Troubleshooting motors and controlers

[Boneless]

Hi all,
New member, wish I found this site earlier this year so good ideas,

Anyhoo. I have a Trailmaster miniX gokart I put a Vevor 2000W, 48v 12ah kit on for my kid. It was a great starter kart as it has a tourque converter so I could play with gear ratios and find what worked well. And the kart had an adjustable motor plate so you can just slide things to adjust chain tension which is sweet. I'm using a mobility scooter battery set up, which is 4 x 12v 12ah batteries. And the Vevor motor kit off Amazon was like $120 and included everything but the gas pedal and brake switch. And it has reverse, which is a back saver since my kid is often in need of help getting away from things. It also has a key ignition and power level meter. And three speeds, which lets me keep it chill for my kid but we can rip around faster.

However, about a month ago my kid noticed the power was dropping when he hit the gas even after a full charge. Usually we get about 20-60 min on a charge. I have a second battery set up so we swapped it and it did the same thing. I checked all the wires and no short or draw I can find. But if you hit the gas it's like there is a major draw. With a volt meter hooked to the battery it will drop to 36v pretty much as soon and you give it power under load. And 36v is the motor cut off so it doesn't go anymore. If no one is on the kart it revs right up and the volts stay at 48v. I have no idea what normal is, but I put the kart together in March and we didn't have a problem all summer and that kid drove it pretty much every day.

Does anyone have advice for testing the controller and the motor? I understand you get what you pay for and replacing it is pretty cheap. But if I only have to replace one part that would be good. I reached out to Vevor about is it should have a 1 year warranty but they seem to be avoiding any real diagnoses or admittance of fault or problem. I searched the forum but don't see any tests recommended.

Thanks in advance

 

[Whitetrashrocker]

Im not a electron wrangler, but that sound like a dead battery.
Will charge and show voltage, but when a load is put on it, the amps just aren't there anymore.
Maybe one of our sparkys can comment and give a better answer.

 

[pinkpanda3310]

I tend to agree with Whitetrashrocker. Lead acid batteries don't perform well under high load. If you suck the guts out of the battery like the following it will shorten the life ;
- stomp the throttle regularly
- completely drain the battery every run
- combining previous 2 points will most certainly shorten the life

The only other possibility that springs to mind is the motor has gotten too hot at some point and weakened the permanent magnets. This causes the motor to draw more current to make up the required power. Drawing more current can go one of two ways ;
- more current = more heat, so the motor will overheat again, exacerbating the problem
- more current = sucking the guts out of the battery as explained above

It doesn't sound like a controller problem to me

 

[pinkpanda3310]

I'm not sure if this method works for lead acid batteries but you could try it. Charge the battery till it's full. With the charger still connected use a multimeter to check voltage > disconnect the charger and see how much the voltage drops on the battery. In all cases the voltage will sag a little bit. I would think you're batteries are going to sag several volts straight away as it sounds like they're at the end of their life. Look up expected battery voltages to give you an idea - https://www.google.com/search?ie=UT...oid-browser&q=lead+acid+battery+voltage+chart

 

[Boneless]

Thanks for the input.
I initially thought battery as well. But I have a second set of batteries, which are new in the box and got the same result. I picked up two sets and set one aside not knowing the life of the batteries. Since the new batteries resulted in the same drop I was then thinking there is either something up with the motor or controller. Also, we wired up his little razor e-motorcycle to use two of the batteries and he's been running that with the old batteries since the kart died with no problems from the batteries. If anyone has one of those razors this setup lasts a long time compared to the stock batteries, though they do stick out on the sides a bit.

Since the motor will run well when not under load I ran it for a while in the air and did not notice any excessive heat from the motor or controller. But again, it wasn't under load. It only goes like 10 feet before the motor kicks off so I can't really run it to check to them getting hot under normal conditions, but I also was not paying any attention to it, so it may have cooked itself and I didn't notice.

 

[pinkpanda3310]

The batteries that you were keeping unused, were they connected to a battery maintainer or did they just slowly drain flat over that time?

Google Search

 

[Boneless]

The batteries I bought were similar to these, https://www.amazon.com/Mighty-Max-Battery-Replacement-DURA12-12F2-4/dp/B094PY62C4 thought from Walmart. And I bought them in August. I did try them fresh from the box and got the same result and then gave them a charge which was very quick before the charger clicked off, maybe half hour at 2 amp, so I'm assuming they had a pretty good charge anyhow. Got the same result with the new batteries after the charge as the old batteries on a full charge.

Voltage is 50.2 fresh off the charger, so 12.55 per cell. Though I didn't think to try each one. That is a little low based on the battery chart, but that may be my charger.

 

[pinkpanda3310]

You bought the batteries in August but it's possible they were manufactured months prior. One set you cycled (used) and the other set weren't touched for months. The second set really should have been charged before first use. They were likely halfway flat and then you drained them (deep discharge). The fact that they charged "quickly" is also a bad sign, it means they now have low capacity. In other words - end of usable life. A good SLA battery charges over 14 volts so your batteries at 12.55v after charging means they're in pretty unhealthy condition.

 

[Boneless]

Interesting. So maybe two sets of bad batteries then? I will admit the first set was purchased in February and we didn't get the cart rolling until late April and they worked fine out of the box, no charge. Although that first drive was only for a few minutes and then they got charged. And they have had a lot of cycles this summer. But these new batteries didn't have the time to be sucked down. I simply hooked them up and since the results were identical, that's it. 30 seconds attached, maybe 10 sec of run time. But who knows when they were manufactured or sat on a shelf.

But they are cheapo batteries so I don't really doubt they could be bad. I've been using a 48v, 2amp charger so I don't have to disconnect the batteries. Maybe I'll try running them parallel and hook it up to a 12v charger.

It is odd though that they always have worked fine on the razor though. I would think if they were not holding charge that machine would also be doing odd things. It has a similar low volt cut off.

Do you think an automotive battery load tester would work? I've been thinking since they are smaller it would not. Maybe I'll run them to napa and ask.

 

[pinkpanda3310]

Napa likely has high quality testing gadgets and will be able to advise you much better than I can

 

[Boneless]

So, napa said their tester was for larger batteries and tested the batteries as bad. I suppose that's because it's testing for AMP draw, like from a starter. According to the guy like in the range of 400amps, which these little cells are not.

I did separate each cell and charge and all charge to 12.68 after being pulled off the charger. So, according to tables that's good.

As one final effort I gathered up 4 car batteries out of our cars and linked them up. Same deal, though to a lesser effect. The cart would move but slowly, so not kicking off like on the smaller cell batteries.

I was able to find a blog post testing brushless motors. Essentially it said test resistance across all three to each other and look for an odd pair. You should be 0 but also not infinity. I get Yellow x Green 2.0, Y x Blue 1.5, and the odd one was G x B which initially tested 1.7, but when I went to double check it was between 2.6 and 4.8, and seemed to fluctuate. So, maybe an issue?

Then with power to the motor check voltage to the motor across all three wires using the shell of the motor or the negative terminal. Doing that I get the same voltage across all three which I think is good.

Again, random blog post. Coming from a RC past, not having a negative on the motor is so odd. And the hall sender is in the motor on this model. So the there is a wire connector to that which seems to be working and the voltage changed between 0 and 5v.

 

[pinkpanda3310]

Bugger. That's disappointing Napa couldn't test your batteries. Given you tried your car batteries and still had mostly the same issue, it's starting to look like it might not be the batteries. Also makes the problem harder to diagnose over the net.

I need to ask, is there any binding or stiffness in the drive train?

When you tested the motor phase wires, did you disconnected it from the controller?.. as the controller will interfere. That test is to find faults in electrical connection but will not show anything if the magnets are demagnetised. There are methods to test if the magnets have weakened but you need a reference point i.e. a second exact same motor to compare results (or preferably have tested your motor when new). I don't know if there's a method to test it after it's been weakened...??

BTW there is no "negative wire" on the motor because it is a 3 phase device. The controller does magical stuff and converts dc current to 3 phase.

Hall sensors are really outside my knowledge. It could be the problem but I really don't know enough to guess about that.

That's about the limitations of my knowledge so I don't think I can help much from here, sorry. It could in the end be the controller but I've never heard of one misbehaving like that before...?!

 

[Boneless]

Well thanks for the help. I also noticed there is quite a bit of resistance in the motor itself. I can't say I remember that when I assembled it, but it was a while ago. Do these motor have much resistance? When I disconnect the chain to the motor the wheels spin much more freely. So, no physical catches I can find. Bearing all seem good. Cart rolls real nice.

I will also add Vevor has been communicating with me but only to tell me they are working on the problem and will get back to be in 48 hours. Which they do, to tell me they are working on the problem.

Tempted to just buy another kit and swap out parts till I find the problem. The bummer is any other brand of 2000W motor is as much as the whole Vevor kit with the controller. So I might as well buy that and take a chance. Doesn't work, amazon takes returns.

 

[Whitetrashrocker]

It does sound like the motor with all your feed back.
Can you get just the motor?

 

[Functional Artist]

It does sound like the motor with all your feed back.
Can you get just the motor?

Yup, I'm thinkin' so too

Sounds like a position sensor, in the motor, "failed"
...so, (1) of the (3) phases isn't working
&
When ran without a load, the motor is able to "skip" over the "missing" phase
...but, when trying to run it, under a load, it isn't able to do the "skip" anymore

Yup, should be able to buy just the motor

* Personally, I prefer to use plain 'ol 48V brushed motors
...seem more powerful (for their size...brushed ~1,000W vs. brushless ~2,000W)
...& more reliable too

 

[Boneless]

Well after lots of back and forth with the company they sent me another motor and it seems to work. I will admit it's currently 10F so everything is slugish. And the voltage does seem to drop from 4 bars to 2 when you hit the gas it's not as fast as it should be. But he drove it for probably 20 minutes in the cold and it never died.

 

[EdwardWare]

I’d suspect the batteries first too. A weak battery can show 48V sitting still but collapse under load like that. Since you tried another pack and got the same result, I’d check each battery individually under load and make sure one isn’t dragging the whole pack down.
Also check the battery connections and main cables - a bad connection can act the same way. I’d test there before replacing the controller.