Post by Burkeomatic on Sept 30, 2022 5:26:37 GMT
Well, if you don't know about what happened and why I am here, read this.
undergroundfoamies.proboards.com/thread/234/aliexpress-dumpster-batteries
I was essentially too lazy/intimidated to build my own liIon packs. Well, now I need to.
If you don't know, LiIon packs have the ability to store more energy. So a 7000mah 4s 18650 pack should be about the same size and a little less weight than a standard 4s 4000mah. However, the compromise is that you get a lower C rating, or you can't pull as many amps from a battery without damaging them.
18650, and their big brothers 21700s of course come at a compromise themselves. In general, the larger the capacity, the lower the sustained current draw they can tolerate. So a 3500mah cell may only be able to withstand 8 amps, while a 2000mah cell can withstand 30 amps. You can get close to the best of both worlds, but it will cost you.
I have about 100 bucks coming back to me from the aliexpress dumpster battery debacle, so I have decided to give it a whirl and make my own. I am not going to start with the biggest and best batteries, but I am going to start with some respectable ones. 18650 batteries has a sale going on, so I picked up a few of the following.
8x EVE 25P 18650 2500mAh 20A Battery at 2.50 each = 20 bucks for a 40a/5000mah battery
8x Epoch 30P 18650 3000mAh 15A Battery at 4.25 each = 34 bucks for a 30a/6000mah battery
You can easily get up to 10 bucks per cell, but I thought those would give me a worthwhile result while I learn, and if I mess something up, well no biggie.
I will be running these in a 4s2p configuration, so the EVE batteries will result in a 14.8v pack with a 40a discharge max and be 5000mah. When you parallel cells, the capacity and c rating or amp draw adds. The epoch batteries will net me a 6000mah battery and 30a discharge.... still adequate. For comparison to a lipo pack, a 5000mah with a lowly 20a c rating should provide 100amps. So while these are adequate for something like our foamies with small motors, in the grand scheme of things, they do have low current draw. When you see someone generically talk about c rating for LiIon packs, they are more than likely full of crap, as the cells aren't typically rated by C rating, although that does work its way into some of the lingo.
I intend on using these packs for my dolphin and my dragon, but I will end up constructing the dragons packs out of 21700 cells as I have more room, and they have higher discharge and storage values.
ATOMRC dolphin. The plane pulls about 20-22a on takeoff for a few seconds, and if I need to climb about 50-70m in a few seconds to regain FPV signal, I may pull that much too. But normally the plane cruises between 4-6 amps and 8-10 amps if I want to get there quicker. Both of the above batteries are more than adequate.
Reptile Dragon 2, which is a twin, on takeoff it draws around 30-35 amps, and cruising it takes around 7-8 amps. The Eve would be adequate, but an 18650 pack would be made of expensive cells, and molicel 4200mah cells with a 45amp current rating are 6 bucks each, so that would be way better. 48 bucks for a 8400mah with a 90 amp capacity.
So I spent 80 bucks at www.18650batterystore.com/ for the above batteries, some self adhesive fish paper, nickel strips, and insulating donut thingies, and I spent another 40 bucks on ebay for a spot welder. Spot welding is considered far superior to soldering as far as the 18650s go. I have soldered them in the past, but it isn't advisable as they are heat sensitive. I also got some balance plugs of amazon, 10 for 7 bucks. All I need is heatshrink and they are good to go. So I am all in for 150 bucks I think, and I won't have a ton of dumpster batteries for my money.
As far as picking out cells, the vape bros know more about battery cells than 99 percent of the RC world. There is a rockstar of battery testing in their little sphere known as ''mooch'' and he does really good indepth battery reviews, and posts them for all to see, and tests them extensively.
I hope to demystify this stuff, aggregate the information for you all, and take some of the intimidation out of it, as most of the stuff is fragmented, and opinions on batteries are like buttholes, everyone has them. Hopefully I will be able to take you all through the build process, not shock myself and burn my house down, and see what you think or if this whole thing is for you.
undergroundfoamies.proboards.com/thread/234/aliexpress-dumpster-batteries
I was essentially too lazy/intimidated to build my own liIon packs. Well, now I need to.
If you don't know, LiIon packs have the ability to store more energy. So a 7000mah 4s 18650 pack should be about the same size and a little less weight than a standard 4s 4000mah. However, the compromise is that you get a lower C rating, or you can't pull as many amps from a battery without damaging them.
18650, and their big brothers 21700s of course come at a compromise themselves. In general, the larger the capacity, the lower the sustained current draw they can tolerate. So a 3500mah cell may only be able to withstand 8 amps, while a 2000mah cell can withstand 30 amps. You can get close to the best of both worlds, but it will cost you.
I have about 100 bucks coming back to me from the aliexpress dumpster battery debacle, so I have decided to give it a whirl and make my own. I am not going to start with the biggest and best batteries, but I am going to start with some respectable ones. 18650 batteries has a sale going on, so I picked up a few of the following.
8x EVE 25P 18650 2500mAh 20A Battery at 2.50 each = 20 bucks for a 40a/5000mah battery
8x Epoch 30P 18650 3000mAh 15A Battery at 4.25 each = 34 bucks for a 30a/6000mah battery
You can easily get up to 10 bucks per cell, but I thought those would give me a worthwhile result while I learn, and if I mess something up, well no biggie.
I will be running these in a 4s2p configuration, so the EVE batteries will result in a 14.8v pack with a 40a discharge max and be 5000mah. When you parallel cells, the capacity and c rating or amp draw adds. The epoch batteries will net me a 6000mah battery and 30a discharge.... still adequate. For comparison to a lipo pack, a 5000mah with a lowly 20a c rating should provide 100amps. So while these are adequate for something like our foamies with small motors, in the grand scheme of things, they do have low current draw. When you see someone generically talk about c rating for LiIon packs, they are more than likely full of crap, as the cells aren't typically rated by C rating, although that does work its way into some of the lingo.
I intend on using these packs for my dolphin and my dragon, but I will end up constructing the dragons packs out of 21700 cells as I have more room, and they have higher discharge and storage values.
ATOMRC dolphin. The plane pulls about 20-22a on takeoff for a few seconds, and if I need to climb about 50-70m in a few seconds to regain FPV signal, I may pull that much too. But normally the plane cruises between 4-6 amps and 8-10 amps if I want to get there quicker. Both of the above batteries are more than adequate.
Reptile Dragon 2, which is a twin, on takeoff it draws around 30-35 amps, and cruising it takes around 7-8 amps. The Eve would be adequate, but an 18650 pack would be made of expensive cells, and molicel 4200mah cells with a 45amp current rating are 6 bucks each, so that would be way better. 48 bucks for a 8400mah with a 90 amp capacity.
So I spent 80 bucks at www.18650batterystore.com/ for the above batteries, some self adhesive fish paper, nickel strips, and insulating donut thingies, and I spent another 40 bucks on ebay for a spot welder. Spot welding is considered far superior to soldering as far as the 18650s go. I have soldered them in the past, but it isn't advisable as they are heat sensitive. I also got some balance plugs of amazon, 10 for 7 bucks. All I need is heatshrink and they are good to go. So I am all in for 150 bucks I think, and I won't have a ton of dumpster batteries for my money.
As far as picking out cells, the vape bros know more about battery cells than 99 percent of the RC world. There is a rockstar of battery testing in their little sphere known as ''mooch'' and he does really good indepth battery reviews, and posts them for all to see, and tests them extensively.
I hope to demystify this stuff, aggregate the information for you all, and take some of the intimidation out of it, as most of the stuff is fragmented, and opinions on batteries are like buttholes, everyone has them. Hopefully I will be able to take you all through the build process, not shock myself and burn my house down, and see what you think or if this whole thing is for you.
