Battery current Output??

[EV_dub]

Just heard again from hipower.

they sujested the following:

"First, Using 72V80AH pack, offer nominal 240A current, max 400A current, 72kg weight.
for 48 pcs of 3.2V 40AH single cells, each 1.5kg, 64*112*160mm."

"Second, Using 72V50AH pack, so peak is 8C could nearly 400A current, normal would be 150A.
less normal power, but still offer large current, 45.36 weight".

They claim a 50ah battery that will deliver 8c for 15sec and 5c for 30sec.

"3 years before we offer LifePO4 battery for pure electirc.
In 2008 we developed high power type for Hybrid EV offer 3C norminal and 5C burst".

The 48 x 40ah will weigh to much for my moto-x bike. need to keep it close to 40kg.

I had a look at lifebatt but a little expensive for my pocket unfortunitly.

[retepsnikrep]

The lifebatt 8/16ah pack I have for sale weighs 20kg

I do not recommend 50ah highpower cells for the discharge rate you are looking at, they may work but you should be aiming for an average drain of 1C max IMO with a peak of 150A (3C)

You could try 20ah A123 pouch cells they can do an easy 10C apparently plus nice and light.

[Jeremy]

You could try 20ah A123 pouch cells they can do an easy 10C apparently plus nice and light.

I've been seriously thinking about these, Peter. As you say, they are pretty light and nice and compact, plus, at $2.50 per amp hour (~$0.78 per Wh or $50 for a 20Ah cell) plus shipping, duty etc each they aren't too expensive for what they are.

I've also been looking hard again at conventional LiPo, as the prices are now pretty good and they are significantly smaller and lighter than LiFePO4. The obvious snag is the potential fire hazard if they are abused, but being able to buy genuine 15C discharge cells for ~$0.41 per Wh makes them tempting for a bike.

I've been thinking along the lines of buying lots of these: http://www.hobbycity.com/hobbyking/stor ... h_4S1P_15C to build a pack, most probably a 16S pack with a total capacity of 30 Ah (24 of those packs, wired as a total pack of 16S 6P). This would give around 60V at 30Ah, weigh around 11.5kg, be capable of delivering 450A continuous or around 600A peak and cost a total of around $720 plus shipping etc. Plus, being small, the individual packs are easy to fit into the awkward confines of a bike frame.

The folks on the ES forum seem to be having success with using/abusing these packs, which makes me think that they may be a good option for an electric bike or motorcycle.

Jeremy

[retepsnikrep]

Jeremy

I ordered 52 of the 20ah a123 cells a couple of weeks ago which are enroute as we speak
For my next Insight upgrade adventure! The lifebatt 8ah were too small to stand the 50A regen but coped fine with 100A discharge.

I agree Li-po are an option but I think their cycle life/calendar life is not as good?

Peter

[EV_dub]

Thanks Jeremy,these packs sound quite promising.

40 packs will give me around 72v 40ah, 20kg and cost around $1200

Just wandering what you meant by 16S 6P?. I see you will need 6 parallel x 4 series to make 60v 30ah.

What were you thinking for BMS for these batteries?

[EV_dub]

The lifebatt 8/16ah pack I have for sale weighs 20kg

I do not recommend 50ah highpower cells for the discharge rate you are looking at, they may work but you should be aiming for an average drain of 1C max IMO with a peak of 150A (3C)

You could try 20ah A123 pouch cells they can do an easy 10C apparently plus nice and light.

Thanks for the offer retepsnikrep. Only problem is that I will need another 16ah pack to make 32ah total.
Looking at around 1200quids.

[Grumpy-b]

I actually find the specs being offerd as rather confusing. My berlingo has cells with a 100amp capacity. They are able to deliver up to about 200amp, but their stored energy is 100amp at 6volt. Most of the lithium versions I have been offerd have been quoted as having say 100 to 140 a discharge in normal use, but this equates to 2 or 3 c, and the cells are say 50amp. Presumably they only have the same power available and as such can only give up the equivalent of 50amp storage so they would only last half the time.

I guess this is too simplistic, but it also seems that one could think that the cells are up to the task, but would always be bing used at a constant C much greater than 1. Presumably thier life would ultimately have to reflect this.

Grumpy-b

[Jeremy]

Jeremy

I ordered 52 of the 20ah a123 cells a couple of weeks ago which are enroute as we speak
For my next Insight upgrade adventure! The lifebatt 8ah were too small to stand the 50A regen but coped fine with 100A discharge.

I agree Li-po are an option but I think their cycle life/calendar life is not as good?

Peter

I'll be interested to hear how you get on with these cells, as they sound pretty good. The only problem I can see with using them is the need to find a simple way to terminate the tabs.

LiPo cycle life is certainly poorer than LiFePO4, but will probably still be OK for the sort of use I have in mind. Mind you, if those A123s live up to their expectations, then I might yet change my mind.

Jeremy

[Jeremy]

Thanks Jeremy,these packs sound quite promising.

40 packs will give me around 72v 40ah, 20kg and cost around $1200

Just wandering what you meant by 16S 6P?. I see you will need 6 parallel x 4 series to make 60v 30ah.

What were you thinking for BMS for these batteries?

I was thinking at the cell level, rather than the pack level (each pack has four series cells).

I have a spare 16 channel Fechter/Goodrum BMS (the one developed over on the ES Forum) and can adjust the shunt and LVC voltages on this to match LiPo I think. Failing that, I could make up some more of the 4 channel DIY shunt boards I made up for the electric boat, as they are cheap and easy to build, then use a couple of cheap Cellog 8's for monitoring and LVC.

Jeremy

[GregsGarage]

I actually find the specs being offerd as rather confusing. My berlingo has cells with a 100amp capacity. They are able to deliver up to about 200amp, but their stored energy is 100amp at 6volt. Most of the lithium versions I have been offerd have been quoted as having say 100 to 140 a discharge in normal use, but this equates to 2 or 3 c, and the cells are say 50amp. Presumably they only have the same power available and as such can only give up the equivalent of 50amp storage so they would only last half the time.

I guess this is too simplistic, but it also seems that one could think that the cells are up to the task, but would always be bing used at a constant C much greater than 1. Presumably thier life would ultimately have to reflect this.

Grumpy-b

I think the confusion lies in accidentally mixing up 2 characteristics of batteries, the energy they can store (amp-hour capacity) and the amount of power they can deliver (C-rate, a 1 C discharge will use all the batteries energy in 1 hour). Lithium cells are very good at storing lots of energy but lead acid, Nicad and NiMH are better at delivering lots of power (generally speaking, depends on the actual battery construction). For example Hawker AGM batteries are still very popular with drag racers because they can deliver lots of instant power. I have a portable jump start pack that has a 10ah lead acid battery, but it will deliver many hundreds of amps to start a car. Peter has found this as well, he is having to go to a 20ah lithium cell to handle the currents that can be easily handled by a far smaller (in amp-hour terms) NiMH battery in his Insight project.

When looking at a application for lithium cells I believe it is very important to look at what the manufacture calls the "standard discharge/charge" rate. For most large lithium prismatics this is around 0.3C to 0.5C. I am sure that as the technology matures it will improve, but what it means is that you should be aiming for a vehicle range of 2 hours driving if the "standard discharge" is 0.5C. Given the price of lithiums it does make the pack even more expensive, particularly if you don't require 2 hours of range.