modding my ebike motor controller for less current consumption - Page 1
Forum section: electronics / general

author: m3vuv
author_rank: Super Contributor
timestamp: November 05, 2020, 11:12:32 pm
content: hi all,ive a 48v homebrew ebike with a 1kw brushless hub motor powered by a 1.5kw controller,it goes like hot snot,but not for long,i want to cut the power down for more range,inside the controller there are what looks like 3x nichrome wire shunts in paralell next to 3x 2 watt 1k resistors in paralell,would it be best to cut a shunt or resistor?,i assume these are for current sensing,maybe have them switchable,would that be viable?

author: Siwastaja
author_rank: Super Contributor
timestamp: November 06, 2020, 01:58:58 pm
content: If you are looking at improving the efficiency of the thing, that basically means you need to understand how to design such controller,andbe better with it than the original designer.It's going to be a daunting task.Unless the design is piss poor, the current measurement shunts are only a small portion of the total loss. MOSFET conduction and switching loss, possible snubber loss, and input capacitor loss are also significant, not to forget wiring loss (including PCB tracks). If you still want to reduce current measurement shunt loss, the only way is to reduce the value of R then increase the amplification, or adjust the algorithm to compensate.In fact, unless the design sucks catastrophically, the efficiency is already way over 90%, so even if you are able to improve it by a few percentage points, it's meaningless forrange. For thermal management, improving efficiency does often make sense.

author: Ian.M
author_rank: Super Contributor
timestamp: November 06, 2020, 02:07:54 pm
content: Use less throttle!There'll be a throttle 'sweet spot' where energy lost (as I2R losses, switching losses, wind resistance and rolling friction) per mile is minimized. Setting up to log current and speed will help you find it.

author: tom66
author_rank: Super Contributor
timestamp: November 06, 2020, 05:11:53 pm
content: The power consumption of your ebike will be driven entirely by how aggressively you use the throttle. While you can modify the controller, you would only be able to affect e.g. when its current limit kicked in, which I suspect is not what you want.One thing you could do, if your bike uses a potentiometer throttle control, is add a resistor in series with the pot or from the wiper to ground, which will reduce the throttle response. Or you could just drive it more gently.For any given vehicle load and speed, the power consumption will be roughly the same.

author: m3vuv
author_rank: Super Contributor
timestamp: November 08, 2020, 07:39:59 am
content: im not worried about eficiency ,i just want more range and less power,its a hall throttle,i guess i could stick some diodes in series in the signal wire i suppose.

author: Whales
author_rank: Super Contributor
timestamp: November 08, 2020, 08:06:14 am
content: QuoteAre you certain they're fully in parallel? That's just a bit odd. Trace the tracks and be sure.Apart from modding the current shunt: another area of interest is reducing the throttle ramp rate. If the throttle is analog then this might be doable with R, C and a diode; but often throttle ramp rate limiting is done in software, unfortunately.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 08, 2020, 09:34:50 am
content: So the problem is with the actual throttle twist command being too aggressive so you find it difficult to drive "carefully" and end up doing heavy accelerations and drive too fast?

author: m3vuv
author_rank: Super Contributor
timestamp: December 03, 2020, 06:59:20 pm
content: no i just want more range,at the moment it does about 50mph but only for about 7 miles,i just want to cut the current consumption for more range at say 30mph max,im not good with the throttle lol.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 04, 2020, 10:03:52 am
content: I would add a resistor in series or parallel (depending on how it's wired) with the throttle potentiometer to reduce the maximum setting.

author: Circlotron
author_rank: Super Contributor
timestamp: December 04, 2020, 10:32:58 am
content: Quote from: m3vuv on December 03, 2020, 06:59:20 pmFor a car at least, with air resistance the amount of tractive effort goes up with the square of the speed and the amount of power needed goes up with the cube of the speed. That means if you halve the speed you need only 1/8 the power to push the air aside as before. There is still tyre rolling resistance, but going slower will help a lot.

author: Ian.M
author_rank: Super Contributor
timestamp: December 04, 2020, 10:46:55 am
content: Is there any chance you can get open source firmware for the controller which would let you mod the throttle mapping?Otherwise, if you don't want to replace the controller with an open source one or at least one that has a 'tuning' utility, interposing a mod board in the throttle circuit would probably be the best option to limit speed and acceleration. How is the existing throttle wired and what type of sensor does it use?N.B. there are some serious safety issues - the mod board must cut the throttle near-instantly if you slam it closed, and must never generate an un-commanded throttle signal.