Duracomm Power Supply Problem?

[srk]

I spec’d a Duracomm DPS-45 (looks the same as an Iota DLS-45) for a transportable base control station (with an XTL2500) and found a problem as soon as I tried transmitting – the transceiver shut down. Tried low power TX and the same happened. Investigation revealed voltage was dropping – to 8 or 9 volts! I tried a known load (75W, 12vdc lamp) on the PS and there was no drop. The antenna (mag-mount) was on a close-by cabinet (6 ft away) so I moved it further away and found less drop. So it appears RF is playing havoc with the switcher. Out of curiosity, I tried keying a 5W HT from a couple of feet away and saw a couple of volts of drop with that. I decided to try a DPS-30 that I have elsewhere and saw about a volt drop when the TX antenna of the mobile is a few feet away. That’s better but still a bit concerning. Does it sound like the 45A supply has a problem? Or is this common on switching supplies? I don’t plan on having the TX antenna that close to the rig but the 5W HT keying up close by is definitely a possibility.

[Bat2way]

Shouldn't do that at all. May just be simpler to go with a magnetic (transformer) type and call it a day.

[Jim202]

Sounds like a poor electrical design that is RF sensitive.

You could try to install some RF bypass caps to reduce the
problem. You might also try calling the company and try
to talk with one of the design engineers about the problem.

Most companies don't even bother to worry about any
RF issue with their design. The bottom line is cost. The
more time and parts translates to an added expense
that may only effect 0.01 percent of their product. In
most cases it is not worth their time to RF proff the
power supply to any radio transmitter. They would
rather handle it on a case by case basis.

Jim

[tvsjr]

I wouldn't be installing anything. Duracomm is supposed to produce high-quality power supplies. That power supply is about $200, my distributor cost.

I'd call the company and complain loudly... make sure you point out who you work for - see if that gets them a bit more motivated.

[srk]

I spoke with the company before I determined it was RF related and they were quite willing to RA the unit and replace it as faulty. I spoke with them again today and described the RF "sensitivity". They did not think the problem is common but did suggest some ferrite cores on the DC output might help. I have another 45A coming that was backordered. When it gets here I can compare and see if it is just one bad unit. In the mean time, I guess I’ll try some chokes on the outputs. The case on the PS is not bonded to negative but there is a grounding lug that they say can be jumpered to negative. I tried that with little effect so the RF may well be doing its deed via the output leads.
Thanks for the help - I'll update.

[fineshot1]

Did you try grounding the DPS-45 cabinet ground lug? Its a switcher of course and the industry standard is to have that grounded for RFI & EMI reasons.

EDIT: Sorry - to be more specific I am refering to earth ground.

[srk]

I haven't tried "earth ground" to the case but I did try DC output negative to the case per the manuf. directions. That actually makes it worse - apparently drawing more RF in on the negative lead. I don't currently have a handy source for earth ground - it's a transportable rack system - but I could try accessing earth ground from the AC source. Would that be prudent?

[fineshot1]

Yes - if you have to try running about a 10 gage wire to any temporary earth ground spot you can find - ie: cable rack ground; just to see if it reduces or eliminates the rfi/emi emissions problem.

[srk]

I ran some 10ga from AC ground to the case lug... no change. I tried some random ferrite cores (what I had laying around) on the DC output and saw some change - for better and for worse depending on the core and placement. I'll have to play some more with the smaller DPS30 and... see how the other DPS45 behaves when it gets here. Thanks.

Shawn

[RFdude]

Thanks for the warning about Duracomm PS. I'll avoid them.

Be glad that the voltage sags under your particular RF influence! The other common RF caused malfuntion with switching power supplies is that the the switcher partially or fully conducts. If you are lucky, the switcher over voltage protection will be set to a sane level that won't cause damage to your load. It will short the output and either blow an input fuse or keep the PS in an over current foldback mode. I've seen this happen with other power supplies. The mobile radio display got very bright before the OVP killed the output. Wouldn't want to do this too often.

RF Dude.

[srk]

RFdude,

I don't know enough yet to advise against using Duracomms. I'll have to see how it resolves. I may have a lemmon... or maybe two! I have more coming so I'll see. I also have seen a brief rise in voltage when the radio keys - but it's hard to characterize with my DVM. Since these are going in portable packages, I really want to use switching supplies if possible.

PS - I have found that the problem exists only in the UHF (440-470) range. The supply seems to have decent immunity with 800 and VHF.

Shawn

[fineshot1]

Shawn - I have a IOTA DLS 55 on a MastrII 220Mhz repeater with no rf noise issues. I have a IOTA DLS 75 on a 1.2Ghz Knwd homebrew rptr with no rf noise issues. Before I had the IOTA's I had some older Todd Engineering 45 & 55 amp switchers with no rf noise issues. I did once have a Todd Engineering supply that did not like the 220mhz nearfield from the MastrII and I had to replace. Most good quality switchers in my experience are fine but once in awhile you can get a quirky one. Good luck.....dan

[M1225]

I had some similar problem with my iota power supply at home it seems rf can play tricks with the power supply. First I had a vhf base antenna to close to the supply and every time I keyed up it would switch to charge mode. I eneded covering the charge controller in foil to shield it and that solved the problem untill I moved the antenna. seems uhf is a difrent beast even without the charge controller pluged in it finds it way in to the unit. I have the unit grounded as well and that did not help a bit. so I learned not to key any uhf hts in the room becouse it couses the gfci outlet the unit pluged into to trip when its pluged into that outlet.