48v 240W USB-C PD wheelchair charging?

[slomobile]

I haven't seen this done yet but it seems within the realm of possibility now. 240w certified USB cables and chargers are available.

https://www.usb.org/usb-charger-pd

A 48v 40AH pack ought to have about the same range as 24v 80AH lead chairs if limited to similar speeds.
Full charge in about 8 hours. Top up through your phone charger on the road.

Anyone want to give it a go?

[daveonwheels]

that cable will melt in two seconds.

[Burgerman]

Well yes it would work but a bit too slow, since I charge lead chairs at 12A via XLR and much more via anderson normally. And how big is a 240w USB supply? I have a 130w dell one here now..

And then how do you use 48v on a 24v chair?

Better to use 2 of these in series stuck together... https://www.ebay.co.uk/itm/335268791429
And a simple voltage inverter chip on the chair for 28.8 or 28.2v. That would result in an 8A 24v lead charger.

[LROBBINS]

I think that you are going to have difficulty finding the tiny leads to a USB-C port. Moreover, these chargers are actively configured by the connected device (PC or other) via USB handshaking. It may be doable, but will be a big project (and risks your chair if you get it wrong).

[Burgerman]

The idea that a 48v supply could be smaller and not need heavier wires due to halving the current is a good one for travel purposes though. But why use phone chargers. Theres lots of simpler 48 and even 96v very compact industrial use supplies. So say a 250 watt 48v power supply. And just use a small eBay buck inverter set to your prefered charge voltage.

That would make a pretty compact travel charger.

There are CC/CV buck/boost efficient inverters available cheaply and just one small board. That could live on the chair. Or inside the power supply. To drop the voltage to what we need. Then we can set current and voltage. As long as we set a slightly low voltage and dont charge for more that 8 to 10 hours then theres no battery danger/damage.

Added.
This is a compact charger. 20V. 240watts. 12A. This with a simple boost inverter from ebay will do a 24V 8A powerchair charger. And no communication needed.
https://www.ebay.co.uk/itm/155509269182

And used with something like this CC/CV set to your needs. https://www.ebay.co.uk/itm/386372020389

[slomobile]

The idea was not to Frankenstein something together, but fully adopt the USB PD 3.1 standard including their 240w certified USB-C cables, GaN chargers, certified 240w USB receptacles, charge controller ICs on the chair and use 48v batteries on the chair with 48v motor controllers that cut the duty cycle by an additional 50% to be safe with existing 24v motors, or just use 48v ebike motors.

I'm thinking Ebikes were one of the reasons this was developed. Fast charging server/workstation class laptops being another. However phones were the first real examples a year ago as far as I know. https://www.gsmarena.com/realme_gt_neo_5_240w-12067.php

GaN is capable of much more power handling with less heating than silicon at 48v. At 96v SiC is a bit better semiconductor. 48v is right in the GaN sweet spot and still below the 60v dc where more high voltage user protections are required.

[slomobile]

I think I'm gonna try this. I have a design in mind that is sort of split into 2 48v ebikes with user in the middle. Like a frame runner, but motorized. https://by-conniehansen.com/product/rac ... me-runner/

[slomobile]

$18 each, 20AH Toshiba SCiB LTO cells 2.85Vmax 2.3Vnominal
17S per pack. 2 independent packs so one can be charging while the other discharges.
34 cells = $612 plus shipping https://batteryhookup.com/products/2-3v ... matic-cell
8.8kg or 19.4lb per pack. Swappable.
116 x 22 x 106 so total pack length about 374mm or 15" x 4.6" x 4.2"

• A new adjustable voltage mode enabling a range from 15V to one of three maximum voltages
(28V, 36V, or 48V) depending on the available power allowing the device being powered to
request specific voltages to a 100 mV resolution.

So I need a charging algorithm and charge monitor, then just tell the power supply what voltage I need. Not a lot of hardware to build.

[Burgerman]

Why LTO?
Theres a reason we dont use them. Terrible energy density. They are great fit in places like a boat or a solar storage battery. But you wont find many in EVs althought theres some Because they take up valuable space or limit range. Where the important bit is getting as much Watt hour into the least size. So you dont need to be lugging a massive battery around to get similar range.

Energy density order:
So EV cars mostly use laptop firework lithium ion batteries for best range and small packs.
Wheelchairs and burning dont go well together, so we use the 2nd best energy density, LiFePO4 as these dont burn.
Then thers a bunch of horrid to charge chemistries that are problematic in one way or another.
Then theres LTO
Then lead...

You also need a fire starter. I mean BMS.

[Burgerman]

Wiki
The 230Ah cells we commonly fit in place of grp24 are 155 to 160 wh/kg but this doesent show the physical size difference which is also huge.
The small cells are typically less, and high C rate ones also less. Hence variation.

You literally need double the mass/size of LTO. For same storage ability (fuel tank). But that weight needs more energy to shove around so you get less range too.

[Burgerman]

For what its worth, LTO was some of the ealiest developed lithium battery technology. But the energy density issues mean that they are not commonly used. Lead manages 35 to 60. Depending on type/size.

[slomobile]

Why LTO?
The amount I need comes in under 40Lbs,
Fits in space unneeded by anything else.
As safe as LiFePo4
Can be charged in subzero temperatures
Very high charge/discharge rate
Very long cycle life. Over 20,000 cycles.
I can leave a discharged chair in the freezing van over night and be mostly charged before I reach Memphis. And I'll never need another set.

[Burgerman]

Why LTO?
The amount I need comes in under 40Lbs,

That could be halved with LIFEPO4 or better still storage capacity (range) could be approx doubled.

Fits in space unneeded by anything else.

So does lifepo4

As safe as LiFePo4

True. Possibly more so due to low energy density. But higher connections and BMS cell counts decrease reliability and safety long term though.

Can be charged in subzero temperatures

True. But if you had twice the capacity of lifepo4 you probably dont need to till it warms up some anyway.

Very high charge/discharge rate

LiFe can have high or low discharge rates. I have some 25C lifepo4 packs here. But with double the capacity compared to a LTO pack it wouldnt matter. It is effectively halving the required c rate anyway.

Very long cycle life. Over 20,000 cycles.

Cycle life depends on many things. With a small pack that gets worked heavily and discharged more deeply then cycle life drops quite severely compared to a lightly loaded pack. So in real terms a LFP pack wih double the capacity would likely match the cycle life. Even if you only discharged LTO by say 50% daily then the LFP with double the capacity wouldnt need charging as often. So each cycle is then 2 days long. So it would only need half the cycle life to live the same length of time. But that charge every 2 days thing means even a 5000 cycle lifespan and I would expect more, is 27 years. But you wouldnt discharge that deeply with a doubl sized pack in reality. So you would get north of 30 years. How long do you think the chair/van/you will last?

Thats why a bigger pack always wins. Why a slower C rate discharge always wins. Why a limited charge/discharge level allows 3 to 10x the cycle life. Its why a Tesla with lithium ion fireorks and a 500 cycle limit on its 21700 cells doesent last 18 months! They look like they will be good for 2 decades or more.
I have chairs here with too small packs made up from old style cells that are now 15 years old and they have the same capacity today as they did when new.
If you fitted LTO or LIFE (LFP) and did so with a larger capacity pack (same weight/size) they will all outlive your van or chair and possibly you! With the big advantage that you will have double the storage.

I can leave a discharged chair in the freezing van over night and be mostly charged before I reach Memphis. And I'll never need another set.

That applies to both chemistries is treated properly! At least if its not freezing. How often will this occur? If its often then you have no choice.

[slomobile]

Can be charged in subzero temperatures

True. But if you had twice the capacity of lifepo4 you probably dont need to till it warms up some anyway.

... So each cycle is then 2 days long. So it would only need half the cycle life to live the same length of time.

I can leave a discharged chair in the freezing van over night and be mostly charged before I reach Memphis. And I'll never need another set.

That applies to both chemistries is treated properly! At least if its not freezing. How often will this occur? If its often then you have no choice.

It all comes down to freezing really. I know that isn't a thing you all deal with much over there. It is difficult to know if it will freeze on any given night. And bringing the chair in to keep it warm overnight is difficult and painful for me.
In Memphis, there are 56.1 days annually when the nighttime low temperature falls below freezing, which is one of the warmest places in Tennessee.

Since I like to leave my chair inside the van, on charge overnight while I sleep, it is impossible (for me) to treat LFP and my back properly. At some point, I WILL accidentally leave them plugged in through a freeze. I've never had any lithium battery last me more than 4 years.

Even with lead my average cycle time is longer than 2 days. I sometimes don't leave the house all week, or 2, so my chair in the van isn't touched. However when I do go out, sometimes its camping or a multiday road trip and I need to charge at every opportunity to last through each day. That is where the rapid recharge comes in handy with LTO. I'm planning to abuse them. I rarely do anything "properly".

[Burgerman]

A simple thermostatic charge switch set to say 2C would prevent any charging below freezing. Some BMS systems also have a built in thermostat too. And then theres those heat pads. Those can be thermostatic and never allow the battery to go below 0C. They only take a few watts. All those would do what you need and are commonly available.

Theres no way lithium cannot work below 0C as the biggest adoption of Electric cars, and the biggest tesla adoption is Norway. They work fine. Millions of them. Yes you will find the odd hater looking for trouble and hits/$$$ on youtube. But the rest just get on with it!

Norway. -50c in places. No problem.
Norway the capital of the EV adoption! They have a greater number of EVs than any other place on earth.
https://www.visitnorway.com/plan-your-t ... tric-cars/

[Burgerman]

Secondly, electric cars are cool! They are silent and don't create noxious fumes. And you can drive for several hundred kilometres before you need to charge. Not that charging is a major problem in Norway – we have more than 3000 public charging stations, and 7753 fast chargers, all over the country. Say goodbye to range anxiety!

The easiest way to find a charging point is by checking ladestasjoner.no's map. To make sure you have access to charging stations, it's important to register with the major providers in advance. Norway has about ten of them.

“Even in the northernmost parts of Northern Norway – an area with huge distances, more reindeer than people, and really low temperatures in the winter – you can get around easily in an EV,” says Christina Bu.

If you want to take a road trip through the country, you can easily rent an electric car from most rental companies. In Geiranger and Flåm, eMobility has even set up a rental service for a scooter-car (a small four-wheeler) with two seats and open sides. Perfect for sightseeing!

-50 centigrade in the north in winter. And they work just fine.

[slomobile]

"A simple thermostatic charge switch set to say 2C would prevent any charging below freezing. "

Why? So I can wake up on a freezing cold morning, get to my destination, then realize the chair is dead?
I want the damn thing to charge overnight. That is why I plugged it in!

Electric cars work in Norway because you tell the car when you are on your way to a charging station and it preheats the battery using energy stored in the battery. Why should I add thermostatic switches and range stealing battery warmers when instead I can use a battery that works perfectly well in cold temperatures and has no other drawbacks in my particular use case?

Do you have stock in LFP or something?

[Burgerman]

Stock? No. As I said if it works for you...

Why? So I can wake up on a freezing cold morning, get to my destination, then realize the chair is dead?
I want the damn thing to charge overnight. That is why I plugged it in!

It wouldnt matter. LFP would stll have twice the charge anyway. So you would have whatever would have been remaining in your small LTO as well as a the other extra 100% as the LiFe PO4 since it would be double the capacity... And that also means that taking a few watts out precharge or using the charge current to stop the battery freezing or to warm it a few degrees would be negligable and so it would be charged just fine anyway regardless of the cold!

But whatever. You can charge a cold tesla just the same. You can save waiting time by heating as you drive but its not essential. The first part of the charge just warms the pack. Takes around 10 to 15 mins. The rest of the time the charge alone warms the pack anyway. Its not a big issue. It needent be on your setup either. And you would have double the capacity too. But its your funeral!

[slomobile]

The first part of the charge just warms the pack. Takes around 10 to 15 mins.

Sort of correct.
I see it stated this way a lot and it can mislead people familiar with warnings about charging lead that can be safely ignored. For most lithium electric cars, no power is being sent into the battery to warm it up from frozen as is done with lead acid. Instead, the electrical power that would have gone into the battery is sent through resistance heaters. Once the battery is sufficiently warm (beware of of frozen remnants) then they can begin actual charging, and the internal resistance will produce sufficient heat to keep it from refreezing.

Of course there are resistance heating blankets for lead acid too, but they arent as necessary because as long as you start at a very low current, lead acid can tolerate charging while frozen.
With most lithium chemistries charging while frozen can plate the anode with lithium metal ions instead of intercalcating. That permanently reduces battery capacity and increases resistance. If enough plating builds up, it can puncture the separator and create a short inside the cell.

[Burgerman]

But if you have double the capacity as you would, you can afford 2% of that to warm the battery. You dont need it hot. Just a few degrees above freezing. Like my fridge. Just because tesla uses the charger to warm the battery doesent mean you must do it that way. And they dont have to. They can chose to heat it from inside the car for performance or charging reasons without a charger. Tesla actually heat water, and pump that around.

But it would likely take very little power to keep the battery above freezing especially as its in a car rather than outside and that alone may keep it from getting really cold. The inside of my car doesent freeze when the outside is covered in ice. So actual power level may be pretty low. Esp if insulated.