Tongsheng 750w Xh18 controller not working at all

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shaunysc   1 µW

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Tongsheng 750w Xh18 controller not working at all

Post by shaunysc » Mar 28 2021 7:30am

Hi all,

I just installed above after testing it successfully. Following install and shortening power cable nothing seems to work.

Where could the fault lie, and how can I tell. I could I have pulled too hard on cable. Can something have blown: a fuse, the controller or the display. I'm afraid I did inadvertently test with position and negative swapped over, but I think this was after it didn't seem to o work, but it could have been before. If so could this 'blow' something.

Any help gratefully received.

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amberwolf   100 GW

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Re: Tongsheng 750w Xh18 controller not working at all

Post by amberwolf » Mar 28 2021 9:01pm

Unfortunately, if power was connected backwards, it's more likely than not that damage has occured to various components, from the main capacitors (big cans) to the shunt to the low voltage power supply (that makes the 12v and 5v for all the brain and control and sensor stuff). If power was left connected long enough to overheat them then FETs can blow up from this too. How long that is, varies. (sometiems it takes a bit for the caps to blow up too, but sometimes they do it immediately).

However, I've had one controller that was given to me after having it's power reversed that blew the shunt and the main capacitors, but the FETs and LVPS were still good, and after replacing the shunt and caps, it worked fine for me for years. :)

But I have a few others sent to me that are in my junk parts bin because they didn't survive power reversal, blowing some of the FETs in one, and the main LVPS regulator and downstream stuff like the MCU in others. :(

Is this a potted controller, or can it be opened up to examine the internals?



Another thing that can happen is the battery itself (or rather, it's BMS) can be damaged from the reversal, if it doesn't have sufficient overcurrent protection. If it is, then there will be no output (or just a ghost voltage usually well-below the normal voltage).

The BMS can also just turn itself off to protect the battery, and require being hooked up to it's charger (with the charger connected to the wall outlet), to reactivate it.

If either of these has happened, it's even possible that there is nothing wrong with the controller at all, and it's just the battery not providing any voltage.


Do you have a multimeter?

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