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Razor mx500 (mildly modded)
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Discussion Starter · #1 · (Edited)
Alright so I got a mx500 with 3 12v 18ah batteries that ended up with a short in the stock motor. I went ahead and ordered an 800w 36v replacement motor already and will be running it off my bridge modded mx500 speed controller.
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With that said I'm curious what range you can play in when it comes to bigger motors on stock controllers (or even modified stock controllers). I know the mx500 and mx650 share the same speed controller and yet they have different motors (500w vs 650w) so clearly you can increase the wattage of a motor beyond a certain speed controller rating... but by how much before you start seeing problems? I'm not saying throw an 1800w motor on a 500w controller necessarily, just curious what the safe range is. Any tech guru's got answers out there?
 

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They have 15 amp Chinese mosfets 750 watts is 15.625 amps the problem is when you push mosfets past their Max capability they generate heat and that heat builds up causing internal resistance of the semiconductor so that you will never get the maximum performance out of the motor speed controls are really cheap I mean really really cheap modders might as well pair the motor with the right speed control!!!
 

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Razor mx500 (mildly modded)
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Discussion Starter · #3 ·
They have 15 amp Chinese mosfets 750 watts is 15.625 amps the problem is when you push mosfets past their Max capability they generate heat and that heat builds up causing internal resistance of the semiconductor so that you will never get the maximum performance out of the motor speed controls are really cheap I mean really really cheap modders might as well pair the motor with the right speed control!!!
Fair enough, but figuratively speaking it's plausible to run a larger motor than the speed controller is rated for as the mx650 runs a 650w motor off a 500w speed controller, so I'm curious as to what the largest difference between the two someone could get away with before performance or reliability becomes hindered. 150w? 300w? 500w?

I know they're cheap, I'm just asking as a generally speaking type of question lol
 

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What's your poison? Mine is 40:1
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Yeah wattage is not the enemy. Its the amperage that causes the problems. The 800 watt motor has more amps that it draws than the 500 watt.
And considering 800 is the biggest, you shouldn't have a problem. But I can't remember what the amperage is on the 800 watt. Eventually it will wear it out.
 

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Razor mx500 (mildly modded)
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Discussion Starter · #5 ·
Yeah wattage is not the enemy. Its the amperage that causes the problems. The 800 watt motor has more amps that it draws than the 500 watt.
And considering 800 is the biggest, you shouldn't have a problem. But I can't remember what the amperage is on the 800 watt. Eventually it will wear it out.
And by wear it out you're referring to the motor... or speed controller?

Also I just compared a 36v 800w that I ordered to an oem replacement 500w and according to the manufacturer specs they are both 24A motors... does that seem odd?
 

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That does seem odd on the specs, my buddies 24 volt 500-watt motor pulled 26.7 amps. However yes I mean the controller will eventually wear out. But they do normally anyway. I have a very old mx500 with the flat throttle on an old scooter that's been overvolted. And then I ended up putting in a fast scooters 36 volt 1000 watt controller and gained 1-2 mph. The old controller was 10+yrs old
 

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Discussion Starter · #7 ·
That does seem odd on the specs, my buddies 24 volt 500-watt motor pulled 26.7 amps. However yes I mean the controller will eventually wear out. But they do normally anyway. I have a very old mx500 with the flat throttle on an old scooter that's been overvolted. And then I ended up putting in a fast scooters 36 volt 1000 watt controller and gained 1-2 mph. The old controller was 10+yrs old
Good to know! My final goal (in due time) is to run a 48v 30ah Lipo battery, 48v 2000w speed controller and brushless 2000w motor. I figure that should make it trail capable and good for several hours between charges.
 

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The 500 and the 650 use the same mosfets you would have to open up the speed control look and write down the numbers and letters off of the mosfets then go online and look up the data sheets the data sheets are going to tell you all the characteristics of the mosfets how much amps they can pull how much voltage it takes to trigger them their duty cycle the efficiency curves and so on and so forth from that information you can figure out how many mosfets are in the circuit and how they are running them in series or parallel most of the ones I've seen are both and actually calculate how much current they can actually handle...


Now that we know and have that information yes you can go online and look at data sheets for other transistors and find ones that have the same similar characteristics that can dissipate more amperage and solder them in there and have a whatever you could imagine as long as you could cool it speed control.

It's kind of a lot of work and money for a speed control at some point you would want to upgrade it to lipo and brushless and at that point you don't care about spending money on it and you just go for a USB programmable speed control that you can program easily with your computer.

You would probably need soldering equipment like my station at work
 

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Or, just do real world testing. Lol
Tested many stock controllers with overvolting and anywhere in between 250w-650w. With all positive results. The 500w overvolted is roughly 750w. Only ever had problems when the label says whatever and I push it for more, it hesitates. But I also had way more controller than motor and it was the lead acid batteries holding it back.
Lithium is definitely the way to go and in my opinion the first upgrade.
 

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Discussion Starter · #10 ·
Or, just do real world testing. Lol
Tested many stock controllers with overvolting and anywhere in between 250w-650w. With all positive results. The 500w overvolted is roughly 750w. Only ever had problems when the label says whatever and I push it for more, it hesitates. But I also had way more controller than motor and it was the lead acid batteries holding it back.
Lithium is definitely the way to go and in my opinion the first upgrade.
It was gonna be my first upgrade too but I couldn't pass up 3 brand new 18ah batteries lol. I might just make that my next purchase though, in due time... these batteries are a month old now so my daughter and I are gonna abuse the **** out of these first.
 

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If I picked up a bike and it came with 3 brand new batteries I would have used the crap out of them for as long as I could as well. Spend money on other upgrades and then upgrade the battery.
 

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Discussion Starter · #12 ·
If I picked up a bike and it came with 3 brand new batteries I would have used the crap out of them for as long as I could as well. Spend money on other upgrades and then upgrade the battery.
Yessir! At least that's the plan anyways lol... money is a scarce resource around here with 5 kids age 11 and under, hence my speed controller bridge hack lol!
 

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I definitely understand you there. You got to use old school hot rod tricks to save money.
Lol
 

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Good to know! My final goal (in due time) is to run a 48v 30ah Lipo battery, 48v 2000w speed controller and brushless 2000w motor. I figure that should make it trail capable and good for several hours between charges.
Damn! That would be one heck of a bike. Probably 35+ easily. Probably get sketchy at those speeds.
 

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There was a guy on here he built one with a 1800 watt motor and a programmable USB speed control with a custom built li ion pack using genuine Samsung ( the same 18650s that are in the Tesla cars) cells he posted videos of the bike trying to throw him off every time he gassed it up lol

It just goes to show you that if you use good quality parts how good you can make those bikes.

A lot of people use that eBay crap get disappointed with their build and then give up...

Also keep in mind those garbage battery packs from eBay you know the ones I'm talking about the ones that burn people's houses down while they're charging them they only work good in low torque applications like balance boards big wheels and stuff like that where you don't need a lot of torque like what you need on a dirt bike!!!
 

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Discussion Starter · #17 ·
Damn! That would be one heck of a bike. Probably 35+ easily. Probably get sketchy at those speeds.
Yeah but I'd be happy at 25 - 30mph max and having a lot of low end grunt. I weigh 185 and my oldest daughter is about 125, we both use it daily and I'd like it to be a lot more trail capable than they are in stock trim. I'm not necessarily looking for wheelies and burnouts (though that would be an epic bonus) just being able to handle some of the rough terrain of New Hampshire with ease and do so for a couple hours between charges to really enjoy what nature has to offer is the goal
 

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Discussion Starter · #18 ·
There was a guy on here he built one with a 1800 watt motor and a programmable USB speed control with a custom built li ion pack using genuine Samsung ( the same 18650s that are in the Tesla cars) cells he posted videos of the bike trying to throw him off every time he gassed it up lol

It just goes to show you that if you use good quality parts how good you can make those bikes.

A lot of people use that eBay crap get disappointed with their build and then give up...

Also keep in mind those garbage battery packs from eBay you know the ones I'm talking about the ones that burn people's houses down while they're charging them they only work good in low torque applications like balance boards big wheels and stuff like that where you don't need a lot of torque like what you need on a dirt bike!!!
I always appreciate advice from the wise... could you offer up some reasonably priced examples of what would be a suitable Lipo battery replacement for us so we keep our houses? That's information that I think many could benefit from.
 

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I would recommend building them in packs of three rows of seven so 21 cell packs of 18650s

The quality of the cells and the capacity are going to depend on your run time as well as the quantity of cells.

Obviously building more packs and stacking them together will give you more run time or you can have separate packs and just swap them out to keep the fun going

Use a quality high amperage BMS ( battery monitoring system ) this device controls the balancing and charging of each cell it's also the safety to disengage charging or use at any sign of trouble

There is no reason to go over a how-to or details on how to construct the battery here there are plenty of YouTube videos and websites specifically on calculating voltages and figuring out amperage draws as well as the construction and how to of lipo 18650 packs.
 
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