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Old 02-06-2008, 01:00 PM   #421
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Stetler17:

That's a great question. Unfortunately as you'll see below, the answer isn't as straightforward as we'd all like it to be. We have the simple answer, and then we have some complications that need to be factored in to the simple answer.

1) The Simple answer:
For pure horsepower, (expressed as punch on the track, or maintaining voltage under load on the bench) you need to look at the Mah capacity of the pack, and it's C rating.

So with the Core 5000mah pack as an example:
5000mah divided by 1000 = 5 amp hours.
5 amp hours x 20C = 100amps.

So the Core 5000mah pack can deliver a total of 100amps of power.

Using arbitrary #s here, what if there was a 3500mah pack rated at 25C? How would it compare?
3500mah /1000 = 3.5amp hours
3.5 amp hours x 25C = 87.5amps

Your example of a 30C 3000 pack would then be capable of 90amps

So even if it's a higher C rating, it may not be capable of the same actual output as a lower C pack with more Mah of capacity.

2)The complications.
This is where the lipo industry has gotten ugly in the flight side of the hobby, and unfortunately it's fixin' to get ugly here with cars as well.

Firstly lets define "C" rating:
Oh wait - that's right, no one has a standard definition of what that number means! (seriously)

To ME: The C rating means that the pack can output "X" many amps for the duration of it's capacity WITHOUT doing either of two things: 1) dropping below 3.0v/cell, and 2) heating up beyond 140degF (max safe lipo temp).

The C rating comes from the following math, again using the CORE pack as an example:
First, you must actually have and use some serious discharging equipmnet including voltage and current monitoring/reporting along with a temp gun. Hook up the pack, and throw a load on it. The CORE 5000's were reportedly 20C packs, so I conservatively threw 80A at one to see what happened to the voltage and temperature for the first discharge cycle.

5000mah of capacity, so again /1000 to equal 5 amp hours of capacity.
Find the maximum amps you can discharge with (for the whole capacity) without dropping voltage below 3.0v/cell or the pack heating beyond 140degF. In this case we'll use 100A as that figure for round #'s (it was a touch higher in actuality).

5 amp hours divided by 100Amps of discharge capability = 20"C".

Again: that's MY OWN definition of what C rating means. Unfortunately, most packs out there DON'T live up to the ratings given for them, according to my my own definition/testing/determination.



And here's where the problem lies (whoops - did I just say lies?).
1)Not many folks have access to 100A+ discharging equipment.
2)From the simple answer above - if you have the choice between two packs with the same Mah capacity, and one was 20C and the other was 23C, everyone would buy the 23C pack.
3) There's no real testing/performance standard either in the lipo industry, or the hobby industry.

So when you add up all three of the above items, you begin to realize what the consumer is really facing right now. What does 15-20-25-30C really mean???? By what (and who's) definition was the C rating determined? Were packs actually discharge tested? Are the brands just using what the factories tell them the C rating is? (and again - by what standards are the factories using?) Are they just flat making up numbers higher than anyone else's just to sell packs?

When it comes right down to it - If I wasn't restricted by my own morals and professional integrity, I could advertise the CORE pack as 35C and probably sell 10x more than we already are. Think about it - WHO out there is an unbiased party and has discharge equipment capable of 175 amps to prove my claims wrong?

So the moral of the story here is a repeat of what I've already said should be important to the consumer: Do you trust who you are dealing with? Do they have years and years of application and industry experience with the products they're selling? Do they really know everything about it in order to support you with accurate advice and safe usage guidelines? Personally, I think these reasons plus a good dose of honesty are :-)
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Old 02-06-2008, 01:13 PM   #422
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That is a lot more information than I've received anywhere else.

No real surprises as far as C ratings and industry integrity.

It is looking more like cycling the packs and determining an average voltage at 35 amps is going to be my/our only recourse to compare pack A to pack B. Back to NIMH methods I guess. Not knowing how many amps a particular chassis/track/motor configuration can pull will limit the end user from being able to quantify the mah/c ratings. I can only assume that 100 amps , such as your Core 5000, is plenty for our application.

I sincerely thank you for your honesty and willingness to post such information,

Mark
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Old 02-06-2008, 02:27 PM   #423
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Hi Mark,

Looking at voltage for a 35A discharge will give you only a coarse look at the ultimate capability of a range of 5000mah packs. The difference between say 15C and 20C may only be in the hundreths or maybe tenths at most. Between a 20C and 25C, it'll be much lower than that.

As far as motor/ESC capabilities go: Racing ESCs generally top out at around 70-80A continuous capability (continuous amps without thermalling/blowing is the only real way to rate ESCs too, but that's not for this thread ) and the fastest low turn brushless racing motors generally top out at around 50-70A continuous. Now "more" is always better of course, but when you know the upper limits of the other components involved, as long as you've got a good solid REAL 80A+ capability from your pack, you won't be giving up much if anything on the track.

The more toward stock motors you go - the less capability you need to maintain top performance. With the crazy mod stuff the pros throw down on ultra traction carpet, you'll still easily see/feel the punch differences between the very best of the packs available today.

I've been lucky to have positions within the industry where I was expected to learn and know everything about everything and as fast as possible, in order to disseminate it out to the consumers. I feel it's my happy obligation to the community to share, teach, and continue to learn from everyone else. We all spend a lot of money playing with our toy cars, and the more informed everyone is, the stronger our industry will grow, and the more people we'll all have playing alongside us.
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Old 02-06-2008, 05:29 PM   #424
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Quote:
Originally Posted by Shawn Palmer View Post
Hi Mark,


The more toward stock motors you go - the less capability you need to maintain top performance. With the crazy mod stuff the pros throw down on ultra traction carpet, you'll still easily see/feel the punch differences between the very best of the packs available today.

Shawn

I race with Mark, and we have been collectivley gathering info, and track testing lipos. I want to thank you for your honest answers.

You finally answered the main question we had in your last post. We are running on a high traction big dirt oval with crazy mods. ( I just ordered a Speedpassion 4.5, and a 2.5).

Knowing these circumstances, from what you posted earlier, battery A (5000 20C) will outperform battery B ( 4000 20C) because of the constant amps (A =100, B=80). I have that part down.

The other real question is will Batt A (5000, 20C) outperform Batt C (4000 25C) or are they about even because they have the same constant amps (100). (Assuming all rated values are actuals, not made up by the sellers!!!)

Again thank you for your time and knowledge. I know what you are saying about trusting the makers/ assemblers of the pack. As you may know there is another Co on here that is advertising a batt at 20 C, when the cells' manufacturer is only rating that cell at 16C.


Thanks
George
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Old 02-06-2008, 07:27 PM   #425
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Sprint5h:

Your example (20C 5000 vs. 25C 4000) would result in identical performance in theory... in a perfect world. Assuming of course that the "C" ratings are true and accurate and by the same standards.

To add just another lovely nugget to Shawn's post.... not only is there no standard by which cells are tested to determine a C rating, but the data from a test is open to interpretation.

What that means is that you can take the discharge graphs with all the data (volts,amps,mah,temp.... etc) of a particular cell and show it to 3 different companies and might get 3 different C ratings, because it's a judgement call to some degree. It's like watching a slo-mo replay of a catch/fumble/incomplete pass.... no matter what there's always people on all sides.

There's also the issue of what capacity is used as a basis to calculate the C rating. That's where many companies have fudged things to get a high C rating, without just making up #'s. Take a 5000 20C pack for example: If a company decides in it's infinite wisdom to call this pack a 4500 or 4600 pack then it magicly becomes a 22C pack using the same 100A rating. (Or there might be a "5000mah 22C" that REALLY is a 20C)

A combination of some of this stuff shows that you can't really assume ANYTHING based on the label. I bought a couple 3s 3500mah cheapie hong kong packs once to use for TX packs... that were called 15/20C but actually performed at less than 10C to be generous.

Clear as mud....

Last edited by glassdoctor; 02-06-2008 at 07:38 PM.
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Old 02-06-2008, 08:43 PM   #426
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Quote:
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Sprint5h:


Clear as mud....

Thanks for the info. I see what you are saying. I could take a 5000 20C and call it a 4000 25C...Wow I thought these lipos were supposed to put an end to all of the battery stuff....


So, I guess it really has to come down to track testing for my application. The only problem with that is buying 4 or 5 batteries that cost $100 to $150 each. And before anybody posts it I will have a Core as soon as I can...

Thanks for clearing the mud out of the water, at least I can swim now....

Last edited by sprint5h; 02-06-2008 at 08:58 PM.
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Old 02-07-2008, 05:36 PM   #427
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I still would like to see 35 amp discharge numbers on one of the 5000 Core Lipos. Not to compare against other Lipos but to have an idea on how it stacks up against a Nimh 6-cell pack. Anyone?
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Old 02-07-2008, 05:38 PM   #428
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Remembering about the problems with LRP's and Lipo cutoff voltages;
A friend ran two races and some practice with a Lipo and wondered why it was occasionally cutting out, once we got his car back to the pit we measured the Lipo voltage, 5.6V

This was using a Nosram ISTC which is the same as the fancy LRP Sphere TC with the fan.

Don't worry about the Lipo, only a Trakpower

I don't bother with the cutoff settings on my ESC's but then I never do more than one race without putting some charge in.

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Old 02-07-2008, 05:42 PM   #429
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Quote:
Originally Posted by Skiddins View Post
Remembering about the problems with LRP's and Lipo cutoff voltages;
A friend ran two races and some practice with a Lipo and wondered why it was occasionally cutting out, once we got his car back to the pit we measured the Lipo voltage, 5.6V

This was using a Nosram ISTC which is the same as the fancy LRP Sphere TC with the fan.

Don't worry about the Lipo, only a Trakpower

I don't bother with the cutoff settings on my ESC's but then I never do more than one race without putting some charge in.

Skiddins
I just set my radio timer for 5 minutes then i stop when the timer goes off
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Old 02-07-2008, 06:23 PM   #430
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Shawn,
From what I have heard, you guys have already sent packs to ROAR for approval. Do you think they will be approved in time to run them at the ROAR Carpet Nats next month?
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Old 02-08-2008, 08:05 AM   #431
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i need saddle pack lipos, anybody make them???
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Old 02-08-2008, 08:32 AM   #432
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i need saddle pack lipos, anybody make them???
maxamps
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Old 02-08-2008, 08:35 AM   #433
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Sigearhead:
That's the intention yes
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Old 02-08-2008, 09:16 AM   #434
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i need saddle pack lipos, anybody make them???
http://www.trakpower.com/
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Old 02-08-2008, 08:24 PM   #435
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maxamps

tahnks man!!! i found them, and i am gonna buy them!
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