Inverter Wiring

[Pete Masterson]

I can't say how earlier 'bird inverters are set up... On my coach the
transfer switch appears to be integrated with the inverter. The
transfer switch selects the inverter if not other 120 VAC is
available (from shore power or generator). The inverter 120 VAC
output passes through (in my case, with dual inverters) 4 circuit
breakers that "protect" the inverter 120 VAC circuits.

These CBs are located in a separate spot a short way from the main
120 VAC power distribution panel (in my case, behind a door on the
engine bulkhead in the bedroom).

It is my understanding that earlier year coaches may have had
separate inverters, transfer switches, and chargers -- and many of
the earlier inverters had a circuit breaker on the inverter that
protected it from overload.

Later "inverters" have combined the transfer switch, inverter, and
charger in a single unit -- some with on-unit circuit breakers, some
that (should) use external circuit breakers, and some with both.

However, no matter how your coach is physically wired up, if you plan
to add a significant new load (such as a basement freezer that might
draw as much as 8 or 10 amps), then it seems like a wise precaution
to add a secondary inverter just for that device or upgrade the
primary inverter to handle the additional load. Since a freezer has
an electric motor, it's probably wise to ensure that you have full
sine wave current from the inverter to avoid the potential for motor
overheating and less efficient operation (that will eat amp-hours
from the batteries). Of course, a dedicated circuit from the inverter
to the freezer is wise.

I realize that this doesn't actually answer how the transfer between
the inverter power and shore power are accomplished. I can only guess
that the inverter output is passed to the appropriate circuits
following the main 120 VAC distribution panel, leaving it to the
transfer switch to keep inverter/shore/generator power separated.
Perhaps someone else can explain how BB set up that part of the
wiring...

Pete Masterson
'95 Blue Bird Wanderlodge WBDA 42
aeonix1@...
On the road at Edinburg, VA



On Oct 21, 2008, at 12:53 PM, Gregory OConnor wrote:

> Pete, there is a group of switches that stand between the 120V
> electric panel and the receptical/appliance. when you power on the
> inverter I believe the inverter sends 12volts to the On On switch
> and removes shore/gen 120v (what ever the transfer switch is sending)
> and paths the power from the inverter.ON1= shore/gen ON2=inverter.
> If the switch fails one of the inverterpowered paths wont switch
> between the two choices
>
> Wierd thing is I cant seem to understand how the
> receptical/appliance is then protected. The power no longer rus thru
> the houshhold style pandnel breaker box but goes directly from the
> inverter total output source. I guess any leg once powered by
> inverter then has the ability to draw 12.5 amps (or 30 amps if the
> individual inverter is a 3600watt). would be good to understand the
> protection of circuit wires when you add a larger inverter and more
> demand.
> Greg94ptCa
>
> --- In WanderlodgeForum@yahoogroups.com, Pete Masterson
> wrote:
>>
>> The inverters in a BB are set up with their own distribution
> wiring
>> (separate from the main 120 vac panel). So, follow the output
> wires
>> from the inverter and you should find a distribution system
> (possibly
>> with circuit breakers) somewhere nearby. You can 'join' a new
> wire
>> there (or set up an additional circuit breaker) to run to the
>> location of the freezer.
>>
>> Load: you first need to determine what the general load on the
>> inverter is at present. What devices are attached and how many
> are
>> used at the same time? It may be that all the available load is
>> (potentially) used up by the existing appliances.
>>
>> Appliances almost always have watt or amp ratings on them (usually
> on
>> a tag by the manufacturer's name on the back). To ease
> calculations,
>> convert all ratings to either watts or amps. (Amps x volts (120)
> =
>> watts or Watts divided by volts (120) = amps) So, a 1500 watt
>> inverter can handle about 12.5 amps in total. You should leave a
>> couple hundred watts (2 amps or so) "free" to allow for
> calculation
>> errors and electrical efficiency. Motors (which don't "like"
> certain
>> types of inverters) prefer "true sine wave" power -- something an
>> older inverter may not provide. Motors (the freezer compressor)
> also
>> draw as much at 50 more power at start up than their rating, so
>> allowance must be made for that, as well.
>>
>> In all probability, the inverter on your coach is already wired up
> to
>> use most of its maximum rated power for the appliances already
>> attached. I expect, depending on the size of the freezer, that
> you
>> will find that it draws anywhere from 6 to 8 amps up to around 10
>> amps. (Remember to add for the brief overload for motor start up.)
>>
>> So, the solution(s) are (1) upgrade the existing inverter from a
> 1500
>> watt unit to a 2500 watt, true sine wave unit or (2) add a second
>> inverter of about 1000-1500 watts (depending on the size of your
>> freezer) to handle only the freezer circuit.
>>
>> Keep in mind that the additional 'juice' required for the
> inverter
>> will come at the expense of the batteries. If you only use the
>> freezer/inverter while on the road, the engine alternator should
> be
>> replenishing the house batteries to offset the load, but while
>> parked, the house batteries will need to provide the inverter
> power,
>> and I know from personal experience (I have a home-style 22 cu ft
>> side-by-side refrigerator-freezer) that refrigeration can draw
> down
>> batteries rather quickly. You may need to consider adding
> additional
>> house batteries (or otherwise increasing the available amp-hours)
> to
>> compensate for the additional demand.
>>
>> Pete Masterson
>> '95 Blue Bird Wanderlodge WBDA 42
>> aeonix1@...
>> On the road at Edinburg, VA
>>
>>
>>
>> On Oct 20, 2008, at 8:42 PM, Don Spithaler wrote:
>>
>>> Guys---I want to set a small freezer in one my outside bays.
> There is
>>> a plug there but how do I wire it to run off the inverter while
> going
>>> down the road? How would I know if it will run off a 1500 W
> inverter?
>>> Thanks
>>> Don Spithaler
>>> 89 SP 36'
>>> Butler, PA
>>>
>>
>
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