Will two of these be a good battery pack?

[rosjen]

HobbyKing Online R/C Hobby Store : ZIPPY Flightmax 5000mAh 6S1P 20C
Excellent value at about £31 each!!

So for about £100 (for charger as well) you can have a 10ah 44v battery pack
They even have a European warehouse


Tell me this is too good to be true

 

[jerrysimon]

And how are you going to make sure the cells remain in balance

Yes its too good to be true

PS and that would be a total of 44v, 5Ah given that connecting them in series doubles the voltage only and not the capacity.

PPS a more viable solution if your willing to take a risk

36V 10AH LIFEPO4 Lithium Battery electric bicycle bike on eBay (end time 01-Dec-10 09:15:26 GMT)

Regards

Jerry

 

[rosjen]

of course it's only 5ah - what was i thinking

Is balance everything? from what i read here many people don't even use a BMS and have no problems.

 

[rosjen]

i already have a very good ping 10ah but as I only use 2ah per day i was thinking of a smaller setup

 

[jerrysimon]

of course it's only 5ah - what was i thinking

Is balance everything? from what i read here many people don't even use a BMS and have no problems.

Not if you use A123 cells (though they need to be balanced intially) but the ones you reference must have a BMS or be balanced often. Lithium Polymer are also highly flamable if abused

Regards

Jerry

 

[jerrysimon]

i already have a very good ping 10ah but as I only use 2ah per day i was thinking of a smaller setup

Ok here is your answer

You will need to buy a balance charger initially to get them balanced but mine have remained in balance since then, for over 10 months using a cheap 36v charger. I have one at home and one at work.

Regards

Jerry

 

[jerrysimon]

And more detail Here

Regards

Jerry

 

[rosjen]

Thanks Jerry, that looks like the kind of thing I need. will reduce the bike weight by at least two K

 

[jerrysimon]

Yep for short commutes its a perfect solution.

Regards

Jerry

 

[daniel.weck]

Incidentally, I have just posted a comment about maintaining and charging 10Ah versus 2.6Ah packs. See here:

http://www.pedelecs.co.uk/forum/electric-bicycles/7165-new-battery-fair-prices-2.html#post90737

 

[averhamdave]

I have considered the option of using such Lipos for a long time and have noted the repeated negativity on here towards them - not without foundation though I'm sure.

I'm used to these large Lipos as my main hobby is flying large RC Helicopters - for which these batteries are being sold by Hobyking. (who incidentally are a very reputable supplier).

Regarding balance - they need balancing about one in four charges. More frequently would be nice but not an absolute must. If just using a couple of these - would balance charging be such an headache?

The fire issue is real but grossly exagerated. You would only be pulling 2 or 3C current on a 20C battery and providing you had appropriate low voltage warning (Cycle Analyst) I think the "explosion" risk is negligible.

Incidentally 12s = (12x4.2) = 50.4v off the charger. You would really want a pair of the 5S batteries (even cheaper).

Serious question, I would really appreciate anyones technical comment on the above as I'm sure it would be a runner.

Many thanks as usual, Dave

 

[Scimitar]

I was seriously considering HK lipo packs, but the sheer pita of unhooking, hooking up, being bloody careful all the time, just put me off.
I went for Bosch Fatpacks instead. Cheap-ish, simple, one charger, no fire, no explosion, no unhooking, no BMS, more or less fit and forget, and easily expandable for more range.

 

[jerrysimon]

Dave,

Like you I too am very familiar with Li-Poly batteries through RC interest. You are right in the ebike application they are not being abused as much as we do in RC.

I think maybe if you have this background then it would be ok to use them, but personally I would not recommend joe public to use them in this application otherwise.

Those fatpacks look interesting I thought they require a BMS

Regards

Jerry

 

[NRG]

RC lipos on here do get a negative reaction some of it justified but a lot is not (!)

I use them on my Peugeot, see http://www.pedelecs.co.uk/forum/electric-bicycles/5465-peugeot-revisited.html?highlight=Peugeot

They do need careful monitoring of charge and discharge but they remain in very good balance as long as you start out with a pack with good cells in the first place. There is no need to break packs down and reconfigure for charging. It's quite easy to configure packs for bulk charging and use something like the battery medic device to provide balance if necessary or a dedicated balance / BMS unit from TPPacks.com.

There is no other affordable battery type that has the power density that these RC packs have, 20+ C discharge rates are easily achievable and while it can be argued nobody needs this outside of the die hard enthusiasts over on ES it does mean the batteries hold up extremely well over time and use, the voltage remains high under load and will give excellent performance.

Issues start when cells get over discharged, below 3v and then charged up to and over their rated 4.2v.....they really do not tolerate this and will 'let go' in a very spectacular way...if they are top n tailed to 4.1v and 3.2v they remain safe and will give 800+ full charge discharge cycles. With Lipo you just need to be aware of the pit falls, if you master this then 15Ah battery with 20c discharge weighing under 4.5Kg can be yours.....

 

[averhamdave]

Thanks chaps for the constructive responses. You have confirmed exactly what I had alsways believed - its just that I was starting to think that I must be missing something somewhere with electric bikes - but obviously I'm not!

 

[NRG]

At 4.1 volt the cell will be as full as it needs to be around 95 to 98 %, the problems happen when they are charged to 4.2 volt. In a similar way on discharge the cell is just about depleted at 3.2v, take it below 3v and damage will occur.

 

[averhamdave]

At 4.1 volt the cell will be as full as it needs to be around 95 to 98 %, the problems happen when they are charged to 4.2 volt. In a similar way on discharge the cell is just about depleted at 3.2v, take it below 3v and damage will occur.

Intelligent chargers used in RC applications charge and balance at 4.2v per cell. Controllers usually limit the low voltage limit to about 3.6v. I am not aware/have seen a lipo discharged down as low as 3.2v but then again we are pushing these batteries discharging at up to 30 or 40C. Larger RC Helicopters running 12S/5000mah battery set ups can be consuming batteries at a rate of up to 5kw.

 

[NRG]

Yes, agreed they do, but for longer life and safety 4.1 to 4.15 should be the maximum. The RC chargers don't take this into account and aren't therefore intelligent enough 3.6v would be about 60% DOD so for an e-bike there's still useful capacity remaining.

Yes, RC use means much higher discharge rates so at 3.6v for flying is probably a safe low limit, we can go lower on our bikes but by 3.2v we are well and truly over the 'cliff'. Also, the packs on e-bikes will be larger at 10 / 15Ah so the voltage will hold up somewhat better.

 

[averhamdave]

Yes, agreed they do, but for longer life and safety 4.1 to 4.15 should be the maximum. The RC chargers don't take this into account and aren't therefore intelligent enough 3.6v would be about 60% DOD so for an e-bike there's still useful capacity remaining.

Yes, RC use means much higher discharge rates so at 3.6v for flying is probably a safe low limit, we can go lower on our bikes but by 3.2v we are well and truly over the 'cliff'. Also, the packs on e-bikes will be larger at 10 / 15Ah so the voltage will hold up somewhat better.

Thanks (and understood!)
Dave

 

[NRG]

Now here's an interesting RC battery, link picked up from ES...

20000mah 22.2V 20C RC Lipo Battery For Big Airplane RC Battery products, buy 20000mah 22.2V 20C RC Lipo Battery For Big Airplane RC Battery products from alibaba.com

Some of the claims in the spec. may be dubious but even if these cells can only deliver 10C they would still make a very powerful pack good enough for a DIY bike, 20Ah at 4.4Kg Apparently, there is a simple LVC/HVC 'BMS' available as well: $15!