Home-made battery tester

[GadgetBoy]

I'm thinking of building a battery tester (for household cells, AAAs, AAs, Cs, Ds, 9V) from scratch, using an analog volt meter and load resistor, while also making it look kinda retro and steampunky.

What are your opinions of what size of load resistor(s) I should use to get an accurate reading of battery strength?

[jeroen79]

That will depend on what kind of battery you want to test.
Which chemistry? What capacity? What current? Single cell or battery?

[Sceadwian]

Use a Mosfet and opamp driven from a sense resistor fed from a DAC so you can program a constant current load instead of a fixed resistance. Then you can sweep the current draw and monitor the voltage curve to fully characterize the cell.

I'm thinking of building a battery tester from scratch, using an analog volt meter and load resistor, while also making it look kinda retro and steampunky.

What are your opinions of what size of load resistor(s) I should use to get an accurate reading of battery strength?

[GadgetBoy]

That will depend on what kind of battery you want to test.
Which chemistry? What capacity? What current? Single cell or battery?

Excellent question, I should have been more specific (and have edited my original question). I was thinking for general house-hold cells, AAAs, AAs, Cs, Ds, 9V, etc. Nothing fancy like LiPo's or what have you.

[GadgetBoy]

Use a Mosfet and opamp driven from a sense resistor fed from a DAC so you can program a constant current load instead of a fixed resistance. Then you can sweep the current draw and monitor the voltage curve to fully characterize the cell.

That's quite a bit more complicated than what I was planning for (although, couldn't I pretty much accomplish the same thing with a pot?).

Also, OpAmps and DACs are something I have basically no experience with, so I'm interested in the idea, just wouldn't even know where to start.

[Sceadwian]

But what fun is that?

Use a Mosfet and opamp driven from a sense resistor fed from a DAC so you can program a constant current load instead of a fixed resistance. Then you can sweep the current draw and monitor the voltage curve to fully characterize the cell.

That's quite a bit more complicated than what I was planning for (although, couldn't I pretty much accomplish the same thing with a pot?).

Also, OpAmps and DACs are something I have basically no experience with, so I'm interested in the idea, just wouldn't even know where to start.

[DTJ]

As you are starting out, why not use a rotary switch to select different load resistors for the different battery types.

Have a look at the data sheets for the batteries to get an idea of some load resistor values to try.

All the 1.5V cells can use the same meter range. You will have to add a voltage divider for testing the 9V batteries. Perhaps use low value R's for the divider and they can also form the load.


Alternatively have a battery holder to suit each cell type with a load resistor connected across the back. Use a rotary switch to connect the meter to each battery holder/load resistor combination when selected.

[JagV12]

The cheap China made BT-168 that I bought has these specs :
1.5V : 4 ohm load, 1.0V = low 0.9V = replace
9V : 215 ohm load, 6.5V = low, 5.3V = replace

[GadgetBoy]

But what fun is that?

I'm interested in trying if you can give me some advice on where to start.

[jeroen79]

Since you mentioned retro and steampunky, how about a rheostat?
You can add a scale with different celltypes marked to set the test resistance/current.

[GadgetBoy]

Since you mentioned retro and steampunky, how about a rheostat?
You can add a scale with different celltypes marked to set the test resistance/current.

I was thinking something along those lines, with a nice big clunky switch and some big chunky retro carbon resistors.