Battery conditioning

[NRG]

Not as I understand it, it works in the same manner as other systems, the difference being the BMS can go into a sleep mode thus saving the battery from a slow discharge if not used for a while. Most other systems will continue to draw a small amount of power from the battery.

As our batteries are relatively small in capacity compared to cars top and tailing at 20% is not pratical as range will be severly reduced...but as mentioned in another thread the new Kalkhoff 18Ah battery is probably large enough for you to be able to have some sort of top n tailing of the charge / discharge to increase life alas it would have to be done manually.

 

[flecc]

does the hardware do this already with the Panasonic system? ie when charging, the 5 lights light up and then go out = 80% charge (like the Toyota system), or do I need to turn it off manually at 4 lights or 5 lights before they go out to equal 80% charge?

On the Panasonic 10 Ah battery, if you turn off as the fifth LED lights when charging, the charge will be at roughly 80% and you'll avoid the high charge extreme that stresses. You'll also have to avoid discharging below the lower 15 to 20% of charge to get the most benefit, so this means you can only use about 60% of your full range.

So test on one of your typical routes to find your maximum range from a full charge to the fast flashing LED stage, then use 60% of that as your maximum mileage on a bike odometer before recharging to the fifth LED coming on. All a bit fiddly though, unless you rig up an optical sensor circuit to sound an alarm, or better still, switch off the charger as the fifth LED lights.
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[tillson]

If you ride a repetitive and regular route, such a commuter to and from work, you can use a cheap time clock in conjunction with the charger and keep the battery charge level between 20 and 80% quite easily and without any additional fuss. Of course, if you have a particularly long commute, or are unable to re-charge at work, then this won’t be possible.

I’ve been doing this for a few months and battery deterioration seems to have stabilised. However, it’s a bit too early to tell for sure yet. Maybe after about a year of testing this charging regime it will be possible to say if it’s worthwhile.

 

[flecc]

The de-stressing by avoiding the charge extremes won't necessarily achieve the best battery life though, since there is one remaining life-affecting factor, the discharge rate in use.

Unfortunately the complexity of the Panasonic system means the user affects this in three interactive ways. First, the pedal pressure on the torque sensor affects the power delivered and therefore the discharge rate. Second, the cadence used if below the power phase down point maximises the discharge rate relative to the other conditions. Third, the power level selection as "High" increases the discharge rate.

Obviously high pedal pressure at a low cadence with "High" power selected gives the battery a comparatively rough time.
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[tillson]

The de-stressing by avoiding the charge extremes won't necessarily achieve the best battery life though, since there is one remaining life-affecting factor, the discharge rate in use.

Unfortunately the complexity of the Panasonic system means the user affects this in three interactive ways. First, the pedal pressure on the torque sensor affects the power delivered and therefore the discharge rate. Second, the cadence used if below the power phase down point maximises the discharge rate relative to the other conditions. Third, the power level selection as "High" increases the discharge rate.

Obviously high pedal pressure at a low cadence with "High" power selected gives the battery a comparatively rough time.
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It would appear that laws of Physics / Nature just don't want mankind to be able to store electricity.

 

[10mph]

First, the pedal pressure on the torque sensor affects the power delivered and therefore the discharge rate. Second, the cadence used if below the power phase down point maximises the discharge rate relative to the other conditions. Third, the power level selection as "High" increases the discharge rate.
Obviously high pedal pressure at a low cadence with "High" power selected gives the battery a comparatively rough time.

It seems to me that what you say implies dont use the maximum watts your motor is capable of. If the voltage is 24V and the max motor power is 250w then this will be 10.4 A from the battery. Presumably it is this high current peak that is shortening the battery life. If on the other hand I very rarely need to draw 10.4 A because of the way I ride the bike (ie avoid speed & hills and put plenty of power in from my legs to reduce peaks), and if I thus keep the battery power down to say 100 watts for nearly all the time, I will only draw 4.2 A and this will be a lot kinder to the battery.

 

[flecc]

It seems to me that what you say implies dont use the maximum watts your motor is capable of. If the voltage is 24V and the max motor power is 250w then this will be 10.4 A from the battery. Presumably it is this high current peak that is shortening the battery life. If on the other hand I very rarely need to draw 10.4 A because of the way I ride the bike (ie avoid speed & hills and put plenty of power in from my legs to reduce peaks), and if I thus keep the battery power down to say 100 watts for nearly all the time, I will only draw 4.2 A and this will be a lot kinder to the battery.

The principle of this is correct, but the figures are wrong since the 250 watt figure is a notional one for legal purposes. All e-bikes are far more powerful, but the manufacturers use "licence" by quoting a notional average output over time. The basic Panasonic system peaks at around 400 watts on each pedal thrust, depending on the factors mentioned, but the average looks about 250 watts as this Kalkhoff Agattu output graph shows:

 

[flecc]

It would appear that laws of Physics / Nature just don't want mankind to be able to store electricity.

Absolutely right, electricity is very much a dynamic thing only. Of course we don't store it in batteries, merely change it into a chemical state with potential. But as in all energy conversion, there are substantial losses in both directions which make for poor efficiency compared with the very effective and efficient electric vehicles fed with external power via wires or rails.

Roll on trolley-bikes (or trolley-trikes).
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[blackrat]

Thanks guys, this all seems to make sense. It is just possible that I will be able to do this. My ride is 11 miles each way, on the middle setting I get home with one solid light showing from fully charged. Using the middle power setting on the outbound journey and full power to get home gives me a slow flashing red light at the end.

I will have to see what difference charging to the five lights on and not waiting for them to go out will make to my remaining charge at the end of the ride.

Blackrat

 

[CeeGee]

Don't forget that no matter how carefully you try to look after your battery they still have a short life and will die of natural causes -
an ebike battery is not for life, it is for a couple of years.

Colin

 

[flecc]

an ebike battery is not for life, it is for a couple of years.

Colin

Perhaps a bit gloomy Colin. I'm still using the Phylion test battery I got from Wai Won Ching of eZeebike in January 2008, so three years old. For about a year I haven't been able to use full throttle continuously, onkly short term, but that's not a problem with my powerful motor. I'm still getting an average e-bikes power output, something in the order of 400 watts max.

I don't know the range, but it covers what I normally do throughout the local area so would be useful to many. Of course a hard riding long distance commuter would have found it useless at two years, but the great majority of e-bikers are just utility users doing shopping and local leisure trips.

The enthusiasts that this forum has as members are the exception, not the rule. As I observed to someone else recently, in the four years that this forum has existed we've gained some 4000 members internationally, but in that time over 100,000 e-bikes have been sold in the UK alone and no-one knows how many millions internationally. Kind of puts things into perspective.
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[10mph]

Flec,
Interesting graph. I cant read the time scale units. If in seconds this represents a 30 minute ride. So how long are those 400 watt+ spikes? At that graph scale possibly each spike represents several turns of the crank from a burst of rider pedalling. If that is the case with what time constants does the control system regonise the power is above the required 250 watt average and bring it down to that?

 

[flecc]

I don't know the time units since I didn't carry out that measurement, but the control system does not regulate the power down to 250 watts as you suggested. As I said before, the 250 watts is a notional average figure which could easily be exceeded longer term with a strong rider continuous input accompanied by a slow cadence and high power setting.

It just happened that the average rider who took that measurement averaged about 250 watts or a trifle below. The variations were due to the rider input changes with the hilly territory of the ride.

"Slugging" in the circuit has probably wiped some of the detail, since each pedal stroke gives a distinct rise and fall of power from as high as the settings and pressure allow down to a low point. Oddly enough this does tend to vary bike to bike, some showing a slight tendency for the power to run on while others can have distinctive responses to the input.
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[NRG]

Flecc I'm struggling with your figures, perhaps I've misread them. 400w or even 500w peaks on the Panasonic system means a battery draw of 15 to 20 amp draw IE: a 1.5 to 2C draw from the battery. This is not out of the norm and all but the cheapest of batteries are capable of sustaining this amount of current draw, in fact the limit is more than likely set by the BMS. So this should not in practice have a significant effect on life.

In practice BLDC controllers employ PWM to control motor voltage and by consequence will limit battery current by programming to protect the battery, so I don't think the factors listed previously have a large affect (if any) on battery life.

 

[pictsidhe]

Quite a few batteries will gain abit of capacitry over the first few cycles, if you don't cycle fully, it will probably just take more. Lead acids really don't like being run down, others are better, but have their limits, lithium about 3V, NiCad and NiMH about 1V.

Battery conditioning is an overcharge to even out the cells, most chargers do this automatically on a full charge now, my DeWalt drill (NiCad/NiMH) needs to be left for a while after 'full' though, probably due to it being fast charger.

The battery cycling thing stems from one satellite running NiCads and a badly designed BMS, cycling batteries is NOT REQUIRED for any chemistry if they are used properly, that satellite discharged the batteries exactly the same amount each day, but cut off at too high a voltage, if it had run down to 1V per cell, there would not have been a problem and none of this cycling nonsense. /rant

Lead acid batteries are simple, they are best kept fully charged at all times. Lithium ones last best at medium charge in storage, full charge degrades them faster, running them low possibly kills them faster so if you do run them low, charge fully, if you take a week to flatten them, charge less often, it is hard to give exact guidelines as batteries and use vary so much but I'd be inclined to charge them at 1/2 - 2/3 discharged if not hammering them. Try the manufacturers data sheet for your exact battery. I'm not entirely sure about NiCad and NiMH but autocycling chargers annoy me greatly as it reduces life...

 

[flecc]

Flecc I'm struggling with your figures, perhaps I've misread them. 400w or even 500w peaks on the Panasonic system means a battery draw of 15 to 20 amp draw IE: a 1.5 to 2C draw from the battery. This is not out of the norm and all but the cheapest of batteries are capable of sustaining this amount of current draw, in fact the limit is more than likely set by the BMS. So this should not in practice have a significant effect on life.

In practice BLDC controllers employ PWM to control motor voltage and by consequence will limit battery current by programming to protect the battery, so I don't think the factors listed previously have a large affect (if any) on battery life.

I agree, my expression "giving the battery a rough time" was relative, in fact that Agattu system is capable of over 900 watt peaks and tested at that. My reference concerned longest battery life though, and as you know, when looking for extended life from lithium batteries it's best to aim for using the central area of charge between 20% and 80% of content, and using it at the lowest C rate possible. In that sense 15 amps and more from a 10 Ah battery probably isn't commensurate with getting the longest possible life.

Personally I just use these batteries however it's most convenient and accept the replacement costs and frequencies. I think that's the best way and if someone doesn't feel it acceptable, it's probably best they don't use an e-bike.
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[flecc]

The battery cycling thing stems from one satellite running NiCads and a badly designed BMS, cycling batteries is NOT REQUIRED for any chemistry if they are used properly, that satellite discharged the batteries exactly the same amount each day, but cut off at too high a voltage, if it had run down to 1V per cell, there would not have been a problem and none of this cycling nonsense. /rant

All very well for the chemistry, but bad advice for some systems with battery integral meters. The Panasonic battery integral battery meter circuit like some others requires re-zeroing from time to time by running the battery to almost empty. On the latest Panasonic e-bike batteries, which have a fast flashing LED point to indicate the meter zeroing point for empty, that's also vital for the capacity measurement function since both content and capacity measurement are very dependent on correct zeroing for accuracy. It's easy to get to a 20 to 40% reading inaccuracy otherwise, especially after a cold weather spell with lowered chemical performance.
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[NRG]

Ah, OK Flecc, thanks for the clarification.

I agree, my expression "giving the battery a rough time" was relative, in fact that Agattu system is capable of over 900 watt peaks and tested at that. My reference concerned longest battery life though, and as you know, when looking for extended life from lithium batteries it's best to aim for using the central area of charge between 20% and 80% of content, and using it at the lowest C rate possible. In that sense 15 amps and more from a 10 Ah battery probably isn't commensurate with getting the longest possible life.

Personally I just use these batteries however it's most convenient and accept the replacement costs and frequencies. I think that's the best way and if someone doesn't feel it acceptable, it's probably best they don't use an e-bike.
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[jbond]

All these rules of thumb (charge 20-80%, keep below 2C discharge rate) feel like they may not always be true now. We've got 2 chemistrys out there and two or three cell types out there, all with different characteristics. I'm not at all sure the same rules apply to a A123 LiFePo Cell capable of 20C vs a LiMn prismatic cell capable of 2C. And so on. I also feel that a built in BMS supplied by the manufacturer ought to enforce good practice limits, though of course commercial reality may mean that it's programmed for performance rather than life span.

 

[flecc]

All these rules of thumb (charge 20-80%, keep below 2C discharge rate) feel like they may not always be true now.

But these are really fundamental, though the optimum figures may be arguable.

We are dealing with chemical reactions, and the fiercer the reaction, the shorter the life, regardless of what chemical reaction is under consideration.

It follows that the C rate be kept low in both directions and the reaction (charge content) limits be avoided since they are in reality forced high stress and exhaustion points.

Regardless of the chemistry, satellite practice has shown how ten year lives are obtainable with any type using these rules, and the Toyota Prius has long put that into commercial practice with their now dated NiMh chemistry having a guaranteed 8 year life.

I'm wary of examples and comparisons using tool and RC model batteries since their working conditions are usually so radically different from e-bike usage.
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