I recently read an article entitled "20 Tricks of the Trade" (for RVers) and one of the items said "Never start your vehicle or run the generator while you are plugged into shore power." While starting the generator, if nothing else, would be wasteful and noisy, I want to know why starting the engine while still on shore power is a no-no. It seems to me that pulling in the slides and raising the jacks are very power intensive and when I start my engine to do these, I have always stayed on shore power to draw from it until completing these 2 tasks so that I didn't drain the batteries unnecessarily at the start of my journey. It has been my understanding and expectation that the Trombetta solenoid and BIRD would properly manage and isolate the power sources.I've probably done this 100-150 times without incident. Am I lucky, or is the advise in this article flawed? If it is sound advise, please explain why.

I think the potential risk is that with many RV wirings, when you start the engine, it pulls from both the engine and the house battery. If you are plugged into shore power, there could be a risk of pulling too much power. I don't know how likely that really is or not.With my clipper, my boss is actually wiring it so the engine only pulls from the engine battery by using a delay switch. After about 20-30 seconds, once the engine has started, the house switch will connect and the house battery will charge from the alternator. There will be a toggle switch in the dash so that if the engine battery is dead, I can jumpstart the engine from the house battery - otherwise, I'm only pulling power from the engine battery.

Winnebago actually recommends the engine running when extending and retracting the slides on my 2013 40U Journey. Because of the power requirements.

I never worried about starting the RV plugged in or not, generator running or not.I think that some people have a 'theory' that it is dangerous, while reality is that the design protects us from anything going wrong.The generator can be run safely while plugged into a 120 volt outlet. There is a safety device to prevent any danger from this.You can start the engine or generator while plugged in or not. You really do not save all that much power by leaving the RV plugged in while putting in or out the slides. While the motor might draw as many as 65 amps, this is less than 1 minute, so only 1 amp hour. .. . .That is the same amount of power consumed by a light bulb over 1 hour. Same with the water pump, it will consume 7.5 amps per hour. However in that hour, it will also pump 2 GPM or 120 gallons. So you can empty the water tank with only about 5 amp hours of power, really in-significant. Have fun camping!Fred.

Been RVing from 60,s never had a prob,. Starting engine while plugged in. See no prob. either.Gen will over ride shore power conn. Just hope your auto transfer switch is working as it should.

rvluckyorwhat wrote:I want to know why starting the engine while still on shore power is a no-no. As others have indicated, for short periods it isn't a problem.You will simply have two charging sources connected to the batteries at the same time.....which is not a problem, short term.

starting engine while plugged in to short power

23 Replies

Ductape
Explorer
Jul 20, 2015
All you're mandating is moving the wear from one set of contacts to another. No sale.

Edit: "short power"? That would cause problems! ;)

Gotta love that autocorrect.
dougrainer
Nomad
Jul 20, 2015
1. NOTHING wrong with starting the chassis engine when plugged into shore power.
2. Staring the Genset when plugged into shore power IS a NO NO. The reason being--- Ideally, you NEVER want a load when activating the 120 transfer box relay's. Odds are, IF you start the Genset when plugged in, you will have a good amount of load (AC units and such) already running. When the Transfer relay's open and then close to Genset power, THAT load spike affects the points in the relay's and will degrade them over time. Will cause them to arc and burn slightly. Over time this adds up until they do not make a good contac and fail. Some RV'ers will turn the 50 amp gang breakers OFF at the RV breaker panel, before connecting Shore Power or activating the Genset. Then once the Shore or Genset has transferred, they turn the breakers back ON. Doug
rvluckyorwhat
Explorer
Jul 20, 2015
Thanks to everyone who provided relevant answers. Full disclosure: I am an electrical engineer so I was able to sort through the answers where people made statements that were irrelevant, or just plain wrong, in their explanation and dismissed those outright. Among the remaining responses, I would summarize them as mostly gravitating towards the notion that running the engine while attached to shore power as not being an issue, and nobody shared a story of that ever causing a problem. However, one dissenting opinion seemed to come from a contributor who is very experienced, very prolific on this site, and viewed by some here as very knowledgeable.

This morning, I called the company who published the original article (a very well respected company in the RV industry, I might add) but after being bounced around to a couple people, I still wasn't able to find the person to take responsibility for writing the article or to provide reasoning or justification for what they wrote. The last person I spoke with took my information and said he would look into it and get back to me, but I'm not holding my breath.

So next, I decided to call my RV manufacturer (Thor) and see what their tech support people recommended. They said using shore power while the engine was running isn't a problem and that it could even help with jack operation. I'm not going to recommend this solution for every RV because it clearly depends on how systems are wired and what components are used.

"Never start your vehicle or run the generator while you are plugged into shore power."...fable, lore, or fact...I don't know. I'm going to continue my RV hookup and unhook process the way I always have. It never has caused me any problems, and fundamentally, the way I've been doing it seems intuitively sound to me.
MEXICOWANDERER
Explorer
Jul 20, 2015
Years and years ago. DW was puttering around in the bedroom, so I eased out of the driveway and crawled down the street. Heard shouting. Looked in the mirror. She had departed because she "had a feeling" she forgot something in the house.

Man I'll tell ya, it was a very cool and silence filled first half of that weekend.
Clay_L
Explorer
Jul 20, 2015
A lot of us often run the generator and engine at the same time while driving so that the house AC can be used.

While getting ready to leave I always run the engine as I retract the slide and levelers as recommended by my Winnebago manual.
This provides a higher voltage for the motors involved which is easier on the motor.
I leave shore power on so I can leave the house AC on while getting ready to leave.

I use a departure check list so I don't forget to unplug from shore power.
bdpreece
Explorer II
Jul 20, 2015
If you own a Monaco coach and follow the manufacturers directions this would be a pain. Monaco wants you to start the coach and bring up the air before retracting the slides. In order to bring in the slides you then have to shut down the coach since the interlocks will not let the slides work with the key on. Don't see anything in my manual on disconnecting before starting engine and running the slides without being plugged in puts a heck of a strain on the batteries.
Canadian_Rainbi
Explorer
Jul 20, 2015
wa8yxm wrote:
Often start while hooked to shore.. BIGGEST DANGER.. Forgetting to unhook from shore.

That's why I never do it!

About 30 years ago I noticed something in the sideview mirror: a Power cord chasing me down the street!. Not much left of the plug. :E :S
MEXICOWANDERER
Explorer
Jul 20, 2015
Hmmm I would assume a bit of common sense be used in qualifying a decision. A genset is on a different electrical system than a battery. Inverters perform a switchover of around .020 seconds. Myself I like to see starter motor transients clamped at the source but that is a different horse than starting the main engine. Starting a generator while plugged in renders battery voltage lower than 12-volts when the converter is on the same circuit
I wouldn't mind seeing the specific points listed for a shore power disconnect.
Ductape
Explorer
Jul 20, 2015
By that logic when mobile I must shut down the genset every time before I crank the chassis prime mover. Horsefeathers.
time2roll
Nomad
Jul 20, 2015
rvluckyorwhat wrote:
I've probably done this 100-150 times without incident. Am I lucky, or is the advise in this article flawed? If it is sound advise, please explain why.
Advice is flawed.
Otherwise let the author explain the exact issue.

If it ever was an issue we would have heard it right here in Tech Issues.