Is there a easy way measure battery inner resistance without profession measuring tool?
I only have multi testers and electric components and some shunts.

 

Depends on the size and amperage rating of the battery.
You can do this with a shunt resistor but you will need very high wattage rated shunt resistors for bigger batteries.
The method is to draw a substantial current from the battery using a shunt resistor of known value.
Measure the voltage across the battery and compare it with the battery voltage when under no load.
Use Ohm's Law and do the calculation to determine the internal resistance.

If the voltage drops to half the no-load voltage, then the internal resistance equals the shunt resistance.

 

Yeah, that possible but current flow is tremendous so may damage the battery. No other way without damaging the battrey?

 

You are dealing with extremely low resistance value and also currents with a large magnitude.Keep in mind that ordinary car batteries are designed for only 20% or so discharge, in ordinary use. That being said, you could fabricate some very low value resistors from carbon rod, and make a plot of current discharge versus rod length, to try to observe a maximum current point, which occurs when the load resistance equals the internal battery resistance. It might be advisable to research the topic first, to see what sort of current/resistor magnitude this experiment involves.

 

Read that too long ago to remember where was a clear method and explanation. A search now produced too many results to go trough them. You pick :

----> https://duckduckgo.com/?q=measure+battery+internal+resistance&t=canonical&ia=web

 

Yeah, that possible but current flow is tremendous so may damage the battery. No other way without damaging the battrey?

You can measure the internal resistance at any current flow. I assume it's not a constant, though, so unless you can measure at a current near the relevant value, a measurement at much lower current may not be all that useful. I wouldn't want to extrapolate too far.

 

Read that too long ago to remember where was a clear method and explanation. A search now produced too many results to go trough them. You pick :

----> https://duckduckgo.com/?q=measure+battery+internal+resistance&t=canonical&ia=web

This is a good basic primer for quick testing: http://data.energizer.com/pdfs/batteryir.pdf

You would need to scale the current values to the needed ranges for the battery type, capacity and usage load.

 

Is there a easy way measure battery inner resistance without profession measuring tool?
I only have multi testers and electric components and some shunts.

The usual method is to pulse 2 different load resistors onto the battery and measure the terminal voltage for each current draw - you can calculate the internal resistance from the difference between them.

There should be published specifications for internal resistance - from that; you can guesstimate the lowest current values you can get away with and still get a meaningful difference between the 2 loaded terminal voltages.

 

http://batteryuniversity.com/learn/article/rapid_test_methods_that_no_longer_work

Be aware that measuring the internal resistance in certain batteries may not tell you much (nothing?) about the health / capacity of the battery.

 

Read that too long ago to remember where was a clear method and explanation. A search now produced too many results to go trough them. You pick :

----> https://duckduckgo.com/?q=measure+battery+internal+resistance&t=canonical&ia=web

What a great information. Thanks!

 

This is a good basic primer for quick testing: http://data.energizer.com/pdfs/batteryir.pdf

You would need to scale the current values to the needed ranges for the battery type, capacity and usage load.

Wow, another great information. Thanks!

 

The usual method is to pulse 2 different load resistors onto the battery and measure the terminal voltage for each current draw - you can calculate the internal resistance from the difference between them.

There should be published specifications for internal resistance - from that; you can guesstimate the lowest current values you can get away with and still get a meaningful difference between the 2 loaded terminal voltages.

Yes, I think that's the good and easy method can do test at my home. Thanks!

 

try to observe a maximum current point, which occurs when the load resistance equals the internal battery resistance.

Not so. You're thinking of maximum power transfer.

 

Not so. You're thinking of maximum power transfer.

You are correct ... Maximum Power Transfer. Presumably, that would be a good reason to determine a battery's internal resistance.
Current magnitudes associated with load resistance values that are less or greater than the internal resistance do not correlate with increased power transfer.
Some additional information here:
http://www.electronics-tutorials.ws/dccircuits/dcp_9.html

 

You are correct ... Maximum Power Transfer. Presumably, that would be a good reason to determine a batter's internal resistance.

It's a good way to make the battery explode. 50% to r and 50% to R. But that could be 50% of 1000 W.

Maximum Power Transfer is usually meaningless in battery circuits as the internal resistance is usually much lower than load resistance as we are also interested in the efficiency of power transfer.

 

I just changed the carbon filters in my Reverse Osmosis drinking system. Took one of the canisters apart and there's this very large carbon block with a resistance of about 47 ohms. The diameter is about 2 7/8 inches and the length is approximately 9 inches. It has an internal diameter of about an inch and a quarter. I have NO IDEA how much current it could handle or even if it would disintegrate under a load. But it IS a resistor of sorts. I also have hardly an imaginative idea for making the electrical connections. Maybe hose clamps and some copper wire.

I really don't know why I posted that. Large shunts can be hard to come by (I'd think).

Maybe this afternoon I'll go short a car battery with this giant resistor and see what happens.

12 volts (older battery, 12.05 volts at rest) with a 47 Ω resistor should draw 255 mA. Not a very big load, so, that's going to be 3 watts. I suspect this huge resistor won't get hot.

[edit] Just took another one apart. This one has a resistance of about 19 ohms. So I guess it depends on how many minerals they've filtered out.

Took a 13.8 volt power supply and an old automotive light bulb. Touching it to far ends of the filter cartridge the bulb lit but not at full brightness. As I slid the bulb closer to the other probe the brightness increased. When I checked the apparent resistance from end to end using a DVM I got about 19 ohms. As I slid the leads closer and closer together the resistance hardly changed. At the closest possible without touching probes I gout about 16 ohms. Maybe this is too large a surface for my DVM to measure accurately. But imagine that - using a resistor to dim an automotive parking light bulb.

 

Maybe this afternoon I'll go short a car battery with this giant resistor and see what happens.

Be sure to film it. And be sure you script the dialog to include the most famous last words in Wisconsin, "Hold my beer and watch this!"

 

Wayne: Even at 19 ohms, a 12 volt source is only going to deliver 632 mA. 7.6 watts. I wouldn't expect any fireworks. Even on my test bench, lighting an automotive bulb didn't produce any unexpected sources of excitement. And that was with a 13.8 volt (19 amp) supply. The small metal contact I held against the carbon DID get a little warm, but my fingerprints are still readable.

 

Wayne: Even at 19 ohms, a 12 volt source is only going to deliver 632 mA. 7.6 watts. I wouldn't expect any fireworks. Even on my test bench, lighting an automotive bulb didn't produce any unexpected sources of excitement. And that was with a 13.8 volt (19 amp) supply. The small metal contact I held against the carbon DID get a little warm, but my fingerprints are still readable.

Be careful, all you need is one little slip for there to be a direct wire to battery terminal contact weld with possibly hundreds of amps from even an old car starting battery.

 

My last two carbon filters read 9Ω and 24Ω. So if I use the most aggressive filter (9Ω) it should still draw 1 1/3 amps (16 watts). I MIGHT see some water vapor turn to steam, but that'd mean I'd have to produce 203.4 degrees F (at 4550 feet elevation). 16 watts can probably do that but probably not immediately. AND with the evaporation of moisture the resistance should go up. Some of these cartridges were just removed two days ago, they're probably still wet. One of them has been out for over a year. I'm confident it's pretty dry. Probably the one that reads 47Ω.

OK, just finished a test and a video: Got an unexpected result. When probing this particular filter I got 22 ohms from end to end but that was with the meter probe points touching the carbon element. I wrapped a copper wire around the element and twisted it tight and measured the resistance at 6.4 to 6.5 ohms. I then hooked it directly to my power supply (13.8 V @ 19 amp capability) and measured the voltage across the two contact points. Voltage dropped down to 9.8 volts, so the power supply was struggling a little, but using my infra-red temp probe it read 70˚ F. THEN I made a video. Sorry to say there were no spectacular results.