Batter power fall-off?

[allen-uk]

Probably a schoolboy error coming up, but never mind.

When a battery gets low, or rather lower than full charge, does the power get perceptibly less, or does it maintain full power all the way down to dead?

It might just be another illusion, but running mine down as far as I dare before its first full charge, it seems that at least on throttle (which I use due to one-leggedness) there is a bit less oomph than previously.


A.

 

[Mussels]

Depends on the bike, my last one seemed to keep the power up right to the end but the current one has a noticable power drop half way.

 

[flecc]

Most do suffer some loss of power as the battery content reduces, but the rate at whioch that happens varies by bike specification. Those bikes which are speed regulated by the battery voltage rather than be controller limiting suffer this the most.

I have one like this that flies at 18 mph with battery warm off the charger but limps along at 14.5 mph on the last 20% of charge.
.

 

[allen-uk]

When I first rode the bike a couple of weeks ago, I went to a few of my local hills, some which had given me trouble on my unpowered bike in the past, and others which I had NEVER ridden up without stopping and walking instead.

And I was amazed that I could get up all of them - not sailing up, but with some human effort plus the motor, I got up them.

So, today, still not having charged the battery (down to 2 lights now), I went out and did the hills again. Or tried to. I JUST about made it up the worst ones, but the old familiar heart-thumping symptoms were back, and my legs felt weak.

So is this just the way Wisper batteries and motors perform? I had thought (wishfully, maybe) that the battery was like a petrol tank, and just went from full to nearly empty without any change to the performance of the engine. But it seems that there is a large drop in torque as it gets lower.

Which, if true, puts a different interpretation on the 'range' - I knew I wouldn't get anything LIKE the maximum, being around 120kg, but I thought that for the limited range that I WOULD get (say 15 miles), I wouldn't lose out on battery POWER.

Two other possible factors: one, it's very hot and sultry in London today, but I don't really think that's making this level of difference. Two, unlike the first test ride, this time I'm using the gears, to give my legs a break (viz. on the first ride I was in 7th all the time, and this time I dropped down to 3 or 4 as I went up the hill). Still pushing my legs round as hard, if not harder, and certainly pushing them round FASTER than before. Does this make any difference?

Why no charge yet? Well, Steve at Wisper recommended that I run it down as far as I dared (at least to 2 lights, if not 1) and then give it a 'conditioning' charge. Which I shall be doing overnight, so them thar hills again tomorrow.


Allen. (Wisper 905 se)

 

[eddieo]

battery's are nothing like a fossil fuel power source. Once you have gone through the pain in the ass conditioning cycles you will probably charge regularly and have full power available most of the time

I think you really need to run a battery down until wheel stops x 2

It is a real pain trying to get those last two lights out. just ride around locally on throttle till nearly flat. I then tilt the bike and tape open the throttle and leave run till flat.

once this is done you can begin to enjoy your bike

 

[rog_london]

I have a Wisper 905 SE (2008 model). The performance does drop off initially but from about one quarter down to three quarters discharged there's little change. As you get towards the end though you'll definitely notice it.

Most batteries lose a bit as they discharge. They also generally do better in warm weather. As Flecc says, how much you may notice depends on how smart the controller is, as some compensate for the drop in battery voltage better than others.

Many have three lights on the handlebar to indicate roughly how much is left. These are just voltage-triggered, in that the green light goes out after about one quarter discharge and the yellow one goes out somewhere below half way discharged. If the red one goes out you won't be going anywhere under power as it has shut off completely.

You may notice that the green and yellow lights go out right away if you're climbing a hill - that's because the motor is hitting the battery hard and its voltage drops accordingly. Those lights only give you any idea at all when you're drawing no power.

Those with several lights on the battery itself tend to be more accurate as they monitor the total drain, though some are better than others and that system can drift off over time as most don't re-sync when you recharge, only when the battery is completely empty, which most of us prefer to avoid.

Rog.

 

[Mussels]

So is this just the way Wisper batteries and motors perform? I had thought (wishfully, maybe) that the battery was like a petrol tank, and just went from full to nearly empty without any change to the performance of the engine. But it seems that there is a large drop in torque as it gets lower.

This may be a case of ignorance is bliss. When I had my 905 the motor drew less power than my 906 and I wouldn't notice any power drop until the battery cut out, that was a couple of years ago so your 905 might be quite different.
With my current 906 the voltage drop is quite noticable and slightly annoying but it doesn't drop below the old 905 performance, so although the bike is still faster the noticable drop in power makes me feel like something is missing. I could rectify this by turning the power setting down but there's no way I'm doing that.
There is the possibility that the battery has changed in the last two years but Wisper have said the cells are the same and I haven't noticed a difference in range.

 

[z0mb13e]

The power loss on my 905 is quite noticeable even on a shortish (16 mile run).

I have recently notice that the 'power lights' (on the handle bars) drops to red much more quickly than it used to. The first leg of my commute all is well until I get to the big hill climbing back up into bmth. The lights drop to red as I am powering up the hill and have struggled to recover as they used to. The bike is almost a year old. I know the lights aren't a good indicator as they relate to the battery voltage more than anything but it is all interrelated P=I*V etc)

Anyhoo - I tried a reconditioning a few days ago, hooked the bike up on a shelf in the garage and taped the throttle open and it was still going after about 6 hours, after the usual run to and from work. This week the lights have been behaving much more like they did when I first got the bike. Power drop off is less noticeable however I am experiencing the power brown outs that I used to see when the bike was new (particularly going up a hill, the sudden lurch forward as the motor cuts out and then it kicks back in again after a brief pause).

So after another conditioning the battery seems to be giving as much power as ever.

But overall my 905 does slow down, particularly in pedelec mode after about 12 miles or so depending on the conditions. The throttle usually continues to keep the bike at 15mph with input from me.

This fits with what I know about batteries (and I'm no expert) as the battery discharges the voltage drops, internal resistance increases and the power output decreases.

 

[Alex728]

I ride from Ipswich to my friends house at the Norfolk/Suffolk border area and would agree that past Stowmarket (which is about 12 miles) the power drops off slightly (although there is plenty there by the time I've reached the journeys end at 26 miles).

 

[allen-uk]

Thanks for the replies.

Well, for now I'm going to put it down to my great weight (120kg+) and hope that as that comes down and as I get fitter, I'll notice the power fall-off less.

But it has been a bit of an eyeopener to find that my projected 10 mile round trip to the local hospital will be fine on the out-run, but I'd better just watch out for big hills when I'm nearing home!

Allen.

 

[eddieo]

You are worrying about nothing, the bikes performance is stronger then that.....you should notice no change on a 10-20 mile trip. I am 16-17 stone and a few of us on here are heavy. But you are right your legs do get stronger so you learn to assist more.

 

[allen-uk]

I think you really need to run a battery down until wheel stops x 2

It is a real pain trying to get those last two lights out.

Too right eddieo!

Two lights this morning, but it felt fine, so I went out for 7 or 8 miles up all the usual hills - hardish work, but they usually are, and require a fair amount of leg input.

Still two sodding lights when I got back, so I rode around locally for 20 mins - I live in a series of cul-de-sacs joined by a slight hill (very slight - more of a long slope), and went round and round just on throttle (except for the slope, where I HAD to pedal, as otherwise I'd have fallen off).

Anyway, round and sodding round, to the point where even on the flat the throttle was scarcely moving me, and on that slope, not at all - so I assumed I'd at least got it down to one light, if not NONE.

Stopped, checked battery lights. Still TWO!

How (in-)accurate are the battery indicator lights? This battery is most definitely an ex-battery at the moment, whatever the dopey lights say, so I'm going to have to charge it overnight, however many lights are on.

I'll let you know further developments.


Allen.