12V LiFePO4 and NOCO Battery Discussion

[stoatwblr]

This topic for EV primary batteries has been discussed extensively on just about every EV forum (including this one), so perhaps we should keep this thread focused on our i-MiEV 12v lead-acid battery. Thank you.

I'm interested from the POV of replacing the (ancient) 12V FLA in my 2012 imiev with a LiFePO4. I'm in southern UK so severe deep freezing isn't an issue but putting inside the cabin will allow a diesel heater under the snout - as the traction batteries seem to be down to around 60% I can't really afford to lose too much range on a 24 mile daily commute

The attractive part is that fully BMSed 22Ah units seem to only be about 25% more than FLA these days - and potentially small enough that they could share the battery tray with a webasto if heat issues are dealt with

 

[JoeS]

...I'm interested from the POV of replacing the (ancient) 12V FLA in my 2012 imiev with a LiFePO4...

Nowadays, I think that is a great idea! In the last couple of years there has been an explosion of "12v" LiFePO4 batteries on the market with integral BMS', and the prices continue getting better as the competition heats up. Here in the US, RV'ers, especially, have glommed onto them, appreciating the deeper cycling abilities compared to lead. I have heard glowing reports about, for example, a company called Battle Born and its superb BMS and the excellent matched cells that it uses, although they are rather pricey. (Disclosure: I have no financial interest in this company)

The key is a BMS that can handle a steady-state 14.4vdc (20°C) that the i-MiEV produces when driving and one that will NOT cut out open circuit if it's not happy at the high end. At the voltage low end we don't need to worry unless the dc-dc fails.

Does anyone know what the temperature profile is of the i-MiEV dc-dc, as I would be concerned that at very low temperatures the resulting voltage might be too high for a BMS?

If you can find a nice small battery with the appropriate terminal configuration, go for it! - and do let us know how things turn out.

Slightly off-topic -
I've recently been experimenting with paralleling '12v' LiFePO4 with Gel cells and am in the middle of daily testing using my solar trailer as an energy source and feeding an inverter to run my home refrigerators during daylight hours (long story as to why I would want to do that...). Monitoring the current in both directions for both the Gels and LiFePO4 to see how well they share. So far, so good - the Headway LiFePO4 cells stay wonderfully balanced using a Heltec capacitive balancer, I've limited the Aussie Plasmatronics solar regulator upper voltage to a conservative 13.50vdc (I may go up to 13.60v if all goes well), and the 12.20vdc low voltage shutoff has not happened, yet...

 

[Mitsi]

I just bought a Noco NLP30 Lithium Ion battery which allegedly has a built-in BMS. Yet in their manual they specify using a Lithium Ion battery charger. The charge voltage is specified at 14.6V and max charging current of 24A. Any objections to dropping this puppy right in there and letting her charge it herself? Our 12V lead/acid is on it's last legs and I thought this would be a great idea, until I RTFM. :|
https://no.co/products/lithium/powersport

Matt

 

[JoeS]

Hey Matt - "Mitsi" (that's what I named our first i-MiEV), welcome to the forum.

Good question, and one I've been mulling over as I've built my own LiFePO4 battery but haven't installed it yet as I'm still tinkering with the BMS.

I looked over the specs of the NOCO NLP30 LiFePO4 battery and here are my thoughts -

1) Cell balancing
Their description sounds impressive and it looks as though they have continuous active balancing. I wouldn't worry about it as it's in their best interest to keep those cells balanced no matter what you do.

2) Overvoltage protection
Presumably by opening the connection. Edit: this voltage is probably slightly above 14.6v, which is high already. You'll never see it as the i-MiEV dc-dc is 14.4v (or a bit less in hot weather). Besides, they say it recovers when an external load is applied.

3) Undervoltage protection
Again, presumably by opening the connection. I doubt if you'll ever get there, certainly not when driving unless there's a fault in the i-MiEV. It might happen if you leave the car parked without a float charger for a few weeks. They say it recovers if you put it on a charger.

4) Charging Voltage
They say 14.6v but that's already rather high (edit: actually at the absolute upper voltage limit) for LiFePO4, so the i-MiEV's 14.4v (or a bit lower) will be just fine, as long as the NOCO cells remain balanced. I normally charge my LiFePO4 cells to 3.4v (x4= 13.6vdc) edit: as that's close to the charging knee above which there's not much energy.

5) Battery Capacity
They say 8Ah (and even say 32Ah lead-acid equivalent) so you'll be just fine as long as you don't let the car sit unused for more than a couple of weeks, and just put a float charger on it if you do.

6) Overcurrent Protection
They say it will recover when the external load is removed, but they don't say what happens if the maximum 24A charging current is exceeded; however, they also spec a continuous discharge current of 80A, so whatever protection they have will still allow that much current to go into the battery.

7) Maximum Charging Current
This 24A spec is the only one I might be concerned about, as the i-MiEV dc-dc has the ability to feed a discharged NOCO with a higher current. Since the i-MiEV supplies a constant regulated voltage I suspect that the battery current will be self-limiting as soon as its voltage has reached that 14.4v voltage limit. In any case, be sure to have a fully charged NOCO when you first install it, which should minimize any initial high current. Since you're in a continuous-use scenario when you're driving, I don't see a problem as the dc-dc will simply keep the voltage constant and the battery will just sit there floating. The problem occurs if you've not driven the car and allowed the battery to be discharged by the i-MiEV's vampire loads. They don't say what happens if you exceed 24A charging current - I'd be inclined to call up NOCO and ask them, but be sure to tell them that the voltage is constrained to 14.4vdc max.

8) Terminals
I see that the polarity orientation matches the i-MiEV OEM battery; however, in order not to butcher the connection, you might consider a terminal adapter, something like this - Edit 1 Dec.2021: the shorter post with M6x1.0 screw that comes with the post fits perfectly!

https://www.amazon.com/XS-Power-580-Adaptor-Thread/dp/B004XH67B2
Edit: or maybe this taller post (check the NOCO dimensions for best fit):
https://www.amazon.com/XS-Power-586-Adaptor-Thread/dp/B004XH69MY

9) Low Temperature
LiFePO4 don't like being charged at low temperatures, and they spec -10°C as their lower limit. Edit: This IS a major problem in your part of the world - see subsequent discussions, especially http://myimiev.com/forum/viewtopic.php?f=23&t=3067&start=60#p44032 Hopefully you have a garage that doesn't get that low. In NOCO's User Guide they say it recovers when it gets back to in-spec temperatures, but doesn't say if it cuts out by going open circuit. They simply say the BMS doesn't allow charging below -10°C. You might ask NOCO that question as well.

My Conclusion (debate welcomed) -

All that having been said, I'd go for it and install the NOCO but do charge up the battery to 14.4v before installing it, and please do let us know how it works out.

Yet another edit:

... Yet in their manual they specify using a Lithium Ion battery charger. The charge voltage is specified at 14.6V and max charging current of 24A...

You do realize that NOCO wants to sell you their charger? Any modern regulated charger will work for you. If it doesn't have a lithium setting, then just set it to Gel (or maybe even AGM - read the charger specs) to avoid exceeding the 14.6v upper limit. Their battery 24A maximum charge current limit is pretty high and most portable chargers are lower than that, so no problem.

 

[JoeS]

Well, I put my money where my mouth is and just purchased that NOCO NLP30 on Amazon Cyber Monday for $140 instead of $200, as I had given one of my i-MiEV AGMs to a friend and the old FLA can't possibly keep going much longer. Will report back on this NOCO's performance after I install it.

 

[ed5000]

I just bought a 12 volt, 50Ahr lithium lifepo4 battery with built-in bms for my mini-grid system in my home for general charging of misc. devices like cell phones, tablets, radio control lithium polymer batteries and some led lighting i have installed.

I've had this system since 2007 since I first bought my Harbor Freight thin film solar charging system with a 20% off coupon. Back in 2007 when my local utility charged me 8.9 cents per kwhr I was consistently saving $5 per month for every cell phone I moved over from the "big grid" to my "mini grid". When I moved my broadband router over I began saving $10 per month. I still have my "mini-grid" system even though I have roof top solar now because it works so well and has been very reliable for a long time now although I have up graded all the parts a few times along the way.

The latest change to my mini-grid is this Lifepo4 battery plus a solar charge controller rated for lithium batteries. I've only had this battery for a few weeks now but so far the battery has been amazing. I run all my loads on this battery but they never use more than the surface charge off the battery. Ie the battery's voltage at rest is 13.3 volts but by next morning it still is sitting at 13.3v. The lowest I've seen is 13.2v so far although I admit this is a brand new battery.

I'd just like to say I would give it a try. Like Joe says just watch the maximum designed charge rate of the battery while trying not to exceed that and keep an eye on low temperatures. There are actually lithium batteries out there that have built in heaters for low temp situations. I'm finding some of the price points to be about the same as lead acid so this might be a good time to give it a try.

Btw: This 50Ahr battery is only a little larger than our I-Miev aux. battery but weighs much less.

 

[Mitsi]

Well, I put my money where my mouth is and just purchased that NOCO NLP30 on Amazon Cyber Monday for $140 instead of $200, as I had given one of my i-MiEV AGMs to a friend and the old FLA can't possibly keep going much longer. Will report back on this NOCO's performance after I install it.

Awesome, we can compare notes!

 

[Mitsi]

Thanks so much for addressing this JoeS!
After researching a bit, your thoughts very much mirror mine, but it's great to have a second opinion.
I did get some car battery size terminals with #8 screws the Noco required. They are brass or copper.
I'm thinking about getting a Noco charger to keep it float charged when idle. 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 ***** 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 ***** 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 ***** light will relent once we've driven far enough for her to have the data.

Sounds like you got an awesome deal on the NLP30. I paid about $300 Canadian. Wasn't thinking "Black Friday".

 

[JoeS]

...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 ***** 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 ***** 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 ***** 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 ***** 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 ***** 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.

 

[JoeS]

My Experience With NOCO NLP30

The battery came in less than a day with free shipping from Amazon, and I don't even have Prime!
It is so light, even compared to my own LiFePO4, that I can't help wonder if they left out something.
I'll be doing some testing, such as charging/discharging the battery at various voltage and current levels, measuring its charging and discharging Ah, and in general want to get comfortable with the NOCO before installing it into the i-MiEV.

Three things right off the bat:
1. Terminal post adapters that I recommended (in an earlier posting) fit perfectly, with no drilling required. I had misread the spec sheet and the NOCO terminal thread is indeed M6x1.0. Corrected the above posting.
2. The NOCO arrived with unknown charge level, but measured 13.15vdc.
3. My Battery Minder lead-acid battery charger did not want to work with this LiFePO4 battery (too smart?), so I resorted to an older charger with manual settings. I have a number of adjustable-current power supplies which would have worked as well. Charging at 2A as I write this...

(to be continued)

 

[JoeS]

Here's the link to the NOCO website for this NLP30 battery, which itself has links to the User Guide and Data Sheet.

https://no.co/nlp30

INITIAL TESTING

One thing to note about some LiFePO4 batteries is that, after charging, they settle down to some quiescent voltage below their charging voltage. This NOCO behaves like that as, after being fully charged to 14.2v it has settled down to 13.34vdc, very reminiscent of my Headway LiFePO4 cells.

CHARGING

I elected to use my West Marine 30A charger because each of its charging voltage and charging current settings can be independently programmed. For my first charging test I charged at only 2A. Initial as-received voltage was 13.15vdc, and I set its first charging voltage to 14.2v while measuring Ah delivered. It absorbed only 3.3Ah to get there before the charger cut off. Cranking up to 14.3v and finally 14.4v produced an increase of only 0.1Ah, with the charger cutting out almost immediately, indicating a fully charged battery. I'm personally not comfortable with the manufacturer's 14.6vdc recommended charging voltage and didn't go there.

DISCHARGING

I have a West Mountain Radio CBA automatic constant-current tester which allows me to set the discharge current and cutoff voltage while accumulated ampere-hours are being recorded. I set the current to 2A. NOCO does not list its low voltage cutoff protection circuit voltage limit, so I chose 3.00 volts per cell or 12.0vdc, and let it run. It had a fairly flat curve for most of its discharge, initially dropping immediately to 13.0vdc (from about 13.5v soon after charging), and only dropped rapidly at the tail end (typical for LiFePO4), recording 7.86Ah capacity. Nothing unusual.
Edit: here's the photo of the screen (sorry about the poor quality - long story):

RECHARGING

I recharged using 14.2v at 2A and recorded 7.7Ah. Didn't bother charging any higher.

CONCLUSION

The battery meets its stated 7.8Ah specification, even though I didn't run it at the lead-acid battery industry standard of a (very slow) 20-hour rate as that doesn't necessarily apply to lithiums.

COMMENTS

1) There is no access to the individual cells inside the battery so I can't check to see how well the cells are balanced.
2) I was surprised that the battery had been shipped with a (7.8-3.3)/(7.8) = 58% State of Charge which is rather high when compared to shipping other lithium chemistry batteries.
3) The manufacturer specifies a charging voltage of 14.6vdc which is right at the upper voltage limit of LiFePO4. I don't know why it's so high since the application the battery is intended for is motorsports and conventional ICE voltage regulators operate between 13.5v and 14.5v (the i-MiEV dc-dc is around 14.4vdc at room ambient temperature). I'm presuming the internal cell balancing does not rely on this 14.6v maximum to be applied, as its marketing blurb touts "auto-enabled, advanced battery management system that provides maximum protection, performance, and bi-directional cell equalization for long-lasting stability" Whew!

WHAT'S NEXT

Even though I'm itching to install this battery into the i-MiEV, I'm going to play with it a bit more and next see how it performs at higher currents, although I'm chicken to test its maximum 80A maximum continuous current rating (as that would last less than 7.8/80 = 0.0975*60 = 5minutes and 51 seconds. Peak ICE starting current is spec'd at 700A.

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.

 

[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 ***** 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 ***** 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 ***** 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 ***** 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 ***** 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 ***** 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 ***** 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.... :roll: '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. :idea:

 

[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/bu-808-how-to-prolong-lithium-based-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... :ugeek:

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. :idea:

Simply google "iCarSoft i909" and also check out this Reference thread which is still a work in progress:
http://myimiev.com/forum/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! :shock: 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 :!: :!: :!: :shock:

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. :lol:

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