Exercise genny while on shore power?

[J-R]

New to on board generators. Parked for the winter with 50 amp service, and it's time to exercise the genny. Do I have to disconnect first?

2006 Bounder, Onan 5500, ATS

[MrWizard]

In conditions such as changing 120v power inputs
Or generator restarts

I give the AC at least 5 minutes of fan only run time, to reduce internal heat, and head pressure on the compressor, this reduces lock rotor amps on the compressor motor thus lower startup load, when switching to cool mode
A really big help when using a generator to power the RV AC

[Boon_Docker]

Thanks, Mexico & Bobbo

[Bobbo]

Boon Docker wrote:
I'm curious, why the 3 minute wait?

Air conditioner compressor head pressure. Turn off the air conditioner and you don't need the 3 minutes.

[MEXICOWANDERER]

It may allow for gas pressure compressor bleed down.

[Boon_Docker]

I'm curious, why the 3 minute wait?

[wa8yxm]

Ok one rule when switching from GENERATOR to SHORE or back is OFF for 3 minutes

So As someone up thread said
Go out. Flip breaker to OFF,, go back in side, count to 3 minutes and Crank that puppy up... shut down and 3 minutes later (See note) flip breaker back on

Option 2: Flip main breaker in RV Inside) off Wait 3 minutes. Crank it up And then reset breaker. When done flip breaker off. Kill genny, wait 3 minutes and flip back on

NOTE: I rigged my rig with a "SURGE GUARD" (TRC/Southwire) unit in line with the SHORE power only.. So I shut genny down went out and flipped breaker on and the TRC counted down the better part of 3 minutes. Then CLUNK power on.

I had a somewhat unique power install

Shore----Hughes Autoformer installed.. Hard wired TRC/Southwire Surgeguard converted to plug in----- Auto transfer switch.

When the RV was "Totaled" I pulled both the Autoformer and the surge guard.

And now.. For a radio net so end of post.

[4x4van]

Bobbo wrote:

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.

Yes, I admit that it is possible. Lots of things are "possible". But understanding how an ATS works tells me that it is highly, highly improbable for the ATS to connect to both shore and generator at the same time. Switching with heavy loads can cause arcing and damage the contacts, possible making them stick, but they can still only make contact with one side or the other, not both. An ATS is just a large relay.

Yes, we hear of the occasional claim of it happening, but very seldom (among 100s of 1000s of RVs in use), and never have I been convinced that what the poster "thinks" happened actually did.

[wopachop]

edatlanta wrote:
My 3rd ATS is going strong, but I do now check the wiring lugs inside the unit once a year to make sure they are still tight.

Things that go bump in the night or bump up and down highways need to be checked.

I took my service panel cover off to access my converter and clean all the sawdust they left in there. I found many loose wires all over the place. 120v. 12v side. I checked every single screw i could find.

My friend has a toyhauler. Noticed the 120v outlet in the bathroom had black smoke marks. Sure enough the connnections in the back were loose and arcing.

[Cummins12V98]

magicbus wrote:
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

ZACTLY!!!

[edatlanta]

We all have our story based on our experiences so here is mine.

I full time since August 2010. I have an onboard Onan and exercise it every month for one hour under load. The load will be a/c's in a/c season and electric heaters in heat season. I NEVER fail to exercise it and it works great whenever I need it and it has a little over 600 hours on it now.

I always turn off my main breaker at the power pedestal when I fire up the generator. During the past 10 years I have had to replace 2 ATS's. The first one that failed was replaced with a different brand due to the original one not being produced any longer and was ultimately recalled by several RV manufacturers. The second one failed due to burned wiring inside the ATS which I think was caused by loose wiring lugs. My 3rd ATS is going strong, but I do now check the wiring lugs inside the unit once a year to make sure they are still tight.

Things that go bump in the night or bump up and down highways need to be checked.

[MrWizard]

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

[Bobbo]

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.

[Bobbo]

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.

[pianotuna]

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.