Dig a little deeper, I've found them for various LTO and LiFePO4 cells and they're generally rated at 20% of the max C rating. Perfect world numbers obviously. Of course if you don't drive every day or don't cycle them that's in your favor too and ideally we size them that we're not running them at 10C outside of a couple dozen competitions per year.
It could be that I was working with low grade cells also. Even if real world we get 50% of the manufacturers claimed numbers that's fantastic. I wish more of this marketing would be standardized and talk about average DOD during testing and preferred charge/discharge that gave those numbers as well as temperature ideal resting charge/ storage charge etc
I'm running a 1993 Suburban w/ 5.7L TBI. Seems it could care less if I'm charging at 15.6 ish. I've already swapped to LED headlights, so that isn't even an issue. I'm running Taramps, so I'm limited to 16v for now.
You're dealing with different chemistry cells hopefully if you're doing drones. Even the e-bicycle guys are mostly scoffing at the high weight and size of LTO and even LiFePO4, can't imagine the weight of these is worth the tradeoff for applications where size and weight are critical.
Makes sense. If I'm going to externally regulate I'm going for 18, which might happen if I have the time. I do have another 6 cells unused just in case. Stephen said his amps won't like >15V so I'm not going to push my luck there. I don't know what we'll do in my brother's car. We'll have to see how high it charges with whatever is in there and see if he thinks it's worth externally regulating.
question. Why don't they make single cells in higher voltages such as 6v/12v etc? Wouldn't it make more sense to have less cells in series and more in parallel for more ah and less cells altogether.
In the case of 6s3p you pretty much have 3-6cell 40ah batteries which are wired in series to increase the voltage to typical 12v automotive levels. You then wire the sets in parallel to combine the 3 40amp hour batts into essentially 1 big 120amp hour batt..
I understand that. Wouldn't it make more sense to have less cells in series to reach nominal voltage desired (12-16v)?
The only way I'd consider 5S is if you were running, say, my Jeep stock which only charges at 13.6-13.8. Most vehicles will probably attempt to charge over 14.5 at lease occasionally which will be bad for them. Stick to 6s. I expect 120AH would be rock solid for 5K (more on that later).
So 1/8X4" copper bar was like 210-220 per 12 foot section after shipping. Barely even considered aluminum. By the time you get thick enough to get around the inferior ampacity you're almost the same price as copper anyway and why cheap out? I called up Storm, they seem to do mostly custom bus bars, talked to their tech, decided on copper... no regrets. Nuts and washers were just whatever from Fastenal but still 75 pieces per bank plus some 1/4 20s to bold ring terminals, used 2 hardened drill bits 1/2" plus the 1/4" one, took some life off my step bit, bought a big tube of dielectric grease and some cutting oil, sawzall blade, and one of those sanding flap discs for my angle grinder. All in probably 600$ in consumables and hardware to do these two banks. The point being whatever you do, you'll need to either buy bussing solution (there's a couple existing ones that were less cost effective) and you'll need to buy other odds and ends before all said and done.
For one, we definitely need something non conductive, and we want these to be snug in the box and the box very securely fastened to the vehicle.... also need to figure out a way to easily connect wire in and out. I wound up using 2x3s since I have a pile of them I got for free.
I've run a couple Stetsom.... had great luck with Brazilian myself but they are considered time bombs and lots of shops won't repair them. I'd consider buying one on ebay/amazon with 3rd party warranty, otherwise I'd be hesitant still.
That's the limitations of the battery chemistry. Way beyond my pay grade, but that's why these LTOs are 2.7V and the LiFePO4 are 3.5..... this lower cell voltage is considered one of the downsizes of the technology. Same as super caps, something about the technology only allows for low voltage.
Series gives you voltage parallel gives you reserve (amp hours). Each S adds 2.3V nominal, each P gives you 40AH (of these cells I'm using anyway, but you get the idea).
Yes. That's one of the big things that pushed me into these 40AH cells over the smaller A123 LiFePO4 cells I was shopping out before. I believe they could probably make these bigger still as far as reserve (AH rating) but probably will never make LTO greater than 2.3V nominal. That's likely a hard limit based on their chemistry.
Okay. Thank you for all the info. I am ready to start my diy build. Good tp know about the voltage on the cells and why they can't be bigger.
I've posted the name of the company I bought from. I would totally recommend them. Not sure if they have a large minimum order though? Perhaps try to get a group-buy together? I got a couple lower per-cell quote but those companies seemed a little dubious. I'd vouch for the guys I dealt with anyway, I'm very pleased with product and service.
I did a ton more research after my comment and it turns out that there are many people who work with electric bikes who state that manufacturing is vital for longevity of LTO cells and that could be a big reason why I have a more negative view of them. I have worked with LiFePo4 but not LTO (yet, anyway).
