how to measure leakage current of NiMH battery?

[young707]

I have a 5x NiMH AA battery in series to power a bunch of LED.
The open & close circuit switch is a reed relay.
I want to measure the current flow value when the relay is open and close.
How best to draw the discharge rate chart after the relay is closed?

I assume the current is very low when the relay is opened. What kind of current meter (with minimial internal resistance) should I use?

Thank you.

 

[itsmoked]

Use a reasonably good DMM (Digital Multi Meter).

Plug in the leads to measure current then place the leads so the current from the battery(ies) has to flow thru the meter, which you've set to measure current.

That's all there is too it, except! All batteries self discharge with time. Some MUCH faster than others. For that you need to look at the manufacture's data sheets, as measuring it yourself is completely impractical.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[young707]

Thank you. We need to make very precision conductive measurement for a open reed relay circuit.

We want to determine the openned relay may cause current leakage for 2 years storage of serially connected 5 AA NiMH batteries.

That is why we seek the mininal resistive load in series to the circuit at the point of current measurement (internal resisitive load of the Ammeter.

Thank you.

 

[itsmoked]

Ah.. You have other more serious problems. NiMH batteries self discharge faster than all the rest. I'd expect them to be dead in 2 years with nothing hooked to them. You should seriously consider regular carbon or alkaline batteries.

A reed switch can't possibly leak enough to affect the otherwise grim result.

To test your case do precisely follow my above description only use a meter with a microamps sensing capability. Most new DMM can do this. Just make sure you don't activate the relay while sensing in microamps or you may damage the meter. I'd be interested to hear your leakage results.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

high-end reed relays are typically in the >>gigohm isolation:

http://www.keithley.nl/data?asset=57514

http://www.meder.com/kt_reed_relays_en.html

http://media.digikey.com/pdf/Data Sheets/Coto Technology PDFS/SIP Series Reed Relays.pdf

I second the notion of using alkaline, etc., batteries.

TTFN
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[young707]

Yes, we already have same model using disposable Alkaline batteries.
The model I am working on are rechargeable models.
I use a simple Fluke hand-held multimeter scale of 300mA. But did not see any leakage current.
I am searching for ammeter with 10-6 scale.

Is there any way to remedy this 5x AA NiMH in series self-discharge? After long storage of months, can we zap and re-awake these rechargeable batteries?

 

[IRstuff]

"Fluke hand-held multimeter scale of 300mA"

Seriously? We were talking about gigohm isolation, which means leakage current on the order of nA or pA, which are nowhere near 300mA. Even a uA scale might be insufficient to see the leakage of a decent switch.

If you're going to let the batteries sit idle for 2 years, why is there a need to use rechargeable batteries? What exactly is the purpose? If you have to, you can certainly do trickle-charge or even periodic charge, but that seems to be counter-intuitive to the notion of using batteries in a long-term idle situation.

Perhaps, you should start be describing the requirements and the intent.

TTFN
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[itsmoked]

There is nothing you can do to 'fix' the batteries. You just have to recharge them regularly ~> every couple of months.

Since you haven't said what your product is it's not possible to give any other suggests that might otherwise help.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

You might be better off using a long shelf-life primary cell such as a lithium-ion type. Some claim 15 years or more life before self-discharge kills them. With the self-discharge problem taken care of you can worry about leakage paths.

If you're trying to measure ultra small currents then Keithley's instruments are among the best. They ain't cheap, but it's a difficult measurement; your multimeter is frankly useless for this purpose.

The following might be useful reading for you:

http://www.keithley.com/knowledgecenter/knowledgecenter_pdf/LowLevMsHandbk.pdf