possible LTO super charger?

[polynoth]

I thought obsessively today about LTO batteries, and I Was frustrated with the fact that they are able to be charged at such a high C rate, but that house service here in the states, even 240 services, can not reach the full potential of LTO quick charging. I Was racking my brain for ways to actually charge the batteries at home at a really high C rate, at the pack level. The following might be obvious to someone with more experience, but with my limited understanding of theory, I was not sure if it was even possible. (and I Do not plan on implementing this without having a much better grasp on it, assuming it's even possible. )
Would a battery to battery charger be feasible? I thought that I could have a larger capacity LTO bank at home that can be charged at a slower rate, and then used to rapid charge another pack. I Am aware that direct pack to pack wiring without the same AH and charge will lead to the packs attempting to equalize, so that is a no go. then I thought, could it be as simple as using diodes to prevent back flow, perhaps a Voltage regulator circuit to keep the Constant voltage / current, and perhaps a circuit to control the rate of discharge from the full pack?. a few ideas popped into my head, Like MPPT chargers for example. I assume that it IS possible and that it is just beyond me right now.
I know they make battery to battery chargers, but they seem to be for lead acid and like 12V to 36V. I am aware that LI batteries need to be charged in a more precise manner, and I am familiar with using meanwell chargers to charge packs with a cycle analyst. I Was thinking that as long as the pack that is being used to charge the other pack has a voltage and capacity high enough to provide CV and CC for the whole charge, with a high enough C rate to handle the rapid transfer... and that you developed a circuit to funnel in the juice within the parameters that It would be a go. thoughts?

 

[john61ct]

What kind of Watts / output voltage / current range you talking about?

PSUs in the 1000W to 3-4 kW are not expensive nor hard if in a fixed location, add circuits if the dryer / microwave / EV charger circuits are already occupied.

Battery to battery is do-able but very wasteful of the energy, and solid circuitry devices are needed, get more expensive past 40-60A capacity.

And not sure about maintenance like balancing, load testing etc at 1S level, 1.8Vpc is the floor and 2.85Vpc (14.25V at 5S) is Full right?

maybe 2.7V at rest?

Just picked up a bunch of TDK Lambda 600W units that can likely parallel up to 5kW at that setpoint if needed, under $40 each.

 

[john61ct]

Ideal is to look for auto-switching PSUs that needed 240Vac to get max output but are happy to work within a normal US 10A 110Vac at a lower rate.

Some even take 2-3 AC inputs so you can work off multiple separate citcuits, even combine a campsite powerpole with a couple of different model gensets, say 6-8kW total.

Go for under $70 delivered sometimes too they do.

 

[polynoth]

I was thinking more specifically of an off the grid set up, battery to battery. I was thinking about something that gets full use of the high C rate of discharge and charge for LTO. so, I was thinking a pack made of 25S LTO yinlong 40ah cells to be charged, 60V nominal.. they are capable of a 10C charge and discharge rate. I found a BMS that limits it to 200A, so that would be a 5C rate... thats 200A . so, I Was thinking that the pack doing the charging would have to be 70v 72v nominal ish. same bms limits on that pack. I just could not wrap my head around how to go about this in theory. that is 67.5v at 2.7v per cell, maxed out its 2.8v per cell, but I was thinking about undercharging slightly. we are talking about 25 thousand watts. an insane amount of power. I was not sure if it would work the same using batteries to charge batteries, with the circuitry to limit the flow in one direction, and having enough juice to keep up the constant charge voltage and current from the host pack, of course.

 

[polynoth]

er, 12.5k watts at 5c.

 

[polynoth]

of course, I dont need to do this, It was just fun to think about it being possible. I was happy to stick with a saner 2kw charger or so, and still charge in a reasonable amount of time.

 

[polynoth]

if I am being realistic, I was already thinking about paralleling some power supplies to get to about 5kw, and then being able to charge the pack in just over a half hour. that is still insane. thank you for the feedback though.

 

[john61ct]

Hey for some setups that's well under 1C.

But the upstream circuits become the bottleneck very quickly, hence my suggestion to utilize several at once.

The real problem for mobile use is all the space and weight the big old affordable units take.

Newer like Flatpack S series, 3kW each are very dense, petite, can be programmed via CAN and ganged together. But not cheap.

If you want real Wild West, check out @methods ' plans for tapping into EV fast-DC charging stations!

https://www.endless-sphere.com/forums/viewtopic.php?f=16&p=1442995

https://www.google.com/search?q=site%3Aendless-sphere.com+ev+station+method

 

[polynoth]

If you want real Wild West, check out @methods ' plans for tapping into EV fast-DC charging stations!

https://www.endless-sphere.com/forums/viewtopic.php?f=16&p=1442995

https://www.google.com/search?q=site%3Aendless-sphere.com+ev+station+method

yeah, I saw that a while back. pretty rad, but I am nowhere near learned enough to go that route, yet. I am going to stick with what I know for now, and accept that I can charge my pack in under an hour, and learn a lot more before I try anything like that.

 

[john61ct]

#meToo

 

[stan.distortion]

How about doing it on vehicle, li-ion for capacity and li-po for burst power, kinda like warp capacitors It looks like just linking the two sets of packs together via BMS should work.

 

[spinningmagnets]

I have an LTO "suitcase" pack for a backup. I am using 6S to attain 12V nominal, since a car alternator can put-out 14V DC (some people use 5S for 12V)...

6S X 2.4V = 14.4V

In order to access the feature of the long life of the LTO chemistry, I would recommend 2.2V per cell as the LVC, and 2.6V as the top charge. LTO is known to last thousands of cycles (not a typo). It can charge/discharge at low temps, and it also commonly has a very high current rate per volume, however...the fact that it can last decades is it's shining characteristic.

 

[amberwolf]

@OP:

It should work fine to use the grid to charge up the "charger pack" during the time you are not home, within the limits of your house system, then use the charger pack to quickly charge the vehicle pack. You'd have to have a DC-DC converter from the one to the other, acting as the charging current limiter and voltage-regulator, and that might be expensive, but there's no reason the basic idea wouldn't work if you can get the total Wh you need out of the house system during the time you're gone.

How about doing it on vehicle, li-ion for capacity and li-po for burst power, kinda like warp capacitors It looks like just linking the two sets of packs together via BMS should work.

Doesnt' help for charging quickly, which is the point of the OP.

 

[polynoth]

@OP:

It should work fine to use the grid to charge up the "charger pack" during the time you are not home, within the limits of your house system, then use the charger pack to quickly charge the vehicle pack. You'd have to have a DC-DC converter from the one to the other, acting as the charging current limiter and voltage-regulator, and that might be expensive, but there's no reason the basic idea wouldn't work if you can get the total Wh you need out of the house system during the time you're gone.

How about doing it on vehicle, li-ion for capacity and li-po for burst power, kinda like warp capacitors It looks like just linking the two sets of packs together via BMS should work.

Doesnt' help for charging quickly, which is the point of the OP.

I was thinking that.. for some reason I didnt think it was that simple. I thought I had to be wrong. Thanks!

 

[polynoth]

I have an LTO "suitcase" pack for a backup. I am using 6S to attain 12V nominal, since a car alternator can put-out 14V DC (some people use 5S for 12V)...

6S X 2.4V = 14.4V

In order to access the feature of the long life of the LTO chemistry, I would recommend 2.2V per cell as the LVC, and 2.6V as the top charge. LTO is known to last thousands of (not a typo). It can charge/discharge at low temps, and it also commonly has a very high current rate per volume, however...the fact that it can last decades is it's shining characteristic.

Yes. The cold weather here in Wisconsin and the high c rate combined with decades of use is why I want lto thanks! I'll pay the weight penalty and low power density penalty for that. Planning a heavy ebike human bio hybrid velo thing for year round commuting last winter was too cold on my normal ebike

 

[polynoth]

In order to access the feature of the long life of the LTO chemistry, I would recommend 2.2V per cell as the LVC, and 2.6V as the top charge..

I am glad you brought that up, I was under the impression that I could get 10,000 cycles at 2.8v.. I noticed that some LTO cells have a 2.3v nominal charge, some 2.4. the 2.3v nominal says 2.7v max and the other ones say 2.8. the yinlong cells, in particular, say 2.4v nominal, 2.8 max, and 10,000 charge cycles at 100% d.o.d. I was thinking about charging them to 2.7v, because of this apparent difference in this particular cell., already. but If you recommend 2.6v, that is what I will go with.
What do you charge with this case? do you just keep it for random power needs on the road, and run a power inverter off of it, or do you use it for Ebikes in particular with some sort of voltage regulator?
FYI, I really appreciate you and all that you do for the Ebike scene, a great deal of what I know, I have learned from an article you wrote, or one of them inspired me to look into a topic further. I am kind of fan boying right now, but yeah. I really appreciate all of ES, but you, amberwolf, dr bass, liveforphisics and a few other super users have really facilitated my learning here. much appreicated.

 

[polynoth]

How about doing it on vehicle, li-ion for capacity and li-po for burst power, kinda like warp capacitors It looks like just linking the two sets of packs together via BMS should work.

yeah I considered that. but, LTO, particularly yinlong 40ah cells can handle 400a constant both charge and discharge. that is an insane 24KW at 60v. sure, they are heavier and lower voltage, but for my application that does not matter. what matters is that they can be charged in extreme cold, discharged as well, and have an extremely long cycle life at 10k cycles over 100 percent dod... that is decades of use . plus, they are much, much safer than lipo. I like lipo, for applications where weight is super critical, but in my application, cold weather use is a priority, as I will be commuting in winter.

 

[spinningmagnets]

Initially it was just an experiment, and it is still evolving. I have a set of super-capacitors that will allow the case to start my 4-cylinder car.

I had calculated that I could accomplish my goals with 5S LTO, but I have recently decided to use 6S so when the case is charged by a car alternator, it can never be accidentally overcharged by a BMS failure. Of course this also means that my 6S pack will only charge up to maybe 2/3rds of the possible "range" of run time with a 14V input.

6S X 2.6V = 15.6V

As part of this experiment, I just got a cheap DROK DC/DC converter to take the 52V of my ebike packs and I can charge a variety of projects. I have a cordless NiCD powered radio I like, and it takes an odd voltage. I can use it to also charge the LTO suitcase to a full charge if I want. I've seen a dead 12V car battery (14V when fully charged) that was re-filled enough to start the car by using an 18V / 5S lithium cordless drill pack through a resister for five minutes.

I have a 100W solar panel in my closet that can use to charge the LTO case during a power outage, I believe the solar panel puts out 15V?...

I've also heard that LTO can be drained very close to zero volts without damage (yet to be seen).

 

[dustNbone]

Not sure what your limitations are locally, but here you get 100A service to a house, with 200A available upon request.

So that's about 23kW (230V*100A), though you'd probably want to limit your charging to 70A so you can keep powering the rest of your house.

But with 200A service, you've got all the power you need and then some.

 

[stan.distortion]

Hopefully LTO will start to phase out li-ion before too long, it really does sound like a big jump forward

 

[Punx0r]

Technically LTO is lithium-ion

It's unlikely to replace other lithium chemistries for mobile applications because the energy density is too low. As this thread demonstrates, super-fast charging is not always an advantage because there are practical limits to how much charging power is available. Being able to recharge your phone in 10 seconds sounds like it could be useful until you realise the charger is the size of a small suitcase and costs more than the phone

 

[john61ct]

And anything new takes decades to gain even minor share in this market, familiarity issues, LTO voltages are so much lower, whole infrastructures need to evolve.

By which time next new big thing's on the horizon.

Between LFP, the higher-density LIs and LTO, each is going to have their advantages for different use cases.

 

[stan.distortion]

Ok, so the charging amps on these things are totally crazy, they'd need a BMS bigger than the ESC... hang on a mo, if pack voltages where close to 220v wouldn't that mean the ESC could be plugged directly into a 3 phase power line to charge them? Not planning on doing that btw! Just thinking out loud.

EDIT: Re the OP, so long as the stationary batteries are higher voltage than the LTOs would it make sense to use the regenerative side of the ESC in place of a BMS?

 

[polynoth]

Not sure what your limitations are locally, but here you get 100A service to a house, with 200A available upon request.

So that's about 23kW (230V*100A), though you'd probably want to limit your charging to 70A so you can keep powering the rest of your house.

But with 200A service, you've got all the power you need and then some.

Yeah, I don't have my own house... I have 30A useable here. the most you can get here in my area, even when you own a house is 100A service. I plan on buying one soon, and I will get the upgrade in service when I do!

 

[jhaz6471]

I thought obsessively today about LTO batteries, and I Was frustrated with the fact that they are able to be charged at such a high C rate, but that house service here in the states, even 240 services, can not reach the full potential of LTO quick charging. I Was racking my brain for ways to actually charge the batteries at home at a really high C rate, at the pack level. The following might be obvious to someone with more experience, but with my limited understanding of theory, I was not sure if it was even possible. (and I Do not plan on implementing this without having a much better grasp on it, assuming it's even possible. )
Would a battery to battery charger be feasible? I thought that I could have a larger capacity LTO bank at home that can be charged at a slower rate, and then used to rapid charge another pack. I Am aware that direct pack to pack wiring without the same AH and charge will lead to the packs attempting to equalize, so that is a no go. then I thought, could it be as simple as using diodes to prevent back flow, perhaps a Voltage regulator circuit to keep the Constant voltage / current, and perhaps a circuit to control the rate of discharge from the full pack?. a few ideas popped into my head, Like MPPT chargers for example. I assume that it IS possible and that it is just beyond me right now.
I know they make battery to battery chargers, but they seem to be for lead acid and like 12V to 36V. I am aware that LI batteries need to be charged in a more precise manner, and I am familiar with using meanwell chargers to charge packs with a cycle analyst. I Was thinking that as long as the pack that is being used to charge the other pack has a voltage and capacity high enough to provide CV and CC for the whole charge, with a high enough C rate to handle the rapid transfer... and that you developed a circuit to funnel in the juice within the parameters that It would be a go. thoughts?

Hello

All the stats for LTO are for one cell only. Not in a series of cells.
Pushing the limits of series of cells charging them is where the problems show up

1) The internal resistance and the slight capacity difference, causes the cells at different time rates to full condition
1a) Above 90% full , the go to 100% quite fast (soda bottle shape graph)
2) It is possible to use 23kw charging , you need to control max amps. LTO's are greedy, they are capable of burning external
and internal connections in a heart beat . I do not recommend it to try.
3) If you cross all I's and dot your T's , I am not saying that is impossible.
4)Most electric meters these days have load meter billing . If you pull 23kw the electric company will charge you a lot higher rate
than 5kw rate for longer usage. They will hand you the bill without using any lube.

Car starting only uses 3-6 watts of power depending on how big and compression ratio
Yinlong cells
40ah 6s at 14.4 v @1600 CCA 450 usable watts
40ah 6s at 13.4 v @1400 CCA
30ah 6s at 14.4 v @1100 CCA
30ah 6s at 13.4 v @900 CCA

40ah 5s at 14.4 v @1750 CCA 425 usable watts
40ah 5s at 13.4 v @1450 CCA

Using 6S setups only need a volt equalizer in a car battery
Using 5S setups should have a BMS and volt equalizer in a car battery

Starting a car with these cells only uses @.006% to .021% of the capacity . Barring any "Murphy's Law" problems these batteries
should last a extremely long time.