Battery Internal Resistance Measurements

[BJ43]

Interesting. So is it safe to surmise that the higher the C rating the lower the internal resistance of the bat?

Probably, except different manufacturers kind of fudge their numbers. Best to have the meter or Baps lab. I was really surprised with the A spec. Most of my DIY mods have a meter that reads both imput and output. I had never seen less than .2v drop on any batteries and most .4v and more, but I have just used 18650s and a few mods with 14500s. Just recently, I finally decided to try some lipos in my mods and am slowly changing some of my retired units.

 

[mikepetro]

I am trying a different route, hopefully I will end up being able to take similar resistance measurements though. It uses a Kelvin 4-wire style probe, similar concept to a temperature compensated RTD.

It has a 400 milliohm range with a +/- 1% accuracy.

 

[mikepetro]

Probably, except different manufacturers kind of fudge their numbers. Best to have the meter or Baps lab. I was really surprised with the A spec. Most of my DIY mods have a meter that reads both imput and output. I had never seen less than .2v drop on any batteries and most .4v and more, but I have just used 18650s and a few mods with 14500s. Just recently, I finally decided to try some lipos in my mods and am slowly changing some of my retired units.

BJ, are you referring to the voltage drop of just the battery input between pre-fire and post-fire, or are you looking at the delta between input and output?

 

[DrMA]

I am trying a different route, hopefully I will end up being able to take similar resistance measurements though. It uses a Kelvin 4-wire style probe, similar concept to a temperature compensated RTD.

It has a 400 milliohm range with a +/- 1% accuracy.

You can't measure the IR of an energized battery with a regular Ohm meter. The voltage difference between the leads interferes with the resistance measurement and may even fry your meter, so be careful.

 

[keyman]

I have a friend who flys RC planes with me and he has been using this charger for checking IR but not sure if it does a single cell?

Value Hobby R/C Hobby Store (Addison, Illinois): GT POWER X-CHARGER C6 6S LiPO Charger

 

[BJ43]

BJ, are you referring to the voltage drop of just the battery input between pre-fire and post-fire, or are you looking at the delta between input and output?

I have a meter connected to a battery and I get two readings, one static and one under load when I press the fire switch. Have no idea what you mean by the delta,,,

battery input between pre-fire and post-fire

 

[mikepetro]

You can't measure the IR of an energized battery with a regular Ohm meter. The voltage difference between the leads interferes with the resistance measurement and may even fry your meter, so be careful.

I havent got it yet but I know it supplies up to 200mA to the circuit under measurement so I figured it wouldnt work with a live power source. I may have to buy one of the hobby meters for that.

This will still serve me well though as I am also interested in switches and contacts and quick disconnects etc. Trying to understand how big of a role they play. For example, if I want to measure current how much does the ammeter add, if I use a switch to switch the ammeter in and out of the circuit how much does the switch add. Wondering if I can find a CT to do the current measurement instead, using a separate small bat for the ammeter. (Never seen a CT this small though) I also want to rate Sta-Kons vs bullet connectors, and that kind of stuff. Then there is the wire, how does regular wire compare to low oxygen copper, stranded vs solid etc. I know solid is less resistance but by what magnatude, enough to make a difference? Really just wanting to understand it all.

I deal with big stuff all day long but this high current low voltage world is new to me.

 

[mikepetro]

I have a meter connected to a battery and I get two readings, one static and one under load when I press the fire switch. Have no idea what you mean by the delta,,,

battery input between pre-fire and post-fire

Thanks BJ, that was what I was after. Are you using "min/max" to get the 2 readings, or are you eyeballing it in realtime?
(delta/difference/vdrop, ie difference between pre and post)

 

[BJ43]

Thanks BJ, that was what I was after. Are you using "min/max" to get the 2 readings, or are you eyeballing it in realtime?
(delta/difference/vdrop, ie difference between pre and post)

See for yourself. Russian 1.3 ohm R41 at 5.02v.. Imput volts at 7.47v when fired goes down to 7.42/3.
Clic pic for video.

 

[keyman]

I hope this is the right thread to post this in.

I sometimes order lipo's from here, I get an email from them about every 10 days with certain lipo's on a flash sale. They have a USA warehouse and my orders usually go out within a day or 2 but the shipping/tracking info is a little late getting to me.
RC/Hobby/Store:China Hobby,battery

I'm not certain but last year when I ordered some lipo's from Hobbyking they wanted you to register the same day you received them for any warranty. Also when it comes to charging lipos I don't leave the house when there charging and try not to leave them stored for a long time fully charged.

 

[DrMA]

I have a friend who flys RC planes with me and he has been using this charger for checking IR but not sure if it does a single cell?

Value Hobby R/C Hobby Store (Addison, Illinois): GT POWER X-CHARGER C6 6S LiPO Charger

Looks like that charger can do LiPo's from 1 to 6 cells in series. However, be aware that you can't just plug it into an outlet; it requires a DC power supply sold separately.

 

[Phone Guy]

Where can I get that meter in the first page of this post? It looks like a ohm meter capable of reading internal resistance levels of batteries

 

[bapgood]

Where can I get that meter in the first page of this post? It looks like a ohm meter capable of reading internal resistance levels of batteries

Turnigy 7 in 1 Mega Meter Battery Checker/Watt Meter/Servo Tester (USA Warehouse)

 

[BJ43]

Using lipos in series so I have a ?. What is the best charger to use that only charges thru the balancing plug? I have this one but it is only .8 amps. Very slow to charge large batteries. Only need 2s to 3s.

Hobbyking DC-4S Balance Charger & Cell Checker 30w 2s~4s (USA Warehouse)

 

[bapgood]

Using lipos in series so I have a ?. What is the best charger to use that only charges thru the balancing plug? I have this one but it is only .8 amps. Very slow to charge large batteries. Only need 2s to 3s.

Hobbyking DC-4S Balance Charger & Cell Checker 30w 2s~4s (USA Warehouse)

That's a good question....you have one more than me

I looked at HK and they are all 800mah. You probably won't find one much higher than that since you are charging via the dinky balance wires.

 

[BJ43]

That's a good question....you have one more than me

I looked at HK and they are all 800mah. You probably won't find one much higher than that since you are charging via the dinky balance wires.

Found this one, 2 amps. Meter doesn't read voltage just %.

http://www.hobbyking.com/hobbyking/...20_Balancer_Charger_2S_4S_USA_Warehouse_.html

 

[Phone Guy]

I like those battery tester by turnigy, but that seems expensive for $40 just to check internal resistance. Anyway to do it with a regular volt meter?

 

[bapgood]

I like those battery tester by turnigy, but that seems expensive for $40 just to check internal resistance. Anyway to do it with a regular volt meter?

No, the dmm's that I have seen don't measure that low.

 

[DrMA]

I like those battery tester by turnigy, but that seems expensive for $40 just to check internal resistance. Anyway to do it with a regular volt meter?

If you have a precise multimeter, apply a known resistive load to the battery and measure current (I), unloaded voltage (Vo) and voltage under load (Vl). Then the battery IR=(Vo-Vl)/I (approximately)

 

[bapgood]

I have been asked several times how to power the Turnigy 7 in 1 Mega Meter if you don't have lipo's.

I would suggest either using a 9v battery or a 12v power supply and make an adapter to tie into the "volt port". I have done both and both work.

Here is an example I tried this morning using a a 9v battery tab from radio shack - Fully Insulated 9V Battery Snap Connectors : Battery Snap Connectors | RadioShack.com and a servo connector (but I would recommend the JST balance connector below)




The meter needs to see voltage on the second two pins from the left (or pins 1 and 2), the first pin is the battery negative. So wire both of the right two wires of the connector to the battery or PS positive and the left connector wire to the battery or PS negative.


I would purchase this and use the end outlined by the box - JST-XH Parallel Balance Lead 2S 250mm (2xJST-XH) (USA warehouse)