Lithium volts

Power wheelchair board for REAL info!

POWERCHAIR MENU! www.wheelchairdriver.com/powerchair-stuff.htm

Lithium volts

Postby davidpaul » 06 Oct 2021, 14:36

Just fitted the Lithium battery in my sons chair, set the volts at 26v and the speed shown on the screen is 7.4mph, can the volts be raised anymore ? what problems could there be at higher volts ?
and is the on board speedo reliable ?
davidpaul
 
Posts: 281
Joined: 17 Jun 2013, 21:21
Location: Camborne, Cornwall

Re: Lithium volts

Postby duke1 » 06 Oct 2021, 14:57

hi this is a thread talking about the how wheelchairs measure speed, https://www.wheelchairdriver.com/board/ ... =2&t=10866 cheers
duke1
 
Posts: 601
Joined: 13 Jul 2014, 17:09
Location: southeast england

Re: Lithium volts

Postby davidpaul » 07 Oct 2021, 09:54

Thanks, I've tried using a app one my phone but it seems to have problems registering at lower speeds, is there a better way of measuring low speeds ?
davidpaul
 
Posts: 281
Joined: 17 Jun 2013, 21:21
Location: Camborne, Cornwall

Re: Lithium volts

Postby Burgerman » 07 Oct 2021, 10:53

Time V distance.

Measure a distance or use a known one. And a stopwatch.

GPS is or can be VERY accurate, but not over short distances and phone aps only display full numbers anyway. Why? Because GPS is only accurate for position, over many samples. Averaged over a period of time.

Take a look at this. This is much more info than most GPS aps will show you on my PC. This is a STATIONARY computer and GPS tool.

It is connected to both GPS and Glonass systems. So two lots of data and two different averaged points. This was over about 10 mins or so.

If the GPS system was actually accurate all these points would be in the same position. And averaged over say 2 or 3 mins they give an accurate position. Remember I am not moving. And after a few mins, those two green circles are the AVERAGE position determined by GPS and Glonass. The rest are every sample, position.
Attachments
Image4.gif
User avatar
Burgerman
Site Admin
 
Posts: 65050
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: Lithium volts

Postby Burgerman » 07 Oct 2021, 10:56

Number of sattelites etc:
Attachments
Image1.gif
User avatar
Burgerman
Site Admin
 
Posts: 65050
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: Lithium volts

Postby Burgerman » 07 Oct 2021, 11:14

Data, raw, averaged, etc. Over time. Remember accurate position is ESSENTIAL to determine speed. The longer the distance covered, the greater the accuracy because it averages all the errors. If you drive 100 meters a 10 yard position error is now a small percentage. (10% error). So 1mph becomes 1.1 or 0.9 worst case.
Attachments
Image2.gif
User avatar
Burgerman
Site Admin
 
Posts: 65050
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: Lithium volts

Postby fishinjunky » 07 Oct 2021, 20:22

davidpaul wrote:Just fitted the Lithium battery in my sons chair, set the volts at 26v and the speed shown on the screen is 7.4mph, can the volts be raised anymore ? what problems could there be at higher volts ?
and is the on board speedo reliable ?


What are you using to charge it with?
Invacare tdx sp
Bounder 300M 200ah lifepo4
fishinjunky
 
Posts: 1041
Joined: 11 May 2021, 02:28
Location: West Virginia United States

Re: Lithium volts

Postby davidpaul » 07 Oct 2021, 21:01

fishinjunky wrote:
davidpaul wrote:Just fitted the Lithium battery in my sons chair, set the volts at 26v and the speed shown on the screen is 7.4mph, can the volts be raised anymore ? what problems could there be at higher volts ?
and is the on board speedo reliable ?


What are you using to charge it with?


https://www.hobbyrc.co.uk/isdt-p30-1000 ... dc-charger

Charges at 30 amps, discharge is only 3amps
davidpaul
 
Posts: 281
Joined: 17 Jun 2013, 21:21
Location: Camborne, Cornwall

Re: Lithium volts

Postby Burgerman » 07 Oct 2021, 21:06

You gain a small amount. 24V lead is around 12.8v to 12.6v most of the day. x2 obviously. So 25.8v but it sags under load. Quite how much it does so is dependent on load, and internal resistance and peukert. So a safe voltage figure that gives enough extra headroom to get good steering control while say climbing a slight hill is around 22V. A lithium ion phosphate 8S pack is around 26V when you are driving around. How much that drops again depends on use, load, motor impedance battery impedance etc. But set to 25V seems to work OK as theres usually far less drop under load.
So the difference is 22V to 25V. A 3V difference. Subject to fine tuning the thing.

And obviously you cant set it to say 30V and expect a speed increase if the battery doesent have 30V! All that will happen is that you will lose steering control by half (it can slow 1 wheel, cannot speed up the other) and downhill will go faster at the cost of steer control and regeneration current.

So what will you realistically gain. 22V to 25V is as high as you should really set that from my experience and tests. Thats an 13.5% increase. So if the chair does 6mph stock it will now do 13.5% more. So 6 = 6.81mph 6.5 = 7.3mph so not a huge gain. But noticible.

It will likely not show up on the display unless you set that too in programming to display say 7.3mph in DESIGN SPEED and 7.3mph in DISPLAY SPEED. All it does is tell you that you are going that programmed speed when the stick is fully forwards. Even if you are up against a wall and stalled. It doesent know the wheel speed.
User avatar
Burgerman
Site Admin
 
Posts: 65050
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: Lithium volts

Postby davidpaul » 07 Oct 2021, 21:12

I've been naughty and set the volts at 26v been out for a ride with my son today, so far no problems and with the slightly bigger tyres and increased voltage she's nearly 2mph faster about 8.2mph, my sons fairly happy with that ;)

Mod's so far - 120a control module, 200ah lithium battery, changed the drive wheels to 8" with 15.5" diameter tyres

next mod's are - alloy battery box to give the cells some more protection, and the front and rear wheels are being spaced out further to give extra wheelbase for extra stability and lowering the castor wheels to compensate for the larger drive tyres
davidpaul
 
Posts: 281
Joined: 17 Jun 2013, 21:21
Location: Camborne, Cornwall

Re: Lithium volts

Postby Burgerman » 07 Oct 2021, 21:13

If he cares about control when going up a hill for e.g best to set 25V. You will not lose much speed at all.
User avatar
Burgerman
Site Admin
 
Posts: 65050
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: Lithium volts

Postby davidpaul » 07 Oct 2021, 21:22

Burgerman wrote:If he cares about control when going up a hill for e.g best to set 25V. You will not lose much speed at all.


Ah ok will reset to 25v
davidpaul
 
Posts: 281
Joined: 17 Jun 2013, 21:21
Location: Camborne, Cornwall

Re: Lithium volts

Postby davidpaul » 09 Oct 2021, 21:52

What should I change the low voltage cut off too when running lithium ?
davidpaul
 
Posts: 281
Joined: 17 Jun 2013, 21:21
Location: Camborne, Cornwall

Re: Lithium volts

Postby Burgerman » 09 Oct 2021, 23:01

Its irrelivant. You want to do 2 things.

1. Fit enough Ah so that running them low is never required. If you got 65 miles range, not an issue!

2. If you dont fit enough Ah, and so must run them low, you cannot set a low cut off for the pack, because the 1st cell to become discharge may go way below 2.5V even if the rest of the pack is up at 25V... So in this case you need a cell log. Or to do a few discharge cycles with your pack and note the actual pack voltage when the first cell hits say 3.100V. And use that. Although thats not very accurate and variable.
User avatar
Burgerman
Site Admin
 
Posts: 65050
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: Lithium volts

Postby davidpaul » 09 Oct 2021, 23:04

ah ok, it's a 200ah battery pack
davidpaul
 
Posts: 281
Joined: 17 Jun 2013, 21:21
Location: Camborne, Cornwall

Re: Lithium volts

Postby Burgerman » 09 Oct 2021, 23:12

So you should get a lot of miles and you will wear out before you lose a couple of lights on the display. When you do, use a cell log, to see actual cell voltages. What will happen is that they all stay roughly the same all day. When the first cell to become empty gets to that point its voltage drops off like a rock.

And you have no way to know when that will happen. But its unlikely to do so before you go 50 miles. Depends on terrain. But I tire out long before my chairs do.
User avatar
Burgerman
Site Admin
 
Posts: 65050
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: Lithium volts

Postby davidpaul » 10 Oct 2021, 16:46

Ok thanks, we've cycled 27 miles this week so I'm thinking to charge once a week, we probably wont be doing much more than 25m in a single ride, the lead batts would did a max of 22m and that was with flashing battery bars, so we can now comfortably do our circular ride without fear of flat batteries :thumbup:
davidpaul
 
Posts: 281
Joined: 17 Jun 2013, 21:21
Location: Camborne, Cornwall


Return to Everything Powerchair

Who is online

Users browsing this forum: LROBBINS and 84 guests

 

  eXTReMe Tracker