Mobility scoter power measurements.

Well of couse it might be predominately up hill in one direction as well. Trying to work all of that out from normal usage seems hard to do. What you really need is some kind of standard usage course which is always the same, and I don't see any way to be absolutely sure you never get stranded on it, unless you keep a small reserve battery for the purpose. Brian

Hi Brian,

Yes, if I wanted to do real scientific tests / comparisons I would have to use the same weight rider over the exact same course in the same conditions (temperature can play a big part on battery efficiency) but this was more a 'can we draw any general conclusions' from any of those figures.

I am actually in the process of arranging emergency 'get you home' solutions and the first part was to re-wire the batter / motor looms with a common connector so that I *could* plug either battery directly onto the motor if all the electronics failed.

The next step will be to make up a remote pushbutton with a 12V relay that gives a more usable on/off control (either to the rider or support person) and possibly via a independent / generic speed controller and remote handset.

With a spare tyre / tube (the wheels are already treated with Punctureseal), a small hand pump and the spanner that fits both the wheel retaining bolt and the split-rim nuts, that should cover every likely failure other than the motor / transaxle. ;-)

I was thinking about an additional battery but once we have a reasonable idea about the worst-case range, we shouldn't really need it (and lifting just one of the existing batteries is enough!). I'm not sure if there is enough space to fit any battery that would be big enough to guarantee we could get home or to a place where we could get rescued from, but I'll think about that one. ;-)

Cheers, T i m

I don't know what your meter says about its measurements, but in general an Ah figure is the number of amps integrated over the time that it ran for. If you keep the meter on for longer the Ah figure won't increase, but it won't decrease either (it'll keep adding 0 amps for the extra hours). Same goes if some minimal load was on (0.1amps for N hours won't make much difference)

If this thing was powered off a battery with a flat voltage curve (so 1 amp with a fresh battery is the same energy as 1 amp with a nearly flat battery) it would tell you what size of battery you needed. The Wh figure will tell you more accurately about energy. Either way your draw isn't constant so this accuracy doesn't help much.

That would tell you what you were losing in charging too.

Peak amps tells you what max battery current you need (CCA on a lead acid, peak current on a lithium ion). If you measure the voltage sag at the motor controller it'll give an idea of losses in cabling and due to battery internal resistance.

If you watt-count the power that went into the battery, and record what comes out, you can determine how much capacity there is left. That's what laptops do. Some of the watt-counter meters I pointed you at will do that - maybe yours does.

Theo

Careful, TNP will have you adding a Raspberry Pi running Linux to do all the battery management and reporting if you want the Rolls Royce of systems. Plus a SIM to call you up if it thinks she might have trouble on the way.

Or perhaps a little I/C engine and generator for diversity :-)

On Tue, 22 Sep 2020 20:59:03 +0100, newshound snipped-for-privacy@stevejqr.plus.com> wrote: <snip>

;-)

Funnily though, an issue that has come up with both the Mrs and my Mum on the scooter is simultaneous use of the (thumb) throttle and (hand) brake. The power of the scooter can easily overcome the (pressure they can put on the) brake and there is no interlock on it. It would be easy to fit one that 'cuts' the power when the brake is applied but the problem is when they release the brake again and the throttle is still applied to any degree. ;-(

It's possible that if I inhibited it using the 'charging inhibit' pin that may already require the resetting of the throttle before it would allow you to re-apply it but if it doesn't, I'd need to ensure that was the case via some sort of 'monitor' circuitry. An Arduino would probably be ideal and I have the truth table for the throttle function so it should be easy to interface.

I could also fit a remote inhibit at the same time. ;-)

Yeah, one of those suitcase generators on a trailer ;-)

Some have a 12V battery charging output and even on 12V the scooter nearly went though our fence when I was testing the motor supply polarity to drive connection from a small battery the other day so that would be fine. ;-)

(We also discovered how 'strong' the braking was from the regen function the other day when two of us tried to push it. Turn off the 'ignition' and then it was much better but you are still spinning the motor). When one of the (lighter) youngsters dropped the power off quickly when going downhill fast on a loose surface I saw one of the back wheels lock up (It has a diff so the other one could have been spinning). ;-)

Cheers, T i m

I believe that's the case here.

Oh, so I can take the Ah value as a straight (average) amps drawn, irrespective of time, even if idle.

Understood.

Ok.

Ok. OOI I had a couple of those Lidl clip-on LED bar scale stepped 'voltmeters' taped to the back of the scooter yesterday and it was pretty predictable when watching them when walking behind Mum as she went up hills and over humps etc. You would see the voltage be depressed and then they would bounce back again (pretty much together) as soon as the load came off. [1]

True, other than I'm guessing there would be charging losses in any case? In the end I just put it on charge as I'd need to make up some adaptor connectors as the connectors on there are gendered so 'Source' would have to go to the charger and not the battery. [2]

Yeah, I was quite pleased to see it only at 60A. The connectors I used are XT90's so should carry a continuous current of 90A (tested up to about 200 for 10s before failing) with no issues. An average of around

I can't quite get to the motor (it has a short cable) but could certainly get close and could measure the drops on both +ve and -Ve. Not sure how that would work ITRW being a PWM at all but full speed (potentially)? I do have one DMM with a peak hold so that might be of use on the 'return' (non switched) side of the power loom?

I did look at some but I think discounted the full bi-directional ones as they only had a max current of 30A or so? ;-(

I was also hoping that my understanding of how the built-in 'battery meter' works is that it does monitor the energy in though the charging pin on the speed controller and what it sees sent out to the motor and drives the battery meter accordingly?

ATM, it's obviously way out as after 7 miles it should have been showing at least 75% charge but it was still 100%. ;-)

I think this is what happens when you charge the batteries off the scooter, as I have been doing recently.

Cheers, T i m

The usual failure point with little electric buggies of any type is the batteries. Best way to minimise that is a) monitor battery health b) carry a charger

NT

Lead acids are about 75% energy efficient

NT

Hence why I have re-equipped all the dissimilar power connectors that were physically keyed with a common connector that is visually keyed so that I have more flexibility.

eg, If it came to it I could connect just one battery directly to the motor to enable me to get at least close to a vehicle accessible road.f

Outside of general capacity, how could I 'monitor' for a catastrophic failure, broken internal inter-cell connector etc?

And generator and camping gear I'm guessing? ;-)

On our typical dog walking route, we are nearly as far away from mains power as we are home itself. ;-(

Given the batteries are (currently) capable of doing the medium loop (5m) twice on one charge, as long as we ensure they are fully charged before we leave, we should be ok from a battery 'capacity' pov.

According to the user manual, from new it would have had a maximum range of 25 miles:

'Maximum driving distance (cruising range) is based on an ambient temperature of 20°C, a 100kg driver and a battery which has reached optimum capacity, a constant driving speed of 6mph / 9kph with 70% battery power discharged.'

Cheers, T i m

c) walk more often

In this case ... at 90 and not driving most of her life (although she passed her test at 50 first time and did drive a bit), and running the house and working / shopping locally (on foot) Mum has probably walked more than many, over her life.

She can still walk but because of bunions and other (mostly) physical issues she can't walk far, certainly not ~5 miles so *those* trips out she does on the scooter (and with us).

I got a Whatsapp message from her to our family group earlier notifying us she was going (walking ~1/4 mile round trip) to her doctors surgery to get her flu jab (just so we knew where she was).

Before lockdown she would regularly walk to the supermarket and come back with the 2/4 wheel trolley we bought her loaded to the gunnels (and often stuff on top and carrying more by hand)!

Cheers, T i m

in most cases that won't work, both will be dead.

monitoring for those is both patently obvious and pointless. monitoring capacity might be more sensible

If you want, I can't see much point though, like much you post.

NT

Maybe in your cases but in mine, when I know the range, it would

'Monitor' with the intent of early warning of an internal failure is patently obvious how? Yes it would be pretty obvious it had happened when it did but that's not my understanding of the purpose of 'monitoring'?

I know.

Would be more useful, but again, only to predict the effective range, not protect against any likely *unexpected* failure.

Hence why I was offering alternative means of powering / controlling the scooter as an emergency 'get you home' solution.

No, we wouldn't want, but that would be the requirement if it was late and we had to wait for the battery's to gain sufficient charge to get us to safety. The suggestion of the use of 'a charger' was yours not mine.

Then why bother (yet again) replying to it, especially when it's obvious you didn't really understand it and offered nothing practical?

Are we back to the swamp cooler thing? Do I need to get John to explain it all to you?

Cheers, T i m

no in all cases the most common failure is batteries flat.

The point of it is to protect against people getting stranded on buggies. It turns the unexpected into the foreseen.

good

I'm glad you figured that last bit

I offered the one most used solution but nvm

If he stops being lazy & learns the physics then I won't object.

NT