Permobil High Battery Voltage

[swalker]

I have received a High Battery Voltage fault on my Permobil C500 wheelchair several times.

The typical situation is that I charge the wheelchair fully. I then take the wheelchair in my van to our local gondola and ride the gondola to the top of the mountain.

I then descend over 2,000 feet vertical on various trails covering a distance of around 7 miles.

There is a very small amount of up and down as I make my way down the mountain. After about 2 or 3 miles of riding, the wheelchair will come to an abrupt halt and display the High Battery Voltage fault code.

Cycling the power clears the code, but it return very quickly unless I ride the wheelchair uphill for a bit.

The permobil documentation states this fault will arise if it detects the battery voltage has risen above 35 volts.

Permobil's suggested corrective action is to check the charge level and conditions of the batteries, ensure the connections between the batteries and the control system are tight and not damaged, and ensure the connection between the batteries and circuit breaker/main fuse are tight and not damaged.

I suspect that the sustained downhill riding with the motors acting as generators and producing energy to charge the batteries is likely a contributor to this problem.

I would appreciate it if you could share your thoughts about what is going on and potential ways to remedy it.

Thanks

Steve

[Burgerman]

If your batteries are charged fully, before you start to decend then there no way to fix anything. Decending continues to charge the batts as you say. And this is not a controlled CV charge, just raw re-generated power.

The permobil documentation states this fault will arise if it detects the battery voltage has risen above 35 volts.

Correct. But the 35V does not mean the battery has REACHED 35v (hopefully!!!) but the noise/spikes on the regeneration has exceeded this value. You would need an occiloscope to see these. The system is designed for a nominal 24V lead battery With adequate headroom so that regeneration and noise is not an issue. But KEEP regenerating and the power just overcharges the battery.

That means that while on charge it may reach 29.4V on AGM batteries max. The moment its off charge this falls to 26.something. In use on the flat, the voltage never exceeds that other than in regeneration spikesup to maybe 30V for a few millisecs (regen + spikes, noise). Even some small amount of downhill no problem as the 35V is the HEADROOM the system needs. Which is why you cannot safely use a higher voltage battery like Micka7405 did. Theres likely trouble ahead for her.

In your case you will be damaging your battery through overvolting though. There are a few solutions.
1. Fully charge, but remove say 5Ah with a dump load device before you leave. Trial and error, and a voltmeter will show you what is the correct amount to remove. Dont let the continual regen voltage exceed 30V or you are damaging your battery. 32V max for a few secs.

2. Better way. Fit a 30V, 100W or 50W zenner diode across the battery with a heatsink. So it wastes any regeneration voltage that tries to push the battery over 30V. And does nothing below this.

Continued. Fit one of thes (see link) for e.g.. Be careful of polarity. Or it will do nothing. It will go low resistance and absorb any voltage above 30V and waste this as heat. Actually, better to use 4 in parallel for reliability, across the 24V battery cables/or battery terminals. Ideally they need a heat sink to screw into that is iolated from the chairs frame. As on a long downhill they will get hot. https://uk.farnell.com/solid-state/1n33 ... dp/1672889

[swalker]

Thanks, Burgerman.

That was exactly what I had figured the problem would be.

Empirical evidence shows that if I drive the wheelchair for a little over a mile on flat ground before riding the gondola up I can avoid the fault.

Of course, I would bet I am still damaging the batteries while descending, because I would expect the regeneration to be pretty significant...likely more than 30 volts.

Steve

[Burgerman]

Driving a mile takes about 1.5 to 3Ah out. And if that avoids the problem then you should probably remove around 4 to 5Ah before leaving home to be sure you dont get an over voltage situation on your batts. The only way to figure that out for sure would be a voltmeter. As you drive down your route.

But the Zenner Diodes would be better. They would clamp the voltage to a relatively safe level even if you went down everest. So if it were me I would use either a couple of 50 to 100W 15V ones on each battery. Or 4x 30V 50 to 100w Zenners ones across the whole 24V battery. Then you are safe to charge and go.

[Burgerman]

Watch carfully. For those that dont get regeneration.
These two wheels/motors are connected ONLY by wires. Nothing is turned on, no battery on board. Regeneration is very powerful.

Turn one, and the one it connected to in parallel is turned too. Because the one i turn generates power that drives the other one.

http://www.wheelchairdriver.com/gopro/m ... ration.mp4

In a powerchair, as you go downhill, every time you decelerate (slow down), the chairs momentum drives its motors that feed the power into the controller. Which has no option but to sent this to the battery. And it can be quite a chunk of power in a short pulse as you slow. The problem arises when your battery is quite full. And you decend a hill... Then its not just a short pulse. And it overcharges the battery and voltages rise substantially. And battery damage and if done hard enough errors and shutdowns. This happens as you suddenly decelerate and a pulse f energy hits the battery. But no errors.

But if you live at the top of a hill, bigger problems!

[Jay_x]

where are you taking a gondola up a mountain and then riding down? that sounds awesome!

[swalker]

It is awesome!

I live at the Vail ski area in the Colorado mountains. There are two gondolas I can ride to the top. I can ride a variety of trails down to the bottom.

There are many mountain biking trails that I used to ride in my pre wheelchair days, but those are not suitable for a wheelchair.

It is great to watch all the mountain bikers making their way down as I ride the gondola up.

Steve

[slomobile]

I assume the PM already has some clamp diodes and this extreme downhill is just exceeding their capacity to dissipate energy.
Additional clamp diodes on the battery protect the logic circuits and voltage regulators in the PM,
but the high regen voltage is still passing through the output devices in the PM before heading to the additional clamping diodes and battery.

Do we know what devices are used in Rnet 120A outputs, and what voltage they can handle? Even if the devices themselves can tolerate higher voltage, it might heat soak the PM cooling fins and lead to excess temperature alarm.

Would it make any sense to diode clamp the motor wires instead?

[Burgerman]

but the high regen voltage is still passing through the output devices in the PM before heading to the additional clamping diodes and battery.

Its designed to do that.

There are non to stop anything as far as I know. It just throws an error at 35V. And if you measure regen voltage as you release the JS going as speed it reaches around 32V for an instant. But you need a fast voltmeter to see its peaks. Mine reads peak/average/low/ as well as the instantanious readout. And is high frequency.

But you dont really want anything over 30V getting to the battery. So just add some heavier zenners across the pack.

[ex-Gooserider]

Agreed w/ the solution of adding zener's, but I'd be sure to put a fuse in series with them... One of the failure modes of Zeners is to go short circuit, which is likely to at best shut you down, and at worst cause much smoke and exciting flames... This was an issue that Brit bikes w/ electrics by Lucas (aka the "Prince of Darkness" and the alleged reason the Brits drink warm (Lucas made refrigerators)) were notorious for.... They used a Zener for voltage regulation and it was prone to failing short and shutting down lights and power w/o warning - usually at night entering a curve at speed....

I'd also add a current limiting resistor to avoid any chance of exceeding the Zener's rating.

ex-Gooserider

[Burgerman]

Lucas made fridges?

[greybeard]

and the alleged reason the Brits drink warm (Lucas made refrigerators).

ex-Gooserider

Ha! Brits drink at the perfect temperature of around 54 Fahrenheit which actually allows us to taste the perfection of the stuff and not suffer "brain freeze" with every gulp.

[Burgerman]

When I was in the US looking for I was told they had "both" kinds by the serving wench. Bud and bud light... Neither of which is . Just pretty poor attempts at lager.

A bit like the bar in the movie blues brothers. Where the owner said when asked what type of music do you have here? She replied we have both kinds. Country AND western...

My local pub and most others, have at least 4 real lagers, and then around 5 or 6 "beers" and real ales, guest brews, and 101 other options like guinness, brown ale, pale ales, bitters, milds, and many many others. I was amazed at how few of these things that we take for granted here are missing completely in the US. Although that was 30 years ago. So things may now have changed.

[ex-Gooserider]

Lucas Electrics had a really horrible reputation - supposedly their less than ideal design was essentially forced on the British auto and bike industry by gov't rules requiring the use of UK produced parts instead of the better systems from Germany (Bosch / Marrelli) or the Japanese.... There are at least some that say the electrical issues and the resulting reputation damage were a factor in the general demise of the British motor industry...

At any rate the saying about Lucas making refrigerators was one of the many rude jokes about their electrics - whether there was any truth to it or not isn't really relevant.

BM, I agree with you about the swill put out by Buttwiper, however most places in the US now offer a far wider range of choices, though many may be cans or bottles rather than draft.... Any decent bar or restaurant will have at least a half dozen choices including one or two darker brews. If you go into a store of any size that sells you will see a HUGE number of choices, many will have over 100 brands / flavors. We have had a huge 'Craft Brewing' industry develop over the last few years and most have started selling cans in addition to 'brew-pubs' that combine micro-brewery and restaurant... That said I wish there were more stouts and porters instead of an endless stream of IPA variants... (I prefer that hasn't been run through a horse before serving.... )

ex-Gooserider

[Burgerman]

Cans are for soft drinks, or junk etc.
Bottles are a bit better, but even "draft" s that use C02 on nitrogen are all the equivelent of going to macdonalds for a steak.

You see all these bar pumps with the long handles, they are for real s, of all kinds. They are actual pumps, takes a fit barmaid toy pull one. And theres a lot of bottles, and co2 powered lager and other s that are looked down on by purists too.

Have a look here.
Quick image searck
https://www.google.com/search?q=uk+pub+ ... irefox-b-d

[greybeard]

Proper only comes in wooden barrels that need careful handling. They are bloody heavy. Easy enough to move around once you get the knack but it needs skill not strength to lift them on to the still for tapping and spiling. Those were the days!