(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:
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
Single component solution would be best, since it would be easier to wateproof for riding in rain
Solutions I have researched so far:
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
Step down converter:
- 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
Sorry if I've missed anything obvious - I feel like I could have researched some of these things more, but I did try. And in fairness they are bloody confusing if you have no real prior knowledge!