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BMS Replacement

Started by ag4go, January 10, 2023, 12:55:07 PM

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Sorry if this has been talked about before.

The BMS went out on my RR6+, fortunately they replaced the battery under warranty but now I have a battery pack which is almost new with a bad BMS. Has anyone replaced theirs in a RR6+?What did you replace it with. I have seen several on Amazon both 20 and 30 amp. I am considering the 20 amp model as a 750 watt motor at 54 volts draws around 16 amps and at 54 volts a little more than 13 amps.

Anyone have thoughts?  I am more concerned about getting it inside the case.


ag4go, how did you come to the conclusion that you have a bad BMS and not only a blown fuse. I have a friend that has a bad battery on his RR6+ also. A couple of times while riding it shut down completely.  Then after trying numerus things it restarted again, but now the battery is completely dead and he can't get it to turn back on or take a charge. He said the battery was over 3/4 charged when he turned it off. Now it won't do anything. 


The battery showed nothing. The display on the battery would not light and even when put on the bike it would appear completely dead. I knew the battery was not dead. I contacted RAD and they immediately  replaced it. Since I received a new one, I opened the pack and verified the batteries were indeed charged but the BMS board was bad. I did some testing with my DMM and verified  all fuses were good. Now I have 52 Li-on batteries with no home. I have thought about using these batteries to replace some battery packs around the house but thought it might be a good idea to have a spare.


@DickB did a great write up/document on BMS replacement in the older Rad Rover battery. It's probably very similar in the new one. You should check it out.,1647.msg8335.html#msg8335


@DickB wrote an excellent article on BMS controllers and was very helpful. Unfortunately this was not for the RR6+ battery. Finding a controller to fit inside their enclosure is proving to be difficult. I will pass on my finding once the project is complete.


Well, I said I would report back when I replaced the BMS and am doing do now.
First my issue was that the battery appeared dead. No lights, no charge, nothing. It was like the internal batteries were completely gone. I was hoping that maybe both fuses would be blown and it would be an easy fix but unfortunately both fuses were fine. I measured 53.4 volts across the battery terminals so I could only assume that the BMS had failed. I did a little more searching for a bad component but no luck. I had originally thought I would just use the old batteries for replacing some packs around the house so I completely gutted the battery but then later decided a backup battery for my RR6+ would be better.

First I had to come up with a layout so I could get 13 banks of 4 parallel batteries. After doing so (BTW, I have a battery spot welder so this was not a problem). Then I had to decide on a 35A controller for a BMS. I found one on Amazon for about $20 dollars that split the charge circuit from the load circuit. ( I fused the charge circuit at 10 amps and the discharge at 25 amps. I chose 25 A because that is the biggest fuse I had in my fuse drawer.. I wired the battery with little problem but I did need to lengthen some of the small control wires. Next I ordered a 2 amp 54 volt ebike charger from amazon to charge them. I didn't want to use the Rad changers in case I blew it up I wouldn't lose either of my chargers. I plugged everything up and had no issues. After about 3 hours the charger shutdown and I had a fully charged battery. Now  I had to put everything back in the case. The batteries would go back in with no problem but the charger wouldn't fit, do I cut a hole in the top of the case and then slit the case to make a "U" slot at the load end of the case. I then found a small plastic case that was the same width as the Rad case and about 4 inches long. I cut a hole in the bottom of one end so it would line up with the hole in the case and fed the wires from the Rad case up to the plastic case where I could fit the BMS. Then used some black silicon sealer from the local hardware store to secure everything back in place, I let everything dry and then the moment of truth, I knew the charge circuit worked but hadn't been able to test the rebuilt battery on the bike. Fortunately yesterday was a warm day and was able to test. I installed the battery and turned the bike on, success so far. Set the PAS to 1 and so far so good. Next to try under full load. I set the PAS to 5 and took off. I never ride and PAS 5 so this was a new experience. I went up a down a bumpy gravel road for about a mile and everything seems okay. and it fits my bike without any problems. The only negative about this is that the built in battery level monitor no longer works but the one on the bike does so this is not a huge issue.

Things I would do different,
1. Use smaller wired for the discharge circuit.
2. The PC board I made to hold the fuses would be 1 long board and use less wire between the 2 ends.

Other than that I am completely happy. I will be keeping this battery as a spare.

Here is a picture of the finished battery.



ag4go, good job, looks good. Would you be williing to do one for another person?  Where are you located, I'm from Wisconsin?


Sorry, I live in Virginia and I really don't want to take on the liability. I am willing to share what I know and have learned on the subject. I am by no means an expert, just someone who like to tinker.

Quote from: rjp on January 20, 2023, 07:33:11 AM
ag4go, good job, looks good. Would you be williing to do one for another person?  Where are you located, I'm from Wisconsin?


ag4go, I fully understand. Thanks anyway. Keep us posted if you have any problems with the up grade.


Ag4go, nice repair. Making "it" work and making it look acceptable is difficult at times. You've done nice work. Congratulations.