Charging LTO at Max Speed?

Batteries, Chargers, and Battery Management Systems.
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Charging LTO at Max Speed?

Post by Username1 » Apr 20 2020 10:16am

I recently learned about LTO and and i'm really impressed with it, so much so i'm considering making my own battery...

But my question is about the possibility of charging at full speed (10 minute at 6c). I didn't see any examples of people trying this, so i'm wondering is there anything preventing it? For example i'm considering a 12S 40ah pack (1150wh). To charge at 6c would need about 6900w, which seems doable at home with 220v 40A i think...

Is the problem the charger? I can't seem to find a purpose made charger for something like this (especially at low voltage). I'v only just started to learn about charging, but don't some power supplies have the required cccv or whatever to essentially act as a charger? I understand this wouldn't be cheap but if it's actually possible, where would you look for a charger that could accomplish this? It just seems so epic, i'm a little surprised nobody has tried it.
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Re: Charging LTO at Max Speed?

Post by 999zip999 » Apr 20 2020 10:52am

220v x 40amps 8,800 watts at the plug is this right ?

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Re: Charging LTO at Max Speed?

Post by Username1 » Apr 20 2020 10:56am

Yeah but you gotta use less to not trip the 40a breaker. In my example you only need 6,900 which is fine i think.

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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 20 2020 11:39am

It is completely straightforward, just buying stuff.

Bigger issue is LTO takes up a stupid amount of weight and space for a given Ah capacity

to the point if you need decent range, you end up with a cargo area full of just your packs.

Better for stationary use, or maybe city buses.

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Re: Charging LTO at Max Speed?

Post by Username1 » Apr 20 2020 12:49pm

Yeah but other than the size/weight, it's almost the holy grail of batteries. The density isn't even that bad, i mean it's a lot better than lead acid. For my use 1kwh with that size/weight is totally fine and in exchange i get a super battery.

- not affected by extreme temperature
- lasts basically forever
- can charge in 10 minutes
- extremely power dense
- no risk of catching fire
- very tolerant of over/under charge

As for it just being a matter of buying stuff... maybe so but any idea where i can find a charger like this?

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Re: Charging LTO at Max Speed?

Post by Username1 » Apr 20 2020 5:58pm

So i realized i would actually need 10s (not 12) due to space. This means 24v nominal, so i looked into lower voltage chargers/power supplies some more, and found there's some very high amp ones in 12v...

I found this 12v 250a battery charger. https://www.taramps.com.br/en/produto/p ... 0-amperes/ Not sure if this charges this kind of battery correctly buy anyway...

It has settings for 12.6v, 13.8v, 14.4v and can be adjusted up or down 3% on each setting. If i use 12.6 and adjust up 3%, that gives me 2.6v per cell‬ which is perfect. So the idea would be to use 2 of these at the same time. Is it possible to connect these somehow to double the voltage? If not maybe i can charge the battery in 2 seperate 12v pieces.

Also 6c charging is actually 240a not 250a. Do you think this minor increase would cause any problems or excessive wear on the battery? I know these batteries can also be charged with 10c, but not sure in what circumstance etc. If you see any problems with this idea please do point them out.

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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 20 2020 6:51pm

No, those are ballpark numbers, that's just a rounding error.

Look forward to pics, what sort of bike? Or EV?
Username1 wrote:So i realized i would actually need 10s (not 12) due to space. This means 24v nominal
Voltage should not be determine by lack of space. Propulsion these days is at least 48V, maybe 36V, now really curious what the use case is.

Unless you're scavenging free parts, get the right voltage charger.

Ampacity / speed charging can always be increased if you actually need to by stacking in parallel, much safer & easier than series connections, which requires modding.

Breaking up the pack every time you charge will be a pain.

Do you really need such a high rate? Fuses alone will cost hundreds, crimpers for wiring heavy gauge as well.

I hope you're not doing this just for bragging rights.

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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 20 2020 6:56pm

Maybe do not get your final charger yet (I reco Elcon or Brusa), that will not cost too much less than a good used pack.

Link to your source for cells?

Charge in 12V units at a low rate for running / testing purposes, thus NBD if you find you need to change the voltage of the system.

Or if you find LTO doesn't suit.

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Re: Charging LTO at Max Speed?

Post by Hillhater » Apr 20 2020 7:05pm

Username1 wrote:
Apr 20 2020 12:49pm
.... other than the size/weight, it's almost the holy grail of batteries.
For a mobile application, size/ weight IS the holy grail. (+ cost )
There are lots of other battery options for 6C charge rates, and long life.
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Re: Charging LTO at Max Speed?

Post by Sunder » Apr 22 2020 1:34am

Hillhater wrote:
Apr 20 2020 7:05pm
Username1 wrote:
Apr 20 2020 12:49pm
.... other than the size/weight, it's almost the holy grail of batteries.
For a mobile application, size/ weight IS the holy grail. (+ cost )
There are lots of other battery options for 6C charge rates, and long life.
I don't know about that. In gas/petrol motorcycle circles, nobody seems to mind that a 20kg, 20ish litre tank only goes 200-300km or so (depending on riding style and engine size). That's because it can be refuelled in 2 mins.

Likewise, in buses, nobody seems to mind that that the range is short, because it can be recharged at each stop pretty quickly.

I think the two holy grails are interchangeable. It either needs to be small for the range it offers, or charge ultra fast and still have a reasonable range.

I know of batteries that can be charged at 6C. And I know of batteries that have a long life. But aside from LTO, what can take a 6C charge and still have a long life? LiPo will take the charge, but it's cycle life is badly compromised by high rates of charge. LiFePo4 has 3000+ cycles, but 6C charges on those will damage their power density very quickly. Most other chemistries I can think of that has either characteristic would have a worse energy density than LTO.
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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 22 2020 2:05am

And LFP may be a bit denser than LTO, but still way less than half compared to the other LI chemistries commonly used for passenger EVs.

I agree that with those latter 6C may be too stressful if not outright optimistic.

But remember, pre-heating changes everything in that regard - in theory anyway.

Personally I reckon the key with getting great longevity in this scenario is going to a massive capacity pack (say as big as the LTO would have been 8-D ), and

thus bring the **discharge** C-rate way down (1-3C ?), **and** allow for lower average capacity utilization, whenever possible staying far from either of the voltage shoulders, cycling SoC around the midpoint.

Those two factors will so greatly extend lifespan (3x ? 10x ?) that going to, say 3-4C when fast charging is needed, will be more than compensated.

Plus **huge** absolute power discharge rates are available on demand when needed, so long as **average** C-rates are kept low.



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Re: Charging LTO at Max Speed?

Post by Username1 » Apr 23 2020 3:04am

This isn't for anything too crazy. It would be used in a scooter type ebike, so size/weight is not a big deal. My main reasons for LTO are because it would be used both heavily and in subzero temperatures.

After looking at my space option further, i think i'v decided on 10s 60AH yinlong cylindrical cells. This would give 1440wh at 24V. This won't be a high power application. I want maybe 20mph. When combined with fast charging, this is enough range for me. I'll have to either find a motor which support 20mph at 24v, or i guess i could rewind one if needed.

Image

A question i have... Looking at this chart for LTO batteries, 0.5c discharge (similar to what i might use) at -20c results in only around 75% energy available when draining to 2v. That's ok with me, but would this apply the same way for charging a cold battery? Because charging a cold battery at 6c would be worthless in that case, because of how little energy you would get out. If that's the case i might have to insulate this battery if i want useful fast charging.

On the topic of chargers... I'v been looking like crazy and the closest thing i'v found is that 250A 12V charger i linked above. There just doesn't seem to be many actual high amp battery chargers, especially above 12v. I was checking out power supplies too, but they mostly seem to cost thousands of dollars... From my understanding (which is admittedly very bad), i think i would need to skip the CV phase to achieve this 10 minute fast charge, so i guess i would only need to find a more basic power supply with CC charging?

If those "prochargers" can be used, they do sell a 180a version which would be 360a in parallel or exactly 6c (not sure if that can be done). I would need 2 sets of 2, with a split battery. But the battery splitting seems pretty simple to do. Would this be possible, or does anyone know of a better power supply i could use?
Last edited by Username1 on Apr 23 2020 3:56am, edited 1 time in total.

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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 23 2020 3:51am

Username1 wrote:I guess i would only need a power supply with CC charging? If that's the case, hopefully that makes it cheaper/easier to find. If i ever felt like charging to maximum, i could always get a much lower power CCCV charger to use overnight.
I already explained, CC-only vs CC/CV is not a matter of different hardware.

Just how you terminate, and how soon.

A dumb PSU coupled with a HVC cutoff gives you CC-only. Let it keep going after the circuit reaches the Absorb setpoint, you are now doing CV stage as well.

_______
Don't expect your charger(s) to cost less than the batteries - quality and high amp rates together are not cheap.

Did I already reco Elcon? Proper chargers those.

It is normal to stack chargers or PSUs in parallel to multiply amp rates. Gives flexibility too when a high-amp 240Vac circuits isn't handy.

Mean Well HLG series PSUs are great, available in any voltage you want, I think up to 360W each.

_______
Yes an insulated box and silicon heating pads afe easy to rig for pre-heating cells before charging.

Or bring the crate inside charge in a heated space - carefully, but LTO is as safe as LFP.




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Re: Charging LTO at Max Speed?

Post by Username1 » Apr 23 2020 4:05am

Didn't realize there wasn't a hardware difference. I did look up those companies you recommenced but i didn't find anything high enough amp. I know you can stack them in parallel but it think it required too many to be practical or cheap enough.

I was editing my last post when you replied... What do you think about using 4 of those 180 amp pro chargers (2 parallel x2). Can those charge my batteries properly? It would only cost about $1400 compared to the even more crazy expensive power supplies i'v seen. Would give exactly 6c at 26v. I just don't know if they'll work.

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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 23 2020 4:12am

I would not use cheap Chinese for that.

Ex telecom and server room secondhand much more trustworthy, stuff on eBay goes for hundreds originally cost thousands.

Lots of example here, search the threads, Eaton, Huawei, TDK Lambda, Cisco tons of ideas.

Again, $400-800 would be a realistic budget.

Of course you can start with just 3-4, then add more later.

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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 23 2020 4:15am


Username1 wrote:Didn't realize there wasn't a hardware difference
Please reread

viewtopic.php?p=1548381#p1548381


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Re: Charging LTO at Max Speed?

Post by Sunder » Apr 23 2020 7:09pm

Right. In front of a PC with a few minutes now.

CC vs CV, and is there any real difference? When you pull back the curtain, the Wizard of Oz is just physics. Physics based around Ohm's law, or V=IR, or Voltage = Current x Resistance.

Assume you have a 20S LTO pack, with 1mOhm per cell - in other words, damn good quality. You also have a "perfect" charger with unlimited capacity, and you have super conducting everything in between. I.e. all your connectors, BMS and wires have no resistance.

20S @ 1mOhm per cell = 20mOhm.

When your battery is flat, the voltage is 36v (Assuming dead at 1.8v per cell).
When your battery is full, the voltage is 56v (Assuming full at 2.8v per cell).

So your perfect charger puts out 56v, to a battery at 36v, or a 20v differential.

V=20
I=?
R=20mOhm

20=I*0.02
20/0.02=I
I = 1000amps.

In an ideal world, you could put 1000A into this battery. In the real world, you don't have a charger that can do that much. A non perfect charger has three options:

1. Burn up
2. Cut off
3. Regulate its own voltage down, until it puts out the maximum current it can, then keep that current... constant. For such a process, I think marketing should come up with a great name... Like "Constant Current".

You with me so far? So where does the constant voltage come into it?

Well, at some point, you will not be able to push enough current into the battery. Let's say you have the deep pockets and contacts of Elon musk and bought a 100A charger.

V=IR
V=100*0.02
V=2v

That means when the potential difference between the battery charger and the battery is 2 volts, the battery will pull exactly 100A, and any less, the current will drop. It simply won't take any more current.

In other words, when the battery voltage reaches 54v (56v-2v=54v), you will be putting in 100A. At 54.1v, you will be putting in 95A. To do this, the charger remains at a constant 56v, and the battery limits the current through its internal resistance. The charger no longer needs to protect itself through constant current limiting, so it keeps the voltage constant. Again, the marketing people came up with a great name, and called it "constant voltage".

So, during the initial charging phase, when the charger can't keep up with the battery, it down regulates to a constant current, and when the battery can't keep up with the charger, the charger keeps a constant voltage and lets the battery "regulate". The whole process is called "CC-CV" and never "CV-CC" because the constant current phase always has to come first.

This is also why reputable LTO manufacturers like Toshiba, claimed "80% charge in 6 minutes". Because you can't carry 6C all the way to full. The last part of the charge has to slow down due to Ohm's law, unless you do a big gamble, and keep the current constant, and keep raising the voltage beyond the desired termination voltage (to keep the potential difference high enough to make the most of the charger's capability).

If you wanted a CC only charger, you would buy a charger that is well over voltage of the battery pack so that Ohm's law will not limit your charge rage. You would need to know/test the internal resistance of the battery, and you would use a cut off at a calculated voltage. BUT, as packs age, and as the temperature changes, so does its internal resistance. This obviously has implications for safety as well, so it's rarely done in anything consumer.

Hope this helps you understand what John is saying. Everything he is saying is right, don't get me wrong, I'm not correcting him on anything. But I'm giving you the "why", if you care to understand it.

My humble opinion is that 6C charging for a decent sized pack is almost impossible unless you're in Norway. (Power points in Australia are most commonly limited to 2400w - EV car chargers are most commonly 6600W and rarely up to 50kw, but I'm talking hens teeth rare, not diamond rare), so there's almost no point going over 2400w.

It's also much more practical to design your pack so it's used as 48v, but charged as 12V. It's expensive to get 48v chargers at anything over 20A or so. But old server PSUs are almost always isolated so they can be put into parallel, and are very cheap to get to 2400W, often needing only 2.
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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 23 2020 10:16pm

OP please ignore this
Sunder wrote:When your battery is flat, the voltage is 36v (Assuming dead at 1.8v per cell).
When your battery is full, the voltage is 56v (Assuming full at 2.8v per cell).
That is "live", good for protective cutoffs correct?

My understanding is (please feedback)

isolated at rest, 100% SoC may be ~2.55V resting?

2.50V with surface charge released?

Under any significant load, quickly falls to ~2.4something

2.0 is good as **rested** empty 0% SoC

2.1V per cell as the LVC under load for higher C-rates,

bit lower OK for House, sub-C rates

2.0 for propulsion-level (very high) rates

maybe lowest LVC in "limp home emergency mode" 1.8Vpc


_______
> This is also why reputable LTO manufacturers like Toshiba, claimed "80% charge in 6 minutes"

Why past tense there?

> It's also much more practical to design your pack so it's used as 48v, but charged as 12V. It's expensive to get 48v chargers at anything over 20A or so.

Not true for ex-telecom gear, sometimes even NOS, from incredible high quality makers.

But HVC is needed for automating charge termination.

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Re: Charging LTO at Max Speed?

Post by Sunder » Apr 23 2020 11:17pm

There is about 7% between 2.5 and 2.8 in my cells. and about 5% between 1.8 and 2.0v, but I chose those numbers just as much for ease of calculations than anything else.

Past tense? Because I saw it in the original SCiBs, but I don't think I saw that on the latest datasheets. Not implying anything untoward.

Just had a look on eBay in Australia. There's a 48v 1RU DC power distributor for 100A for $40. That looks really nice, but not really portable. Might snap it up just as an insanely large stationary DC power supply. Will need to be mindful of current I draw though. One DIN rail mounted one for 32A, but even that was $500 second hand.

Not sure where you're at, but perhaps that country has a bigger market for ex-telco gear.
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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 23 2020 11:29pm

North America, and yes huge, so much churn in the industry starting with Nortel.

But I get great value gear from Israel all the time, maybe subsidised postage?

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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 23 2020 11:32pm

A big trend now is high-voltage distribution at 270-370Vdc

then DCDC buck converters at Point of Load, 200-400A units easily stacked for high amps

Gives great flexibility for EV / ebike + off-grid mobile / House bank storage. . .

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Re: Charging LTO at Max Speed?

Post by Username1 » Apr 24 2020 12:40am

@sunder Amazing explanation. I think i'm understanding way better already.

So basically if you took a discharged battery and began charging it at it's maximum voltage, the battery would (on its own) suck in massive amps, because the difference in voltage between the charger and battery is high. This massive amp draw is due to voltage x resistance = current.

So if the charger could provide these very high amps, it would destroy the battery right? Because you would be well above the c rating of the battery.

So rather than destroying the battery, the charger begins by providing whatever voltage is needed for the amount of amps you want, and then raises to voltage to maintain those amps as the batteries voltage rises (because you must maintain the same voltage difference between the battery and charger to get a constant amount of amps).

If i have this right so far... It sounds like the only thing the charger can DIRECTLY adjust itself to output is volts, and then the amount of amps that comes out is based on what it's connected to. Does this mean the charger monitors it's amp output somehow, and changes its voltage based on that?

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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 24 2020 1:44am

Username1 wrote: So rather than destroying the battery, the charger begins by providing whatever voltage is needed for the amount of amps you want
The source just tries to put out the setpoint V which is just a maximum. The only regulation is capping the V after that setpoint is reached, CV stage.

The battery V being lower, means the **combined circuit** is somewhere in between, if the maximum current "offered" is a high C-rate then the circuit V is closer to the source's V and rises faster, if amps are low then circuit V stays closer to battery V longer, rises more slowly, reaches CV setpoint at a higher SoC.

Low resistance or larger Ah capacity battery will draw all available current

e.g. a lead battery with CAR of 0.2C size of 500Ah can only draw 100A, while with a LI bank that can draw 5C, only a 20Ah pack pulls the same 100A.

A battery does not usually get "destroyed" charging too fast, but it is not good for longevity, as you can tell by the temperature rising. But pre-heating the cell allows for less or no damage at a faster rate. A cold cell gets more damaged by a much lower rate.

However, a high-CAR chemistry might **easily** destroy the charge source circuitry, if that device does not have good current-limiting, or at least overcurrent protection (latching or hiccup).

That is why vehicle alternator/VRs originally designed for lead, often get smoked when an ignorant installer just "drops in" a lithium battery.


> then raises to voltage to maintain those amps

The charge source just keeps putting out the max setpoint. It is the SoC rising that brings up battery voltage, thus the **combined circuit** voltage "negotiated" also rises.

The current starts to fall as battery resistance rises and/or voltage delta shrinks, nothing to do with the regulating circuitry, just natural electricity phenomena.

> the only thing the charger can DIRECTLY adjust itself to output is volts, and then the amount of amps flowing is based on what it's connected to

It only keeps V from going over setpoint.

> Does this mean the charger is somehow monitoring it's amp output, and changing its voltage based on that

No.



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Re: Charging LTO at Max Speed?

Post by Addy » Apr 24 2020 2:06am

john61ct wrote:
Apr 24 2020 1:44am
> Does this mean the charger is somehow monitoring it's amp output, and changing its voltage based on that

No.
You are incorrect. A CC-CV charger certainly is monitoring it's amp output and changing it's output voltage to keep the current regulated. The current doesn't magically limit itself to the right value.

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Re: Charging LTO at Max Speed?

Post by john61ct » Apr 24 2020 2:17am

Again, I am not getting into "inside the black box", just what is observed from measuring the outside.

Charger is during Bulk stage striving to bring circuit V up to the setpoint (if separate battery V sensor then measuring that directly),

current stays as high as possible.

The current dropping as the circuit voltage rises is not due to charge source regulation.

It is not by any means a "constant current" at that point, often long before CV stage is reached.

Thanks for correcting from that "internal workings" POV, but there are variations, and at this level of discussion I think overcomplicates the issue.

Like a DCDC converter actually using AC internally? Not interested, just give me input, output and IRL efficiency.


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