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Old 08-24-2013, 12:35 AM   #31
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Back to the topic of discharge rate. There's really no reason to discharge at 35 amps, this is old school when brushed motors that pulled more current where being used for stock racing and batteries varied way more than they do today.

If i remember correctly when using my Novak data logger peak current draw (on throttle coming out of a corner) is around 20-25 amps for a 17.5 brushless motor. You can't really count from a dead stop, which would draw the most current, as this condition only occurs once.

Attached are 2 graphs showing discharge curves at various currents. You can see the curves from low to high current are very similar with the only difference being a voltage shift. It appears the voltage delta difference from 10-20-30 amps is linear so one could extrapolate a voltage level for a 30 or 40 amp discharge from a 20 amp curve if they wanted. But the whole idea of doing this testing is to see which battery has the flattest discharge curve to 360 sec, which a 20 amp discharge definitely shows.

So i think your 20 amp testing is very relevant.

Here's and interesting site that talks about batteries for those that are interested.
http://batteryuniversity.com/learn/a...charge_methods
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Benchmarking the Best 2S Lipos-2008.9.6_13.39.34_5817.jpg   Benchmarking the Best 2S Lipos-tp-extreme-5000-discharge-curve-graph.gif  
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Old 08-24-2013, 08:05 AM   #32
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Originally Posted by bkspeedo View Post
Back to the topic of discharge rate. There's really no reason to discharge at 35 amps, this is old school when brushed motors that pulled more current where being used for stock racing and batteries varied way more than they do today.

If i remember correctly when using my Novak data logger peak current draw (on throttle coming out of a corner) is around 20-25 amps for a 17.5 brushless motor. You can't really count from a dead stop, which would draw the most current, as this condition only occurs once.

Attached are 2 graphs showing discharge curves at various currents. You can see the curves from low to high current are very similar with the only difference being a voltage shift. It appears the voltage delta difference from 10-20-30 amps is linear so one could extrapolate a voltage level for a 30 or 40 amp discharge from a 20 amp curve if they wanted. But the whole idea of doing this testing is to see which battery has the flattest discharge curve to 360 sec, which a 20 amp discharge definitely shows.

So i think your 20 amp testing is very relevant.

Here's and interesting site that talks about batteries for those that are interested.
http://batteryuniversity.com/learn/a...charge_methods
NOT TRUE.

First, VOLTAGE is SPEED.

NOT all batteries discharge voltage is LINEAR from pack to pack.
If that was the case there would be no need for this topic.

Best packs will keep the voltage HIGH throughout the discharge curve.
Cheaper lipos will drop there voltage faster.

25 amps maybe for blinking class (no boost) but in a boosted class your amp draw would be alot higher.

Maybe in a perfect world....
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Old 08-24-2013, 08:22 AM   #33
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if i had a device that would discharge at greater than 35a, and provide the great features/ease of use like the GFX i would do that instead!
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Old 08-24-2013, 08:39 AM   #34
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if i had a device that would discharge at greater than 35a, and provide the great features/ease of use like the GFX i would do that instead!
+1

Icharger duo
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Old 08-24-2013, 09:45 AM   #35
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Anyone tested the Orion Carbon range of batteries?
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Old 08-24-2013, 10:09 AM   #36
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I understand the voltage is speed.

Unless i'm completely blind the discharge curves i attached to my post show the curves for a low amp draw to high are basically the same. So yes every battery is going to be different but your not going to see much of a difference between 20 amp and 40 amp curves for each individual battery.

My meaning is if you discharge 20 different batteries at 20 amps and the same batteries at 40 amps and overlay the curves, with about 95% certain-tee you'll see the same delta in voltage shift for each individual battery. If you where to remove the delta voltage difference for the 20 and 40 amp curves by the same amount for all, each batteries curve would be with a few percent.

This is all theory but unless someone can show otherwise i personally don't see the need to discharge a battery at 40 amps to show the performance difference between batteries.

In the US NO ONE races with timing any more.
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Old 08-24-2013, 01:53 PM   #37
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I understand the voltage is speed.

My meaning is if you discharge 20 different batteries at 20 amps and the same batteries at 40 amps and overlay the curves, with about 95% certain-tee you'll see the same delta in voltage shift for each individual battery. If you where to remove the delta voltage difference for the 20 and 40 amp curves by the same amount for all, each batteries curve would be with a few percent.

In the US NO ONE races with timing any more.
Thanks for your comments bkspeedo,

I tend to agree with this, to a degree.

I've seen this in my own testing where the discharge curve for each pack is shifted, but the shape remains the same, at 20A, 10A, & 5A rates. In other words, you could predict with a high degree of accuracy how the pack will perform at lower currents if you had the 20A numbers.

That said, I personally haven't had the chance to discharge beyond 20A since I don't have the right equipment just yet, so I'm not willing to guarantee the same would hold true once we put more load on each pack (i.e. 35A or 40A).

Either way, i'd love the chance to try it.

I don't know about the rest of the nation, but locally for me, all classes are blinky except for a handful. At my home track, our expert sedan class is super stock 13.5.
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Old 08-25-2013, 09:34 AM   #38
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Thanks for your comments bkspeedo,

I tend to agree with this, to a degree.

I've seen this in my own testing where the discharge curve for each pack is shifted, but the shape remains the same, at 20A, 10A, & 5A rates. In other words, you could predict with a high degree of accuracy how the pack will perform at lower currents if you had the 20A numbers.

That said, I personally haven't had the chance to discharge beyond 20A since I don't have the right equipment just yet, so I'm not willing to guarantee the same would hold true once we put more load on each pack (i.e. 35A or 40A).

Either way, i'd love the chance to try it.

I don't know about the rest of the nation, but locally for me, all classes are blinky except for a handful. At my home track, our expert sedan class is super stock 13.5.
Bkspeedo - I don't want you to think that I was attacking you and the information you posted. If you though so I apologize.

I understand the voltage discharge curves may hold true for low discharging, but I find at a higher discharge curve 40-45 amps or more in the cheaper lipos to fade fast as IR increases rapidly.
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Old 08-25-2013, 06:02 PM   #39
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Bkspeedo - I don't want you to think that I was attacking you and the information you posted. If you though so I apologize.

I understand the voltage discharge curves may hold true for low discharging, but I find at a higher discharge curve 40-45 amps or more in the cheaper lipos to fade fast as IR increases rapidly.
No offence taken, just rebutting in our discussion. This is the fun part of RCtech, hearing everyone's opinions and deciding if it could be true.

I know people out there, especially the oval crowed have done this kind of testing I just wish more people posted there findings.

I have an iCharger 306B that I've never used to discharge a battery. I'll give it shot this week and post some test results for very well used RevTech and OHP packs against some brand new IP 7600 i just bought.

I've only run 1 of the 4 i bought but I will say these things hold there voltage. My OHP's after a 5min 13.5 blinky TC run come of with a voltage level of 7.75, This IP is sitting at about 7.95 for the same run. To be fair my current OHP's probably have 300+ runs on them. There Ir's are around 0.003 ohms and IP is around 0.001.

What kind of load works best for discharging, power resistors or light bulb tree?
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Old 08-25-2013, 07:36 PM   #40
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+1

Icharger duo
The duo is interesting, but I don't think the discharge is as good as the gfx.
The duo is the only charger I bring to the track..
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Old 08-25-2013, 09:37 PM   #41
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No offence taken, just rebutting in our discussion. This is the fun part of RCtech, hearing everyone's opinions and deciding if it could be true.

I know people out there, especially the oval crowed have done this kind of testing I just wish more people posted there findings.

I have an iCharger 306B that I've never used to discharge a battery. I'll give it shot this week and post some test results for very well used RevTech and OHP packs against some brand new IP 7600 i just bought.

I've only run 1 of the 4 i bought but I will say these things hold there voltage. My OHP's after a 5min 13.5 blinky TC run come of with a voltage level of 7.75, This IP is sitting at about 7.95 for the same run. To be fair my current OHP's probably have 300+ runs on them. There Ir's are around 0.003 ohms and IP is around 0.001.

What kind of load works best for discharging, power resistors or light bulb tree?
Absolutely, it's great to see more info.

For regenerative discharge mode, I use resistors or a car battery. If you plan to use resistors, just remember it'll still get VERY hot, so proper cooling is needed.

On your 306B, it'll go up to 30A discharge.
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Old 08-25-2013, 09:39 PM   #42
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The duo is interesting, but I don't think the discharge is as good as the gfx.
The duo is the only charger I bring to the track..
Man, all you guys have better equipment to do these tests than i do. I need to upgrade.

Icharger Duo (4010) does up to 40A discharge. GFX iirc, only goes up to 35A.
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Old 08-25-2013, 10:50 PM   #43
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All this equipment won't Work better than a good old track test/laptimes, etc....
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Old 09-24-2013, 06:44 PM   #44
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I just found this thread and must admit, independant testing is great!

However, the charts are getting quite crowded and is not really an accurate comparison of batteries.

Is there any chance you could re-plot the data to show the voltage v mah drawn, or even better: % capacity (on a mah basis). A voltage v mah drawn through to dead would also be great. I think here also, tabulated data would be really nice instead of charts.

What you're doing then is comparing apples v apples. At the moment, on a time scale of course the higher capacity batteries are going to test 'better' than lower capacity batteries, but that is not really accurate. voltage v % mah would be the most representative test.

Adding a column to the first table with 'measure mah' next to 'stated mah' would also be very handy - work out who is lying the most!

You already have all of this data, it's just a matter of presenting them in a differant format.
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Old 09-27-2013, 07:51 AM   #45
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