Svard75 said:
It’s a Chinese emotorbike rebranded to a local company known as the emmo dx. It appears to have a QS rear hub motor. The controller is as indicated and the battery is 72v 24ah. Not much about 1700whr. I believe the motor is 2000w. During my commute there are a number of hills and one is quite steep. It dies drastically. About 15km/hr slower and a voltage sag of 8v. I’ve opened the battery pack and the bms is a 50a unit. I’ve upgraded the wires right from the cells to 2x16awg per cell with 4 banks all joined to 8awg right to the controller. This seemed to provide a little more juice (about 1km/hr more on the uphills).
What do you think would be the best approach to get just that little bit more umph uphill. The rest of the ride is perfectly good. I have no issues reaching speeds of over 60km/hr.
Given these specifics, we should do a little analyzing and troubleshooting before modifying anything.
How steep is the hill? If you have a smartphone you can get free apps that measure inclines, and even map them with GPS to a path on a mapping site. Knowing what the actual slope is will help you determine the power required to go up it at a specific speed. If you can't measure the slope, at least see if it is listed anywhere, like on a warning sign for the road (sometimes they do this on mountains, for instance). It's better to overestimate it than underestimate it, for these purposes.
You'll also need an approximate weight of you plus the bike (because it takes a certain amount of power to go a certain speed up a certain slope). A good guess is ok, just overestimate rather than under.
By "dies drastically" do you mean that it actually powers off?
If so, then that means the BMS has shut off the output to protect the BMS and cells from damage.
If it doesn't actually power off but the motor ceases to run, then that means the battery is sagging so much that the controller is shutting down to protect the battery from damage.
In either of those cases, you need either a second battery in parallel with the first, or a complete replacement battery that is capable of the power level you're after.
If it is just slowing down radically, but the motor doesn't stop moving, then there are two possibilities, and it could be a combination of both, or either by itself.
The first, most likely, is the battery simply can't output the current needed to provide the power, so the voltage drops so much that the maximum available motor speed drops.
The second is that the controller can't output enough power to the motor to maintain that speed under that load. We'll need to know how much power that load is before we can determine if this is part of the problem or not, so we'll need the hill slope and the weight of you and the bike.
BTW, the BMS has a shunt in it too, so it can protect the battery and prevent damage (and fires). Did any of your wire upgrades bypass this? It may look like the ones in the controller, or it may look like a little black square with metal tabs on the end, surface mounted to the board. There may be several in parallel. I ask because if they are bypassed, then the battery isn't protected, and forcing the controller to draw more may then allow the pack to be damaged. I'd recommend not bypassing or modifying the BMS shunt even if you do the one in the controller.
Most of the cheap batteries are cheap because they use cheap cells, cheap construction methods, and little or no QC. This leads to problems with them even in normal usage, and can be worse when used outside their original design limits (which typically already push the limits of what they coudl do in the first place). It isn't always a problem...but ti can be, and the harder they're pushed, the more likely it is.
Does the systme you have have a display screen with buttons on it to change controller settings or modes? If so, there may be a setting for current limit or power limit in there, that you can change safely rather than the relatively uncontrolled shunt mod method.
If a shunt mod is your only option, then this is the way I would do it. It will take some tracing out of circuits, but Fechter's method works and is controllable and undoable, where actual shunt mods are neither. :/
This thread is one that has posts describing the process. https://endless-sphere.com/forums/viewtopic.php?f=2&t=29097#p1428919 If you're willing to trace circuits in the controller and draw them up, we can help you figure out where to put the potentiometer.
If you prefer one of the uncontrolled shunt mods, we can try that too. While you're fairly certain to get enough more power out of the controller to go up the hill, it's less certain if the battery and controller will survive that undamaged over time. Depends on the quality of the battery itself, as well as the design of the controller and quality of it's parts (and whether they are counterfeit or real), whether there will even be a problem or not (many people do shunt mods without failures, but there are no guarantees; I've blown up controllers the very first time I used them after modding.