What's the weak link now?

MattZ

100 W
Joined
Jul 14, 2021
Messages
101
I mean something other than the guy putting the bike together, that one's obvious.

It's a 29" MTB, 2000w DD motor, KT 18 FET controller rated 22A / 45A max, 52v battery with a 30A continuous BMS.
I cooked the 20A rated / 40A max, 12 FET controller in less than a month. At some unknown point in the future AliExpress will get around to delivering the 18 FET controller and I'd like to avoid cooking something else so quickly.
I'm thinking the BMS is the new weakest link and I should probably set the C5 parameter to 05, which would lower the controller max amps to 33.8.
Does that sound like a good idea? I have a temporary 18 FET 45A max controller on there now but it has no display so I'm flying blind regarding wattage. Nothing feels like it's getting hot but I'm gun shy now since nothing felt like it was getting hot before but then it got real hot real fast, and direct replacements take a month to get delivered.
 
I think that limiting the current with the controller is enough. However, you could look at the c rate of your battery and gauge of the copper wire between the battery and the controller for a weak link.
 
RunForTheHills said:
I think that limiting the current with the controller is enough. However, you could look at the c rate of your battery and gauge of the copper wire between the battery and the controller for a weak link.
OK thanks. The wire is 12 gauge silicone going to XT60 connectors. Battery is a jumbo shark with a weird 5 pin connector (2 large pins, 3 small, but nothing connected to the small pins).
C rate is something I haven't dug into yet. I'll have to read up on that.
 
Your battery is the weak link. You didn't cook your controller because it was too much for the motor, it just died because sometimes thats how it goes with this stuff from china.

But now your battery is going to suffer, if you don't run it on something closer to 20-25 amps. Even if its got some really good cells in it, with high c rate, its not going to like even 33 amps.

Not sure what you mean by 2000w motor, but it sounds like a wide one, with lots of copper and magnets in it. So it can handle the big controller. But your battery is not going to last for years. If its a really good battery, it will work fine for awhile, but just not for 3 years.
 
dogman dan said:
Your battery is the weak link. You didn't cook your controller because it was too much for the motor, it just died because sometimes thats how it goes with this stuff from china.

But now your battery is going to suffer, if you don't run it on something closer to 20-25 amps. Even if its got some really good cells in it, with high c rate, its not going to like even 33 amps.

Not sure what you mean by 2000w motor, but it sounds like a wide one, with lots of copper and magnets in it. So it can handle the big controller. But your battery is not going to last for years. If its a really good battery, it will work fine for awhile, but just not for 3 years.

Thanks Dan. I had not considered the current draw would have such an effect on the life span of the cells. I'm not surprised the controller died young, I had suspicions about the combination in the kit. It's just frustrating that it takes so long to get a replacement, US stock is very limited.
It's an UPP battery and I've seen a lot of debate here about the quality of them so I bought the protection plan along with it which I don't usually do.
The Amazon listing for the kit described the motor as 2000w, they didn't list details of poles or windings.
 
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