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Discussion Starter #1
I'm working with/testing a YALU 3000W 70A 48 60 72V BOMA Brushless BLDC Electric Motor Controller from Alfa Wheels (~$100.00)
Controller YALU 3000W 70A 48 60 72V f BOMA GoKart Brushless BLDC Electric Motor | eBay

Controller Features and Specifications
  • 48 to 72 Volts, rated, 3000 Watt
  • 70 amps Peak (almost 5000W peak!)
  • 120 °
  • Connecting diagram: Please look at picture showing cables and functions
  • Features/ Connects to:
    • Battery
    • Motor (3 cables, power)
    • Motor (5 cables, hall effect)
    • Power lock switch (turn it on and off)
    • Brake switch (kills the power when braking)
    • Reverse switch (Reverse is half speed)
    • 3 Speed selector (Hi-Mid-Low)
    • Speed Signal
    • Throttle (hall effect throttle) 3 cables
    • Cruise Control (connect to temporary switch for Cruise Control
    • Self Learn (To calibrate with new motor)
To power/control a 60V 2,000W brushless motor (~$125.00)
Specs:
  • 60V DC
  • Rated 2000 Watt, 42 amps
  • Rated 5600 RPM
  • Chain drive (11 teeth sprocket) #8 chain 8mm pitch
  • Type of motor: DC, Brushless (BLDC)
  • Reversible
Dimensions:
- Diameter: 4 1/4"
- Length (no shaft): 5 1/4"
- Length (with shaft): 6 1/4"


There is NO wiring diagram, available (that I could find) just a wiring definition
...but, it does not mention a contactor.

So, is there a minimum voltage or amperage where a contactor is recommended, required or necessary?

Also, what about pre-charging?

Is 60VDC of "inrush" current enough to damage the "cap's" in this controller?
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Ohm's law dictates that at high voltages with low resistance amperage goes sky high. It's that current which one tries to eliminate. Also the pre-charge lets you do a health check. If the power provided is dumped/lost/wasted you know that connecting the bigger relay won't be a good idea...

When a device is connected and caps are empty is when the biggest inrush current flows. It's a magnitude of 60amps.
Or your inverter has an system integrated.

I think you should use a contactor and a pre-charge resistor. They won't need to be from HV systems since you have 60vdc and 70amps.
 

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Discussion Starter #5
A lot of info. But nothing saying what you're using it in and how.
I'm testing it on Excalibur my racing style go kart (test vehicle)


Ohm's law dictates that at high voltages with low resistance amperage goes sky high. It's that current which one tries to eliminate. Also the pre-charge lets you do a health check. If the power provided is dumped/lost/wasted you know that connecting the bigger relay won't be a good idea...

When a device is connected and caps are empty is when the biggest inrush current flows. It's a magnitude of 60amps.
Or your inverter has an system integrated.

I think you should use a contactor and a pre-charge resistor. They won't need to be from HV systems since you have 60vdc and 70amps.
IIUC a controller that is capable of 70A (peak) will only produce that much current if/when connected to or powering a motor that can draw/use that much current
...but, this 60V 2,000W motor should only draw ~33A constant & maybe 60A for split second "spikes" or peaks

I build a lot of vehicles. I started off with 24V & 36V scooters & then, lots of 48V go karts & now I'm working with 60V
...& probably 72V systems next

So, I'm looking for actual criteria for if/when a contactor &/or pre-charging was necessary (& why)

I'm using a 125VDC 65A circuit breaker to protect the system & as a "main cut-off switch" (for storage & maintenance)
...& I believe, it should be able, to be used as, a "manual cut-off switch" in the event of a "runaway" situation
(as far as I understand, that's the main purpose/job of an electronic contactor)

* A pre-charge function could be easily be incorporated into the system (a momentary switch & a resistor)
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You might want to go ahead and remove the cover of your controller to examine the circuits and write down the value, rating, etc of the input capacitor, and go ahead to order a replacement--because if you don't use a pre-charge circuit and contactor then it is only a matter of time until it blows.

When a capacitor is given a large DC voltage step, such as 0 to 60V on startup, its initial response is like a direct short circuit to ground--there is a huge inrush of current to fill the empty capacitor. This inrush can cause internal damage and is the reason to use a precharge to limit the current to a safe rate. The contactor is then energized after the capacitor is full in order to by-pass the precharge circuit and provide a low-impedance path for the main operational current. The contactor has precious metal surface contacts with very low resistance, but it does not like to be switched while current is flowing, due to arcing across the contacts which damages the surface and increases the resistance.

Sure you can go ahead and try it and run it without the circuit for awhile, but it's a gamble until the controller caps blow, then it might be costly or impossible to repair.

Pay now or pay later, either way an education is a costly expense.
 

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Kennyboy says what I meant. Perhaps I should have stated the law which dictates the charging of a capacitor.

Anyway what you could do is place a fairly high resistor over that switch. Then you have your pre-charge fixed. The only thing is the controller will be always live so adding a second switch is needed then.

But remember switching on in the wrong order is still a weak spot then.
 

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Contactors have several purposes, but none of them is to actually switch heavy current on and off - they CARRY heavy current. If you want them to last. People love to cite ohms law, but it's a lot more complicated than that for caps and the circuits they hang on.

Also, a breaker should be used as a protection device, not as a switch. If it were my project, I'd have a bright red disconnect switch that's accessible no matter the kart's orientation.

Your speed controller may already have a precharge relay in it, since it has an on/off switch input. Several ways to find out.

I really like the packaging you've done there. What kart frame did you start with?
 

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Discussion Starter #9
Contactors have several purposes, but none of them is to actually switch heavy current on and off - they CARRY heavy current. If you want them to last. People love to cite ohms law, but it's a lot more complicated than that for caps and the circuits they hang on.

Also, a breaker should be used as a protection device, not as a switch. If it were my project, I'd have a bright red disconnect switch that's accessible no matter the kart's orientation.

Your speed controller may already have a precharge relay in it, since it has an on/off switch input. Several ways to find out.

I really like the packaging you've done there. What kart frame did you start with?
Well...I/we kinda went thru BRB's & manual vs. electronic contactors & even pre-charging, a few years back.
Here is the thread, if interested.

From what I understand, a contactors job is to connect & carry the "heavy current"
...or disconnect & sever the "main power supply" from the controller
...but also, to be able to the break the "flowing current", if/when necessary
(like in an emergency runaway situation or like when the low voltage cut-off, limit has been reached)

I asked the original question, "is there a minimum voltage or amperage where a contactor is recommended, required or necessary?"
...because this is a higher voltage system (60VDC) (compared to what I'm used to working with)
...& this is a HUGE controller
...with probably some "good sized cap's inside
...that are capable of drawing & releasing a lot of amps.

I mainly wanted to know (if anyone knew) if there is "actual" criteria for when a contractor is necessary/

Thanks!, my Excalibur kart is built from scratch.
It's made outta regular old 1/2" schedule 40 waterpipe & based on a common "racing" design.
I just incorporated the battery "trays" into the chassis. :sneaky:

I first tested it with (2) 48V 1,000W motors, powered by (4) 12V 15AH SLA's
...it ran ~45 minutes, while draining ~345Wh out of the pack.

Next, I tried a 48V 35AH Lithium battery pack
...but, the (2) motors seemed to be drawing too much from the pack & causing some heating issues
(I aborted the test @ only ~250Wh used)

So then, I removed (1) motor & tested it again
...it ran like 3 hours, while draining ~936WH out of that pack.

* I've probably put ~10 miles on this thing, so far :)

Now, I'm trying a 60V 2,000W motor
...& then, maybe even try/test (2) of them :cool:
 

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So if you can determine the size of the input capacitor in your controller, then you can calculatus the stored energy to charge it up,
E = .5 x C x V^2

The voltage squared term goes up quickly. When you went from 30V to 60V system, you doubled the voltage, but the energy went up x4 or more depending upon the caps.

With no resistance of an inrush current limiter device, the charge up happens nearly instantly. The current will be 60V divided by the resistance of the wire from the battery to the controller. If you used a 1 ft piece of 20AWG, 10mR per foot, then the inrush current would be 6,000 Amps. This would likely exceed any current ratings of the capacitor, the current would arc over and punch thru the electrode foil layers and short out the cap at least, and worst case explode. Any switch device used to turn ON the system will also be subject to this large current and sparking and arcing that may occur and damage the switch.

There is no one-size-fits-all rule of thumb. Each system and situation must be evaluated. But over 30VDC is considered getting into the lethal region and requires due diligence.
 

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Discussion Starter #11
So if you can determine the size of the input capacitor in your controller, then you can calculatus the stored energy to charge it up,
E = .5 x C x V^2

The voltage squared term goes up quickly. When you went from 30V to 60V system, you doubled the voltage, but the energy went up x4 or more depending upon the caps.

With no resistance of an inrush current limiter device, the charge up happens nearly instantly. The current will be 60V divided by the resistance of the wire from the battery to the controller. If you used a 1 ft piece of 20AWG, 10mR per foot, then the inrush current would be 6,000 Amps. This would likely exceed any current ratings of the capacitor, the current would arc over and punch thru the electrode foil layers and short out the cap at least, and worst case explode. Any switch device used to turn ON the system will also be subject to this large current and sparking and arcing that may occur and damage the switch.

There is no one-size-fits-all rule of thumb. Each system and situation must be evaluated. But over 30VDC is considered getting into the lethal region and requires due diligence.
Yes, I agree & thank you that's the kind of info I was looking for.

I was under the understanding that once you get over 48V then, you were getting into the lethal range.
(where the current can penetrate dry skin etc.)

I've noticed, many times, the spark/arch when connecting the power to my 48V controllers & initially energizing the caps.

Again, that's the reason for this thread, because this system is over 48V & there is no mention of or provision for a contactor or a pre-charge circuit.

To help expand the conversation a bit more, I went ahead & opened this controller up.

I also, did a quick video, to help show/document the inside of this thing.
.
 

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8mA of AC through the heart can kill you, so it's not as simple as voltage.

That inverter output can kill you even though it's only on a 48V battery.
 

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That was a good job to open it up and get some pictures. On one of the pictures of the little black caps on the phases i could see the part number, CD228H, and used that to find the vendor is Nantung or Nantong. They have many varieties but i couldn't read the number on the big blue caps, but you read off the value so we know they are 470uF 100V.

They have 2 blue caps in parallel with an unpopulated spot for a 3rd. So the total is 2x 470uF = 940uF, and the stored energy is 1.69 Joules.

With nearly 1,000 microFarads uF, it would be to your benefit to use a pre-charge circuit or device.

Maybe something simple like an NTC thermistor would work for you, but it's a little pricey at $33.

You need some switch for ON/OFF, maybe a big red panic button or E-Stop button switch could be used for that and you could just manually pre-charge your caps with a sufficiently sized resistor across the switch contacts. Then you don't need all the extra wiring and battery taps to operate the contactors. For a street car you would need full blown contactors, but a gokart could get by with a big resistor and switch.
 

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Discussion Starter #14
With no resistance of an inrush current limiter device, the charge up happens nearly instantly. The current will be 60V divided by the resistance of the wire from the battery to the controller. If you used a 1 ft piece of 20AWG, 10mR per foot, then the inrush current would be 6,000 Amps. This would likely exceed any current ratings of the capacitor, the current would arc over and punch thru the electrode foil layers and short out the cap at least, and worst case explode.

Any switch device used to turn ON the system will also be subject to this large current and sparking and arcing that may occur and damage the switch.

There is no one-size-fits-all rule of thumb. Each system and situation must be evaluated.
Thanks for the replies (y)
...it really helps me to learn more &/or clarify things that "I think I know"

Ever notice how more information almost always generates more questions?

1.) How long does it take to charge up the caps, thru the precharge circuit?

Like for a DIY precharge circuit (resistor & push button/momentary switch)
...& also,
On my ElMoto, I shut down the entire system (right @ the circuit breaker) after every use (to eliminate parasitic draws)
...the next time I go to use it, I engage the circuit breaker (powering up the system)
...then, turn the ignition key to "on" (to energize the 12V system)
...then, turn the Run/Stop switch to "run" (to turn on the SC)
* kinda just like the stock ICE system was set up

But, I now realize that this scenario only allows for ~30 seconds of precharge, before the contactor get's engaged & the full voltage is connected to the controller.
* I haven't had any problems for over 500 miles :)

2.) Does this "any switch" refer to a DIY precharge circuit? (resistor & push button/momentary switch)
...or the controllers On/Off circuit ? (power lock or KSI)

3.) For a precharge circuit, what if the "switch" was connected in/on the controller side of the resistor, instead of the battery side?

Wouldn't it only have to deal with & switch the reduced current that's "now" being let thru the resistor?

4.) As for the On/Off (power lock), it connects a relay that just turns the SC's "logic" on/off
(it's VCC/pack voltage but, draws & thus switches less than an amp)
...the caps draw their energy thru the big/main power wires

Would that "relay" be considered an internal contactor?
 

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to answer #1,
the time to fill the capacitors would be: t = 6 x R x C , where R is the resistor and C is the total capacitance, which in your case is 940uF. It will occur much quicker than 30 seconds. You can pick a time that you would like it to occur such as 1.5 seconds, then substitute this into the equation and solve for R. This will be the resistor value to achieve that pre-charge timing.

2) This only applies to the switching device in the main power line from the battery to the controller, such as a diy push button or E-stop, or a relay or contactor in this path also. If switching is done before precharge, then that device becomes the path for the hellacious current.

3 and 4) i'm not following your question. Probably a drawing of a circuit schematic is needed. The diy resistor/switch has these two in parallel and the resistor is manual touched across the terminals using your hand, held for the time calculated above, then the switch button is engaged to complete the path and the resistor is removed. If the resistor is attached to one side of the switch, then the open leg will have pack voltage on it--not a good idea to leave it floating and flopping about.
 

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Discussion Starter #16
to answer #1,
the time to fill the capacitors would be: t = 6 x R x C , where R is the resistor and C is the total capacitance, which in your case is 940uF. It will occur much quicker than 30 seconds. You can pick a time that you would like it to occur such as 1.5 seconds, then substitute this into the equation and solve for R. This will be the resistor value to achieve that pre-charge timing.

2) This only applies to the switching device in the main power line from the battery to the controller, such as a diy push button or E-stop, or a relay or contactor in this path also. If switching is done before precharge, then that device becomes the path for the hellacious current.

3 and 4) i'm not following your question. Probably a drawing of a circuit schematic is needed. The diy resistor/switch has these two in parallel and the resistor is manual touched across the terminals using your hand, held for the time calculated above, then the switch button is engaged to complete the path and the resistor is removed. If the resistor is attached to one side of the switch, then the open leg will have pack voltage on it--not a good idea to leave it floating and flopping about.
Kool! the start up procedure, I use, for my motorcycle should be fine.

3.) DIY precharge circuit
I drew up a diagram of the DIY precharge circuit that I have in mind.
...the red lines = pack voltage / constant current (VCC)
...blue lines = pack voltage / reduced current (VRC)

4.) "Would that "relay" be considered an internal contactor?" This would be a NO
Because, we saw, how the big power wires (red & black) connect directly to the main "rails" inside of the controller.

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So, NO there is NOT a relay or contactor in between the batt pack & the caps.
...& without an internal "switch" there can NOT be an internal precharge circuit.

FYI:
I took a pic of the power monitor.
Notice, when the system is switched "on" (power lock plug shorted) it shows the pack voltage (64.36V)
...the wattage of the device (SC logic) is registering @ 1.2W
...the power draw (amps) is showing 0.02A
...& energy use in Wh is showing 0Wh
 

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That looks like it will work with the correct sized resistor (value and power rating). What about adding a fuse in that line or in the Negative side path? The breaker is probably not a DC rated device is it?
 

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Discussion Starter #18
That looks like it will work with the correct sized resistor (value and power rating). What about adding a fuse in that line or in the Negative side path? The breaker is probably not a DC rated device is it?
A fuse in the precharge circuit?
...what would be the purpose, for this fuse?

Yes, this breaker is DC rated.
It's a MidNite Solar - 50 Amp 150Vdc DC Circuit Breaker MNEPV50
Their usually used in solar installations. (pics in post #5 show the specs)

I have a 10W 1KJ resistor, that came with a 36V 200A contactor, that I bought from Kelly Controls, that I can try/test.

So, to test this DIY precharge circuit, I assembled the (10W 1KJ) resistor with a small switch (rated 0.6A @ 125VDC &/or 0.3A @ 250VDC)
...installed it onto the CB mount/housing
...& connected it "across" the CB terminals

I didn't "do the math"
...but, it seems to function as anticipated :)

Here is a video describing the concept & testing it out. :sneaky:

Are these results, what's to be expected?



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i was referring to a fuse in the red wire path from the battery pack positive terminal, or in the wire to the negative terminal. This was before i saw the actual breaker.

Did you get a datasheet with the breaker? Did you check the polarity of the breaker for installation?

The microswitch with the resistor looks like a good method to do the precharge. You got lucky that it works ok without checking the math--i would call that semi-functional.
 
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