Battery current measurement

[torrent99]

I used to get paid to fix the old services radio equipment, I was glad to see the back of it.

Everytime I go home to Lincoln, I always spend a few minutes gazing into the windows of John Birkett's electronics shop. Crammed full of old services gear from Lancasters, Spitfires, Vulcans etc etc. always wondered who bought it!

Anyone for a WW2 altimeter?

 

[rog_london]

Well, I've bought a Maplins meter and done the conversion. I've not had time to test it on current yet, but I can confirm that it does say DC when you put a DC voltage across the wires.

I understand that its not for everyone, but I love this kind of project. Personally I'd rather have this to play with than half a tank of petrol for the car, which is what the money might otherwise buy.

Thirty years ago I used to be a radio ham, which when I think about it was quite expensive and totally without practical benefit. Great fun at the time though. The best part was buying real ex-services gear and making it work. Beautiful silver plated coils, glass encased vacuum variable capacitors, and big transmitting valves. Marvellous.

Pete

Are we talking about the same thing? The part number quoted (L61AQ) was for that plug-in wattmeter Maplin's sell. It's specified for AC voltages between 180 and 250 VAC (there's a spec sheet which comes with it and it's also available as a PDF download). No mention of DC at all.

When you power the unit (by plugging it in to the mains) it does a 1-second reset during which it powers all sections of the LCD display, and there is no DC indication, although there is a minus sign which normally never gets used. I can't help thinking that this is just about the most unlikely choice of a starting-point for measuring DC current it's possible to pick, so I'm guessing that somewhere along the line we're not talking about the same thing at all.

Rog.

 

[Sector]

Early test results

I'm still short of time to do some proper testing, but I managed to lash together a 20 ohm load from wirewound resistors and the results are as follows. This is using a NiMh 36 volt battery as the power source.

Maplin Meter/ Old digital Avo
Reading
39.6v / 39.9v
1.91A / 2.0A (+/- 0.1)
76w
71va
pf 1
0.00 kWh (I didn't run it long enough to get a reading)
When I pressed the Hz button it displayed "dC"

These tests wer hampered by the fact that the Avo would only work on the 10 amp range for current so the Avo current reading could be out by 5%. Also the Avo voltage and current readings couldn't be taken at the same time.

Note that the "live" must be used as the postive connection, otherwise the voltage readings are about 3 volts lower than they should be. This is evidence of diodes in circuit I suppose.

I think the Maplins meter should be adequate for the first job I have in mind: comparative testing of my Ezee batteries to find out which has most capacity left.

Yes, Rog, I agree that there is no reason at all why the L61AQ 250vAC power monitoring device should work on DC. I feel a little screwy using it like this but the guy who first tried out the mod was in a different league for lateral thinking.

Now I've just got to think of an automatic way to disconnect the battery when the voltage gets low (31.5v?), then I can start battery testing. Any ideas anyone?

Pete

 

[rog_london]

I'm still short of time to do some proper testing, but I managed to lash together a 20 ohm load from wirewound resistors and the results are as follows. This is using a NiMh 36 volt battery as the power source.

Maplin Meter/ Old digital Avo
Reading
39.6v / 39.9v
1.91A / 2.0A (+/- 0.1)
76w
71va
pf 1
0.00 kWh (I didn't run it long enough to get a reading)
When I pressed the Hz button it displayed "dC"

These tests wer hampered by the fact that the Avo would only work on the 10 amp range for current so the Avo current reading could be out by 5%. Also the Avo voltage and current readings couldn't be taken at the same time.

Note that the "live" must be used as the postive connection, otherwise the voltage readings are about 3 volts lower than they should be. This is evidence of diodes in circuit I suppose.

I think the Maplins meter should be adequate for the first job I have in mind: comparative testing of my Ezee batteries to find out which has most capacity left.

Yes, Rog, I agree that there is no reason at all why the L61AQ 250vAC power monitoring device should work on DC. I feel a little screwy using it like this but the guy who first tried out the mod was in a different league for lateral thinking.

Now I've just got to think of an automatic way to disconnect the battery when the voltage gets low (31.5v?), then I can start battery testing. Any ideas anyone?

Pete

Well, I learn something new (almost) every day. I see what you mean about the 'DC' indication - it actually comes up using segments of the (usual) digit display.

Rog.

 

[Alex728]

I'm still short of time to do some proper testing, but I managed to lash together a 20 ohm load from wirewound resistors and the results are as follows. This is using a NiMh 36 volt battery as the power source.

Maplin Meter/ Old digital Avo

Oh, it was a digital one - I have to admit when I saw Sectors original post on this subject I had visions of him cycling down the road with an original Avometer strapped to his handebars, and wondered "wouldn't that give false readings due to the needle being rattled about"?

 

[Mussels]

Oh, it was a digital one - I have to admit when I saw Sectors original post on this subject I had visions of him cycling down the road with an original Avometer strapped to his handebars, and wondered "wouldn't that give false readings due to the needle being rattled about"?

I think the weight of one of those beasts would have caused a performance drop in itself.

 

[torrent99]

I think the weight of one of those beasts would have caused a performance drop in itself.

Yeah, but there's something comforting about those old analogue meters....

 

[Mussels]

Yeah, but there's something comforting about those old analogue meters....

The accuracy being a big one, DVMs were around when I worked with them but they were too unpredictable.

 

[Sector]

Antique radio gear

Mussels
I now have a picture in my mind of you carrying a load of battleship-grade radio equipment and several big black Avos. Mussels or Muscles?

Torrent99
Is Birketts really still operating? It's worth a trip to Lincoln to have a dose of nostalgia. The near-equivalent in Leicester was called Eley Electronics and closed years ago. Marvellous shop in its heyday, and a nice distance for a bike ride.

I can't remember ever seeing another Avometer 2001 like mine. I've just had a look around the web for Avometers and found a site where they are listed like museum exhibits. Maybe it will be worth something one day.

Pete

 

[torrent99]

Mussels
I now have a picture in my mind of you carrying a load of battleship-grade radio equipment and several big black Avos. Mussels or Muscles?

Torrent99
Is Birketts really still operating? It's worth a trip to Lincoln to have a dose of nostalgia. The near-equivalent in Leicester was called Eley Electronics and closed years ago. Marvellous shop in its heyday, and a nice distance for a bike ride.

I can't remember ever seeing another Avometer 2001 like mine. I've just had a look around the web for Avometers and found a site where they are listed like museum exhibits. Maybe it will be worth something one day.

Pete

Oh yes, John Birkett's is still open, unchanged in years. The shop window is a treasure trove of fascinating gadgets of yesteryear.

 

[rog_london]

The AVO Model 8 is only just deceased.....

Mussels

I can't remember ever seeing another Avometer 2001 like mine. I've just had a look around the web for Avometers and found a site where they are listed like museum exhibits. Maybe it will be worth something one day.

Pete

Funny you should mention Avometers being museum exhibits - they were in fact still being manufactured by Megger until recently, and were available from RS at an eye-watering £925 for the latest model (which still looks almost exactly like my Model 8 Mk III, purchased new in 1965 from AVO themselves when they were located in Vauxhall Bridge Road). That cost me £25 (about a week's wages). The last model is the Mk 8. Mine is still working perfectly.

I suspect the reason they are still in (limited) demand is that they'll continue to function in electrically 'difficult' environments, e.g. where there may be very high voltages nearby or possibilities of EMP which would destroy modern electronic meters.....

Rog.