suggestions for a temporary "clean" 12v feed at home

[Minerva]

This winter, one of my pet projects is building a Raspberry Pi with open plotter to replace my aging Windows tablet on the boat.

I've got it mostly there, but one item I can't yet get set up is the Weatherfax; the mains to 12v dc adaptor I have is too "noisy" for the weather fax.

I don't have spare leisure battery at home and as my set up is in my pottering shed at the back of the garden, it's too far to run some hot-wires from the car battery. Any suggestions, short of buying a new leisure 12v battery or taking one from the boat (6 hour round trip)?

It's a Nasa Target SSB so very low demand with power consumption 300mA @12v

The obvious answer is to leave it 'til the spring and set it up on the boat, but then time demands will be on Antifouling and recommissioning, not playing with gadgets... It's been quite fun getting an Arduino heading sensor, a spare NMEA mast head wind instrument wired in and the AIS info, and remote display to multiple devices all working nicely so far next to the heater in my shed.

I'm almost tempted to buy a Radar scanner to add in too!

 

[Caladh]

Something like this ? https://cpc.farnell.com/pro-elec/pe...MI7vG99f3FgwMViYuDBx0rCg2KEAQYCCABEgIO-PD_BwE

 

[Minerva]

Something like this ? https://cpc.farnell.com/pro-elec/pel00848/ac-dc-psu-12v-2a-2-1mm-dc-plug/dp/PW04264?mckv=s_dc|pcrid|224680288544|kword||match||plid||slid||product|PW04264|pgrid|48556615353|ptaid|pla-886327310628|&CMP=KNC-GUK-CPC-SHOPPING-945655906-48556615353-PW04264&s_kwcid=AL!5616!3!224680288544!!!network}!886327310628!&gclid=EAIaIQobChMI7vG99f3FgwMViYuDBx0rCg2KEAQYCCABEgIO-PD_BwE

It's one of those I'm using just now - from an old router or something.

 

[rogerthebodger]

Try fitting some high microfarad minimum 20 Vdc Electrolytic Capacitor, in between the power supply and the device you are powering

This will smooth the voltage output
https://cpc.farnell.com/multicomp/m...ial-5mm/dp/CA08146?st=electrolitic capacitors

 

[Minerva]

is it the voltage fluctuations that make the connection noisy and introduce the static into the Weatherfax signal?

 

[rogerthebodger]

is it the voltage fluctuations that make the connection noisy and introduce the static into the Weatherfax signal?

Yes

An Electrolytic Capacitor, will smooth any voltage fluctuation and noise from the power supply.

The higher the microfarad rating will more voltage fluctuations will be smoothed.

I had interference on my VHF radio from a PWM solar regulator and 2 100 mF caps eliminated the interference on my VHF

 

[Alex_Blackwood]

Try fitting some high microfarad minimum 20 Vdc Electrolytic Capacitor, in between the power supply and the device you are powering

This will smooth the voltage output
https://cpc.farnell.com/multicomp/mcumr35v475m4x5/capacitor-4-7uf-35v-radial-5mm/dp/CA08146?st=electrolitic capacitors

If trying this, the capacitor should be in parallel with the load and if an electrolytic capacitor is used you must ensure that the correct polarity is observed. Otherwise it goes "POP"

 

[Minerva]

Brilliant. So this is new to me, so please forgive the daftie questions; do I just buy a capacitor and put it inline with the power feed - i.e positive feed from the transformer in one leg and out the other to the SSB radio?

I presume a breadboard with a suitable box with two sockets either side for power in/out would be just the ticket?

 

[RAI]

I still have a working NASA CRT Navtex. It is sensitive to noise. I found the capacitor noise suppression only partially effective. Another battery works best.

 

[rogerthebodger]

Brilliant. So this is new to me, so please forgive the daftie questions; do I just buy a capacitor and put it inline with the power feed - i.e positive feed from the transformer in one leg and out the other to the SSB radio?

I presume a breadboard with a suitable box with two sockets either side for power in/out would be just the ticket?

No

The positive of the Cap goes to the positive output form the power supply and the other lead minus goes to the negative lead from the power supply.

As Alex said its in parallel with the power supply output the positive then goes to the plus of the equipment you are powering and the negative goes to the negative of the equipment you are powering

 

[William_H]

Almost all power supplies now days use switch mode technology. Where 250vAC is rectified to about 340v dc which is rapidly switched ina small transformer to create low voltage high frequency AC which is then rectified to make 12v dc. The beauty of this is that a sampling and feedback mechanism ensures exact 12vdc output. The output will have an electrolytic capacitor connected inside.
If the interference to radio receiver is coming down the output line as intimated above. Then yes an electrolytic capacitor connected across the output may help. The capacitor acts like a low capacity battery. However an electrolytic capacitor has internal inductance such that it may not soak up all the high frequency variations. It is usual to fit a small ceramic capacitor like 1000pfd (that is .001 microfarrad) https://www.jaycar.com.au/100nf-50v...os=4&queryId=4e2e6cb2305f55e30d460f83ab1f1ecd also across the output lines. Keep leads as short as possible.
An improvement on this is to add inductance in series with the output positive line. This can be made by winding coils of wire around a ferrite rod or better a torroid. The wire needs to be heavy enough to carry the output current but as many turns as possible. (like 20 turns). The coil goes before the capacitors. Or have 2 lots of capacitors before and after coil.
As RAI suggested interference to a radio is not always coming down the power supply line. It can in fact radiate from the power supply itself or even back through mains wiring. A battery then becomes one option.
Back in the old days power supplies had a 50 hertz transformer inside. You may still be able to find one that delivers 12vdc at 300ma. It will be characterised by being noticeably heavier than the modern switch mode style. Unfortunately they have a some what unregulated output voltage so may produce 14.5 volts with no load and barely 12v under full load. This may be OK. You need to check.
Or you could make one up from components, https://www.jaycar.com.au/6-3-15v-1...os=1&queryId=ab0621097cc0f2cccdcfa6f0a6a7ba8d plus a bridge rectifier https://www.jaycar.com.au/2a-600v-i...os=3&queryId=874eb244966f1584b51b2367d3eac1a3 plus electrrolytic capacitor https://www.jaycar.com.au/2200uf-25...os=5&queryId=49d020e041c1917f9e23df7cc33b86d3. (You will need a linear regulator as below.)
You may have a very old battery charger also with transformer. Which perhaps could be used.
If the output voltage is higher than needed like 15+ volts DC you can fit a regulator integrated circuit. 7812 is the key number. https://www.jaycar.com.au/7812-12v-...os=1&queryId=f1223618e86339f8060be3fd487f1979 this is connected between the positive supply output and the radio with a negative connection. It should be mounted on some aluminium for a heat sink. NB the mount is live.
This old style regulator is called a linear regulator and along with a 50 hertz transformer and rectifier is completely noise free. May be the only option to a battery.
From your question on electrolytic capacitor connection may be the linear regulator is beyond your skill. PM me if you want help. ol'will

 

[wonkywinch]

MyDEL MP-705 8 Amp Linear PSU for £35 or something cheaper like this enclosed 12V PSU for £13 - https://cpc.farnell.com/mean-well/rs-15-12/power-supply-ac-dc-12v-1-3a/dp/PW05300

Those "wall warts" are cheap and cheerful and can be quite noisy electrically as the devices they power usually have additional voltage protection and supply smoothing components inside them.

 

[Ardenfour]

No. Smoothing cap connects across the supply lines, ie, in parallel. Pos to pos, neg to 0v.

 

[Alex_Blackwood]

Just to keep it simple. Remember polarity is important with electrolytic capacitors. Capacitor can go anywhere in the DC line, preferably as close as possible to the unit being supplied.

 

[Refueler]

I have a couple of high power HP Computer PSU's .... providing clean regulated 12v and 5v to workshop gear.

Loads on eBay .... all you have to do is jump a couple of pins to trigger the unit to power up and away you go ... plenty of online info on doing it.

Or just buy a sufficient wattage PSU on eBay designed to power LED systems etc. They are smoothed and clean ...

Just a ?? 300mA @ 12v .... that's very low demand ... on Receive ?? What about Transmit or is it just Rcvr ??

 

[Alex_Blackwood]

I have a couple of high power HP Computer PSU's .... providing clean regulated 12v and 5v to workshop gear.

Loads on eBay .... all you have to do is jump a couple of pins to trigger the unit to power up and away you go ... plenty of online info on doing it.

Or just buy a sufficient wattage PSU on eBay designed to power LED systems etc. They are smoothed and clean ...

Just a ?? 300mA @ 12v .... that's very low demand ... on Receive ?? What about Transmit or is it just Rcvr ??

I think, with all due respect, the OP wants a simple quick fix, not a major engineering project, dodgy videos and lessons in electrical engineering theory

 

[jwilson]

How about a small 12v 2AH to 4 AH lead acid battery as used in some burgar alarms etc. £10-15 and readily available.

 

[wonkywinch]

How about a small 12v 2AH to 4 AH lead acid battery as used in some burgar alarms etc. £10-15 and readily available.

Plus then another £x for the associated charger.

 

[Refueler]

I think, with all due respect, the OP wants a simple quick fix, not a major engineering project, dodgy videos and lessons in electrical engineering theory

That is a silly reply to be honest ....

The setup is so simple you don't need lessons in anything ... just connect pin x .. pin b .. its no major project.

I bought two of these :

HP Power Supply / Netzteil HSTNS-PA01 337867-001 406421-001 1300W | eBay

Maybe an idea to actually check out something before condemning ??? Maybe you'll be surprised ..

 

[CliveF]

You wont be needind much power to run that. Get a model aircraft power lipo from the likes of Hobby king.

some 12v 2200mAh batteries are on sale at the moment for about £6 - 7