Small LiFePO4 batteries

[Arbol]

Hello, I have seen in several posts in this forum that some users have their own DIY small LiFePO4 (and / or A123; I am not sure if A123 is LiFePO4 or not) batteries.

I am still defining which kind of e-bike I do need, but one clear possibility would be a Brompton with say a Q85 (or one of these tiny motors I also have seen in this forum, which I believe are not Nanos, but something even lighter, 1.2 kg).

However, when one looks at the usual Chinese suspects (Ping, BMSbattery, Greenbikekit, elifebike ...), LiFePO4 batteries are either 9 Ah or bigger.

But I believe for urban usage, one could cope with smaller batteries, especially if one is willing to pedal. And I want to pedal, I want to exercise. The reason for the motor is just to jump-start during the first say five minutes, and if some day I feel tired. But in general, I tend to believe my electricity consumption would be quite low. Also, probably I could charge at work.

I have seen tiny batteries, such as 1.1 Ah (18650 I believe) and 2.3 Ah (26650 I believe). I believe these small batteries are attractive for weight purposes (if they weight 1kg, a Ping 36V 10Ah weights 3.7kg, so 2.7kg saving; the Titanium package for a Brompton saves around 700g for a cost of several hundred pounds, for comparison purposes), and also, one could adapt the real battery needs over time in a more flexible way than with a big battery package.

The problem, of course, is that I do not know how to assemble everything. From what I have read, one needs a BMS / PCM to safe charge and distribute the current efficiently for all cells.

But then one DIY-er said that at least with some cells, even a BMS was not necessary.

http://www.pedelecs.co.uk/forum/electric-bicycles/8212-a123-batteries.html

And then I guess one needs connectors / other small pieces to make everything work.

Is it reasonable to assume that a person that does not know about this, could assemble his own DIY LiFePO4 small battery? Is there a "guide for dummies"?

Thanks!

Edit: I do not consider LiPo batteries for safety and number-of-cycle reasons.

 

[Deleted member 4366]

Those 18650 A123 cells are not so easy to find now. IIRC the original A123 factory closed down. You can still find the cells, but you have to be careful, especially from Chinese suppliers, whether they're genuine and can produce the current of the originals.
I found these from Hobbyking:
Genuine A123 Systems 18650 1100mAh LiFePo4 Cell w/ tabs

At 1.1 AH 3.3v each, you need 24 to make a 2.2 aH battery. When 30 Samsung cells will make a 6.6aH battery able to give 18 amps, I can't really see the point.

Whatever cells you use, you don't need a BMS. Instead you connect balance wires and group the cells in two packs of 5S or 6S, and use a lipo charger to charge and balance them. You don't have to balance every charge, but for the small extra effort, why not?

The charging procedures are the same whatever cells you use, so Lipos become very attractive. It's the best way to get a lightweight battery. The number of charge cycles isn't really an issue, because they're a quarter the cost of A123, and anyway, they should do 500 full cycles, which is two years use, when there may well be something new.

You can use a BMS with any type of cells as long as it's programmed to the right voltage. Lipos are the same voltage as normal Li-ion batteries (3.0v to 4.2v), so you can use a BMS from a scrap battery, although I'd test the LVC and HVC before using it as set-and-forget.

 

[Alan Quay]

The problem with a small battery like this will be current delivery. Assuming a discharge rate of about 1C, then a 20Ah battery can deliver 20A (lots), a 10Ah will give you 10A (enough). 3A is probably not worth having, as it's giving about 100 watts at 36v.

In theory, if you upped the voltage you could get away with it. This is probably not practical though.

 

[jerrysimon]

That the beauty of the 2.3Ah A123 cells is that they will deliver 60A constant even if at that they will drain in about 5 mins lol

They are still available if you check my post here however I think there are better alternatives, though as Mike says you need to look carefully at your peak/constant current requirements.

As Dave states an alternative is to go Lithium Polymer though not advisable unless you are CERTAIN about how to use them safely.

Regards

Jerry

 

[Arbol]

Whatever cells you use, you don't need a BMS. Instead you connect balance wires and group the cells in two packs of 5S or 6S, and use a lipo charger to charge and balance them. You don't have to balance every charge, but for the small extra effort, why not?

The charging procedures are the same whatever cells you use, so Lipos become very attractive. It's the best way to get a lightweight battery. The number of charge cycles isn't really an issue, because they're a quarter the cost of A123, and anyway, they should do 500 full cycles, which is two years use, when there may well be something new.

You can use a BMS with any type of cells as long as it's programmed to the right voltage. Lipos are the same voltage as normal Li-ion batteries (3.0v to 4.2v), so you can use a BMS from a scrap battery, although I'd test the LVC and HVC before using it as set-and-forget.

You argument is quite suggestive. In fact, lipos have an appeal to me. I am a physicist, and a quite systematic person. So I believe I would not be prone to commit errors with lipo management. But lipos seem to go against two important requirements: safety and "plug & play-ness".

I live an apartment, and I have read several horror stories about lipos. I do not have a specific place where I could charge my lipos with say a few meters of separation of "anything else". And I do not want to be two hours in the same room as the charger to check that something is working properly.

I have seen there are "safe bags". Would it be reasonably safe to charge lipos inside a safe bag and leave the room, inside an apartment? or is this too risky and not recommendable?

On the other hand, smallish LiFePO4 packs are safe but they are not "plug & play" either. Couldn't one have a LiFePO4 of say 5Ah, but with a BMS, such that one does not need to rebalance with a lipo charger (in fact, one would not need a lipo charger at all)?

Ping offers a 36V10Ah, but it seems too bulky, at 3.7kg. Something of the weight of its 24V10Ah (a little more than 2kg) but at 36V would be great. But I guess his cells are 10Ah.

 

[Arbol]

however I think there are better alternatives, though as Mike says you need to look carefully at your peak/constant current requirements.

As Dave states an alternative is to go Lithium Polymer though not advisable unless you are CERTAIN about how to use them safely.

Which are in your opinion the better alternatives? The Li-ion Samsung?

Regarding " unless you are CERTAIN about how to use them safely": I know I could learn, and I have a friend who uses Lipos, so he could teach me. My concern is not so much about being certain that I manage everything properly, but that even if everything is done right, could it be that lipos "explode"? Or in most cases, lipos failing means the user has done something wrong?

 

[Arbol]

What about this LiFePO4 at HobbyKing?

ZIPPY Flightmax 4200mAh 5S1P 30C LiFePo4 Pack

Two in series would accomplish 36V. Total size and price, scaling with competitors, is decent. Would this be a "Plug and play" solution, ie only need a LiFePO4 charger, or it would require a more complex setup, such as balancing with a LiPo charger from time to time, due to absence of BMS?

 

[Sacko]

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.

The benefits with these packs, is their configurability. Here are 4 6s 5000mah packs I am putting together for someone. They will be bulk charging using a BMS (just need to solder it up).

44.4v nominal 10ah pack


100.6v nominal 10ah pack flat


100.6v nominal 10ah pack cube

 

[jerrysimon]

Which are in your opinion the better alternatives? The Li-ion Samsung?

Regarding " unless you are CERTAIN about how to use them safely": I know I could learn, and I have a friend who uses Lipos, so he could teach me. My concern is not so much about being certain that I manage everything properly, but that even if everything is done right, could it be that lipos "explode"? Or in most cases, lipos failing means the user has done something wrong?

Lipos are safe if used correctly but IMHO I don't think they are plug and play. I personally would not leave them in my office or charge them in the house. I think the risk is quite low as I said if you know how to use them but when they fail they fail spectacularly. I would certain not make them up for someone else.

All batteries have some risk I guess most through short circuit most likely.

Sako when those LiFe Turnigy packs first came out a couple of years ago, they had mixed reviews in the ebike application. If they are now better then I agree an excellent option


Regards

Jerry

 

[jerrysimon]

What about this LiFePO4 at HobbyKing?

ZIPPY Flightmax 4200mAh 5S1P 30C LiFePo4 Pack

Two in series would accomplish 36V. Total size and price, scaling with competitors, is decent. Would this be a "Plug and play" solution, ie only need a LiFePO4 charger, or it would require a more complex setup, such as balancing with a LiPo charger from time to time, due to absence of BMS?

They seem to have a poor write up

Jerry

 

[Deleted member 4366]

This battery is relatively light, high discharge and plug and play. It can also be mounted in the triangle on the front of the seat tube:
36V9AH panasonic lithium ion battery for e-bikes-GreenBikeKit online store for electric bicycle components-GreenBikeKit.com

 

[Scimitar]

Which are in your opinion the better alternatives? The Li-ion Samsung?

What would suit you down to the ground would be what I've got - a battery pack made of Konion cells. Actually 6x Bosch 36V toolpacks paralleled up to give 15Ah, but you could do with fewer.
Unfortunately Konion cells are no longer made, which strikes me as daft, as they are inherently much safer than most other lithium chemistries. Just out of sheer caution, I don't over- or dis-charge them anyway, but if I were to do so, they'd not be as likely to bite me in the ass and burn the house down as some others would.

 

[cwah]

Why konions are safer? I've read several fire thread from them

 

[Geebee]

These are cheaper, higher capacity and get good reviews. ZIPPY Flightmax 5000mAh 5S1P 20C

I charge in the house but on a cast iron hearth in the lounge in a safety bag (whilst I am sitting in a chair nearby), I also store them in the house in a saftey bag and use them on the bike in the safety bag
I have read of a user having a large LiPo "explode" in the bags with no problem except smoke, short circuit in poor wiring from memory was the cause.
Most accidents I have heard of have been physical damage or over charged/discharged, treated with commonsense I feel they are acceptably safe.

To give an idea of my saftey standard for batteries, I won't charge a phone over night as I have seen few batteries puff up in phones and we have all seen fire stories about them.

 

[Arbol]

This battery is relatively light, high discharge and plug and play. It can also be mounted in the triangle on the front of the seat tube:
36V9AH panasonic lithium ion battery for e-bikes-GreenBikeKit online store for electric bicycle components-GreenBikeKit.com

This one is interesting, thanks. I have been looking at the pictures, and I do not see how the battery mounts to the tube. Do you know if it is a general standard, valid for all kind of tubes?

 

[trex]

the mounting support (black blob at the front with wires) is clamped to the seat tube or down tube.

The battery is then slotted into it. A bit flimsy IMHO, the Bagier bag system as reported in this thread http://www.pedelecs.co.uk/forum/electric-bicycles/15611-pas-sensors.html seems better:
[video=youtube;gAwwBvirAAM]http://www.youtube.com/watch?feature=player_embedded&v=gAwwBvirAAM[/video]

 

[Deleted member 4366]

A few more details here, where you can see the clamp:
BAT-BX3691B

 

[peerjay56]

... the Bagier bag system as reported in this thread http://www.pedelecs.co.uk/forum/electric-bicycles/15611-pas-sensors.html seems better:

The split sensor for pedelec is such a simple idea, it's a wonder more don't do it. It would certainly save a lot of faffing with the BB

 

[Scimitar]

Why konions are safer? I've read several fire thread from them

They must have been sorely abused, in that case.
Probably abused because the clowns with them thought they were fool-proof. No lithium cell is.

 

[jerrysimon]

Agreed. I am not sure about Konions, but with A123 cells you can cut them in half or put a drill through them without any fear of combustion.

Both A123 and Konions cells can be under or over charged without fear of combustion though good chance you will ruin them, less so with the A123s.

I am sure most ebike battery fires are caused by shorting, though as I understand with lipos you have to be more careful to monitor voltages as again this can lead to problems. I used small lipos for years in my RC models and never had any incidents. Was only drawing a few amps. I did try puncturing an old one once

It smoked a lot but did not catch fire.

Regards

Jerry