BBS02 Voltage fluctuations!

[fighting_haggis]

Hi folks I'm new to this forum and I have limited ebike knowledge but im pretty sound with electronics. I'm looking for some help to an issue I'm having. I have bbs02 750w 48v 20ah.

The problem I have is when I switch the bike on everything power's but the voltage readout on the lcd fluctuates up and down! The bike won't move when this is happening. Its completely random, I can turn it on and everything is fine. Ride it a bit and boom, voltage is all over the place again and bike stops working.

I have dismantled my battery and tested bms output and its stable at 52.3v. Tested cells and battery output before bms and all stable.

Where does the lcd read voltage from? Can the lcd be causing the issue? Motor controller? I don't know, it's driving me mad! I don't want to buy a new battery or controller to find out the problem still exists.

Any help would be greatly appreciated.

 

[Annieolnie]

Have you tried continuity and resistance testing in case you have a chafed wire or bad connection somewhere on the frame?

 

[fighting_haggis]

Have you tried continuity and resistance testing in case you have a chafed wire or bad connection somewhere on the frame?

I haven't checked continuity or resistance no. I will give it a try tomorrow. I have visually inspected all cables as they are external and there doesn't seem to be any damage.

 

[fighting_haggis]

Have you tried continuity and resistance testing in case you have a chafed wire or bad connection somewhere on the frame?

All checked and sound! Still have no idea what's going on.

 

[Annieolnie]

This is a problem that's out there. Electricbike.com, (diagnosing voltagedrops) has a thread with a number of possibilities. Some people have battery cradle connection issues, one person had the bms plug in his battery only half attached. Someone else had the amperage in their controller set too high. Can you borrow a battery to take yours out of the equation and see if that works? Who made your battery and what sort of cradle does it have? Another cheap experiment might be to get the programming cable, dongle and the Speeed app to check your programming and, or lower your amperage. You seem to know electronics, go to the above mentioned thread and tell me what you think. If you are comfortable going over your bms board, that's another good place you could start. Let us know what you find.