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mikerenz66
08-11-2005, 01:35 AM
I would like to know how many ohms are lipos- if most major brands are same, alittle different?? I like to use Thunder Power lipos. 3S 2000mah or above.

TIA

Mike

Matt Kirsch
08-12-2005, 01:29 PM
You can get an idea of the relative internal resistances of cells by their C ratings. A cell with a higher C rating has a lower internal resistance.

In that case, current-generation Thunder Powers are about average, middle-of-the-road.

Exact internal resistances should be available from the manufacturer. Truthfully, most people aren't concerned with that value.

GeraldRosebery
08-12-2005, 10:19 PM
Your question is a curious one. What do you really need to know? Are Thunder power OK or is there a "better" brand?

mikerenz66
08-12-2005, 11:11 PM
Your question is a curious one. What do you really need to know? Are Thunder power OK or is there a "better" brand?


In most software for motor calculations they require input for ohms. Just not sure what the ohms are for a pack since its not listed on the label.

Mike R

GeraldRosebery
08-13-2005, 01:07 AM
Are you sure they are not asking for motor resistance? That is usually published with the motor. Pack resistance is almost never available.

mikerenz66
08-13-2005, 02:41 AM
Are you sure they are not asking for motor resistance? That is usually published with the motor. Pack resistance is almost never available.


www.andersonparkflyers.org (http://www.andersonparkflyers.org) I use there free motor calac program. The top entry is for the pack. If you select custom instead of off the list of what they have, you need to enter something for ohms. I am sure this has a bit of affect on the rest of the calaculations. I entered different values in ohms and came up with different numbers for amps/ volts / watts.

Is there a way to test for it??? Multimeter??? I use one to check my lipos... volt wise. I tried ohms, but it never measured it on my meter.

Mike R

nate1001
10-06-2005, 11:21 PM
I bought a duratrax ice charger and that tells you the resistance during discharge as long as the voltage is above a certain amount. I have a 3 cell 1320 thunder power I'll try and tell you the resistance.

Fred Marks
10-07-2005, 02:21 AM
I would like to know how many ohms are lipos- if most major brands are same, alittle different?? I like to use Thunder Power lipos. 3S 2000mah or above.

TIA

Mike

Mike,
If you purchase Kokam cells from FMA Direct or one of our distributors or dealers, you will know exactly what the internal resistance is because e we tell you in the attached that has been posted several times in the forums and will appear permanently in the FMA Direct Li Po Tech Compendium on our FMA web site. The KOK 3200, e.g., has an internal resistance of a bit over 3 milliohms depending on SOC where the competing cell mentioned is about 16 milliohms depending on which cell you receive and those are variable. Please look over the following to see in Section II, the impact of Internal resistance on temperature and voltage depression.

(https://www.fmadirect.com/site/fma.htm?body=rc_appNotes)

hoppy
10-07-2005, 02:59 AM
I would like to know how many ohms are lipos- if most major brands are same, alittle different?? I like to use Thunder Power lipos. 3S 2000mah or above.

TIA

Mike

Mike,
From what I've read, it is not a simple thing to define. Here is a post from a professional cell tester on the subject of measuring cell resistance.
http://www.rcgroups.com/forums/showpost.php?p=4303911&postcount=287

Fred Marks
10-07-2005, 03:24 AM
In order to have any "apples and apples" comparisons, all bateries are tested per international standards, not to some variable scheme that is not standardized. The accuracy that you get in the precise application you use a pack in is compromised to some unknown degree by the fact that the operating point may vary quite a bit from the actual operating point. however, that variation will be pretty consistent as it applies to both cells. The measurements for the Kokam cells are done to the internatiional standards because far more cells are marketed to OEM users that have operating points close to the standard mesurement. When measurements are made that do not comply with theinternational standard, it is far too easy for resuts to be bent to fit a situation that makes one pack or another look better. It is also important to note that the liklihood of locating any internal resistance data for other vendors is slim.

In that case, then the most appropriate measure of the effects of internal resistance shows up in the voltage depression that occurs with increasing current and the cell temprature incurred by the multiple of internal resistance times amps squared that is reflected in the data attached.

Independent testing is now underway that will be reported in the next few days that should tackle the isssue of measurement of IR at heavier loads.

nate1001
10-08-2005, 04:14 AM
The internal resistance of my 3 cell 1320 mah thunder power battery is 171 milliohms. This is at 2c or 2.6 amps. Thats the highest it dishcharges lithiums. I'll have to use nicd or nihm to get a resistance with a higher load

Fred Marks
10-08-2005, 07:53 PM
The internal resistance of my 3 cell 1320 mah thunder power battery is 171 milliohms. This is at 2c or 2.6 amps. Thats the highest it dishcharges lithiums. I'll have to use nicd or nihm to get a resistance with a higher load

Nate: I am puzzzled that your TP pack is 171 milliohms. The KOK 1250 3S pack would be under 25 milliohms and holds voltage much better than a NiMh at load. The attached Ragone chart tells you relatively how much better Li Po is than the best of the NiMH. Note the position of the GP 3300 relative to Li Pos. I should not have expected a TP pack to have nearly that high an IR. The jpg is a little cruddy, so please open
(https://www.fmadirect.com/site/fma.htm?body=Support)

and open Section II of the Li Po Handbook for a better view.

ragbag
10-08-2005, 09:43 PM
I own Motocalc and Electricalc software and they both ask for the internal resistance of the battery. So this is a good question.

I understand FMA has sent an update on their batterys to Electicalc recently, but I haven't checked.
By George
Gainesville FL

Fred Marks
10-08-2005, 10:47 PM
I own Motocalc and Electricalc software and they both ask for the internal resistance of the battery. So this is a good question.

I understand FMA has sent an update on their batterys to Electicalc recently, but I haven't checked.
By George
Gainesville FL

You should be able to use the IR data from Post 8 in Electrocalc

FM

ragbag
10-09-2005, 01:01 AM
You should be able to use the IR data from Post 8 in Electrocalc

FM


It was on the hard drive before your post. I could see what you were pointing to.

Thanks for the heads up though.

George