Scratching my bald head about a brownout

[Americanrascal]

Our Cummins Onan 5500 seems to work well. Today something went haywire when I did the monthly excercise.

It started and cranked out 115-120 volts on each leg initially today. But then it kicked out a Brown Out warning on the power management panel showing leg 2 was only getting 82 volts when the rear A/C came on. I immediatly shut down. At the time I had the forward A/C running on Leg 1 and it was running fine on about 115 volts. During the run I had my shore power surge protector hooked to the 50 amp house outlet but I had the power off during the entire cycle.

To check things out after shut down, I then connected shore power showing 120 volts on each leg and both A/C units ran fine. No brown out.

Next I removed shore power and surge protector from its wall connection and cycled the 2 breakers on the generator and fired it up.

Everything ran fine during that excersise--- no brown out.

I sense soemthing is amiss but not sure where to check.

Any ideas on what I need to be looking for? Surge protector when connected but with no power??? Weakening breaker on the generator? Transfer switch?

Thanks Joe

[powercat_ras]

The 5500 has a single 120 VAC 45 maximum amps output that is fed thru two circuit breakers on the generator thru two hot wires to two terminals on the automatic transfer switch. Something is making poor electrical connecition on the Leg 2 feed side. Could just be bad wire to terminal connection or a bad breaker or the contactor going bad in the transfer switch.

I'd do easy stuff first - toggle circuit breakers on generator, open cover on transfer switch ( WITH GENERATOR OFF, SHORE CABLE UNPLUGGED, INVERTER OFF ) and look for signs of overheating on wire connections and burnt contacts on contactor if the open frame type. Hopefully the problem won't be internal to the 5500.

Good luck.

[eyecando]

Originally Posted by Americanrascal

Our Cummins Onan 5500 seems to work well. Today something went haywire when I did the monthly excercise.

It started and cranked out 115-120 volts on each leg initially today. But then it kicked out a Brown Out warning on the power management panel showing leg 2 was only getting 82 volts when the rear A/C came on. I immediatly shut down. At the time I had the forward A/C running on Leg 1 and it was running fine on about 115 volts. During the run I had my shore power surge protector hooked to the 50 amp house outlet but I had the power off during the entire cycle.

To check things out after shut down, I then connected shore power showing 120 volts on each leg and both A/C units ran fine. No brown out.

Next I removed shore power and surge protector from its wall connection and cycled the 2 breakers on the generator and fired it up.

Everything ran fine during that excersise--- no brown out.

I sense soemthing is amiss but not sure where to check.

Any ideas on what I need to be looking for? Surge protector when connected but with no power??? Weakening breaker on the generator? Transfer switch?

Thanks Joe

Sounds like the AC unit may have had a hard time starting or maybe it was trying to start at the same time as some other high current device. It’s also possible a starting capacitor could be weak.

Or maybe the generator had issues picking up the load since it had not been started in a while.

If the problem cleared up, I wouldn’t worry about it unless it reoccurs.

[Morich]

I agree with the ideas above but one thing that can slip up and make an AC hard to start is one to review.
If we try to start the unit too soon after it has been running, it can still have high pressure built and that can lead to very high starting current!

Any chance of a malfunction at the thermostat. We've had times when I turn the air off and my wife coming down the hall finds it off and tries to turn it on!

But a dirty contact in a breaker can also be cleared when you turn it off/on, so I might wait on this one.

[Americanrascal]

I completed a retighten and proper torque on all the generator and transfer switch connections day before yesterday. Also checked the connections on the breakers on the generator. All the connections were properly torqued on the transfer switch at 45 inch lbs as prescribed.

I did find what may have been a loose spade connection on one of the 2 breakers on the genny. I tightened it up and reconnected. Then I ran the genny under load with 2 heat pumps running ---all fired up and ran well. I also checked the terminals with the heat gun and there was little if any heat gain on any of the connections.

Both heat pumps/A-C's started and ran fine no voltage drop out on the genny.

The power management system or the starting capacitor does not cycle on both units at the same time, but sets a delay. Maybe its not long enough. The high pressure switch may also be a factor I need to watch as I had one fail before causing me to replace an entire heat pump.

Going forward, when operating with the genny we are going to manually delay the start up of the second heat pump for several long minutes.

At the moment all seems good. Thanks for all the input it was very helpful.
Joe