Small LiFePO4 batteries

[Arbol]

I don't think I have seen a build yet, where someone has used the LiFe Turnigy packs. I have used them for other applications and they have been excellent.

I had overlooked this comment. Sacko, when you say "I have used them for other applications and they have been excellent", could you please comment a bit more?

In particular, how would you rate these batteries for e-bike usage? Would they need a BMS (or charging via lipo charger), or they could be charged using usual lifepo chargers?

 

[jerrysimon]

Please note Lipo and LiFePO4 cells require different charging voltages. Typically LiFePO4 cells are 3.3V are rest and 3.6V fully charged and Lipos 3.7V at rest and 4.2V fully charged.

This is where a BMS takes away any complication in that all this is taken care for you including max discharge values. Some argue thought that if a BMS fails it could also ruin the cells.

With my Konion and A123 cells I have never used a BMS. However my packs are small, the cells remain in balance really well themselves and I tend to check them every couple of months and re-balance them manually if needed.

My first A123 12s1p pack was balanced when I first built it and then only bulk charged for a year with no balancing before I lost two cells. These were easily then replaced. I probably now balance them about every 3-6 months. So far it looks like the Konion cells hold their balance even better than the A123 cells.

Regards

Jerry

 

[Sacko]

I used them for small amp draws of approx 5amp cont 12 amp bursts in a 90 size electric heli, to power the servos etc.

From memory Internal resistance was around 3.6ohms, measured from my Cellpro Powerlab PL8.

I would certianly use a BMS, possibly one from Bestech (cheap and effective!). You definitely need some for of battery management. If using a BMS you could use a bulk charger you are referring to.

As mentioned above, voltages are very different between the chemistries.

LiFe will hold @ 3v continuously throughout the discharge. When the pack has minimal capacity remaning though towards the end of the cycle, the voltage drops drastically.

From a personal point of view, I would use LiPo just because the cells are cheaper, lighter and offer higher discharge rates.

I suppose it all depends on what you intend to use it for, and how many amps you intend to pull from them.

 

[Deleted member 4366]

You can use any type of cells without a BMS as long as you charge them with a charger that balances them, which is most lipo chargers. Also, you can et the charging voltage in most lipo chargers, some do it from a menu of cell types, others, you just set the maximum cell voltage. Even the cheapo iMax chargers do that. The main problem is only being able to charge 6 cells at a time, so you have to split the pack, and put the two halves in series for operation, and parallel for charging, which means that a permanent installation is not practical.

 

[jerrysimon]

The main problem is only being able to charge 6 cells at a time, so you have to split the pack, and put the two halves in series for operation, and parallel for charging, which means that a permanent installation is not practical.

Yes i.e. not plug and play.

Regards

Jerry

 

[Sacko]

The main problem is over dis-charging the cells as well as over charging them.

A BMS will look after your cells, making sure you do not harm them on a cell level.

 

[Arbol]

OK, I think I understand: if I wanted to charge with a lipo charger, I should physically disconnect the series connection of both batteries in order to be able to charge them (one battery, one charger). This would be cumbersome.

Now, the second solution, a BMS. If I understand correctly, if I have say 12s in LiFePo4 (e.g. 2x6s, such as Turnigy 4500mAh 6S2P 30C LiFePo4 Pack these are 6s not 5s like the link I posted a few days ago; also it is Turnigy, which I believe is a better brand than Zippy; and 4.5Ah is more than 4.3Ah), I could connect these 12s to a 12s BMS, and this would provide several layers of protection (LVC, HVC ...). In addition, the BMS would do the balancing automatically, so I could bulk charge with a LiFePo4 charger, which is much simpler than a LiPo charger + power supply.

In fact, if I understand correctly, usual LiFePo4 batteries such as Ping, in fact are a wrap up of cells + BMS.

So, in theory everything is clear (if what I have described is correct; if not, please correct me).

In practice, the problem is that I do not know even how to start: if I have 12s cells and a 12s BMS, what should I do? I guess I would need connectors and cell holders. But I would not know what to do. Even there is the dreaded word "soldier". Should I soldier anything? Is there a guide for dummies how to create a LiFePo4 battery out of cells and BMS?

Thanks for your help, guys / gals.

 

[Sacko]

Yes, the above is correct

Endless-sphere.com • View topic - 24s BestechPower BMS Thread

Endless-sphere.com • View topic - 24s BestechPower BMS Thread

 

[Arbol]

Wow, then this opens a whole world of possibilities. I am just looking at ebay, but for Li-ion there is:

UltraFire Rechargeable 3.7V 5000mAh 26650 Li-ion Battery 2X 4X 6X 8X | eBay

for a bit more than 30 pounds, plus the cost of the BMS, one would have a 36V 5Ah battery! And very light, about 900g plus the weight of the BMS.

Apart from the BMS vendor suggested above, is there a cell vendor that people in this forum may recommend?

Edit: as a reference, I have found an interesting vendor, with cells of reputable brands http://www.ebay.co.uk/sch/ecoluxshop/m.html?item=360726072155&rt=nc&_trksid=p2047675.l2562

Edit 2: with the strategy of having a BMS, would it be possible to have a configuration in parallel, say a 10s2p? For example, one could have 20 cells http://www.ebay.co.uk/itm/2x-Genuine-LG-ICR-18650-Li-Ion-2800mAh-3-7V-Rechargeable-Lithium-BATTERY-LGABC-/360734405201?pt=UK_ConsumerElectronics_Batteries_SM&hash=item53fd723251
for a cost of 90 pounds (plus the BMS) giving a 36V 5.6Ah for a weight below 1 kg.

Edit 3: the LG link above shows the Ultrafires et al are not very reliable, and reputable brands are much better.

 

[jerrysimon]

Except all batteries are not the same. Many of the cheap torch batteries cannot handle the constant current draw resulting in voltage sag leading to low performance and the BMS cutting out. In addition the capacity of those batteries are often way over specified. You need to check the constant/peak current discharge specs.

So for those LG cells for example Max. Discharging Current : 5600mA

Means you would need at least 3 or 4 in parallel depending on your constant current draw.


Another consideration is how you are going to connect the batteries together in packs. Some of the other links include the supplier spot welding them in the series/parallel blocks you require. Soldering them together yourself is risky in that you will be applying heat direct to the end contacts leading to possible damage to the cell. Some suppliers will sell them with tags already spot welded onto each cell which you then solder to each other. But again much better to get them to spot weld the series/parallel blocks up for you.

A lot of this info is detailed extensively over on endlessphere under the battery technology forum.

Regards

Jerry

 

[Arbol]

Just for reference, I have found a seller that does the spot welding:

eBay

 

[Arbol]

Another minimalistic approach would be a q75 / q85 / keyde with a 6s HK LiFePo4 4.5Ah. This would be 24V, so not very powerful (and possibly current would be low) but weight would be extremely low. And one would only need a lipo charger + power supply, but that would be basically "plug and play". Also, it would be quite cheap.

 

[jerrysimon]

Just for reference, I have found a seller that does the spot welding:

eBay

Yep that is the one I have used and linked to in the past. Very reliable but now unwilling to post to the UK under current battery restrictions on air freight to the UK except using more expensive approved shippers. Whilst still a good deal, you need to order 40-60 plus cells before it becomes worth while.


Regards

Jerry

 

[Deleted member 4366]

Many of the Ultrafire batteries on Ebay are cheap fakes with poor performance. Be careful. The same applies to some other types as well. Best to go with reputable cell suppliers.

 

[jerrysimon]

Note that reliable seller also now seems to be listing Konion (cell nickname for SONY-US18650V and VT) cells again ready made up in 5s2p packs.

Sony US18650VT for Makita BL1830 LXT Lithium ion 18V 18 Volt Repair Battery Pack | eBay

I purchased 8 of those to make up my current 36v, 3Ah and 6Ah packs. Lots of info on these cells over on endlessphere here. These cells perform really well are relatively safe, reliable and hold their balance (without a BMS) even better than A123 cells.

Again though I don't think those prices include shipping to the UK (if you select them they wont let you buy them from a UK ebay account) for free and you will have to pay extra for a different shipping method.

Jerry

 

[Arbol]

Interesting. From the Sony link, one can see the cells have already tabs, and the documentation with images is quite good. But it says the purchaser has to soldier the BMS to the cells. I do not know how to do that. Which tools would I need to do that? In general, which kind of technician could do something like this, locally?

 

[cwah]

Anyone interested in the Panasonic NCR18650PD?

I'm thinking maybe to get them from another supplier, who can give better price. But I need to buy something like 1500 cells lol.

 

[cwah]

Actually I've just seen this:

http://www.embedded-world.eu/fileadmin/user_upload/pdf/batterie2011/Sonnemann_Panasonic.pdf

Apparently the highest energy density are the NCR18650A cells:

http://www.orbtronic.com/batteries-chargers/panasonic-3100mah-ncr18650a-li-ion-rechargeable-18650-battery-cell-made-in-japan

I need to learn more about them, at 250wh/kg. I could have a 1000wh pack under 5kg with bms and case!

 

[jerrysimon]

Interesting. From the Sony link, one can see the cells have already tabs, and the documentation with images is quite good. But it says the purchaser has to soldier the BMS to the cells. I do not know how to do that. Which tools would I need to do that? In general, which kind of technician could do something like this, locally?

The instructions are to re-cell Makita drill packs. For ebike use its simply a case of connecting balance leads, balancing them once then connecting them in series for a 36v pack made out of the two 18V 5s2p packs. You DONT need a BMS. You can also use four packs and connect two of the packs in parellel for a 5s4p to make a 18v 6Ah pack then two of these in series for a 36V, 6ah pack. If you follow the endlessphere link is shows you how people harvest them used from dud drill packs and make up their own ebike packs. Buying them from this ebay supplier means you get new cells and they are already made up for you.

As I said I have used these to make two 3Ah (1Kg) and one 6Ah (2kg)pack and in my opinion for lighter power applications like mine, they are even better than A123 cells.

Its a shame that seller won't post to the UK now as at that price you could have a 36V, 6Ah pack for £90!

cwah those cells have mixed reviews on endlessphere and I doubt they will retain balance so well without a BMS. I guess with a BMS they will be fine though.





Jerry

 

[cwah]

Yes you have to use BMS, but they are 2 times lighter so even adding a BMS would give you a lighter pack.

Let's say for example you get the NCR18650PF (new model of the PD with better soldering end):
18650 2900mah 10A discharge Panasonic NCR18650PF 3.6V high power battery cell

47g/cell at 2.75AH capacity and 10A discharge.

So you have a 10s1p or 36V2.75AH at 470g. Add a 100g bms and 100g wiring/wrapping and you have a 670g pack

A bigger pack of 36V5.5AH would weight 1.1kg.

Isn't that much better? Konion and A123 cylindrical have around 95wh/kg. The new cells around 210wh/kg. Apparently if you charge them to 4.1V you can reach 2000 cycles:

That's really compelling, however, these are all manufacturer data..