Wednesday, October 26, 2011

Project: Converter Swap–WFCO 9835 for PowerMax Boondocker PM3B-45

Well, I went through all the song and dance and jive doing all that wiring upgrades and relocating the converter in my backlogged projects series only to discover that my original converter, the WFCO 9835 35-amp deckmount, was on its way out. 

In the past, the popular unit of choice has been the Progressive Dynamics 9200 series with its remote charging pendant, however, I am not seeing a 35amp model in the line up over at, the lowest amperage rated unit they have is a 45amp model, which is likely overkill for my rig.

So, I fired off an email to Randy over at inquiring as to the fate of my old converter to verify that my suspicions were indeed true.

My email dialogue went like this:


RedneckExpress/JoeChiOhki wrote:

Howdy folks . Late 2008, I bought a WFCO 9835 deckmount converter from ya guys and been using it without issue up till just recently.
I'm trying to figure out whats going on with it, as I've moved it from where it was originally installed (roughly about 11' away from the batteries) to where it is now, (roughly 2' from the batteries) and now its acting strange.
The unit is making a constant "clicking" sound when listened to up close. Before, the unit would perpetually stay in 13.6 volt mode, doing the desulfation boost every 24 hours) which I figured was because it was 11' away on 4 gauge wire. So, I moved it to its new location, which is right on the other side of the wall from the batteries.
Once moved, the unit was performing as normal, but now actually going into boost, and staying there (Left it alone for 3 days, it never went out of 14.8 volt bulk). I figured this was due to the fact that my two Group 31 Trojans were at the end of their service life, so I replaced the batteries with two new of the same make and brand and now the unit clicks constantly and the lights pulse. The batteries are connected correctly, and all contacts were cleaned and polished to ensure good connectivity.
Also, the unit can no longer be run on the generator. Before, it worked just fine, but now, whenever it is switched on the generator starts cycling (revving up and down like a load is being added and removed rapidly), something that only happens when the converter is used, nothing else causes this.
Is any of this normal for the unit? I personally think something has gone out in the WFCO unit. I cannot find any articles specific to the 9835 online, most of the problem threads I find are related to the older 8000 series units.
Thanks for any enlightenment you can provide on this bugger. Either way its gonna likely have to be replaced, as I don't want it damaging the $400 in new batteries I just installed!

Randy@BestConverter wrote:

Hi Matt,
While I don't know what, something has failed internally and it will need replaced. Anything or nothing could have caused it to fail.
I would not recommend another WFCO unit however. The Powermax Boondocker is a much better performing unit and has a better warranty. They never come back. Thanks and here is a link if you decide to replace it.

RedneckExpress/JoeChiOhki wrote:

How does the PowerMax Booster Compare to say the 9200 Series Progressive Dynamics unit? wrote:

Similar except its a constant current based charger, uses a slightly higher voltage (14.6 max) for faster charging and has 3 year warranty. I prefer it. If you are fimiliar with constant current versus constant voltage, there is no questions the job gets dont better and faster with a current limited unit. Both are good units though.

RedneckExpress/JoeChiOhki wrote:

Oh yes, and I forgot to ask, but what is the AC wattage usage of the 35amp/45amp PMB units? Their detail pages on the website don't list anything in particular. wrote:

I don't have it on the website yet but they are vitrually identical to all of the other is you find another table.


Wanting to make certain I didn’t make a repeat of buying the WFCO-grade of converter again, I started up a thread over on and got folks opinions and in the end, decided to take Randy’s advice and a chance (not too many of these PowerMax Boondockers out there yet amongst the RV community that I can see) and ordered a 45 amp PowerMax Boondocker Smile.


My parcel arrived in fairly short order, this morning 30 minutes after I left for work, in fact Smile with tongue out.


When I got home from work, I dug into it Smile

First off, as you can see, the PowerMax, on the right, is almost double the size of the older WFCO unit, on the left,  I originally had, but its shorter in overall height compared to the WFCO.  The only thing I ‘m not 100% thrilled about is that the PowerMax is completely flush, where as the WFCO was offset a bit to allow air space between the unit and the surface it fastened to.

So far, the PowerMax is running substantially cooler than its predecessor under similar conditions.  At the moment, I’m not even generating enough load to cause the cooling fan to cycle on.



Sadly, I had to drill a couple more holes in my dinette seat Sad smile, but at least they’re hidden underneath a cushion. 

Swap out was pretty straight forward and took very little time, I was done in under 45 minutes Smile.  Simply disconnect the battery wires (Negative first!) after unplugging the unit and unbolting it from the underside of the dinette seat and doing the reverse (after marking and drilling out the new bolt holes) for installation of the Boondocker.

Original WFCO


PowerMax installed



Once I had everything hooked up, I flipped on the power switch and nothing exploded or caught fire, which to me is always a good thing!

Once it had been on for a couple seconds, I flipped the switch on my voltage meter to check what mode the PowerMax had decided it needed to run in.   According to everything I’ve read, the unit starts in 13.6 volt mode, then checks to see if the batteries need more and will go up to the 14.6 Boost mode, or down to the 13.2 float mode if the batteries do not need charging.

Much to my joy, she went down to 13.2 volts, something I don’t think the WFCO ever did, which is why my Trojan’s died an early death as they were being constantly boiled, even with water being added regularly, eventually the plates degraded to the point of no return.

As I sit here, typing my blog entry, the converter is still working just fine and still happily at 13.2 volts.  My lights no longer flicker and so far, I’m happy with the PowerMax Boondocker.

I still need to see how she performs in a recharging situation and operating off the generator.  I wasn’t able to use my generator with the WFCO on my last two participations on the Fall Colors Rally,

Thanks for following along, I will keep ya’ll posted as things progress!


  1. just a thought. You could have used a stand off of some sort to create you air gap for in a stack of washers, or even a nut on each bolt between unit and mounting surface.

  2. Yeah, I just thought of that, but the unit is still running rather cool under normal load conditions, so I'll keep an eye on it and add the spacer if I start seeing it getting hotter than I'd like.

    The gap on the old unit didn't really do much for heat abatement in the end, so I'll watch and adjust as needed :).

  3. Thanks for the install info and photos! Great stuff.

  4. I'll be buying one.

  5. Thanks for all the support, to date the unit is still performing well and the fan in the unit is definitely temperature based vs load based, meaning the fan only comes on when the unit actually gets hot, not when you turn on that 3rd light fixture like my old WFCO did before.