NiCd can be charged quickly too. LiIon has the advantage for power density (both by volume and weight), which is rather important for aircraft. It's greener, too; much better looking on the government teat.
place:
don't see how they can continue to use this battery,
My bet is the battery. Cambridge University researchers only recently found that fast charging Li accelerates whisker growth, resulting in internal shorts and fire.
ure:
Damn customer returns. We told them not to drill holes in it....
Sno-o-o-ort >:-} ...Jim Thompson
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cture:
That picture is of the battery in the Boston fire. That may be the one that exploded or was cut apart by NTSB in their Materials Testing Lab. NTSB is just going to ask Yuasa what's going on, the battery is over their heads.
present.
I think a better option would be LiFePO4, which is now the chemistry of choice for DIY EVers. It does not have quite the high current capacity of Li-Ion, which can be as high as 30C or more compared to LiFePO4 of about
3-5C, but it is safer. There is a major cost difference as well, with Li-Ion cells as low as $0.20/Wh compared to about $0.35/Wh for LiFePO4. I have found some NiMH batteries for about $0.20/Wh and the energy density is not bad. As a comparison, SLAs are about $0.16/Wh and flooded deep cycle batteries are as low as $0.06/Wh. Good for a tractor, barely usable on acar, and pretty much a no-go on a plane.
The electronics for battery monitoring, protection, and charging is quite interesting and I am now working on a design for a single-cell monitor and charge balancer using a little PIC10F320. It will be able to read the cell voltage during charging, and bypass the charge when it reaches the top balance point (about 4.2V for Li-Ion and 3.6V for LiFePO4), and it will also signal the health of the cell with flashing LEDs. It will also have an optoisolator which connects in series to a charger which will be disconnected if any cell reports a fault. Similar monitoring will detect a weak cell on discharge to shut down the motor controller, and it will have a reverse connected Schottky diode to limit cell reversal if the excess discharge is not stopped.
A more sophisticated system will incorporate a transmit and receive daisy chain using optoisolators between cells and a master controller which can send commands through the string and receive cell status information on each cell, and also perform cell trimming by controlling the bypass load. There are some interesting discussions on BMS design and implementation on the
forum
since about 8AM EST).
Here is a preliminary schematic for the simpler design:
Here is a similar commercial design:
I am considering using small cylindrical cells in series for my electric
tractor project. I will be evaluating several cheap cells from China and
Hong Kong, 3000 mAh NiMH AA cells and 3200 mAh Li-Ion cells, as well as
1800 mAh LiFePO4. I don't really believe their specifications, so I will be testing them for true capacity. I want to put 12-24 cells in series in agarolite or steel tube (possibly EMT), which I think may reduce the chain reaction meltdown that has been reported with rectangular "prismatic" cells. I found some valuable information on fire protection for cells:
Paul
The 787 is a gold mine for Hamilton-Sundstrand:
"The Hamilton Sundstrand APS 5000 auxiliary power unit (APU) for the Boeing 787 Dreamliner is undergoing cold-weather testing to complete certification testing for cold-weather starts, operation during heavy snow and freezing rain, and exposure to de-icing procedures. Testing of the APS 5000 APU tailcone section began last November in Fairbanks, AK.
APUs provide power to aircraft while they are on the ground and in-flight backup power. The APS 5000 APU is rated at 1100 shaft hp and is designed to start and operate throughout the full range of the 787 operating envelope up to 43,000 ft. Hamilton Sundstrand Power Systems (HSPS), based in San Diego, CA, currently has more than
13,000 APUs in military and commercial service, including the APS 2000 for the 737 and APS 3200 for single-aisle Airbus aircraft. HSPS has been in the aerospace business since 1957 as part of Solar Turbines.In addition to the APU, Boeing chose Hamilton Sundstrand to provide the
787?s environmental control system, electric power generation and start system, remote power distribution system, primary power distribution system and high-voltage dc equipment racks, emergency power system, nitrogen-generation system, and electric pump subsystem.Rolls-Royce also chose Hamilton Sundstrand to supply the gearbox system for its Trent 1000 engine being developed for the Boeing 787. And Kidde Aerospace & Defense, part of Hamilton Sundstrand, is supplying Boeing with the complete fire protection systems package for the 787. The 787 program is expected to generate more than $8 billion in revenue for Hamilton Sundstrand over the life of the program."
electric.
Far from it. The 787 does not use bleed air, but has lots of hydraulics.
The hydraulic system in the 787 no-bleed architecture is similar to the one in the traditional architecture. There are three independent systems -- left, center, and right -- that collectively support primary flight control actuators, landing gear actuation, nose gear steering, thrust reversers, and leading/trailing edge flaps.
The primary power source for the left and right systems are engine-driven pumps mounted on the engine gearbox. In addition, the left and right systems are each powered by an electric-motor-driven hydraulic pump for peak demands and for ground operations.
......
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On a sunny day (Thu, 17 Jan 2013 16:58:33 -0500) it happened "P E Schoen" wrote in :
I see voltage divider R7 R8 on the gate, 500 Ohm versus 1k, and the Vdd of the PIC has an othe r 100 Ohm in series. That makes 600 versus 1000, do you still have enough gate drive counting in production spread of that MOSFET?
I will read that tomorrow, its midnight here now...
I would have used velcro.
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Yes, I was using the 1k as a series limiter for the overvoltage LED which I will be removing. So the resistor to GND will be 10k. The FDD6530A MOSFET is characterized for 2.5V gate drive and even 2.0V, but I need to make sure the circuit will operate even down to a cell voltage of 2.5V, so I can't afford much voltage drop. Usually the MOSFET will only be turned on for charging bypass, at which point the cell voltage will be 3.4 volts or higher, but it might also be used to "bottom balance" cells in which case it would be turned on until the cell is drained to its minimum safe level.
Sleep well .... unless you have a laptop with Li-Ion cells ready to self-destruct under your pillow!
Some of them are aptly named:
Paul
their
Hmm. Over their heads is not a good place for a "potential" incendiary bomb that is "currently" being investigated. :)
Paul
eir
mb
You can look in their online technical library and see their previous deali ngs with the battery are mostly to do with fire suppression systems. Their lab is mainly concerned with materials failure analysis. It's unrealistic t o expect any more out of them than a forensics on the fire origin between t he battery, wiring, or charging electronics, maybe.
totally electric.
Okay: "The Boeing 787 reflects a completely new approach to onboard systems. Virtually everything that has traditionally been powered by bleed-air from the engines has been transitioned to an electric architecture. The affected systems include:"
blah blah blah
d .
OK thanks, I guess it would be a little safer perfecting them on the roads. Where at least you can stop the car and get out.
George H.
My new schematic for the BMS, showing two adjacent cells and communication system. Instead of the optoisolator being on continuously and draining
5mA from the cell, it is just pulsed for about 10 mSec, which should also beenough for the green LED to flash, indicating normal operation. The optoisolator transistor provides a low pulse on the next BMS cell monitor, which lets it know the previous cell is OK, and if its cell is also OK, it passes the signal to the next BMS monitor, and eventually back to a master control unit, which expects to see a regular sequence of pulses indicating all cells are OK.
The communication could be refined by using an RS232 protocol and various data packets for command and response. Each cell monitor would have its own sequential address, such as an 8 bit for 255 cells (address 000 is the master). Thus the master could send a request to read the voltage of cell
007, and it would respond with Addr=0 Data=638 which would be a 10 bit ADC reading which the master could interpret as, say, 3.19V.I'm planning to use a more powerful PIC with perhaps 14 pins and much more flexibility for various functions, but I'm looking at using the tiny and
cheap PIC10F320 as a challenge, and because I have a couple of development boards I bought awhile ago for about $5 each.
This should probably be in a separate thread on BMS design. There are a couple on
Maybe the Dreamliner could be converted to all electric!
Paul
I forgot to add the link to my new schematic for the BMS:
Paul
(snip)
???
You will be in trouble with discharging Li-Ion long before you get anywhere near reverse polarity.
Yes, I considered that and the Schottky diode is an optional item that is probably ineffective. The proper way to protect against this is to shut down the device that is discharging the pack. I had thought about using an SPDT relay to disconnect the weak cell and bypass it with a short circuit so that the rest of the pack can continue to operate. But for large packs in EVs the current involved can be hundreds of amps, with 300 VDC or more, and possibly inductive loads. There is usually a large safety interlock contactor which can be tripped in case of a problem, but that should be done only if other means cannot reduce the discharge current.
However, I am looking into a concept where perhaps 8-12 small cylindrical batteries could be packaged in a series module of 24-36 volts with some protection and monitoring circuitry. If a large number of such modules were connected in parallel, a relay in series with the pack could open upon a
fault and it would not be switching much voltage, since other modules would keep the voltage equal. This would provide some redundancy since the loss of one pack out of several would only reduce the total available energy rather than cutting it off entirely. This could be important in an EV. And if each module were enclosed in a fireproof sheath, a destructive energy discharge (fire) in one cell would not spread to others, as it often does with prismatic cells with plastic cases compressed tightly together. Also, the cylindrical cells, I think, tend to vent radially so the debris would tend to disperse toward the protective casing rather than other cells.
I'm still in the R&D stage of this project and I appreciate constructive
input on various facets of the design.
Thanks,
Paul
Not knowing much about the process of aircraft failure investigation but looking at the silver strip in the left foreground I see it has two black staggered lines, and by its position gives the impression of being some sort of standard scale.
The steps on one line are about 2.5 times the size of the steps on the other. I'd not be surprised if those markings are inch and centimetre,
which in traditional volume units would make the battery about the size of a breadbox
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