(I'm very much a beginner with electronics, so I apologise in advance)
I’m trying to use a 48v battery on my 36v ebike controller. The controller itself can deal with the higher voltage, but it has a hardcoded limit of 44v, which it reads from a wire coming from the display.
So my aim is therefore to lower this voltage somehow. The parameters are:
Tvs diode:
My main reasons for asking instead of just trying these things are:
I’m trying to use a 48v battery on my 36v ebike controller. The controller itself can deal with the higher voltage, but it has a hardcoded limit of 44v, which it reads from a wire coming from the display.
So my aim is therefore to lower this voltage somehow. The parameters are:
- Input is 39-55v, output needs to be between 29-44v
- Current on the wire is 80-120ma
- It would be great it if this could be done proportionally, or with a constant voltage drop, instead of just regulating to a set output voltage
- Single component solution would be best, since it would be easier to wateproof for riding in rain
Tvs diode:
- Guy here used one for this purpose (52v battery but otherwise same situation) and he said it worked
- But I’ve read that they’re not supposed to be used continuously like this, only for spikes in voltage - does that mean it could fail if used like this?
- Also have no idea how to choose one for specific voltage drop - have read many explanations and data sheets but don’t understand difference between clamping, breakdown and working voltage. The guy in the linked post seemed to choose based on breakdown voltage = desired voltage drop, but this doesn't seem to be what breakdown voltage should mean?
- To calculate the series resistor, I would need to know the resistance of the load, correct? I’m not sure how to find this - do I measure resistance across the voltage sense wire and ground while the display
- I have one of these (appears to use a LT3800) This has a constant output and is large, so not ideal. But I would also worry that it would draw too much current? I've tried to measure the current it draws with no output, but I doubt that is particularly useful information. I tried to figure it out from the datasheet, but I don't really know what half the symbols mean
- Every mention of using a resistor for this purpose (that I've seen) has said not to do it, but not said why (although i assume this is because fluctuating current would change the resistance too much?)
- Also wasn't sure how to select the resistor value for a desired voltage drop. Is the V in V=IR meant to be the drop, or the voltage of the circuit?)
- From what I’ve read, this doesn't work once you apply a load?
- Only just found these so haven't looked into them: using high power LEDs in series, or zener + transistor circuit
My main reasons for asking instead of just trying these things are:
- Not wanting to exceed the mA level that I have witnessed on the line, because I don’t want to break anything
- Not knowing whether my lack of understanding might lead to something breaking
- Need something reliable, i.e. that won't fail halfway up a hill