Argument thread: Low specc batteries don't kill ESC's. Or do they?
 

Allright, im in all out war with this dipstick from RCU who continuously states that there is no way that todays brushless systems, especially the ESC are damaged by batteries that are subpar both in quality and specc.

I was under the impression from day one of owning my first brushless truck, the Savage Flux that using Lipos and especially nimh batteries that are incapable of feeding the MMM with enough current results in the MMM going *poof* as we have seen many times before with alot of peoples MMM setups. But is this truly not the case? This guy states that the lipos should be exploding and smoking as a result of using below specc batteries for an application. Well, I sure as hell aint seeing Lipos going puff, but I sure as hell am seeing alot of MMM making smoke when the Lipos or Nimh arn't up to par.

We discussed this topic at length already. So why the hell is the theory that subpar batteries ARE NOT responsible for ESC failures appearing?

http://www.rc-monster.com/forum/showthread.php?t=24142

http://www.rc-monster.com/forum/show...ighlight=zippy

I want this settled once and for all, are using batteries either lipor nimh that are not up to specc capable of ruining ESC's or is it caused by some other force of nature according to this guy?

http://www.rcuniverse.com/forum/m_10...m.htm#10025159

I'm seeing MMM' going poof in these vids, not lipos.

[YOUTUBE]91oQcK585eQ[/YOUTUBE]


[YOUTUBE]z4GbTiqeS-Q[/YOUTUBE]


[YOUTUBE]Wf00JUvU2QI[/YOUTUBE]

I dont see how a battery would be at fault ..
the only way would be is if the pack was marked wrong........

and it was a higher voltage than marked.
and the chances of that are VERRY slim.

looks like a average esc failure

the second vid dont know for shure.. but i dont see how a cap can make a esc fail as the cap is on the Voltage INPUT side of the esc not on the Output of the FET's of the motor output.
a short there would make it fail yes .

and the third just look at the landing all types of things could have went wrong...............


a Bad spec battery would just not come up to the rated voltage or amperage or the "C" rating and would just be like a low battery.
and a low batt would NOT do this.

Yes bad batteries cause ESC's to fail - Yes damaged CAPs cause ESC's to fail - Yes manufacturing defects can cause ESC's to fail - YES damaged motors can cause ESC's to fail - YES water can cause ESC's to fail - YES mechanical damage can cause ESC's to fail - YES damaged servos can cause ESC's to fail - Excess voltage can cause ESC's to fail (although my good old MM took 6s like a trooper)...

Basically a lot can cause ESC's to fail...

IIRC the reason inadequate packs could harm the ESC was due to ripple current, ie. the batteries' resistance was too high and was causing the voltage to sag under load, then rebound to a level the ESC couldn't handle. Feel free to correct me if I'm in any way incorrect.

if the voltage was to "sag" it would be like runing on a low batt ..

so under that
that would be every time your battery went low your esc would smoke.
I don't see this.

i have seen ALOT of esc's go bad in plenty of ways and for plenty of reasons.

but in all my time in electronics and teaching electronics I My self have NEVER seen low voltage make a device fail that catastrophiclly with total distruction
but low voltage can damage the low voltage regulator.

The first video by the amount of smoke it was NOT the battery it was the drive fet's that Failed that is The Only way you will get that mutch smoke and fire.
as 12 to 24 fet's fail but most of the time only 2 to 4 will "give up the ghost" .

and if a servo kills a esc it would not smoke that bad as there is ONLY 1 to 3 regulators and seperate from the motor drive fet's that is used for the servo drive inside the esc and 1 small transistor dont have the mas or material to produse that mutch Venting smoke and or fire.
and not all three will go as the design for a 3 stage regulator only the first or the last one will go.

we use to burn fet's and older style regulators up for fun in electronics class my students got a big kick out of it
and were learning at the same time.

Anyone have an advil!

Freeze/Radio - Ripple is correct... I suggest you search on that term and perhaps filter on user BrianG or Patrick (aka CEO Castle).

There have been numerous posts on how ripple kills esc's - Back EMF voltage from braking when running close to ESC's max rating is the other culprit.

I told you guys:lol:

Search: Keyword(s): ripple ; Posts Made By: Pdelcast

If the voltage is constantly sagging the system draws more amps to make up for the power loss and hence compiles the problem. If the LVC is set high that can sometimes be triggered too. If they are running maximum volts then ripple is most likely, as Arctik saying.

Not really - An ESC is never always pulling current from the battery it is a very fast switch pulling current very fast through each phase. You don't even see this pattern on an Eagle Tree as it is happening so fast.

The max voltage point was related to back EMF when braking - the breaking force is converted back into energy and shunted via the ESC into the battery. These spikes can be very high... If they get too high and the battery can't take the energy quickly then the ESC can say enoughs enough... This is worse when ESC's are running close to there rated voltage as the ESC obviously has less voltage "head room".

Have a look through BrianG and Patricks posts...

Why does the voltage sag then?

cant take it anymore, lets not forget people, these are AC MOTORS. which equals inductive load. the esc does not pull power from the batteries, the MOTOR does. the esc simply meters the flow to give linear throttle control. highest current draw is at startup not wot like a brushed motor. the motor will take all thats available unless something stops it, the esc. if the power is not there to be taken from the battery the motor will fry anything in its path in an attempt to get what it wants, usually the esc. setup will dictate how much load is present, ie. gearing. higher gearing means more load and more heat. the easiest and most relevant example is the NEC's requirement for voltage in our homes, no lower than 116 and no higher than 124. try running an ac appliance on 100 volts and see what happens. so yes crummy batteries CAN fry a speed control. caps and other componets cant keep up with the giant surges from the motors when the voltage in the pack dips below the point where it can supply the current being drawn.

next time your a/c kicks on watch how the lights dim momentarily. this is the max current at startup im talkin about. if voltage is low on your service the breaker will trip in your panel instead of blowin stuff up. maybee we should ad breakers to our esc's and be done with all this nonsense for good. lol....

ok, it would appear that late nights, drinkin, and assumptions have gotten ther best of me once again. seeing three phases on a motor meant a/c in my mind, but 3 phase brushless motors are indeed a reality. oops! yes im highly oppinionated, and yes im a jerk but still it would seem that the same principals of an a/c motor would apply to a 3 phase d/c motor as well. if im wrong feel free to lay in as deep as you would like, wont bother me a bit, but being as hard headed as i am, will probably still argue anyways out of pure pleasure at that point!

Oh, Freeze, u so crazy.

That makes sense to me. I do understand the esc is just a gate (or series of gates). But what if the power is not there to be had, ie;crappy battery?

Then the ESC does not see the current.

If the battery can't supply it, etc etc.

If you open a fire hydrant, and there's only 15 psi at the hydrant, does the hydrant explode?

So the only way sub-par batteries can break the esc is through ripple and over voltage?

water is not electricity and is bound by completely different laws, that said using your analagy you forgot load. What if there was something on the other end that wanted 115 psi. Something will give. Again speedos don't push power that is why the are not rated as maxiumum output only max current it can pass on.

Freeze....after reading some of your posts over on that thread on RCU it seems you have anger issues. I now see why people get fed up with you, and I also see how you have been banned from multiple forums. Maybe you should take a chill pill and quit starting drama. It is rediculous how childish you act when things do not go your way. Telling people to "fu** off a**hole" just because they do not agree with you is really messed up of you! End of rant :)

OK...

so let's say we have a pumper truck hooked up to the fire hydrant.

What happens then?

Not addressed here but really basic is heat.

Load on the motor will dictate its draw from the batteries. If you gear a motor to pull 100wats, that is what it does. So if you have 100 volts you only need 10amps. And likely the wires in the system will be rated for that 10amp draw. So will other components of the esc, connectors, etc. So lets say your battery cannot provide the required voltage and it starts dropping, well the load is still there so the amps spike, in turn dropping the voltage more, causing more amp spikes, a viscious circle if you will.

Some of us here used to run nimhs, voltage drop and amps spikes were pretty common, as nimhs had a hard time keeping up with brushless, and that is why you would see alot of 30cell series nimh setups, as higher voltage lowers amp draw on a fixed load.

So crappy batts will drop voltage under load, and if the load is enough it will cause higher amp draws, which casues everything to heat up and can lead to equipment failure. Usually the esc goes first, but I have seen solder joints melt, motor windings short, and batteries go poof before the esc lets go. In fact i had a really stout MM back in the old days that together with a 7xl killed many a maxamps pack, and did some damage to a few nimh packs with a 7s motor.

Subpar batts are a problem, kinda like using bad gas in your car, that can cause issues too.

We arent talking about water, the analogy simply doesnt work when you start getting into specifics or trying to blur the two subjects.

Voltage will drop when when current rises, that is the key thing to remember about batteries, so buy batts that can supply sufficient current before they become over-worked. The MMM system has been observed to pull peaks in excess of 120 amps, so lipos that can provide a maximum continous current of 120amps are recommended; they will however only be supplying about 20-40amps continously in reality, with 120-130amp peaks lasting mere milli seconds..

So you're saying water pressure does not drop when something pulling said water through a pressurized system?

Sorry, but in this analogy:

Motor:pumper truck::ESC:hydrant::water supply for hydrant:battery

Electricity, for the most part, works like water, guys.

It's too basic an analogy

You could always adapt an RC to run on pressurised water...then the analogy is perfect. Electricity is far more complex than water & can't be simplified into hydraulic pressure - sorry just doesn't work

That was my understanding. I was getting a little confused though :oops: Thanks for posting Linc.

+1
I have to honestly say I felt confident that this thread was a super complete waste of time, after it's all said and done and especially James Posted I've come to a little better understanding about these failures. I knew Batterys could def be a culprit but The Pimple made it easier for me to grasp how and why.

Electricity is not that complex. It's electrons flowing one way through a system. hydraulic flow is really no different than electrical flow. If you really wanted to, you could build a 3 phase hydraulic stator motor and a system to properly feed it.

If you don't understand the analogy because you don't understand fluid dynamics, that's fine. Don't pretend electricity is more complex than fluid flow, though.

The point is, if the battery can't supply the amperage, then the battery can't supply the amperage. People post a LOT about "ripple current" and simply accept it as fact without understanding it (kind of like how people assume fluid dynamics and electrical flow are different), yet nobody has offered a proper explanation.

From how ThunderbirdJunkie understands it, ripple current is from a battery not being able to supply the drawn current, then suddenly supplies it, and stops, and continues that cycle.

Is this accurate?

No... That is not correct...

briang

Basics of brushless motors

http://www.cirrus.com/en/pubs/whiteP...ess_motors.pdf

OK, so it's not the ripple current itself that kills the ESC, it's the FET's inability to switch fast enough.

That makes sense. So it's not current killing the ESC at all, just substandard parts.

Hmm, water is quite a bit different than electricity. I have felt electricity and it is not wet. I can't wash my hair in electricity, and my water faucet works quite a bit different from my MMM.

All kidding aside, you have to factor amp spikes, in both directions. Heat and its effect on materials that conduct electricity is very important. Kinda like friction. If you do not factor friction into physics equations they are very simple, however we do not live in a friction-less enviorment so it is kinda important.

The battery has to be able to output a stable voltage at high current levels while also having low internal resistance to keep from getting hot, and also accepting a charge back from the regen brakes. The esc has the task of controlling the motor and ducting the electrons to and from the battery.

I am by no means in full understanding of how this stuff really works, but I do know that the battery is the single most important part of these brushless systems. I have experiemented with alot of different batteries and there is a difference.

Here is an excerpt from a review of the Castle Phoenix ICE controller, which can measure voltage ripple as part of it's data logging feature. The context is from the airplane/heli side of things, but regardless it sheds some light on voltage ripple and how low-spec and low quality batteries can cause problems.

"Battery Ripple Voltage: This is a really cool feature that no one else has implemented in an ESC. If you wanted to try and measure this any other way you’d need a lot of high-end lab equipment to do so. Basically, if you could graph the battery voltage between the pulses of the controller which happen tens of thousands of times a second, you’d be looking at a ripply line, not a flat line. As the controller allows energy to flow from the battery, the internal resistance of the battery affects (causes) the voltage to drop, even in that millisecond. This isn’t necessarily a bad thing when the battery and motor are properly matched, but it is a very good way to determine if, indeed, the battery is up to powering a particular application.

Generally speaking, higher discharge batteries will provide better performance and have less voltage fluctuation with changes in load, so lower ripple voltage. Let’s take this a bit further. The big capacitors on the controller are used to smooth out that ripply voltage. This is important because the FETS need to have a stable voltage or bad things can happen. The capacitors can only smooth out so much of this ripple. If the ripple exceeds the capabilities of the capacitors, you have a much greater chance of the controller letting go. This isn’t a defect of the controller, it’s just the physics. Use the ICE’s ripple voltage readings as a relative number. Try different packs in the exact same machine with the same gearing. Those with lower ripple voltage are the ones best suited for that application. The others may simply not be up to running that particular setup.

So, the ripple voltage measurements finally give you a scientific way to compare the C rating of a battery pack with other packs. This is something that consumers have needed for a long time. You are no longer at the mercy of the marketing guys’ declarations of C ratings. You’ll now have the ability to produce graphs that prove which packs are better!

If you happen to have a charger that displays battery internal resistance, this is also indicative of C-rating. Combined with the ripple current data you can determine if a particular battery is either up to the task for your application or starting to age.

Say you have a 500 size model and you’re running a 20C pack and have a 3D setup. You may very well see a big ripple. If you were to change the battery to a 40C rated pack, the ripple will decrease and the flight efficiency will increase. That 20C battery could be old, or just not up to the task for the kind of demands your power system is putting on it. It may fair better in an airplane application that draws less current, thereby allowing you to get some more life out of it.

The ripple will be more pronounced with a lower C‐rated pack in a high demand application, whereas the higher C-rated pack will reduce the ripple. To get a baseline, log when your battery pack is new and then check it periodically to monitor its health. You can also look at the wattage data and determine when the battery starts to head south, since the wattage will drop."

Dude, not to be a "freezebyte" but the 3rd person diatribe is not necessary. If you say "I" or "me" we will understand. Not the traxxas or savvy forum...

This is badass. May have to get one of these escs just for this feature. Make myself a bench testing setup with a ducted fan jet (big one) and a variable inlet to provide some resistance. Then I can test some packs and see how they really compare.

This does answer the op question quite well.

enough with this water crap. it is not the same, nice try though. you might be an expert in that area, congrats. when have you ever worked with REAL electricity? not this measily sub 600 volt stuff either. show me water that will seek a path to ground at all costs. is it going to jump out of your cup? no. if you stand too close to a full pool will the water arc out and hit you because you are dry no. show me a pipe which water will flow through that has a resistance value. show me a capacitor for water that will correct power factor(voltage lagging behind current). water in no way behaves like electricity other than the fact that it flows. sure electrons do the same but they dont flow through a pipe or hydrant or any of that. electrons flow due to a difference in potential. fluid dynamics are fluid dynamics for a reason, it fluid. electricity is electricity, it behaves in one manner, it wants ground, and wont do anything for you until you give it that. water will do whatever you tell it to in the vessel you give it. there are a few excelent posts in this thread, all with the same underlying theme. if the power is not there to be taken other componets will fail trying to make up for this, being subpar has nothing to do with it. heat is a byproduct of current, and will destroy things in a hurry. most obvious is the fact that when the voltage sags under load the three giant caps on the mmm will compensate for the voltage lagging behind the current, when they cant keep up other componets take the brunt of the excess current and fail. dont claim to know it all but believe me when i say i am alive today because i know how electricity works.:mdr:

Excellent, no getting around this info!!!

really just the proverbial tip of the ice burg. didnt even get into transformation, but should be enough to hilight most common charactoristics. on a side note, why spend good money on quality motors and speedos only to skimp on batteries. nevermind quality or price or whatever, but with low amp ratings? your electrical system is only as strong as its weakest componet. in no way am i conciously trying to be rude or anything like that just enjoy electricity and the things it has allowed for me in my life so far. will share what i know about it willingly in hope that it might interest someone as much as it has myself. not to mention the electric r/c car..........

Sheesh guys! lol.

The water analogy works for a very basic understanding of electricity. It works ok for the most part when dealing with DC, but falls apart very quickly with AC. And our ESCs running pulsed DC is effectively AC (no one said AC has to be a sine wave). So, it is very difficult to use the whole water example effectively.

In short, water pressure=voltage, restriction in a hose=resistance, water flow=current. That's about all you can do.

Slim: Actually, if you think about it. Water would "jump" from a cup if enough pressure is present. It would either blast a hole in the bottom (signifying breakdown of the "insulator" which is what happens with HV), or splash out. :wink: