Dubious Electrical Idea

[eagle19952]

Richard: When I did the electrical on my last bus, I chose to make it with just one 50 amp leg. I put a jumper wire in the panel to reach the other bar. I worked fine since I do not have 240v loads.  I thought at the time that it was probably unique.  However, when I bought this bus it had a similar setup.  This makes it either a very large coincidence or that there are a lot more out there who used similar logic. As mentioned, the shore cord is 25% light and therefore easier to handle and store.  The marine panel looks interesting but I would probably go with a more budget solution.

Eagle: Thanks for the reminder to have some bypass system in case the inverter fails.  On my present system I manually move the plug from shore to generator.  The transfer switch switches from shore/generator to inverter.  Even that has a bypass system though.  Since the transfer switch probably should be replaced, I thought that this might be the time to change the system a bit.  Although it generally works fine, there have been times when I forgot to turn off the water heater when the system switched automatically to inverter. In that case, it does not destroy the batteries but does let them run down to around 10v for the inverter to close down.

Now, I wanted to throw out a hypothetical idea.  Suppose instead of using two small boxes, I just use the box I have now changing it around a little.  What if I put all the non-inverter loads on one bar with one more circuit for the inverter?  The inverter could than feed the other bar where all the low amperage circuits would be.  Is there something inherently evil about that? In my case there could be a problem due to the generator, which actually does supply 2 50 amp legs to the panel. Of course that could be modified but I am not sure that is alright to do.

I understand what you're doing.
obviously the inverter charger needs to be on the shore leg.
on mine, i just tell the inverter i'm on a 30 amp source..
i think it keeps my pole bill lower..when rv parks meter.
my refridgerator has been on the inverter since 2002.
and yes, I full time.
on the road or in NP's gen time every 36-48 hours snaps the batteries full in no time (130 amp charger)
But, you create a nightmare for the next owner

[Lin]

It need not be a nightmare for the next owner if it is documented.

Is there anything wrong with using only one leg off the generator?

[solardude]

It works with a standard 50 amp rv receptacle.  The plug is wired to only three blades (hot, neutral, ground).  I actually have removed the fourth blade from the plug since it serves no purpose.  I only have a 30 amp connection at home, so we use a common adapter pigtail.

Very interesting. Many people that do this kind of stuff don't understand power correction costs, most if not all commercial electric accounts get charged fees for power factor and unbalanced power usage. Residential does not get charged for power correction.

So if you and several others are all pulling off a single leg, I would think the fees for the campground could be pretty large.

There are special transformers that will take 240 split phase and transform it into a single leg, and vise versa. I think they are called autoformers.

SD

[solardude]

Is there anything wrong with using only one leg off the generator?

Yes, an unbalanced load will burn the windings eventually. As I mentioned above this is what an autoformer is for, it will automatically balance the two sides of split phase.

SD

[eagle19952]

It need not be a nightmare for the next owner if it is documented.

Is there anything wrong with using only one leg off the generator?

Many bus owners have a hard time grasping conventional electrics.

[Lin]

Solardude:  Suppose several campers were doing as we do and draw off only one leg, would the extra commercial charges also occur if they were roughly divided between the two legs or only if they all were pulling off the same leg?  It would seem probable that people choosing which leg to use would be random and thus be divided. The autoformer looks interesting.

Another question then-- Our generator is really supplying two 50 amp legs, so we have real 240v at the panel even though we do not use it.  When traveling down the road we generally run only the front AC, so the load is completely on one leg.  Is that therefore also weakening the generator?

Eagle:  I do not know whether I will actually try this, but it does seem intriguing because it would be so easy to do; just little more than rearranging the breakers (I love easy these days).  With that in mind, I suppose I could simply replace the transfer switch and be done with it and just keep remembering to turn off large loads when switching to the inverter.

[richard5933]

There should be a way to wire your generator to the load center so that the entire capacity is available and not just one leg. When I talked to the tech at Wrico he was recommending this if I did not have any 240v loads.

[Lin]

Thanks Richard, that makes sense.  I will try to research that although this is a 40 year old Kohler.

[eagle19952]

Solardude:  Suppose several campers were doing as we do and draw off only one leg, would the extra commercial charges also occur if they were roughly divided between the two legs or only if they all were pulling off the same leg?  It would seem probable that people choosing which leg to use would be random and thus be divided. The autoformer looks interesting.

Another question then-- Our generator is really supplying two 50 amp legs, so we have real 240v at the panel even though we do not use it.  When traveling down the road we generally run only the front AC, so the load is completely on one leg.  Is that therefore also weakening the generator?


Eagle:  I do not know whether I will actually try this, but it does seem intriguing because it would be so easy to do; just little more than rearranging the breakers (I love easy these days).  With that in mind, I suppose I could simply replace the transfer switch and be done with it and just keep remembering to turn off large loads when switching to the inverter.

My inverter fed sub is jumper-ed to feed both legs being 120v on both sides.
works fine. 3kw Xantrex Freedom Marine.
My main is 240v (one leg to each side per standard code wiring) as my heat and AC are 240v. I am an all electric coach.

I am at a loss to understand why (if) a gen puts out 240v then why wouldn't one
(a.) wire the coach to use it
(b.) wire the coach to use it
(c.)

[richard5933]

Thanks Richard, that makes sense.  I will try to research that although this is a 40 year old Kohler.

We must have the same generator then...

[Lin]

Eagle: That is necessary for an all electric coach, but for one the uses propane it can be considered optional.  We have two AC's (35 foot bus).  We rarely use more than one at a time. The water heater is ten gallon 120v.  Once the water is heated, it will generally stay warm most of the day if turned off.  Even if left on, it only draws current intermittently.  There is not need for 240 except if we really just wanted 100 amp instead of 50 amp capacity. I find that 30 amp requires power management, but 50 amp covers us fine.

The coach was wired to function off one leg.  However, the PO installed a 7kw generator that is supplying on two legs.  I think that he must have just got a deal on the generator and installed it as is to his already installed 120v system. As a result, the panel is sharing one leg to both bars when plugged into shore, but the two bars are fed separately when the plug is moved from the shore receptacle to the generator receptacle (the jump wire is in the shore receptacle). However, if I wanted to try to transform the system to use one bar for large loads and the other bar for inverter loads, then the generator would apparently be best modified to produce only 120v.  One of the interests in this hobby is the ability to solve a problem in an unconventional way on a small scale just for the fun of it.

Richard: Did you change the generator from 240v to 120v?

[solardude]

Lin, if you have an older Kohler, odds are in your favor that you can configure it for a "center tap" to combine both for a single 120VAC output. It is usually pretty easy, the instructions are normally under the control panel.

SD

[richard5933]

Richard: Did you change the generator from 240v to 120v?

That's a trick question, right?

Our generator has two 30-amp breakers on the output. To be honest, I can't remember how it goes into the transfer switch without looking, and I can't do that right now as the bus is in the shop getting a/c work done. I'll get back to you with more details when I can look at the connections and/or the manual from Custom Coach, but I believe that each of the 30-amp outputs feeds one side of the load center. Our coach has two separate legs coming in from shore power, each powering one side of the load center as well. But, since our load center is a marine panel circa 1974 it is only set up for 120v - I don't think that it's even possible to install 240 breakers in the panel. We have electric heat running parallel to the LP, but it's all 120v. Same for our two-burner cook top and our hot water heater. All 120v.

I'll check on the connections with the generator and post again.

[Van]

Lin, if you have an older Kohler, odds are in your favor that you can configure it for a "center tap" to combine both for a single 120VAC output. It is usually pretty easy, the instructions are normally under the control panel.

SD

Lin if I remember correctly my old Kohler output had a jumper on the back of the 2 breakers that I removed to make it 240.

[buswarrior]

A busnut with bigger power needs, but all 120, can do both:

1) wire the generator for straight 120 for perfect balance on the windings, and
2) leave the coach wired with 2 sides in the panels, to access the required 50 amp power poles.

Having the correct bigger neutral sizing in the right places for this strategy is VERY important, as there is no balancing between the hots, the neutral will see ALL the power.

Beware of vendors... they have been the source of many busnut power problems, there are some who know less than you!!!!

But are great pretenders...

happy coaching!
buswarrior