Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

measuring max battery current with multimeter

Status
Not open for further replies.
neazoi

neazoi

Advanced Member level 6
Joined
Jan 5, 2008
Messages
4,123
Helped
13
Reputation
26
Reaction score
15
Trophy points
1,318
Location
Greece
Activity points
36,954
Hi my multimeter has a voltage and a mA/A plug.
I am trying to find out how much instantaneous current can a homemade battery supply.
How can i measure this with the digital multimeter? What procedure?
 

Multimeter gives RMS value.

Im = Imsin(wt)

Irms = Im/sqrt(2) = 0.707 Im

Im = Irms * sqrt(2)

Irms is the value you get in multimeter.
 
  • Like
Reactions: neazoi

    neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating
A max current needs a voltage specification, can be short circuit current (Vbat = 0) or current at specific voltage.

Decide if the multimeter can stand the expected current range, then you can measure current in series with a load resistor. Otherwise measure voltage across the load and calculate current.
 
  • Like
Reactions: neazoi

    neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating
The DMM's I've had contain a fuse which will blow if you try to measure more than 200 mA...
Except on the 10A range, the fuse is not in the circuit.

Therefore it's a good idea to set the meter on the 10A range to take the first current reading.
 
  • Like
Reactions: neazoi

    neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating
connect your multimeter in series with a variable resistor and now keep multimeter in 10A range, when the supply to this ciruit is given, you will be able to measure the current drawn by the resistor, now by varying the resistance you can also find the maximum value of current that your battery could supply.
 
  • Like
Reactions: neazoi

    neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating
You state " instantaneous current", so are you referring to a peak capability in response to a pulse/transient in the load or the maximum current available?
Some meters have a 'peak hold' function if it is the former. For maximum current the previous post should work.
 
  • Like
Reactions: neazoi

    neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating
No that is ok, maximum current should be enough.
At the beginning I thought that the meter could be connected in parallel to the battery terminals, when set to the current setting, but you refer to connect a resistor in series with the multimeter. That is ok.
Varying the value of this resistor, when should I find out that the battery can no longer supply current? Maybe I should also monitor the voltage of the battery terminals until I notice a significant voltage drop?
 

vignesh ssvv said:
connect your multimeter in series with a variable resistor and now keep multimeter in 10A range, when the supply to this ciruit is given, you will be able to measure the current drawn by the resistor, now by varying the resistance you can also find the maximum value of current that your battery could supply.
Click to expand...

I wouldn't suggest that unless you are actually using one of high wattage wire-wound variable resistors.
On the other hand you may want to create smoke effect so a standard pot would be fine for that :p
 

alexan_e said:
I wouldn't suggest that unless you are actually using one of high wattage wire-wound variable resistors.
On the other hand you may want to create smoke effect so a standard pot would be fine for that :p
Click to expand...
I thought so.
Maybe 1w resistors could be used instead, or these cheap 5w wirewounds to find a value close to the max current. When should I find out that the battery can no longer supply current? Maybe I should also monitor the voltage of the battery terminals until I notice a significant voltage drop?
 

Hi use carbon rheostat for unknown current values first use the multimeter to get the max current and then change connections and make it voltmeter to measure the voltage which you allow to be the lowest voltage of given circuit and right now measure the current delivered by the battery, and I think 1W and and 5W resistors wont be enough what is your battery AH and v rating??
 

I purchased several 1 ohm power resistors at Radio Shack.
Each rated 10W.
10% tolerance.

They have been very handy, in different combinations of series and parallel.

Also the 10 ohm value.
 

Venkadesh_M said:
Hi use carbon rheostat for unknown current values first use the multimeter to get the max current and then change connections and make it voltmeter to measure the voltage which you allow to be the lowest voltage of given circuit and right now measure the current delivered by the battery, and I think 1W and and 5W resistors wont be enough what is your battery AH and v rating??
Click to expand...

This is just a little homemade chemical battery shown in this page qrp.gr/energy-harvesting about at the end. I would expect it to be less than 100mA
 

If you use the separate resistors option you can also get away with just using one meter reading the voltage and calculate the current through the known resistance combinations.
It will be interesting to see your results.
 

for a small battery It will a have high internal resistance with 1 ohm and 2 ohm in series nothing before them, be ready and short it and find the current, and don forget to put the multimeter rating where it wont reach...
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top