Exercise genny while on shore power?

It's not about which one will control the ATS ,
It's about the ATS possibly being slow and sitcky and crossing the power feeds, it's about bad habits, doing something the wrong way, until the cumulative damage to the ATS contacts reaches the point of disaster
If somebody can not bother (does not think it's important) to unplug the shore cord when exercising the generator, are they going to be bothered to take the time to shut down heavy loads before pushing that start button, will they shut down and then restart the A/C or the Heat Pump ? Natural human desire will get more lazy and do less work for that chore each month, up until the day something goes wrong and bad caca happens

Note: I don't consider the WH electric element or electric heaters a dangerous to the generator load, several portable heaters would certainly be a decent current load, but the danger to switching loads is electric Motors specially compressor Motors with their heavy stall currents, back emf from mismatched non synced power phase cycles between generator, and shore power, the generator will not be phase matched to the shore power already being used by the motor, switching a running compressor motor will cause an EMF SPIKE and HARD HIGH current spike on the GENERATOR, if a contact in the ATS happens to stick, the generator is the no contest hands down looser in the power output bout with shore power, and it might not be the only thing to suffer
Note 2: this forum has had this discussion many times,but in reverse order of connections
Most times it is about pluging into shore power at the campground when arriving with the generator running and A/C on.. The RV owner does not want to shut down his A/C for ten minutes or so needed , stop AC switch power restart AC ,
And we get 1 or 2 something went wrong topics each summer because of this, damaged generator or both genny and the A/C, the ats was already tanked because of doing this previously

4x4van wrote:

way2roll wrote:
Not just hearsay, I've heard of real cases of things getting screwed up when running the genny and shore power at the same time.

Ummmmm....isn't that the very definition of "heresay"?;)

Seriously, there is no need to disconnect, but it is a good idea to shut down any heavy loads (A/C, WH, etc) prior to firing up the generator. If the transfer switch works, it will simply switch over to generator power (after a short delay for warm up/rpm settling). If it doesn't, it will remain on shore power. There really is very little possibility for it to connect to both at the same time. The contacts can only be in one position at a time; it is a "break, then make" system.

I'm glad you said "very little possibility for it to connect to both at the same time." That is tacit admission that it is possible and could happen. That is the perfect rationale for unplugging first. Small risk but large consequences, with piddly (a technical term) effort required to absolutely prevent.

dieseltruckdriver wrote:

Bobbo wrote:
Depends. You need to exercise it once a month for 2 hours with at least 50% load. Can you get a 50% load on it while still plugged into shore power? When I had an on-board genny, I used the A/C in the summer and a pair of space heaters in the winter, but I had to unplug from shore power for that.

Why two hours? I am not being snarky, I am being sincere.

My brother works on electric motors and said to make sure to give the windings a regular workout, but he said it doesn't need to be a large load, but they do need a load. I have been doing monthly runs on my Hondas for over 10 years, and running them 10 or 15 minutes, enough to warm up the oil good and give them a load.

That is quoted from the ONAN manual with my previous RV with a built in generator.

magicbus,

I think lots of folks (including me) are on limited budgets. I have to save in advance for repairs and/or upgrades.

Since the safest transfers are made with no load, I chose to NOT have a transfer switch. After all, one has to manually remove all loads, and then restart them after the generator is warmed up.

Then, along came hybrid load support inverter/chargers--which by their design include a transfer device. Once in a while (like when the Magnum hates a gfci) I long for the days of double conversion.

way2roll wrote:
Not just hearsay, I've heard of real cases of things getting screwed up when running the genny and shore power at the same time.

Ummmmm....isn't that the very definition of "heresay"?;)

Seriously, there is no need to disconnect, but it is a good idea to shut down any heavy loads (A/C, WH, etc) prior to firing up the generator. If the transfer switch works, it will simply switch over to generator power (after a short delay for warm up/rpm settling). If it doesn't, it will remain on shore power. There really is very little possibility for it to connect to both at the same time. The contacts can only be in one position at a time; it is a "break, then make" system.

Is it COVID or do people normally worry this much? If you have to ask the question, just go out and flip the breaker on the pedestal to OFF.

Dave

To ABSOLUTELY GUARANTEE the impossibility of mutual conduction I gave a 10 pound knife switch mounted on the kitchen wall 5' off the ground child safe. It is a 4 conductor 4 gauge knife switch. Even earth ground is isolated. The Scott connection 3 to single phase transformers in the generator shed do not need to be worried about. So when I isolate for warm up I charge batteries and allow 10 minutes after oil temp has reached 190°F to de moisturize the oil. The KATO has a CL750 Luberfiner bypass filter so it takes longer to exercise it. Bypass filters are a miracle de sooting gizmo for diesels especially for high sulfur fuel. They and RAcor S series fuel filters have saved my rear too many times to count.

This is close.

"So a few weeks ago i started up my generator without realizing that the power switch for my fridge was on still. The generator tripped and a small amount of smoke came out near my inverter/converter and fuse panel. I replaced both of those and power still was not coming from my generator. So after some troubleshooting and finding out that my generator was in fact producing power, I landed on a fault in my auto transfer switch. I just located the switch, and it is attached to the back of the housing of my inverter/converter and fuse panel and I can't even open it. Has anybody else run into this problem? and what did you have to do to fix it?"

http://www.rvforum.net/SMF_forum/index.php?topic=115268.0

Find me a single post of such disaster.

time2roll wrote:
Anytime you start the generator it is a hot transfer unless you turn everything off including the converter and electric water heater. You could use the main breakers to cut power and save the transfer switch but then someone will say the breakers should not be used as a switch either. As I said the list never ends.

You act as though no one has ever had a disaster when on shore power and started their genny. Like the possibility of this problem doesn't exist. And reducing loads is just plain common sense. It's a risk and an expensive one given the minimal level of effort to prevent it altogether. But we get it, you've planted your flag and dying on that hill. I think most agree it's bad advice not to unplug first.