Savage Flux Eagle Tree Data

[fastbaja5b]

Just need some opinions on this:

I only had ONE pack hooked up to the logger



Note the drop to 6.42 volts on a 119 Amp spike. Is this too much of a drop?

Pack is a Harris RC 5000mah 30C Lipo from this site:

http://www.harrisrc.com/lipo1.htm

[MetalMan]

119amps on a 5000mah pack is 23.8C, so if the cells dropped to 3.21v on that burst then yes, that is too much of a drop considering a 30C rating. But you also have to factor in losses due to wiring and the accuracy of the logger's shunt (current measuring device). Can you find out the voltage and current on the next largest current spike? That way we can verify the results.

[fastbaja5b]

Considering I am using a 100 Amp Eagletree logger, I suspect there are some inaccuracies as the voltages are recorded at Amps outside the ideal range.

That said, my other Harris pack got to 6.38 in similar conditions, and a Reedy 20C 7.4V 5000mah hardcase Lipo got to 5.89 on a brief drop, so that to me reinforces the assertion that you need a battery rated for at least 125A in the Flux (given a high amp spike of 119)

I put the same Reedy battery straight into my Slash VXL (no top up charge) and got a voltage drop to 6.89 volts under a 79 Amp Load there.

It's not a perfect measurement, I'm sure the eagletree's use of fake deans doesn't help, wire lengths etc etc but it's all learning.

If anyone wants a copy of the log files just drop me a PM, happy to share!

[J57ltr]

I don't see any problems with your data, the more amps you pull the more the voltage drops. That's a lot of amps and there is no way that the voltage is going to stay at the same level. I see a 4S A123 pack drop to 6 volts @ 175 amps. Heck even on my 60 amp power supply I test amplifiers with drop voltage in short bursts 2-3 volts @ 35 amps or so, that's just the way it is. A goes up V goes down. Is it going to hurt your batteries? You haven't exceeded the 30C of the battery so I would doubt it. Your run just looks like you were just doing a few high speed runs. I don't think your eagle tree is an issue at all. I have strapped my Fluke meter set to record and gotton the same voltage values as my eagletree, and they both have about the same sample rate 100ms.

Jeff

[zeropointbug]

I wouldn't say 3.2v/cell at ~24C is fine, especially considering the rated 30C. They are obviously over rated, or my new Hyperion G3 packs are underrated, because I get 3.7v/cell at ~22C discharge, they are rated for 35C/65C.

[Mentat]

I was kinda wondering about what you guys are talking about here, instead of starting a post (some people seem to think that is a bad thing) I thought i would hijack this one. What is considered to much of a drop on a 4s1p 5000mah 25c pack? What is considered to much of a drop in a 4s1p 5000mah 20c pack? Running CC Mamba Monster 2200kv combo. The packs in reference never get over 95f and the motor has never hit 140f

[Mentat]

Originally Posted by zeropointbug

I wouldn't say 3.2v/cell at ~24C is fine, especially considering the rated 30C. They are obviously over rated, or my new Hyperion G3 packs are underrated, because I get 3.7v/cell at ~22C discharge, they are rated for 35C/65C.

How do you figure the true Discharge ratings? I wanted to see what my Zippy packs are doing and these Turnigy packs

[J57ltr]

Originally Posted by zeropointbug

I wouldn't say 3.2v/cell at ~24C is fine, especially considering the rated 30C. They are obviously over rated, or my new Hyperion G3 packs are underrated, because I get 3.7v/cell at ~22C discharge, they are rated for 35C/65C.

I'm kind of new to this stuff, but isn't the C (or Capacity) rating just the amount of current the pack can sustain without damage. To me it has nothing to do with how well the voltage is going to hold, rather how much current it will put out without damage. I have seen some voltage/current charts for some batteries but I haven't seen them listed for 30C and 60C rates.

The ones I have dropped quite a bit. I agree about some over rating and some underrating, but there may be some differences about what is over/ underrating. One engineer may say that at full discharge the cell must not drop past “x” value, another may specify a different value. This industry is fairly new so very few standards have been developed.

Jeff

[suicideneil]

Aye.

For comparsions sake, manufacturers should state the C rating at a specific voltage, then use that as the standard figure. 3.2v per cell is a nice number given its what most people tend to set their lvcs for these days, although the C rating at a few different voltages would be handy too (3.0v, 3.6v etc).

[zeropointbug]

Yes, manufacturers don't state the voltage drop at their rated C specs... this, like BrianG said in a post week ago or so, is the game manufacturers play on us. But there are a few companies that actually give you discharge charts that are true, such as Flightpower.

Neil, I think two voltages would be sufficient for rating a pack, such as 3.2v and 3.7v for example like you said.

Like this:

-Max safe continuous C discharge with a 'standard airflow'
-C rating @ 3.7/cell average discharge (over the discharge curve)
-C rating @ 3.2/cell average.....
-and a MAX safe burst current, which is already stated IMO


There is such discrepancies between C rating from brand to brand, because each one has a different safe operating temperature, which is what it comes down to in the end. But for heat dissipation, it's not just about voltage drop, the Coulomb efficiency matters as well, which is when you increase the discharge currents you decrease the discharged capacity of the cell (mah capacity).... this turns into heat as well, IIRC. Now each brand cell is different this way, some will loose more than others. I believe this to be true because I know that A123 cells don't seem to heat up as much as they should compared to lipo, given their voltage drop under load... this is because they are the most efficient battery on the market I have seen when it comes to Coulomb efficiency.

Basically, it is impossible to tell you what the typical voltage drop is for a given rated cell.... because there are no STANDARDS!!!