hey I got a quick theory question, something that hit me while driving around. so the nmhi battery is sorta like the old ncad battery I'm used to in the rc days right.. flat line voltage in the usable charge area and then bam, it just dumps I think we used to call it when it dies.

the lithium are very linear in their usable range,(also why you need a low voltage cut off, since they don't dump when dead) so in a way a good nmhi battery would drop less actually voltage while under load in its narrow window like say how these car/trucks use them than the lithium would over the same band under load. not a ton, but say a almost volt drop I see on the lithium under a 50amp load would be way less on a nmhi, say 4tenths of a volt and then drop off quickly as a sign it needs to crank the engine?


that would explain what I think I've seen since I installed these compared to when I first got my truck before it starting doing the lurching that is expected with dying nmhi.(by then you could bearly get it rolling before engine cranking) I wasn't used to the truck yet, and didn't have any data to look at but it sure feels like these lithiums while lasting a ton longer with a nice steady 10amp load like say ac on max 100deg day compared to these, but it's not as significantly better taking off and staying in electric mode. leaves me wondering if the nmhi programing is seeing the lithium linear voltage curve under load and thinks it's the nmhi voltage dump that happens and triggering the engine sooner in some cases.

as you have said somewhere, the mpg isn't really dependent on driving around slowly on electricity. it's more about being a really good stop and start mode while in long lines, and helping make the low rpm tq loss of the late intake valve closing engine still feel like a v8. most of the fuel efficiency coming from the cam design and good tranny gearing than being able to drive slowly on battery a mile or so, since all that electricity comes from the engine anyways. which would explain why I'm getting as good, if not better than I'd expect real world mileage for the epa rating. without the 4cyl mode, and my wife always gets low end of the epa rating in everything she drives lol. my old 96 tahoe got a legitimate 12mpg with her diving haha. more like 15 with me

just wondering your 2 cents. good or bad.

 

There are different types of Lithium. The Tesla lithium and the type of Lithium used in phones, RC cars, etc., does indeed have a "linear" curve where there's a strong correlation to voltage and state of charge. Towards empty, it falls off in-between, that drop off and full, it's a mostly straight line:



Your Lithium is Lithium Iron Phosphate, LiFePO4 or LFP. LFP has a "flat" curve like NiMH; however, it is even "flatter" than NiMH meaning it will hold a voltage to a deeper depth of discharge. Looking at it at a block level, NiMH has a 0.2V working range per cell. That's 2.4V/block. LFP is about 0.4V/cell or 2.0V/block. Both chemistries experience the drop-off, but LFP's is later.



Thus, at the lower end of the charge range, for a given voltage, LFP will be higher than NiMH, thus the computer thinks the LFP is at a higher state of charge than it actually is, so it treats it that way. Thus, LFP is closer to the drop off, so it happens sooner than it would for NiMH at the same voltage.

Temperature also plays a big role. LFP voltage is little affected by temperature. NiMH is significantly affected. NiMH SoC can't be computed without knowing the temperature, thus it's going to alter the computed SoC for the LFP even more significantly.

 

interesting. thanks.

so you feel like it's never fully charging them, so they live on the lower end, guess that would make sense.
temp wise they seem to be way cooler than I saw with the old battery, probably lot to do with the packs being damaged by the time I could see the Temps, these run in the 80s most of the time, 85 being about the highest I've noticed. I saw up in the 100 at the end of the other packs.

there's a tsb from years ago, that seemed to deal with state of charge reset. after some maintenance of the customer complained about the bucking and stuff, like a dying battery. they wanted the tech to Rev the engine up to 2k until reaching 70% charge, then if I remember right you took off the 12v battery terminal for a certain amount of time, and then when you put it back on that would be 60% now. I have wondered what that would do with these packs, but I've not tried it. and since everything seems good so far, I shouldn't mess with it. but also as you say, soc means nothing really at this point since the math it's doing doesn't match the battery type. so not sure that would have an effect anyways.

I just looked at the last oil change and was bummed it's only been a little over 3 months. I'm really curious how these will test out at 1 year and at 2 years.

 

the other day it was warm enough to run the ac, high 80s here and I was about to screen record a quick 10min run up to a sandwich shop. took the back way so I could get a decent amount of time on the battery. maybe it will give a bit of an idea how they are working and maybe compare to what you're seeing from yours.

this is torque app, so the refresh is painfully slow. you can see it scan thru the cell voltage so slowly it can't keep up sometimes with load changes. but anyways, about a 5.5amp load from the ac and stuff stopped at red lights. I put the throttle position % on screen but 19.22% is 0%, I meant to offset that in the graph but I forgot. hopefully you can get an idea how much throttle can be used before the engine starts. I put rpm on the screen, so when it's 0 it's in auto stop, you can see when it starts. for the amps, positive is discharging the battery and negative is regen charging it. the graph behind the number seems to update faster than the number haha. the top scale is set to 100amps. so when you see it spike off the top of the scale on restart, that's over a 100amps. these trucks are brutal on startup.
at the 8min mark took a back way, it's a little up hill road but I was able to keep it in electric only for a good half mile or so before hitting a red light. I only did it for the log, normal driving id be in doing 35 or so up that road, besides in parking lots I don't really worry about trying to drive around on electric only these days. but wanted to get a long 50amp load time incase anyone wants to compare to their batteries.
it's not flat at all around here, so I put GPS height up, it's from the phones GPS so I don't know if it does any good. at 5:40ish starts a about a half mile of down hill, I tried to get it to show the max cell voltage during a good decell. it's not Colorado or something, hills is all I got haha
Temps in the left in inlet, 4 sensors and then the outlet temp. above that is the max and min cell voltage. I really should take all the individual cell voltage out, it might refresh faster since all you really need is max and min


now for the most boring 10min video every uploaded to YouTube haha

 

just got back from a 2000 mile round trip towing my car on the trailer. I'd say a good 2500lb trailer and 3400lb car. so right around the recommend limits. had tq app up for a while along the way..it seems interstate driving it doesn't use the battery much, little peaks with throttle but Temps looked to run mid 80s most of the trip. was able to tow around parking lots easly under 10mph in electric. hit Houston traffic just before rush hour but it was raining, so lots of stop and go at low speed, so it did use them there, never saw above 90deg Temps thou. outside was 80deg at the time.

I did almost miss an exit once so hard braking under load I saw a charge rate of 95amps flash up for a refresh cycle or 2 and then drop down. that might be the limit gm put on regen. never seen over 85 before that.

 

95 amps is about 28.5-34.2 kw(300-360 volts)

 

i would do the Hood latch switch mod so you can control the auto stop better...

 

Hi S Keith, I am taking delivery of my lithium packs within the week.
I would like to create a thread that gives people solid before and after data.
My current battery is still decent, but I tow max weight on a regular basis and gas is not getting cheaper.

I figured you know what data to extract. Did you not create this specific test I can log and share here?

Thanks in advance,

 

https://electricvehicleforums.com/fo...36/#post266599