Noob question re: battery choice

[NRG]

Hi all,

I'm new to e-bikes and have been reading as much as possible over the last few weeks but I need the help of the experts here. I'm putting together an e-bike as an experiment for casual use....I've made a few errors already, I bought a Chinese Ebay kit 24v 500w and found I could have done better from AlienOcean I don't want to make any more mistakes if possible

As the kit is already on it's way I'm a bit stuck so will have to go with it, being 24v I *thought* it would be easier to use SLA's in combinations to get the required voltage and Ah....24Ah seemed to be a good choice given the loss due to the Peukert effect.....however with more reading 36v or higher would appear to be better...

So my question is should I stick with SLA or go with a 24v Ping or other LIFePO4 pack? I've identified some good SLA's from Denka and Yausa (like the TEV range) that promise longer life and come in at $140 or so for two but the size and 14.5Kg weight is a bit of a problem.

The Ping 24v 20Ah comes in at $344 and just under 5Kg but I'm not sure if that includes delivery...would a 500w motor kill the Ping pack?

I'm sort of leaning towards the Ping but I'm still a bit unsure....

Many thanks

 

[Fecn]

The Ping pack is a good choice. The life expectancy is far higher than for SLA, so it works out cheaper in the long run. LiFePO4 batteries have a Peukert number of about 1.05 (very good) and deliver a very stable voltage even under high currents.

The 20Ah ping pack is pretty much ideal for a 500W motor.

 

[NRG]

Thanks Fecn,

Ping confirmed the 20ah would be a good match and at avery good price.

However, I'm tempted to go SLA in the short term as winter is approaching and I doubt I'll get the best use out of the Ping until spring next year...

 

[daniel.weck]

This German supplier ships to ay European country, and their 485 Euros battery looks very good:

"LiFePo4 Akku 38.4V/9.5Ah in Industriegehäuse (ca KW44)"

ElfKW product ordering

Pedelec-Forum - Einzelnen Beitrag anzeigen - LiFe-Akku von ElfKW ( 38.4V, 9.5 Ah )

ElfKW battery overview

 

[NRG]

I've decided to knock the SLA idea on the head, to get the Ah I need the batteries are just too big and heavy....so I've returned to the Ping battery but I've also been reading up on Endless-Sphere about LiPo batteries and would like to get Fecn (or anybody else) opinion on these vs LIFeP04.

It's a little more expensive to go LiPo but the weight and space saving size of them is quite compelling IE: the weight for an Ah like for like battery is under half the and the size about 25% smaller. (2.15Kg vs 4.9Kg)

I've read about the charging and discharging issues and think I could handle it with a good intelligent charger and LVC warning device, however, is there anything else I should be aware of?

Thanks in advance!

 

[themutiny]

Ican onlyspeak personally on this. The weight saving on lipoly is fantastic, however there is some trade-off. I don't think they deliver as much current as a normal li-ion, and the voltage drop is very quick. I cannot compare to a Ping. If you will mainly be cycling in favourable conditions, I guess the lipoly will be adequate. There is of course the difference in useful workinglife to consider also - I believe this is firmly on th side of the lifePO4

 

[daniel.weck]

This 9.5Ah battery shape is good for putting inside rack-luggage or even in a large frame bag (good price too, I wonder about shipping charges to the UK):

activeshop24.de - LiFePO4 Akku - 36V 9,5Ah - inkl. Balancer - NEU

It's probably less easy to package-protect than my 10Ah Ping though (due to the difficulty to source/make aluminium casing of suitable shape).

 

[Fecn]

I've decided to knock the SLA idea on the head, to get the Ah I need the batteries are just too big and heavy....so I've returned to the Ping battery but I've also been reading up on Endless-Sphere about LiPo batteries and would like to get Fecn (or anybody else) opinion on these vs LIFeP04.

It's a little more expensive to go LiPo but the weight and space saving size of them is quite compelling IE: the weight for an Ah like for like battery is under half the and the size about 25% smaller. (2.15Kg vs 4.9Kg)

I've read about the charging and discharging issues and think I could handle it with a good intelligent charger and LVC warning device, however, is there anything else I should be aware of?

LiPo batteries do offer a better power to weight ratio than LiFePO4 (Ping) batteries, but I don't trust LiPoly batteries... particularly not cheap ones. I bought a bunch of 18650 LiPoly cells from DealXtreme last year. Because I didn't need them all at the time, 6 of them went into storage (40% charge level... check/top-up every couple of months), but even with no usage an perfect storage conditions, one of them still died utterly after 9 months. I think if you get high quality cells then you are fine (e.g. my laptop battery is now nearly 4 years old, but still has around 70% of it's original capacity), but they cost a fortune (such as the £395 for the Panasonic packs). The panasonic packs however use Lithium Manganese technology, which has a power density much closer to LiFePO4 anyway. The 260Wh panasonic pack weighs in at 2.3kg I believe... whereas a 290Wh 9-cell (29.7v, 10Ah)Ping pack would weigh in at around 2.53kg. Basically, I don't really trust LiIon batteries as I've had so many bad experiences with them over the past 10 years, and in spite of the claims each year that all the problems with LiIon have been fixed now, the batteries I bought less than a year ago still went wrong.

LiFEPO4 technology has a lot of promise, but hasn't really been thoroughly proven in the field yet. Estimated lifespan for LiFEPO4 cells is around 10 years, but nobody has had them on the market for that long yet, so it's only a few cells on test in laboratories which have been tested this thoroughly. This may explain why it's so hard to find people saying bad things about them... or maybe it's because LiFEPO4 is a safer and more reliable technology to use in the first place. The LiFEPO4 chemistry was described by it's inventor as 'rust plus mud', which is a pretty accurate description, and also explains why you can just throw them in the trash when they're dead without having to worry about recycling. LiFEPO4 doesn't explode or busrt into flames if you overcharge it... nor if you short circuit it. The other advantage that LiFEPO4 has over LiIon is that the output voltage is very very stable for the majority of the batteries discharge cycle. Fully charged, my ping pack sits at 29.7v. After 80% of the capacity is used, it's down to 29.4v. (To contrast this, my LiPoly pack starts at 29.4v when fully charged, but has dropped to around 27v by the time 80% is gone). In the case of my bike, each volt dropped from the battery means 15W less peak power to the motor.

Charging LiIon or LiFEPO4 packs both need a specialised Battery Management System to balance the charge levels of different cells in the pack. With Lead-Acid, NiMH and NiCD technologies, when a cell is fully charged, it starts converting the excess charge into either gas bubbles, or heat. Lithium based cells don't work the same way - The fully-charged state is very much a question of how much lifespan you want from the battery (e.g. charge a LiPoly pack to 4 volts per cell and you will probably get 1000 cycles. Charge to 4.1vpc and get 700 cycles... 4.2vpc and 500 cycles. 4.3vpc = 250cycles. 4.4vpc = 100 cycles... but at 4.5vpc you catch fire/explode) - As such the BMS is critical to ensure that all cells reach the same full-charge voltage. As long as your battery pack has BMS then all you need to charge is a fairly dumb fixed-voltage charger.

I'm very happy with my Ping pack (9-cell, 29.7v, 20Ah), and would recommend that over an unbranded/unknown LiPoly pack anyday.

 

[daniel.weck]

The good thing about Ping is the possible layout/packaging customizations that are available. For example (message from Li Ping):

"
Actually, we can make our 48v20ah pack into two parts for weight distribution in saddlebags. And we have made many such packs for our customers. Please pay attention they're not two 48v10ah packs in parallel or two 24v20ah packs in series, but just one 48v20ah in two parts. Because there's only one 48v BMS to control both parts.

Anyway, we can also make two 48v10ah packs for you to connect them in parallel, but you need to add diodes in the circuit to avoid current between the two packs. Attach a diagram of 3 packs in parallel for your reference.
"

 

[NRG]

Thanks for the reply Fecn, many points to ponder....I'm looking for more of a plug 'n' ride solution so the Lipo, although tempting, may not be best for me. The last thing I probably want is to be faffing about with balance charging and LVC problems....

Anyhow, my plans may have changed yet again as of last night....I've just learnt my kit is 'lost' somewhere in Shanghai! So I'm in 'discussion' with the seller....might be a blessing in disguise....time to give those Alien kits another look!

PS thanks Daniel, didn't know Ping could re-size the packs, something to keep in mind.

 

[daniel.weck]

PS thanks Daniel, didn't know Ping could re-size the packs, something to keep in mind.

EDIT: The V-Power BMS electronics seem to be flawed ! I would stick with Ping. See here: Endless-sphere.com • View topic - ebay LiFePO4 sellers to avoid: ep-battery, volgood

---

V-Power seems to be a reliable (* beware the not-so-good BMS, see update message above) manufacturer as well (although Li Ping is demonstrating obvious expertize with the evolution of its BMS system...not so transparent with V-Power):

vpower.hk

eBay Store - LiFePO4: E Bike, Scooter, LiFePO4 Battery

Prices are similar to Ping, even cheaper (including BMS and strong charger). They are flexible with the cell layout inside the battery pack (and their BMS is quite a large independent electronic circuit board compared to the fixed/taped-on Ping mini-board), for example my 10Ah Ping battery dimensions are 150x105x150mm, here are V-Power choices:

210 x 180 x 75 mm
110 x 180 x 140 mm
345 x 110 x 75 mm

36V 10AH V2.5 LiFePO4 Battery Pack

36V 10AH LiFePO4 Battery Electric Scooter E Bike Safe - eBay (item 220496891866 end time Nov-17-09 05:58:42 PST)

 

[NRG]

Thanks to every one who replied, I've finally hd my money refunded so I can now start to look at alternatives, the Alien kits are looking good at the moment but the limited Ah batteries are of concern as is the recent discussion on freewheel ability of the motors...maybe nothing to worry about...anybody have an alternative supplier suggestion?

Ideas would be most welcome...