Just plain NiMh battery packs

[ITSPETEINIT]

Everyday a School Day!

I bow my head to the greater good, Everyday is a school day. regards FatPete

Inm praise of Flecc.
I was never so overjoyed until I left school (or so I thought I had until post school qualifications reared their beautiful head - beautiful as it turned out).
Knowledge is beautiful and I beg you to enrich my world Flecc.
My LITHIUM Manganese batteries are already showing signs of serious decline - on which I should like your comments. I know the basics - "down by 20% in the first year - don't deeply discharge", etc:

1. Lithium-ion 37V 10Ah - bought July 2006 - 28 miles range on flatish terrain- falling to 25 miles (in Torq) and now reached 18 miles (in Sprint 7) moderate hilly terrain as below. Never abused: deeply discharged for 3 conditioning cycles. Used mainly for distance cycling of 15 - 20 miles: taken off the bike "when the yellow light remains on whilst on a level road". Always recharged after a journey no matter how short.

2. Lithium-ion 37V 10 Ah - bought May 2007 - best range 22 miles - moderate hilly terrain (ie up to 500 meters/7%) (in Sprint 7). Never abused (by me): deeply dischatged 3 conditioning cycles. Used mainly for distance cycling 15 miles +. Best range 18 miles. Taken off the bike and recharged "when the yellow light remains on whilst on a level road". Always recharged after a journey however short.

3. Lithium-ion 37V 10Ah - bought June 2007 - same as above para 2.

All three batteries seem to be performing in much the same fashion BUT not like the first did in the Torq.

I've noticed that there are many batteries that look much the same and are sited on the bike behind the seat tube. Might they be compatible with the Ezee range of cycles with some simple modification? e.g. like an adaptor plug (you can probably tell I've never seen the battery off a Wisper bike - so forgive me if it's a daft question).

One lives in hope that NiMH come back soon as they appear to suit my cycling philosophy much better than the "Faint-hearted Lithium"
Peter

 

[flecc]

The advice I give is generic for Li-ion Peter, but is also dependent on individual battery quality. I've made mention on my website about inconsistencies in this, and have suffered the same sort of thing you have.

Two batteries bought with the Torq, close serial numbers, but one definitely inferior to the other eventually becoming unusable in cold winter weather at nearly 6 months old due to cutting out. The other one eventually followed this cutting out, but not so badly and is still usable in most circumstances at a year old. The third battery replacing the first one has been better from the outset, from which I conclude that the Phylion Company are learning and getting better gradually.

I can't quote ranges as you can, since most of my runs are shorter, but the fact that you are quoting those longer ranges shows that you have used those distances which increase aging.

Howver, I think that product inconsistency is the biggest problem, and like you, for me it's an NiMh future until something better comes along. That could be higher capacity Li-ions which would do the trick, or a better technology.

There's no reason why someone elses battery internals cant be used if they fit in the case, and the Wisper ones could be a candidate. I don't think there'd be much point though, since a wisper 905e user has already had the same cutout problem and there are very few manufacturers of these batteries anyway. The innards of another could well be from the same stock.
.

 

[flecc]

Further to my reply Peter, a healthy Li-ion battery should lose no charge at all while standing. The voltage after charge will settle over many hours as the battery cools, but once settled should remain the same, even for many months.

The inferior one of my batteries does lose charge as indicated by a continual slight voltage loss, so it's clearly not healthy. It's likely that a cell is responsible, but it could also just be a failing in the individual cell control circuit that each cell has. Yet another inconsistency that upsets life predictions, and it might be interesting for you to check yours for charge maintenance.
.

 

[coops]

NiMH suits my usage - I regularly make long trips to full discharge.

You say a discharger is essential for long NiMH life flecc:
How much difference do you calculate the discharger makes from running till empty between most recharges? How much less capacity decrease per annum would you say?
Is it possible or advisable, then, to get a charger with refresh discharge built in for use with ezee batteries do you know, flecc? The Twist NiMH replacement battery charger you found can't be used for that purpose? My ezee NiMH charger seems very fast, about 2h 45min full charge: its rated as 2.6A output, is that normal or too fast for long battery life? Sorry for all the questions & apologies if you've answered this elsewhere .

Stuart.

 

[flecc]

I have no estimate of how much longer life discharging gives Stuart and have never seen any tested evidence on that. I base what I say on observations that others get around two to three years life on NiMh on many bikes using a mix of chargers which frequently have no discharger, or it's function isn't used by owners.

By contrast, Twist series batteries used with fairly regular use of the Refresh (discharge) function seem to last to four years and even beyond, true of my own two batteries too, one given away and still in use at nearly four and a half years. Not very scientific, but it fits with expert advice that NiMh should first be discharged nearly down to 1 volt per cell once every few charges, so what evidence I have indicates this is good advice to give, and it obviously does no harm.

Speed of charge does affect life, but I have no measure by how much. My own experience with very fast chargers (1 hour) on smaller cells is that it quite seriously reduces life, this being related to the way NiMh also cannot discharge beyond a certain rate, unlike NiCad.

Your charger is like mine in that time, but that's not too high a speed for cells designed for high discharge. It would be too fast for regular consumer D cells, but I would ideally prefer more like 4 hours nonetheless.

With discharging, there's a balance to be struck though. NiMh batteries have been quite cheap, while the Giant Twist charger currently costs at least £120, from some dealers £140. That's over 1.4 times the price of a Powacycle battery with the same number of cells, but of larger capacity.
.

 

[coops]

Thanks for the full answer flecc .

So even if I use 2 Ezee NiMH, at those sorts of prices for a discharger its touch & go whether its possible benefits would be cost effective even over the lifetime of both?...

If I could get a discharger for less though, it sounds like it may be worthwhile: I'd always like to try to get the best out of my batteries, plus a 2nd charger is handy to have .

Can the Twist replacement charger (with refresh) you found can be used with Ezee NiMH though flecc, or would an alternative need to be found, preferably with a lower charge current nearer to 1.5A?

 

[flecc]

No, the Twist is 24 volts Stuart, so the charger no good for the 36 volt eZee battery.

Any old charger won't do, it's cut-off circuit has to match the thermistor in the battery. The trouble is that chargers rarely have their spec available, so there's a big guessing element involved. Just because a 36 volt charger is shown as for NiMh isn't enough. One supplier of chargers has just supplied someone with a 1.8 watt one for their Twist battery, but it cuts off too early, so is no good.

The error can be large. For example, the Powacycle NiMh charger if tried on a Twist battery will often cut out at a half hour, charge barely started.
.

 

[coops]

Ok, I see its complicated! Thanks flecc.

I guess I'll play safe, keep it simple & just carry on as I am then (unless or until some bright spark finds a suitable charger with a refresh facility ), regularly running down the battery fully at least every few charges or so: easier to do with two NiMH batteries anyway, as you've pointed out before .

 

[BigBob]

Slightly Off Topic

I find this whole topic fascinating and although I have very little (read no) experience with batteries for ebikes I do have a reasonable amount of experience of cells in another application.

That application being R/C car racing which has been my sons' hobby for nearly 20 years. For those of you that don't know, the electric powered versions of these cars run 6 cell sub-C 'packs' powering 540 size electric motors of various winds depending on class run, track conditions etc.

Our usage and demands are somewhat different to ebiking - we try and extract the MAXIMUM energy out of the cells in a 5.5 minute period (the length of a race).

20 years ago the majority of re-chargeable cells seemed to be made (or at least marketed) by Sanyo and were designated SC1200. The SC standing for Sub-C, the size and 1200 being their capacity in mah. These were NiCad cells.

Over the years the capacity grew from 1200mah to 1500mah and in aropund 1989/90 a new type of cell appeared - the 1700SCE. There is some dispute as to what SCE stood for - Sub-C Evolution was the common theory - but the extra 200mah was highly sought after. They were however extremely fragile and it was not uncommon for the top racers to throw thier 'packs' away after one run because they were no longer dependable.

A whole new industry grew up supplying 'Matched' Cells - a process of charging and dis-charging individual cells to find 6 that had similar characteristics. These were then soldered together into one 'pack'. Out of a carton of 400 cells perhaps 10% would 'cut the mustard' as top race packs, a further 30% would be 'good' race packs and another 30% would be OK as 'Club' packs for beginers and novices. The remaining 30% would be re-cycled for 'non-competitive' uses - drills, torches etc.

During the 90's the next major development was the SCR (R for RACING) 1700 Although of no higher capacity, these cells were much more durable and tended to hold a higher voltage immediately off charge - something we look for to improve performance.

Nicads grew in capacity over the next 10 years or so to 2400mah - exactly double the very earliest and were far more durable.

During the reign of NiCads the advice for getting the best performance out of them ranged from dis-charging them to 1v/cell and storing them with a 1 ohmn resistor across them to dis-charging them and storing them short-circuited (yes, really).

Charging currents were generally in the range of 1amp/cell and the cut off point was either detected by a delta voltage (the voltage a pack reduces by when it is fully charged) of around 35/40Mv per cell or a temperature peak of around 40/45 deg C.

Sorry if this has proved boring to some, and I know it's not strictly relevant to this forum ,but I thought some might find a bit of 'alternative battery history' interesting.



BB

 

[flecc]

Not at all boring Bob. It's true NiCads can be fully discharged, but of course they work differently from NiMh which are a form of fuel cell, albeit a closed circuit one.

Cell matching for series of NiMh cells is a similar problem, and also probably the reason battery manufacturers don't like making very large capacity ones for series use and want to escape into producing Lithium variants.

The irony is that Lithium rechargeable batteries need individual cell circuits for charging and monitoring, and if they'd only put the same individual cell circuitry into NiMh, but for charge balancing instead, cell selection would not have been necessary and production made easy.

I'd love to say "Live and Learn", but they only seem to do the live bit!

So we suffer Li-ion batteries that don't do the job.

In fact NiCads are terrific for e-bike use, maximising motor power and never at risk of protection cutout, but of course they can't have the capacity we need for a decent range.
.