MGM article on voltage under braking & lipo quality

[othello]

The eagletree micropower logger does record positive amps (not negative) with an increase in battery voltage while braking.



Latest log recorded yesterday with 8s2p A123 while making speed passes. Notice the amp spikes (20-25A) while the green rpm curve is falling. I never recorded amp spikes as high as described in that article.

Basicly they say use an 8s ESC when running with 6s lipo and keep resistance as low as possible (connectors, batterys, cables ...) to minimize voltage spikes while braking.

[BrianG]

Does the ET truly not log negative current, or does it just not show it because the graph starts at "0"? Could someone set the min value of the graph at some value and see? I could do it, but I'm at work :shhhh:

[zeropointbug]

Interesting there, I have never seen a positive voltage rise after braking, but then again I do not brake that often, and I do not pound on the brakes, I'm quite easy on them.

Don't forget adding caps to the ESC, I am not sure how many you would need to reduce these voltage increases to a decent level, but probably you can't have enough... you would need something of capacity with very low esr.

I will do some tests sometime soon with my Revo under hard braking and the eagletree, see what we get for comparison.

[othello]

I found a better graph i posted some time ago (while i was running 10s1p A123) where i pointed out braking Amps and the corresponding rise in voltage. The green curve depicts motor rpm.



@BrianG
When opening the eagletree logfile with excel you won't notice any negative value. There is no way you can differentiate between amps flowing to the motor and amps flowing to the battery when using an eagletree logger (other then looking at the voltage).

@zeropointbug
The Kontronik Jazz 55-10-32 ESC is rated up to 43V (10s lipo). With 8s A123 (25V average) i'm well below it's rated max voltage leaving enough headroom for braking voltage spikes. Even with 11s A123 (36v average) i do not have issues while braking with the ESC. I too tend to run my ESCs below their rated max specs to avoid premature failing.

[zeropointbug]

Yah, I have ran 7s1p and 2p packs for 2 years now through my Quark with no issues... and when I got my G3 lipo packs, it started to cog alot, and do weird shutdown hiccups. This is an ESC that should never have even been designed for 6s lipo, according to alot of ppl on this board, including myself.

After I did the modifications to the esc, it has never ran so good, and I mean awesome. We will see how it holds up in the years to come....

[florianz]

good find; but honestly, what I can't understand is that these expensive esc's are not free of trouble. I have one of these cheapo-plane esc's, modded with some bigger caps. never cogged, no matter how bad the abuse is, it works.
so when I see people spending 200,- for just a controller, which burns after 2 weeks, I wonder if that stuff is worth the money...

they say, expensive must be betta!!! sure??

Myself, I don't care as I could not spend that money for the controller...

[TexasSP]

I think part of the deal with MGM is that each controller they make hardware wise is generic across the board and the programming is what makes it car, boat, or plane. Whereas CC and others make specific controllers for specific uses. I believe it's silly to do it this way. They might as well just down rate the controllers when being used for cars versus planes etc. One thing I did with my MGM though is run an external bec. The firmware and interface still left a lot to be desired, and it heated up quite a bit more/quicker than my MMM. It was a solid controller though although I do not feel it was worth the extra money for me.

[BrianG]

That's interesting because most of the reports I've seen say that MGM actually heat up less. On second thought, I don't see why it would be either way, most ESCs use similar, if not the same, FETs. And heat comes from the rdson value and slew rate of the FETs. I'm sure some comes from copper losses too, but again, they are all built basically the same way. Curious.

[zeropointbug]

Yah hehe, built in a similar fashion, but rated completely different I know! Example:

MM vs. the Quark controller

They use the very same FET's yet CC was wise enough, and not cheap to rate it at 3s lipo and 100 amps... Quark was TWICE cells rating and 25% higher current rating, and we all know that when both controllers are run on 4s lipo and same setup, they run pretty much the same temp, if not, the MM being cooler. And yes, the Quark has some higher voltage caps (a dollar extra cost IF that), so why does one controller cost twice as much as the next one? With the same, if not worse build quality, same core components, etc....

But, I can't complain too much, as my Quark is working wonderfully on 6s now.

[snellemin]

Quark is super smooth, compared to the MM back when it first came out. Quark has a nice metal case, compared to the plastic case of the MM. Quark fet board is heatsinked on both sides, whereas the MM only on one side. I personally liked my Qaurk 80B in speedruns over the MM. But I just recently blew the Quark up with some overvoltage. But when it comes to power, Luciano's 1/10 ESC is mini monster compared the MM and Quark when it came to power capability.

I have some 10S A123 datalogs that shows the voltage rise during braking as well. It's harder to see in my lower voltage setups.

[zeropointbug]

I don't think some poopy heat pad/spreaders on each side is good... the top FET's are not heatsinked, only heat spreaders to absorb the peaks in heat output from the FET's.

[Sammus]

Originally Posted by florianz

good find; but honestly, what I can't understand is that these expensive esc's are not free of trouble. I have one of these cheapo-plane esc's, modded with some bigger caps. never cogged, no matter how bad the abuse is, it works.
so when I see people spending 200,- for just a controller, which burns after 2 weeks, I wonder if that stuff is worth the money...

they say, expensive must be betta!!! sure??

Myself, I don't care as I could not spend that money for the controller...

hey if you cant tell the difference good for you. I tried a million different cheapo chinese air escs before buying a monster. I can't stand the motor startup algorithm used in air escs. it's optimised for a propellor driven vehicle and isn't made to stop and start like cars often do *shudders* ill never go near another air esc.

[zeropointbug]

air esc in a surface R/C = crap

[Sammus]

Originally Posted by zeropointbug

air esc in a surface R/C = crap

a more concise version of the point I was making above

With the right software, why wouldn't an air-esc be just as good as any other car esc?