Ways to protect MMM when used with subpar batts

[himalaya]

Originally Posted by shaunjohnson

what is a GOOD low resistance?
i'm gonna test the resistance of my turnigy today

I follow my equation to make the judge:

IR ≤ 370*S/(Ah*C)， mΩ， @23℃

This equation is just my personal summarization, none official. It came from my observation to many LiPo discharge curves officially published by manufacturers as well as third party test guys. I found at the middle of discharge process all decent LiPo cells drop their voltage to around 3.4V/cell under full C-rating discharge current, that is roughly 370mV voltage drop, 10% of LiPo norminal voltage, S is the number of serial cells in a pack, Ah is the norminal capacity, C is the rated maximum discharge rate.

Note temperaure plays HUGE role in IR performance, IR can be doubled when temperature drops 20+ degrees. That is one of the reasons why there are more LiPo puff complains in winter.

I wrote a short article on this:
http://bbs.rcfans.com/viewthread.php?tid=236520
Sorry it was written in Chinese, but the graphs and simple calculation process will make some sense.

[suicideneil]

Originally Posted by Bernie Wolfard

El Cheapo,

You are correct. If you lower the system voltage with everything else the same the max RPM of the motor is lower (Kv * voltage). It will spin up less aggressively when pulling the trigger and have an overall lower amp draw meaning less heat, more run time less stress on the whole system etc. You only get into trouble if you try to match the speed of a higher voltage system with a lowering one by lowering the gear ratio. Bernie

Part in bold is what had me thrown, in relation to the wording of the original question.

Some idiot in RCU is claming that subpar batteries don't kill ESC, some other force of nature does. It should be the lipos that should be exploding and smoking. WTF is this crap? Now I dunno what to think

http://www.rcuniverse.com/forum/m_10...m.htm#10025185

[suicideneil]

You're doing it again man, you're getting drawn into arguments with trolls ( theydontwantmusic is a seriously A-class troll & hater ) and haters and letting yourself get confused. The subject of batts killing escs has been covered extensively- sub-par batts will kill escs due to ripple current. If the esc doesnt go pop, the batts certainly will though, as that old guy found out...

Since the thread is up and going again I thought that I would mention that I also run Turnigy and Zippy lipos. I also used to have some Rhino batts when I had my heli but have since sold them.

Anyway they perform better than their price would indicate. No real issues other then the last Turnigy 5000 40C packs I bought. In one of the 3S packs one of the cells lagged behind on the initial charge and it was taking my charger ages to bring it up. Being impatient I made an adapter and just charged that one cell @ 1A till it came up to 4.2V. Since I have put about 20 cycles on that particular pack and cells have always stayed within .01-.02 volts of each other. I don't know whay the initial charge was being so difficult but it hasn't happened since and that was the only Turnigy/Zippy batt that did that on me.

What does piss me off about these batteries is their discharge wires. 8awg wire is just overkill IMO. If I needed them then my ESC would have came with them too. Also the way the wires come out form the pack on the side is a bit of a pain for my application (Revo). What I did is stripped the packs and removed the 8awg wires. I replaced them with 10awg wires and also bent the end of the wire at a 90 degree angle so the wires will come out from the top. Fits much better into my Revo now. Also I replaced the pissy heat shrink they come with with much thicker heat shrink. They are half way to hard case now. LOL.

Anyway for me they do the job just fine. My truck can do standing backflips on Zippy 4S 5800 30C set up and is just stupid fast on Turnigy 6S 5000 40C setup. Batts are cool. Pretty much ambient temp unless I do continuous speed runs or drive through grass and even then they just get warm. My MMM stays pretty cool too (as do my other ESCs: HW and Quark). When I am bashing in the yard the fan hardly comes on (I wired a little LED so I can see when the fan is running). About the only thing that gets warm is my motor and even that is within Castles recommendations.

I think that Zippy/Turnigy are great cells but their assembly could be better. For someone who knows what they are doing with their batts and exactly what they are asking from them you should be just fine. I will keep using them.