Range Discrepancy?

[Scooterman]

Hi, why is such a discrepancy between theoretical range and maximum potential range? It's a bit confusing how they've worded it. Taking the lower figure of 22 miles doesn't sound very far? I weigh less than the standard 100kg, but against that run with slightly softer tyre pressures, it's slightly quicker than 8mph (9.3mph), plus there obviously hills.

There's a nice local town (windsor) I used to regularly visit in car which is 11-12 miles away. I've never risked it on the scooter, and wouldn't especially now as the batteries are about 18mths old and had a lot of use. But I was wondering whether I would get there and back with a new set of leads without too deeply discharging them and shortening their life cycles?

NB: it's an S700

[Burgerman]

In a word. Amps. The following mostly applies to chairs, rather than scooters at least the turning bit!

Drive at 3mph and it uses 8A. Drive at 6mph and it uses 16A (for half the time) so range/distance covered all equal right? But the battery itself is SMALLER in Ah when you take 16 Amps from it rather than 8. So range at higher speed is maybe 30% less.

Also... If you accelerate hard, climb a street ramp, or zero turn, you may take 100 to 200A from the battery. 10 to 20x more than driving in a straight line. So its easily possible to get a red battery light in 40 mins of turning regularly. This happens to me when leaf blowing around the drive and garden, and working in the garden with the strimmer for e.g. Because every zero turn, and theres maybe hundreds of them in 30 mins, sucks 150A from the battery for a second or two. When you do this that is pulling power out at over 2C or closer to the 30 minute rate. See chart. Motor LOAD makes all the difference.

Look at this CAREFULLY.
Drive or accelerate fast, or spend some time vaccuuming your house, and you are discharging your lead bricks at the 2 hour rate or higher. See how that battery shrinks.

And then theres another problem. The battery voltage isnt related to state of charge. It drops, or is depressed considerably if you take out high currents for a while, say a hill, lots of turning indoors cleaning or cooking, etc. So that now your battery has shrunk, AND the voltage is lower than the actual state of charge says it would be, if you were to wait 12 to 16 hours or so for it to recover. So the chairs electronics see the voltage drop below 18V and reduces power to be sure to 'keep alive' and maintain control. So range drops even more. Since it thinks your shrunken battery is also now dead before it is...

Another reason the tennis court test doesent work is that it presumes a 5 hour rate. LOOK AT CHART! But even if not doing much turning/hills etc then you can easily use up a battery in TWO hours. Lets say you get a real 10 to 12 miles range. And are in a 6 mph slow chair. 6MPH X 2 HOURS is 12 MILES... So compare the 2 hour and the 5 hour battery size on the chart above... Is it any surprise that the ISO test is a joke?

[foghornleghorn]

Hi, why is such a discrepancy between theoretical range and maximum potential range?

The test just exists so you can compare two wheelchairs and hopefully tell which will go further. It has no true comparison to real life use.

Theoretical range is with a 100kg user on smooth concrete with correct tyre pressures and no obstacles or weather taken into account but with a bit of steering and stop/starting.

Maximum potential range is with a 25kg child driving it on smooth concrete with the tyres inflated to bursting point, no obstacles, no steering, no stopping and starting, no lights/indicators, and a following wind.

[woodygb]

But I was wondering whether I would get there and back with a new set of leads without too deeply discharging them and shortening their life cycles?

Both of the erroneously calculated ranges that you have quoted assume 100% Depth Of Discharge.

Hi, why is such a discrepancy between theoretical range and maximum potential range?

Because they have used the WHEELCHAIR ISO 7176-part 4 distance calculation for the theoretical calc and your Scooter is not a WHEELCHAIR.

[woodygb]

NOTE:- That manufacturers of mobility wheelchairs and scooters are ... I believe ...obligated to quote the ISO 7176-part 4 distance.

In general your scooter will be more efficient than a wheelchair over the same route / distance due mostly to the steering being done mechanically .

[Burgerman]

In practice the easiest way to tell the COMPARATIVE range is just to compare 4 things.

Battery size.
Speed.
Weight.
Use!

All else being equal, then this is what counts. There may be some minor efficiency differences between motors but its just lost in the noise. Different brands and different makes of chairs/controllers etc has practically no affect on real world range.

Battery size.
2x the Ah will take you around 3x as far. Because of Peukert. So AVOID SMALL BATTERIES.

Speed.
A chair that is 4MPH will give approx twice the range of one that is 8MPH all else being equal.

Weight.
A light chair, and a light user will have MUCH better range. An all up weight of double, gives HALF the range. This really matters. A heavy chair may be 190KG without the user. And a light one may be 100KG... And a light user may be 45KG. A heavy user may be 130KG. Remember, double the weight, LESS THAN half the range. (Because Peukert...)

Worst case with BIG 70Ah battery is: 8mph chair, 130KG user, 190KG chair, and get 4 to 6 miles real world range.
Same chair, same route, without the heavy seating options so 130KG, and a 50KG user, you will get 16 miles range at least.
Same light chair with 50KG user 6MPH motors and get 25 miles.

USAGE
Straight lines on level surfaces, get huge range.
Indoor, along road edges with lateral drainage camber, on hills or in shops, with carpets and lots of turning, get less than 1/4 of the above huge range...

Woody: Both of the erroneously calculated ranges that you have quoted assume 100% Depth Of Discharge.

Which isnt possible anyway even if you try. Unless you do so over 24 hours with a low current discharge like a small light bulb.

But I was wondering whether I would get there and back with a new set of leads without too deeply discharging them and shortening their life cycles?

Every discharge shortens the battery life. The greater you discharge them the more you damage them.

You get many 1000s of cycles at say 30% discharged.
2000 at 50%
You get 4 to 500 at 80% discharged.
And you get 20 to 30 at 100% discharged...

As you can see a slightly smaller battery will need replacement MUCH sooner! And as a battery ages it becomes smaller anyway! So the rot causes faster rot...

[Scooterman]

Hi, why is such a discrepancy between theoretical range and maximum potential range?

Because they have used the WHEELCHAIR ISO 7176-part 4 distance calculation for the theoretical calc and your Scooter is not a WHEELCHAIR.

Your reply is funny but so true! I didn't think of that

In general your scooter will be more efficient than a wheelchair over the same route / distance due mostly to the steering being done mechanically .

I agree, plus the scooter only has one motor. I reckon (gut instinct) a scooter has got to be 30% more efficient than a powerchair.

[Scooterman]

In practice the easiest way to tell the COMPARATIVE range is just to compare 4 things.

Battery size.
Speed.
Weight.
Use!

You get many 1000s of cycles at say 30% discharged.
2000 at 50%
You get 4 to 500 at 80% discharged.
And you get 20 to 30 at 100% discharged...

As you can see a slightly smaller battery will need replacement MUCH sooner! And as a battery ages it becomes smaller anyway! So the rot causes faster rot...

I never realised until you drove the point home about how important battery size is. It's easy to grasp 'weight' and 'use' from years of using a manual chair. I also found COG made a big difference to rolling and turning resistance. Probably more so in a manual chair though than a powerchair because a manual chair has small solid castors, mine has 4".

Within the three class categories for scooters, 1, 2, 3, they all use basically the same size batteries, controller (s-drive), and probably motors. The bodywork is the only think that is different. But they're probably all knocked out in injection moulded plastic factories in the far east.

So say for my little scooter: 38Ah batteries, 70A controller, 4mph, 65kg, it can be worked out mathematically by the industry. Yes I see what you are all saying.

Everyday is a school day

[Burgerman]

I agree, plus the scooter only has one motor. I reckon (gut instinct) a scooter has got to be 30% more efficient than a powerchair.

In a STRAIGHT LINE no matter one motor or two, if battery, speed, weight are equal, then range on a long run will be the same.

In a rear drive or front drive chair, in a situation where theres a transverse slope for draining water of the footpath, or road edge, the chair can be using up to THREE TIMES as much power to go in a straight line compared to a scooter, depending on CG, angle of slope etc. So 1/3rd the range. Turning left right, can need 10x more current, so 10x less range if you are cleaning the house for an hour or so before you start out...

Range depends totally on usage.

[Scooterman]

Battery size.
2x the Ah will take you around 3x as far. Because of Peukert. So AVOID SMALL BATTERIES.

Every discharge shortens the battery life. The greater you discharge them the more you damage them.

You get many 1000s of cycles at say 30% discharged.

As you can see a slightly smaller battery will need replacement MUCH sooner! And as a battery ages it becomes smaller anyway! So the rot causes faster rot...

I've been reading about Peukert (mainly applies to lead acid), and it's so true what you say, and all because Peukert is an exponential value.

And lead acid discharged by say 25% gives nearly as many cycles as lithium discharged by 75%. Although me saying that is not a fair comparison because lithium is giving you an extra 50% of usable charge. But as you mention on the main website, granny popping up to the co-op once a day on her scooter and charging it every night will get many cycles and hence good value from her leads.

[Scooterman]

Peukert’s Law must be the main reason why I noticed more difference than I would have imagined by going for lower Ah lead acid in my small scooter.

The original Sunrise Gel, were 35Ah.

I thought I'd go for a brand, so went for Sonnenschein 28Ah (they don't make 35Ah)

But I noticed more of a drop in performance than the 7Ah difference would ordinarily indicate.

[Burgerman]

You will. And because the average DOD is also higher, the smaller battery deteriorates fast, and so gets even smaller at an accelerated rate. And that makes things get much worse at an exponential rate. So that you are almost fully discharging the battery or whats left of it, in a very few miles and killing it. So in a very short time you have really bad range.

[Scooterman]

Re: Peukerts law there are some handy online calculators that are fun to play around with.

I've been inputing some values for MK 75Ah gels. And the calcs closely match MK spec sheet.

[woodygb]

viewtopic.php?t=923&p=11010#p11010

[Scooterman]

http://www.wheelchairdriver.com/board/viewtopic.php?t=923&p=11010#p11010

Thanks woody. I shall have a read of the thread tomorrow. I've genned up on too much battery technology and charging theory this weekend, my brain has turned to mush!

[Burgerman]

That was 7 years back. Many of us have learned a lot since then. Esp me. One reason I built this site!

[ex-Gooserider]

Going back to your question about going to the distant town... My guess is that you MIGHT be able to do a round trip, but at best you'd get home with badly discharged batteries, with consequent reduction in their lifespan...

OTOH if you haul a decent charger along, and are able to sit around for a few hours in town and charge before heading back, you wouldn't be doing anything to terrible to the batteries and not get out of the comfortable range...

Or do a Lithium conversion and not have to worry about it as much...

ex-Gooserider