48v controller w/ 36v battery pack Low Voltage Cutoff

[lightmind]

I have a 36v 750w hub motor with a 36v LiFePO4 20AH Battery Pack. I ordered a controller, but was shipped a 48v controller instead of a 36v controller. I think the controller should work with the 36v battery, but the cutoff voltage must be higher than the 36v battery pack can provide. Otherwise I can't think of a reason why it should not work.

Will this controller work with the 36v battery? I should only need to change the LVC...

The controller is a chinese model brushless w/ hall effect (I am reluctant to send it back, have to pay for shipping & long turnaround). Have $$$ tied up in the battery, don't want to reinvest in a 48v battery pack.

Anybody know how to change the LVC? Or, why it will not work?

Thanks!

[jateureka]

Easier to buy a 36V controller than modify your 48V one.

[wesnewell]

It will be a simple matter to change the LVC once you know how. But don't expect anyone here to tell you how do it unless you provide some info about it. Pictures of the inside along with other info like make, model, board numbers, etc. might get you what you want. Or maybe someone would be willing to trade a 36V controller for your 48V controller.

[dnmun]

you wanna use a 36V controller with a 48V battery. 16S lifepo4 will drop down to 34V or so before cutoff. the controllers are designed to be used with SLA batteries, not lifepo4. someone may have a hack that will get your LVC down to 25V. but you may have to adjust the input power resistors to keep the 12V rail from dropping too low.

[d8veh]

It is possible to change it by changing a resistor on the pcb. IIRC, the hack involves cutting a track to isolate the surface mount resistor and soldering a normal one in place of it. In principle, there's two resistors that make a voltage divider to a pin on the main processor (pin 14?). There was a thread on it about a year ago. Perhaps someone can provide a link. The resistor in that thread was R12, but the search engine won't search for a word that small.
I found some info here:
viewtopic.php?f=16&t=7361
and here:
viewtopic.php?f=16&t=7361

[dogman]

Eat some of your cost, and sell off the 48v controller on our for sale new section. Then buy a 36v controller. Cheaper to ship it to somebody near, than back to china. Or keep it for later, when you want 48v.

If it's really the vendors fault you got 48v, lean on him HARD to discount the crap outta your next 36v one.

[lightmind]

Thanks for the info!

Here are pics of the controller PCB. I believe, after reviewing the links, that the LVC is set by R01A, B, C. They are all 1K ohm currently.

Just need to know which resistors to change and their values for 36v pack, to maybe +-32v LVC (or whatever is correct).

I'm new to this, but I do have a great deal of electronics experience and the tools I need.

I sincerely appreciate the time and experience you share with this newbie...

[Jeremy Harris]

you wanna use a 36V controller with a 48V battery. 16S lifepo4 will drop down to 34V or so before cutoff. the controllers are designed to be used with SLA batteries, not lifepo4. someone may have a hack that will get your LVC down to 25V. but you may have to adjust the input power resistors to keep the 12V rail from dropping too low.

I think you may have made a typo there, and meant 43V rather than 34V. 16S LiFePO4 absolute minimum is around 2.7V per cell, and this is really pushing it a bit, 3 V per cell would be safer. 16 x 2.7 V = 43.2 V. A 16S LiFePO4 pack that runs down to 34 V is pretty much into guaranteed dead cell territory, at about 2.125 V per cell.

[Jeremy Harris]

Thanks for the info!

Here are pics of the controller PCB. I believe, after reviewing the links, that the LVC is set by R01A, B, C. They are all 1K ohm currently.

IMAG0219.jpg

IMAG0220.jpg

Just need to know which resistors to change and their values for 36v pack, to maybe +-32v LVC (or whatever is correct).

I'm new to this, but I do have a great deal of electronics experience and the tools I need.

I sincerely appreciate the time and experience you share with this newbie...

No, those three resistors are the power supply dropper resistors, not those that set LVC.

This controller is programmable from the port on the left, I believe, but I don't know off hand which programming utility to use to set the adjustable parameters, like LVC. My guess is that the LVC potential divider may be the three surface mount resistors to the left of those big power resistors, but the only way to be sure is to trace the tracks back and check the values of these resistors.

[lightmind]

Those three resistors to the left of the power resistors (thanks) are SMD 1K ohm resistors wired in series.

[wesnewell]

Those three resistors to the left of the power resistors (thanks) are SMD 1K ohm resistors wired in series.

I wouldn't think those would be for LVC, but I'm only familiar with my controller. It has a spot for up to 3 resistors across a common path. At 72V it only had 2 across it. I had to add one (which lowered the resistance) to raise my LVC to 88V from original 62V. IIRC I think I ended up with ~1200 ohms across it. Didn't measure it before I started. I know the one I added was about 5k ohm of a 0-12k var.

[Jeremy Harris]

Those three resistors to the left of the power resistors (thanks) are SMD 1K ohm resistors wired in series.

Maybe. It's hard to tell without tracing the tracks and seeing whether there is another resistor to 0V connected to this chain, with the connection point going to the ucontroller. It's quite common to have several resistors in series in the upper leg of the LVC potential divider, to reduce the power dissipation per resistor and make it easier in production to build to different voltages, just by swapping values around.

If you can power the controller up and measure the voltage at the end of the resistor chain, or better still, trace the circuit, then I think we could determine what changes might be needed.

[lightmind]

Thanks,

When I have time I will put it on the bench and see if I can identify the LVC circuit and perform some measurements. Will post when I am done.

[lightmind]

Well, I decided to order the correct 36v controller and forego the mod. I realized that as much as I love tinkering and desire to learn all about the technology around e-bikes my time is limited, and other projects are higher priority. Seems like there's always more to do and the days go by faster. At some point I do plan to research and understand the controller circuits.

Many thanks for your help, I really do appreciate the specialized talent here!

You haven't seen the last of me though, I am just getting started... and I really like my bike's new upgrade. Makes riding a helluva lot more enjoyable.