Voltage question

demogo

Well-known member

Donor 14 years: 2012-2025
Joined
Jun 30, 2007
Messages
14,952
Reaction score
2,102
Location
Texas
OK, so this isn't an arcade voltage question but I'm not sure there is a section for a question like this.

I have a battery powered fan. It takes 8 D cell batteries.

Sometimes it works; sometimes it doesn't. I've tested all of the batteries before I put them in the fan and they were all right around 1.57v -- they are old batteries but had never been used.

At first I thought it was a battery seating issue but taking them out and reseating them fixed it once and didn't other times. When I probed the "ends" of the line of batteries when the fan was running I'd get the voltage I'd expect for it to work.

I was probing 3 of them in a line and it was showing ~4.5v as expected when it was running when suddenly the fan stopped w/o me having done or touched anything. And the DMM was showing -7v! Then it was showing -11v. Maybe 10 seconds later the fan started again and the -11v became the expected 4.5v. At no point had the fan or probes been touched.

If it's showing -11v (and the fan not running), if I remove a battery later in the circuit then the -11v immediately disappears and is replaced with ~4.5v again.

Any idea of what's going on here? What would cause the voltage to swing from ~12v overall to a negative voltage where the fan isn't running?

Is this a FAN electrical issue doing this to the batteries or a battery issue doing this to the fan?
 
It's a connection issue with the batteries. Consider replacing the 8 batteries with a wall wart power supply. It will probably be a much more reliable power source.
 
Any idea of what's going on here?

those digital mulitmeters show all kinds of useless data
they are extremely sensitive and display all kinds of misleading/useless information
if you performed the same test with an analog multimeter, you would see the needle go up or down when testing for
voltages/pulling the probes off/ battery circuit disconnecting
 
Cheap / bad DMM may have trouble taking a good voltage reading of a supply like a battery when there is no load.

Put a resistor in line with one of the DMM leads in that case. Buy a better DMM (mastech ones are dirt cheap and pretty functional). Or check unloaded supplies with an analogue meter.

I like the wall wart idea. Just get the voltage and current needs right.
 
It's a connection issue with the batteries. Consider replacing the 8 batteries with a wall wart power supply. It will probably be a much more reliable power source.

Well, it's part of my hurricane supplies; it's a battery operated fan so a wall wart power supply won't help me very much. :)
 
Back
Top Bottom