Rescue system for my Tri-cycle mobility scooter - Page 1
Forum section: electronics / projects

author: jjj333
author_rank: Contributor
timestamp: July 26, 2025, 03:07:52 pm
content: Hi, about 2 years ago, I bought that Chinese 60V 800W scooter, and so far everything has gone OK. I then bought a small range extender petrol motor that generates 60V 1000W. The problem started when I tried to charge the battery with that petrol motor. It blew the BCDC controller, and I got stranded at night 6 km from home. People saw me (I'm 83 y.o.) and came to rescue me. In the end my friend towed me with his Nissan safely home.Since I enjoyed electronics all my life, I thought of adding a rescue system, consisting of brushed motor 60V 800W, a 60V 10A battery, and a simple PWM controller.Could you knowledgeable experts please give me some good advice on my circuit idea. That would be of great help.It could have been that the petrol motor's output needed some smoothing that destroyed the BLDC controller.

author: RJSV
author_rank: Super Contributor
timestamp: July 27, 2025, 03:50:21 am
content: Looking at your schematic, I realize that, with all the lithium systems I don't actually know the limits, for (your) directly connected generator to 60 V battery...lead-acid that is.Automotive alternators include an overvoltage cut-out, if I remember correctly, and you might need that, which would cut out of the circuit at something like:60 volts + 1/12 x 60 or = about 65 volts, (probably more, like 68 volts)All just educated guess, as 12 V nominal lead acid types have about 12.7 volts, measured when fully charged, no heavy load.I'd try to ask a mechanic, about limiting the charging voltage, at some nominal value above 60 V.Maybe a fuse wouldn't hurt, as well.Is this an extra, 2nd. motor you would add ? Don't forget that's going to be some significant weight, compared to your groceries, etc. being transported.

author: RJSV
author_rank: Super Contributor
timestamp: July 27, 2025, 04:05:41 am
content: BTW, Proper term would be 'Petrol Generator' or Alternator. Have you tried contact the makers, of your new 60 VDC gen ? Maybe they have an application notes, describing a couple simple hook-ups. Did they advertise as a scooter back up or range extender, they might have sample schematic.I might recommend skipping the PWM control, and just use a 3-level speed control (manual with a knob). After all, getting stuck out on the road is no fun, and crude controls don't have as many failure modes, (or hassles getting it to work satisfactorily in the first place.)

author: RJSV
author_rank: Super Contributor
timestamp: July 27, 2025, 04:34:40 am
content: (with the little that I know, automotive, lol)I believe the older cars, before the electronics revolution back in 1950's and 1960's, had regulators described like this:Configured very much like a relay, but where the spring force is balancing the magnetic force in such a way, semi-calabrated, to OPEN up a pair of contacts, if voltage rises too high.Maybe at 10 V or 11 V that voltage isn't high enough, but a little more, like at 13 V that contact opens up.In a voltage regulation function, I believe that open circuited switch then reduces the Alternator field...thus causing a substantial reduction in Alternator output. It (was) an ON-OFF type of crude control, but worked well (for 1938).A bit later, in this control scheme, the Alternator output drops, and the relay will go back to 'closed' switch, and again restore the Alternator function. Result is the older cars would cycle between the two extremes, and voltage would 'cycle' somewhere NEAR an average value, (as the control point).

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 27, 2025, 04:43:02 am
content: Quote from: jjj333 on July 26, 2025, 03:07:52 pmThe biggest challenge looks to be mechanical.How do you isolate the existing motor, and link wheel drive to your backup motor ?Aliexpress have many PWM controllers 20A-100A+ for 48-70VYou may not need 800W 60V for limp home ?

author: RJSV
author_rank: Super Contributor
timestamp: July 27, 2025, 04:52:38 am
content: OR...another option would be, (since you want a 2nd. motor,) just keep everything new as completely separate, generator simply to a PWM controller, and then power the backup motor.

author: jjj333
author_rank: Contributor
timestamp: July 27, 2025, 06:22:59 am
content: Thank you, dear RVSV... for your help. The last piece of short advice is what I want to implement (i.e. keep my system separate from the vehicle's system). The mechanical part is no problem because I'm good at it. For safety, I use a thermostat firmly attached to turn off the power in case the 10A battery overheats.The petrol motor is designed to charge the vehicle's battery. It worked several times until it destroyed the BLDC controller (>>via its Chinese obsolescence scheme ).That's why I don't ever charge the vehicle's battery again via this petrol motor and thought of adding a totally separate system that just drives the back wheel via a pulley.You gave me a good idea... that I should change the cheap brush motor controller potentiometer to a 3- or 4-click switch because it is easier to adjust via a lever than adjusting the potentiometer while I'm driving. I can do that via resistors.This vehicle serves for my shopping. It has a speed of 40 km/h and can carry 3 people. The Chinese petrol motor manufacturer is unavailable. I guess what broke the BLDC controller was maybe a strong ripple current from that petrol motor. That's why I thought to add a couple of big uF electrolytics to smoothen its output. Actually, I was more worried about my circuit idea. Initially, I'll check the motor and battery temperature often to avoid serious damage. I'll see if I can remove the current limiter because most of the power will be dissipated/ used by the brushed motor. The worst that can happen is that the 10A battery overheats, but it won't happen because the thermostat is going to turn off the supply current at 40°C.