tewharaunz
Posts: 12
Joined: Mon Nov 30, 2020 8:23 pm
Location: Charteris Bay, New Zealand

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

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.
2012 I-Miev "Black i"
Boffingham
Posts: 31
Joined: Thu Sep 23, 2021 6:16 pm
Location: Ottawa, Canada

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

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?
Located in Ottawa
2012 SE with Nav
tewharaunz
Posts: 12
Joined: Mon Nov 30, 2020 8:23 pm
Location: Charteris Bay, New Zealand

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

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
2012 I-Miev "Black i"
kiev
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Location: The Heart o' Dixie
Contact: Website

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

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.
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?
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JoeS
Site Moderator
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Location: Silicon Valley, California

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

tewharaunz, interesting problem you've posed, with kiev providing a great start for your troubleshooting.
tewharaunz wrote:...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.
tewharaunz wrote:..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.
EVs: Two '12 Wht/Blu SE Prem., '13 TeslaMS85, three 156v CorbinSparrowsLi(NMC), 24v EcoScoot(LiFePO4)
EV Conversions: 156v '86 Ram PU, 144v '65 Saab96, 48v1kW bike
RIP(2021) ICE: Orig.Owner '67 Saab96V4, '88 IsuzuTrooper; '76 MBZ L206D RHD RV
tewharaunz
Posts: 12
Joined: Mon Nov 30, 2020 8:23 pm
Location: Charteris Bay, New Zealand

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

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
2012 I-Miev "Black i"
Don
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Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

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

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
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kiev
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Re: 12v charging when plugged in but not in “ready”

tewharaunz wrote:...

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?
kiev = kenny's innovative electric vehicle
JoeS
Site Moderator
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Joined: Thu Dec 15, 2011 5:47 am
Location: Silicon Valley, California

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

tewharaunz wrote:...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.
EVs: Two '12 Wht/Blu SE Prem., '13 TeslaMS85, three 156v CorbinSparrowsLi(NMC), 24v EcoScoot(LiFePO4)
EV Conversions: 156v '86 Ram PU, 144v '65 Saab96, 48v1kW bike
RIP(2021) ICE: Orig.Owner '67 Saab96V4, '88 IsuzuTrooper; '76 MBZ L206D RHD RV
pbui19
Posts: 200
Joined: Tue Jan 07, 2014 12:17 pm

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

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-Voltmete ... NG_ADAPTER

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