3 ms·

Higher energy density makes electric planes a little bit more reasonable, but they'd still be quite range-limited compared to gas. For some use cases, that mig

by elihu 6y ago

Higher energy density makes electric planes a little bit more reasonable, but they'd still be quite range-limited compared to gas. For some use cases, that might be okay. I'm more interested in how this affects cars. Getting four or five hundred miles out of a battery pack that's lighter than what's in a typical Tesla would be a great thing, especially if it's cheap. I'm currently working on an electric conversion of a Mazda RX-8. I just bought about 450 pounds of lithium iron phosphate batteries. They're the most expensive component, and provide about 27kwh; maybe enough for 100 miles if I'm lucky. I sort of assumed that in about ten years or so I'll probably replace the whole pack with whatever great new technology can provide more range with less weight, and probably cost less too. It would be wonderful if we had awesome batteries now. (I considered used tesla modules; they have much better energy density, but they're more dangerous and they wouldn't have fit well in the odd-shaped places I wanted to put them.)

highfrequency 6y ago
Sweet project! How much did the batteries cost? I see this works out to ~130 Wh/kg--did you avoid batteries with higher energy density for cost reasons, or are they just difficult to get?
- elihu 6y ago
  The batteries cost me about six thousand dollars. Lithium iron phosphate is generally recommended for conversions because they're about as safe as you can reasonably expect a battery to be and tolerant of abuse. Used tesla packs have much higher energy density and are actually reasonably inexpensive, but I couldn't really figure out how to make them work in my setup. They're awkwardly long and don't really fit where I wanted to put them, and need liquid cooling. They're also quite a bit more dangerous if they're damaged or catch on fire, which is unlikely in a vehicle carefully designed to protect them but considerably more likely in conversion. So I went with the simpler, safer option. LG Chem has some pretty good batteries as well, but I would have needed multiple series groups connected in parallel, which would have required a pretty complicated battery management system to keep everything balanced.
  - phaedrus 6y ago
    I have a largish 20AH 48V LiFePO4 I bought from PingBattery.com ten years ago for powering a dual motor e-bike project. I ended up also using it to power a mobile robot (rover) project, and sometimes used it for emergency power during blackouts. I went with lithium iron phosphate because it was perceived safer and more durable. Over the past ten years when it wasn't bouncing around inside a rover or e-bike it spent months or years on a shelf when I forgot about it. Most recently I've dusted it back off and use it to power a large shop fan. Because of it's long storage and infrequent charging/balancing the subset of cells that actually power the microcontroller in the BMS were alarmingly low compared to the others, but after a few cycles it seems to have recovered and all but one of the low cells has balanced to the others. The battery still seems to perform well overall.
jillesvangurp 6y ago
Any range you can achieve with batteries in a plane it's basically going to decimate operational cost and be unbeatable from that point of view for missions falling into that range. There are a number of products in development that have interesting enough range that they are pre-selling well because there are companies out there that can fit that in their missions. Double the range, and there are going to be more such companies. There are a number of battery companies looking to improve energy densities by a factor of 2x to 7x. It's increasingly looking like a matter of when; not if we hit 2x-3x. Five years seems reasonable; even quite long given the constant barrage of announcements from various companies and research groups. These improved batteries will likely be expensive initially and not produced in mass volumes right away. But could be perfect for niche markets where volume and cost are less of a concern; i.e. aviation. Tesla's battery day next month is going to be interesting as well. Rumors are currently flying about longevity and energy density of that particular battery. It's clearly going to be better than what they are currently shipping and some insiders seem to hint it's quite close to the magical 400 wh/kg that e.g. Elon Musk has been citing as a minimum viable battery for electric flight. Another thing to consider is that a lot of already announced electrical airplanes are equipped with what are now already obsolete batteries. That's not because the companies behind them are stupid but because certifying planes just takes a very long time and does not allow for massive technical overhauls in between. So, there are some gains to be had by simply updating existing designs with newer off the shelf technology as it becomes available. Second and third generations of a lot of the products that are close to production ready are going to be interesting in the next few years and in some cases, manufacturers are already planning such products. Doubling or tripling ranges is going to be very disruptive in that market.

by elihu 6y ago

highfrequency 6y ago

Sweet project! How much did the batteries cost? I see this works out to ~130 Wh/kg--did you avoid batteries with higher energy density for cost reasons, or are they just difficult to get?

elihu 6y ago
The batteries cost me about six thousand dollars. Lithium iron phosphate is generally recommended for conversions because they're about as safe as you can reasonably expect a battery to be and tolerant of abuse. Used tesla packs have much higher energy density and are actually reasonably inexpensive, but I couldn't really figure out how to make them work in my setup. They're awkwardly long and don't really fit where I wanted to put them, and need liquid cooling. They're also quite a bit more dangerous if they're damaged or catch on fire, which is unlikely in a vehicle carefully designed to protect them but considerably more likely in conversion. So I went with the simpler, safer option. LG Chem has some pretty good batteries as well, but I would have needed multiple series groups connected in parallel, which would have required a pretty complicated battery management system to keep everything balanced.
- phaedrus 6y ago
  I have a largish 20AH 48V LiFePO4 I bought from PingBattery.com ten years ago for powering a dual motor e-bike project. I ended up also using it to power a mobile robot (rover) project, and sometimes used it for emergency power during blackouts. I went with lithium iron phosphate because it was perceived safer and more durable. Over the past ten years when it wasn't bouncing around inside a rover or e-bike it spent months or years on a shelf when I forgot about it. Most recently I've dusted it back off and use it to power a large shop fan. Because of it's long storage and infrequent charging/balancing the subset of cells that actually power the microcontroller in the BMS were alarmingly low compared to the others, but after a few cycles it seems to have recovered and all but one of the low cells has balanced to the others. The battery still seems to perform well overall.

jillesvangurp 6y ago

Any range you can achieve with batteries in a plane it's basically going to decimate operational cost and be unbeatable from that point of view for missions falling into that range. There are a number of products in development that have interesting enough range that they are pre-selling well because there are companies out there that can fit that in their missions. Double the range, and there are going to be more such companies. There are a number of battery companies looking to improve energy densities by a factor of 2x to 7x. It's increasingly looking like a matter of when; not if we hit 2x-3x. Five years seems reasonable; even quite long given the constant barrage of announcements from various companies and research groups. These improved batteries will likely be expensive initially and not produced in mass volumes right away. But could be perfect for niche markets where volume and cost are less of a concern; i.e. aviation. Tesla's battery day next month is going to be interesting as well. Rumors are currently flying about longevity and energy density of that particular battery. It's clearly going to be better than what they are currently shipping and some insiders seem to hint it's quite close to the magical 400 wh/kg that e.g. Elon Musk has been citing as a minimum viable battery for electric flight. Another thing to consider is that a lot of already announced electrical airplanes are equipped with what are now already obsolete batteries. That's not because the companies behind them are stupid but because certifying planes just takes a very long time and does not allow for massive technical overhauls in between. So, there are some gains to be had by simply updating existing designs with newer off the shelf technology as it becomes available. Second and third generations of a lot of the products that are close to production ready are going to be interesting in the next few years and in some cases, manufacturers are already planning such products. Doubling or tripling ranges is going to be very disruptive in that market.