DIY Battery

[halfmedley]

This question will probably highlight my general ignorance of all things electrical (no, I'm not proud of it) but reading through Flecc's article about recelling a Lafree battery got me thinking. Instead of dismembering a Powacycle battery, would it be possible to construct a battery from the high capacity D-cells you can now get for cameras? Ansmann make a 10,000mAH (10aH?) NiMH D-cell which is freely available on t'internet. They're not cheap but once you'd constructed a battery from them, you could at least replace worn cells on an individual basis. Or am I just dreaming?

 

[flecc]

If you have a look at the Lafree replacement charger thread, you'll see that Sav has recelled with a 10 Ah cell pack following my details, so no need to use individual cells which work out much more expensive. Replacing worn cells is not on, mixing new with old would cause all sorts of problems and hasten the end of other cells. In any case, cells in a properly charged pack don't wear individually. On the pack I removed at four years old, the cell imbalance was only as follows. In other words, it was near perfect:

Battery Cell Voltages at over 3.5 years – Lafree Twist 24 v 6.5 Ah

Front--- Centre--- Rear bank

1.312--- 1.304--- 1.305
1.303--- 1.306--- 1.301
1.312--- 1.301--- 1.300
1.312--- 1.311--- 1.302
1.310--- 1.302--- 1.306
1.304--- 1.309--- 1.300
1.312-------------1.312

The key thing to know though is the need for a thermistor installed into the cellpack and matching charger when using NiMh. Charging without one risks wrecking the cells. The charging methods with cameras etc often fall well short of what's needed for a long life with good performance.

Chargers sometimes come with a matching thermistor, indeed I think Sav has one which he might sell on to you if you explore this further. Also, I can help with how you place and connect the thermistor.

 

[halfmedley]

I suspect such electrical wizardry is beyond me! In essence though I was really just wondering if there was any fundamental difference between the D-cells found in an e-bike battery and the high capacity D-cells made by the likes of Ansmann?

 

[flecc]

No, with NiMh they'll be the same halfmedley. The wizardry wouldn't be beyond you I'm sure, it's always much simpler than it sounds. That's the trouble with all technology, it always sounds much more complicated than it really is. Anyone who can wire a 13 amp plug and make a simple solder join can re-cell a battery, or build up a replacement battery with the thermistor that comes with a charger, if given the basic instructions and help.

 

[Flying Kiwi]

I suspect such electrical wizardry is beyond me! In essence though I was really just wondering if there was any fundamental difference between the D-cells found in an e-bike battery and the high capacity D-cells made by the likes of Ansmann?

I believe the Ansmann D cells only come 'untagged' and with the standard protruding nipple (for want of the correct term ) on the positive end. No this has nothing to do with graffiti, tagged cells come with a little strip of metal ready spotwelded to each end for connecting purposes and both ends are flatter than the everyday batteries we buy in the shops. In some cases this could mean the longer standard D cells dont fit in the space provided for a tagged cell.

 

[halfmedley]

Hmm...I was just wondering why manufacturers use proprietary cells in custom designed battery packs (which are then expensive/difficult to replace or become unavailable in a few years time) when suitable off-the-shelf D-cells are on the market. Then, if they must be gathered in a battery pack then make said battery pack accept standard D-cells? I'm sure there's a good reason why this isn't so but I'm too daft to spot it!

 

[flecc]

I think it's just compactness halfmedley. Having a battery that's both light and small is a big selling point with e-bikes, and the sum of the cell end projections that Flying Kiwi mentioned can knock perhaps a couple of centimetres off the height of the battery (eZee), or make it slimmer (Giant).

One of the reasons for the rush to Li-ion etc is that the cells can be rectangular and therefore use the available space better to make a more compact battery. NiMh have to be circular so even with staggered packing, there's still much wasted space in a case.

 

[flecc]

Also, the cellpacks aren't expensive or difficult to replace as you said, quite the opposite. It's individual cells that are far more expensive and much more complicated for anyone to assemble. 10 Ah cells are typically around £10 each or more, but a pack of 20 can be around £140, £3 per cell cheaper and pre-assembled for convenience. The layouts are standard in two formations usually so re-celling is possible even if a battery is discontinued. For once things are on our side.

 

[halfmedley]

Interesting points Flecc as always...as this all relates to NiMH, is it safe for me to assume that a Lithium ion battery can't be re-celled? Apologies if that is another daft question.

 

[flecc]

I never think there are any daft questions halfmedley, if an answer is needed, the question is always valid and should be asked.

You're right, Li-ions can't be re-celled at present. The reasons are that as a new technology, there's too wide a variety of types and protection circuitry incorporated. In addition, the risk of fire in some types if maltreated means it would be too dangerous. In my view, it's likely Lithium batteries will be superceded by a future type or by fuel cells before recelling Li-ion arrives.

 

[halfmedley]

Hmm...food for thought certainly, makes me wonder if the Li-ion battery is something of technological wrong turn. Doesn't seem to be much of an improvement over NiMH in terms of performance, and if they can't ever be re-celled then they're not particularly "eco" either. Hydrogen/oxygen fuel cells now there's a thought, or maybe ultra-capacitors might be the answer, they're getting close to battery performance and can be recharged in moments. Cost a fortune at present though no doubt.

 

[flecc]

I agree with you, NiMh is certainly my favourite in terms of reliability, long life and low cost, and that's definitely based on experience rather than just opinion.

I don't think we'll see ultracapacitors if fuel cells are successful, since it probably wouldn't be worth the expenditure on research. That said, I think hybrids like the Toyota Prius are an ideal use for the ultracapacitor , since only a relatively short term energy transfer is necessary most of the time.

 

[Sav]

Just to back up what Flecc has said. I was surprised how easy it turned out to be to recell thanks to Flecc's guide and a bit of Googling to find the 10Ah cellpack.

Weather's not been condusive to riding far and I've had manflu for the last few days, so I've yet to get an estimate of the increased range, but increased it definitely is,

Sav

 

[flecc]

I've had the same problem with the 8Ah pack Sav, the constant wet and/or windy weather preventing any really long runs in neutral conditions to assess range. Like you, from the runs so far I know it's improved quite a bit.