Generator Automatic Transfer Switch
The Parallax ATS 5070 Automatic Generator Transfer Switch
My Coachmen Pathfinder RV, motor home has an ATS5070 Automatic Transfer
It malfunctioned. I am writing this much, much after the time of the
don't recall for sure but the failure MAY have been related to when our
house took a lightening hit. We were lucky and only a few devices were
Anyway, for more than a year, I manually connected the correct wires
when I needed to run the generator. When I retired Aug 1, 2015 I
finally had a chance to work on my backlog of special projects like
To start, lets consider the wire colors. In my unit all wires are the
correct colors. Don't assume this is true on your unit, measure it and
confirm before getting
too close! When these
circuits are live, there is dangerous electricity present.
You NEED TO
MEASURE to confirm that
conditions are as expected before starting work. Also, be sure that
nobody is around to 'turn on' or to 'plug in' the circuit that you are
working on. This can also cause an unexpected dangerous condition.
Black = L1, HOT wire
Red = L2, HOT wire
White = Return (or Neutral)
Green = ground
Bare (no insulation) = ground
L1 and L2 are HOT!!!
The White Neutral, also called the Return wire should NOT be Hot!
HOT means that if you connect a voltmeter from this wire to ground you
will read that electricity is present. So, when the circuits are
active, you should read about 120V from either the Black or the Red
wire to ground.
The White wire is the Return wire. Electricity must have a way to
'come' and it must have a way to 'go back'. If one of the two are not
connected, the light won't come on, the motor won't run. The White wire
is the path the electricity uses to go back, hence the term Return
wire. The Black or the Red wire is the path for the electricity to
Putting a voltmeter across the Black and the White wire should read
Putting a voltmeter across the Red and the White wire should read about
Putting a voltmeter across the White and the Ground should read 0V. It
is dangerous if this is NOT 0 Volts, get a professional to look at
It is usually allowed to have the White wire directly connected to
ground wire. In my house, both white wires and ground wires are both
connected to the same large, common connection buses.
However, sometimes they are NOT connected and in this case, it would be
possible to have a voltage difference between these wires. Not an OK
thing but a possible thing.
One final item, if you put a voltmeter across the Red and the Black
wires, you will probably get about 220V. On my generator, L1 and L2 are
'in phase' so in this case reading across these two wires reads at 0V
difference between these two wires. Please be strongly aware that these
wires are both at 120 V (to ground) it is simply that that are both at
the same 120V, they are both very HOT, at the same hotness, and both
deserve appropriate respect!
In the ATS 5070 there are:
2 Heavy Duty Relays
1 Bridge Rectifier, RS207L
1 Time Delay Relay, E174797
1 SPDT switch attached to the Heavy Duty Relay that controls the Wht
and Blu wires
The Heavy Duty Relays
connect the control panel (the internal house AC wiring) to:
either the cord (that plugs into the campground power outlet)
or the generator.
These are effectively electrically activated big DPDT switches. (DPDT =
double pole, double throw)
The 'no electricity' state of the Heavy Duty Relays is to connect the
Cord to the Control Panel, to the internal house wires.
These relays stay in this state where the Cord is connected to the
Control Panel unless/until the generator applys power and the Bridge
Rectifier and the Time Delay Relay work their magic.
The Bridge Rectifier
has 4 terminal connectors:
2 AC line inputs
a + DC output
and a - DC output.
The job that the Bridge Rectifier does is to change a little bit of AC
electricity from the generator into + and - (plus and minus) DC
This little bit of DC electricity does two jobs:
it tells the Time Delay Relay that electricity from the generator is
present and to begin a 'timing' cycle
and it will provide the electricity to the heavy duty relay coils that
will cause those relays to change where the control panel electricity
comes from (from either the cord or from the generator). It is the
power to 'switch' those Heavy Duty Relays.
The Time Delay Relay
waits for DC electricity coming from the Bridge Rectifier.
When it detects DC electricity from the Bridge Rectifier, it begins a
timer cycle that lasts maybe a couple minutes at most (I haven't timed
When the timer completes it's cycle, then the internal relay (inside
the Time Delay Relay) switches and applies DC voltage to the coil of
the Heavy Duty Relay that controls the Wht and Blu wires.
This causes this relay to switch, disconnecting the Cord and connecting
the Generator WHITE neutral return wires to the internal house wiring
This also causes that attached SPDT switch to connect the second Heavy
Duty Relay coil to the DC output from the Time Delay Relay.
The second Heavy Duty Relay now has electricity on it's coil and it now
also switches, disconnecting the Cord and connecting the Generator Red
and Black wires to the internal house wiring.
Note that this second Heavy Duty Relay switches a fraction of a second
after the first Heavy Duty Relay switches. The returns are connected
first then the hots are switched over.
When generator electricity stops arriving (when generator is turned
off), the Heavy Duty Relays switch back to their deactivated, 'no
electricity' (no Generator electricity) state where the Cord wires are
connected to the Control Panel, the house wires.
It is a over simplification but it is valid to think of the Heavy Duty
Relays as being big switches that switch over when generator
electricity is applied to their coils. In the absence of generator
electricity, these relays connect the Cord electricity to the house
wires. When Generator electricity is present to cause the relays
activate, to change states, they then connect the Generator electricity
to the house wires.
Upon testing my non-functional ATS5070, I discovered that my Bridge
Rectifier did not show correct resistance readings. I was within
reasonable driving distance to a Radio Shack and they stock a 4A 400V
full waver Bridge Rectifier that has close enough specs to work in this
device. I bought one, dropped it in, applied AC to generator L1 and Wht
leads, and tested for appropriate Bridge Rectifier function (that would
be reading a Plus voltage on the + pin and a - voltage on the - pin)
and while I was reading those values, the big relays toggled over to
their other state. Urica! I installed it in my RV and to my profound
joy, it once again is working correctly. No more hand jumping the
generator wire to the house wires when I need to run the genny.
I did NOT find the exact Time Delay Relay part number on the Internet.
are some time delay relays that seem like they should work OK.
I will buy and keep in stock a Bridge Rectifier and a Time Delay Relay
anticipating that since I brought my raincoat, it won't rain.
(I have purchased a ICM102 'Delay on Make Timer' to replace the E174797
Time Delay Relay if it ever fails. This replacement device will provide
similar functionality. It will need to be correctly wired and is NOT
just a drop-in replacement either electrically or
I was frustrated with not finding any useful circuit description on the
Internet. I figured out the preceding information by observing my
unit, tracing where the
wires went, and observing printing on components like '+', '-', and
'AC' on the bridge Rectifier and 'NO' on the SPST switch. If I would
have had the schematic diagram shown below, that would have made the
diagnosis process much easier but at that time, I had not yet found
that diagram. At this point, it confirms what I had determined. I
provide it as a significant aid to other owners attempting to fix or
maintain units that they own.
Be careful, observing appropriate safety precautions when working on
electrical circuits and good luck.
Please send any corrections, comments or suggestions to:
I include the below ATS5070 Schematic Diagram because I was unable to
relocate it after about 2 hours of Google searching. This is with the
knowledge that it does exist out there somewhere! I think I originally
found it off a link on some RV forum discussion page. Anyway, I was not
able to refind it to included it as a link to that source.