How big a converter do I need

[skloon]

Took out my new to me 92 Sunflyer= a few electric glitches and the hum from the converter started my dogs howling- I would assume that newer ones don't make that much noise but how many amps do I need and anybody familiar with the Boondocker line  ?

[Rickf1985]

I have a 45 amp Boondocker in my 31 foot Chieftain and it works great. I don't hear any hum but the fan does run when it is working. Mine has a split system where the converter is up front and the electrical panel is all the way in the back under a bed.

[skloon]

That sounds similar to my set up- the converter is mounted under the passenger seat while all the 110v stuff is in back beside the bed-

[Rickf1985]

In his case, he has the same exact setup as mine so I know what he will run into. If he goes too big on the charger then it will pop the breaker in the panel since it goes through that before going to the batteries. The solution is to bypass the breaker for the charging circuit in the coach since the new Boondocker is internally protected. BUT! You do have to take into consideration the size of the wire that was originally installed in the vehicle for the charging of the coach batteries. The original charger was something like a 20 amp charger so you are going to have maybe 12 gauge wire. You put a 45 0r 55 amp charger on there and you are asking for trouble so be careful with that.

[tmsnyder]

That's a valid point Rick but it might not be an issue. 


Assuming 15V output at 55A DC from the converter/power supply, that's 825W.  Assuming 70% efficient (it's most likely more efficient than this), it's going to use 1180 W to make that 825W.  At 110 V AC, the amperage draw is only going to be 11 amps max.   My assumptions are conservative, so the actual value will be less.  So it seems like the 55A power supply could safely be on a 110V AC, 15 Amp, 14 gauge circuit at a minimum.

[DRMousseau]

Can I poke my nose in for a moment?


If one is looking for a simple replacement, simply replace it with something similar to what your system was originally designed for. The term "converter" originated with very early systems that did nothing more than allow available AC to supply the needs of early travel trailer and motorhome DC systems that typically relied on the vehicle battery and engine charging systems. Later equipped "Converter/chargers" additionally allowed the AC charging of independent "house" battery systems of later equipped travel trailers and motorhomes. That charging component and rating has now become the most important consideration in current RV systems.


That chosen "amp rating" you may be considering, will be greatly dependent on the battery bank, the current AC and DC wiring and service systems, and the typical needs or use of you, the consumer. Since ALL 12v components COMBINED (furnace, fans, lights, pumps, etc.) seldom draw greater than 10-20amps max at any one time, then it's easily seen that a minimal converter is all that's really needed.


But since the CHARGING part is most important, then it's usually best to consider and choose the most efficient charging/converter of greater capacity and modern design, to reduce charging times and prolong battery life. While a 20A unit will certainly supply your needs, one of higher rating will charge and restore your battery bank faster and usually more efficiently. Keep in mind that your battery bank, wiring and battery cables, MAY not be adequate to fully benefit from a charging/converter of large capacity, including your shoreline and/or AC supply sources.


Rick is right, in that the "charging" wiring to the battery bank of most systems is rather inadequate for big upgrades and some are "protected" as he described. Kinda like the cable difference of a "trickle" charger, "quick" charger, and a "starting" charger of automotive use. With greater current, a larger cable is often necessary and is kept as short as possible to prevent voltage loss. While the difference between a 3A trickle cable and a 20A rapid charge cable is small yet significant, is also obvious that a 40-65A charger will need a bit more. This mostly a matter of efficiency in charging, rather than a danger, as this IS NOT typically a cable of power draw as in a heavy short cabled starting charger that may be called upon to draw immense current to the starter. DC power draw in today's systems is from the batteries, NOT thru the converter/charger. Much different than the old "converter" systems of days long past.

[Rickf1985]

Thank you, That is what I was talking about, not the AC supply wiring. The DC wiring that has to carry the charging current.  And I did not pick up on his statement about already having a 45 amp charger, most old units, mine included which is the same as his, was a 25-30 amp charger. Going to 45 amp was pushing the DC wiring and 55 amp would have been over the limit.

[DaveVA78Chieftain]

OK everyone step back and take a deep breath.
One thing I try to always do if I can is look at the parts and wiring diagrams to first understand what I am starting with.  Assuming, as most here have done in this case, the setup is like what we usually see can be way off base.

To start, this is a 92 Itasca Sunflyer which originally had a little different setup than what most of you are familiar with.
I am about 99% sure it came with a 40 amp Triad Ferro-Resonant Transformer Converter/Charger under the passenger side front seat which does not operate the same as a Magnetek (B-W) 6345 power center.  This Triad Converter/Charger feeds separate DC CB.s and a standalone DC power center (not integrated like the Magnetek 6345).   I believe the converter wiring is 8 gauge.
This Sunflyer converter stock wiring setup is essentially the same style used with the modern Progressive Dynamics and/or Boondocker converters where the converter output feeds directly to the battery (no seperate charging section nor transfer relay).  In this case, in addition to a battery disconnect relay there is an independent pushbutton style circuit breaker panel seperate from the AC/DC power center.
The net result is, the noisy 40 amp Triad Ferro-Resonant Transformer Converter/Charger can be directly replaced with a 45 or 55 amp Boondocker or Progressive Dynamics 3/4 stage converter.
For AC input side, given the original unit was 40 amps, the increased AC current draw will be minimal.
For the DC side, the issue would be that the output push button CBs in the DC CB Panel are limited to 40 amps.
So, in this case, I think I would limit this to a 45 amp unit.

[Oz]

Did you make any decisions based on the info given, Skloon?