USB Conundrum - One for the boffins.

[OldAgeTravellers]

At home I use a 4G router with a phone port and a phone sim for home telephone and internet. When away I just move the HUAWEI router to the MoHo and plug it in to the Pointing MiMo antenna and all is the same as at home but…….
I noticed that the phone mains block was 5.5 volt 0.5A dc which sounds like usb voltage. I checked it with a multi meter and yes it was exactly 5.5v. So I cut an old USB charging cable and soldered it to the phone cable after cutting the plug block off and after checking the polarity of course in case the makers had miss-used the colours. I plugged it into a Samsung USB phone charger and yippee it was charging the phone on the cradle and I had a dialling tone. I then plugged it in to my 12v multi USB outlet in the MoHo and the lights lit up, the answering machine talked to me and the phone was charging but showed a message “Phone Line Disconnected”. Confused am I!
I ordered a USB pass-through voltmeter/ammeter from Amazon which arrived next day and started testing various USB outlets. Here are the results with the phone connected to the pass through USB socket:-

Samsung mains phone charger. 5.11v 0.08a. Phone line connected
12v power supply as recommended by Lenny HB 5.5v 0.00 a No phone line?
Good quality ciggy USB. 5.08v 0.00 a. No phone line?
Cheap ciggy USB 5.19v 0.00 a. No phone line?
12v buck converter USB from Amazon. 5.08v 0.00 a. No phone line?
finally……
Power Bank Battery. 5.16v 0.067a. IT WORKS!!!

Can anybody throw some light on this for me please. Ok I can get it working while off-grid by using the power bank battery with a permanent charge from one of the ciggy chargers but why is USB power derived from 12 volt system different to the mains.
OH, forgot to say, all the tests above were for the base unit only with the phone off charge but in all cases the unit would charge the phone but with the 12v chargers would still not connect to the phone line.
I can post pictures and links if required.
Sorry for the long post but thanks for reading.
Steve

 

[Lenny HB]

In addition to +/- connections on the charger there is probably a 3rd sense wire that needs to see a voltage for it to enable.

 

[OldAgeTravellers]

In addition to +/- connections on the charger there is probably a 3rd sense wire that needs to see a voltage for it to enable.

Hi Lenny, but why does it work with a mains charger and a battery bank?
Steve

 

[OldAgeTravellers]

In addition to +/- connections on the charger there is probably a 3rd sense wire that needs to see a voltage for it to enable.

OH and the USB phone charging lead I dissected had only 2 wires red & black.

 

[Off da Grid]

This may help but YOU DO THIS AT YOUR OWN RISK, according to Bigclve.com on YouTube the other 2 wires need to be soldered together this tells the device that the cable is a charger only.

^{_{Subscribers  do not see these advertisements}}

 

[IRHP]

A standard PSTN phone works on 50v dc ( give or take) from the copper phone line. I’m assuming you plug a normal phone into the phone port on the hub. Something in the hub must do a dc/dc conversion to supply 50v to the phone. Some if the power sources aren’t giving the correct feeds for the dc/dc converter to work???

 

[OldAgeTravellers]

This may help but YOU DO THIS AT YOUR OWN RISK, according to Bigclve.com on YouTube the other 2 wires need to be soldered together this tells the device that the cable is a charger only.

Thanks but as above there were only two wires in the USB charging cable and it works on a mains charger.

A standard PSTN phone works on 50v dc ( give or take) from the copper phone line. I’m assuming you plug a normal phone into the phone port on the hub. Something in the hub must do a dc/dc conversion to supply 50v to the phone. Some if the power sources aren’t giving the correct feeds for the dc/dc converter to work???

Yes but it is so odd that it works on mains and power bank but not 12v USB.

 

[IRHP]

Thanks but as above there were only two wires in the USB charging cable and it works on a mains charger.

Yes but it is so odd that it works on mains and power bank but not 12v USB.

But USB are 5v not 12 so something has to step it down then step it up so there will be a lot of losses. I suspect just not enough current there for the hub to provide 50v for the phone.

 

[OldAgeTravellers]

But USB are 5v not 12 so something has to step it down then step it up so there will be a lot of losses. I suspect just not enough current there for the hub to provide 50v for the phone.

Thanks for your help and taking an interest. I suspect it is something like that but the 4G router which I presume is what you are calling the hub is powered from a separate stabilised 12 volt power supply and I would think that it supplies the telephone line voltage and that works fine with a dumb corded phone which has no power.
The base station of the cordless phones for some reason is not detecting that line voltage when powered from USB chargers powered from 12 volt. I suspect it is a current issue but when the phone is on the base station it can get enough current to charge its batteries but still not enough to detect the line even when not charging the phone batteries. Perhaps the chargers powered from 12 volt have some electronics that needs the third wire mentioned above but why there should be a difference with good quality chargers powered from the mains I just can’t figure out and the two wire USB lead that I have used for the plug used to charge phones just fine.
Ok I can live with it as I can use the power bank charged from a car USB But it would be far more convenient if I could find a USB power source that would do the job from the habitation batteries When off grid.