NiMh Life

[flecc]

Re: NiMh battery life, much depends on the battery and charger design and quality.

For the best part of four years I used a twist for everything, utility cycling, trailer towing etc, and in daily use often seven days a week.

Coming up to four years old I recelled one battery just to return the range to a full distance, it otherwise still performing ok but with range slightly more than halved. The second four year old battery not recelled I've passed on to Forum member Alan Terrill who is using it as a "get-home" back up and it's still working ok.

In small part this long life is due to the quality Panasonic cells, but the most important factor was the excellent Metco charger with it's regularly used "refresh" discharge facility. The Metco charger was Giant's temporary stopgap that I bought when the original Panasonic one failed very early.

The biggest failing of the NiMh chargers supplied with many e-bikes is the lack of a discharge facility, this being essential for a long NiMh life. Running an NiMh to empty once every five to ten charges depending on frequency of use is a good substitute. Basically run it to empty at least once a month, easiest done if you have a spare battery to get you home of course.
.

 

[andrewelectricbike1]

How often are you refreshing? I generally do it once a week after 10 charge discharge cycles.

 

[Pageant]

Sorry guys,

I didnt realise that this part of the forum was open for posting - I have just posted a futher query/under the thread "Just plain NiMH battery packs", should I have put it on this section instead?

Richard.

 

[andrewelectricbike1]

Yeah go on. Floodgates are officially open

 

[Pageant]

Okay, I have cut & pasted this from the other thread as it seems to fit better here

Quote:
Originally Posted by flecc
The biggest failing of the NiMh chargers supplied with many e-bikes is the lack of a discharge facility, this being essential for a long NiMh life.
.

Hi Flecc,

As I have only had the Windsor NiMh pack and charger for a week I would obviously like to keep the battery in its best condition. I understand what you are all saying about fully discharging the battery.

I use the bike purely for leisure (retired). I often use it just for 4-5 miles a day just to get out of the house. I think I am getting about 15 miles of good power from the battery before it feels like it is not giving the same assistance (throttle 'low' light comes on when throttled hard). I am pretty sure I have just had 15.8 miles since my last charge and the battery now reads 24.2v on my meter.

As there is probably not much assistance left in it - should I recharge it now, I have not got a "refresh" facility so would I be better off "hooking up" the back wheel off the ground and taping up the trottle until battery is empty.
The only other option would be to continue to use the bike until battery was exhausted, but that would probably be when I was a distance from home and I would end up pushing it back....then I would be exhausted. (I must try and remember to put a postit note or something on the battery with a note of mileage at last charge) - I would try and use the bike until it was totally flat but my wife would not be too chuffed with my "Can you come and pick me up please?"

Richard

 

[Pageant]

Sorry - please ignore my post above, I pasted it here not realising that Admin had already moved it here from the main section of the forum

 

[flecc]

How often are you refreshing? I generally do it once a week after 10 charge discharge cycles.

Yes I think that's fine Andrew, and when the Twist was in use all the time mine was about that. The Twist is laid up now as a reserve bike as the Q bike does all of it's former work rather better, but I'm maintaining the Twist's recelled battery with a monthly full discharge and recharge, using the Metco's discharge facility. During each month the battery loses about 20 to 30% of the charge anyway due to the natural rate of about 1% loss a day.
.

 

[Martinm]

I am probably missing something here but how do you discharge a NiMH
battery ? I have heard people say you use a light bulb but how ?

 

[flecc]

That should never be done Martin.

NiMh cells shouldn't be discharged to below 1 volt or they can be damaged and refuse to charge again. E-bikes take care of that by cutting power just before that low point is reached, and that constitutes a satisfactory discharge. That leaves you needing to pedal the bike home though.

To make it more convenient to complete a discharge without having to risk running out on the road, some bikes have a charger with a discharge feature. This is usually a button pressed when a battery getting low on charge is connected.

Then the discharge function takes the cells down to about 1.1 volts and then commences and completes a full charge.

Sadly most bikes don't include these better chargers these days. However, it's soon learnt how far one can be ridden to a fairly low point, and that's a good enough discharge for a good battery life.

It's only necessary to discharge once in a while, say around once in ten charges or once a month.
.

 

[mastanlem]

Nihm batteries on Sparta

Hi Flecc,

With regards to discharging of the battery. Sparta recommends topping up after every ride. When the power starts to fade the bike can be calibrated. Do you think that this Calibration discharges the battery.

Thanks Marina

 

[flecc]

Hi Marina.

No, on the Sparta the calibration just re-registers the battery's changed state in the bike's complex electronics so that it continues to give you good indications of the battery status and also draws current appropriate to the battery's state at that stage in it's life. With a sophisticated system like that, discharging is not so important, and that's especially true when a battery is lightly loaded as it is in your bike.

Only a couple of other e-bikes approach that standard of control system, the majority just give their batteries a rough time, with only the owners left to care for them.
.

 

[mastanlem]

Nihm batteries

Thanks Flecc,