Off-Grid DC-DC Converters

MoeMoe Posts: 60Solar Expert ✭✭✭✭
Can anyone here attest to the RFI or lack thereof from 24VDC (nominal) to 13.8VDC converters such as those from Samlex? Any other recommended brand? (am interested in 25-30 amp output)

Thanks!

Comments

  • mike95490mike95490 Posts: 7,874Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters
    Moe wrote: »
    Can anyone here attest to the RFI or lack thereof from 24VDC (nominal) to 13.8VDC converters such as those from Samlex? Any other recommended brand? (am interested in 25-30 amp output)

    Thanks!

    So I looked at the SDC-30 24VDC-12VDC Converter, 30 Amp
    http://www.samlexamerica.com/customer_support/pdf/SlickSheets/SDC-30_SlickSheet.pdf
    and their data sheet does not actually address your concerns
    It's 92% efficient, 30A cont, 35A surge. They list some EMI specs, that I am not familiar with, so I can't advise about them. I also did not see any prices there, but someplace else, I see it listed for $124 http://tinyurl.com/5kljyl .

    BUT, I can tell you what I have done with a 48V system. I needed a DC-DC converter for a project, 48V battery bank/ PV array, with 12.0V LED drivers, that did not like 12.5V, or even the 13.8V charging voltage. I used a DC-DC commercial module, and was very happy with it. It had a high freq inverter, that was easy to filter out with a small cap.
    AEO10B48N-L bought from Digikey.com

    Your application, is VERY demanding, 13.8V @ 30A = 414W output is likely close to 450W input, @ 24V = 19A draw from the batterys The Samlex may be your only choice.

    The Emmerson I used,
    http://www.powerconversion.com/products/websheet/365/AEO AEO10B48N-L
    is highly efficient, but limited to 10A @ 12.0V I don't think they can be "stacked" or ganged to create the 30A you are looking for. 450KHz switching, 40mV ripple. They are UL listed & have a 2 yr warranty though, at $60 each, module only, and you have to create a way to hold and connect it. What I did: http://www.naturalstudies.org/Photo_galleries/LED_driver/

    There are other DC-DC converter vendors out there, but 10A is the usual limit for wire leads the the devices use.
    Here's another mfg:
    http://www.lambdapower.com/products/product_index.htm#dcdc
    the 25A PAH300S24-12 $150 may work, but the Samlex is less $.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • MoeMoe Posts: 60Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters

    Thanks, Mike. The 30A is just for a little reserve. It's for ham gear that peaks at about 20A when transmitting, with average power used considerably lower. That's why the RFI concern.
  • BrockBrock Posts: 630Solar Expert ✭✭✭
    Re: Off-Grid DC-DC Converters

    Oh, in that case you could get by with a smaller converter, maybe rated just above your normal consumption and just put a small 12 7ah battery on the 12v side. It will smooth out and noise and give you plenty of punch for transmitting.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • MoeMoe Posts: 60Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters

    Thanks, Brock. I have no problem using a good old Astron linear power supply rated 16A continuous / 20A peak for transmitting 100W CW and SSB or PSK31 at up to 50W (usually 25). Just thought I'd get a larger converter for DC power. I do have one of those Universal 12VDC/9AH AGMs like you mention for the HT during power outages and think that's a great idea to use it to smooth out the converter power if necessary.

    However, I was hoping someone here might be using one off-grid and could address their power quality or RFI problems. Have also ask on QRZ.

    Thanks again,
    --
    Moe
  • mike95490mike95490 Posts: 7,874Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters

    The Emmerson I used,
    http://www.powerconversion.com/products/websheet/365/AEO, if you buffer it with a 12V flooded battery, and set the trim resistor to the 12V float charge (12.9V?) for your battery, should do fine, 40mV @ 450KHz is not very much, and could be further reduced with another bank of caps (currently used a single 20uF low ESR)

    I can send you the gerber files for the PCB I used, and I may even have one (PCB) laying around I could sell you.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters

    moe,
    using a battery will not work as the converter will not charge the battery proper and rfi can still go beyond a battery. stay with the idea of a bit extra for the converter as this minimizes taking it to the limit and the larger capacity may handle any heat excesses better. as to rfi/emi, i couldn't tell you, but i suppose you could contact samlex to see what they say about it for your application. you not only don't want interfered with on your radio from any rfi/emi from the converter, but you also don't want the rf from your radio to interfer with the converter's operations. if they say it's good then buy it and in fact buy it anyway from any place that will take returns if you decide against the product for whatever reasons.
  • MoeMoe Posts: 60Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters

    Thanks, Mike. I've bookmarked that link for future reference.

    Thanks, Niel. The battery would have to be connected temporarily if at all. I learned the hard way what leaving a battery on 13.8 volts would do. The original converter/charger in our Airstream was a single-stage with no float mode and the original batteries didn't last long. When we replaced them with expensive Lifeline AGMs, we also got a 3-stage charger. Besides the proper float voltage, the bulk mode reduced generator run time.

    I'll fire off an email to Samlex and see what they say. This isn't an immediate need--just some early planning for a future full-time, off-grid cabin, and it goes back to the refrigerator issue. With a propane frig, a moderate 12 volt system should supply all our other needs and be compatible with a wider range of RV and marine appliances, much less amateur radio gear. With an electric frig, it's looking like a 24 volt system might be more practical but with the need for either a DC-DC downconverter or less efficient DC-AC-DC with an inverter feeding a 13.8V power supply.
  • jacobsjacobs Posts: 72Solar Expert ✭✭
    Re: Off-Grid DC-DC Converters

    I've struggled with basically the same problem for the last 15 years. I have a 144vdc and a 12vdc system. The 144 volt is for the inverter (most household needs) and the 12 volt is for my ham gear and our Sun Frost refrigerator. For awhile I used an old Todd charger (DC to DC converter) but it was too troublesome so I increased the number of my 12 volt pv panels. If I had it to do over, I would use an AC Sun Frost and an AC power supply for my ham gear all powered from my 144vdc system....much much simpler.

    All the converters I have ever used all produce some RFI. I think the best way to deal with RFI on HF is to shield as much of your coax in metallic conduit as you can and move your antenna further away from the house.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters

    jacobs,
    although that is a way to lessen the rfi if encountered, it is also possible to add more filtering to the input and output of the converter which is the problem source. this should prove easier to do than in dealing with 60hz utility type ac problems as the frequency of the converters are much higher and is therefore easier in theory to filter out. i say in theory because the filtering should have short leads not far from the output of the converter and be in a grounded metal casing or at least a metal casing attached to the metal casing the converter may have.
  • VicVic Posts: 2,906Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters

    Hi Moe,

    While I have NO direct experience with DC/DC converters in this application, I am NOT optimistic that you will be free of RFI for Hammie Radio use. THis is perhaps a worst-case situation -- you are using the output of the converter to power the radio Transciever. This implies that there could be significant lead lengths between the converter and the radio. If you must do this, would run the converter output in metallic conduit, by itself. You could try it first without conduit, or perhaps try shielded cable if you can find such cable with sufficient condutor size. If you are going to keep the lead length short, then the radio will most likely need to be close to the converter.

    Samlex is a good brand, and they do make Switch-Mode AC/DC Power Supplies for the Ham market, so perhaps they are sensitive to RFI aspects of all of their products.

    Good Luck, 73, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters

    if the converter is outputting rfi/emi the conduit probably will not stop it as it could enter the radio via the dc input connections. this is why i stated to filter the output of the converter. i also mentioned filtering the input to the converter because it could radiate from there as well. the conduit will lessen that which is picked up via the air, but i'd hold off putting it in conduit unless the determination is that it is airborne from the wires and filtering didn't cure it enough.
  • WisJimWisJim Posts: 59Solar Expert ✭✭✭
    Re: Off-Grid DC-DC Converters

    I've been using a Solar Converters Inc DC to DC converter, 12-24 volt 20 amp for over 10 years with no complaints. I haven't noticed any interference at all from it, but I do get some from my inverter, and they are both in the garage, away from the house a bit. The company lists versions up to 50 amps in some voltages. They also work as a battery equalizer if you want to use 12 volts from part of your 24 volt battery string, but I haven't used it that way. http://www.solarconverters.com/eqlist.html
  • VicVic Posts: 2,906Solar Expert ✭✭✭✭
    Re: Off-Grid DC-DC Converters

    Yes, Neil, thought that I placed FILTERING in the post, before shielding. Was a quick post. Sorry.

    YES, Common-Mode filtering should be placed on the input and output of the converter. My recent experience is that almost all of the RFI from switching devices is line-conducted. These emissions then radiate into the antenna(s) from the leads connecting the switching device. This often means that shielding of the interconnects can be very effective. If possible, try using type 31 Ferrite material for HF frequencies. Generally, the lower bands are those most affected. And if necessary, place a common-mode choke on any coax feedlines. Avoid open wire antenna feedlines if possible.

    Manufacturers often omit the RFI filtering from their switching devices, as the materails in the filter are expensive, and often slightly reduce the efficiency of the device. Some use filtering to get emissions compliance, and then omit the filters in production to save $$.

    Suppose that the OP should contact the manufacturer(s) of the subject device regarding the emissions compliance if any. Then buy the unit and test it. Then do any/all things needed to make the system work. Some switching devices have such HORRIBLE emissions that suppression by mortal persons is very difficult.

    At my comm site, have tried to do as much shielding as possible, as it is more difficult to do after construction is complete, and have tried to do the best job on filtering as I can. It is all experimental. The MPPT CC's are difficult as the PV array interconnects twix each solar cell are also antennas, and I have made no effort to shield each of my solar panels -- there are limits.

    Good Luck, and any results would be of general interest. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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