Aaron,

If the link led to a DPST relay, I apologize for not searching more
carefully; you must use a DPDT relay, which will, indeed, be a little more
expensive. They're frequently available on eBay for pretty good prices; I
can't give you a number off-hand, but it will probably be from
Potter-Brumfield. Be sure the coil is 120 VDC NOT vac or you can't use
the capacitor to slow operation, which is definitely desirable. It would
be simple to use a lower voltage DC coil, but would complicate the circuit
by requiring a step-down transformer.

Since your house circuits are only set up for 30A load, the Onan will only
supply that current to them through the NO contacts of the relay. Whatever
method you use to supply the 2nd A/C from shore power you'll need to
utilize for the Onan also. It would, of course, be quite simple to add
another relay (requiring only 15A contacts) in parallel with the transfer
relay to handle the Onan, but it will be simpler and easier to just provide
a socket from the Onan, BEFORE the auto transfer relay, to plug the 2nd A/C
into. Another option to paralleling the primary relay would be to include
a second relay after the primary one.

Sorry if I offer too many or too complex options -- my extensive parts
inventory and 60+ years of electronics education and tinkering dominate my
thinking.

Ken H.


On Sat, Sep 2, 2017 at 10:09 AM, Aaron Bush wrote:

> Well, this is very interesting - I understand about not including the
> inverter. I thought I would need a 50 amp switch because the onan power
> would be
> running through it - but you are saying that is not the case, that I only
> need a 30 amp switch which would be activated by my 30 AMP shore power, not
> the onan? (Onan would be the default power so only the contacts would be
> experience more than 30 amps.)
>
> Also, hashing this over with a friend who is more familiar with
> electronics than I am, then reviewing some switch terminology - I'm pretty
> sure I need
> a DPDT relay, but the one you linked to below is DPST.
>
> Are you thinking of a way to do this with a ST switch? Either way, if I
> can do it with one really, one diode and one capacitor, then I think I can
> handle that.
>
> Please realize this post makes me sound a little more electronics savy
> than I really am.
>
> Aaron
>
>
>
>
>
>
>
> Ken Henderson wrote on Fri, 01 September 2017 21:38
>> Aaron,
>>
>> You overestimate the cost and complexity of a DIY auto transfer switch.
>> Here's a first-look relay for $18.49:
>> http://www.mouser.com/ProductDetail/TE-Connectivity-PB/T92S7D22-110/?qs=
> sGAEpiMZZMtSzCF3XBhmW6vMa%2fMpJxoP71VMV4XEUfE%3d
>>
>> Only one relay is needed if you only want to transfer between shore and
>> generator -- just delete all the connections and components in the
> Inverter
>> section.
>>
>> But if you're not comfortable with that level of electrical fabrication,
>> stick with the factory-built solution. But remember that with your
>> isolated ground system, you shouldn't need a 50A switch. I believe
> you'll
>> find that all commercial transfer switches operate just about like my
>> diagram, meaning that the shore power will never see the Onan's combined
>> Neutral and Ground connection.
>>
>> HTH,
>>
>> Ken H
>>
>>
>> On Fri, Sep 1, 2017 at 9:29 PM, Aaron Bush wrote:
>>
>>> Ken Henderson wrote on Fri, 01 September 2017 15:36
>>>> Aaron,
>>>>
>>>> I'm with Rick; your solution needn't be too complicated; the Coachmen
>>>> should have had separated Neutral and Ground busses.
>>>
>>>
>>> That's correct - my busses are separate at all boxes on my coach - the
>>> ground and neutral are only connected at the generator and that
> neutral is
>>> not
>>> switched anywhere, nor is the ground from the generator. The comment
> about
>>> the neutral and ground busses being connected was not mine, and it's
> not
>>> actually the problem that I have. I guess the *simplest* thing for me
> to
>>> do would be to put in a double pole breaker at the main generator box
> - but
>>> that still leaves a convoluted set-up with more boxes, more wire, and
>>> certainly more junction boxes and wire nuts, than I actually need.
> Also, if
>>> I
>>> get rid of the excess boxes and wire I will gain some usable storage
>>> space. Also doesn't resolve power for my 2nd AC on shore power. So
> toss that
>>> idea.
>>>
>>>
>>> Quote:
>>>> As for the switching, I'm not sure ordinary 50A Automatic Transfer
>>> Switches
>>>> will recognize the 30A plugs you intend to use. Further, there
>>> complexity
>>>> and cost are not justified. Here's DIY version of a 30A transfer
> I've
>>>> used, without attention, for the past 19 years:
>>>>
>>>> http://www.gmcmhphotos.com/photos/g3484-automatic-120-
>>> vac-power-source-selection.html
>>>>
>>>> It's simply wired; in fact, mine's in excess space inside my replaced
>>>> circuit breaker panel (that's probably not Kosher, 'tho').
>>>
>>>
>>> Mmmmm, this seems a bit complicated to me. It's certainly a little
> more
>>> than I'm easily comfortable with in terms of electrical diagrams -
> but it
>>> looks like I would need two of the power relays ($50 each), two
> diodes(14
>>> cents each), and two capacitors (don't know the price.) That puts me
> at
>>> around before the capacitors $100, about $50 less than the switch I am
>>> looking at. Basically you built your own automatic transfer switch
> correct?
>>> It
>>> might be worth $50 of my money right now to pay some one else to
> build it
>>> for me. I would probably enjoy doing that if I had a little more
> time for
>>> it.
>>>
>>> I'll double check on whether the PD52 transfer switch will work with
> 30
>>> amps - I believe it will, but the connection instructions for that
> switch
>>> are
>>> not entirely clear.
>>>
>>>
> Your proposed 2nd A/C solution is certainly workable, but in the
>> past when
>> working on 30A service coaches, I've just added a separate 15A CB box
> and
>> line cord for the 2nd A/C.