Memory Wire for in home headunit

Thread Starter

John Deere

Joined Mar 19, 2016
14
Hi everyone, newbie here.

I have a car head unit wired into an old Computer PSU and it really works well except for the memory wire.
Have made the psu switchable instead of having to turn it off at the wall all the time as each night when I leave my workshop I dont want to have it running all night.
When I switch the psu off using the switch the psu goes into standby but the memory of the headunit is not retained due to both the power and memory wires plugging into the same 12v supply.
I have found a 5v 1.5amp standby supply that stays on when the psu is in standby, my question is could I plug memory wire into the 5v supply and have the memory on the headunit retained or would there not be enough amps or volts?
Cheers Reuben
 

blocco a spirale

Joined Jun 18, 2008
1,546
Try it, it won't do any damage but I suspect that 5V is too low. If the current draw on the memory wire is low enough, it may be practical to use a battery to back it up. If you have a multimeter, measure the current draw.
 
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Thread Starter

John Deere

Joined Mar 19, 2016
14
Hi Blocco, thank you for your reply.
When you say "If you have a multimeter, measure the current draw." What do I measure and how, yes I have a multimeter.

Cheers Reuben.
 

Pencil

Joined Dec 8, 2009
271
What multimeter do you have?
Post a picture of the meter or state the brand
and model number and we'll see if we can give
some specific instructions.
 

blocco a spirale

Joined Jun 18, 2008
1,546
Hi Blocco, thank you for your reply.
When you say "If you have a multimeter, measure the current draw." What do I measure and how, yes I have a multimeter.

Cheers Reuben.
Set the meter's dial to the lowest DC current range and connect the leads in series with the memory wire i.e. disconnect the memory wire from the 12V power supply and connect the red meter lead to +12V and the black meter lead to the memory wire feeding the radio. Don't connect the feed that actually powers the radio as this may affect the reading.

Hopefully, you will see a very small number. You may need to select a different current range in order to get a useful reading.

Remember: When the meter is set up to measure current, don't connect the meter across the output of the power-supply as you would if you were measuring voltage.
 

Thread Starter

John Deere

Joined Mar 19, 2016
14
Hi.
Have done as you asked and I get a reading of 0.66, is this amps?
Multimeter is a medalist DT-830B, hope this helps. Was just a cheapy from the local store lol.
Now when I tested the current I set the meter to 20m DCA and put the red lead on 10A on the meter, is this correct?

Thanks so much for your help so far, Reuben.
 

blocco a spirale

Joined Jun 18, 2008
1,546
Hi.
Have done as you asked and I get a reading of 0.66, is this amps?
Multimeter is a medalist DT-830B, hope this helps. Was just a cheapy from the local store lol.
Now when I tested the current I set the meter to 20m DCA and put the red lead on 10A on the meter, is this correct?

Thanks so much for your help so far, Reuben.
The 10A socket is usually only for measuring large currents (up to 10A), for small currents in the mA range I would expect the red lead to be in the same socket that's used for measuring voltage and resistance etc.
 

Thread Starter

John Deere

Joined Mar 19, 2016
14
ok have uploaded A photo of what i have done......
the red cable from meter goes into 12v power source from psu.
the black cable goes into red wire from stereo.
and as you can see yellow wire from stereo is unplugged.
Thats the reading i get.
am i doing it wrong?

WP_20160320_002_1024x576.jpg
 

blocco a spirale

Joined Jun 18, 2008
1,546
That's correct, the current draw is 4.37mA.

4.37mA isn't much but it's probably too much for a practical non-rechargeable battery back-up battery solution. A 1Ah battery would last, very approximately, 1000/4.37 = 229 hours = 9.5 days.

So, we've gone round in a circle but it could have proved useful, at least we know how much current is needed. Your original plan to use a small, low power PSU is viable but it should have a 12V output.
 

Thread Starter

John Deere

Joined Mar 19, 2016
14
Geez I'd love to have your brain lol.
ok thank you.
So when you say it should have a 12v output are you when the psu is in Stand by?
I've also uploaded a couple of photos of two PSU's.
WP_20160320_003_1024x576.jpg

WP_20160320_005_1024x576.jpg

The smaller one is running the head unit now and the larger one I maybe have for spare or perhaps and amp, not sure yet.
Cheers Reuben.
 

Thread Starter

John Deere

Joined Mar 19, 2016
14
Hi Blocco,
My DC to DC booster didnt work.
I have the constant 12v wire connected into the booster which is being supplied power from the 5v 2amp stand by feed and the switched wire connected to the 12v feed from the psu, as soon as you try to turn the radio up the radio cuts out. It retains memory but im thinking that there is not enough amps coming out of the 5v feed.

If you swap the constant and switched wires around it wont retain memory but you can get any volume you like with out it cutting out.

What am I doing wrong or is just the fact that the booster only gives you more volts but the amps still stay the same?

the booster I got is this one....
DC Voltage converter Down/Up Buck Boost -Voltmeter

NOTE: This module is step-up and step-down converter and has an onboard voltage display. The performance is more than LM2596 and LM2577.
Data Indicators:
In+: Input positive
In-: Input negative
Out+: Output positive
Out-: Output negative
Size: 47x41x16 (length*width*height)(mm)
Weight: 23g
Display Color Blue
Input voltage: 5.0-25.0V
LED Indicator : YES
Output voltage: 0.5-25V(Adjustable)
IN/OUT Power : 25W(MAX)
Input current: Rated current MAX 2A
Output current: Rated current MAX 2A
S1 : Choose and remember the output state
OFF/ON: Control the output state335284435.jpg
 
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