Mistral Cut Out ?

[SEATALTEA]

A quick question, I remain a committed Mistral commuter clocking up 105 miles during my 7 day working tour but encountered a hiccup yesterday.

My riding style has changed somewhat as my fitness has increased, the bike is fitted with SPDs now and on the flat I am using the electricity to quickly get me up to speed but then often riding with the assistance off. I'll roll the throttle on when climbing slight inclines to maintain speed and only turn 'S' mode on when the hill gets really steep.

The last 1/4 mile before I arrive at work is a short but steep hill and on the flat before I begin to climb I'll belt along in 6th and quickly switch to 1st when the hill begins, switch to 'S' and pedal like fury. I can climb without stopping normally but yesterday had to come to a complete halt due to traffic.

The bike was in 'S', 1st and I rolled on the throttle when I set off again on this steep hill.

Almost immediately the battery light died, the assistance stopped and I had to pedal away on a hill like this / feeling the full weight of the bike.

At the top when it was level the battery lights came back on along with the assistance, it's been fine since.

So my quick questions is.........did the bike cut out because it had 'overloaded' ?

 

[flecc]

Probably the high current drain caused the voltage to drop so far that the safety cut out operated. This is the most likely event on lithium ion batteries.

The earlier battery troubles that you may have read of on very high powered bikes like the eZee Torq usually first showed their deterioration in this way.

It doesn't mean your battery is necessarily failing though, just that circumstance was too much for the cell discharge capability.
.

 

[SEATALTEA]

Thanks flecc I had guessed that something like that was the case, your knowledge is invaluable.

 

[rooel]

I think flecc's suggestion is probably correct, but do check that all connections are secure. Even the three pin plug which goes into the battery can sometimes be slightly dislodged, and vibration will make and break the connection.

However it is as flecc says more likely to be severe voltage drop due to temporary high demand.

 

[Danny-K]

I've been away all week - and what a lot of new threads to catch up on.

I experienced a similar early cut-out, going from a full set of lights to no power in an instant which I posted on here. As Flecc's answer here is along the same lines as given to me, it does lend credence to those who cite this phenomenon of lithium battery behaviour as a reason for preferring NiMh cell batteries which will always have some power on offer, however small, whereas in the same circumstances the lithium battery will shut-up shop and go home without you. (Think it was the Brompton Sparc people's site I was reading, who offer the bike with NiMh batteries for this very reason).

We were enjoying a bit of an 'Indian summer' before this recent cold spell, so I would suggest that very cold weather might be a time to be more circumspect with sudden loads on the lithium batteries, as like you, the problem has not reoccurred on my bike either.

 

[Blew it]

It's the capacity!

This problem with Lithiums was quickly discovered by those of us who were early adopters of Li Ping's LiFePO4 batteries. The modest amps demand made by British bikes were easily met, but our American cousins were making enormous demands on his batteries, way above the 1 to 1.5C discharge rate he advised.

The answer of course was, to purchase a Ping battery, not based on the range required, but its capacity. The higher the capacity, the better it's ability to deliver under continous high demand without voltage sag.

Wisper made several upgrades in battery capacity during the 905's evolution. We might like to think that was to increase it's range, but I suspect it was more likely intended to prevent voltage sag during peak loads. The fact that the range is also increased being an added advantage.

I'm confidant that "DannyK"'s Salisbury, fitted with a Ping LiFePO4 battery, would never cut out under continous maximum demand. Unfortunately, Li Ping has been unable to source further supplies of the 5 ah cells he used in the construction of the small but high energy density packs that myself and other forum members are using to great effect.

Finally, lets not lose sight of the progress that has been made in battery technology in the past 12 months. As I type this, I can see the Wisper 905 parked in the dining room ( it's a great conversation piece). That tiny battery will propell that bike for THIRTY FIVE MILES. Have you any idea how much lead acid you would need for the same mileage!. Put it this way, you wouldn't want to run over your foot with it!!.

All the best and g'night

Bob

 

[zammo]

can anything be done about the cut-out?

Probably the high current drain caused the voltage to drop so far that the safety cut out operated. This is the most likely event on lithium ion batteries.

That seems like the cause for my cut-out problems. I have an original 2-year old Ezee Sprint (7-speed) and the cut-out has started happening often. Thankfully it doesn't require a full turn of the key to "reset" it after cutting out. I just turn the throttle again (usually turn the throttle more slowly the second time) and the motor picks up again. The bike isn't ever under sever load: flat area, relatively light rider, and I always pedal as well as using the motor.

Other that the cut-out bike is fine. I have felt that the cut-out happens less when I 'condition' the battery by running it nearly empty before re-charging rather than charging it every night regardless of how empty it is, but it could be my imagination.

Is there anything that can be done about the cut-out? A sneaky resistor somewhere for example? or is a new battery the only option?

 

[UrbanPuma]

Is there anything that can be done about the cut-out? A sneaky resistor somewhere for example? or is a new battery the only option?

You could try altering the way you ride the bike. This can be acheived by riding in a higher gear and putting in more legwork on hills, which eases the pressure on the motor.

 

[flecc]

Is there anything that can be done about the cut-out? A sneaky resistor somewhere for example? or is a new battery the only option?

A new battery is the only realistic option other than hardly using the power.
.

 

[zammo]

A new battery is the only realistic option other than hardly using the power.

Thanks. That's what I assumed. My commute is completely flat with no hills to climb so it's not a question of overloading and I'm tip-toeing around the problem already so cannot use the motor even less. I find myself putting in a lot of effort to stop the cut-out occurring which - given that the bike is quite heavy to ride as 'normally' - is tiresome and defeats the whole purpose.

Time to start saving for a new battery. Thanks again for confirming the diagnosis.

 

[flecc]

In that case it's definitely a new battery Zammo. The good thing is that today's batteries are very much better.
.

 

[Rod Tibbs]

I have been following this thread with interest because like Seatalthea I have a Mistral. It is now five months old and has given perfect service. The last time I was out on it I was using Pedelec S Mode plus a bit of throttle override when it suddenly felt as if the chain was running on the side of a cog. I can only describe it as a vibration. Immediately the motor lost power, I hopped off to see what was wrong, suspecting a twig caught up in the frame and rubbing on the side of the tyre or something, but all seemed well. It restarted OK but repeated the situation a little further into the ride.

I must confess I did not look at the battery LED's because a battery problem was the last thing on my mind.

Now that I have read the correspondence I am coming round to feeling it may be the battery cutting out. It happened once more on that ride, and my son reported a similar occurrence when he borrowed the bike yesterday.

I have one month before my battery guarantee runs out. Should I think in terms of claiming on this?

Advice would be much appreciated.

Rod

 

[flecc]

I have one month before my battery guarantee runs out. Should I think in terms of claiming on this?

Advice would be much appreciated.

Rod

If you run it and confirm it seems to be the battery through the LED behaviour Rod, it's definitely worth claiming. In any event the bike shouldn't be doing this whatever the cause, so a warranty claim is in order.
.

 

[Rod Tibbs]

Thanks for that Flecc. I will try and get a another run or two on it as soon as I can in order to analyse the power consumption more closely and then I will take your advice and make a claim.

Rod