I have a 1/8th scale truck.
it is running a 120amp speed controller, off a 4 cell lithium polymer battery.
SO, the batteries nominal voltage is 14.8volts, and fully charged voltage is 16.8volts.
I put a clamp on amp meter on the battery cable...
yes, thats 160amps at about 14 volts... 2.2kw from a 500 gram battery.
Now! the issue is, that the speed controller seems to go into "protect"
it wasn't until a few test runs, that I realised the heatshrink on the speed controllers capacitors had split, I can only assume that the capacitors got to some stupidly high temperature.
what capacitors would I realistically need to handle a 150amp discharge rate, repeatedly?
thankyou for ANY input!
it is running a 120amp speed controller, off a 4 cell lithium polymer battery.
SO, the batteries nominal voltage is 14.8volts, and fully charged voltage is 16.8volts.
I put a clamp on amp meter on the battery cable...
An externally hosted image should be here but it was not working when we last tested it.
yes, thats 160amps at about 14 volts... 2.2kw from a 500 gram battery.
Now! the issue is, that the speed controller seems to go into "protect"
it wasn't until a few test runs, that I realised the heatshrink on the speed controllers capacitors had split, I can only assume that the capacitors got to some stupidly high temperature.
what capacitors would I realistically need to handle a 150amp discharge rate, repeatedly?
thankyou for ANY input!
An externally hosted image should be here but it was not working when we last tested it.
Disclaimer: I don't really have a clue, don't even know what the circuit looks like, however...
Maybe you can use the existing caps as a guideline. Since whatever cap is in there now is good for 120 amps, I'd guess that two of them connected in parallel would be good for 160 amps.
Of course if you do that, something else might decide to go bang.
Alternatively, if it's still working, maybe you can stick with the existing caps and focus on trying to keep them cool with heatsinks or a fan or something. Getting rid of the plastic sleeve would help ventilation for a start.
How do you get 160A out of a 120A controller anyway? Isn't it supposed to have current limiting or some kind of overload protection?
Cheers - Godfrey
Edit: Just saw Richie00boy's comment. Reminds me - you need to keep the MOSFETs cool too.
Maybe you can use the existing caps as a guideline. Since whatever cap is in there now is good for 120 amps, I'd guess that two of them connected in parallel would be good for 160 amps.
Of course if you do that, something else might decide to go bang.
Alternatively, if it's still working, maybe you can stick with the existing caps and focus on trying to keep them cool with heatsinks or a fan or something. Getting rid of the plastic sleeve would help ventilation for a start.
How do you get 160A out of a 120A controller anyway? Isn't it supposed to have current limiting or some kind of overload protection?
Cheers - Godfrey
Edit: Just saw Richie00boy's comment. Reminds me - you need to keep the MOSFETs cool too.
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The speed controller works by pulse width modulation. The capacitors on the modulation board just control the frequency of the modulation and do not carry the >100 amp current. If your controller is going into protection and shutting off and you are drawing 140 amps through a 120 amp controller it would seem that you have a motor with shorted windings that would need to be replaced. You can replace the capacitors with low ESR high frequency 105C° capacitors of the same value. The plastic has split because of the repeated over heating of the controller and will happen again unless you replace the motor.
the controller is rated for 120amps constant, and some stupid, impossibly high current peak, that it will never do.
the esc and motor are fine together, the 160amps is the peak current.
The mosfets aren't actually getting hot (50 degrees celsuis for the heatsink), just the capacitors seem to be, they are directly across the battery, so I'm wondering if an insufficient battery isn't helping.
The motor doesn't have shorted windings, it only has something like 5 turns to begin with and functions perfectly, for about 3 minutes
YouTube - 18072010016.mp4
the esc and motor are fine together, the 160amps is the peak current.
The mosfets aren't actually getting hot (50 degrees celsuis for the heatsink), just the capacitors seem to be, they are directly across the battery, so I'm wondering if an insufficient battery isn't helping.
The motor doesn't have shorted windings, it only has something like 5 turns to begin with and functions perfectly, for about 3 minutes
YouTube - 18072010016.mp4
If they're connected directly across the battery, they're just soaking up the ripple current. Adding more caps to share the workload should help and can't hurt anything.
It may be worth checking your wiring as well. Any extra resistance between the battery and the controller makes life harder for those caps. So long/skinny wires and wimpy/tarnished connectors are bad. Shorter, thicker wires are better.
The + and - wires should be close to each other as well to minimize inductance. (see pic below)
Better batteries might help too if all else fails, but I'd consider that a last resort as I'm guessing they're scary expensive.
Cheers - Godfrey
It may be worth checking your wiring as well. Any extra resistance between the battery and the controller makes life harder for those caps. So long/skinny wires and wimpy/tarnished connectors are bad. Shorter, thicker wires are better.
The + and - wires should be close to each other as well to minimize inductance. (see pic below)
Better batteries might help too if all else fails, but I'd consider that a last resort as I'm guessing they're scary expensive.
Cheers - Godfrey
Attachments
I had shortened the wires after posting this, and it didn't seem to help, I've got about 5cm from the speed controller to the socket, then about 12cm from the plug to the battery.
I'm using connectors rated for 160amps.
They are 10awg cable on the battery, and 12awg on the speed controller.
This battery is rated for 125amps constant, 175amps peak. Cost $US40.
I could get a battery rated for 175amps constant, 230amps peak for about $US70...
I'm using connectors rated for 160amps.
They are 10awg cable on the battery, and 12awg on the speed controller.
This battery is rated for 125amps constant, 175amps peak. Cost $US40.
I could get a battery rated for 175amps constant, 230amps peak for about $US70...
the controller is rated for 120amps constant, and some stupid, impossibly high current peak, that it will never do.
the esc and motor are fine together, the 160amps is the peak current.
The mosfets aren't actually getting hot (50 degrees celsuis for the heatsink), just the capacitors seem to be, they are directly across the battery, so I'm wondering if an insufficient battery isn't helping.
The motor doesn't have shorted windings, it only has something like 5 turns to begin with and functions perfectly, for about 3 minutes
YouTube - 18072010016.mp4
The caps are probably faulty, if the ESC is matched to the motor AND BATTERIES. What value and voltage rating are the caps?
Is the ESC rated for the ~16V that you're getting from the lithium batteries? It may only be intended for use with NICADs or MiMh. Lithium batteries are a comparatively new thing in RC models, a 10-cell pack of NICADs only runs 12.5V fully charged. Lots of buggies used to run 6- or 8-cell packs, IIRC. I'm a heli man myself, and a bit rusty at that.
w
35volt capacitors, 220uF, 4 in parallel, Rubycon brand, 105 degree rating.
esc is rated for 2-4s lipo, its intended for lipo use
35volt capacitors, 220uF, 4 in parallel, Rubycon brand, 105 degree rating.
esc is rated for 2-4s lipo, its intended for lipo use
Funny. Not much to do but replace them all... or ask the manufacturer, or send it to them for servicing, giving the details you've posted here, which is probably the preferred option.
If it's intended for LiPos, then it'll have a cutoff circuit that is intended to prevent you over-discharging them. It recognises the number of cells, then sets a lower limit for the incoming voltage and cuts off when it reaches that. This may be what's kicking in, but the diagnosis is complicated by the overheating caps. They're almost certainly not being caused by the battery, but could be responsible for a low voltage being seen by the cutoff circuit. You might get some insight by putting a DMM across the input voltage and monitoring that from start to cutoff.
w
not sure the manufacturer speaks very good english.
it has a lipo cutoff, but, the esc is indicating overtemp, and its not actually shutting down, just running slow.
cut off can be set for 2.6/2.8/3.0/3.2/3.4 volts per cell and it auto detects the number of cells.
I believe the default is 3.0, most of them are too low anyway!
these runs were all done on a fully charged battery, so I dont think the lipo cut off is the issue.
it has a lipo cutoff, but, the esc is indicating overtemp, and its not actually shutting down, just running slow.
cut off can be set for 2.6/2.8/3.0/3.2/3.4 volts per cell and it auto detects the number of cells.
I believe the default is 3.0, most of them are too low anyway!
these runs were all done on a fully charged battery, so I dont think the lipo cut off is the issue.
I was going to suggest this, but it looks from the picture like there are already 2 fans in there, or is it just one for the motor? Is it possible something is obstructing the airflow, or that the ESC fan is intermittent?
It's difficult to know what to suggest otherwise, other than replacing the caps on a speculative basis, unless you feel up to drawing a schematic of the circuit. I don't really understand why an ESC would need that much capacitance in there even if it has a BEC.
w
If that is a fan on the ESC, is it possible to turn it round so that the airflow is reversed?
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there is a fan in the speed controller.
the capacitors are actually mounted externally, I believe there is a thermistor on the PCB between the mosfets, so when the capacitors get hot, they heat up the thermistor too, without the heatsink warming up.
The fan is currently sucking air in through the top, blowing it out through the heatsink, and out the sides of the speed controller, and through the capacitors.
I'll try swap it to make better use of convection, and also so the capacitors get the air before its warmed by the heatsink
the capacitors are actually mounted externally, I believe there is a thermistor on the PCB between the mosfets, so when the capacitors get hot, they heat up the thermistor too, without the heatsink warming up.
The fan is currently sucking air in through the top, blowing it out through the heatsink, and out the sides of the speed controller, and through the capacitors.
I'll try swap it to make better use of convection, and also so the capacitors get the air before its warmed by the heatsink
ok, I used this again today.
the heatsink got to 50 degrees, while the capacitors were at 90...
I do not understand this!
however, I have another similar speed controller, and it runs three 1000uf 25volt capacitors.
so..
120amp speed controller - 880uf/35v capacitors
150amp speed controller - 3000uf/25v capacitors
I think I need more capacitance! maybe this 120amp was meant to have like four 470uF 25volt, but they ran out
the heatsink got to 50 degrees, while the capacitors were at 90...
I do not understand this!
however, I have another similar speed controller, and it runs three 1000uf 25volt capacitors.
so..
120amp speed controller - 880uf/35v capacitors
150amp speed controller - 3000uf/25v capacitors
I think I need more capacitance! maybe this 120amp was meant to have like four 470uF 25volt, but they ran out
120amp speed controller - 880uf/35v capacitors
150amp speed controller - 3000uf/25v capacitors
I think I need more capacitance! maybe this 120amp was meant to have like four 470uF 25volt, but they ran out
I think part of the answer lies in the 35 volt rating. AFAIK, ESR (electrical series resistance) of a capacitor increases with voltage rating (someone correct me if i'm wrong here), so it's more likely to get hot. Also less capacitance means more ripple current which at this level is bad bad bad for caps, so yeah you need more capacitance, but try to get 25 volt low ESR caps.
I agree ultra-low ESR is needed. It's probably more important than the amount of capacitance.
Thinks: Heat is proportional to power dissipation which is I squared times R.
I'm not sure about ESR increasing with voltage rating. I've heard the opposite suggested as well.
It's best to look at the specs though, and aim for low ESR, high ripple current and high temperature. Caps intended for SMPS could be good, or maybe solid caps?
Thinks: Heat is proportional to power dissipation which is I squared times R.
I'm not sure about ESR increasing with voltage rating. I've heard the opposite suggested as well.
It's best to look at the specs though, and aim for low ESR, high ripple current and high temperature. Caps intended for SMPS could be good, or maybe solid caps?
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