good lead acid battery in there and see what voltages you have when charging and when in Ready , but if you don't have one handy, that would be an expensive troubleshooting technique

With your old battery, when in Ready you also had less than 13 volts? It does sound like your old battery was probably shot and in need of replacement??

I have used Mazda Miata AGM batteries in all 3 of our cars for the past 5 or 6 years. They self discharge a little slower and are rated at 25 AH. If it turns out that there's nothing wrong with your DC to DC, it may just be that your replacement choice isn't compatible with the DC to DC - It is different from charging with an alternator. It would certainly be interesting at least to see the voltage with a lead acid when in Ready

 

[kiev]

...

No OBD codes because the OBD port stopped connecting to Hobdrive a few months ago (around the same time the 12v charger stopped while ready.

That's a very important piece of missing information; it sounds like a defective relay circuit that supplies 12V to loads related to the EV-ECU and the key switch.

Is there anything else that is not working properly that you need to disclose?

 

[JoeS]

...Yes, it was happening before I changed the lead acid battery for a ithium one. The differences was the usable AmpHours were so much less, so I couldn't go as far before getting a 3 beep warning and shut down. The Lithium battery has 18 AmpHours but 17 of them are "usable" so it is comparable if not a bit larger capacity than the lead acid one...

David, sounds like you have a good handle on the lithium's suitability. Kenny (kiev) has you on the right troubleshooting track for the charging issue.

 

[pbui19]

can you monitor the 12v in Ready ? i use one of these monitor in the cigarette plug, mine shows 14.1v in Ready confirming DC-DC op; and usually 12.7-13.5 in Acc, prior to going into "ignition" (sorta a health/SOCharge check)

https://www.amazon.com/aceyoon-Voltmeter-Cigarette-Protection-Compatible/dp/B07QZS36F2/ref=sr_1_7?crid=3DEDSMH3VXFZX&keywords=cigarette+voltmeter+gauge&qid=1637458339&qsid=146-0025959-7746707&sprefix=cigarette+volt%2Caps%2C228&sr=8-7&sres=B01N00I4TM%2CB0773BYS6P%2CB00SXZDKTW%2CB085G5PM35%2CB07QZS36F2%2CB08PCMJRR2%2CB00UCEAKYU%2CB09726J6KQ%2CB07D7S2ZBM%2CB07HHTZ1L5%2CB012FDUHRK%2CB00SXZAI4W%2CB08ZC9PDX4%2CB01KWQXB7K%2CB01JA627KU%2CB08138GVMH&srpt=CHARGING_ADAPTER

 

[tewharaunz]

pbui19,

Excellent point. I've been measuring it at the battery terminals but that will be influenced by the 12v battery charge level.

Also for Kiev,
There is power to the OBD port, but it stopped connecting. I've been successfully using a wifi dongle and hob drive on an iOS device and it connects with the dongle, but cannot "see" the car. On the weekend, I tried a bluetooth dongle and an Android device with Torque app (just to see whether it would connect). and it was able to connect to the dongle but also couldn't "see" the car. I wish I had a cabled OBD so I could rule out wireless connectivity issues...

Still chasing....

David

 

[tewharaunz]

OK, I've done some more diagnostics, and it definitely charges when plugged in but not when it is running.

I haven't been able to connect with Hobdrive but there is power on pin 16 and less than 2 ohms between pins 4 and 5 so not sure what's going on...but I don't know of whether clearing any codes would help things...

Not sure what to do next. It's summer now, so I can easily drive in "low 12v usage mode": no radio, no fan, not sure if I can disconnect electric power steering. However, when it rains I get nervous using the wipers, and have the leave the windows open to avoid turning on fan.

Does anyone know whether the key and the charging port use different circuits to activate the DC/DC converter?

FYI, I followed the service manual diagnostic procedure for OBC/DC-DC unit and didn't find any glaring problems...
I-miev Inspection Procedure 9: Power supply system of on board charger (with some added tests from later bulletins)

Step 1: yes, battery voltage OK
Step 2: yes, looks undamaged
Step 3: yes, A-06x and A-08x relays bench tested and both function properly
Step 4: yes, voltage from A-06x terminal 4 to earth is 13v
Step 5: yes, with motor switch ON, voltage from A-06x (terminal No. 3) to earth is 13v
Step 6: yes, continuity between A-08X (terminal No. 1) and A-06X (terminal No. 3)
Step 7: yes, C-108 looks undamaged
Step 8: yes, with motor switch ON, voltage from C-108 (terminal No. 66) to earth is 13v
Step 9: yes, A-06x terminal 4 to earth is 13v (Same as step 4?)
Step 10: yes, continuity between A-08X (terminal No. 1) and A-06X (terminal No. 3) (same as step 6?)
Step 11: yes, continuity between A-06X (terminal No. 2) and C-108 (terminal No. 66) EV-ECU
Step 12: yes, connector E-03 looks undamaged
Step 13: yes, continuity between A-06X (terminal No. 1) and E-03 (terminal No. 2)
Step 14: yes, resistance from E-03 (terminal No. 10) to earth is 2 ohms or less
Step 15: yes, earth cable looks undamaged (removed and cleaned)
Step 16: yes, earth cable less than 2 ohms
Step 17: yes, voltage between E-03 (terminal No. 7) to earth is 13v
Step 18: yes, continuity between auxiliary battery and E-03 (terminal No. 7)
Step 18a: yes, with motor switch on, voltage between E-03 (terminal 8) and earth is 13v
Step 18b: yes continuity between A-08x (terminal 1) and E-03 (terminal 8) [edited typo and removed reference to terminal 2]
Step 19: yes, C-106 seems undamaged
Step 20: yes, continuity between C-106 (terminal No. 11) EV-ECU and E-03 (terminal No. 12)
Step 20a: yes, continuity between C-111 (terminal No. 116) and E-03 (terminal No. 4)
Step 20b: yes, continuity between auxiliary battery and E-01 (terminal No. 1)


Cheers, David

 

[PV1]

I've been successfully using a wifi dongle and hob drive on an iOS device and it connects with the dongle, but cannot "see" the car. On the weekend, I tried a bluetooth dongle and an Android device with Torque app (just to see whether it would connect). and it was able to connect to the dongle but also couldn't "see" the car.

CANbus not working properly and the car's falling back to a secondary communication circuit? Surely that should throw a warning light of some kind. Also, the red battery light should be lit indicating a problem with the 12 volt side.

On the driver's side of your car, the main wiring harness runs under the trim at the bottom of the doors. Have you inspected the harness for signs of rodent damage? Maybe even check the backside of the OBD port. Might even be as simple as the pins got pushed out and are shorting against something.

Kind of interesting to have range anxiety because of the 12 volt battery. That doesn't happen all that often.

 

[JoeS]

tewharaunz, sorry you're still dealing with this, and some of us need to go back to poring through the workshop manual in an attempt to unravel this mystery with you.

In the meantime, in order to delay your 12v battery range anxiety with a quick and dirty fix, I'd be inclined to grab any old 12v battery (the bigger, the better) and strap it down in the passenger footwell and feed the car's auxiliary outlet ("cigarette lighter") through a 0.1Ω resistor, figuring at worst there will be a 1v∆ which would max out at ten amps. Might monitor it with a voltmeter as you drive. I have an EV converted old-school pickup that I drove for years for short hops to town (~30km round trip max) that I never bothered putting in a dc-dc but just ran with a large AGM which I manually recharged at home.

 

[kiev]

OK, I've done some more diagnostics, and it definitely charges when plugged in but not when it is running.

Does anyone know whether the key and the charging port use different circuits to activate the DC/DC converter?

Step 17: yes, voltage between E-03 (terminal No. 7) to earth is 13v
Step 18: yes, continuity between auxiliary battery and E-03 (terminal No. 7)

Step 18a: yes, with motor switch on, voltage between E-03 (terminal 8) and earth is 12v

Step 18b: yes continuity between A-08x (terminal 1) and E-03 (terminal 8) [Also on terminal 2 on A-08x]

Step 20: yes, continuity between C-106 (terminal No. 11) EV-ECU and E-03 (terminal No. 12)
Step 20a: yes, continuity between C-111 (terminal No. 116) and E-03 (terminal No. 4)


Cheers, David

Steps 17 and 18 check that the 12V Hot All The Time supply to the OBC and DC Converter (DCC) is present and okay.

18a: checks that the key-switched 12V supply to the DCC is working, okay.

18b: checks the wire over which the supply of 18a is carried, okay.

18b: [Also on terminal 2 on A-08X] ??? what does this mean? That there was continuity to chassis?

20: checks wire that carries the enable signal for the OBC, okay

20a: checks the wire that carries the enable signal for the DCC, okay

So it seems that the wiring is intact.

My guess is toward something different in how the EV-ECU receives its power supply when charging and when going to READY.

The EV-ECU has a Hot All The Time 12V supply in addition to Switched 12V supplies. And it operates in different Modes to control functions of the car.

The DCC is a dumb box with no CAN control; it just needs the enable signal from the EV-ECU, called "DCSW" on the schematics.

i can imagine there is a diode-OR circuit in the EV-ECU such as shown here for the OBC block diagram [ 3 diodes can supply the 12V drive for the EV Control Relay]

that is also used for the DCC, although not shown in this diagram

If one of these diodes were blown open, then that could explain how the DCC works when charging but not when in READY.

 

[tewharaunz]

Thanks to everyone for their help.

I'm now convinced that the 12v aux battery is not being charged at all (it never shows over 14v, whether plugged in (EVSE) or in ready.

I've managed to keep commuting through a sunny Dec/Jan with a 20w solar panel on the dash, so I only had to put the 12v on the charger every 5th day. Unfortunately, we've had some cloudy days recently and I'm back to 12v top up every day or every other day if I won't need to use the wiper.

I've followed the service manual and traced all the connections all the way to the E01 and E03, but the next step in the manual is to replace the DC/DC converter. Is there any (easy) way to test the operation of the DC/DC converter?

Kiev, I assume since I'm getting signal to E03 the diodes you mentioned in your message are inside the DC/DC converter?

Also, does anyone know where the DCSW wire goes into the DC/DC converter?

Thanks again for everyone's patience and generous help.

Cheers, David

 

[kiev]

i'm inclined to think that maybe your lithium 12V is not suitable to the task. The DCC will not activate if the 12V buss voltage is not within expected range. Maybe the BMS of that lithium battery is defective or limiting current somehow. It might be worth putting in a fresh fully charged lead acid.

What is the open circuit voltage of the 12V?

What is the voltage with the car in READY?

Did you read thru the other thread at the posted link? The DCSW is a 12V signal to cause the DCC to start and goes to the DC/DC board in the bottom plenum of the OBC. What is the voltage of DCSW that you are reading?

The three "OR-ed" diodes are shown in the the EV-ECU in the diagram of my previous post. Those are shown to provide the supply voltage for the EV Control Relay.

You could put a clamp-on current probe on the big white wire out the DCC or at the input to the 12V battery to see if any current is flowing, meaning the DCC was working when charging or in READY. It sounds like you don't really know if or when it is working. There are fuses on the DCC, both input and output. If it is not working at all, then that would be the first thing i would check.