9 volt battery eliminator hum

[Techman]

It looks like the supply is designed to be around 9 volts when fully loaded and delivering a constant half an amp.

I've got a several similar ones. There's one that states it's 13.8 volts at 100 mA which I use for charging a hand held and off load it's well over 17 volts and drops to around 16 volts while charging as it's not delivering anywhere near 100 mA.

Obviously those battery snaps are going to short out if you let them touch each other. I meant that the colour coding on the leads was nothing to worry about, which I think most people would have realised!

I think that it looks like there's a fault with the second radio and also that the unregulated power supply in this case is totally unsuitable for the required purpose, so needs to be sent back, unless the OP can find another use for it, or fit a regulator.

[ajgriff]

Yes and the rather high voltage is probably highlighting or causing component breakdown in the RT7. It would be interesting if James could measure the current with the PP9 connected.

Alan

[ssnjimb]

Hi

See attached pics

no battery connectors were short circuited during these tests.

Iam new to using a multimeter so hopefully the results are correct.

7grb92eq is the rt7 Off
fiwfxzmw is the rt7 On

Lh1fibq is the r200 Off
uctvfz_A is the r200 on

that was the multimeter set to (see last pic)
wxbc6hga

hope this helps

James

[ssnjimb]

Am I using the correct setting on the multimeter ?

James

[ms660]

Looking closer at the photo's, a meter lead is in the wrong socket in the voltage reading photo's, I don't do DMM's so not sure if that will affect the voltage readings so far....

Lawrence.

[Cobaltblue]

I think its on current as per Alans request.


However I suspect the Meter is across the battery instead of in series with it.


If I'm right your measuring the short circuit current of the Battery.

Have a look here

https://www.allaboutcircuits.com/tex...ammeter-usage/


Cheers


Mike T

[cathoderay57]

For the voltage measurement in Post #56 the range is correct and the positive meter lead is in the correct socket but it looks like the negative lead is in the current socket not the centre one marked "COM", which is where it should be for voltage measurement. Worth re-measuring. If it is still measuring 17.8v on load then stop using it immediately and purchase a regulated 9v supply as suggested by others. The hum on the RT7 is probably the poor thing protesting at the over-voltage and it won't last long in that condition. Once you've got a decent power pack then measure the on-load current by disconnecting the positive supply lead and putting the meter on the current range with the red meter lead to the positive supply of the power pack and the negative lead to the vacant radio supply connector. For the current measurement the red lead needs to be plugged into the left-hand "10A DC" socket and the negative into the centre "COM" socket, and switched to 10A current range. Hope that helps.

[Graham G3ZVT]

The left hand socket brings in a 10A current shunt, you will probably never need it. Bung it up with something as a precaution.

All other current, voltage, and resistance measurements on this meter are made with the center and right-hand sockets. When making a voltage measurement first make sure you are on the appropriate volts range and not a current/amps range then connect the probes across the voltage source to be measured.

To measure current, select the appropriate Amps range, then break the circuit at the point you want to measure, and complete the circuit using the meter. In other words place the meter in-series with the battery or whatever.
You would expect a reading in the order of 40 mili-amps for those radios.

As a precaution, don't leave your meter on an Amps range, in case you forget the next time you use it to measure voltage, as the meter will present a near short circuit as you have seen.

[ajgriff]

Oh dear, I didn't notice the meter lead connections in the first set of pictures. As well as the advice already offered you might want to dig out the little instruction booklet that came with the meter as this will explain the correct lead connections for the different measurements.

If we are to solve this one you really need to get accurate voltage and current readings. However, do keep the time that the radios are connected to the eliminator as short as possible until we can be sure about what is going on.

Alan

[Keith]

Hi James,

Are you saying that the radio still hums when switched off??

[ajgriff]

Yes but it might be the eliminator that's humming. This has not yet been clarified by James.

Alan

[flyingtech55]

Will you please take a picture of where you plug the external power supply into the radios showing the little embossed diagram of the polarity of the plug/socket.


TimR

[Cobaltblue]

Originally Posted by flyingtech55

Will you please take a picture of where you plug the external power supply into the radios showing the little embossed diagram of the polarity of the plug/socket.


TimR

Hi Tim


There's no plug it's battery snap to battery snap check the link in Post #4


Cheers


Mike T

[flyingtech55]

Ah yes...I see. I didn't click on the link. I'm wondering if the polarity is correct. The OP seems to be connecting his meter in a number of very 'creative' ways. The snap connector things on the eliminator should be the same way round as an actual battery and the polarity confirmed by attaching the meter leads in the roughly conventional and time honoured manner and plugging said leads into the meter according to the makers diagram on the front of the instrument. Looking at the picture in the link, the polarity according to the colour codes of the wiring looks reversed.....correct for charging a battery but incorrect as a battery eliminator.


TimR

[Cobaltblue]

Hi Tim


Keep reading been through the polarity


Cheers


Mike T

[flyingtech55]

Yes, I see that, but we haven't actually seen the meter connected correctly with the leads in the correct meter sockets with the red meter lead connected to the 'nipple' and the black meter lead connected to the 'claw' of the eliminator connectors and the meter displaying the result.


However, not my problem happily. Signing off now, busy day tomorrow.


Tim

[ajgriff]

Is anyone close enough to Cheltenham (see post #29) to call in and give James a hand?

Alan

[Scimitar]

No but I have offered to help if he drops in. We are not far from Cheltenham, although that depends of course on which part!

[ssnjimb]

Hello

I will recheck with the correct settings later today.

We are next to gchq.

James

[dave_n_t]

Originally Posted by ssnjimb

Hello

I will recheck with the correct settings later today.

We are next to gchq.

James

James,


I'm happy to take a look. I'm in Leckhampton. I'll send you a PM (private message).


Dave