Testing the big 15 and 20Ah LiFePO4 cells is tough! *Pics*

[swbluto]

Yeah, I'm in Shanghai, China. Of course there is cheaper labour available here but once you have staff it changes everything. They need to be trained, paid every month, kept busy and do a good job. I'm pretty much where I could keep a guy busy full time but I just need to take that jump and find someone that is at least reasonably capable.

Shoot, I must bite my tongue. It appears the per-capita income of Shanghai is about $9000. The minimum wage rates in the US suggest an annual full-time income of 2080*7 = 14560, so the wage difference doesn't appear to be that much different. I was thinking about the dirt cheap labor in China, like to the south, where the wage is something like $4000 / year.

Parti time it would likely have to be. I'd think it might be maximally beneficial if you take advantage of your particular relative advantages such as interacting with customers, building the website, etc. and take advantage of the cheap labor rates. By focusing on customers and marketing, you'd maximize sales which would likely offset the additional cost of labor. But, this is something that can be done after sales growth justifies it. If there's just not enough product demand, then it might not justify it (Although, I think there's probably a lot of demand.).

 

[cell_man]

There's plenty of people earning terrible wages in Shanghai too don't worry. I do agree with what you are saying, it doesn't make sense for me to be doing too much of the day to day hands on stuff and it can't continue for much longer if I want to grow. I'm still quite bogged down in packs that I've promised but most of these cells should be gone soon and I'm gonna avoid getting too involved in the hands on stuff in the future and rather just buy/spec finished products where possible. However, it's all been a valuable learning experience and will not do me any harm in the long run. I also value my time far more than what the average worker gets paid around here or what most are willing to pay for work done.

 

[CroDriver]

Just to show how reliable Paul (cell_man) is...

I wired over $20k to him and he delivered everything as promised. I haven't counted the cells nor tested them but they arrive one box after other. I should have 350 cells by the end of this month in my shop. Paul, I hope you can get more of this great stuff or that A123 will sell directly to me when they see what I'm about to do with them

 

[cell_man]

Thanks Mate The next batch will be on there way in the next couple of days. They're already cleaned and wrapped in plastic, just need to box them up and the courier will be here to collect when they get back from the May day holiday. Finger crossed I can get some more.

 

[countermeasure]

CroDriver,

350 pcs of 20 Ah cells?! Dang. You must be going for a record or something.

I want pictures during assembly and complete packs. Battery pron. Bring it on!

 

[amberwolf]

I definitely hope you get more of these cells; eventually I'll have a real job earning enough money to buy a bunch from you, and I'm sure you'll be long out of the ones you currently have in stock.

I was thinking about the dirt cheap labor in China, like to the south, where the wage is something like $4000 / year.

Wow. They make more than I do these days. (though I am working far less hours than they are, I'm sure).

 

[themotorman]

RE FETs at high current. I bet that the gate fails first!! You need to make sure that you do not have too much inductance that will reduce the gate voltage then you will be in the resistive part of the FET and boom!! It is very very hard as you say to switch at such low voltages BUT the problem is in inductance NOT low voltages. From v=Ldi/dt it takes hardly any inductance to make the gate drive useless.. using mosfet gate drive at max voltage for the FET would be my first pathway. High power schotkies on the gate to handle reverse volts might help but get the inductance down.. you could also try tuning the inductance with caps ( high current ones too ) and may be get the peak out from the intitial switching period. The Millar cap on the fet is the problem and you are stuck with that. You might be better off to use giant SCR's , although that would mean the current would flow until the battery was destroyed the SCR's could handle the current fine. You get one run per battery so make sure the data is well recorded.

 

[peterperkins]

I'm now running 50 of Pauls A123 20ah cells in my car project.

Maximum loads is 5C (100A) for short periods usually < 10S and maximum charge is 2.5C (50A) again usually for < 10S

Not as stressed as Luke's testing!! But it will give an idea of performance in a more gentle setup.

So far at 5C discharge they remain solid around 3.15V at 20C (Temp) I have them all in large block with no forced cooling and soldered tabs.
Self heating appears to be low and on the few shortish trips i have done so far they only heat up by a few C in use.

The higher voltage under load than the stock nimh cells in a mk1 honda insight also gives me a bit more power :wink:
Probably at least another couple of Kw from the 10kw motor

Pics etc are on this thread. http://www.insightcentral.net/forums/modifications-technical-issues/16928-a123-20ah-lithium-install.html

I report back in due course. Lets hope paul can get some more 8)


I forgot to ask, what is the recommended maximum temperature for these cells?

 

[cell_man]

Thanks for dropping by Peter. Your work is really outstanding, especially the implementation of the BMS and the factory look of the finished article, top job

There's no sign of more cells just yet but you never know. I'm gonna concentrate on the A123 26650s for now. Not as ground breaking as the pouch cells, but not to be sniffed at either.

Your figures are very good, it doesn't sound like the cells are being stressed in any way if they are only dropping to 3.15V under load. I suspect the load is not very constant and I can't see you having any heat issues. AFAIK 60degC is where things start to get bad, but they need to be hit with very heavy constant loads to get anywhere near that from my experience.

 

[peterperkins]

Thanks Paul. I have set my BMS to trigger heat alarms at > 45C so that gives me some headroom.

 

[etard]

Awesome work on the Insight Peter, I didn't know people were modding these, I guess if there's room for improvement or performance gains, someone's gonna try it.

I am wondering why though. Is it to go electric more often then not or you just weren't happy with the battery side of things?

 

[peterperkins]

Etard

Stock nimh pack has 4ah useable capacity this has 20ah and can be grid charged.
Ageing Stock packs go out of balance giving IMA errors and have high self discharge rates so are not very effcient.
Stock packs are very time consuming to repair.

Electricity is cheaper than petrol, so more electrciituy i use more mpg i get.