Magnadyne DC-12 power supply question

[graywoulf]

I have an old Magnadyne DC-12 power supply that is rated at 12VDC at 4 amps and I just plugged it in for the first time in years but when I checked the output voltage, it reads at 18VDC. Is this a normal reading with no load on it or does this present a problem? I want to use it to power a couple of mobile CB radios but not until I find out if it is safe to do so. Thanks for any and all advice on this.

 

[SteveSimpkin]

That sounds like either an unregulated transformer-based power supply or a regulated supply that has damaged regulator circuitry. What is the model number?

Ideally you would want to use a regulated power supply that always puts out a constant 13.8 Volts when it is loaded or not. A regulated 12V supply would be OK too. Make sure the current ratting is enough to run all of the devices you plan to power with it. Most CB radios draw around 1.5A when transmitting so a 3-4A supply would be fine for your application.

Consumer electronic devices designed to run off of a car's 12V power source (13.8V when the engine is running) aren't usually designed to withstand more than 16V.

 

[graywoulf]

Hi Steve and thank you for your information. DC-12 is the only model number I see on the unit. I found one like it on eBay but I cannot find any other information on these anywhere on the internet. I think that it has seen better days myself and I would not trust it to power my radios. I was wondering about using an old desktop PC power supply in place of it as I have a spare one available. Does that sound like a good option?

 

[SteveSimpkin]

Graywoulf,

A PC power supply may not be the best solution for this application. Depending on the supply, they may require a minimum current load on several of the outputs, may require additional wiring to fool the power supply into thinking there is a motherboard present so they will turn on and are often electrically noisy.

You would probably be better off using something like the following inexpensive power supplies.

https://www.amazon.com/Schumacher-P...TF8&qid=1541184326&sr=1-1&keywords=B0012BL8LG

https://www.amazon.com/Pyramid-Benc...&ie=UTF8&qid=1541184251&sr=1-1&keywords=PS8KX

 

[graywoulf]

Thanks Steve for your help. I think I will go with the Schumacher brand. I found one on eBay for less than Amazon's price plus shipping. And since my Realistic_TRC-465 CB radio already has the lighter plug wired in, it is a perfect match. I am surprised to hear you say what you did about using a PC power supply though. I have a set of plans on how to convert one to a multi voltage benchtop power supply. And you are right in that a connection is necessary to trigger the power supply on. But the other option is easier at this point. Thanks again for your help and suggestions.

 

[DJ11DLN]

Late to the party here but I'm glad to see that you decided to get a good supply. I've been out of CB for decades but I still remember the anguish when a cheap 3A power supply lost its regulator and fried my pet Cobra 29 in about 1980. Taught me that power supplies weren't a good place to save pennies.

 

[graywoulf]

Late to the party here but I'm glad to see that you decided to get a good supply. I've been out of CB for decades but I still remember the anguish when a cheap 3A power supply lost its regulator and fried my pet Cobra 29 in about 1980. Taught me that power supplies weren't a good place to save pennies.

You are absolutely right about not pinching pennies on a power supply. I am just glad that I thought to check the old Magnadyne out before I hooked it up to my TRC-465 radio. I am sure that it was a good product in it's day though. It had belonged to my late father in law who was a trucker for nearly fifty years.and was in his workshop along with his Cobra 29 WX NW ST CB Radio. I just hope that the radio is OK but I will not know until I get the new power supply. I actually found the Schumacher PC-6 power supply at Walmart for $15.99 but I had to order it. It was a free pick-up item too.

 

[jassing]

Some cheap power supplies put out more volts than they are rated for -- but once you put a load on it, the voltage drops. So I would find something (like a light bulb) and hook that up, then measure the voltage...

 

[graywoulf]

Some cheap power supplies put out more volts than they are rated for -- but once you put a load on it, the voltage drops. So I would find something (like a light bulb) and hook that up, then measure the voltage...

Thank you very much for that suggestion. I will give that a try.

 

[DJ11DLN]

You are absolutely right about not pinching pennies on a power supply. I am just glad that I thought to check the old Magnadyne out before I hooked it up to my TRC-465 radio. I am sure that it was a good product in it's day though. It had belonged to my late father in law who was a trucker for nearly fifty years.and was in his workshop along with his Cobra 29 WX NW ST CB Radio. I just hope that the radio is OK but I will not know until I get the new power supply. I actually found the Schumacher PC-6 power supply at Walmart for $15.99 but I had to order it. It was a free pick-up item too.

Also you might pull the cover off of that 465 and check for deteriorated electrolytic caps if you haven't already done it. Be a shame to waste a good old radio because of some failed parts that would be cheap and probably fairly easy to replace.

 

[graywoulf]

Also you might pull the cover off of that 465 and check for deteriorated electrolytic caps if you haven't already done it. Be a shame to waste a good old radio because of some failed parts that would be cheap and probably fairly easy to replace.

Thanks for the suggestion but actually, my 465 is in perfect working order. I bought in on eBay a while back and it even had a Realistic powered mic that came with it. I am experienced with tech repair but I would not know what to look for as far as looking for deteriorated caps anyway.

 

[DJ11DLN]

Thanks for the suggestion but actually, my 465 is in perfect working order. I bought in on eBay a while back and it even had a Realistic powered mic that came with it. I am experienced with tech repair but I would not know what to look for as far as looking for deteriorated caps anyway.

Goo seeping out of them onto the board and surrounding components is usually the telltale. It may look like hot glue but tends to remain in a semi-liquid or gel state rather than solid. A lot of equipment has died from these. It can even be NOS, they don't have to be powered to give up the ghost, it is a "time" issue vs actual wear.

I'm glad it's working for you and I wish you much enjoyment with it. I sometimes miss the days of CB, I had a lot of fun with it before 11M turned into such a cesspool in the mid-late '80s and beyond.. Maybe one of these days I'll give it another try.

 

[graywoulf]

Goo seeping out of them onto the board and surrounding components is usually the telltale. It may look like hot glue but tends to remain in a semi-liquid or gel state rather than solid. A lot of equipment has died from these. It can even be NOS, they don't have to be powered to give up the ghost, it is a "time" issue vs actual wear.

Thank you for that tutorial. I will open it up to see what is happening with it. 👍