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Discussion Starter · #1 ·
My Sevcon Dragon 8 died after a water-tight compartment cracked and the controller became unknowingly waterlogged in a recent storm. I was testing a recent battery upgrade and all of a sudden the controller stops running the motor and gives me 7-flash error code (which the manual says is over/under voltage at the battery/motor).

I can't diagnose the controller further since I don't have the tools and anyways it's locked with a master password (set by previous owner's mechanic, and can't be retrieved), and with Sevcon ignoring the DIY community so completely, I think the controller is scrap at this point.

I'm riding a 200KG motorcycle with a 72V 6kW UVW encoder Chinese motor powered by a 24s2p LiFePO4 battery rated at 150A continuous.

I'd love to get a little over-sized controller so I know I'm not running it at its limit, and I need one that supports reversing (pushing this thing backwards to get out of a driveway/tight-curve SUCKS). I'd love to hear what you guys can recommend.
 

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You can reverse any motor with some relays/contactors.

Unless it's a trike or has a sidecar, or you're disabled, having reverse seems kinda sissy to me, though. I think you don't NEED reverse, you'd like to have it.
 

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Discussion Starter · #4 ·
You can reverse any motor with some relays/contactors.

Unless it's a trike or has a sidecar, or you're disabled, having reverse seems kinda sissy to me, though. I think you don't NEED reverse, you'd like to have it.
I wouldn't know how to reverse it with relays, since I'd have to fool the controller to read the encoder backwards as well as flip the phase wires. I guess I could do it with 3 massively-rated relays and 3 regular ones, all controlled with a single high-amperage switch. Seems like an expensive, error-prone and complicated setup. Will probably cost me more time and money than a controller that natively supports reversing.

Also, sure, I don't need it. When I first built this motorcycle, I had to disconnect a couple fuses just to charge it. Running it would require me to always apply a bit of throttle or the controller would cut off (bad config) and if I tried to run at open throttle the BMS would cut off and I'd have to either restart it over Bluetooth, reset it by shorting a couple of wires or wait a few minutes for it to reset itself. I didn't have to improve on any of those. The motorcycle worked, but it was very inconvenient and dangerous (almost fell over once when the BMS cut off unexpectedly and I went from full acceleration to coasting).

However, reversing would've been a deal breaker. This bike has a turn radius of about 1.5-2 meters. That means that I have to reverse it often. More than once per ride. It's heavy, awkward and makes the riding experience crap. I'd probably just take my car places, if I had to push it around every time I got on it.
 

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Yeah, it gets old fast, but get caught a few times and you plan your parking.

Also sucks running out of gas a half mile from the station...you THINK it rolls easily until you have to push.

On the throttle, you could have put a small resistor on the wiper terminal of the throttle pot to bias it on...
 

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Discussion Starter · #6 ·
On the throttle, you could have put a small resistor on the wiper terminal of the throttle pot to bias it on...
Actually it's a hall-effect throttle, but yeah, I could've biased it. I solved it at the controller level, which seems cleaner IMO.

Because I'm a novice, and this is a road-legal bike (plate, registration and all), I try to minimize the workaround and hacks. I don't want any questions asked that I'll have a hard time answering on the annual inspection. Granted, EVs are new enough that inspectors don't know enough to ask anything, but that's just a matter of time.
 
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