Lightweighting and aerodynamic optimization of a subcompact car.

[neptronix]

You need to find a better battery supplier if that is the level of his advice and knowledge !

I was very surprised at his level of advice and knowledge.
His pros/cons for each option lined up with we know about lithium batteries.

The dealbreaker was how lithium batteries respond to being fully discharged if i accidentally left the lights on or something. A SLA can be revived without much damage, just jump start the car. A lithium battery can have a number of failure states preventing that from happening & result in a tow or a purchase of a lead acid battery.

Li starter batteries have been factory fitted in some european cars for over 10 years !

And why dont you check yourself ,.. a simple google search will throw up dozens of replacement 12v Li car batteries !
This is just one example, but there are many other cheaper options
iTECH1420CA Lithium Car Battery 12V Stop Start 1420amp 60Ah
and this shows the presence of BMS and temp protection in even the cheapest 12v battery
(note.. this is only a 100a discharge battery )

Not the case here in the USA.

Spent 2 days trying to find a lithium battery that:

- Specified cold cranking amps, so i could be sure my car would start in the worst case winter scenario. Almost no batteries specified this.
- Was from a brand that'd been around for a while, had long warranties, and listed all relevant specs instead of hiding the not so great ones.
- Could prove the engineering of the BMS/etc was good.
- Had equal cold cranking amps but was lighter than the 21lbs SLA.
- Didn't cost 10x more than a regular lead acid replacement.

This is the closest i got to that, but, it can't take a >80A charge, and my alternator is 100A, so i think that's pushing the battery too hard.

DL+ 12v 60Ah Dual Purpose 1000CCA Starter Battery Plus Deep Cycle Performance

We could buy it's bigger brother:
DL+ 12v 135Ah Dual Purpose 1000CCA Starter Battery Plus Deep Cycle Performance

But it's heavier than the lightweight SLA, and i don't have any use for this huge capacity at the moment..

So, SLA it is for now. Will probably pick lithium as my next battery though.

 

[scianiac]

I too have had dreams of replacing this giant block of lead with some nice LFP cells but yeah many of the commercial options are terrible, I believe many have no BMS at all. I've seen a very popular name brand LFP Motorcycle start battery die because it had no BMS.

If I were to do it though I would just buy some high discharge cells, easy enough to find their performance specs to know they'll be up for the job. Then install a standard maybe 200A BMS connected to the fuse box and then connect the starter solenoid directly to the battery with no BMS. Don't have to find a large enough BMS, not going to kill the battery leaving the lights on and by setting the BMS cutoff voltage a little higher it would be possible to bypass the BMS and still start the car even if I did leave the lights on.

Only other consideraion is the cold but a decent BMS will have a cold temp charging cutoff so maybe that combined with a battery heater on a thermal switch set to go on when it's below that BMS cutoff temp.

 

[Hillhater]

I was very surprised at his level of advice and knowledge.
His pros/cons for each option lined up with we know about lithium batteries.

The dealbreaker was how lithium batteries respond to being fully discharged if i accidentally left the lights on or something. A SLA can be revived without much damage, just jump start the car. A lithium battery can have a number of failure states preventing that from happening & result in

Well you must be easily surprised, because he obviously doesnt know much about the commercial 12v lithium battery market ..even though he sells them !
I would bet money that those Braille lithuim batteries do have a full BMS in them ,..the same as other similar products.
And as i said that BMS will control the charge rate, high and low voltage protection, temp protection etc etc.
So over discharge/low voltage damage is not a factor !
Failure rates are a furfy also,..and unlikely with a multy year warranty.
Also i cannot understand your concern over CCA, even that G30 Braile has over 900 CCA.. a figure you would never need.
I would be surprised if you car draws more than 4-500 amps for cold starts ( the Braille AGM is rated at 550 CCA !)
Why would you consider those DL batteries over that G30 Braille ?….it does all you need and is lighter .
….regards charging from a “100 amp” alternator …..put a ammeter on yours sometime and check exactly what charge current the alternator actually puts out ? Remember , charge current is determined by the SOC of the battery and auxilliary load. ( and the BMS settings for lifepo !) . car batteries rarely drop below 80% SOC.
i have a 180a alternator, and it never charges at more than 55-60 amps
i dont put much faith in “Brand names” for batteries ( remember the A123, UASA, and recent LG fiasco’s ?) ,..and prefer to just serch for on line full reviews to weed out the chaff.
As i said, if you are really worried about starting failure or worse, just carry one of those cheap pocket lithium jump starter packs…
….(most people i know carry one anyway,..just because commercial Pb battery quality is crap !)
PS: How do those 1lb , 10 ah , tiny packs manage to cold crank a 6 cylinder diesel, or a V8,..multiple times.. before needing a recharge from a usb port ?

 

[neptronix]

I too have had dreams of replacing this giant block of lead with some nice LFP cells but yeah many of the commercial options are terrible, I believe many have no BMS at all. I've seen a very popular name brand LFP Motorcycle start battery die because it had no BMS.

See, this is no surprise, especially from a USA standpoint, where we don't do electric things as well as our counterparts. There are also a lot of

If i had a secondary car, i would consider the roll your own LTO battery. They may not need balancing, and can also take a rapid charge. They are like ultrasafe, but very heavy RC Lipos. If the energy density were to increase. ( and it seems Toshiba & others are still making incremental improvements ).

For a car they can certainly pump out the energy but you need a lot of it to have somewhat equivalent capacity to a car battery for the 'i let it sit for 3 weeks scenario'.

Too bad i can't just pick up some brand new A123 20AH pouch cells at this point.

If I were to do it though I would just buy some high discharge cells, easy enough to find their performance specs to know they'll be up for the job. Then install a standard maybe 200A BMS connected to the fuse box and then connect the starter solenoid directly to the battery with no BMS. Don't have to find a large enough BMS, not going to kill the battery leaving the lights on and by setting the BMS cutoff voltage a little higher it would be possible to bypass the BMS and still start the car even if I did leave the lights on.

The only problem with the BMS is that it may on occasion need to handle >200A during say, cold morning starts. Now you might need a 300A BMS. Braille dude tells me, this is a main reason they don't use a BMS in the racing batteries. It would be too big and expensive for consumer's tastes.

Then again this is the perspective of a racing battery company, so consider the source.

Only other consideraion is the cold but a decent BMS will have a cold temp charging cutoff so maybe that combined with a battery heater on a thermal switch set to go on when it's below that BMS cutoff temp.

A battery heater would help make lifepo4 a better case for winter driving. At ~0F, the internal resistance of many lithium chemistries goes up about 4x. If you can get this down to a 3x penalty ( which wouldn't require a significant amount of heat energy )

Possibly to simplify such a device by simply having a hobbyking connector hanging out of the engine bay that you could plug a small RC lipo into for a minute or too and wake the battery up, instead of designing some electronics to do it automatically for you.

Well, maybe next round i'll get more experimental.

 

[neptronix]

Well you must be easily surprised, because he obviously doesnt know much about the commercial 12v lithium battery market ..even though he sells them !

It's a company that sells exclusively to racers, of course he doesn't know much about the commercial market at large, i feel you are missing some important context..

 

[scianiac]

The only problem with the BMS is that it may on occasion need to handle >200A during say, cold morning starts. Now you might need a 300A BMS. Braille dude tells me, this is a main reason they don't use a BMS in the racing batteries. It would be too big and expensive for consumer's tastes.

I think you missed my point, honestly a 100A BMS would be fine depending how many accessories you have. The idea is the starter solenoid is bypassing the BMS so no starting current is going through the BMS, only everything else. So you don't need a big BMS and you won't kill the battery anyway since the car won't start without everything else connected to the battery, that is unless you bypass the BMS, presumuably with a temporary jumper you keep on hand. That would allow you to start the car even if you left the lights on and killed the battery since the BMS would have cut out and saved that last little bit of juice for another start. And a programable BMS would allow you to set that cutoff high enough so you did have enough go even in cold weather to get it started. It has even more functionality then the lead acid in that way.

Another option is also adding one of those big 12V supercap banks you can get for cheap now to add a bit more initial boost in cold weather. I actually had one of those connected with my car battery for awhile and it was able to limp a shot battery along for a few months longer.

 

[neptronix]

Oh, i'm sorry, i did miss that point!
This isn't a bad idea!

 

[nicobie]

Yes it is. No need for a BMS in the start circuit.

 

[scianiac]

Although I foresee one small issue, it would require a BMS that can switch the positive, like a contactor BMS. You have to keep chassis ground connected which possibly everything is connected to.

 

[amberwolf]

This is the closest i got to that, but, it can't take a >80A charge, and my alternator is 100A, so i think that's pushing the battery too hard.

Do you expect to discharge the battery enough without running the alternator for the battery to reach an SoC that could draw 100A? If so, it might be an issue. If not, it should be fine, since it can't force 100A into something that is at a charge / resistance level that doesn't draw that much. (but you know this ).

And as i said that BMS will control the charge rate, high and low voltage protection, temp protection etc etc.

Hmm. Unless you mean something else entirely by "control the charge rate", I haven't seen a BMS in a "simple" starter (or similar) battery that can do this. (those that are integrated into traction packs or other complete car systems could and do, but not the generic fits-all starter types that I am aware of)

Unless the BMS has a CC (or other form of analog current limiting) DC-DC built into it's charge "port" (and there is a diode or other reverse-current protection on the discharge port, since those two are paralleled to the car's electrical system), *or* it has direct computer control over the alternator speed or voltage, or the alternator has such a DC-DC built into it, and the BMS has direct control over that, then the BMS cannot control the actual charge *rate* because it can't directly control the current flow into the cells.

All it could do is disconnect the battery cells from the car's electrical system whenever overcurrent is detected for long enough to trigger the disconnect. If it could do this fast enough to be a form of PWM, then it would be able to do it in the style of a "bad boy" charger, bursts of overcurrent then no current, averaging less than overcurrent, but still letting the cells experience that.


For an on/off only BMS (the only kind I've seen so far) if it is smart enough to "know" that a certain difference in voltage between the cells and the car's system will cause a current overlimit, *and* it has a monitoring-only connection to the car's system, it would then be able to just stay off entirely, leaving the battery disconnected from the car's system, until the car voltage drops enough from load or lowered RPM (idle, etc) that the difference in voltage wont' cause overcurrent. But I haven't seen this kind of system before either.

 

[neptronix]

Do you expect to discharge the battery enough without running the alternator for the battery to reach an SoC that could draw 100A? If so, it might be an issue. If not, it should be fine, since it can't force 100A into something that is at a charge / resistance level that doesn't draw that much. (but you know this ).

I'm unsure.
My car has a 100 amp rated alternator, so i'm sure there are times that it will draw 100A.
There are times where i go weeks without driving my car, so the likelihood of low state of charge is high. This could make for some high charge amps.

During winter it can be down to -20F out here. Any battery is severely handicapped. So if i chose a lithium battery next time, it better be gangster in the cold.

LTO sounds exciting for this purpose. Toshiba has a SCiB they are working on that has 50% better density. That'd put it right at hobbyking lithium pack level density.

Niobium Titanium Oxide (NTO) anode | SCiB™ Rechargeable battery | Toshiba


I'm reminded of watching liveforphysics repeatedly crank a 1.8L with a 2.5lbs turnigy nanotech pack a decade ago.

Damn, i kind of want this next generation 150whr/kg niobium stuff on a bike now that i'm reading about it
Here are is some info on Toshiba's possibly unobtanium car battery:

https://www.global.toshiba/ww/products-solutions/battery/scib/next/namari.html


What a little beast!

 

[amberwolf]

During winter it can be down to -20F out here. Any battery is severely handicapped

Are battery warmers a possibility?

Or for short enough periods between operation, insulating the battery? Or both?

 

[neptronix]

Yeah they are a possibility for the next car battery and a really good solution for making lifepo4 work better.

 

[Hillhater]

It's a company that sells exclusively to racers, of course he doesn't know much about the commercial market at large, i feel you are missing some important context..

No !.….look at their product range, most of their batteries,..AGM and Lithium,..are for domestic road vehicles.

 

[marty]

You need to find a better battery supplier if that is the level of his advice and knowledge !
Li starter batteries have been factory fitted in some european cars for over 10 years !
And why dont you check yourself ,.. a simple google search will throw up dozens of replacement 12v Li car batteries !
This is just one example, but there are many other cheaper options
iTECH1420CA Lithium Car Battery 12V Stop Start 1420amp 60Ah
and this shows the presence of BMS and temp protection in even the cheapest 12v battery
(note.. this is only a 100a discharge battery )

$1200 for a battery

Bottle Rockets - 1000 Dollar Car

A thousand dollar car, it ain't worth nothin'
A thousand dollar car, it ain't worth sh_t
Might as well take your thousand dollars
And set fire to it
A thousand dollar car ain't worth a dime
You lose your thousand dollars every time
Oh why did I ever buy a thousand dollar car

A thousand dollar car is gonna let you down
More than it's ever gonna get you around
Replace your gaskets and paint over your rust
You still end up with something that you'll never trust
A thousand dollar car, its life was through
'Bout 50,000 miles 'fore it got to you
Oh why did I ever buy a thousand dollar car

A thousand dollar car ain't gonna roll
'Til you throw at least another thousand in the hole
Sink your money in it, and there you are
The owner of a two thousand dollar thousand dollar car

If you only got a thousand dollars
You outta just buy a good guitar
Learn how to play and it'll take you farther
Than any old thousand dollar car
If a thousand dollar car was truly worth a damn
Then why would anybody ever spend ten grand
Oh why did I ever buy a thousand dollar car

 

[Hillhater]

You outta just buy a good guitar

I agree it is a rip off! When for $100 you can buy a lithium pocket jump starter !.. ( just HOW do they work )
..and that guitar wont be much help when your car wont start on a cold morning !

PS… the common argument is that the lithium battery will last 5+ times longer than a Lead lump ,..hence the economics are better, without the inconvinience of replacements.

 

[A-DamW]

Yeah they are a possibility for the next car battery and a really good solution for making lifepo4 work better.

Have you considered using ultra/super capacitors?
A little over 10 years ago I was faced with the prospect of replacing the two group 31 lead acid batteries in my 5.9L cummins diesel pickup at a cost of $500-$600.
I was already aware of Maxwell brand ultra-capacitors at the time, so I found some on ebay for~$300.
Long story short, the capacitors have been starting my truck for over 10 years flawlessly in sub-zero temps and show no signs of slowing down/degradation.
I would be happy to go into further details if there is interest.

 

[neptronix]

Given the really energy density of supercaps/ultracaps..

Does said truck need to be on a charger every day?

 

[A-DamW]

They actually have a very low *energy* density, like 3.65Wh/kg, so ~100 times less than lithium.
But *power* density is ~6000W/kg, so ~2-10X more than lithium.

Have not hooked a charger up in at least 5 years, and I think that was a random incident involving testing some new headlight relays.
I should note, I do have a very small lead acid(~8 years old!) car battery in parallel with the caps to provide some reserve capacity,
but I have run the caps solo for months at a time with no problems, I probably have near zero/zero parasitic drain in the elec. system.

Some other notes in the apple/orange comparison:

Typically rated for ~1,000,000 charge discharge cycles.
Typically capable of delivering rated current down to -40F.
Can discharge to 0V with zero degradation, they are just capacitors after all.

 

[neptronix]

Ah i see.

You know, this would be a more interesting addon for a lithium battery, because the net weight could still be lower than a SLA.. and you'd circumvent the downside of llithium that way.

Well, something to think about during the next battery change

 

[Hillhater]

but I have run the caps solo for months at a time with no problems, I probably have near zero/zero parasitic drain in the elec. system.

How do you power the auxilliaries, lights , AC, etc ?…..straight from the alternator ?

this would be a more interesting addon for a lithium battery, because the net weight could still be lower than a SLA.. and you'd circumvent the downside of llithium that way.

I have a suspicion that is how they manage to get those tiny pocket sized 10ah lithium jump starter packs to crank a big V8 and diesels ?
….but never seen any confirmation .
PS:….what “downside” of lithium are you refering to ?

 

[neptronix]

I have a suspicion that is how they manage to get those tiny pocket sized 10ah lithium jump starter packs to crank a big V8 and diesels ?

50-200C lithium chemistries have been around for a bit ^_^

PS:….what “downside” of lithium are you refering to ?

Poor cold tolerance. It can get down to -28C in my area. In this condition, IR is usually 4x higher. So I would need something like A123 20C packs (new) to handle this.

Would be better to chose a high energy density lithium and let some supercaps make up for the shortfall during winter, because the supercaps are more weather tolerant.

I don't know if you win or lose weight wise compared to a lead acid battery though, because supercaps are heavy/big AF

 

[harrisonpatm]

How do you power the auxilliaries, lights , AC, etc ?…..straight from the alternator ?

This just came up on my feed:

If you skipt to 2:20: the battery is for starting the car and running accessories when the engine is off. When the engine is on, all accessories are powered from the alternator... in this case for this model car. Surely not every car is like this, but still, it's an interesting experiment.

 

[Chalo]

Would be better to chose a high energy density lithium and let some supercaps make up for the shortfall during winter, because the supercaps are more weather tolerant.

I don't know if you win or lose weight wise compared to a lead acid battery though, because supercaps are heavy/big AF

In between, but cheap AF:

50,000 CYCLE BATTERY! 12v Sodium Ion 5.6Ah 25C 140A

PLEASE READ THE DESCRIPTION CAREFULLY. Shipping to Lower 48 USA states only via Fedex Ground Shipping. Note that this item can't ship to PO boxes. No international shipping including Hawaii, Guam, Puerto Rico. Non-USA customers click here. The battery that can outlive you! 50,000 deep...

jag35.com

Not rated for super hot or super cold temps, though.

 

[Hillhater]

When the engine is on, all accessories are powered from the alternator... in this case for this model car. Surely not every car is like this, but still, it's an interesting experiment.

Yes, and as we discussed earlier in this thread, most modern cars have ECUs and “smart alternators “ that cut output when the engine is under load, so it could not be used on those