Battery / controller question

[allotmenteer]

I have a query regarding the operation of my hub motor kit.

The battery is a 24V li-ion 6.8 Amp Hour. It has 7 cells in it and when it is fully charged my multimeter reads 29.0 V. (this would be 4.14V per cell).

The controller has 24V 15A stamped on it. It also has 20.8V on it. The rest of the writing is Chinese. I assume the 20.8V is the cutoff voltage.

Now, when I ride the bike till the motor cuts out the battery reads 26.4V (3.77V per cell).

What is happening here? I thought that the low voltage cut-off for li-ions would be about 3.0V or so (maybe less) which is to protect the battery from over-discharge.

Is my controller being very cautious and cutting the power well before this in order to preserve / extend battery life?

I have found that if I disconnect the battery and reconnect then I can get a little bit more distance out of it before it cuts out again.

Perhaps the reading taken when the battery is not under load is 26.4V but as soon as the load is applied the voltage plummets. Would this be correct?

I wonder if anyone can shed some light on this behaviour.

 

[flecc]

Both of those are completely normal with Li-ion Paul, and equate to my experience with the eZee system. The controllers are set cautiously for both safety and cell life reasons.

As you correctly surmise, the voltage under load drops, and the drop is proportionally more as the cells empty due to the internal resistance rising.

Again I have the same past experience with disconnection and replugging. This rests the electrolyte and enables chemical recovery, chemical exhaustion being a factor with these batteries. The longer the rest, the greater the recovery, but this is on a sliding scale.

For example, use the battery on some tough protracted climbs and you'll get cut out earlier than usual. Fifteen minutes later you'll be able to carry on for quite a while, almost to the usual range.

Alternatively, run the battery until cut out in easy conditions, rest it for fifteen minutes and the recovery will only be very small, perhaps only a few seconds. This second case will always give the better range though.

 

[allotmenteer]

Ah that would explain a ride I did a couple of weeks ago up a few big hills in a short period of time. The battery died much sooner than I thought it would, after only 6 miles, still about 2 miles from home. When I got home and disconnected the battery I measured the voltage and it was more than the 26.4V it reads when empty so I reconnected the battery and managed to ride another 1.5 to 2 miles on flatish ground before the battery gave up entirely.

From now on then I shall make sure I pedal a bit harder on the hills to reduce the load on the batteries and avoid this premature battery exhaustion.

Perhaps I need to buy a drain brain to enable me to get the most out of the kit. Does anyone know the best place to buy them? A UK site / or equivalent piece of kit.

 

[flecc]

No drain brain needed Paul, just resigned acceptance of the current state of battery technology.

NiMh gives a more peaceful life to those inclined to worry about these anomalies, since they're more consistent in their lower performance.

 

[ITSPETEINIT]

EZee cycles - Battery Voltage check.

I am still in the middle of the fault disgnosis of two 10Ah Li-ion batteries with 50 Cycles.
It occurred to me that perhaps I could check the Voltage/Amperage with my Multimeter (a galvanometer type) when they are FULLY CHARGED, of course.
Which of the two contact points in these batteries and positive and negative?
Is there anything I should look for/try to make a useful test/check?
I need to know the polarity because (I think) if I put the multimeter probe onto the wrong contact point it will blow the fuse in the meter?
Peter

 

[flecc]

As shown in my cable routing diagram here Peter, the positive is the front connection furthest away from the slide part of the battery.
.

 

[ITSPETEINIT]

Positive or Negative

Thanks Flecc
Peter

 

[allotmenteer]

The battery is a 24V li-ion 6.8 Amp Hour. It has 7 cells in it and when it is fully charged my multimeter reads 29.0 V. (this would be 4.14V per cell).

The controller has 24V 15A stamped on it. It also has 20.8V on it. The rest of the writing is Chinese. I assume the 20.8V is the cutoff voltage.

Now, when I ride the bike till the motor cuts out the battery reads 26.4V (3.77V per cell).

What is happening here? I thought that the low voltage cut-off for li-ions would be about 3.0V or so (maybe less) which is to protect the battery from over-discharge.

Is my controller being very cautious and cutting the power well before this in order to preserve / extend battery life?

I have found that if I disconnect the battery and reconnect then I can get a little bit more distance out of it before it cuts out again.

Perhaps the reading taken when the battery is not under load is 26.4V but as soon as the load is applied the voltage plummets. Would this be correct?

Update: I have now received a replacement battery under the warranty and have been out for a spin. This battery took much longer to charge from flat the first time (just over 5 hours I think) than my first battery (just over 3 hours).
I went out for an hour last night until the battery cut off and when I got home it read 25.2 volts (3.6 V per cell). Again when I disconnected and reconnected the battery there was still some power there.
I also did 14.5 miles on undulating terrain before cutout which is the best I've done so far.
It looks like my previous battery was faulty from the outset as it never took as long to charge and cutoff at 26.4V.

 

[ITSPETEINIT]

Ezee Torq - Why no NiMh battery

Out of curiosity, since having trouble with Li-ion batteries on both Torq and Chopper, I looked at 50 Cycles web site and noted that NiMh batteries are available ONLY for Sprint and Quando (presumably that means not for Torq or Chopper. Why are the Torq and Chopper now excluded from the NiMh one?
I recall that when I bought the two bikes both types of battery were on offer.
Peter

 

[flecc]

And NiMh also on the new Liv model.

It appears to be an up market thing, the better bikes with the Li-ion, those more towards the budget end with NiMh, probably due to the cost savings I would think.
.