Has anyone tried to re-cell a pack with hybrid batteries ?

[chazpope]

I wonder how it would work, they are supposed to perform better in the cold

 

[flecc]

Could you explain what you mean by "hybrid" batteries Chas, not a description of any battery type I know.
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[Mussels]

I've seen them for sale in Maplin, more expensive for less capacity. There's scant information on them and I don't see the point myself.

 

[flecc]

Thanks Mussels, I've looked at them on Maplins and they appear to be a return of an old technology since I bought a set of these AA rechargeable alkalines more than a decade ago when they were made in Canada. If the life is to be believed, they now last much longer, but I doubt if the discharge rate would be adequate for our high powered bike motors, judging by my previous experinence when I just stopped using them, returning to NiMh or disposables.

I've just checked and I still have those original ones, then called "Pure Energy" batteries and made by Amherst of Nova Scotia.
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[RobinC]

I take it you mean the low self discharge type NiMH type batteries. I hadn't realised they were also better in the cold. Until recently these were only available in AA size but I see Maplin now have in them in D size also.
They are definately better for occasional use application e.g. digital cameras.
Generally more expensive than standard NiMH at the moment, maybe this will change in the future. I don't know if they are better for the higher current requirement of a ebike.

 

[NRG]

New technology Flecc, introduced in 2005. The hybrids are low self discharge NiMH with lower internal resistance than NiMH. They are more suited to high current applications than NiMH and hold their voltage better under load.

Maplin list some 8Ah D cells....I wonder if that is a typo for 800mAh? If true you could build a 36v 8Ah battery from 30 cells for 150 quid....balancing and charging would be another matter though!

Low self-discharge NiMH battery - Wikipedia, the free encyclopedia

 

[flecc]

Thanks NRG, I'd heard of those but not under the hybrid name. Strange that a search for hybrid on Maplin following Mussel's post showed those rechargeable alkaline types.
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[NRG]

Here's a another new type that I found whilst trawling the net, anybody know about NiZn?

PowerGenix NiZn rechargeable AA batteries - High Power | Eco Friendly Blog and News (Rechargeable NiMh and NiZn Batteries)

Nickel-zinc battery - Wikipedia, the free encyclopedia

 

[flecc]

Yes indeed, in fact there's an amazing array of new and fairly new types around currently, but behind most there lurks various problems. Many are only suitable for car use, being either too bulky or too heavy for two wheelers. Others are in the technological dead end of fast charging, and some just not suitable for upscaling.

Some end up in unexpected places, for example Li-polymer was originally developed as an ultra fast charge, low density, low capacity system, but has ended up as quite the opposite, slow charging with high density and capacity.
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[chazpope]

What I meant was in fact 8Ah Hybrid D cells form Maplins (code N62GU) - 6.99 a pair!

I asked because I used them to re-cell my bike's 24V pack - check result here

 

[flecc]

Thanks Chas, this is what hybrid batteries entered in Maplin's search gave me:

Hybrid - the next generation rechargeable battery

which are described as having alkaline benefits, similar to the old ones I mentioned, but I think their wording may be misleading.

It will be interesting to see how yours works out, let us know what bike are you using it with.
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[RobinC]

What I meant was in fact 8Ah Hybrid D cells form Maplins (code N62GU) - 6.99 a pair!

Did you mean £9.99? The price I see online.

I did see these D size Hybrid cells in stock in my local Maplin last week but I didn't look at the price, I was just interested to see they existed.

Robin

 

[jerrysimon]

Surely these cells won't have the ability to discharge at high rates i.e. 10amp + and maintain their voltage ?

Even made up into packs I don't think they would make a good ebike solution.

Regards

Jerry

 

[NRG]

Ah, so they are 8Ah, interesting.

Jerry, that depends if they can discharge at C2 rate which I haven't found out yet....

 

[Mussels]

Did you mean £9.99? The price I see online.

I did see these D size Hybrid cells in stock in my local Maplin last week but I didn't look at the price, I was just interested to see they existed.

Robin

Maplin has had a good sale on it's batteries and I got some at 60% off, maybe that's ended now.

 

[jerrysimon]

For a 36v battery your gonna need at least 30 of them and some sort of BMS as I suspect they will have to be balance charged.

Might work.

Regards

Jerry

 

[averhamdave]

Just trawling through "NiMh D cell batteries" on e-bay, I see that they are commonly available up to 10a, 3C discharge and 1000+ recharge cycles. Given that I would have thought they were very suitable for e-bikes.

I see they are availble fron China for £3.99 each!

Jerry, what are your reservations based upon and given they are wired in series is balance charging necessary and why would a BMS system be necessarily needed. I'm no expert but am genuinely interested in the subject.

 

[NRG]

From what I understand deep discharge of NiMH is not good for their health as the cell goes into reverse polarity causing damage and reducing its useful life. Also during charging as the cell reaches full capacity the cell will reverse cell polarity indicating the cell is full, however, the cell cannot absorb any more charge as it will be damaged so it must be switched to trickle charge.

With cells in series this all becomes critical to ensure the cells are more or less at the same charge and discharge state to extend life. Now imagine if a single cell is failing and there's no BMS, that cell will be over discharged during use as the good cells will continue to hold voltage and supply power and during charge the bad cell may never reach full charge holding down the cell pack voltage slightly so the other cells receive more charge than they should but are unable to absorb it.

 

[Fecn]

NiMH batteries do not need a BMS. With NiMH batteries, any overcharge is given off as heat. They do not go reverse-polarity when fully charged, but there is a small drop-off in the cell voltage as the battery starts to burn off the waste energy as heat - This small drop-off in the voltage is used by some chargers (called delta-V termination) to detect when to stop charging the pack.

If an NiMH pack becomes unbalanced, it can normally be bought back into balance again with a C/12 14-hour long trickle charge (also called a Formation charge), which allows the cells to all reach the same level of charge. The amount of waste heat given off with a 14-hour trickle is low enough that the cells can be left charging indefinitely without damage. As such, all the fully charged cells just throw off any extra charge as heat, and all the discharged cells end up fully charged.

It is only with the continuous use of very fast chargers when NiMH packs can become unbalanced as the cells can't get rid of the waste heat fast enough to balance with each other again. In this situation, you have little choice but to run a low-current deep discharge cycle.

NiMH cells are not damaged by being taken all the way down to 0.00v per cell - However, the cells can be damaged if they are forced into reverse polarity. In a battery pack arrangement, whichever cell reaches 0v first will then have a reverse charge pushed through it by all the other batteries in the pack. For this reason, it's not usually a good idea to totally flatten NiMH packs, but instead to discharge them using a very low current down to around 0.85v per cell (e.g. a 36v pack should be discharged to around 25V) - It is exactly this kind of low-current discharge that Cytronnex recommend for reconditioning their NiMH packs. (I think they say wheel off the ground, motor on until the cut-out)

I've built my own NiMH pack for my bike with great results, so I'd totally recommend others trying the same thing. My only words of caution for people making their own pack are..... Build in some safety features. NiMH cells will explode if overcharged. Build a 72 degrees C thermal fuse into the wiring in your pack. It'll cost you about 30 pence, but you'll thank me for it one day.

 

[NRG]

Thanks for the correction Fecn , I've learnt something new