BigClive's clock-based battery meter

[kalel]

Edit: I thought about using the projects forum, but since it's a beginner question and not my project, it will fit better here.


(starts at about 54 seconds)

I'm not sure I fully understand how this great looking battery meter works.
What seems awesome is that everyone can make one. But it would be good to understand it properly first.

I think I understand the basic points:

- Clock is reset to 0, then battery is inserted
- Battery is discharged at a relatively steady rate
- Clock keeps counting time until the battery is discharged to a point, then it stops and we can read the Ah value at where the clock stopped working.

But since the Quartz movement seems to stop at about 1.2 volts, Clive added a reed switch and another resistor and battery compartment. I'm not sure how these additions work.

An additional question is, without adding a lot of complicated parts, how accurate will this method be for comparing batteries? Just as a guess, of course.

[glarsson]

The cell under test is discharged through the resistor and reed relay coil. When the cell no longer can hold the reed relay closed it will open and disconnect the cell powering the clock movement, therefore stopping the "clock".

[kalel]

The cell under test is discharged through the resistor and reed relay coil. When the cell no longer can hold the reed relay closed it will open and disconnect the cell powering the clock movement, therefore stopping the "clock".

Thanks. Yes, that seems reasonable.

Any guesstimate around what battery voltage that might be?

[glarsson]

Depends on the reed relay and coil. Doesn't matter really as the cell voltage drops quickly when the cell is empty. At least for the NiMH cells Clive was testing. The "clock" is not intended to be a precision imatrummet.

[kalel]

Depends on the reed relay and coil. Doesn't matter really as the cell voltage drops quickly when the cell is empty. At least for the NiMH cells Clive was testing. The "clock" is not intended to be a precision imatrummet.

Of course. It's just a very interesting one.
As a beginner, I'm fascinated with inexpensive simple solutions that might not be precise or efficient but do work (anything expensive makes it less interesting to make as if something is ruined it might be the end for the project).

I wish there was a website or category with only these types of projects (there might be, just need to find it). Not battery meters, but something focused on very simple to build and understand (few components), quite cheap (also due to the components and no special tools required such as for some SMD parts) DIY projects. Those are attractive to me at this point.

[amyk]

It's just a somewhat better-calibrated and self-indicating version of the toy train in a loop that Dave used for Batteriser testing.

[Zero999]

The trouble is the relay's turn off voltage isn't very well controlled. A voltage reference + comparator could be used to turn off the relay, or a transistor, at an exact voltage. The problem is, finding components that will work off a single NiMH cell.

[glarsson]

The NiMH cell voltage will fall rapidly at the end, så will a well controlled turn off voltage be visible on the clock face?

[RoGeorge]

He, he, old tricks, no need to complicate things:
http://www.talkingelectronics.com/projects/BasicElectronics-1A/BasicElectronics-1A_Page3.html#2

[glarsson]

mAHr?

[CJay]

You should really ask Clive about his big clock, he's been more than willing to discuss it in the comments on his videos before.

I guess what matters is if it's dependable and repeatable though, what he can demonstrate reliably is the difference in capacity if that's the case.

[glarsson]

Of course. It's just a very interesting one.
As a beginner, I'm fascinated with inexpensive simple solutions that might not be precise or efficient but do work (anything expensive makes it less interesting to make as if something is ruined it might be the end for the project).

Perhaps this solution is interesting?
It's 1980. Need power to new Ungar temperature controlled soldering iron; 24V AC @ 2A. Need lamp indicating when iron is heating. How to solve this?
First image shows a hand wired reed relay. The coil is in series with the soldering iron.
Second image shows diode and resistor driving base of NPN transistor. Diode and lamp connected to collector. No DC power available, everything is AC!
Reed relay opens and closes at 2x50Hz. 24V AC through reed relay, diode, resistor and transistor base. Transistor is turned on at 50Hz synchronized with 24V AC lighting the indicator bulb. Still works but I'm now using a modern JBC station.

[I2C]

First Post! Good to meet everyone.

I love the idea of Big Clive's battery-tester clock, not super accurate but the results are all relative to each other regardless. Because the clock's drop-out voltage was often above the "dead" voltage of the batteries he was testing, he made a simple relay using a reed switch connected to the battery being tested, when the battery was dead then the relay would go open-circuit and the clock would stop.

Dave has made a good video on a simple constant-current dummy-load circuit which could be turned into a more-accurate battery tester (I'm considering making one myself). Take a look: