Controllers WITHOUT LVC & Mods For Same

[CompuTutor]

Having controllers with dedicated LVC trip-points embedded,
when the available chemistries can conflict, is a real hassle.

Manufacturers try to sell product for dedicated series counts,
like 36V/48V, and leave out any chance of using non-standard
series-count builds from surplus sellers because of this.

They NEVER include a choice of chemistries,
so we're all basically all screwed there...

I have several battery chemistry packs I'm comparing, as example,
and I have had to mod my controller with a rotary switch,
to just compare these battery packs to each other.

I don't even know why modern controllers have this function,
it is, and should always be, governed by the BMS anyway...

I've since gone to inexpensive controllers that handle
ranges instead, like 6-50 volts, to test everything now.

(CNC Spindle controllers as example...)

Good controller makers like EBikes.CA provide us
with programable LVC threshold's, thank god,
but the are far from inexpensive.

My above unit costs me under $20 from China,
the later well over $200 + S&H, see my point ?


Please share any popular LVC mods you've found,
or Models/Links to units that are budget friendly.

Thanks

 

[amberwolf]

I don't even know why modern controllers have this function,
it is, and should always be, governed by the BMS anyway...

Because, as commonly designed, the BMS is there as an emergency cutoff to protect the cells against damage in the event of cell problems. They are not typically made to cutoff except right at the edge of completely empty, or too high current, or some other thing that forces complete shutdown of all power (because a BMS cannot modulate the power out of a pack, it can only disconnect it, which is a last-resort procedure that can endanger a driver, rider, etc from the sudden complete loss of all power).


While not all controllers are designed to do it, a controller that detects a pack near LVC can modulate the power output to the motor to reduce load on a pack nearing empty or that is having a problem that's reducing it's ability to supply power (because it's voltage has dropped), which reduces the voltage drop and lets you keep going instead of suddenly being left with no power at all, until it does reach LVC, where it disables the motor's ability to provide thrust (but still leaves the system powered on, so if you needed regen braking for instance, it could do that).

A controller LVC is almost always setup to be much higher than the BMS LVC, because it's not there to protect the individual cells like the BMS is, but the system as a whole (controller, battery, rider/driver, etc). So it will begin it's protection process (whatever the controller is designed for, either power rollback or motor shutdown) as the LVC is reached or approached, and this leaves the cells much less discharged and much less stressed than if the system depends on the BMS LVC to just cut off all power suddenly.


Some people choose to either use controllers with no LVC or with one set so low that the BMS is actually doing the whole job, which is a lot harder on the pack.

Others will use a programmable BMS that lets you set it's cell-level and pack-level protections to much less stressful points...but the BMS still can't modulate the power, so it will still just turn completely off when these protections are triggered, leaving the rider/driver suddenly and without warning with no motor power...which in many situations is dangerous and could even be fatal in a very small number of those, on some bike / vehicle designs.

 

[amberwolf]

Please share any popular LVC mods you've found,

There are quite a few posts and threads around the forum that you can look for about ways to alter LVC of various controllers with various hacks / mods. Typically these involve reverse-engineering where on the controller the LVC circuit is, how it works, and altering it in a way that does what you want (whatever that happens to be).

Most often it's just a voltage divider from B+ to ground, with it's center tap feeding an op-amp or comparator that then feeds an MCU input.

If it's an op-amp it means the output is usually analog voltage within a 0-5v range (or narrower) that the MCU can read and actually know what the battery voltage is, and do whatever it's programmed to do.

If it's a comparator it means the output is digital, just active or not, so the MCU only knows whether or not LVC has been triggered, and do whatever it's programmed to do.

The former means that if the controller has programmability, you can alter things in that program rather than hacking the hardware, assuming it's user-accessible. But even if it doesn't, you can still just alter the voltage divider and use a potentiometer in place of a resistor (or use a switch (mechanical or electronic) to change between various preset resistor values, which is probably what you're already doing), and tweak the voltage that the MCU sees for any particular actual pack voltage.

This can affect controller operation in other ways, however--if it reads pack voltage and it *also* has a programmed HVC, it may not then operate when the pack is fully charged, becuase it now thinks it is higher voltage than it is supposed to be. So if you run into this issue, altering LVC can be more complex, as you have to build a circuit that detects when the battery is above a certain voltage and bypasses the mod until it drops below that voltage, so the controller doesn't disable itself incorrectly.


The former is simple and straighforward, the mod is the same kind of mod, but it does not affect controller HVC (if it has one, it will be a second separate circuit built the same way as this one but with a different voltage divider on it).

 

[CompuTutor]

Thank you for your time, and replies.

All good points, and I understand them.

But all non-standard surplus packs always available,
and homemade non-standard series-count packs,
still need controllers that don't pigeon-hole people
into a voltage range where charged is one range,
and desired discharged is in the range below it.

Add all the different chemistries ranges available,
and It becomes "Standard Lithium", or bust, right ?

Trust me, having to discharge a pack a few volts
on the side of the road with an old auto headlamp,
to get going again, is something I don't miss, lol...

I'll start my searches another day for mods,
thank you for confirmation I'll find some/many.