WheelchairDriver

Last year I got a Magic Extreme X8 used and put 10x cells 230ah so 32v, then I set 31v voltage output. Works great but it's not what I expected for a $20k chair. Now would like to sell it. Do I leave it as is? Do I put back lead acid bricks?
Also, it had the standard seat which was waaay too big for me so I ripped it apart, used the frame to put my rehab backrest. Now what? I guess I must leave my rehab seat & backrest now otherwise they'll sit on the frame.

Wouldnt that depend on why?

I wouldnt run 10 cells you will cook all the electrolytic capacitors. And depending on which control system, it might not allow it to go faster anyway.

Burgerman wrote:Wouldnt that depend on why?

I wouldnt run 10 cells you will cook the electrolytic capacitors.

Aren't they rated for 35v?

Yes.
But your battery voltage spikes a lot higher than your set 31 volts with noise from commutation. And short spikes from deceleration regen on top. Get a multimeter like my data logging fluke that can measure voltage spikes and noise at high frequencies and you will be surprised!

And you prsumable charge at 3.6V per cell too right?

And depending on which control system, it might not allow it to go faster anyway.

Magic controller allows voltage up to 35v somehow. Others like Sunrise stops at 26V.
And I confirm it's indeed 31v because it goes 13.5kmh.

And you prsumable charge at 3.6V per cell too right?

No, I can't because then I get high voltage error. I charge to around 3.47v.

Magic or sunrise dont make controllers. They are made by companies like curtis wright, curtiss instuments, penny and giles. And are sold as things like rhino, or R-net or rebranded for various companies like prides QLOGIC stuff.

PG stuff 35V peak before error cuts power.
Dynamic 32V
ETC.

But they are intended and desighned for lead, to run at a nominal 23 to 25V in use. Plus or minus a little noise and regen voltage.

Burgerman wrote:Magic or sunrise dont make controllers. They are made by companies like curtis wright, curtiss instuments, penny and giles. And are sold ar things like rhino, or R-net or rebranded for various companies like prides QLOGIC stuff.

PG stuff 35V peak before error cuts power.
Dynamic 32V
ETC.

But they are intended and desighned for lead, to run at a nominal 23 to 25V in use. Plus or minus a little noise and regen voltages etc.

I know but its firmware allows higher voltage parameter. Others just reset if you go too high.

Its too much and will end badly at some point! I tried all this stuff n my attempts to get a chair faster. And with hobby speed controllers. Those intended voltages are for good reason! If you have spare controllers etc and breaking them doesent worry you then great. Why not. I have more fried stuff here over the years trying stuff out than I care to remember.

It wont end badly for me because I'm selling it! So you're saying I should remove the batteries before selling it? Buyer may experience a controller blow off?

I know but its firmware allows higher voltage parameter. Others just reset if you go too high.

Different firmware revisions. They lowered it or limited it at some point to stop people setting it too high. Its not critical with lead batteries as you can only get about 23 volts while rolling/accelerating. Setting it higher just allowed hgher downhill speeds. It isnt meant as a limit to battery INPUT voltage.

Well thats a good possibility. But as long as you tell them that and allow the option... Or just remove 2 cells.

If you have spare controllers etc and breaking them doesent worry you then great. Why not.

Exactly. Considering a controller can be had for $40 on eBay. I don't mind. It worked great. I have 500 miles on it, no issue and a nice speed bump!

Well thats a good possibility. But as long as you tell them that and allow the option... Or just remove 2 cells.

I could keep the controller as well. All others I've had were limited.

Before lithium, I discovered race car batts... Those each have an extra cell. Why? Because most race cars do not have a generator/alternator as it sucks power from the engine. They start a race on a full battery. As its loaded the voltage soon drops below 12V (SAG under load) and gets worse lap by lap.All the ignition system etc want 13.8 to 14.4V... So misfires etc happen.
So along comes the 14V extra cell 12V lead battery! A 7 cell lead brick. These things are deep cycle. That extra cell means that the battery has the same voltage in use as a battery thats connected to the alternator... So cures the voltage drop issue.

So I saw this and obviously put 2 in my chair. Thinking 28V. But its not 28V because a 12V battery isnt 12... its 13.x So now I have around 30+V charged. Worked OK, not massively faster and I forgot about it. About 6 months later I was reminded though when I heard a bang as a capacitor popped. I recognised that smell. Fortunately next to my bed on charge. At 33.6V (2.40v per cell). I looked inside the power module and the capacitors were either top popped open, or can blown off or bulging at the top. Obviously been that way for a while. Still worked. Just. That was an old Pilot plus (PG Drives) 80A power module. So I dont think its a good idea.

These things... Different brand but same idea. They do 12V as well as 14 and 16V AGM.

https://www.summitracing.com/parts/xsp-d1600?rrec=true

Also, do you know what happens on high voltage error? It'll set the electromagnetic brakes yes but does it cut the circuit? Like is it smart enough to see that the motor is generating too much current and cut the circuit.
I suppose it could happen with lead right? Say you fully charge then go down a steep hill for like a km. Will the voltage shoot up?

Did the same on a RC plane speed controller in my bedroom. Usually used 6S lipo packs and wanted to test something. Saw a LiPo on the banch, grabbed it plugged it in. It was a 10S heli pack. The speed controller capacitors literally exploded off the board. Very loud. Scared the crap out of me. When I looked closel it was a 2 to 6S speed controller and it really didnt like 42 volts.

These things...

emilevirus wrote:Also, do you know what happens on high voltage error? It'll set the electromagnetic brakes yes but does it cut the circuit? Like is it smart enough to see that the motor is generating too much current and cut the circuit.
I suppose it could happen with lead right? Say you fully charge then go down a steep hill for like a km. Will the voltage shoot up?

It cant disconnect it. It MUST push any regenerated energy into the battery. But its not how you think. Going down a long hill could overcharge a battery. But its the noise, the spikes of ac overlaid on the voltage that is the problem. You can get that while accelerating never mind going down a hill.
If you look at the energy getting used or regenerated it very noisy! From the sparks and the commutator maybe? I dont know. At very high frequencies its a mass of spikes. Those spikes can be many volts. Above and below the average voltage. You can see it on my high frequency logging meter. Or an occilloscope.

But when I turn my joystick on, it gets harder to push means it's now in "generator" mode. When it's off and I push, is it still sending current to the battery. Why is it easier to push then?

Its motors are ALWAYS a generator. Its just a matter of what happens to the power.

The difference when on is that now that controller wants the chair to be at zero mph as thats what its joystick tells it.
When off the controller isnt allowed to control the chair. That voltage with no current (zero power) has no place to go with mosfets open circuit so just builds volts and can damage mosfets. It doesent brake as no current, open circuit. In the roboteq for e.g they insist you add a big diode across the battery cable breaker or fuse because if that power has no place to go and a breaker trips it makes the voltage shoot up and takes out the controllers mosfets.

When its all turned on, the voltage cant go above that voltage that you set as the maximum peak in programming regardless, for safety reasons to stop a chair runaway down a slope. It will go faster than battery voltage and keep accelerating. That also takes out the controller...

But when you push, with it turned on, the controller now tries to do its job and control the motor speed. The controller makes the motors turn a the speed you choose with the joystick. Thats zero while you push it right? With joystick at centre position then, the controller actually brakes the chair via its motors if you try to push it along. It adds a negative voltage to stop you moving it. To try and stay at 0mph (or zero volts). As you push the chair it develops a voltage. The conroller sees this and adds an opposing force to slow the chair to 0V again. That in turn causes a current. The motor compensation sees this current and increases it. So fights the movement harder still by adding a stronger opposing force. Disable motor compensation and much of that effort needed to push will vanish but some will still be there.
Try reducing it a lot, you will see that it rolls on a slope a lot more and brakes much more gently when you release the joystick.

Anyway, the problem isnt really about a continual voltage. The reason that they use 35 or even 40V capacitors is the spikes on the DC voltage that you get that are above and below the average voltage all the time while accelerating or decelerating. Its components have extra headroom, to cope with that.

The problem is this (wiki):
Voltage spikes = high and low very short term "pulses" of voltage caused by inductance and flyback effect of a coil of wire
EMI = Electro Magnetic Interference
RFI = Radio Frequency Interference

Motors generate voltage spikes, EMI, and radio frequency interference (RFI) which can damage or disrupt circuits nearby. Arcing initially occurs once the motor rotates at the brushes, then the generated EMI from the commutator flows back towards the power supply, RFI goes into the air, and finally as the electromagnetic field from the inductor collapses, a huge voltage spike occurs. The EMI may cease a circuit from functioning or degrade the performance dramatically while the RFI would disrupt any equipment relying on RF. Luckily, there are methods to suppress or at least lower the intensity of the disruptions.

It collapses every time the 16 to 20k per second pulse width chops on and off. The inductor being the motor windings storing energy.

The reason a nominally 24 volt controller uses higher voltage components is to allow some headroom for these voltage spikes. Having a higher base battery voltage just reduces this headroom. Having some regeneration power increasing this voltage further just reduces it some more...

Thats why I say you need to put a occilliscope or a fancy high frequency voltmeter on the job to see whats really happening as its quite surprising. This is why I say that 10S is too much.

Theres a newer version of that thing, that doesent have the flip flop steering I seem to remember reading somewhere. Would that be better?

That's so terrible

https://youtu.be/hB2UqGrg8YA?si=FnpePrwOaFdZAKH8

Got a modified Magic Extreme X8. Now would like to sell it. Do I leave it as is? Do I put back lead acid bricks?

I already have two LiFePO4 powered wheelchairs.
From a buyers point of view I would be looking for an unmodified wheelchair.
My wheelchair is my legs.
Unless I did the wiring I’m never going to truly trust an electrical modification.

Too any customer it will be easier to sell with lead acid bricks.
Most people buying a wheelchair want simple solutions.
If you offer a chair that then also needs a special charger, and a level of knowledge, your possible customer numbers are hugely reduced.

Keep the LiFePO4 cells for whatever you purchase next.
Or sell them separate from the wheelchair.
The cells are probably going to be easiest to sell to a van-lifer ie.someone swept up in the current craze for living in an old school bus like a tramp.

Changes to wheelchair seating is less important.
A buyer will either be OK with any seat, or will have specific seating needs and need personalised seating anyway.
Fit a car seat if you don't want to give away your own personalised rehab seat & backrest.

Burgerman wrote:Theres a newer version of that thing, that doesent have the flip flop steering I seem to remember reading somewhere. Would that be better?

Maybe but it's so low that you get jacked everywhere. I'm thinking about getting a Bounder. It'll probably be as good.

emilevirus wrote:But when I turn my joystick on, it gets harder to push means it's now in "generator" mode. When it's off and I push, is it still sending current to the battery. Why is it easier to push then?

The motor has both electromagnets and permanent magnets. The controller swaps the poles of the electromagnets to make the motor turn as commanded. When the controller is off, so are the electromagnets. You don't have to fight against them to turn the motors, making it easier to push by hand.

It can still generate electricity backwards to the controller/battery, depending on the hardware setup, even when turned off if pushed. I don't know how to RELIABLY figure out how much. I don't believe you could push it by hand fast enough to do damage.