REAL'' BATTERY VOLTAGE NUMBERS !!!!

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There seems to be quite a variance in battery label numbers from different battery matchers and there's really only one way to check your on track battery performance.
First it doesn't matter what your discharging with all your going to do is to form a base line to compare your packs.
A GFX , Integy16x7, 16x8 , Tekin or anything that will discharge at a constant rate of 30 or 35 amps will work fine . "15 - 1157 bulbs "
Charge your pack up as you would normally do on race day and discharge it checking the voltage every 60 sec to the 300 sec mark.

Example


5sec 5.39
60 4.99
120 4.95
180 4.90
240 4.83
300 4.75

These are all at 30amps on a GFX , the average discharge voltage for this pack in a 5 min run [300 sec] was 1.242 volts per cell , which really is the only thing that matters, forget that your pack has 485 sec of run time, on track voltage is key!

Remember this is just a reference and you really can't compare between different dischargers , even the same model , as none of these mentioned are laboratory grade units and do fluctuate.

I've spent alot of time playing with batteries are don't claim to be an expert on this , but if you label your packs this way I think you'll find the better performing ones.

Hope this helps :thumbsup: :wave:

I've had some feedback about people saying their discharge rates are much higher , You have to adjust your discharge amperage to meet your needs and this is just a guide , everyone has diff requirements.
Most racers will still find this quite beneficial.

Thats why there's dischargers on the market that go from 1-40 amps.

NCFRC Why make a broad statement like runtime doesn't matter. Just because in your application it doesn't. As for your method of rating batteries, IMHO your waiting to long between voltages readings to get an acurate gauge of the batteries preformance. And it does matter what type of discharger you use, as it does matter how many amps your pulling from the battery as you take the voltage readings.

NCFRC I did the same thing with my packs the other week. I think you method is just fine. I don't see a need to change it. I think getting number every 30 sec is just over kill or anal retentive. lol

I have to agree with Mike V on this one runtime absolutly matters,even in stock I pay attention to runtime, maybe not quite as important as the mod guys but still important in the overall performance.Remember,the further back in the runtime you stay the better.Lately I've been looking closely at IR #'s as well as voltage,I'm no guru on batteries but IR and voltage seem to have a relationship that makes for some good cells in stock.

Mike is right....

run time is actualy important in all classes of racing...... recently two racers i know had the same voltage cells/packs.. but one had 30 more sec of run time..... they stayed nose to tail for the first 1 min 30 sec of a race then the guy with better run time just started walking of from him.... the longer run time alows in most cases for you to main tain a higher voltage further in the run.

30 sec mesurements are the best i believe byut i know several guys that check every 15 secs... that way they get a even tighter measurement on the votage level thru the cycle.....

Billy

NCFRC,

If you were to plot out your voltage data in excel or any plotting software you would see that runtime on a pack with high runtime and high voltage would/should carry higher discharge voltage longer throughout the pack vs. a pack with just high voltage.

Scott

30 sec mesurements are the best i believe but i know several guys that check every 15 secs... that way they get a even tighter measurement on the votage level thru the cycle.....

Billy

If your Erock, you'll be checking every 5 seconds.............. :tongue:

NCFRC Why make a broad statement like runtime doesn't matter. Just because in your application it doesn't. As for your method of rating batteries, IMHO your waiting to long between voltages readings to get an acurate gauge of the batteries preformance. And it does matter what type of discharger you use, as it does matter how many amps your pulling from the battery as you take the voltage readings.


I dont think you understood his point, He is RIGHT, runtime dosnt really matter if you look at it the way he is talking about, for example

Every round i come of the track with 200-205sec. at 35amps, i know all my packs are 400-410 therefor i use 200-205sec. of runtime this means what ever pack has a higher voltage at 200sec. will out perform another pack with longer runtime but lower voltage at this point.....

but if you run mod then all that matters is runtime,

get packs from good matcher and don't worry about all the bs runtime to me is usually more crucial than voltage in 19t and mod but in stock it don't matter worry about the chassis and driving it will get you farther than the voltage just my .02 cents worth

I'm glad a couple of you understood what I was saying !!!!!!!!!!!!

I realize the whole runtime thing ,but if you discharge at " YOUR " race reqiurement amperage then this works great.

If anyone wants to just be critical then ------------OH well :(


Its always a good thing to try and help a fellow competitor but if they don't want help then thats another issue.

Thanks Davepull and ME21 !!!!!!!!!!!!!!!!!

Happy New Year !

I just look at like this.

i cycled my packs @ 30 amps maping them out @ 60, 120, 180, 240, 300 sec i recorded the voltage at these points. what it showed me was my packs are very close but a couple hold a higher voltage longer. the reason I did it this way is I only have a turbo 30 and before I was running my packs in the order of lowest voltage first highest last. what I found was I was running them some of my stronger packs first (according to this method) of course runtime matters in mod but I also think that if you can get a killer runtime/ voltage/ ir pack and run it in stock it will rip too.

The 180 , 240, 300 sec marks are really the most important as thats where your still going to have good power.
The other thing to note is how many sec's to 4.66 "4 cell " , 7.0 ''6 cell "
Most decent 3800 4 cell packs will go for 360 sec. to 4.66 @ 30a.

Quick trivia -most decent 3700 packs will go for 300 sec to 4.66 , now thats quite a voltage drop.

That's why now a days 3700's are becoming good for scrubbing tires in practice. Just make sure they don't false peak....... :eek:

Every 30 sec's is probably a little more accurate as most popular dischargers check every 5 sec's. 11 #'s vs. only 6

Some manufacture's are building av. voltage cutoff adjustible points into their next model so this will all be figured for you in the near future.

Unless you race in the top level classes at your track this is probably unnessesary information !-------unless you enjoy electrical knowledge as a hobby. :wave:

i have seen packs that cycle way less go fast so if you just need to know this to build confiedence i had a 3300 pack that was 4.60 at 35 go just as fast as a 3800 that cycled 4.80 at 35 use the track for test rusults just my opinion chassis is where it is i give people that are running with me my best motors and batteries week after week and beat them with chassis this is useful info to know when trying to keep track of batteries that have fell off though

I do agree 100% ------ The race is won in the corners ! PERIOD

If you don't have a car that drives good no battery or motor is going to make you win.

Todays IB-3800's are all extremely good cells and most racers should focus on other aspects of their racing.

The last batch of 3800's I checked " DISCHARGED " at over 4015 MAH at 35amps to .90 !!!! They're all good.

I only test my packs before the start of a race season and thats usually only to compare to the #'s 20 cycles ago.

Unfortuately the 3700's are falling into the practice trays these days.
Any good matched 3800 from a reputable supplier should be fine.
Follow their maintainance instructions !!!!

I CHANGED MY TEST PERAMETERS TO EVERY 30 SEC @ 35 AMPS TO THE 300 SEC MARK. as we race 4 min carpet oval and that should be close for what we're doing.

My worst 3800 is an av. of 1.212 for 300 and my best is 1.220 for 300 sec.

Is .008 volts really worth this ??? ITS UP TO YOU :)

For the record... bulb dischargers (or any other resitive based discharger) are NOT constant current... and is nearly worthless for checking battery capacitys and/or numbers. Just to be sure your really discharging at a constant current, you should also be reading the discharge current... If your discharger isn't capable of showing the discharge rate real time... it's not worth much in my opinion.

For the record... bulb dischargers (or any other resitive based discharger) are NOT constant current... and is nearly worthless for checking battery capacitys and/or numbers.

I personally would have to disagree with this. A resistive discharge would actually better mimic a battery discharge in actual use. Remember that a motor is actually a resistive discharge device so the higher the voltage the higher amp rate it will discharge at.

Just as a 6-cell pack will discharge faster then a 4-cell pack when running on the track there is no reason not to try and duplicate that same when testing cells.

The problem with a resistive discharger is... that the higher the voltage the cell has, the higher the discharge rate will be... In the end if you try and compare numbers of cells that have significantly differnt voltage, it will not be like comparing apples to apples... Resistive dicharger may mimic a motor better, but it also adds another variable, which is not generaly a good thing when trying to evaluate something...

It's sort of the same argument you could have about the 'advantage' the CS dyno had because it uses a real battery insted of a power supply, etc... at some level this seems to make sense... but it's still adding another variable into the 'test' and can pretty easily make the data invalid, or misleading.

he problem with a resistive discharger is... that the higher the voltage the cell has, the higher the discharge rate will be
And that is the exactly the way it should be! Just like the way IR is currently calculated... at 1 amp draw at one single point in the discharge. This is some ISO standard that was dreamed up 30 years ago. As RC racers we could give a hoot what the IR is at 1 amp 60 seconds into the discharge. We want to know what it is at 30 amps or more and throughout the full discharge curve.

Resistive discharge is adding the same varible that is used with real world performance. Let's take this exteme example.... it's extreme just to make it clearer but it the same in the real world just in smaller doses.

Say we have two batteries tested in the "normal" method. Both cells have the same run time but one cell averages 1.0 volts and the other 1.2 volts. On the track the battery with 1.0 volts dumps right at the 5 minute mark.

Now if you put in the battery with the 1.2 volts, accourding to the run time on the label, it should also get you 5 minutes of run time. But on the track it will not because the higher voltage causes the motor to pull more amps. According to the "labels" it should have! How can this not be misleading?

With a resistive discharge you would not only have average voltage, you would have average amp draw. This could give you an idea of how much the cell would affect real world on the track performance of you motor.

Fact is a resistive discharger is very linear. Their really is no extra varible added. Surprisingly, bulbs are fairly constant but I will agree that high quality resistors would be better. The main problem with bulbs is that over time the resistance can increase... but this change is very small and so slow to charge that I have found it has little to no affect on the output unless you try to compare numbers that were taken years apart.

There are a number of things wrong with the way cells are presently matched but the current method is the "standard". If someone pushes for a change everyone thinks they are trying to pull something over on the consumer. We also have the matcher not wanting to change because of the expense involved in new equipment and the extra labor and material it take to provide the information racers really need to figure out what really is a good cell.

I personally would have to disagree with this. A resistive discharge would actually better mimic a battery discharge in actual use. Remember that a motor is actually a resistive discharge device so the higher the voltage the higher amp rate it will discharge at.

Just as a 6-cell pack will discharge faster then a 4-cell pack when running on the track there is no reason not to try and duplicate that same when testing cells.

Hank You hit the nail on the head. I have told guys this for years.

there is one company starting to do things differently. axxis racing isacc appears to be going in another direction with the Ib cells. http://www.axxis-racing.com/
i had no idea why one brand had more voltage and another more run time. he schooled me up on cell construction. cool stuff

We see a number of matchers touting "recovery time" and this may be one of the most important factors in accelleration.

If some remember my old Battery Data Center from a few years ago know I came up with a number of tests that go beyond "normal" battery matching. Two of these tests I called the Power Factor and the Oval Test.

With the Power Factor we record the voltage during the heavy load and record the recovery voltage and the amount of time it took the pack to completely recover from the heavy load.

In Oval Test at the 100 second mark we applied an approx. 55 amps load for 2 seconds, dropped back to 20 amps for 2 seconds and repeated this for 4 cycles (don't forget I was doing this 7+ years ago). This shows how fast a cell could recover and what repeated high loads did to the cell.

BTW, I am in the process of rebuilding my Battery Data Center test rig and will have complete data on all of the new cells over the next couple months.

Hank,
I have been using my computer to monitor the data from my GFX via the RS 232 port. I noticed that the dicharge cycle is always interupted at 121, 122, and 123 seconds. I assume is during this time it is doing the IR measurement. Using the data port on the GFX tells a lot. It's an interesting tool. The graphs that you can generate in Excel allow you to overlay all your batteries data to compare them and also compare various charging methods.
Rick<><

Yes , the GFX checks IR at 120 sec point.

I THOUGHT WE ALL AGREED NOT TO OVER THINK THIS , FORM YOUR OWN TEST PERAMETERS AND JUST USE IT AS A BASE LINE COMPARISON

Well if Hank is correct... then we all should sell our CE Turbo35s and GFXs... (while they're still worth something).

Now I don't totaly disagree with Hank's arguments... but I'm also not entirely convinced resistive load is better then some constant amp load. It's a interesting debate about which is theorecticly better.

To me, the biggest disadvantage of the resistive load is... the numbers you'd get would be all over the map when you tested differnt cells (ones with significantly varying voltages, etc...). Maybe over time racers could come to understand the numbers you'd get, but at a very minimum, early on, it would be very confusing. Even in the long run, I'm not sure the numbers would make much sense to most people.

I guess there's always room for more then one way to evaluate a battery, but I think at a very minimum, both resistive and constant current testing would tell you more then either one would by itself.

You can't say or prove which is better , but industry standard is a constant load setting that stays the same as the voltage drops so lets just leave it at that.
Todays cells have terrific voltage for 300+ sec's as this thread started off with and the voltage drop isn't that big a deal.

I won't get into all the numbers ,but the last 3800's i cycled up and checked every 30 sec ''first point 5 sec." to the 300 sec. mark on GFX at 35 amps averaged out to 1.217 -1.218 av. voltage.

Rodney S.

A resistive discharger may be slightly closer to real track simulation from a technical standpoint but it really doesn't matter which you use just as long as your test perameters never change.

JUST USE WHATS MOST FEASIBLE FOR YOU ,DON'T GO CHANGE YOUR EQUIPMENT JUST TO BE TECHNICALLY CORRECT !

NONE OF THIS IS LABORATORY STANDARD , SO CLOSE HAS TO BE GOOD ENOUGH.

THANKS FOR READING THIS THREAD :thumbsup: :wave:

Rodney S.