RFI quiet 24v-12v DC-DC converter recommendations

[K8MEJ]

Apologies if this isn't the right sub-forum for this question. I'm new here.

I'm planning for an off-grid solar + LiFePO4 + inverter/charger system for my travel trailer with the new system running a nominal 24v. To power my existing 12v accessories (tongue jack, electric brakes breakaway system, 12v accessories running from existing DC fuse block) with a 24v-12v DC-DC step down converter. I am a ham radio operator that likes to operate when I go camping myself or when performing STEM demonstrations for Scout events. Consequently, I need to build a system that generates as little radio frequency interference as possible. That's challenging when you consider that the charger & inverter circuitry are both switch-mode power converters and so is a DC-DC converter. All switch-mode power supplies generate a lot of harmonics that create havoc on the HF ham bands. There are FCC Part 15(b) Class B certified, which are supposed to be well filtered to limit the amount of RFI generated. Based on this, I have two questions for the collective intelligence here:

1. Does anyone know of a 24v-12v DC-DC converter that is well filtered for RFI? I can't find anything in the 40-60amp range that holds an FCC Part 15(b) Class B certification. If you have experience with a DC-DC converter that is RFI quiet please let me know.

2. If I build such a system, is there any concern with the low-current 12v power supply coming in to the camper from the tow vehicle via the 7-pin connector? In other words, can the 24v-12v converter handle another 12v power source on the 12v side of the converter?

Thank you in advance,
Ed Jones

P.S. The Xantrex Freedom SW 3024 is the inverter/charger I plan to use because it carries the FCC certification. I am planning to use one or two Morningstar ProStar MPPT 40amp solar charge controllers because they also carry the FCC certification and I have found several discussions where hams say they are RFI quiet. I can't find any solid ham-friendly advice on inverter/chargers. I'd love to use Victron everything, but their MPPT SCC's are known to generate a ton of RFI junk. Their Multi-Plus inverter/chargers hold no FCC listings and I can't find any evidence they are RFI quiet or not.

 

[HaldorEE]

The Victron Orion-TR meets emmisions EN 61000-6-3 and EN 55014-1. Problem is the data sheet doesn't mention if it is CISPR Class A or Class B (comparable to FCC Class A or Class B). There is a big difference between classes (about 10dB).

https://www.victronenergy.com/upload/documents/Datasheet-Orion-Tr-DC-DC-converters-low-power,-non-isolated-EN.pdf

Understanding CISPR 22: EN 55022 EMC Standard » Electronics Notes

Understand the concepts, measurements and tests for CISPR 22, EN 55022 standard for EMC for information technology equipment with comparison to FCC Part 15.

www.electronics-notes.com

Neither does the manual. Curious.

https://www.victronenergy.com/upload/documents/Orion-Tr_Smart_DC-DC_Charger_Isolated/Orion-Tr_Smart_DC-DC_Charger_Isolated-en.pdf

Even more surprising is that this is not listed on the certificate of conformity. Have regulations changed? I recall this being something you had to disclose.

https://www.victronenergy.com.es/upload/documents/Orion-Tr-Smart-2020-12-15.pdf

It must be because these are specified as being vehicular. This is RF emissions spec from the certificate of conformity. The actual standard is behind a paywall.

UNECE Regulation 10: Vehicle Radiated Emissions & Immunity Testing (Annexes 4, 5 and 6) | Interference Technology

Having dealt with the administrative side of Type Approval to UNECE Regulation 10, Revision 5, Amendment 1 (8 October 2016), hereafter referenced as R10.05, in the first three blogs in this series, this installment begins looking at the tests themselves […]

interferencetechnology.com

 

[HaldorEE]

Worse come to worse, you could mount the DC-DC converter inside a shielded metallic enclosure and put ferrites on the wiring in and out. That can knock some of the emissions down. Only concern there is cooling. A metal mesh over cooling vents will permit air flow while still maintain RF shielding.

What frequency bands are you most concerned about?

I design equipment that has to pass FCC and CISPR requirements and have spent more hours at the compliance lab, than I really want to remember. I might have some ideas of what to do to fix emissions problems.

 

[K8MEJ]

Hi HaldorEE. Thanks for your reply. I appreciate the lesson in European emission standards. I can add those to my list when searching for components. I'm hardly an expert on these things, but they seem to get away with poor emissions by declaring them for industrial or vehicular use. What is frustrating is all the electronic junk being sold that don't conform to FCC Part 15(b) Class B devices used in and around residential settings. RFI on the HF bands are already largely useless in the cities, and getting worse every year in the suburbs and exurbs.

I'm most interested in in the frequencies between 3.7MHz to 14.3MHz when operating from my RV.

My goal is to source gear that will cause little RFI so additional shielding and choking measures won't be extensive. I already plan to put ferrite on the outputs of all SPS devices and both sides of the long wire runs from the PV panels (both near the panel and near the SCC). Those long wire runs make for good receiving antennas for hash!

The vast majority of people interested in off-grid or grid-tie solar systems aren't bothered by the interference and hence don't really care or are even aware of it. So, I'm having a heckuva time trying to find practical experience. Of course, once I put my money down on components and then test them, I'll know the answers and can write about them.

I have thought about using hardware cloth or some other small aperture metal fencing to completely line the inside of the storage area under the queen bed, with copper braid connecting the box area with the hardware cloth stapled to the bottom of the bed platform that lifts up. But I really don't want to bother with all that.

Ultimately, I guess I have to decide if I just want to deal with the wire size of a 12v system vs a 24v system and a DC-DC converter.

Thanks again.

 

[JoeHam]

IMHO you’re not going to find something RF quiet regardless of certification. Plan to choke everything.

Mix 31 material will likely be best for 80m - 20m. See here:

Materials - Fair-Rite

Material Data Sheets Tabs Here

www.fair-rite.com

My suggestion would be to use a dedicated 12v battery for the radio to avoid buck converters altogether and try not to run any chargers while on the air.

I picked up a Miady 16 Ah LiFePO4 on Amazon for $50. My 60Ah Bioenno cost more than 10x that about 6 years ago but they both serve the purpose.

73,

W8JH

 

[K8MEJ]

IMHO you’re not going to find something RF quiet regardless of certification. Plan to choke everything.

Mix 31 material will likely be best for 80m - 20m. See here:

Materials - Fair-Rite

Material Data Sheets Tabs Here

www.fair-rite.com

My suggestion would be to use a dedicated 12v battery for the radio to avoid buck converters altogether and try not to run any chargers while on the air.

I picked up a Miady 16 Ah LiFePO4 on Amazon for $50. My 60Ah Bioenno cost more than 10x that about 6 years ago but they both serve the purpose.

73,

W8JH

I have a pile of 2.4" mix 31 torroids for this very reason. I have a bunch of split beads, as well.

I'm not expecting total RFI quiet, but I want to minimize it as much as possible. Right now, just the crappy Progressive Dynamics 12v converter I installed to replace the WFCO one has to be turned off so I can operate within 100' of my camper. I can't solve the problem of all the other crappy converters around me in a campground or RV park, but I can try to reduce the amount I generate so I don't have to turn my solar chargers and inverters off when I want to operate from my camper.

I have a 20Ah Bioenno battery that I often use when casually operating portable. When I want to casually operate from a camp spot when I'm with my family and definitely during two main events per year (Field Day and the Ohio QSO Party), I don't want to have to shut my power in the camper down just to operate. During the QSO party, I usually am somewhere with shore power and I can run everything off pedestal AC, including a PSU in the radio case. But Field Day and boondocking means I'd have to shut down the solar system and buck converters. What a PITA.

I had thought about keeping a separate 12v system but I'd need a DC-DC charger, which is just another switch-mode PSU.

Just wait until our neighbors start installing roof-top solar in the next 10 years. Suddenly all hams that live in neighborhoods are going to have the same problem I'm working on now.

Thanks

 

[JoeHam]

With toroids it should definitely be good enough.

I do Field Day from Middle Bass on battery with a ton of noisy stuff all around the Marina with no problems on my KX3.

See you in the QSO party, I’m usually the only one on from Ottawa county and I see you in the log from 2018 and 2020.

 

[K8MEJ]

I usually pick a county that has few, if any, activations. Last year it was Morrow County at Mt Gilead State Park. I usually add a couple of extra days for DXing and general playing radio. This year I was contemplating boondocking at AEP Recreation Land / Jessie Owen State Park. That's going to depend on how my off-grid solar system works Sometimes I even bring my KPA500/KAT500 for some QRO fun when I'm camping somewhere for more than a few days.

"Portable operating" for me is better described as luggable!

 

[JoeHam]

I usually pick a county that has few, if any, activations. Last year it was Morrow County at Mt Gilead State Park. I usually add a couple of extra days for DXing and general playing radio. This year I was contemplating boondocking at AEP Recreation Land / Jessie Owen State Park. That's going to depend on how my off-grid solar system works Sometimes I even bring my KPA500/KAT500 for some QRO fun when I'm camping somewhere for more than a few days.

"Portable operating" for me is better described as luggable!

Well I run an off grid solar powered KPA500 station at times as well.

48v LiFePO4 battery to a cheap 3kw inverter with grounding and judicious use of ferrites so it can be done.

 

[K8MEJ]

Well I run an off grid solar powered KPA500 station at times as well.

48v LiFePO4 battery to a cheap 3kw inverter with grounding and judicious use of ferrites so it can be done.

Well that's encouraging! I'm just a couple of hours South of you. Maybe some day I can show you my handiwork. If I get this all to work with a reasonable amount of RFI, I plan to write up an article so someone else might not have to spend so much time thinking about all of this.

There is a Victron dealer over in Mount Vernon. I'm going to see if they have a Multi-Plus II 3000 they can hook up so I can see how much a portable AM radio freaks out when they turn it on. If they have an Orion DC-DC converter I could try that, too. The only definitive info I've seen on the web is that the Victron MPPT SCC will wipe out all the HF bands.

 

[JoeHam]

Please post a link to the Victron MPPT RFI information.

I have one permanently mounted 12 ft from my K3s in the basement. Between it and the Schneider CSW 4048 inverter I definitely get some RFI but my life goes on. I operate 160m - 70cm with different amounts of RFI per band. The scope on FT8 helps see the noise.

Been deer hunting in Knox and Licking county for a few decades and never knew there was a solar power place in Mt. Vernon.

You learn something new every day if you’re not careful ?.

 

[K8MEJ]

I'll see if I can find the links. It's been about two months since I last read them. Your experience is very different from what I read. Is most of your operating via FT8? Most of mine is SSB.

I was wrong about the place in Mt Vernon. It's Newark actually. Here's a link: https://www.boundless-ps.com

They focus on RV off-grid power. Their website shows a demonstration board with a Multi-Plus, MPPT, etc. It might be worth the drive just to see how noisy things are.

 

[JoeHam]

Mostly CW with some FT8 and SSB but the FT8 screen is a poor mans RFI scope!

The solar place looks like Mt Vernon, just past walmart when heading out of town towards Apple Valley. I must’ve driven past it 20 times without noticing.

 

[Norm]

I've been on a search to try to find put together a quiet (RFI/EMI) off grid solar system. So far, the only quiet charge controller I've come across is the Morningstar TriStar PWM controllers. There may be other PWM controllers that are also quiet, but I can tell you the TriStar TS-60 PWM is quiet as a mouse.

The big problem with PWM is that I'm forced to use 12v panels for a 12v battery system. The main advantage of a MPPT is that it would allow me to use regular house panels 37-60v to charge a 12v or 24v battery bank. That is a huge advantage because the larger panels are much much less expensive and more plentiful than the 12v panels.

Everything I've read so far indicates that ALL MPPT charge controllers are RFI/EMI noise generators and it is almost impossible to quiet them down. The noise travels everywhere there are cables, even to the panels and the panels even radiate the noise.

Now to DC to DC converters. Everything I've read indicates the converters are noise generators as well and almost impossible to quiet down. It is just the nature of the high voltage switching. This is completely different from the switching power supplies converting 120v AC to 12v DC. Most switching power supplies are very quiet.

There are several folks in various forums that have asked about CC or Converter noise (RFI/EMI). Unfortunately, 98% of the people that answer these give terrible advise based upon articles they have read regarding toroids, building filters, twisting wires etc, etc. Its been nearly impossible for me to find people that actually state EXACTLY what equipment they are using, EXACTLY what if anything they've done to mitigate RFI and what bands of operation (HF) they use. Nearly all of the information I've come across is worthless or in some cases actually outright WRONG.

Anyway. All I can say so far is that the PWM charge controllers and the TS-60 in particular is very very quiet. Now all I need to do is find a 3000w inverter that is also quiet or see EXACTLY what someone has done to mitigate the noise. Pictures would be great.

To the original poster: Have your found any good information regarding DC to DC converters? How about quiet Inverters in the 3000w range? I don't need to run AC but would like to have the Microwave and a couple other items that can run off of the inverter.

 

[K8MEJ]

I've been on a search to try to find put together a quiet (RFI/EMI) off grid solar system......

Hi Norm. For RFI quiet MPPT controllers you can also look here: http://diysolarforu.com . Note, despite the URL being very close to the one for this forum, they are not the same thing. The guy at DIYSolarForU is a retired engineer and a ham. I spoke with he and his wife for about 40 minutes one evening. Lovely people. He claims to have the quietest and most efficient MPPT controller on the market. I've heard great things about the MorningStar Tri-Star MPPT controller, too. It's supposed to be pretty quiet.

In the end, this is what I what I went with: Victron MultiPlus 12/3000/120 inverter/charger, Victron SmartSolar MPPT controllers (still sizing this part of my system), and no DC-DC converters. I have a Victron dealer (http://boundless-ps.com) about an hour from my house and the owner is really cool. He has a demo system in his shop and he added a DC-DC converter temporarily for me. I brought a portable LW/MW/HF radio with a ferrite rod antenna inside (more directional) and indeed did notice quite a bit of trash coming from the inverter and just a little from the MPPT and DC-DC controllers. All were very lightly loaded, however. The noise was primarily radiating from the wiring going in/out of the devices. Moving the radio just a foot away reduced most of the noise substantially. Given this, I figured I could clean up the noise.

I haven't installed any of my gear yet, but I'm going to start soon. My plan is to mount everything inside a box made from 3/4" poplar plywood, including a 3/4" plywood hinged lid. I'll build it all in my garage and do some testing to see how badly it radiates noise. I can make relative dBm measurements with a spectrum analyzer and also see how bad the noise is in my home QTH. I have a Flex-6400 radio, also with an excellent spectrum analyzer. If the noise is enough to bother me, then I plan to paint the outside of the plywood box with MG Chemicals silver-plated copper conductive paint. This stuff is made specifically to mitigate RFI. My thinking is I'll build a faraday cage around all the switching components. I'll use copper foil tape along the corners and top lip of the box and lid, then spray paint. I'll use metalized EMI gasket from Parker Hannifin so there is an electrically Any wires going into and out of the box will be choked on both ends with mix-31 torroidal ferrites. I will probably use MC cable for the AC lines going in and out (bonded to the box) and I might put the DC cables in EMT with cable sized appropriately for being encased in the EMT (trapped heat derates the wire gauge size).

I'll test this in the garage with the spectrum analyzer as well and make measurements and then compare the before and after. All the wiring for the solar panels will also be choked with mix-31 torroids at the panel end, inside my combiner box on the roof, and where they enter the MPPT controller(s).

With some luck, I won't have to go to the effort of shielding the box, but if I do, it'll just take a day to do it and another hour or so for measuring RFI across the HF bands. And the expense, of course.

Anyway, it'll likely be about a month before I have it together enough to test. By June I hope to have everything installed with 1,600 watts of panels on the roof. I'll report my results.

 

[OffGridGuy]

I agree with the shielding and choke plans of attack.

8 years ago I purchased a Newmar 32-12-35A off Ebay, to power my off grid ham shack. Think I paid $100 before shipping.

It takes 20 to 50 volts DC and makes a nice quiet 13.8 volt @ 35 amps. (Both on the DC line and in the air).

Newmar makes higher end commercial power systems and are often spotted in ambulances.

BTW, I also have a Morningstar TS60 and although there is an 'RF Quiet' dip switch. The manual clearly states that using that mode takes your controller out of PWM mode and puts it in 'On Off' charge mode.

It's terribly inefficient and even they say to use it as a last resort.

 

[Norm]

I agree with the shielding and choke plans of attack.

8 years ago I purchased a Newmar 32-12-35A off Ebay, to power my off grid ham shack. Think I paid $100 before shipping.

It takes 20 to 50 volts DC and makes a nice quiet 13.8 volt @ 35 amps. (Both on the DC line and in the air).

Newmar makes higher end commercial power systems and are often spotted in ambulances.

BTW, I also have a Morningstar TS60 and although there is an 'RF Quiet' dip switch. The manual clearly states that using that mode takes your controller out of PWM mode and puts it in 'On Off' charge mode.

It's terribly inefficient and even they say to use it as a last resort.

That's the same controller I have TS-65 PWM. I have never had the need to turn on the dip switch. I find the controller pretty darn effecient. I just want to be able to run higher voltage house panels to charge my 12v system and that takes MPPT.

I'm a little reluctant purchasing a single box that does everything. If it fails, I loose it all. Separate CC, Inverter, Charger & failover/crossover? switch for shore power seems to be a good way to go. I already have an inexpensive inverter that will make a good backup and I can use my PWM CC in a pinch even though it isn't nearly as effecient. Now just want to find clean MPPT and 3000w 12/120v Inverter. I had an older Samlex PST inverter and it had lots of birdies but was usable. It was easy to turn off when I was using my ham gear. The charge controller on the other hand needs to be quiet because I really don't want to have to turn it off when using the radio gear. I read where Samlex has made some changes to their PST inverters to mitigate some of the RFI noise. Not sure how well they do though. You can tell their updated inverter from the old one because the new one has a green receptical where the remote plugs in. I may call around and see if any of the solar stores have one all set up and operational where I can come in with a portable AM radio or something to see how well it does. Their ad I read stated it won't interfere with radio or TV. For whatever that's worth.

 

[HaldorEE]

Hi Norm. For RFI quiet MPPT controllers you can also look here: http://diysolarforu.com . Note, despite the URL being very close to the one for this forum, they are not the same thing. The guy at DIYSolarForU is a retired engineer and a ham. I spoke with he and his wife for about 40 minutes one evening. Lovely people. He claims to have the quietest and most efficient MPPT controller on the market. I've heard great things about the MorningStar Tri-Star MPPT controller, too. It's supposed to be pretty quiet.

In the end, this is what I what I went with: Victron MultiPlus 12/3000/120 inverter/charger, Victron SmartSolar MPPT controllers (still sizing this part of my system), and no DC-DC converters. I have a Victron dealer (http://boundless-ps.com) about an hour from my house and the owner is really cool. He has a demo system in his shop and he added a DC-DC converter temporarily for me. I brought a portable LW/MW/HF radio with a ferrite rod antenna inside (more directional) and indeed did notice quite a bit of trash coming from the inverter and just a little from the MPPT and DC-DC controllers. All were very lightly loaded, however. The noise was primarily radiating from the wiring going in/out of the devices. Moving the radio just a foot away reduced most of the noise substantially. Given this, I figured I could clean up the noise.

I haven't installed any of my gear yet, but I'm going to start soon. My plan is to mount everything inside a box made from 3/4" poplar plywood, including a 3/4" plywood hinged lid. I'll build it all in my garage and do some testing to see how badly it radiates noise. I can make relative dBm measurements with a spectrum analyzer and also see how bad the noise is in my home QTH. I have a Flex-6400 radio, also with an excellent spectrum analyzer. If the noise is enough to bother me, then I plan to paint the outside of the plywood box with MG Chemicals silver-plated copper conductive paint. This stuff is made specifically to mitigate RFI. My thinking is I'll build a faraday cage around all the switching components. I'll use copper foil tape along the corners and top lip of the box and lid, then spray paint. I'll use metalized EMI gasket from Parker Hannifin so there is an electrically Any wires going into and out of the box will be choked on both ends with mix-31 torroidal ferrites. I will probably use MC cable for the AC lines going in and out (bonded to the box) and I might put the DC cables in EMT with cable sized appropriately for being encased in the EMT (trapped heat derates the wire gauge size).

I'll test this in the garage with the spectrum analyzer as well and make measurements and then compare the before and after. All the wiring for the solar panels will also be choked with mix-31 torroids at the panel end, inside my combiner box on the roof, and where they enter the MPPT controller(s).

With some luck, I won't have to go to the effort of shielding the box, but if I do, it'll just take a day to do it and another hour or so for measuring RFI across the HF bands. And the expense, of course.

Anyway, it'll likely be about a month before I have it together enough to test. By June I hope to have everything installed with 1,600 watts of panels on the roof. I'll report my results.

Before you invoke poor old Faraday (he could use a rest), real question is going to be what the problem fundamental frequency is. Lower frequency almost have to be cabling/wiring, higher frequency could be radiating directly from the equipment itself.

Me, I always assume problems are related to cables somehow and shields can be the worst part of a cable.

Ferrite rings can be helpful. Keep return current paths in mind and make sure you minimize loop area on your wiring. Especially the DC wiring between the battery and the inverter/charger.

Single point grounding can make a lot of sense when combating RF issues. You don't want any current traveling through the grounds. That can require you to do things like telescope shields (only ground the shield on one end of the cable). Sometimes adding a capacitive shield/ground connection on one end can be more effective for specific problems.

Welcome to my world, I am an embedded design engineer. Everything I do ends up going through a 3rd party compliance lab for FCC/CE approval. Got a product going in for an FCC pre-scan in 2 weeks.

 

[K8MEJ]

HaldorEE, thank you for contributing to this thread and most importantly, thank you for alerting us that you are a professional EMI/RFI reduction specialist! That info could come in handy. haha.

Seriously, though, my areas of primary concern are 3.5-14.5Mhz. A nice to have would be no significant RFI between 3.5MHz and 30MHz.

 

[HaldorEE]

HaldorEE, thank you for contributing to this thread and most importantly, thank you for alerting us that you are a professional EMI/RFI reduction specialist! That info could come in handy. haha.

Seriously, though, my areas of primary concern are 3.5-14.5Mhz. A nice to have would be no significant RFI between 3.5MHz and 30MHz.

10th wavelength of 14.5MHz is just under 7 feet. So cables and wiring are what you need to focus on.

Definitely use MC Cable and RFI filters on the AC.

I would install one of these on the AC power going into and out of the Inverter/Charger.

Amazon.com: uxcell AC 115/250V 30A CW4E-30A-S Noise Suppressor Power EMI Filter : Industrial & Scientific

Amazon.com: uxcell AC 115/250V 30A CW4E-30A-S Noise Suppressor Power EMI Filter : Industrial & Scientific

www.amazon.com

On the DC side:

Use nylon wire straps or short pieces of heat shrink tubing to keep the DC positive and negative wires going to the inverter as closely together as possible.

Wind your inverter DC cables through one of these (pass both positive and negative wire through the same core with the same number of turns, wound in the same direction). Locate the cores as close to the noise source as possible.

Amazon.com

This RFI filter is designed for AC, but it has a large enough current rating (200A) to work for DC wiring. Not cheap at $60, but not as expensive as I expected.

KB Electronics KBRF-200A RFI (EMI) filter 9945: Amazon.com: Tools & Home Improvement

KB Electronics KBRF-200A RFI (EMI) filter 9945: Amazon.com: Tools & Home Improvement

www.amazon.com