Allegro bus Onan Transfer switch problem

[MVaughn1]

I have a 1997 40' allegro Bus
When i crank 7500 quiet generator
runs normal and then idles down and does not power RV.
shore power works fine.
no breakers are flipped, have tripped breaker om Gen and reset.
same results when disconnected from shore power or Hooked up.
Any suggestions?

[wolfe10]

Mvaughn1,


Welcome to iRV2.


Start by turning OFF and back ON the on-generator breakers.


After that, if you are safe working around 120 VAC, remove the lid to the ATS and check for power IN and OUT with the generator on.

[MVaughn1]

Thank you Wolfe10
I am comfortable with 120 volts.
have reset breakers several times but i need to understand how this works.
Does the Generator cable go the Transfer switch or is that just where the relays stop the passing on of shore power?

[wolfe10]

The ATS has input from both shore power and generator. It allows only one source of 120 VAC at a time into the coach.


Remove the lid and you will see the two IN's and the one OUT that goes to the coach main 120 VAC breaker box.


If no 120 VAC with the generator running on the IN side of the ATS, there is a junction box where generator wiring connects to the cable that goes to the ATS.

[Skip426]

Here's a picture of my transfer switch with the lid off .

Grey cable at the bottom is genset power .
Red arrows indicate the contactors for gen set and shore power .
Green led indicates proper operation .
With all power removed you can press on the black portion indicated by the arrows , hold it in and check continuity through the switch .

EDIT: If your transfer switch is considerably different than this photo , please post a picture and make/model info .

[MVaughn1]

My ATS is still original. PS-245S Power Switch
Todd Engineering.
With Gen running i can flip breaker off on shore power and one coil activates. Green light comes on with Gen. second coil never activates. I can manually make it contact and it makes everything work.
my switch says it has 110 volt DC coils. looks like we have 150 volts dc across coils
pretty sure coil is out, but any idea on the 150 v dc

[MN_Traveler]

If you have 120v from the generator, and you can manually activate the generator supply switch (with power going to the coach), then i would just suspect an old, broken ATS. you will likely need to replace it

[Persistent]

Originally Posted by MVaughn1

I have a 1997 40' allegro Bus
When i crank 7500 quiet generator
runs normal and then idles down and does not power RV.
shore power works fine.
no breakers are flipped, have tripped breaker om Gen and reset.
same results when disconnected from shore power or Hooked up.
Any suggestions?

Possibly an Onan 7500 quiet generator 7.5 HDKAT-41934. See serial number label for correct model number.

It should probably maintain a constant RPM. It probably should not "idles down".

Get Operator's Manual from Cummins. You need an account.
https://www.cummins.com/cm-generator-manuals

Find troubleshooting section and diagnose the issue.

[Skip426]

Originally Posted by MVaughn1

My ATS is still original. PS-245S Power Switch
Todd Engineering.
With Gen running i can flip breaker off on shore power and one coil activates. Green light comes on with Gen. second coil never activates. I can manually make it contact and it makes everything work.
my switch says it has 110 volt DC coils. looks like we have 150 volts dc across coils
pretty sure coil is out, but any idea on the 150 v dc

Todd Engineering went under in 2008 , so parts maybe a problem .

Here's a document on testing the contractors , using an ohm meter .

[Gary RVRoamer]

Originally Posted by Persistent

Possibly an Onan 7500 quiet generator 7.5 HDKAT-41934. See serial number label for correct model number.

It should probably maintain a constant RPM. It probably should not "idles down".

Get Operator's Manual from Cummins. You need an account.
https://www.cummins.com/cm-generator-manuals

Find troubleshooting section and diagnose the issue.

The Onan7500 is an inverter-generator and thus variable speed rather than fixed RPM. It revs up or down to match the amp load.

[twinboat]

Your transfer switch has 2 relays, one for switching the neutrals and the other for switching the hot lines.
Both contactors need to pull in.

Time to modernize , replace it.