Help making a Volvo radio test system (Update)

[MrAl]

I watched Robert's as usual helpful video below:

https://www.bing.com/videos/search?q=fi ... &FORM=VIRE

This got me thinking about making up a simple test system to:

1) Power the radio up
2) Allow the radio to stay on long enough to remove the dreaded 'OFF' if CODE set wrongly (I have one unit that does not accept it's code but I think it had a stuck button)
3) To check the functionality of the unit like CD-input and eject functions (especially 3-CD head units), cassette input eject as well as being able check all the bulbs are working.

Maybe down the line I might add a simple speaker function that would allow checking sound output as well as testing the amplifiers.

I have pig-tails from the 2 larger radio connectors.

I have difficulty following Robert's directions as to which wires to connect for power to get the units functional.

I plan to power this from a trickle charger with 2/4A output capability to save buying a 12V power supply. I also have a couple of 2/6A battery charger is more power is needed.

I want to make sure the system is safe for me to use and also safe for any head units attached to it.

This is a winter project but any design guidance is appreciated!!

Many thanks,

Neil.

Hi Neil,

I would be careful about what i used to power it as some battery chargers can put out a much higher voltage when not loaded properly. Some may even put out sqrt(2) times the nominal voltage of 12v, which is 17 volts and could be as high as sqrt(2)*14v which is 19.8 volts, peak.

Regular power supplies are made to hold a constant DC voltage i would think that would be safer.
You can get some on Amazon for a reasonable price, even find a unit that puts out up to 30v at 5 amps for around $60 and for lower amps around $25 USD maybe. That makes sure the radio does not blow out.

I would hate to hear that one of the test radios blew out on you.

[scot850]

Hi Al,

Thanks for the wise advice. I have had issues in the past trying to use chargers for stuff like this. So on the advice of the other guys I have just bought and received this.

https://www.amazon.ca/gp/product/B0991P ... UTF8&psc=1

I looked at a lot, and many had good reviews, but when you looked at the poor reviews it was mostly from more technical minded people and the biggest issue was actually the reverse to the charger warning you made, in that the voltage dropped off once loaded. I also liked the idea that as again advised to use 3A in line fuses, I can also current limit the output to reduce the (highly likely LoL!!) chance I might fry something!!

I have used waterproof automotive fuse holders that will also allow me to alter the fuse value accordingly.

All marvelous advice and I am trying to make it scalable if I decide to add speakers and amplifiers to the test system later so those can also be tested as well as the link cable for the amp. Maybe a bit of sledgehammer to crack a nut, but with old plastics and door panels and the like to be removed to test on my car, I think this is the prudent way forward!

Neil.

[scot850]

I have a question on using this type of power supply. I can set the Voltage level with no load on the unit, but nothing happens when you try to set the current load. Is this because to set current you physically ned to have it connected to something which takes a load and then adjust up to the load you need? Other than the radios, I don't have anything that I can think of that I can power up to test this.

Thanks,

Neil.

[volvolugnut]

Use 12 V lights for a load? Easy to get, cheap, and available in many current ratings. Also very visible indication of working or not.
volvolugnut

[scot850]

Great idea! Thanks,

Neil.

[abscate]

Children’S tongues make great electrical loads

[MrAl]

I have a question on using this type of power supply. I can set the Voltage level with no load on the unit, but nothing happens when you try to set the current load. Is this because to set current you physically ned to have it connected to something which takes a load and then adjust up to the load you need? Other than the radios, I don't have anything that I can think of that I can power up to test this.

Thanks,

Neil.

Hi Neil,

Yes to set the current limit you usually need to have a load connected so that it draws current and then you can turn the knob(s) to lower the current. For example, if you have it set for 10 volts and then you connect a load and it draws 4 amps and you want it set at 3 amps, you adjust the current pots until it goes down to 3 amps and you will see the voltage drop down too. Then later when you connect to an unknown load if it draws 2 amps you still get the full 10 volts out but if it 'tries' to draw 4 amps the voltage will go to a lower value in order to keep the current at a max of 3 amps. So really it lowers the voltage in order to lower the current, but you can not lower the current if there is no current draw yet so you cant adjust the current (except as follows next) unless you have a load.
There are a couple exceptions, and that is if you adjust the current pots to zero or to maximum. At zero you get little if any current so if you connect it to an unknown load the voltage will automatically go very low, and usually you can then turn the current up until you get to the right voltage unless of course it tries to draw more current than you want to see. You may have to set the current at a non zero value though, but something still low, in order to get out of 'foldback' current limit which some units have. Foldback current limit keeps the unit at very low current output until the load is removed entirely. The other exception is if you turn the current pots all the way up then you get max current, and if you want it lower then you can adjust it, but if the load draws more current then you want it's too late to adjust it, so it's best to start out at a lower current and work it up gradually.

An actual application where the voltage and current adjustments have to be just right is when charging an Li-ion battery cell using a power supply like this. You have to start out at a low current setting before you connect the cell, and have the voltage set to exactly 4.20 volts or less with no load. You then connect the depleted cell and turn the current up to the right level, which is given by the manufacturer of the cell. Some cells can only take 500ma but others can take 5 amps so this varies a lot.

One other little thing to think about, and that is the accuracy of the front panel meters. On these power supplies they usually dont put super accurate meters on them and the accuracy varies a lot from unit to unit, so if you need super accurate voltage setting for example you should check the front panel meter with a known good volt meter. The current meter is not as critical.
There is on other issue with the front panel volt meter, and that is if your clip leads (leads from the power supply to the load) are not heavy duty the volt meter will see a higher voltage than is really at the end of the two leads (at the load itself). That means you have to measure the voltage at the load anyway with a decent volt meter. The variation here depends on the quality of the leads and the way they connect to the load.

The foldback current limit can be a problem with heavy loads that the power supply was not made for. If the load tries to draw 15 amps and the power supply max is 10 amps, it may go into foldback current limit which means you dont even get 10 amps out you get zero or very low. This can be a problem for testing some things like the SAS air pump. I found the air pump on my car to draw more than 10 amps so my power supplies cut back to 0 amps so i cant even see if they run slowly without using a little trick. The little trick is to connect a small but non zero resistance in series with the load (like the air pump). This tricks the power supply into thinking there is a load that is not zero (short circuit protection) and so you still get some current out, like possibly the full 10 amps.

I think that about covers it except a power supply like this 30v at 10 amps max is a good buy for around $100. I paid $250 for mine but got a little lucky when i found another second unit for $60 because someone wanted a smaller power supply so was willing to get rid of theirs for a low price.

Oh i almost forgot. You can actually charge your battery with these power supplies but you have to be super careful to get the polarity right. Positive of the power supply goes to positive of the battery and negative to negative of course. If you flip the connections for even a half second, say goodby to the power supply unless you can trouble shoot it.
The way some of them 'protect' against reverse polarity 'live' loads is to use a high current diode in connected in reverse to the output voltage, so cathode to + and anode to minus of the power supply. That way when you connect a reverse polarity live load the diode conducts and helps keep the internal guts from seeing the reverse polarity, which would blow it out quick. That would mean up to four high current transistors and related circuitry get fried. The diode then is supposed to blow out, but blow out in the shorted failure mode. The shorted failure mode means it shunts all the current to ground and prevents any current from getting into the guts of the power supply. The only problem with this is that if the live load is left connected too long, the diode can blow open, and then back to no protection again. One way around this is to use a fuse on the output that you can connect inline. There may be some that have this already you'd have to check with the manual.

Well good luck with it and maybe you can get back here with some test results once you get going, would be interesting to hear about.

[scot850]

My head is spinning now, and my one remaining brain cell is doing somersaults trying to read and understand that information!

I believe I do understand most of what you are trying to educate me on, but it will take time to absorb into the dense matter of my brain!

It will be a lot clearer when I try this for real, I'm sure.

If/when I get this working, I will do my best to update this thread with the successes/failures and hopefully final working outcome!

Many thanks for your help Al.

Neil

[MrAl]

My head is spinning now, and my one remaining brain cell is doing somersaults trying to read and understand that information!

I believe I do understand most of what you are trying to educate me on, but it will take time to absorb into the dense matter of my brain!

It will be a lot clearer when I try this for real, I'm sure.

If/when I get this working, I will do my best to update this thread with the successes/failures and hopefully final working outcome!

Many thanks for your help Al.

Neil

Hi Neil,

You're welcome, but i guess i should have mentioned also that many things just simply 'run' on voltage and you dont worry about the current. Light bulbs, toasters, vacuum cleaners, computers, and of course radios. Any current limit is there mostly for the protection of the power supply or if there is something wrong with the load connected to it that would make it draw more current and literally burn up.
So in most cases when you power a radio or anything else on 12v with a power supply it's either going to run fine or it wont run at all or just have some minor problem with it. So it's actually much simpler than all that unless you want to do something else with the power supply like charge a battery or power an LED directly. Raw LED's are a special case because they run best when supplied with the right current rather than the right voltage. You set the current and let the voltage be what it will be, unlike a radio or light bulb where you set the right voltage and let the current be what it will be.
Hope that helps

[abscate]

There are three variables at play

Water. Electricity

Pressure or voltage
Flow or current
Restriction or resistance

You can only adjust two, and then the third is determined by Ohms law

Pressure = flow times resistance

Usuallly the resistance is fixed by the load so once you put a voltage on it from a battery , the current then flows.