[Technologic]

Originally Posted by david85

The high voltage cutoff is taken care of my the charger since it dynamically adjusts the charge current and voltage during charging and will shut down when charge is complete, so in effect there is a high voltage cutoff. The high voltage failure of the cell is claimed to be over 10 volts, the charger stops charging at 3.65V (my observations show closer to 3.55V, but its cool outside right now). The low safe voltage is 2.5V, this is considered the 100% DOD mark.

From my observations, there is a significant drop in amps (~25%) by the time you reach that point. There are low voltage alarms that EVs can be fitted with off the shelf, and I don't think it would be hard to adapt an actual low voltage shut off that will disable the main pack if some one is careless in operating the vehicle.

I don't really see the problem with the charger mouted BMS. The 4 cell ballancer that my sample uses seems to work just fine. Seems to me its fewer thigs to go wrong. The ballance time takes about 2 hours after most of the charge has been completed.

There are numerous issues with that kind of charging when multiple cells are introduced. Firstly Lions should be kept over 30% charge at all times unless you want to basically waste the battery.... one slip up where 1 cell drains faster than the next cell and blamo... loss of 16k dollars.

2ndly the overcharge might not happen, but bloating the batteries isn't necessary to hasten their life span significantly. Simply doing a 101% charge can kill the DoD by quite a lot.

Again you need cell to cell regulation and cut off abilities so cell voltages are monitored and kept from dropping too low for LIFETIME safety.

[david85]

Originally Posted by Technologic

There are numerous issues with that kind of charging when multiple cells are introduced. Firstly Lions should be kept over 30% charge at all times unless you want to basically waste the battery.... one slip up where 1 cell drains faster than the next cell and blamo... loss of 16k dollars.

2ndly the overcharge might not happen, but bloating the batteries isn't necessary to hasten their life span significantly. Simply doing a 101% charge can kill the DoD by quite a lot.

Again you need cell to cell regulation and cut off abilities so cell voltages are monitored and kept from dropping too low for LIFETIME safety.

I've taken this one past 90% DOD with no ill effects that I could see. Aside from a drop in performance which is to be expected on that end of the cycle, the temperature went up buy 7 degrees, where on previous tests it went up 5 degrees (celsius) during the course of the whole test. I have heard of the 30% SOC rule, but that was in reference to storage and shipping because of legal regulation that was put in place for 3.7V Lion (cobalt oxide) cells. The info I have for these batteries recommends ~50% SOC for transport and storage.

All of the cycle life projections that I've been given by my supplier assumed 80% DOD or more. Thundersky does show cycle life projections for 70% DOD though (in the 3000 range), but their cycle life projections seem to be more optimistic. I remember seeing a graph once that assumed 50% DOD and cycle life of over 5000, but I can't remember where....might have been TS.

What sort of control chips would we be dealing with if they are to be used on cells that can dump up to 1000 amps?

[Technologic]

Originally Posted by david85

What sort of control chips would we be dealing with if they are to be used on cells that can dump up to 1000 amps?

Well I've read that anything below 25% of a full charge on Lion will cut the life the same way dropping a lead acid below 50% will... this is why voltage cut offs for each cell/battery is so important.

Well the chip itself wouldn't control it... not that you're talking about a large opamp/mosfet anyway even if you needed that kind of discharge.

Remember that amplifiers have been using opamp (chipamplifiers) in the 300-400w range for a long, long time and they're roughly 2 dollars a piece for the very best ones.

I don't know a ton about electrical engineering. Truthfully though you will only have a monitoring chip per cell/battery, not 1 chip guiding all of the cells. And with a 2C max rating you shouldn't be dumping over 400 amps through 1 cell... not to mention (with 48 batteries like you plan) that would yield almost 9000 amps at (18+kw). I don't think you'll use that much, ever... but maybe I'm wrong. If you do... you will need 0000 gauge copper at least.

a 200w mosfet could easily handle the load, though again... you don't need it... all you need is voltage monitors that relay the data when it's too low and too high to a cutoff (that's where you need the large electronic and mechanical switches) but again... 4000w+ amplifiers have been around for years... and are currently so cheap in the sound industry it's not worth talking about. An 4000w sound amplifier is way more complicated than a non-digital voltage monitoriing system, which is why I've always wondered why BMSs are so few and far between

the only answer I have is that the chinese can't engineer well (which I've experienced first hand for many years). But that's why I feel it'd be a sound investment for my project considering I plan to make many more than one custom, ground up car (cloning my 1000mpg equivalent 500lb car for sale sometime in the next year). Not to mention the students at my college (4th engineering program in the US) would easily design something like that for beer money.

All you need is a chip monitoring high voltages and low voltages for every battery/cell that can then engage a cut off relay between that cell and the line (mechanical). Or you can just make it all digital, which would be cheaper if done right, but harder to engineer.

[david85]

So what you are talking about is simply monitoring each cell, feeding that into a central controler or computer, and then thats where the safety system is engaged to either alert the operator or even automatically cut the power. If any one of the cells gets out of speck the safety system activates.

Metric mind has a BMS system. No idea what the price is though.
http://www.metricmind.com/

I remember swapping a few Emails with a representative for Worley Parsons in Singapore last year. Worley Parsons is a big oil company that operates in Australia, south east asia and indonesia. Anyway, they also have a line of LiPo batteries (the older 3.7V chemistry) and Kokam (in Korea) is making their batteries under license. They carry a BMS system like you describe. One chip on each cell, then all communicate to a main PCM. The price was in the $1.60/watt hour range (before the cost of BMS), so I walked away, but they do have a proven product. ProEV racing is using Kokam batteries in their subaru impreza racer.

So you want to build for the market too? Cool, that makes at least three on the forum so far......

[Technologic]

Originally Posted by david85

So you want to build for the market too? Cool, that makes at least three on the forum so far......

I don't want to, I will... within 8 months... the problem is the time to do it currently because of graduate school.

Metricmind, like all DIY BMS systems, is overpriced. He possesses a product everyone one of us "needs" so he charges accordingly being one of the 2 places you can even find a Lithium ion BMS.

I'm hoping to do a full on 0.09cd (with an cross sectional area roughly 1/3 common sedans), 500lb, all fiberglass aluminum 2 tandum seater in the 11,000 dollar finished range with a 100-120mile range off around 8kwh (with kevlar reinforced sides so no side airbags will be needed)... and/or just sell the prepackaged lithium packs + BMS once I'm to that point. Since my making permanent glass molds and welding jigs for the frame I figured I might as well try to sell a few finished cars since they now would qualify for around 5000 dollars in tax credit with the newest bailout bill

Anyway that's precisely what I mean about the safety system... the cells could in fact activate shunts from one battery if it gets full and then it can be "reset" once the charging has completed... it's a fairly simple system to be honest, but very effective... also if one cell goes bad (or reaches low voltage before the rest) while driving it can easily just remove that 1 battery from the pack and you can keep driving with almost no additional hardware.

Material science is where my love is at, but it's a hobby so that I don't begin to hate it. Lawyering will be my actual career. But it's bugged me for a long time that the auto industry is so incredibly slow to adapt to anything. There are so many amazing materials well beyond anything that exists now that would take them 100+ years to implement if DIYers/small companies don't start destroying their regional business.
I'm not really talking about fiberglass, elastomers, etc which have been around for 30+ years and they still don't want to implement. But there's things that only exist in lab settings that can easily be scaled up and drop full sedan weights to 700 lbs, provide oil free engines with coefficient of frictions 1/10th that of oil, and provide crash safety at 200+ mph.

[david85]

I know what you mean. Its a big world with lots of good ideas, but it seems like only the bad ones ever see the light of day. I still can't get over the fact that cars and trucks still rust. One of many reasons why I will never buy a new vehicle. Although yours does sounds like fun. You should see what Lexus is planning...neat stuff.

Well Technologic, its our turn now. Maybe we can do better than those that are holding the rest of the world back. "now all I have to do is build it" heehee.

[david85]

OK back to the original topic.

I got a reply and they do not mind including other sizes of batteries as well and will do what they can to give a good price, but need to know if anyone wants BMS and charger as well. Should I price out everything or just the bare batteries?

[Technologic]

Originally Posted by david85

OK back to the original topic.

I got a reply and they do not mind including other sizes of batteries as well and will do what they can to give a good price, but need to know if anyone wants BMS and charger as well. Should I price out everything or just the bare batteries?

I'm interested in some 100ah packs... maybe 20 or so....

it will depend entirely on price though

[david85]

Originally Posted by sailfish11

Is this order just for 200Ah batteries or can we get other configurations? I'd like 90 or 100Ah, but I'd also need 98 of them so my pack total Ah would be comparable to yours. Can this be added to the order (and what would be the cost)? Thanks!

OK, you didn't specify the voltage so I assumed you wanted 313.6V, and thats what I asked for. The voltage is such that they didn't want to price the charger until you are sure its what you want. Something about it being more difficult to match. But the price did include BMS, Hmm... That seems a little confusing, but anyway heres your price:

$13164.18 (US$)

In my case they priced the charger and BMS seperately, so maybe the BMS cost is simply a flat % of battery price. I asked for 90AH cells.

Technologic, this could give you an idea what yours would cost as well, but I could ask for 100AH anyway if you want.

Originally Posted by RKM

David,

I'm very interested! I think I would be wanting 45 cells 3.2V with 160Ah (if available) for a pack with 23 KWh.

Could you remind us of the discharge C ratings (continuous and max burst) as well as weight per Wh?

Do they provide a suitable charger and BMS for an EV application? Quality and cost?

I'll be very interested to know a cost estimate per Wh. The timing works well for me as I won't need batteries before spring.

Your higher amperage testing of these batteries will let us know how suitable they will be (though the risk remains for long term reliability!). Thanks again for taking the lead on these batteries.

Rob

They seem to like 160AH cells for some reason. Your price includes everything (BMS and charger) and comes to only $7951.36. Thats (sit down for this one guys.......)


$0.345111111111/ watt hour per

This is the first time I have EVER been quoted a price like this for LiFePo4 batteries. I need to find out if this is a mistake or why the big difference. But if its real, I'll drop my 200AH cells like a bad habit if I can't get a comparable price for the larger size because this is a huge difference in price. Indeed we may all want to switch over to 160AH for that price. I will have to ask why there is such a difference.

[Technologic]

Originally Posted by david85

$0.345111111111/ watt hour per

This is the first time I have EVER been quoted a price like this for LiFePo4 batteries. I need to find out if this is a mistake or why the big difference. But if its real, I'll drop my 200AH cells like a bad habit if I can't get a comparable price for the larger size because this is a huge difference in price. Indeed we may all want to switch over to 160AH for that price. I will have to ask why there is such a difference.

I'm very interested at that price point... keep in touch about this.