12v Battery - All You Ever Wanted To Know

[ed5000]

I'm happy to see that most of your numbers match my new Lifepo4 battery. Mine is a AmpereTime 50 ahr I bought through Amazon. I bought this one because the brand has been around for a while and they had mostly positive ratings. The price was $220 plus tax.

When it arrived it also had a charge voltage of 13.1v. At first I was concerned that it was low until I read up on the battery chemistry. Charging it with a 50 watt solar panel so far the highest voltage I've seen is 14.2v although this solar panel is only suppling just under 3 amps maximum during near winter (but very sunny) conditions. Like I've mentioned the at rest voltage has been 13.3 volts as my charge controller reads down to the tenth of a volt.

Again this battery won't fit in our I-Mievs but if anything happens to my car's battery I'll be looking to get the Noco NLP30.

[PV1]

One thing I experienced today is the car with exclamation point idiot light being lit after using a Noco battery booster to get her started.

You'll need to clear the codes to turn the light off. Had this happen with a flat 12 volt battery in Koorz.

Does anyone remember if we have measured what the quiescent current draw is by the i-MiEV when it's parked and either locked (with/without key fob) or unlocked? I'm just curious as I'd like to calculate how many days the i-MiEV can remain parked with this 7.8Ah battery.

Bear sat outside from September 15 to November 30 while locked and NOT on a float charger/maintainer, and started right up. The power needle, though, floated slightly above center for a minute after starting, so the 12 volt was definitely low.

[ed5000]

QUESTION

Does anyone remember if we have measured what the quiescent current draw is by the i-MiEV when it's parked and either locked (with/without key fob) or unlocked? I'm just curious as I'd like to calculate how many days the i-MiEV can remain parked with this 7.8Ah battery.

I just checked the current draw with my clamp on amp meter and it was 0.2 amps with the ceiling led light on then went down to 0.1 amps with all lights off and stayed that way for about 5 minutes. This meter only reads down to a tenth of an amp. I didn't check with the doors locked but I could check if someone would like to know.

[Mitsi]

...Also thinking about setting it up for quick removal for the cold season, but wonder if there are any hazards to regularly removing this battery. One thing I experienced today is the car with exclamation point idiot light being lit after using a Noco battery booster to get her started. Their line is "Starts dead batteries", so yes it does, but I think the idiot light is caused because her memory has lost our driving history which it needs to estimate range. The range reading fluctuates up and down between 50-90kms. I assume that idiot light will relent once we've driven far enough for her to have the data...

You've identified three topics -
1. "the car with exclamation point idiot light being lit after using a Noco battery booster to get her started. " Presumably this was with the FLA? Could you describe exactly what you did? Don't suppose you took any voltage readings? Which battery booster so we can see its specs?
2. "The range reading fluctuates up and down between 50-90kms." Could you elaborate the conditions? It's not unusual to have Range Remaining (RR) vary significantly, especially when climbing hills. Simply turning on the heater reduces the RR by 20%..
3. "I assume that idiot light will relent..." Have you tried to read the fault code using the OBDII and something like the iCarSoft i909?

How long (and how many miles) have you owned your i-MiEV?

Maybe someone else can discuss issues with 12v battery removal. When swapping out 12v batteries I've usually attached alligator clips to the terminals and kept the car alive with an auxiliary 12v battery.

I believe it's referred to as the "MCU warning light"? I was worried had damaged something with the booster. It's the Noco Boost HD, 2000A, GB70. I use it to boost my hybrid Silverado and my dad's old diesel tractor. When you connect it to the iMiev's terminals, it can slide nicely inside and ride along. It's a little freaky though because it cycles, clicking on and off every few seconds, unless you are using the power supplied. I figure it's giving little boosts to the battery. Anyway it doesn't seem to have damaged anything as the idiot light went away and the RR stopped fluctuating. I think when the LA battery died she lost the recent driving history that she uses to compute the range remaining.

Very interested in your analysis about the Noco battery. I haven't put mine in yet, as I measured the charge and it arrived with 13.4 volts. I was going to buy one of their chargers and charge it as well as recondition the old LA. But you are saying that's basically the full resting charge? hmmmm.... 'spend more money?' grumble grumble

We got her brand new Jan. 2017. I did plug in a OBDII and didn't find any fault codes, but I'm not sure I was using the right software. OBDZero doesn't seem to show them, does it? "iCarSoft"? What's that? I'll look into it.

[JoeS]

Does anyone remember if we have measured what the quiescent current draw is by the i-MiEV when it's parked and either locked (with/without key fob) or unlocked? I'm just curious as I'd like to calculate how many days the i-MiEV can remain parked with this 7.8Ah battery.

To answer my own question I ran the following test: attached an external 12v battery through a precision resistor to the Anderson connector I have attached to my i-MiEV battery and simply lifted the negative terminal on the car's battery (to disconnect it) and measured the voltage drop across that resistor.

DISCUSSION -

1) What shocked me is that it made no difference whether the car was locked or unlocked, whether locked manually or with a key fob, or whether the car was accessed and then re-locked without turning the car on (PV1 note). The current was the same! I had presumed that locking the car activated the alarm system which would draw more current.

2) The current fluctuates as the voltage drop varies between 5.0mv to 6.3mv across a 0.5Ω resistor, yielding 10ma-12.6ma current draw. Repeated with a 5Ω resistor and obtained 11ma-11.5ma. I'll put an oscilloscope on this waveform to see just exactly what sort of pulsing the car is doing.

RESULTS -

When the i-MiEV is just sitting there parked, irrespective of whether it is locked or unlocked, it is drawing no more than 12ma average current out of its 12v battery. Using the vernacular of the Tesla forum, this is our Vampire Load.

WHAT DOES THIS MEAN?

Converting the steady-state current load in Ampere-Hours sucked out of our i-MiEV -

12ma x 24 hours = 0.288Ah/day
0.288Ah/day x 7 days = 2.02Ah/week
0.288Ah/day x 30 days = 8.64Ah/month

Our OEM flooded-lead-acid (FLA) battery has a 20-hour discharge rating of 33Ah. The trouble is that FLAs are notorious for high self-discharge rates, typically 1%/day at a room ambient temperature
(ref:https://www.powerstream.com/car-battery-faq.htm)
1%/day of 33Ah means -

0.33Ah/day or
2.31Ah/week or
9.9 Ah/month

Now, these above numbers are additive, so here's the hit our poor little 33Ah i-MiEV FLA battery takes when it is simply parked -

Per Day: 0.62Ah
Per Week: 4.33Ah
Per Month: 18.54Ah

As a rule of thumb, we never want to discharge an FLA battery below 65% if we want a decent life out of it (and need to charge it back up right away). 65% of 33Ah is 21.5Ah or, looking at it as the maximum we want to take out of the battery, the number is 11.5Ah.

Thus, when our i-MiEV had a brand-new battery in it, you wouldn't want to leave the car unattended for more than about 18days (11.5Ah/0.62Ah/day).

Trouble with FLA is that in this amount of time sulfation starts to occur as the SoC drops and battery age gets into play and I've personally not liked that 65% rule of thumb, and ... I'm not going there.

Which is why I always put a float charger on my i-MiEV (solar float charger if left outdoors) when I know the car won't be used for more than a couple of days.

Finally, if dealing with lead-acid batteries, we can cut down that consumption by roughly half if we install an AGM battery instead of a FLA battery because the self-discharge rate of AGM is minimal in comparison.

Now, what sparked this question is:

For how long can the i-MiEV be parked if it is using the NOCO 7.8Ah (verified) LiFePO4 battery?

LiFePO4 has a negligible self discharge rate (compared to FLA) so we can ignore that above FLA number and only be concerned with what the i-MiEV vampire load sucks out of the battery. No hard and fast answer, as it's simply a matter of how long you want the battery to last and you can pick your own number here from Table 1 of this article:

https://batteryuniversity.com/article/b ... -batteries

The answer is: a couple or even three weeks should be ok, or roughly the same amount of time as our with OEM battery.

When/if I install the NOCO, I'll probably feed it with an inexpensive MeanWell adjustable power supply set to 13.4vdc whenever I leave the car unattended for a couple of days or more.
https://www.amazon.com/gp/product/B005T6NG8S

BTW, Battery University has loads of articles and are a good reference: https://batteryuniversity.com/articles

More information than you every wanted to suffer through...

Edit:

We got her brand new Jan. 2017. I did plug in a OBDII and didn't find any fault codes, but I'm not sure I was using the right software. OBDZero doesn't seem to show them, does it? "iCarSoft"? What's that? I'll look into it.

Simply google "iCarSoft i909" and also check out this Reference thread which is still a work in progress:
viewtopic.php?f=19&t=4950

[JoeS]

Long story which you can skip - just go to the last few paragraphs.

So, I had intended to continue my testing using my wife's i-MiEV and then install the NOCO LiFePO4 battery into her car because hers contains an old FLA battery whereas mine has a newer (April 2019) AGM. Well, she took off for town before I had a chance to play with it, but I still wanted to check that 12v quiescent current (which was bouncing around as seen on the DVM) with an oscilloscope. So I went over to my i-MiEV and set things up to test ... only to discover that the 12v AGM battery in my car was reading 12.2vdc, despite the car having been driven a few hours earlier. My wife's 'old' FLA had been sitting at 12.6vdc when I tested it, and that car hadn't been driven for half a day before that. I found this low AGM voltage disconcerting, although I've had no issues with the car whatsoever. The test results are below, after the narrative.

NOCO LiFePO4 INSTALLATION

After doing the measurements (including seeing if the door-locking had any effect - it didn't) and being disgusted with the low AGM voltage I decided to install the NOCO into my i-MiEV. First I charged up the NOCO to 14.4vdc. I kept that 12v jumper wire in place to keep the 12v to the car alive and swapped out the heavy AGM with the ultra-light NOCO (what a difference in ease of doing this!), took out the block of wood I had under the AGM and instead added a block of wood on top of the NOCO and cinched everything up. The only problem is that the battery terminals are now located about an inch further forward in the car than the 151R (either FLA or AGM), so the plastic cover over the battery no longer seats properly in its locating holes in the back because it needs to slip over the red positive terminal and wiring - not to worry, I simply replaced the flimsy plastic nut with a wing nut and cinched it down sufficiently so it shouldn't wiggle off, and for good measure put a Velcro strap around the battery and its rear brace (as I had done with the smaller AGM).

The first order of business was to turn the car on, so I opened the door on the car and the alarm went off, which had never happened to me before! No amount of punching the key fob red buttons would turn off the beeping but it thankfully stopped as I was about to put the key into the ignition. I must have disrupted something with all the locking/unlocking when doing the testing. Anyway, the car went into READY normally and I measured the battery voltage at 14.55vdc - I attribute this high number to the temperature dropping to about 55°F (13°C) - after all, this is December 5, but this has me wondering what that voltage will rise to in cold climates as the absolute upper voltage limit on the LiFePO4 is 14.6vdc and is temperature independent.

Took the car for a drive (pulling six garbage cans the half-mile down to the main road) - no issues at all.

Charged up the AGM and put it on a slow 2A capacity test using the West Mountain Radio CBA. Edit: Result was 18.9Ah, test cutoff voltage being 10.5vdc (this voltage being way too low for the i-MiEV). Posted a graph of this here

Parked the car and put everything away and didn't look at the numbers until just now...

TEST RESULTS

Long story short, the quiescent voltage across the 5Ω resistor was 360mv, with a pulse going up to 420mv every 1.5 seconds. The voltage across the 0.5Ω resistor was bouncing around 33.6mv but was too fuzzy to measure accurately with the ancient scope.

360mv/5Ω = 72ma
33.6mv/0.5Ω = 67.2ma

72ma is six times as much vampire load as my wife's i-MiEV

The cars are identical SE Premiums, but I quickly realized that I have the OBDLinkLX permanently plugged in. (sigh) I'll need to unplug it and repeat the test again... maybe not: Just checked, and the OBDLink LX has a quiescent current draw of 60 ma, but is supposed to have a "Battery Saver" low power mode of 2ma. Wow, that 60ma is exactly the difference between my car and my wife's! So, unbeknownst to me, my poor AGM has been subjected to this since April 2019.

TAKEAWAYS

1. For those of you considering the NOCO (or any LiFePO4) in cold climates, not only do you have to worry about it not charging at low temperatures but you now need to measure the actual regulated output voltage of the dc-dc to ensure it doesn't go above the NOCO's absolute upper voltage limit of 14.6vdc, no matter what the temperature.

2. Do not leave any OBDII adapters plugged into the car if you're not actively using them. Causes unnecessarily-higher 12v battery depth of discharge every time you park.

[JoeS]

Over on the 12v Battery Voltage Usable Lower Limit thread, kiev brought up this important point -

...If the 12V lets go during charging, then OBC damage will likely occur.

If the 12V lets go during READY, there is no guarantee that the DCC will be able to hold up the system. Plus this could be fatal if you are making a left hand turn across oncoming traffic, or crossing railroad tracks, or making a right hand turn to pull out into traffic with a tractor trailer bearing down.

The price of freedom is eternal vigilance--and a fully charged starter battery.

Not only a fully charged starter (12v) battery, but one that is always present - the important point being that we should never ever 'lose' the 12v battery to an open circuit when either charging or in READY.

In the case of the NOCO, I don't think we have any danger of approaching the lower cutout voltage limit during driving; however, from the limited information we have, it may be a real possibility if the i-MiEV dc-dc voltage regulator is temperature-dependent and the temperature sensor 'senses' extremely low temperature and continues raising the voltage to compensate - which is normal for lead-acid batteries; however, if this voltage exceeds the LiFePO4's BMS upper voltage limit and if its protective mechanism is to open circuit the battery, then the dire scenarios kiev painted are a possibility.

Edit: I've reached out to NOCO and asked them to describe what happens if the charging voltage exceeds their upper limit, and what that limit is.

Meanwhile, this brings up the question of the i-MiEV's dc-dc converter voltage output - is it temperature dependent, and, if so, where is its temperature sensor located and what is its voltage-temperature curve?

Over the years we've occasionally talked about it, but I don't recall seeing this answer. Anyone?

[JoeS]

Received an unsatisfactory answer from NOCO in response to my very specific questions asking what the behavior of their BMS is if the charging voltage exceeds 14.6vdc (they parroted back what their website says). Have gone back to NOCO rephrasing my request and asking that someone familiar with the BMS design answer it. The specific concern is whether the battery goes open circuit if our i-MiEV dc-dc output goes over 14.6v at low temperatures. I also asked NOCO at what voltage (above 14.6v) their protection occurs.

Until I get a satisfactory answer from NOCO (or we know that our i-MiEV dc-dc never exceeds 14.6vdc), I do not recommend installing the NOCO LiFePO4 into the i-MiEV when operating at temperatures below 50°F (10°C) (I measured 14.55v across the battery at this temperature when in READY).

In the meantime, I am continuing with my NOCO installed in my i-MiEV...

Also note, I made a minor correction to the above post eliminating any reference to the OBC to avoid confusion with the dc-dc.

If your i-MiEV is sitting out in some pretty cold weather, would someone be kind enough to take an accurate voltmeter and measure the voltage across the 12v battery with the car in READY and provide us with that reading as well as the temperature? Thank you.

Edit: I measured my i-MiEV this morning sitting in the garage: 14.40vdc at 8°C (~46°F) with the car L2 charging.

[Mitsi]

Moderator edit: copy of previous post deleted to save space.

I will check when the temp here in Toronto drops again. It's 13°C today, but will be colder next few days.
I've got a little digi-voltmeter I want to use. It would be nice to put it in the driver's compartment. Are there any access holes through the firewall to run wires? How about plugging one in to the lighter socket? On that note, how about plugging an aux battery in to the lighter socket to boost, or a solar panel or something if using the LiFePO4? Can the fusible link to the dc-dc be removed, and the battery be only topped up by a solar panel or external charger?
Just some ideas roaming through my skull about this.
How about a battery heater, to preheat the battery? Perhaps the LiFePO4 can be preheated when temps are -10°C - -30°C? Haven't had a problem running, so far, at these temperatures, except for the crappy FLA.
Will let know or check back in a few days.

Cheers, Matt

[Lic]

lighter socket has fuse (around 10Amps) so can't be used to charge or boost battery. But I think you can use it to measure voltage in 12v line.