Is this a useful and novel 24v battery?

[AndyOfTheSouth]

Apologies if this is already well known, but I found this battery by accident.

It seems attractive because it offers a low weight option - it also looks well made.

http://www.nec-tokin.com/english/product/pdf_dl/24vbatterypack_e.pdf

Any comments?

 

[flecc]

It's a fairly normal Lithium manganese battery Andy, the weight and size of these is tied to the capability. For example, the 26 volt 10 Ah Panasonic battery weighs 2.2 kilos, the 37 volt 10 Ah eZee battery weighs 3.3 kilos, so you can see the weight ratio is similar.

The only way to make them lighter is to have lower maximum discharge rates, which is really a change in effective working capacity when loaded to the same degree.

The earlier non-polymer types were about 33% heavier, and the next generation lithium-iron-phosphate types will be about 25% heavier than Li-polymer for the same capability. To a considerable extent it's the chemistry used that dictates the weight and that's tied to physical fundamentals.
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[AndyOfTheSouth]

Thanks, Flecc. I didn't mean that the chemistry was novel, just that it was 4ah/1.2.kg. I like the idea of lighter batteries and would accept the lower capacity. Looking around the electric bike outlets, I haven't seen this option. Perhaps I just haven't looked in the right places.

Googling '24v batteries' leads to ones for power tools. I saw one which was 2ah (DeValt?). Would that work with suitable plug/socket adaptation?

In general, the possibility of a small 'get you home' battery seems quite attractive to me.

 

[rog_london]

In general, the possibility of a small 'get you home' battery seems quite attractive to me.

Most of these small batteries don't come into that category unfortunately. Even most of the large ones are not suitable. The problem is discharge rate - for e-bike purposes you need a battery which will withstand at least a 10 amp discharge and, depending on the controller/motor combination, possibly considerably more.

Some technologies work better than others in this regard, but in all cases there is a design trade off between the capacity of a battery of a given weight versus its peak discharge capability. You may note that even in the case you discovered there are two versions of each battery type - one designed for high capacity, and one designed for high discharge.

The peak discharge rate does not appear to be quoted - but I'm willing to bet that their idea of a high discharge rate would be much lower than what you'd need for an e-bike.

Rog.

 

[rooel]

I like the idea of a get-me-home battery too, but in my arrangement the secondary battery is 8 amps against the 10 amp battery supplied with the kit (Alien 24 volt). This kit uses the "handbag" style container (described by the Chinese manufacturers as a "frog") and in one of these I have substituted lithium polymer cells for the original (defective) lithium ion cells, with a substantial saving in weight (1.8kgs against 3kgs).

Recent tests suggest that in warm weather this pairing (one LiIon on the bike, one LiPo in the bag) should be good for up to 50 miles range on a 20 inch Dahon.

 

[flecc]

I like the idea of lighter batteries and would accept the lower capacity.

Unfortunately the outcome isn't linear. For example, take a bike with a 10 Ah battery that has range of 20 miles. With a 5 Ah battery the range would not be 10 miles due to the high current demands of our motors, it might be 7 miles or even less, and with a 2 Ah battery it might not limp a mile.

I did once make up a modular e-bike battery which could be run as a 10, 7.5, 5 or 2.5 Ah. Here's an excerpt from the article on that:

I also carried out test using one and two modules for reduced capacities. One 2.5 Ah module alone was completely inadequate for this powerful motor so the test was abandoned, the A to B test already having covered this anyway. Using two modules for a 5 Ah backup battery weighing 2.5 kilos was more successful. The power was reduced slightly more, probably losing about 15%, but perfectly adequate as "get home" power, but the range was greatly reduced. Instead of the half capacity halving the range, it quartered it to only just 5 miles, this due to the stresses of the very high motor demand on a high resistance 5 Ah source. This usage also generated high cell temperatures due to stress.

So I ended with a half size battery that gave markedly reduced motor power and only just did a quarter of the range, plus running too hot anyway, needing care in use.
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[torrent99]

Googling '24v batteries' leads to ones for power tools. I saw one which was 2ah (DeValt?). Would that work with suitable plug/socket adaptation?

A number of people on endless-sphere have used power tool packs very successfully. Generally though more than one is used to get sufficient current. (They're fairly cheap in the US, but as usual we don't get access to the cheap deals in Europe )

The packs usually used are Bosch 36V Lithium (LiMn based) and DeWalt 36V Lithium (LiFePO4 based).

 

[AndyOfTheSouth]

Thanks for these various comments. Hadn't realise that the size/output relationship was non-linear. Is that why Cytronex have a 4ah battery (if I remember correctly) because that is the smallest size before the power drops off too much?

On the suitability for ebikes of the battery to which I referred... I think the PDF actually says that they are intended for them. I found the link somewhere in endless-sphere. I wonder where they can be obtained? Given the professionalism of the document, I presume they are widely available somewhere in the US. I would have thought that a 1.2kg battery would be pretty useful - I like the sound of the home made version, by the way!

 

[flecc]

Hadn't realise that the size/output relationship was non-linear. Is that why Cytronex have a 4ah battery (if I remember correctly) because that is the smallest size before the power drops off too much?

Cytronex wanted a discreet bottle battery but found that lithium types just couldn't supply the current needed with a small battery for the reasons I've mentioned. Therefore they opted for an NiMh battery. These have largely been dropped from e-bikes in favour of the lighter lithium types, but NiMh have better high discharge characteristics suffering less voltage loss when heavily loaded so that suited Cytronex. They have had to specify very high grade cells though.
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