DIY Electric Car Forums banner,how about chinese supplier

8271 Views 22 Replies 5 Participants Last post by  chinaev
how do you think about EV and lifep04 battery suppliers in China?Are their technology reached maturity level?
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technology seems fine. sales techniques and shipping are questionable.
For the sake of cost reduction,most chinese bosses hire fresh graduates.And lots of brokerage appear when ship the goods.Two real hot potatoes.

May i ask are you a EV conversion engineer?
Pamela Song
a mistake because it makes them look like idiots.

not exactly. I am a semi-retired mechanical engineer with a background in software development, management, and have built one DIY EV ( I am very interested in promoting Evs because I feel they are the key to urban/suburban transportation fo rthe future.

It is amazing! But owing to the battery technical limits,popularization of EV is still hard to realize.A good EV battery must have the ability to fight against bad environment and improve the degree of safety.How fast could your car run?40,60,or higher?
a mistake because it makes them look like idiots.

not exactly. I am a semi-retired mechanical engineer with a background in software development, management, and have built one DIY EV ( I am very interested in promoting Evs because I feel they are the key to urban/suburban transportation fo rthe future.

It is also amazing that you reply to me so fast!:)
I would say Chinese LFP cells are of decent quality, but not great - one thing that definitely needs improvement is the rigidity of the cell casings. The cells tend to swell during heavy use, especially in hot climates and all of the manufacturers require the use of metal plates and straps to restrain this swelling. Unfortunately, having to keep the cells bundled up with the manufacturer's strapping makes it a lot harder to find spots to install them in a vehicle. The end user has no choice but to break the bundles apart and then figure out how to repackage them so they won't swell. This, to me, is totally unacceptable because once the cells start to swell a vicious cycle ensues: the internal resistance increases rapidly with swelling which causes the cells to heat up more which causes more swelling, etc.

Additionally, the datasheets for all of the Chinese LFP cell manufacturers are poor. Some don't even include good dimensional data and even worse is that the manufacturers often change the dimensions of the cells without warning or even updating the datasheet (if it had dimensional data in the first place).

Internal resistance of the cells, even those in the same "batch", can vary wildly. I have personally found a 2:1 variation in cells by recording the difference in voltage drop when rapidly switching back and forth between a 1C and 2C load.

One good thing I will say is that cell capacity (in Amp-Hours) is almost always accurate.

Overall, it does appear that Chinese LFP cells are improving and that bodes well for the future.

It would definitely be nice if they were more widely available in the US.
Because of cell casing swell,you invent LPF cooler,or the same function as BMS.I would like to know,whether or not there is slight influence to LIFEPO4 battery,for example:lithium-ion mobility speed ,the phase transition of Lithium-iron and iron phosphate.I will carefully read your product description on the web when i come off duty.
Pamela Song
what is amazing?

The lack of popularity is part marketing.... most people don't believe they could use a car that has a limited range. In reality a recent DOT study shows that 60% go no more than 40 miles on a daily basis, and 90% go less than 100. Today's LiFePO4 cells can easily be used in a small conversion to achieve 50, 75, or close to 100 miles... 'safer' than sitting on a tank of gas.

My car, which is still a old-tech flooded lead car at just 96volts, has aproximately the same top speed as it did with gas. The motor has the same horsepower almost. Top speed is around 75-80mph on the level. Acceleration is 'enough'. I will be upgrading to 120v of LiFePO4 soon. I had some 'issues' with a wholesaler here in the US failing to deliver pre-paid batteries, forcing lengthy Legal proceedings to attempt recovery. The delivery process from China is the problem, not the batteries themselves.
I am amazing that your web is really a guide for people who want to diy his car.
Electric car is more safer than gas tank car,and the explosion of lifepo4 battery is off chance.Fuel-engined vehicle like a action bomb.Most of time high speed is not necessary.Quite agree with you.
It is really problem to delivery goods to US,there are so many trade barriers.
I bought a pack of ThunderSky cells from a US vendor and have found the quality of the cells to be first rate. I can't say the same for the US vendor. The cells have proven to be well matched in service and they where shipped at very close to the same state of charge (all within 0.01 volt.) I think the written documentation could be better.

I'm going to disagree Tesseract about the cell case. I think the requirement to block the end of each row is preferable to having each cell be made slightly larger and heavier so its case was strong enough without restraint.
Drop shipping from USA is very practicable.I think the reason for your unsatisfactory to the Thundersky US vendor is that there may be just one Employee in his SOHO,not a staff.But i have to say this programme really win lots of customers for Thundersky itself.
Regarding the swell of cell case,how about make the lifepo4 battery also a valve-regulated one as lead-acid battery?
Pamela Song
I think the main reason for the unsatisfactory US vendor is because the one I used is in bankruptcy. I was one of the last people to get their battery order from them.

The chemists have to figure out what can be done to best manage the pressure. My understanding is that allowing them to swell or vent will increase internal resistance. Low internal resistance is very important for EV service. I am having no problems pulling 5C peak currents, with the average cell voltage over 2.9 volts and no cell dropping to 2.5 volts. I found that strapping the cells into groups of 8, using the end plates Thundersky provided, was easy to do.
Bankruptcy?How long is the warranty of Thundersky LFP battery?

Doping modification with kation is a way to lower the internal resistance.May i ask you how to strap the cells into 8 groups? Is it able to lower internal resistance effectively?
And, while some BMSs include some form of thermal management, I would certainly not say that cooling and BMS are the same thing.
i do not mean that BMS and cooling is the same thing,i was wondering what is the product on the web
It's a 300V nominal, 1000A continuous DC motor controller.
What is the competitive advantages of your DC motor controller?
I am sorry, but I believe there is a big misunderstanding. The swelling is NOT heat related! And it is independent of cell resistance. The swelling is SOC level related.
- 0 ~ 90 % SOC = not swollen, regardless of usage.
- ~100 % SOC = swollen, whether sitting on a shelf, charging, or discharging (at any current, and for any cell resistance)
Changing rate of LFP crystal lattice is 6-7% when charging.There will be some volumn change when SOC is 0~90%.
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