Low Capacity Battery

[lemmy]

I've just been out for my first 'proper' round trip from New Malden via Putney, Chelsea, Mayfair, Hyde Park, West End and back via Kings Road and Wimbledon Common, making some stock photographs.

The cameras and tripod are quite heavy and I carry them in a back pack. I weigh 78Kg, cameras maybe another 5Kg. Conditions sunny with high blustery winds. The route has some hills, from Raynes Park arcoss Wimbledon Common and Putney hill on the way back.

My Garmin tells me I did 26.5 miles. The battery was almost fresh charged, I'd done a couple of miles the previous day. Moving average was 10.2mph (slow going Chelsea/ West End). I used eco about 25% of the time, no assistance maybe 10% medium the rest. The battery finished up with 1 LED lit.

That's pretty good. It certainly makes the bike practical transport. I knew I'd had a ride but was in no way tired when I got back. And I would be happy enough to do the same trip again this afternoon.

For what I do, there is nothing else practical Motorised vehicles have all kinds of parking restriction around town. Unassisted bikes, I couldn't carry that weight and cover that distance - after 15 miles I'd be knackered.

One thing on my wish list - I wonder if anyone agrees? A spare battery, not 10ah, maybe 2ah. Light enough to carry without trouble and some 'get you home power' if the trip is longer or more arduous than you'd expected.

For £120, I'd buy one tomorrow!

 

[emissions-free]

I've got a 36V 6Ah battery, that's 12 series, 2 parallel, 3.2V, 3Ah cells. It weighs 2.7kgs including the case and I've used it drive a 500W at 36V motor. If you go much smaller than that the cells need to have quite a high C rating, but it is doable. The cells I've been using are 5C constant, 8C max so even a 12 series should in theory have 15A constant, enough for a 250W motor which typically has a 15A controller limit.

Regarding costs, you need to consider that it still requires a BMS and maybe a charger. Without charger and with the cells just shrink wrapped, it might not be too far off your hoped for price for a 36V 3Ah pack. Should come in at a little over 1kg. A123 cells are really good cells and have a 35C rating, but are more expensive and a 26650 cell is only 2.3Ah if I remember correctly.

 

[lemmy]

So it is do-able, then?

I suppose Panasonic (my bike's system) would have to make it so that it fitted their standard chargers.

I want one!

 

[emissions-free]

Yeah it's do able but you'd need to make sure you've got the right connections for it to fit onto the existing cabling. There's another member who is doing this with A123 cells. Easiest way would be to cut the existing battery cable and make an in line connection that is accessable. You could just disconnect the existing battery and then connect the backup. It's not a good idea to just connect them in parallel. How you'd go about doing that is hard to say exactly but it's possible. However if the bike is still under warranty, you'd want to be careful about doing any mods that couldn't be removed

A small charger isn't that expensive anyway. The standard charger will be the wrong voltage for a 36V LiFePO4 pack. Your bike uses a 36V battery right?

It's late here, so I'm off to bed, but I'll check again tomorrow

 

[lemmy]

Your bike uses a 36V battery )

No, 26v 10ah. But it's still under warranty - only just got it.

What I'd like is for Panasonic to make one for me so that I can charge it in the present charger and slot it in and out like the main battery!

 

[emissions-free]

I can't see any reason it can't be done, it's just a matter of someone actually doing it Getting the right connectors etc would probably be the most difficult part if they use a special type.

An enthusiastic fiddler could quite easily sort it out I reckon. Can't imagine Panasonic knocking 1 up for you though, not for £120 anyway

 

[Tiberius]

Lemmy,

If you want a booster, or a range extender, then a small battery is ok. But you should have it wired in so that it shares the load with the main battery.

http://www.pedelecs.co.uk/forum/electric-bicycles/1261-torq-battery-mod-storms-up-hills.html

Nick

 

[Orraman]

When I got my Panasonic powered Gitane last year there was the option of a 3Ah battery.

I now have a fancy for the new folder at 19.2kg, again with a 3Ah battery.

No doubt the battery is available as a spare.

Dave

Gitane cycles : Origam e-Bike

 

[lemmy]

Interesting! I've hunted around but can't find any lisiting for one as a spare. I'll contact Panasonic themselves, I guess.

 

[Orraman]

£27 Get me home

As you want an occasional 'get me home', then two of these 4cell packs in series should suffice and only £27 the pair delivered.
At 2.2Ah capacity they will be able to supply power for quite a few miles and at 12C discharge they can supply 26A which is more than enough. The connector blades on the bike are of a size that could fit the large automotive push-on connectors.

If you have a suitable 12V power supply or battery they could be charged separately by using only the multi pin balance connector leaving the series connection undisturbed. In the scond link, this charger has 4 independent charging circuits that balance by terminating the charge to each cell as it reaches 4.2V and the LEDs change from red to green.

Dave

Lipo 14.8v (4S) 2200mAh 12C From Heliguy.com

HobbyKing Online R/C Hobby Store : hexTronik Balancer/Charger Dual Charge Capable $28.34

 

[NRG]

I feel Lipo would be a bad choice in a small capacity due to the cell breakdown issues if you discharge below 2.7v. At 2.2Ah it would be very easy to use up the capacity quickly and damage the cell with the real risk of explosion during recharge. Better would be the 5Ah cells from Hobby City with some BM6 LVC monitoring.

 

[daniel.weck]

I feel Lipo would be a bad choice in a small capacity due to the cell breakdown issues if you discharge below 2.7v. At 2.2Ah it would be very easy to use up the capacity quickly and damage the cell with the real risk of explosion during recharge. Better would be the 5Ah cells from Hobby City with some BM6 LVC monitoring.

I was under the impression that the 36V Bosh A123 batteries for power tools include electronic circuitry to prevent damaging the cells ?

 

[Orraman]

Sorry NRG but I can't agree with you.

Much smaller than the 5Ah you put forward as a minimum, 3Ah Panasonic batteries are supplied on new bikes, they are available as replacements and they are Li-po.

In post # 1 of this thread lemmy was seeking a 2Ah battery for light weight.

I do agree that it is important to be concerned about the Low Voltage Cut-off and indeed the charge final voltage.
When model Li-pos were 8c the recommended LVC was 2.75V, the controversy now is should it be raised from 3V to 3.3V, so to cover this the Surface Mount micros that I make for models are user adjustable.

However to my understanding there is a LVC in the Panasonic motor unit.

Dave

 

[Orraman]

Sorry lemmy,

I missed your post, I know of no distributor for Gitane in this country now so one might have to be imported from France. When I enquired the cost was not proportional to the Ah of the battery with the 3Ah being quoted at £240 and that was before the price hike.

Dave

 

[NRG]

I was under the impression that the 36V Bosh A123 batteries for power tools include electronic circuitry to prevent damaging the cells ?

Most likely Daniel but my comment was aimed at the RC Lipo packs which do not...

 

[NRG]

Sorry NRG but I can't agree with you.

Much smaller than the 5Ah you put forward as a minimum, 3Ah Panasonic batteries are supplied on new bikes, they are available as replacements and they are Li-po.

In post # 1 of this thread lemmy was seeking a 2Ah battery for light weight.

I do agree that it is important to be concerned about the Low Voltage Cut-off and indeed the charge final voltage.
When model Li-pos were 8c the recommended LVC was 2.75V, the controversy now is should it be raised from 3V to 3.3V, so to cover this the Surface Mount micros that I make for models are user adjustable.

However to my understanding there is a LVC in the Panasonic motor unit.

Dave

Dave, they will have a BMS no? The RC pack will not. You would need some cutoff protection either DIY with the BM6 to trigger a relay say, controlling the brake cutout switch cct or go with one of the cutouts from TPPACKS.com

Products

Either way I agree a bare Lipo RC pack is a risk...a single 4s 5Ah from HobbyCity is $40 or £25 plus shipping and weighs just over 500g....I would use a couple of these to give a bit more head room with some LVC protection.

HobbyKing Online R/C Hobby Store : Turnigy 5000mAh 4S 20C Lipo Pack $39.95

 

[Orraman]

NRG,

Thank you for the link to tppacks.com.
Their LVC look convincing but 2 off 4 cell LVC will cost $80 plus p&p, vat, customs and brokerage?

Agreed,
Panasonic has a BMS.
RC pack does not, but that also means that there is no constant drain on the batteries so they could retain a useful charge for several months.

I am not so sure now that the Panasonic motor has a LVC so 2 of the Hobby King battery monitor 4S at $3.49 look good for cheap and simple.

Regarding the size of the backup battery it must be horses for courses. Lemmy is already carrying weight and while your 5Ah would come within his price limit it would weigh twice as much and to perform it's function must be carried everywhere.

Dave

HobbyKing Online R/C Hobby Store : Hobby King Battery Monitor 4S $3.49

 

[averhamdave]

I'm following this and similar posts with interest. My thoughts are also towards a diy battery pack. The battery monitoring system from TPPacks seems to solve one of the problems of using and monitoring multiple lipos.

However what is the proposal for balance charging? If I were to build a battery using say 4 off, 4S packs wired to give 28v and 10A how would I balance charge say every 5 discharges (which is what I do with my model heli lipos)?

Has anyone either here, or on Endless Sphere produced simple plans to do what I'm contemplating?

Thanks

 

[jerrysimon]

My sample A123 cells with solder tabs have only just left HK

I wanted to see a sample before I ordered enough to build two 6s packs (around £70 in total), so its gonna be a while before I get round to making the packs up.

6s A123 (and other sized packs) are available ready made up (a little expensive though) with balancing tabs. I plan to just run two in series. I guess for lower voltages you could get a smaller packs and again connect them in series. The cheaper balancers/charger only do up to 5 or 6s balancing which is why I am using two 6s packs rather than one 12s.

It appears these cells can be abused more than Lithium Polymer, though I intent to balance them occasionally.

Regards

Jerry

 

[emissions-free]

Jerry,

you're not gonna use a BMS on your 6s pack right? or have I got that wrong? What charging method will you use?

I'm interested in trying a few of these A123 cells also. A place I've had quite a few samples from can get them but they are a little bit more expensive per cell than a standard but high quality LiFePO4 cell (5C cont, 8C max), plus the capacity is lower.

I've got a cell spot welder lined up Just need to do a few checks to make sure the company doesn't have a bad rep and I'll get it. A bit pricey, but less that I had though it was going to be. Also gonna pick up a discharger/battery analyser but don't know what to go with as yet. If you have much knowledge on these items, I'm all ears. Also need a new scope. I used to use a TiePie USB scope (Dutch company) but they are quite pricey and faster than I probably require at this time so was thinking about a PicoScope (British Company I believe) as they start at quite a reasonable price and was recommended to it by an electronics design engineer friend.

If you haven't used a USB scope before, I highly recomment them, so convenient and combined with a small laptop can make a great little tool for diagnosing problems whilst on the move. They start at less than £200.