Is it possible to downgrade a controller voltage-wise?

[hexadrome]

I bought a 48-72V 60A 3000W generic chinese controller second-hand. Bad buy because I've decided against using dual 36V batteries in series shortly after, but it was very cheap. Now I'm wondering if I can adapt it for a future project since I've another 36V battery left over.

Does anyone know why the more powerful chinese controllers only get build for 48V and upwards? Is it because of the operating range of the more powerful MOSFETs? I've only been able to find 36V 500W controllers with 11A continuous output. At least the one I got years ago is 15A...
Could someone point me in the right direction please? My knowledge of electronics is limited and spotty. I've seen people swap MOSFETs to up the voltage capability of the controller, I assume it would work the other way round as well. If the MOSFETs are the even the right components to swap. And what about the battery cut-off voltage?

 

[E-HP]

Does anyone know why the more powerful chinese controllers only get build for 48V and upwards? Is it because of the operating range of the more powerful MOSFETs? I've only been able to find 36V 500W controllers with 11A continuous output. At least the one I got years ago is 15A...

I think most powerful controllers can run at 36V or lower, but most folks that run high power run higher voltage as well. The Sabvoton, Kelly, and PowerVelocity controllers go down to 24V.
https://www.amazon.com/QSMOTOR-SVMC72150-controller-2000W-3000W-Controller/dp/B07D7TLQVN
https://www.evcomponents.com/kls7230s-300a-72v-sine-wave-brushless-controller.html
http://powervelocity.com/home/55-24f-15kw-sinewavesilent-controller-android-ios-bluetooth-programmable.html

 

[A-DamW]

Well there is one way to find out, hook up your 36v battery and see!

Pretty unlikely to blow anything up. (observe correct polarity, that'll blow most anything up

Maybe post some pics of the controller, with any model numbers/tags/stickers etc.
It may be programmable.

 

[hexadrome]

The controller arrives this friday, judging from the seller's pictures is does not have any label so these two images are the only data I got. I could try hooking it up to a 36V system to see if it will work out-of-the-box, I'd just hate to fry it.

 

[E-HP]

The controller arrives this friday, judging from the seller's pictures is does not have any label so these two images are the only data I got. I could try hooking it up to a 36V system to see if it will work out-of-the-box, I'd just hate to fry it.

You won't fry it powering it with 36V, unless you mix up the + and - conductors. If it turns on with a less than full 36V battery, then it will probably work since LVC for a 48V battery would right around the voltage of a fully charged 36V battery.

 

[slaphappygamer]

Would it be possible that it won’t even power on due to low voltage cutoff?

 

[hexadrome]

That's what I was thinking. Somehow, the controller knows the nominal system voltage and shuts off at the low voltage cutoff point for that system voltage. Now my question is, which controller module is responsible for that? I can solder fine, I'd just need to know where to look/what to swap.
If it's even possible.

 

[E-HP]

That's what I was thinking. Somehow, the controller knows the nominal system voltage and shuts off at the low voltage cutoff point for that system voltage. Now my question is, which controller module is responsible for that? I can solder fine, I'd just need to know where to look/what to swap.
If it's even possible.

It may still work, but if not, there are a few posts on changing the LVC, and it take a bit of guesswork to identify the components that need to be swapped out. I want to mod my spare controller to run 52V (it has an option for 60V or 72V); mine uses a jumper to switch between the two voltages, so when I get around to it, I plan on tracing those wires.

 

[amberwolf]

It won't be damaged by 36v (42v max, 29-30v min), but it might not be enabled (LVC shutoff) below the absolute full charge voltage of a 36v pack.

There is usually a voltage divider somewhere on one of the MCU inputs that's used for reading battery voltage to monitor for HVC and LVC. This may feed a comparator (often an 8-pin chip) between the divider and the MCU and only output a logic-level on/off signal to the MCU rather than the actual scaled voltage.

Sometimes it's used to read the voltage in an analog way, in which case it may be a regular op-amp instead of comparator, or a direct connection from the divider if they really went cheap (but this will blow the MCU if voltage there is ever higher than the divider allows for).

Anyway, you can change the voltage divider resistors (or just one of them) to rescale the voltage for your new expected LVC.


Then the only other typical issue is if the LVPS (low voltage power supply) that generates 12v, 5v, etc to run things from requires a minimum voltage to turn on. In that event you can either use an external LVPS for this, or modify the existing one to run at a lower voltage. It might be use just a big fat dropping resistor to feed an LM317, or it might use an SMPS. (the latter will probably work even at low voltages, but a dropping resistor will liekly have to be changed).