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RobLee
11-30-2013, 12:34 AM
First I want to say hello to all here. I have been a member here and reading and learning a lot the last few weeks. In late Oct this year I bought a used 2012 Cyclone 300C with a 5500 Onan. Over the last forty years this is the tenth RV I had, but only the second one to have a generator. The service tech that did the walk though with us told me not to start the generator while the power cord was plugged in to shore power. He said it could cause a spike that could damage some of the electrical components. I keep the trailer plugged in at home and understand that I need to exercise the generator periodically. Is it really necessary to unplug from shore power before I start the generator or will it automatically switch over and cause no harm?

danemayer
11-30-2013, 06:30 AM
The purpose of the automatic transfer switch is to ensure that only one power source is connected at a time. When you start the generator, the transfer switch allows 20-45 seconds for the genny to get up to speed and stabilize before switching. Here's what the Progressive Dynamics manuals says:



When the shore power is applied the relay is at rest and power is transferred to the panel.

When Generator power is applied there is a 20-45 second delay and then the relay activates transferring Generator power to the panel.

If shore power returns while the Gen power is present nothing will happen.

When the Gen power is removed the relay will drop out and allow the shore side to supply power.

Generator overrides shore power.



Here's a link to the manual (http://manuals.heartlandowners.org/manuals/Electrical/Trnsfr_Switch/Progressive_Dynamics/Progressive%20Dynamics%205100%20Manual%20110538A-English.pdf). If you were supposed to disconnect shore power before starting the generator, I'm pretty sure it would say so in the manual.

RobLee
11-30-2013, 08:47 AM
Thank you danemayer. This is exactly the information I was wanting.

evolvingpowercat
11-30-2013, 09:14 AM
The heart of the transfer switch is a serious relay that can carry a lot of amps thru its contacts. You can maximize the life of the transfer switch by not operating it with large current flowing thru it. This causes an electrical arc across the contacts that removes metal from the contacts, eventually wearing them out.

If you are on shore power and you want to test your generator without disconnecting from shore power, I suggest you turn off any large power drains like your Air Conditioners or any electric heaters.

rgwilliams69
11-30-2013, 10:04 AM
We have run (started) our generator like this several times with no issues, however when we do I notice a slight difference in the cutover than from just the generator kicking in with no shore power. I have noticed that there is still a momentary interruption when it switches from shore to generator, and imagine that the comment about a quick surge/etc. is a probability that would mean you would not want to have your heavy duty draws online when switching like this. From an engineering perspective possible to do, but maybe not advised? All it takes is a little amp/volt problem on some items to put them out of commission...

Also a couple of times we have had our Honda 3000 (normal low consumption generator that runs all the time when we are at the race tracks) on the shore power cable and running and I've started the ONAN generator to run a heavy load (maybe want to use the microwave, etc. and other stuff all at once). This procedure DOES cause the Honda to cycle way up to a very high RPM, and sometimes causes it to cut out completely. Not sure what is going on there but I don't do that anymore either.

Just our experiences.

wdk450
11-30-2013, 11:02 AM
When you start the Onan, it takes ALL of the electrical load via the transfer switch, leaving the Honda generator suddenly unloaded. That is why the Honda generator revs up. The transfer switch disconnects shore power and connects generator power to your trailer's AC distribution (breaker) box when it senses the generator producing power. It switches the power routing back to shore power supply when the generetor stops producing power.


We have run (started) our generator like this several times with no issues, however when we do I notice a slight difference in the cutover than from just the generator kicking in with no shore power. I have noticed that there is still a momentary interruption when it switches from shore to generator, and imagine that the comment about a quick surge/etc. is a probability that would mean you would not want to have your heavy duty draws online when switching like this. From an engineering perspective possible to do, but maybe not advised? All it takes is a little amp/volt problem on some items to put them out of commission...

Also a couple of times we have had our Honda 3000 (normal low consumption generator that runs all the time when we are at the race tracks) on the shore power cable and running and I've started the ONAN generator to run a heavy load (maybe want to use the microwave, etc. and other stuff all at once). This procedure DOES cause the Honda to cycle way up to a very high RPM, and sometimes causes it to cut out completely. Not sure what is going on there but I don't do that anymore either.

Just our experiences.

RobLee
11-30-2013, 01:09 PM
Thank you evolvingpowercat for the comments. That certainly makes good sense to me to turn off the larger power drains to reduce arcing at the contacts. I will be careful of that.