Wish and truth: Camera battery under load

[Andreas Thaler]

While looking for a solution to an error on an X-500, I came across a note about battery voltage in the associated Minolta service manual.

A battery whose voltage is measured without further connection to a load (open-circuit voltage) may still appear to be ok, even though when inserted into the camera it no longer supplies enough current for trouble-free function.

For me, this particularly applies to the batteries that have accumulated over time because, although they are no longer fresh, they still appear to be usable since they haven't had much to do. At least that's my impression.


Test circuit for a camera battery

Minolta provides a small test circuit for the X-500 with which the (terminal) voltage of the battery can be measured under load - i.e. when the camera is switched on.

Battery capacity check

1. A 100 Ohm resistor is paralleled with the battery at normal temperature (25 +/- 25 °C) as illustrated. A digital multimeter or voltmeter is connected to the battery in parallel to the resistor to measure the voltage. In this case, be sure to perform quick measurement.

2. The battery, with its voltage more than 1.4 V. is regarded as normal.

Since I suspect a weak battery to be the cause of the error, I set up this test circuit.

The candidate is a 3V DL1/3N lithium battery that I inserted into the X-500 from my stash of used batteries.

I would like to determine what the voltage of the battery in the camera is.

Without load - i.e. the voltage measured directly at the battery - the result is a voltage of 2.9 volts.

That looks good.

3 volts is the nominal voltage that is written on the battery and that is what my X-500 wants.

The test circuit on the experiment board.

To measure voltage, the multimeter is connected to a 100 ohm resistor, which simulates the load caused by the camera.

I contact the battery with a crocodile clip cable as a switch.

Measured voltage across the resistor: 2.6 volts

This doesn't look so good anymore.

0.3 volts of the 2.9 volt battery voltage drop across the internal resistance of the battery.

Only 2.6 volts drop across the resistor or are available to the X-500 when it is in operation.

But it should be 3 volts.

This could be the reason why my X-500 no longer works as expected.

In order to rule out the battery as the cause of the error, I will connect the X-500 to my laboratory power supply, which supplies a stable DC voltage of 3 volts.

Stable means that 3 volts are available continuously and regardless of time, even under load.

Unlike a battery, which weakens over time as its internal resistance increases. This causes the voltage delivered to be lower.

In addition, here is the calculation of the internal resistance of my battery, which is already considerable at 11.5 ohms.

The higher the internal resistance (due to battery consumption), the more voltage it steals that should actually be available for the camera to work.

In the equivalent circuit diagram, the two measured battery voltages (when idle and under load) are marked blue with M1 and M2.

By applying one of Kirchhoff's laws and those of Ohm, the internal resistance of the battery can be calculated.

(In the sketch, the internal resistance should be on the right side with the calculated 11.5 ohms so that the voltage arrows are in order. But the result remains the same.

Recreated in the circuit simulation.

Above is the expected battery voltage and below is the actual battery voltage under load.


Conclusion

When it comes to testing a camera, the freshest possible batteries should be used to rule out errors due to undervoltage. Test operation on a stable voltage source such as a laboratory power supply would be ideal.

I was about to open the camera to take a look, accompanied by the troubleshooting table in the service manual.

Maybe I can save myself that now

Sequel follows.

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[guangong]

Very interesting read. Impressed by the extent of your endeavors.
On the other hand, this is one reason why I continue to use film and avoid battery dependent cameras.
Again, I admire your labors.

 

[Andreas Thaler]

This leads me straight to the question of how I connect the external power supply via the battery compartment.

Here the battery insert is unscrewed.

The spring in the compartment is for the positive connection, the metal cover on the battery insert is for the negative connection. The cover closes with the chassis (ground) when screwed into the camera.

I don't want to solder so as not to damage the plastic film on the base plate of the camera. This also applies to the battery holder on the insert made of plastic.

So there will be a craft lesson. At least a quarter of an hour of crafting ;-)

This is how it should work with the base plate removed:

The red alligator clip can be easily attached to the positive pole.

For the black one, a loosened screw on the bottom of the chassis provides a mounting point. To do this, I removed the base plate of the X-500.

Now let’s try it out to see if it works with the laboratory power supply.

Oops, I connected the wrong X-500 - they all look the same

The setup works:

Since the tripod connection takes up space, I used a further away screw in the bottom of the housing for the ground cable connection.

2 x 30 quick releases with hand winding.

Everything perfect!

So it's the battery, and it was probably already too exhausted to keep up with series operation.

The electrolytic capacitor in the camera base is new, it should be ok.

Of course there may be a problem further down the circuit with battery operation, but I'll end with this

+++

All information provided without guarantee and use at your own risk.

 

[Andreas Thaler]

Very interesting read. Impressed by the extent of your endeavors.
On the other hand, this is one reason why I continue to use film and avoid battery dependent cameras.
Again, I admire your labors.

Thank you

The tasks come with the problems. So I have no choice if I want to revive my cameras

I hope it is not too abstract and will be useful to others.

 

[Ian C]

Testers for small batteries and single cells have been available for decades. They are essentially the same as the circuit you’ve shown. You first select the type of battery being tested. That places the appropriate resistor into the circuit. When you close the “TEST” circuit, a readout, either analog or digital, displays the relative condition on a “GOOD” to “REPLACE” scale.

There are many versions here for moderate prices:

https://www.ebay.com/sch/i.html?_fr...m570.l1313&_nkw=small+battery+tester&_sacat=0

I’ve used the Radio Shack analog tester for years since it was discussed in an article by Herbert Keppler in Modern Photography in the 1980s.

https://www.ebay.com/itm/305183376788?hash=item470e58c594:g:QA4AAOSw66NlH3uL&amdata=enc:AQAIAAAA0KUwBGFEK1Izo6zuhp7dCiC4RZKB5yZ5gGwj6nTRbJC0gn8osADj3VIXcxUznpL1ShunbN5AryoBkYyasvEWaLwkhY66ncZKWMvVn22fMMIxjkfECQyAhJNlolPR17hy/1K8r5+tK0R5k1OGkVFo7EIGkVP8Kx4BhZy8ot9xZrHr6EA7rZNe7sDXs/+gRUciaDyBhjiM4XXjse7wzKX/KWpvZ5FY4/D64lAzXt/tl+zaW2PHBnwY72BZTBHyKKm8zSG/HG255MdnjGSPEd0qCGc=|tkp:Bk9SR5rR6bn4Yg

Here is the same tester still available new, but without the Radio Shack branding. The following link provides a video showing the tester in operation.

 

[Dan Daniel]

For powering the camera from your power supply, would grounding to an exposed piece of metal like the tripod socket work? I am thinking of automobiles where most of the car metalwork can be considered ground. Well, I don't do much at all with electrical power so could be suggesting something that can cause damage.

 

[Andreas Thaler]

For powering the camera from your power supply, would grounding to an exposed piece of metal like the tripod socket work? I am thinking of automobiles where most of the car metalwork can be considered ground. Well, I don't do much at all with electrical power so could be suggesting something that can cause damage.

Yes, that would definitely be the simpler, and therefore more elegant, way.

I just couldn't connect my ground clamp to the tripod socket which is electrically connected to the chassis.

Thanks for pointing on this!

 

[Chan Tran]

If the nominal voltage of the battery say is 3V most cameras were designed so that they would work fine at lower voltage. You would need a service manual to determine this but for example the Nikon F3 is designed to work with voltage of 2.4V and higher.

 

[Dan Daniel]

I just couldn't connect my ground clamp to the tripod socket which is electrically connected to the chassis.

Get a 1/4"-20 thumb screw at the hardware store and keep it around for quick grounding- go in a couple of threads, attach clip to the thin thumb screw part.

 

[4season]

You've got some really nice tools - love that Gossen multimeter! But ideally, I'd want a power supply which could be current-limited to some very low value, like ~200 microamperes. Here's a portion of Minolta's X700 service manual:

 

[Andreas Thaler]

You've got some really nice tools - love that Gossen multimeter! But ideally, I'd want a power supply which could be current-limited to some very low value, like ~200 microamperes. Here's a portion of Minolta's X700 service manual:

View attachment 353178

The Gossen cost me my savings, but the Voltcraft was almost affordable It can limit the current to a maximum of 250 mA.

Thanks for the copy!

 

[reddesert]

I have some thoughts.

1. Before going deep into/tearing apart a camera it is always good to test with a fresh or known good battery. I have encountered quite a few units that appeared to be faulty or dead with "the batteries that were lying around on my desk" but worked fine with new batteries from my stash in the refrigerator. This is especially true for things that can have higher current draw, like cameras with viewfinder displays needing fresh button cells, or motor drives needing fresh AAs. (I have even bought a motor drive from KEH in as-is condition that turned out to work when I put really fresh batteries in.)

2. Many cheap multimeters have a setting that allows you to test batteries under load. For example the US$8 multimeter I have from Harbor Freight has a setting where you can test an AA and it displays what are effectively milliamps across some internal resistor. I know from using it that a fresh alkaline AA will read about 4.1, an AA with modest use about 3.8, and a battery that reads 3.6 or lower should be used only in flashlights and such. However, all three of these batteries will read about 1.4-1.5 volts with no load.

3. A 1/3N lithium battery when fresh should read about 3.1 V with no load. By the time it reads 2.9 V with no load, it's already on the way out and will be marginal for operating a camera that has more than a bit of electronics. (For example, in Nikon terms a marginal 3V battery might power an FM or FE but fail to power an FA, which has a viewfinder LCD and more metering electronics.)

4. Rigging an external power supply is perhaps most useful if you want to measure the current draw of the camera. Also, you could probably power the 3V camera off 2 AAs, which would be a little easier to deal with and less risky if you happen to short the power, vs shorting a bench power supply.