Controller issue?

Hello everyone, I have a Sun Electrolite Ebike with a 250W Bafang motor/controller, 36V 10AH battery. My problem is the system, (controller/LED power indicator) seems to misread the battery state incorrectly, after fully charged ( to 42.5V) the LED display is at the 1st blinking red position, (meaning it's almost out). So far I've used a DMM and found 42.5V at the LED circuit board, I then used an incandescent 20 watt bulb to manually drain the battery to 32V then recharge back to 42 so it might "learn" the correct voltage, no help. I also rigged a DMM to check battery voltage as I ride, no unexpected voltage sags found. The battery has it's own LED display on the rear and it shows 100% charge as well. I take it there is no adjustment for these systems, I'm curious if I can buy an inexpensive controller and somehow make it work with this setup. Here is a link to the LED "display sensor" as they call it, http://www.jbi.bike/site/product_details.php?part_number=69342 I'm not sure if this is feeding bad information to the controller or vice-versa. I can use the bike but at reduced range since the system shuts down into battery protect mode much too early, any ideas/advise greatly appreciated.

Try disconnecting that display unit.

Perhaps the system has a different low voltage cutoff then what you require. You say its reduced range, so reduced Amp-Hour (Ah) capacity, but do you get reduced speed?

Other then that, lots of people have had success with ebay seller hksunwin. There is a whole thread on his controllers and they are cheap. Basically there are soldered LVC tabs you short out, the lowest being 48V tab, next is 60V.

https://www.ebay.ca/sch/m.html?_ssn=hksunwin&_armrs=1&_from=R40&_sacat=0&_nkw=ebike&_sop=2

Here is one for 36V, random seller I found
https://www.ebay.ca/itm/36V-48V-350W-Electric-Bicycle-E-bike-Scooter-Brushless-DC-Motor-Controller/172955362290?hash=item2844f163f2:g:~XIAAOSwk1hZ9vIF

Hi, thanks for the response, the speed remains the same, this problem just started about 2 months ago, it's the factory controller/display/battery that came with the bike. Seems Sun, (who sold the bike) just used Bafang as an OEM supplier, I only found replacements at one place and they will not sell to the public. I'm gonna take the controller out of it's housing this weekend and see what connections are there, even if I have to install a different controller/display I already have the bike/motor/battery. I got it at a pawn shop 2 years ago for $275 and it's in mint condition, lists for $1,600, (more than I'd ever pay), I think the pawn shop thought it was similar to a Curry bike Wal-mart used to sell around here for $400.

I see your battery is 36V and 10Ah, so you need a new controller for 36V, hksunwin only sells 48V and above.

You must see if the motor runs on halls or is sensorless, then buy a controller off ebay.

A good controller is a company on Aliexpress called Greentime, I am sure they have 36V controllers and the bonus is they run sensorless or sensored(halls).

I am betting your Low Voltage Cutoff is probably set too high.
One way would be to measure the voltage right when charging is done. Ride it until it stops, measure again. A fully charged charged would be 4.20V x 10S so 42V with a cutoff of around 30-32V. A battery with nominal 48V is 54.6V with a cutoff of ~39-40V. So you can see how if you charge to 42V on your 36V battery, and your controller or display is cutting you off at 39-40V, how your range is reduced.

Yea, it's cutting out at 36V so something inside the controller has changed value, I might try installing new caps one I dig it out of the bike, at least I can document the connections to further aid in buying a replacement. Doesn't help when some items are labeled "door unlocking function" LOL!.