#50242  by Amarlo
 Fri Feb 22, 2013 7:22 am
Hi all,
An interesting item concerning lithium batts in todays news, it is at present costing Boeing around $30m a mounth to try and come up with a fix,Chris might be able to give them a few tips ????
Quote,Lithium ion batteries weigh less, charge faster and hold more energy than other batteries of comparable size. But they are also more susceptible to short-circuiting that can cause fires if they are damaged, have manufacturing flaws, are exposed to too much heat or are overcharged.
Regards Dave.
 #50249  by mattn
 Fri Feb 22, 2013 10:47 am
Lithium-Ion Batteries Hazard and Use Assessment is an interesting link for those wanting to learn more than you ever wanted to know. Be warned, it's likely to make you go back to Lead Acids, and think twice about putting you cell phone in your pocket :? ......

It used phases such as "Energetic Failures" and "Thermal Runaway" to describe what can go wrong Lithium Ion cell - essentially the electrolyte is flammable, they have very high energy density, and produce gases when the get over charged. Add this together and what do you have if things go wrong.......
 #50255  by Justintime
 Fri Feb 22, 2013 12:15 pm
Matt, you will also note that such events can occur to any battery chemistry. The petrol tank on your car can explode too but fortunately the vast majority never do. The main point is how likely it is to happen. I assume that the Boeing engineers are fairly capable people, so would have factored all this in before using it on their planes. I note also the military use lithium ion. I had understood the newer lithium technlogies were less fire prone, so the interesting point will be what results from the current Dreamliner investigation.

Dene
 #50256  by Nut17
 Fri Feb 22, 2013 12:43 pm
It is my understanding that the battery chemistry as used in the Dreamliner is significantly different to the cells I have in our van. Out battery pack has never got any warmer than ambient room temperature, even when a solid 130 Amps is being offered up to make coffee, or when there has been around 40 Amps of charge current pumped in. Both my C-Tek mains charger and Blue Sky solar controller have temperature probes attached to the battery.

The main cause of failure - meltdown - fire is when the individual cells end up with differing states of charge. This would not appear to be an issue at this stage as when last tested, all cells were identical to two decimal places. This is after constant use for the last ten months.

Cheers Chris
 #50260  by bull
 Fri Feb 22, 2013 2:17 pm
Nut is correct in that these are two different chemistries. The new Dreamliners were using lithium cobalt batteries, which have a much higher density, but at a cost of excess heat and therefore safety. Due to the long regulatory delays/checks for getting a plane in the air, Boeing had to lock in the battery tech way back in 2008, before the new iron phosphate and manganese oxide technologies had matured.

So for all you LiFePo4 users out there - don't worry, you're safe (and smart)!
 #62282  by Justintime
 Sat Oct 12, 2013 10:19 am
Have joined the Lithium club, but so far only for a small van I am having built. Our main van will change over as our AGM's die.

Attached photo shows the BMS circuit boards attached to each cell to prevent over discharge and over charge. The battery capacity is 100 amp hours and it weighs less than 15kg. I have decided to go with this system as pretty much all the info I get makes me wary of uncontrolled cells, even for LiFePo batteries.
When installed, a relay will be added at the positive end and connected to the primary BMS circuit board to stop any charging/discharging if any abnormal conditions occur. Total cost $1250.00.

I know some will argue not cost effective, but it ticks all the boxes I needed, primarily to do with weight, discharge curve, charge efficiency and stated longevity. Looking forward to seeing how it goes.

Dene


Image
 #62284  by Nut17
 Sat Oct 12, 2013 11:01 am
Hi Dene, Welcome to the club !! :) ;) the cell balancing technology looks impressive. Your post and accompanying photo prompted me to do another measurement of my individual cell voltages. The C-Tek mains charger has not been used apart from 10 minutes on the road returning from the beach last Sunday, and I switched the feed from the solar off last night. The battery monitor showed the battery resting at 197 Amp /hrs remaining (fridge brain takes a little continuous current)
Cell voltages as at 5 minutes ago:

3.320
3.327
3.328
3.325

Should add up to 13.3v but meter showed 13.29

The battery has had a very easy life and seldom gets taken below 130 amp / hrs remaining with only going below 100 amp /hrs remaining twice.

There has been no attempt or reason to attempt any sort of cell balancing with this battery pack, and as today's reading after 19 months of use would help confirm that cell balancing is not an issue with the current technology used in these batteries.

Pierre at AA Solar is now insisting on the fitment of a low state of charge cut out relay to comply with the 10 year warranty requirements, but this was not a condition when he sold me my battery. I do intend to retro fit this relay as an added safety precaution.
 #62286  by Justintime
 Sat Oct 12, 2013 11:30 am
Hi Chris, your experience with lithium and your lack of issues was a catalyst for my decision. However, in the back of my mind, I was concerned about the possible consequences if a cell faults, and the older the battery gets, the more likely that may be. I therefore decided the BMS was the best option for peace of mind. Out of interest, the system was supplied by New Powr, who made some posts on another lithium thread earlier this year. The base battery without the BMS was about $1000.00. I haven't checked, but his BMS system may well be transferable to your battery, and a direct connection from that to a relay is a simple option to protect the battery from not only the low voltage but also other potential issues as well. The fact that AA Solar did not initially require a relay, but now do, simply confirms that this is still new and developing technology.

Dene
  • 1
  • 6
  • 7
  • 8
  • 9
  • 10
  • 12
Pay with Paymate Express