Capacitor Battery help?

[Currymunster]

Hi every one. Thanks for letting me join.
I have a car stereo mounted in a wooden box that I use for work.
It has a 12v psu mounted inside which I bought off ebay.
I would really like to make some sort of capacitor battery to run off the psu and connect to the memory wire of the stereo.
Thus remembering the stations and time every time I unplug and move to different work places. (I'm a plasterer)
I have basic Knowledge but am good with a soldering iron. I used to repair computers on the side so I'm sure I can do it. I just lack the knowhow.
Any help would be appreciated thanks.
James

 

[gophert]

The memory wire draws about 7mA according to this page..

Stereo Memory Wire Draw - Some Data !

www.sailnet.com

that is quite a bit for a capacitor. Even a 1 or 2 Farad capacitor will last a few hundreds of seconds. (A day is 86400 seconds. You'll also need a fairly beefy battery to supply that each day and hopefully recharge it each day. A 9v battery will last about 70 hours and might be enough. The problem is that you'll have to change the battery when the unit is powered up so you don't lose data if you change it when the unit is unplugged.
You might be better off getting another type of radio that doesn't lose programming at power loss.

 

[Diver300]

I would have expected a radio to take less than 7 mA from the memory wire. This one is < 1 mA:- https://www.kenwood-electronics.co.uk/car/rec/dab/KDC-X7200DAB/?view=details (right at the bottom of the page).

I suspect that the Sailnet page showed a reading when the radio had been turned off using the switch on the front. On a boat, you wouldn't want the radio to only work when the ignition is on, so it would be permanently connected to power.

In a car, or with the radio run from a power supply and a 9 V battery, there are two feeds. One to run the radio, and one to keep the memory going, and when there is no power to run the radio, the memory feed may take less power.

However running the radio's memory from from a 9 V battery may not work. I've not had much recent experience of car stereos, but even 20 years ago they had started to move to taking all their power from the permanent supply, and the ignition feed was only to allow the radio to work and took little current. Any radio that has a timer function that allows it to run for a limited time with the ignition off is likely to take all its power from the permanent supply.

What is the make and model of the radio?

 

[gophert]

I would have expected a radio to take less than 7 mA from the memory wire. This one is < 1 mA:- https://www.kenwood-electronics.co.uk/car/rec/dab/KDC-X7200DAB/?view=details (right at the bottom of the page).

This one has low "dark current consumption" because it is an unusual and, hopefully new trend in car radios - it doesn't have a memory wire. No need, ...

memory w/o back-up power

Yes

And, ...
"This unit will keep the radio presets in memory, even when power of the Back-up power line is disconnected"

Summary, the OP should measure the current draw on his memory wire at 12VDC and check if 9v is enough to keep the memory - some units work down to about 4v while some are quite finicky and start resetting at about 9 to 10v (a typical low point during hard starting on a -30°C morning).

 

[Diver300]

It's not clear how much current that accessories take in the standby mode, so I think that the OP needs to measure his radio.

I've come across a wide range of currents. Some accessories have been really quite bad. Car manufacturers look for <100 uA per module. I've seen a vehicle tracking unit take 60 mA when it wasn't running the phone or the GPS receiver, and a rev counter that took 20 mA to remember what colour the dial should be when the lighting came on.

I guess that the <1 mA for the Kenwood unit is to run the clock, and maybe the power switch is active. Some cars remove power completely from the radio when off. The radio stores the settings in EEPROM and picks up the time on the CANbus when turned back on.

 

[Currymunster]

It's not clear how much current that accessories take in the standby mode, so I think that the OP needs to measure his radio.

I've come across a wide range of currents. Some accessories have been really quite bad. Car manufacturers look for <100 uA per module. I've seen a vehicle tracking unit take 60 mA when it wasn't running the phone or the GPS receiver, and a rev counter that took 20 mA to remember what colour the dial should be when the lighting came on.

I guess that the <1 mA for the Kenwood unit is to run the clock, and maybe the power switch is active. Some cars remove power completely from the radio when off. The radio stores the settings in EEPROM and picks up the time on the CANbus when turned back on.

This one has low "dark current consumption" because it is an unusual and, hopefully new trend in car radios - it doesn't have a memory wire. No need, ...

memory w/o back-up power

Yes

And, ...
"This unit will keep the radio presets in memory, even when power of the Back-up power line is disconnected"

Summary, the OP should measure the current draw on his memory wire at 12VDC and check if 9v is enough to keep the memory - some units work down to about 4v while some are quite finicky and start resetting at about 9 to 10v (a typical low point during hard starting on a -30°C morning).

The memory wire draws about 7mA according to this page..

Stereo Memory Wire Draw - Some Data !

www.sailnet.com

that is quite a bit for a capacitor. Even a 1 or 2 Farad capacitor will last a few hundreds of seconds. (A day is 86400 seconds. You'll also need a fairly beefy battery to supply that each day and hopefully recharge it each day. A 9v battery will last about 70 hours and might be enough. The problem is that you'll have to change the battery when the unit is powered up so you don't lose data if you change it when the unit is unplugged.
You might be better off getting another type of radio that doesn't lose programming at power loss.

I would have expected a radio to take less than 7 mA from the memory wire. This one is < 1 mA:- https://www.kenwood-electronics.co.uk/car/rec/dab/KDC-X7200DAB/?view=details (right at the bottom of the page).

I suspect that the Sailnet page showed a reading when the radio had been turned off using the switch on the front. On a boat, you wouldn't want the radio to only work when the ignition is on, so it would be permanently connected to power.

In a car, or with the radio run from a power supply and a 9 V battery, there are two feeds. One to run the radio, and one to keep the memory going, and when there is no power to run the radio, the memory feed may take less power.

However running the radio's memory from from a 9 V battery may not work. I've not had much recent experience of car stereos, but even 20 years ago they had started to move to taking all their power from the permanent supply, and the ignition feed was only to allow the radio to work and took little current. Any radio that has a timer function that allows it to run for a limited time with the ignition off is likely to take all its power from the permanent supply.

What is the make and model of the radio?

Wow! Thanks every one for your input.
Right, it's not got a make as its a cheap Chinese one from ebay for £15?
It's actually not bad but I only wanted a cheap one as I'm a plasterer.
The intructions don't say anything about what it draws apart from the memory wire says 10v to 13.8v
I really didn't think it would draw that much currant! When I get chance a rig an ammetre up on it to see what it's up to but I think that it sounds like a lot more fuss than I realised just for the sake of a retune each time I plug it in.

 

[Flyback]

what about this kind of thing..as attached

 

[Flyback]

Or there's this one... a little simpler
(actually change the resistor to 100R)

 

[Diver300]

If you connect the ignition input on the radio to the power supply, before the diodes, the radio will turn off when you unplug from the mains.