LFP and LTO batteries

[latecurtis]

I was wondering if anyone out there has any experience with LIFEPO4 / LFP or LTO lithium titanite batteries. They both are very safe chemistries compared to lion / lico.
I have been building both with cells from battery hookup and battery clearinghouse for awhile now.
I have questions about Headway 8 Ah 200 amp cells I recently purchased. Also have a question regarding DC to DC buck and step up voltage boosters. I am considering getting one to use for 10S 24V LTO as 20S LTO = about 47 pounds but 10S = 23.5 pounds. They are 18 Ah - Lishen cells I bought about 2 years ago.

I am sorry. This post should be under DIY packs or on its own. Not under 18650 but my first post so not sure how to do that.

Thanks.

LC out.

[latecurtis]

Yes. I ordered 20 of the 8 Ah Headway about 6 weeks ago. I just checked voltage and built a 15S pack without checking for capacity. Big mistake. My first trip was storage and made it 3.5 miles. Less than a mile on the way back and it died. I had to push a heavy e bike about 2.5 miles. There was no pedal chain and I am disabled. I have a knee that was supposed to have total knee replacement surgery back in 2014.

I e mailed BH and they agreed to replace the bad cells. Six cells were < 3 Ah capacity. I told them for a useful pack I would need 12S 2P. That would get me between 8 and 10 Ah. I told them I would place my order in January as on disability and get the monthly check. They e mailed me back saying they were sending me the 16 cells for free and Merry Christmas. Before I got that message I ordered 168 A123 cells for $105 from Battery Clearinghouse.

The A123 cells are cell recovery. I used a small tin snipping tool at first but were some sparks so bought a Dremel kit from Wall Fart for < $20 on sale with a ton of attachments. I will be able to recover all the cells with the tabs intact for soldering and building a 15S 8P pack. It will weigh about 23 pounds total. I have been running 16S - 40V LTO as well and 20S on a 20" BMX mongoose with an 1,800W brushless 3,000 rpm motor. The controller is 35 or 38 amps and rated for 1,500W. It did 32.5 mph on the flat with a speedometer phone app.

The 20" bike rides good considering 47 pounds battery weight. It is because it is low to the ground. I have 7 running e bikes and 6 are 26" or 27,5" or 700c. They do NOT ride well with 36 or 47 pounds of LTO. It is why I invested in the LFP batteries. I have been parallel charging both the Headway and A123 cells. I own a 200W 6S LiPo Skycharger and a 400W 6S Mega charger. The Skycharger fails miserably charging LFP. It reads full < 3.2V. The Mega charger will parallel charge to a full state but takes up to 24 hours sometimes.

If I can get about 6 miles or 8 Ah at 36V 12S - with the Headway cells 12S - 2P I will be able to make use of them for 100 or 200 cycles probably according to what you said. NO I will never order any more. I have about $100 invested in the Headway and $110 in the A123. So far out of 16 A123 four read at 0V. The others 3.3V with a few between 3.2 and 3.3V. The 0V cells did fully recover when parallel charging and after a week were still > 3.2V most above 3.3V. That will be 15S - 8P. 120 cells somewhere between 15 and 20 Ah. They are rated new 2.3 Ah each. so 2.3 * 8 = 18.4 so looking at about 15 Ah.

I will post pictures when I return from Christmas dinner. I almost did not order the LFP cells as was considering a 40 amp 24V to 48V buck step up voltage booster. I still may next month depending on how well the 15S LFP pack works. Daygreen makes the boosters. The cheap 1,500W and 1,800W buck boosters are a really bad joke. A decent 24V to 48V booster from Daygreen is around 85 to 95% efficiency and puts out a constant 48V - 40 amps. No voltage drop under load. However that is according to their specs. I have not spoke to anyone who has used one.

I will take pics. of all my LTO and LFP batteries later. I do understand why you prefer 18650 Lion cells over LFP. I do NOT have a safe place to charge and do still have a 13S - 20 Ah pack and a small 10S - 4 Ah lion pack in my storage. After watching multiple YouTube videos of tragic Lipo and Lion fires I decided to go with safer battery chemistries.

Thank you.

LC. out.

[AZguy]

In the end, there are very good reasons (weight and size - energy mass and volume density - near top of list) that nearly all electric bikes and EV's in general use the same few chemistries and battery contruction... metaphorically speaking it's seldom beneficial to try and reinvent an already well developed wheel...


Having said that there may be very compelling reasons that a particular build would be better off straying from the norm... I recall a guy building up an old school conventional trike for running on flat terrain where weight and size were low on the concern list (he'd even considered just going lead-acid and it was hard to argue against it for his use case)... I think he ended up with four "12v" LiFePO4 batteries in the large rear basket/carrier between the rear wheels and just put a piece plywood (or something) over them to create a new floor in the basket...


Not sure what questions you have about DC-DC conversion...

[latecurtis]

I ended up building a 12S - 2P LFP headway pack. It weighs about 22 pounds with the box. It fits in the lower triangle of one of my e bikes. There is about an inch for pedal clearance. It rides fairly decent. It was 12S 1P with a 12S - 1.2 amp active balancer and 80 amp fuse. I needed a lot of ring terminals rated at 12 gauge to add 6 cells in parallel series to the top and bottom. I used a plastic ammo box which I cut the hinges and about an inch and a half from the length and replaced the top with a piece of plexi -glass so you can see the led lights on the active balancer.

It took me awhile to parallel charge the cells and do capacity tests on about 16 cells and used the best 12 to parallel up to the first 12. I would guess capacity now to be somewhere between 10 and 12 Ah. Good for about 10 miles on a charge. Dimensions are 10.5 by 6.5 by 7" It should out last any 10S Lico 18650 pack two or three times over and worry free indoor charging with 100% safe battery chemistry.

For long range up to 20 miles I will run 16S - 1P - 18 Ah - LTO batteries which weigh in at about 36 pounds. That is for long range 36V set ups. For 48V set ups I am building a three 5S - 8P packs from A123 - 26650 cells I have recovered from modules from Battery Clearinghouse. A single 15S - 8P - 120 cell pack will be too difficult to mount so will be splitting them up. Total weight will be < 25 pounds vs about 43 pounds - 20S - LTO. Capacity should be somewhere around 12 to 14 Ah. Not a bad trade off as far as I am concerned. I will be ordering three 5S active balancers. Looking at two packs in the triangle and one on the top. For my 27.5" dual suspension I may need to mount two on the top bar and one in a front or rear basket as not enough room in the triangle.

1/13/23

yea. No luck stripping 10 or 12 gauge wire. It just fell apart. I should have bought wire already stripped on a roll at Lowes home improvement. But instead am doing it the hard way. Stripping 16 gauge home extension cord. Three strands of 16 gauge together is equal to 11 gauge. Since 16 gauge is only good for 10 to 15 amps three will do 30 to 45 amps. 50V * 30 amps is 1,500W so will run any of my e bikes except for the 3,000W brushless motor which has a 70 amp controller. My 1,800W motor has a 35 or 38 amp controller. That is pushing it but will work as the motor will over heat anyway at full throttle for > 3 minutes. For 25 to 28 mph cruising it will work fine.

I watched a few you tube videos and learned to tin the solder tip , the tabs and then the wire prior to soldering it. The tape I used to hold it in place is 500 degree heat tape. This process will take a long time. My three 5S active balancers will be here Saturday according to the e mail I got today.
Thanks.

LC. out.

[paxtana]

Been a long time since I had a lifepo battery, I know they are more stable but is it common practice to solder directly on the cells?

[latecurtis]

Been a long time since I had a lifepo battery, I know they are more stable but is it common practice to solder directly on the cells?

Hard to say. Its not supposed to be done because you lose capacity from heat damage. But people all over don't know that.

I do know that but in this case I am not soldering directly to the cell. I saved all the tabs which are about 1/2" so much less heat to the cell than with no tabs.

I am still building 15S - 8P - A123 cells. I will post some pictures later when they are finished.

Thanks.

LC out.

[latecurtis]

I use 500 degree heat tape under and over the tabs and between each cell so no sloppy solder can short them out. I also use liquid tape on the series connections. That is my new method. The old method was a sloppy solder job to connect the two cell banks. Before soldering I tin each tab and the wire. Then I use strips of tape to hold the wire in place where needed.

By heating up the insulation with a lighter I am now able to strip long strands of wire so now there is no need to solder the series connections. For the power I striped a 12 gauge and a 16 gauge strip of wire but left about 12 inches of insulation on each , soldered a female bullet to the end and twisted the bare wires together and soldered to all 16 tabs.

The liquid tape will be the last step as need to solder my balance wires to those first for the active balancers.

I will be making custom wood boxes with plexiglass on the top to see the LED lights on the active balancers. I will post more pictures when it is complete.

Thanks. LC. out.



" of insulation. I then soldered a female b

[latecurtis]

As the Hub Motor Turns and the LiPo Fire Burns.

I took a ride to storage approx. 3.9 miles away. I took the bike with the 750W gear reduction motor on the back and 350W Bafang up front with the single throttle. Upon arrival I hooked up the dedicated 43.8V - lFP charger. I then proceeded to fetch the three bike wheels for my next build.

It did not take long to charge to full.. Maybe 15 minutes at 10 amps. I then put the bike I rode there and rolled out my 20" BMX bike with the 1,800W brushless chain drive motor and 1,500W - 38 amp 36V - 48V controller.

I google mapped the trip home and got exactly 3.9 miles. Note the packs measured > 59V together in series. A 12S - 2P - Headway pack consisting of the 8 Ah cells rated at 200 amps each. Old , tired and used. When I did a capacity test on most of the cells they hit 2V and stopped on the 6S - LiPo charger. I had to test at 1 Amp or start at 0.5 amp and raise to 1 amp. It is why I went with 12S - 2P with the best 24 out of 36 cells from battery hookup.

I also ordered 168 - A123 cells from Battery Clearinghouse. My plan was three 5S - 8P packs in series for 15S as I paid about $133 for a dedicated 54.6V - 15 amp LFP charger. My first 5S - 8P - LFP pack in series with the 12S - 8P - A123 pack went 3.9 miles. Full throttle for the first mile and about half throttle or less the rest of the way as I wanted to make sure it made it.

Here are the results.

16.42V / 5 = 3.284V per cell bank - 5S - 8P - A123 pack.

39.6V / 12 = 3.3V per cell bank- 12S - 2P - 8 Ah Headway pack.

3.9 miles.

I did not have my speedometer app. as did not have my phone so could not measure top speed. I do not believe that top speed was > 30 mph but not sure. It did seem fast but doubt it was faster than my LTOs at 50V. (32.5 mph) .That is because LTO is very high performance and much less voltage drop under load compared to LFP. However 3.3V * 17 or 56 working volts is probably about 20 pounds lighter than 50V of LTO.

The only battery chemistry that comes close to LTO in performance is LiPo. I had 12S - LiPo - Lithium polymer packs before and got rid of them when they puffed up. They will compete with LTO in performance but are very unsafe. Lion 18650 cells are about the same but limited by the BMS in discharge and also unsafe. I am content with running LFP and LTO for now.

If I get a big house to rent in the country which might be in my future I will have a very safe place to charge 18650 lion as well as LiPo packs from Hobby King. I already have a 13S - 7P - factory 20 Ah - 1,200W Lion pack and a 4.4 Ah 10S - 3P or 4P Larudation factory 18650 pack. I also have two 90 amp power modules from battery hookup. For now though I prefer LFP and LTO for indoor charging.

Thanks.

LC out.