To calculate the max amps the battery can deliver, you have to know the max amps of the cells you used. For example, Panasonic 18650pf cells can deliver 10A continuous, and I used 3 cells in series in this battery, so the battery can deliver 3 x 10A = 30A. However, you also need to know how much current the BMS can deliver. If I put a 15A continous BMS on this pack then that would be the “weakest link” so to speak, meaning the pack with the BMS could only deliver 15A continuous.
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I placed the first parallel group positive side up, and the second parallel group negative side up. I laid the nickel strips on top of each of the three sets of cells, bridging the positive caps of the first parallel group with the negative terminal of the second parallel group, as shown in the picture.
Remember, if a battery with a certain chemistry can “survive” at 2C, it may actually last much longer if it is sized so that the amp-draw from the controller/motor is only 1C. If it can actually be run at 2C, but it dies in a month with daily use…and yet if sized to run at 1C it lasts a year? Legally the manufacturer is not lying by calling it a 2C battery. There is nothing wrong with that, but…we here want E-bike customers to be aware of the real-world results so they can make an informed decision, and avoid the disappointment that could turn off a lot of potential E-bikers to a wonderful sport and hobby.
As long as you monitor your pack voltage so you don’t go too low during rides, then yes that would work. You’d simply run your discharge negative wire straight from the -1 terminal of your battery out to your controller, instead of from your -1 terminal to your BMS’s B- pad. But that removes the ability for the BMS to cut off the current when the voltage goes too low, so you’ve got to watch for that.
Lithium batteries are also small enough to allow you to place your batteries pretty much anywhere on your bike. This is especially true for people who want to assemble their own pack or use heat shrink wrapped lithium batteries instead of hard case lithium batteries with prefabricated bicycle frame mounts. This can help spread the weight around or hide the batteries to make a stealthier bike.
Just kidding, here’s a little more detail. 1) Yes, actually you could just use one strip of nickel on series connections to make the electrical connection, but one strip of 0.15mm thick nickel strip can only safely carry less than 10A. Ideally you want at least one strip for every 5-7A you plan to pull through the battery. 2) You can definitely do the series connections first, it is just habit for me to do parallel connections first. Also, on larger packs I like to do parallel groups first and then glue them together and do the series connections as I glue each group. 3) People have explored this idea a bit on Endless Sphere, and while it can be done, it has a lot of room for error, mostly in keeping the spring loaded contacts permanently against the cell terminals and in keeping the contacts from corroding. Spot welding is the best method, in my opinion.
It says it is 110 volts (220 are available) but this welder needs a 60 amp circuit (breaker) to work properly so it is not advisable to use at home! anyway, have you found this is a certainty? that you must use a 110 volt (single phase) 60 amp circuit? is this what you are using? have you been having breakers flip when you use your welder on a smaller breaker? (most homes are 20 amp breakers) Or would it just be better to go with their 2 phase (220 volt) 60 amp breaker? I guess I could just pick up another breaker and run it directly from the panel.
Sure, it is possible to solder directly to the cells (though it can be tricky http://electricbikebatterys.com the right tools). The problem with soldering is that you add a lot of heat to the cell and it doesn’t dissipate very quickly. This speeds up a chemical reaction in the cell which robs the cell of its performance. The result is a cell that delivers less capacity and dies an earlier life.
Regarding your second question: I wouldn’t say the max amperage of the BMS is “dependent” on the controller, but it should be chosen with consideration to the controller. Think of it this way: your controller is what decides how much current your battery is going to supply. The controller is basically pulling that current from your battery. If it’s a 20A controller, that means the most it will pull out of your battery is 20A. So if you plan on riding in a style that uses full power for long periods of time (like hill climbing, dirt riding, etc) then you’ll need to make sure your BMS is rated at least 20A continuous. However, most people that ride on flat roads spend very little time at peak current. My ebike’s controller is a 22A unit, but I spend most of my time around 10-15A when cruising. A 20A continuous BMS would be good insurance in that case, because it means my BMS is rated to handle more continuous power than I generally will pull through it.