First run results (48V 1800W on a large kart)

[scorn001]

So to any who are interested, I got everything put together enough to make a test run this afternoon.

Pretty much as I though, it's significantly under-powered. It does go plenty fast when it's able to reach a reasonable speed (level ground, not turning). However when going uphill, it runs out of steam very quickly, if you try to make a turn when going uphill - it just can't do that. Motor will come to a complete stop. I think having the live axle makes those turns very hard on the motor, and even more hard when you are already slowing due to having to make a climb.

The controller would become very hot to the touch, not so hot that you couldn't touch it, but hot enough that you couldn't touch it very long, same with the motor. When first starting, when trying to carry my 200lbs in a turn with no momentum, just trying to slowly get myself pointed the right direction before trying to take off, the chain would clatter and it would all just stop, and the motor would stop responding, I'm guessing this is due to an overcurrent/temperature issue or something with the controller. If I would wait a few minutes, it would work again. Once up to speed, it would do just fine - again, until you hit a hill or started trying to turn again.

My plan is to purchase a 2nd motor and controller and run it on the opposite side of the axle with the same sprocket that I have running on the normal drive side. Not sure how hard it will be - ordinarily there would be no drive on that side so there is no mount point where the motor will need to be.

Anyway, that's what I've got so far. It's fun to see it running, and I can't wait to see what it'll do with 3600W pushing it.

 

[Functional Artist]

Kool, glad you got 'er going
I too have noticed that heavy karts + live axles + big wheels = don't mix too well
...then, we go & add a bunch of batteries (~40 extra lbs.)

Does your controller have a (3) speed option/plug?
...if so, do you have a switch connected?

If not, you may be only running at "medium speed"
...this is the default speed, if a switch is not connected to this plug.

 

[scorn001]

I do have the speed selector connector. All of the very rough documentation I was able to find indicated that leaving the circuit(s) on this connector open was the fastest option (yellow to ground == slow, blue to ground == medium, open == fast).

I remember you posting a video about this, I'll go back and have a look.

Thank you.

Edit: I just went out and tested, on my controller, connecting either the yellow or the blue wire to ground yields a lower top speed.

 

[wheels]

Hey Scorn... how heavy is your cart? I am building a two seater Campground cruiser and i am thinking about adding a second motor. (48v 1800w). My total weight is going to be around 500lbs with two people on it. 35ah batteries dont help with reducing weight.

 

[scorn001]

I honestly don't know. I don't have a way to weight it. I'm out of town right now but should be home on Wednesday. I'll dig out the manual (before my mods) and see if I can find a weight listed.

 

[scorn001]

Sorry I'm just now getting back to this. I got out and looked at the manual and receipt for the original kart and saw no reference to weight at all. I suppose I'd guess without and one in it maybe 150? I know I can lift the back to spin it around or out it on jack stands, but it is heavy. I know that doesn't help much.

 

[wheels]

Ok, thank you. I am probably going with a 60V setup instead of 2 motors.

Thanks again.

 

[Bmr4Karts]

A single 48v 1800w motor can get 300lbs (including rider) moving at 30mph and this setup has the ability to climb hills. If you modify the controller to send 50 amps max it accelerates even better.

The same motor with a 24v 400w controller can make 300lbs go about 12mph with no hill climbing power.

I haven't gotten around to using my 60v motors and controllers yet.

 

[scorn001]

How do you make this modification to the controller?

 

[Bmr4Karts]

Add solder to the shunts to reduce their resistance. Here's a picture of the shunts before I added my solder. The glob that's already there came from the factory. I extended that glob about halfway up that pair of the shunts. The improvement in acceleration is very noticeable and I pull just over 50 amps according to my shunt meter.

 

[itsid]

yeah it's called placebo effect!

I don't need no circuit diagram to see that that black wire has about TWICE the resistance and HALF the current rating of that shunt in stock form it is attached to.

so in the end you did nothing to alter the powerlevel of the MosFets.
those are the only things inside a controller limiting the motor power
(batterywire-busbar-MosFet-phasewire-motor ... nothing else really)
and your's will at least be rated 60Amps.. 200Amps is more likely these days really.
throttle position will determine at which rate they're fired.. but once on they're ON at full power.

WITH the circuit diagram I could tell you what you actually did instead..
I'm guessing that shunt you soldered isn't even really part of the power bars for the mosfets.

Soldering without checking is the equivalent of replacing a blow fuse with a bullet shell..
sure, the lights are now brighter (*cough*) but you might burn your house down


'sid

 

[Bmr4Karts]

yeah it's called placebo effect!

I don't need no circuit diagram to see that that black wire has about TWICE the resistance and HALF the current rating of that shunt in stock form it is attached to.

so in the end you did nothing to alter the powerlevel of the MosFets.
those are the only things inside a controller limiting the motor power
(batterywire-busbar-MosFet-phasewire-motor ... nothing else really)
and your's will at least be rated 60Amps.. 200Amps is more likely these days really.
throttle position will determine at which rate they're fired.. but once on they're ON at full power.

WITH the circuit diagram I could tell you what you actually did instead..
I'm guessing that shunt you soldered isn't even really part of the power bars for the mosfets.

Soldering without checking is the equivalent of replacing a blow fuse with a bullet shell..
sure, the lights are now brighter (*cough*) but you might burn your house down


'sid

sid sid sid, you never fail to amuse. This modification is nothing new. Read up.

The controller monitors its current draw with a shunt. A low resistance piece of wire, it reads the voltage on the wire and from that extrapolates the current draw. Ohm's law and all that.

If we solder the shunt, we lower it's resistance, allowing it to pass more current for a given voltage drop. In effect tricking the controller into thinking it's still drawing it's normal current limit, but it's really drawing more current.

Here's a shunt mod thread from 2008

For over a decade the shunt mod has been proven to increase the current capacity on these chinese controllers. I have a fuse inline with my battery and I also didn't care if I blew this $40 controller. I now pull over 50 amps from this controller which is rated for half that and it gets considerably warmer with improved acceleration (no placebo effect).

I did the same mod with a smaller $20 24v 350w controller for my daughters pink gokart. Before the mod, the cart could not push me if I stood in front of it, tires wouldn't even spin. Did the mod, stuck it back in and now it can push me backwards with ease.

The proper way to do this mod is to measure the existing resistance and add the correct amount of wire to reduce the resistance to get the desired current output. I've also read that solding halfway up is usually safe and that solder alone can work as long as it doesn't get hot enough to melt.

 

[itsid]

and nowhere a diagram to be seen...
that's what I meant

That shunt is more than likey just as I expected part of a protection circuit.
And sure a 40 dollar controller lost isn't the end of the world, it's just the end of 40 dollars

The proper way to do this mod is to measure the existing resistance and add the correct amount of wire to reduce the resistance to get the desired current output.

increasing all of the wiring and tracing (bus bars and such)
can up the controllers capability sure..
and tricking the controller into misreading the currents to stall overcurrent protection then does make sense..
But you haven't said a word about wires needing to be upgraded before did you?
and without that all you do is put stress on the traces mostly..
and turn electricity into heat really
(just disabling the protection)

And HOW is that upgrade of the tracing dialed in.. eyeballing?
not too scientific is it?
calculated? what term has been used?
thermal correction terms in place?
Questions amongst questions.

And yes I know that many people around the internet do the most curious experiments with electric devices...
doesn't mean it's generally safe or to be considered a good idea.

You risk your 40 dollar controller.. feel free, I surely do not stop you.
You can also tell someone that if they are aware that they risk their's that this might be a valid way to do so.
(in case they do follow all steps, not just the bad one)

But I haven't read such "be aware.." statement neither here:

A single 48v 1800w motor can get 300lbs (including rider) moving at 30mph and this setup has the ability to climb hills. If you modify the controller to send 50 amps max it accelerates even better. ....

nor here:

Add solder to the shunts to reduce their resistance. Here's a picture of the shunts before I added my solder. .... I pull just over 50 amps according to my shunt meter.

No, all you mentioned was "solder the shunt"
and that by itself is in fact bad advice
And if the chinese haven't started overbuilding controllers lately... it's also not really much of an improvement until the worst case rears it's ugly head.

So.. what about the "stick with safe advice" mantra?

Yes I drive my motorcycle w/o a helmet if I so desire..
I would never suggest it's a good idea to anyone!
(yes exaggerated example..)

And THAT is what I meant by mentioning the
bulletshell in a fuse holder..
might work.. but as likely to fail catastrophically.
and most of all.. very bad advice!


'sid

PS NOW.. if you have a pcb schematic,
I can tell you what you want to modify and how
to turn your 50 amp controller into a 100a controller..
and in a mostly safe way... but be aware: it's cheaper and safer to just buy a bigger controller

 

[Bmr4Karts]

Like I said before, it's not a placebo.

As for getting a bigger controller it would safer but not cheaper. The controller and motor combo cost almost the same as the motor by itself so it's almost a free controller.

To anyone reading this I suggest trying the shunt mod. Just go to YouTube and search for "motor controller shunt modification." If the controller fails, then you buy a bigger one. The big controller I bought was $500 but I've got a bigger motor and bigger battery to go along with it.

As with all internet advice provided by me, sid, or any other complete stranger that you've never met, you are on your own if it kills you. Now go out and have some fun.

 

[scorn001]

Alright, so this brings up a question I've had, and did some search for an answer before but wasn't able to find anything definitive.

The bigger controller. I understand that there are bigger/more powerful controllers available, but I was thinking that these were pretty much matched with the motor provided. In my case - a 48V 1800W controller goes with a 48V 1800W motor. I was understanding that it was a bad idea to use a 48V 2000W controller with my exisiting motor - I'd need to upgrade the motor as well. Certainly one of the 72V 3000W controllers would be an extrememly bad idea?

What are the rules here? It sounds like I can use a larger/more powerful controller with an existing motor?

 

[Bmr4Karts]

The safe way to plan a setup is everything is stronger than your motor.

Meaning the controller can send more power than the motor needs and the battery can send more than the controller will take.

Using that logic you want a controller that is more powerful than your motor.

I see you mentioned the 72v 2000w controller, that is a very bad idea only because of the much higher voltage. That motor will burn up with that much voltage


What you need to be concerned with regarding the motor is gearing, heat and voltage. Gearing is the part you will run in the most trouble if you have unrealistic expectations for those two motors in your larger kart. I'm already pushing it sending 56v to a 48v motor. I'm actually going to swap out the 48v motor for a 60v motor and use it with my 48v controller.

 

[scorn001]

The motors are actually doing okay with the controllers now. It isn't a rocket, but on the road it has no trouble getting up to about 22 mph, which is plenty on that kart for my kids honestly. It'll go that fast on the dirt too, but the bouncing at that speed is painful.

My weak link now is the batteries. I've got 4 of the 12v 22Ah batteries off Amazon on it. When it's drawing the full 60 amps that output drops about 6-7V. I need to make sure I'm not loosing in the wire to my cutoff, but I'm guessing the batteries are just drooping from the strain. Once the batteries are drained to the point that they sit at about 47-48V, it becomes pretty gutless. Thinking another set of batteries in parallel.

 

[Bmr4Karts]

Good, if the motors aren't getting to warm/hot you are geared properly. If you want more oomph with the same top speed, the shunt mod or larger controllers will provide better acceleration along combined with higher discharge capability from your batteries.

Also, you are over taxing your batteries. With my 66v lithium battery I only see a 4v drop when pulling 260 amps.

I'm hoping you've run at least 10 gauge power wires from the batteries to the controllers? Doesn't cost much more than 12 gauge. Also, don't be afraid of shorting the motor wires if they are way longer than you need. That extra wire is nothing but resistance losses.

 

[scorn001]

The max discharge rate according to the datasheet for the batteries is listed @ 300A, so I was thinking I could do so without damage, and really thought that maintaining a higher voltage with a 60A draw wouldn't be too hard for them, but it's looking like I'm wrong. I need to double check the wire guage but I'm pretty sure it's 8 guage. Should be plenty heavy enough.

 

[itsid]

The safe way to plan a setup is everything is stronger than your motor.

finally we can agree
Yes.. everything bigger than what the motor needs is safe.

...In my case - a 48V 1800W controller goes with a 48V 1800W motor. I was understanding that it was a bad idea to use a 48V 2000W controller with my exisiting motor - I'd need to upgrade the motor as well. Certainly one of the 72V 3000W controllers would be an extrememly bad idea?

What are the rules here? It sounds like I can use a larger/more powerful controller with an existing motor?

Yes you can.. the controller is "kindly offering" Amps to the motor,
it's not force feeding the motor with currents.
So a bigger amperage rated controller is perfectly fine with a small motor.
(it's force feeding voltage though.. so a 72V controller will likey hurt your 48V motor .. different question)

The thing is that controllers (as motors) can be rated either max or constant power..
the max power rating is something you only want to apply for a few seconds,
then it's going to overhead
(and burn out the traces on the pcb, pop a cap, blow a resistor, fry a MosFet... weakest link first)
constant rating is what you want to have matched or exceeding your requirements.
Some list both, some just peak values (sounds more )
So a reliable source is a very good thing to have.
unfortunately internet sellers are not always as reliable as we wanted them to be. Some don't even know what they're selling some just lie in your face. (hence I like to suggest kellycontrollers rather inexpensive and with good quality and honest ratings)

Say if the motor can draw 45 Amps constantly (60 peak) a controller with a constant rating of 50A and a peak of 100A is a good idea..
an "oversized" controller say constant rating of 200A and peak at 400Amps is just running cooler with that same motor attached.
the other way around -a 200Amp motor on a 100Amp controller-
will certainly cause the controller to overheat and die in short order.

a 100peak controller on a 60Amp peak motor cannot be improved with the shunt method!
an "undersized" controller might (if done properly and not just solder blobbed)
at some risk (I too repeat myself it seems.. aaaanyways)

Batteries.. unfortunately the same rules apply for batteries as for controllers..
there's a constant and a peak rating.
the peak is what automotive battery mfgs call CCA (cold cranking amps)
that rating is usually considered to be applied for no more than 30 seconds
(some mfgs claim up to a minute)
Constant discharge rating is nothing you find mentioned on automotive batteries unfortunately.

A rule of thumb is that it's about 10% of the CCA (maybe 15)
and/or in the realms of their capacitance
means a quality automotive battery can be fully drained rather safely over the course of one hour
(a 45Ah battery delivering 45Amps, a 60Ah battery 60Amps, two paralleled 35Amp batteries 70Amps, a 550CCA battery 55Amps and so on)
it's not more than a rule of thumb though.. type matters
wetcells can deliver amps "more easily" than SLAs, more than AGMs, more than Gel cells
and marine batteries more than automotives without overheating.
(batteries too get warm if abused)

Now you got a 1800W motor (let's assume it's mechanical power rating)
it'll draw ~47Amps (about 2200 Watts electrical)
with just four batteries in serial for your 48Volts you want 45-50Ah batteries
with a 4s2p configuration of eight batteries 25Ah batteries should do and so on.

If that 300Amps are Cold cranking amps you might abuse them a little too much already.
even at 15%CCA that'd be 45Amps and just on the upper limit at full power...

Easy to tell if you need to worry though..
just check the batteries every now and again if they got hot after a ride.
Or even better.. get a cheap thermometer with a sensor lead
and wedge that sensor between two batteries
I'd not allow the temperature to rise above 55°C (130'ish F)
especially not if kids are near.
I'd feel much better with it not exceeding 45°C (115'ish F)

'sid