Replacing adapter with batteries?

Question

I have some device with ac/dc adapter [9v, 500mA], and I want to replace the adapter with batteries.

If I used [6 * 1.5v] battries, is that acceptable? do I have to worry about the max current of the batteries? could the current of the batteries exceeds 500mA?

whenever I try to measure the current of the device connected to the battries, it gives me "1" "the upperlimit of the Multimeter", why? how?

And if so, what should I do?

HOW CAN I MEASURE THE MAX CURRENT OF THE BATTERIES OR SOME POWERSUPPLY???

Answer 1

You don't have to worry about providing too much current. The current is determined by the voltage and the load. To need to make sure that you can provide enough current.

In your case, it should work out fine. An AA battery (alkaline) can provide at least one amp, so your 500mA is within spec.

However, AA's have around a 2.5 Amp-hour capacity, so you won't get more than 5 hours (or so) of run time. Of course, the circuit likely doesn't take the entire 500mA, so it'll probably last longer than that.

Good luck!

Answer 2

If you wire your batteries up in series to get the voltage you require, the current will be the same as from a single battery, if you do need to change this you need to wire another set of 6 in parallel.

That having been said, a very quick search showed that most AA batteries are rated to give a max of about 2400mA, which is ample. HOWEVER 500mA is a fairly large current draw assuming that the device actually requires this much, (which it won't) this means you will run the batteries down quickly, although you do have 6 of them...

To use your multi meter to measure current you must place it in series with the supply, so, positive end of supply - positive multi meter probe, (goes through multimeter) - negative end of probe to positive input of your device - negative end of device to negative end of supply (as normal).

MAKE SURE YOU HAVE THE MULTI METER IN CURRENT MODE!!

Answer 3

As @Tim Mottram said: Amp meter has to be connected in series.

But: DON'T SHORT YOUR POWER SUPPLY WITH YOUR AMP METER!

A multimeter in amp meter mode is a device that measure a voltage accross a very small resistor that is connected internally between the two probes of the meter.

If you connect thoses probes to the power supply you will actuall load your power supply with a very small resistor.

Because I = U / R, with R very small, I will be very big. For sure it will be big enough to blow the fuse included into you multimeter. (or blow your multimeter if it's a very very low cost model). A single cell battery would have an internal resistance that is big enough to limit that current and save your meter. But a power supply would for sure have enough power to blow your meter.

Answer 4

Ohms Law, Ohms Law, Ohms Law.

If the voltage is 9V and the load is 30 ohms (for example), the current taken by the load is:-

I = \$\dfrac{V}{R}\$ = 9/30 = 300mA.

If your power supply (or battery pack) is capable of supplying 1000 amps it still has to obey ohms law and that means I = V/R and if the load is 30 ohms it'll take 300mA from a 9V power source.

Don't connect your meter (measuring current) across your battery because you'll measure the full output current from the battery and this might damage your meter or burn small wires.

You current charger is rated at 500mA and is adequate - this means your load takes 500mA or less (maybe 300mA as per my math above). You don't need to measure this to know this.

HOW CAN I MEASURE THE MAX CURRENT OF THE BATTERIES OR SOME POWER SUPPLY???

Put your meter back in its case and make sure the leads are plugged back into measuring voltage because you might forget next time you use it across the AC in your home and then there will be smoke and it'll be your meter burning possibly.

If you want to know how much current a battery can produce, look at its data sheet and don't try measuring it.