Controller wizard - help for pcb lvc mod???

I've done the obvious searching and have populated a general procedure in my head, but I don't have the electronics education/background to be quite clear on:

How to add a trimpot or permanently change LVC on this (or any) controller. I'd think there'd be a wiki or youtube entry that covers at least the basics but haven't found that to exist. Yet.

http://www.ebay.com/itm/48V-1500W-Electric-Bicycle-Brushless-Motor-Controller-For-E-bike-Scooter/132039821755?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2648
It appears to be a basic xie chang 18fet . . . .





Can someone PLEASE tell if these are the proper pcb pads to jumper, or what I'm looking for?

The 64v pads are already jumpered and I'm assuming I add the pot there?
Or maybe replace that thing that's beside the 64v pads with the pot????
ANY details/info will help!!!!!

Also, I'm only assuming the simplest approach to be a trimpot so you can dial it in and/or change it later?

What kind of trimpot is necessary? Does it depend on what you're starting with or is it generic for all generic xiechang controllers?

As an alternative I'd even accept just eliminating LVC alltogether but that's far from ideal since we're not running an actual bms

. . .
Current LVC is supposed to be 42v but that seems like a soft LVC.
Hard cutoff is more like 40v accordign to my meter.
I want to drop to around 31.5v and be able to tweak slightly later. Thanks!

nutspecial said:

How to add a trimpot or permanently change LVC on this (or any) controller. I'd think there'd be a wiki or youtube entry that covers at least the basics but haven't found that to exist. Yet.

Click to expand...

There have been some posts about it, but as every controller is differently designed, there's no one way to do it for them all. Some have external hardware to monitor the LVC, some might not.

Can someone PLEASE tell if these are the proper pcb pads to jumper, or what I'm looking for?

The 64v pads are already jumpered and I'm assuming I add the pot there?
Or maybe replace that thing that's beside the 64v pads with the pot????

Click to expand...

Those are select jumpers for existing resistors next to them. So you wouldn't add a pot there. You'd wire the pot from the left side of the jumper, to the right side of the resistor set. Value of the pot for a given LVC would be calculated from the existing resistors and their LVC values.

I don't know how to create the math formula to figure that out, but there's four values of resistor (marked on top of each) and four LVC values that correspond to each. So it should be easy for someone (not me) that can actually do math to figure out hte relationship between LVC value and resistance.

Each of those resisistors splits the voltage with that 24K resistor in the ratio of R:24K
The formula to calculate the voltage that the cpu reads is R/(R + 24000)

If you look at the 60v resistor, it's 750 ohms, so the voltage the cpu sees is 60 × 750/(750 + 24000) = 1.82v

Now you can change the formularound for any voltage 1.82 = V × R/(R+24000), where R is the value needed to set the pot to and V is your battery voltage.

So R×R + 24000R = 1.82/V or better stll RxR + 24000R - 1.82/V = 0

Now you can solve that for R using this:

http://www.bbc.co.uk/schools/gcsebitesize/maths/algebra/quadequationshirev3.shtml

Using a =1, b= 24000 and c = -182/V

Wow thanks guys! When I get like an hour to figure it all out I'll post 'my' version of 'how-to', to hopefully help dumb people like me lol. It seems really simple and easy!

So the existing jumper is to select which preset for LVC, and those are the resistors in-line with the jumper pads that take down the operating pack voltage in order for the low voltage cpu to read/process.

I'm supposed to jump the properly selected trimpot from 'outside to outside', across the pin that's already jumpered and the resistor beside it in order to bypass/override original LVC with trimpot control. It can be done with any of the pad sets (60 64 72 etc, assuming original jumper is broken first) using the proper equations for correct trimpot version/range is my guess.

And then when the cpu sees a slightly different voltage (within 0-5v range I'm guessing), it sets and enforces the new LVC accordingly. Cool! Now I just need a bit to do the formula comprehension and actual equating for trimpot selection . . . 9s battery enroute to make topspeed reasonable on 29's and improve torque/efficiency curves.

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nutspecial said:

And then when the cpu sees a slightly different voltage (within 0-5v range I'm guessing), it sets and enforces the new LVC accordingly. Cool!

Click to expand...

That's the theory.

There is the unlikely (because this one has jumpers) possibility that it is like some of the dual-voltage controllers where the MCU detects a voltage within a certain range, and then it "assumes" that the pack is then a certain type that has a specific HVC and LVC. If voltage then falls outside that range, the MCU shuts the controller down. But if the initial voltage doesnt' fall within one of it's specific ranges it's programmed for, then it never activates the controller.

Guess you'll see how yours works soon.