Tuesday, January 17, 2012

Parallax 7345 RV Power Converter (SMPS)

See Also:
Parallax 7345 Repair Tips

A friend had a Parrallax 7345 power converter for a RV that didn't work. We know what happened, It's designed for 120VAC only and somehow got hooked up to 240VAC. So it released some of it's magic smoke. (and probably made a big BANG noise I imagine)

Basic Info:
  • The big heatsinks may have 300VDC+- on them, Be careful! (obviously if it's on the heatsinks, it could be anywhere, like those 2 big caps) It doesn't just go away if it's not plugged it either.
  • 45A@13.8VDC (7300 series 45A)
  • 120VAC input
  • Despite the fancy "converter" name it's just a big Switch Mode Power Supply (SMPS)
  • Schematics are not available (Parrallax has on their page "We do not give schematics to anyone perod", or something to that effect), as with most things in the RV universe, they are expensive to replace and don't expect any help repairing them.
The Diagnosis:
It was pretty easy to locate the fault, as there was black stuff all over one spot. (Note: I'd already removed the heatsink from the bridge rectifier in the first picture and cleaned to bottom a bit when I took the second picture)
I looked it over good. It seems a MOV (metal oxide varistor) is missing (vaporized in fact), but that wouldn't prevent it from working, it just shorts the ac line together when they reach a certain voltage, with it gone it should power up, unless something else is broken. Sure enough the line filter next to it had melted a wire clean off, I didn't see it at first because the MOV had left a bunch of residue that hid it.
The other black spot on the circuit board (far left) is under the output resistors, they work fine, but must run a bit hot under prolonged load.

I bridged the broken wire on the filter, sheilded my face and plugged it in. It powered up nicely, made a moderately loud buzzing noise (no load), so I unplugged it and connected it to a 12V battery. Absolutely quiet now, but putting an amp or so into my battery. The battery is connected to an inverter I use for emergency power, so I plugged a toaster in and it jumped right to 45A. I ran a couple toaster cycles then let it fully charge my battery and all seems well.

The Repair:
I couldn't find an exact replacement for the filter, so I had to make a few mods to the board for the one I found. I had to guess on the MOV, I used a 175V MOV (datasheet said 150VAC max) I still have no idea what size would have been right, I even spent a couple hours trying to find how to choose the voltage and still didn't come up with an answer.

But a new MOV and line filter later it's back in service. The good news it the MOV did it's job, protecting all the electronics after it, it should have had a fuse in the AC line and the MOV and line filter may have survived. There was some minor damage to the traces around the line filter and MOV, but nothing too bad. The owner was instructed "Don't hook it to 240 again!", but I think he already knew that.

The other side of the board, nothing wrong here, just in case you want to see it:


I picked up a broken 55A version of this unit. As far as I can tell it's exactly the same board. I'm going to do a post and probably a video of diagnosing and repairing it, but that may be a while. 
I was going to post the correct value of the MOV, but it doesn't have one. The MOV footprint is not populated. I have the numbers off the filter, but google hasn't helped my find anything about it, so it may be a wild goose chase. In case it helps someone:

06847475-000 843TC6
AXM EIA-17-0315-1A


  1. yep

    several capacitors and as good as new !!!

    1. Sure, caps go all the time.
      Seems they don't want anyone to work on things like this anymore, but it's nothing special. Same basic stuff that charges your cell phone. Much bigger of course, but the dangerous voltages are present in either. Just a smps.

  2. Hi Steve,
    I think i blew the exact some components due to a voltage spike from my generator. Can you please post or send me more details on the parts and or where you ordered them from?

    1. Parts came from digikey, I couldn't find an exact match for the line filter and the MOV was vaporized. I will post the part numbers when I find them. The MOV was a drop in, I had to drill holes in the board for the filter. I had numbers off it but couldn't find a drop in replacement.

    2. Line filter was digikey PN:
      M8910-ND - CHOKE COMM MODE W/HDR 1.2MH 16A
      Note: I had to drill holes in the pcb to make it fit, I couldn't find an exact match for the blown one.

      MOV was digikey PN:
      P7231-ND - SUR ABSORBER 20MM 240V 6500A ZNR
      Note: I made an educated guess on this one. All that was left of the old one was one lead. the rest was gone. I would recommend putting a fuse somewhere between this unit and the power supply. you might get lucky and blow the fuse rather than the MOV next time.

  3. Steve,
    Thanks for the info, makes me actually want to look closer at mine. It probably a different problem. Mine has just quit charging the battery. I first noticed that the cooling fan was not coming on, then the battery becoming discharged.
    Do you have any experience with this problem?
    thanks, Dan

  4. I started writing some tips for you, but it got big for just a reply:

    As far as experience goes, I'm newer to electronics than many my age, or at least feel that way, It was a hobby of mine for years as a child, but I mostly abandoned it through my teenage years / early twenties. I've been playing with electronics again, I've learned a lot, but can see a whole lot I still don't know.

  5. Nice Post!! pretty informative..thanks for providing such a nice post.
    Power Inverter

  6. Steve I have the same board and I hope you can help. The converter is only putting 6 amps to batteries. When I took it apart the same resistors on the far left were all black and burnt. My question is what could have caused this and if I fix will the just blow again?

    1. Hard to tell, From what I can tell these seem to be the output current sense resistors, But they look small for that. I've got a 55amp board here, I'll have a closer look at them this afternoon.

      As far as why they failed, it could be thermal stress (many cycles at high currents), a current regulation failure (though since it's still putting out 6A it seems it blew several, but not all of them and is regulating properly), could be an airflow problem, the fan is thermally controlled from the heatsink(s), but these resistors seem to run hot. Lots of dust in it or a clogged up fan perhaps?

      Also hard to tell with the repair, though it should cost you less than $5 to find out. I'll try to measure my resistors and get you a value. You should be able to remove and measure your resistors, it acts like some of them are OK. They should be a fairly low value. I'll get you a link to some better hi-temp resistors that should hold up better and if you space them 1/4" above the board it will drastically improve the airflow over them.

    2. Nope, they're not the current sense resistors. I'll look more later.

    3. Ok, I measured the resistors (together) at 34R, which indicates approximately 170R each. I traced it out and from what I can see it uses a tip31c npn medium power transistor to shunt across the output.

      I'm over my head here, but I think it's an auto-adjusting minimum load to keep the output voltage stable at low currents.

      Advice: measure the resistance across the resistors, if it's around 34R they are probably OK.

      I have to ask, what conditions are you measuring the 6A output? under a heavy load? 50+ amps being drawn from the batteries? Remember It's voltage limited to around 13.8V, so the current will drop off as it starts approaching it's voltage limit.

  7. When I measured the converter was being powered by the genset on the rv. I measured the amps from where the blue and white wires plug into the board in the lower right corner (e1 and e2). I did have lot of dust on the board. I cant tell what color the bands are on R67 -R71.

  8. Ah, e1 and e2 are the 120VAC input. The outputs are heavy white and blue wires that come through the divider plate. They are soldered to J2 and J3. It's probably working properly (worth blowing the dust out though).

    6A at 120V is about 720 watts, that's the same as about 52A at 13.8V. There is some loss, so if it's rated for 45-50A max I'd say that's about what you're getting, or at least that's what going in...

  9. I have a very strange problem with a Parallax 7345 SMPS which I would like to discuss with you.

  10. Steve can you tell me which one of e1 or e2 the black wire connects to on 7345 converter. Woody engbd3@gmail

    1. I think you're referring to the 120v lines? (It's been a while)
      One white (neutral), one black (120VAC) right? It shouldn't matter. Both inputs float, So it will work the same either way.

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  12. Thanks steve a freind told me the same as you did about the e1 and e2 if they were 11p volts ac it wouldnt mater. How ever i did something really stupid when i was putting the 12 volt fuse panel back on i didnt discnect my two coach batteries and shorted the red cable against the metal and now i hve no power from the batteries ive messed something up now im only have poer to microwae and one outlett in the cabinet next to it. You probablly have any sugestions im looking for a blown fuse or breaker somewhere no luck so far.i have heard clicking noice from up arond front near the engine compartmen coming from to solinoids mounted close to each other before i shorted it out. I have had at least three occasions where my ac roof air quits working and by starting up the generator and playing with the two two way switches on the foot of the bed get it to evintually start workin again. I keep thing it was somthing hanging up in the ats or converter as some call it. Any expert advise is greatly appreciated. Thanks from woody in South Texas

  13. Thanks a freind told me the same thing i just wasnt sure the were 120