Getting the most out of an existing nimh battery

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antiscab
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Getting the most out of an existing nimh battery

This is a continuation of discussion of getting the most out of an existing nimh battery:

Antiscab

Hi from Sydney

My Vectrix is approaching 3 years and is past 11,000 km. My battery pack is causing problems with reduced range. I pretty much only use it for my commute (<20km round trip). For the past couple of months I've been coping by charging every night. (I have the old system - my Vectrix doesn't have it's own timer but I connect it to a timer and charge for a few hours in the night.) The last couple of days I'm now getting the red battery light after about 6 or 7 km. When the light comes on almost all the bars on the battery gauge are still showing and the bike still seems to run OK. I'm worried the red light means I my Vecrtix may not keep running for much longer?

I know very little about batteries but after reading posts on this forum, I guess I must have a bad cell or cells.

The idea of conversion to a newer battery system is appealing. The costs you mention in your posts are not out of the question for me. I am very interested. I will keep an eye on the discussion.

its not so much the distance or age that causes problems, rather how often the cells are pushed to their limits (my own nimh pack was 13'450km before conversion with no issues, but had new firmware from the beginning)
out of curiosity, why were you not charging everyday?.

Most of my trips are short. By charging every two or three nights I rarely got down to less than 3 bars on the battery indicator. I was under the impression that it was good to occasionally run the batteries lower so every couple of months I would ride until the speed started to be limited. I pretty much never saw the red warning light and I thought I was taking reasonable care of the battery. Was it a mistake to only charge for 2 or three hours at a time? (Other threads on this forum mention equalisation can take longer.)

does the red battery light stay on?
if it only comes on during acceleration, than the situation is not quite as dire as you may believe.

A bad cell or two will mean very short range, and poor acceleration.

if you are still able to make the 20km round trip, the batteries end of service life may be a bit further off yet.

The red light comes on and stays on. I think there is reduced acceleration on hills but the bike still rides OK in the 50 kph areas. On my trip home in the evening the same thing happens. The red light comes on towards the end of the 8 km trip. So even though I have not recharged during the day, I still get about 6 or 7 km before the warning light.

If my problem is simply a bad cell or two, how do I go about diagnosing this and replacing the cell? I don't want to electrocute myself! Is there anyone in Sydney I could pay to do this for me?

Thanks for the info.

antiscab
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Re: Getting the most out of an existing nimh battery

Antiscab I pretty much only use it for my commute (<20km round trip). For the past couple of months I've been coping by charging every night. (I have the old system - my Vectrix doesn't have it's own timer but I connect it to a timer and charge for a few hours in the night.) The last couple of days I'm now getting the red battery light after about 6 or 7 km.

The red light comes on and stays on. I think there is reduced acceleration on hills but the bike still rides OK in the 50 kph areas. On my trip home in the evening the same thing happens. The red light comes on towards the end of the 8 km trip. So even though I have not recharged during the day, I still get about 6 or 7 km before the warning light.

So to be clear,
do you charge at work at all?
ie, do you do the full ~16km commute on a single charge, while getting red battery light at the end of both ways?

By charging every two or three nights I rarely got down to less than 3 bars on the battery indicator. I was under the impression that it was good to occasionally run the batteries lower so every couple of months I would ride until the speed started to be limited. I pretty much never saw the red warning light and I thought I was taking reasonable care of the battery. Was it a mistake to only charge for 2 or three hours at a time? (Other threads on this forum mention equalisation can take longer.)

getting the most out of a battery pack is a balancing act between the wear caused by charging, and the wear caused by discharging.

basically, the aim is to keep the batteries state of charge (SOC) between 20% and 80%.
This is true of both Nimh and Lithium.

By charging for two or three hours at a time, do you mean you stopped the charge before the bike was showing full bars?
ie during the CPxxx stage?

or were you using a timer so aren't quite sure?

by skipping the equalisation, your battery is effectively balanced at 70% SOC.

Thats because above 70%, the self discharge rate is much higher, so all the cells with a bit more charge self discharge faster, while the cells with a little less charge self discharge slower.

keeping balanced at 70% is actually good practice, as it is more consistent than keeping balanced at 100% SOC.
balancing at 100% SOC is what the original software tries to do.

discharging until only 3 bars remain on every single charge is not so good, as it is possible to reverse the lowest cells.

what is your normal travelling speed on your 8km each way commute?

Basically the slower you go, the lower the SOC at which the red battery light comes on.

The best practice I found was to get the pack balanced at 70%, by never letting the bike do an equalisation, and then always stay above half bars.

If I did need to go further than half bars would allow, than I would do an equalisation, and then immediately use the bike.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

Mik
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Re: Getting the most out of an existing nimh battery

...
...
The best practice I found was to get the pack balanced at 70%, by never letting the bike do an equalisation, and then always stay above half bars.

If I did need to go further than half bars would allow, than I would do an equalisation, and then immediately use the bike.

Matt

Assuming a good 30Ah battery:

17 bars = 100% means that 1.7 bars = 10%

70% SOC is 17-(3*1.7)= 11.9bars .

50% = 8.5 bars

11.9 bars - 8.5 bars = 3.4 bars .

If the energy content of the bars is equal across the range, then one can expect about 60km out of 17 bars meaning 60km/17 bars = 3.5km/bar.

Therefore, this suggested optimal approach would only be suitable for riding 3.5km/bar * 3.4 bars = 11.9km on average.

Or what am I missing?

This information may be used entirely at your own risk.

There is always a way if there is no other way!

antiscab
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Re: Getting the most out of an existing nimh battery

In my mind, it is more like this:
17 (all) bars = 70%
5 bars = 0% (red battery light)
0 bars = -30% (meaning you won't actually get this far)

The self discharge means full bars does not mean full charge.
The self discharge vs SOC profile means the cells will tend to all pass through 70% SOC simultaneously, despite their varied capacities.

staying above half bars on a good battery guarantees you are operating between 20% and 80% SOC.

That gives ~20km @ 100kmh or ~40km @ 60kmh.

The number of bars remaining shouldn't be confused with the actual remaining SOC on nimh. (with Lithium they are the same).

the approximations are rubbery, and move about for the same bike.

If the battery has marginal cells, than restricting usage to a lesser number of bars will be necessary (and needs to be measured).

The 3A overcharge should be able to deal with accelerated self discharge in margin cells.
Its not really overcharge, as no cell would actually get past 100% SOC.

To best make use of this, charging immediately before every ride is ideal (but not always practical).
If commuting, that would mean twice a day (again, if work is friendly).

If you ride immediately after a charge, than the cells have no time to turn the extra charge into heat.
If you don't recharge until just before your next ride, the battery has a long time to cool off, at low SOC, where self discharge is lower at any temperature (even 40+ deg C).

Its all about managing the self discharge and discharge depth to avoid the situation where cells are being reversed.

In my opinion (which is free and you get what you pay for :) ) that was the best way to go about operating a Vectrix, without any modifications.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

Mik
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Re: Getting the most out of an existing nimh battery

So are you talking about a typical, somewhat damaged battery with reduced capacity or a hypothetical, new and "perfect" NiMH battery?

However, I very much agree with the general approach, it's what I have been doing for about a year with my damaged battery. I never got an unexpected cell reversal and no obvious further deterioration of the battery. The key point is not to charge until shortly before you need the charge. And "Never stuff it, never drain it".

At work, I make a compromise and start charging about an hour after arriving, so I don't end up unable to go somewhere else if needed. At home, I have an alternative vehicle for such scenarios. I run the cooling impellers the entire work day to counter-act the heating of the battery from the top down by the sun. It would of course be even better to park in the shade.

I charge for ((12-X)*12) minutes, with "X" being the remaining bars on the charge indicator, before each ride to work or back home. That way the charger stops at 10 or 11 bars. 12 bars means "FULL" for the ~21Ah cells with the most damage in my battery.

The way to work is 20km of mainly hilly 80km/h road, with stop-and-go for the last 6km. For the downhill way to work I need 5 bars, for the way back 6 bars.

Therefore I charge 60min at work and 72min at home. That keeps the battery between 4 bars and 10 bars most of the time. The last 4 bars do hold useful charge, full power to the last bar, but I do not usually use it.

The way to start this is to limit the recharge after a (voluntary or involuntary) deep discharge with reset of the charge indicator to zero.

Use a timer and only charge for long enough to replace 2 bars less than the number of bars you can reliably use. For example, if the last 4 bars are regularly of the "disappearing kind", then charge from empty to ((17-4)-2)= 11 bars, but only before you need the Vectrix. That way, the charge indicator will be much more reliable and further damage to the weak cells is minimised.

This information may be used entirely at your own risk.

There is always a way if there is no other way!

antiscab
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Re: Getting the most out of an existing nimh battery

So are you talking about a typical, somewhat damaged battery with reduced capacity or a hypothetical, new and "perfect" NiMH battery?

Either would be fine,

So there are two effective ways of doing it,
it just sorta depends upon whether you want "full" to be full bars, or "empty" to be no bars.
you just can't have it both ways :)

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

McCulT
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Re: Getting the most out of an existing nimh battery

Matt
To answer your questions: No, I don't charge at work. Without any charging at work, the bike that was showing a red warning light when I arrived at work will now go 6 km or so before the red light comes on again. BTW, when the red light comes on in the morning, there is only one or two bars "used" on the gauge.

Re my charging practice: shortly after I bought the bike I read a post by Mik pointing out that the bike continues to draw quite a lot of current after it has finished charging. So I used a timer to restrict the charging time to around 3 or 4 hours. I set the charge to start in the early hours of the morning so the battery would have cooled right down before charging. It was always on full bars after charging.

Well, i guess I will contact someone with expertise in my local area and ask them to check out my battery. If my battery pack is not salvagable I will probably be after one of your Li kits.

Tim

Tim

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Re: Getting the most out of an existing nimh battery

Either would be fine,

So there are two effective ways of doing it,
it just sorta depends upon whether you want "full" to be full bars, or "empty" to be no bars.
you just can't have it both ways :)

Matt


Yes there is... with better firmware.
The Laird
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Re: Getting the most out of an existing nimh battery

Hi Folks,

I may as well throw in my two pennyworth.

The battery problems described are following the usual pattern for all of the usual reasons. May I respectfully suggest that most of the information to answer this topic will be found in various forum threads two of which are listed below.

'Modifying the Vectrix charger programme' and 'Equalisation with a difference'

Still keeping it simple and hanging on in there,

The Laird:-)

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