Question for you tech experts

[John F]

A question came into my head this morning as I was cruising serenely along on my new Woosh.

As I understand it, my battery runs down in a certain way (can't remember exactly how but I've seen a graph somewhere). Therefore as my King Meter shows the first indicated drop at X miles, logically there might be a way of extrapolating (assuming constant drain as before X miles) to reasonably calculate the point at which the power falls to the point at which the range might be estimated?

 

[tillson]

It probably would be possible if you could guarantee that the miles which follow the point at which you are extrapolating from are identical to the miles already covered. For example, in an extreme case, the first ten miles may be on level ground with a tail wind. Say the meter displays its first indicated drop at this ten mile point. What if the next ten miles are all up a 25% gradient into wind? You are not going to achieve anything like ten miles.

The best policy is to get a feel for the range of your bike over varied terrain. After a short while you will develop an instinct for how far it's going to get you on any particular ride.

 

[John F]

I see your point. However my ride this morning was all on cycle paths around York, which is consistently flat, so my riding would be pretty consistent so the battery demand would be too I think.

I am getting more of a feel for the range. My longest ride so far was 39 miles between charges and at the end the battery was nearly flat (I was using max power setting all the time, which I now realise is overkill)

My confusion is the apparent quick change from an pretty full battery (even after 39 miles) to almost flat after not many more miles. This situation only occurred because I was inexperienced in battery matters, and that letting it get so low is a bad thing. I was rather taken aback and had to pedal home.

Wouldn't it be good if you could say I've got x miles left after the first indicated drop?

 

[tillson]

I'm not familiar with the Woosh but from what you describe, it sounds as if the battery meter is very non-linear. Have you completed a couple of battery conditioning runs (ie run battery from full charged to cut off). My Kalkhoff battery meter was non-linear when new, but after the conditioning cycles, it improved a great deal.

 

[Deleted member 4366]

It's not as simple as you think. The voltage goes down fairly steadily at first, but then starts to accellerate downwards. When the voltage is high, you get more power, so you can use up your battery at a faster rate. Any time that you draw power from the battery, the voltage drops a bit (voltage sag). The more power, the more it sags. Plus, it sags more as the battery becomes emptier. The meter symbols indicate battery voltage, which is why you see them dancing up and down depending on how much power you use.

After a few rides, you will know approximately how far you can go before each segment goes out, so you can get an idea of how much is remaining, but I can tell you that once more than half the segments are gone, you don't want to be too far from home unless it's flat or down-hill for the rest of your journey.

The best way to predict remaining battery is with a wattmeter that can show how many amp-hours you've used. The amp-hours is fairly fixed, so if you have a 10aH battery and you've used 6aH, you have 4aH remaining.

It's best not to run your battery empty if you can avoid it. The closer it is to fully charged, the more power you get because the voltage is higher, so 30% more power when full compared with nearly empty. Also, most problems with BMSs switching off happen when the battery is empty

 

[trex]

I think it's easier to use the King Meter odometer - reset the odometer after charging then assume you have 40 miles to empty.

 

[ghost]

Although I have only ever done 20+ miles on a charge once (22 miles I seem to recall) I was glad it was the middle of summer, had I attempted it in winter I don't think I would have made it.

I find that temperature has a huge effect on battery performance, certainly the speed of the bike and I suspect range too. To do what you say I guess it might be necessary to also monitor battery temperature to predict your 'range' perhaps.

In hot weather the bike flies and the motor howls loudly. At temps of 15c and below it operates slightly slower and quietly. Also I find the controller (or is it bms?) cuts power to the motor more readily in cold weather so requires more leg input uphill or selecting a lower assist level. I put all these down to reduced voltage although more adverse weather (headwinds etc.) in winter all add strain to the system I suppose.

Probably not the place for it but if someone could explain whats happening to e-bike systems when temps change it would be a great help. P.S. should be a sticky really as its relevant to everyone, especially as we enter winter time once again.

 

[Deleted member 4366]

This explains something:
The effect of temperature on rates of reaction

However, like everything, it's not as simple as that.

If you keep your battery in the house, it won't get so cold.
Once your're using it, it heats itself up, so it's temperature is different to the ambient temperature. I guess some installations insulate the cells better than others.

Personally, I've never noticed a loss of power or range in cold conditions, but most of my batteries are well insulated and are well specified. I guess that if your battery struggles a bit in the warm, when it's cold, the difference will be very noticeable. Perhaps a nice coat or muff for it will improve its performance.

 

[ghouluk]

this is interesting, i was about to post that the bh has this effect and its quite noticeable on range more than speed, however just as interest, i pulled the average temperature data for my area, and compared it to my ride data. when i put side by side same time rides, there is no noticeable difference.

I understand that this isn't an exactly accurate way of measurement, but i'd expect any trend to be noticeable.

my battery lives inside the house and the bike in the garage, so maybe its a case of i read it somewhere, and hence convinced myself

 

[John F]

Just been checking out the Woosh Predictor for the 20 miles ride I did yesterday. Interesting reading

For the first time I used the lowest power setting rather than the middle or top.

This is what the Predictor said:-

Commute from home to Riccall - steepest gradient 4.3% (NOTE this ride is mainly very flat)

return: 20 miles, inbound elevation: 69m
At 10mph: outbound consumption: 113WH, inbound consumption: 113WH, return trip: 226WH
At 15mph: outbound consumption: 134WH, inbound consumption: 134WH, return trip: 268WH


So with my 15amp battery giving 36v x 15amp = 540WH I have used 268/540 = 50% for 20 miles giving 40 miles total range at 15mph
or
226/540 = 42% for 20 miles giving 48 miles total range at 10mph

Given that I was using the lowest power, and trying to ride in an economical manner, this would seem to be less than expected especially as the power meter still indicated 100% ? I suspect the claimed range refers to when been ridden by jockies in Lycra (I am 95kg)

I do find the throttle useful though. On min power setting, and with little throttle, I found it fine for the occasional cruise at 12mph. I thought this might not draw too much power

Has anyone any views on this, particularly with regard to the selected power setting and it's effect on range?

Thanks for the advice

John F

 

[John F]

I'm not familiar with the Woosh but from what you describe, it sounds as if the battery meter is very non-linear. Have you completed a couple of battery conditioning runs (ie run battery from full charged to cut off). My Kalkhoff battery meter was non-linear when new, but after the conditioning cycles, it improved a great deal.

Yes I've done one full to empty ride (39 miles) It wasn't intentional.

 

[Deleted member 4366]

As I said before, the only way you can know how much battery you've used is with a wattmeter. Any interpretation from the battery meter is meaningless. You don't need to do any battery conditioning cycles as the meter has no intelligence. It's a simple voltmeter.

 

[tillson]

J

As I said before, the only way you can know how much battery you've used is with a wattmeter. Any interpretation from the battery meter is meaningless. You don't need to do any battery conditioning cycles as the meter has no intelligence. It's a simple voltmeter.

That's not entirely true. The Panasonic three light handlebar indicator splits the range into thirds with reasonable accuracy. Until a conditioning, full to cut-off, run has been done, it is very non-linear.

 

[Deleted member 4366]

J

That's not entirely true. The Panasonic three light handlebar indicator splits the range into thirds with reasonable accuracy. Until a conditioning, full to cut-off, run has been done, it is very non-linear.

John's bike is a Woosh.