Hi folks. I am helping someone setup their built in EVSE for their electric vehicle charging station on their motorhome. It has (I believe) a 12k onan genny. He would like to setup something like we have with ours but would like to use the full capability of his Juice Box 40 amp EVSE for his EV. (Either a BMWi3 Rex or a Chevy Bolt). We have only a 7.5K Onan in our Revolution so it is only 120 volt so it takes a lot longer to charge the car (like 6 times longer). Both of the cars he is looking at are 7.2 KW (I believe) chargers so the'll pull 32 amps. I will be looking for an easy point to wire in an additional Nema 14-50 on the front of the coach as he will use a front compartment to mount the EVSE something we have in our picture below. They do a little dry camping seasonally and this will give them options if there are no DCFC facilities close to where they are. So any body played with their Onan 12K lately?Thanks in advanceJohn

Look for a junction box between the genset and the rig's wiring to transfer switch. This is commonly at the rig's end of the flexible conduit. You could tap at this location. You would need a circuit breaker to protect the receptacle then run to EVSE receptacle.This should be a 120/240 four wire circuit.

enblethen wrote:Look for a junction box between the genset and the rig's wiring to transfer switch. This is commonly at the rig's end of the flexible conduit. You could tap at this location. You would need a circuit breaker to protect the receptacle then run to EVSE receptacle.This should be a 120/240 four wire circuit.I believe it is a Newmar something or other. I won't be able to crawl under it for a another few weeks so I'm trying to get my ducks in a row. We'll be working on it in the desert if this comes about. So would you think the junction box is right at the Onan end (ideal because this is where he wants to put the EVSE). I have a handle on the electrical work but am still trying to work out a weather proof solution which I can't really do till I see what I'm up against. What size is the breaker on the Genny. I'll probably use a 40 amp breaker pair.

I added one at my 10k junction box on the generator.

does a 12K unit have a 50 amp feed (4 wire) or 30 (3 wire)like a 8K?? if it has a 50 amp feed just like the shore power you could tap in to the system fairly easyif its the same as a 30amp 8K you wont get 240V nohow

gutfelt wrote:does a 12K unit have a 50 amp feed (4 wire) or 30 (3 wire)like a 8K?? if it has a 50 amp feed just like the shore power you could tap in to the system fairly easyif its the same as a 30amp 8K you wont get 240V nohowThats the kind of thing I would like to find out BEFORE we start working on this. I have heard various versions of this. I need 240 volts to make it work the way he wants or he'll be stuck with essentially what I have (120) but at higher current. EVSE's will run fine on 120 but most have a 12 amp pilot signal to the car when running on 120. There are some that send a 32 amp pilot to the car on 120 but obviously it is still half the speed of 32 amps at 240. I need somebody to measure across the breakers on a coach with a 12K Onan. Takers??

Do Onan 12K's in Moho's have an easy access 240 cnction

15 Replies

John___Angela
Explorer
Nov 09, 2017
gutfelt wrote:
gsander1 wrote:
Both the 10 KW and 12.5 KW Onans are 120/240.

so both are two 120V line 50 amp just the same as shore power

John your good to go

Volts
120/240
Amps
104 / 52

That will work. I kinda need to pre buy the components (breakers etc) as it will be inconvenient to go and get them at the time. Just found out it won’t be till Some time in January. . Lots of time to plan things out.
Ivylog
Explorer III
Nov 09, 2017
Why do you need to add breakers??? There are two already on the side of the generator...a pretty good indication that it's 240V.
gutfelt
Explorer
Nov 09, 2017
gsander1 wrote:
Both the 10 KW and 12.5 KW Onans are 120/240.

so both are two 120V line 50 amp just the same as shore power

John your good to go

Volts
120/240
Amps
104 / 52
gsander1
Explorer
Nov 09, 2017
Both the 10 KW and 12.5 KW Onans are 120/240.
John___Angela
Explorer
Nov 09, 2017
gutfelt wrote:
John & Angela wrote:
gutfelt wrote:
does a 12K unit have a 50 amp feed (4 wire) or 30 (3 wire)like a 8K?? if it has a 50 amp feed just like the shore power you could tap in to the system fairly easy
if its the same as a 30amp 8K you wont get 240V nohow

Thats the kind of thing I would like to find out BEFORE we start working on this. I have heard various versions of this. I need 240 volts to make it work the way he wants or he'll be stuck with essentially what I have (120) but at higher current. EVSE's will run fine on 120 but most have a 12 amp pilot signal to the car when running on 120. There are some that send a 32 amp pilot to the car on 120 but obviously it is still half the speed of 32 amps at 240. I need somebody to measure across the breakers on a coach with a 12K Onan. Takers??

John
Like I suggested if the 12K has two 120V( hot) outputs like a 50 amp shore power has You can get your 240 if It only has one like a 30 amp system then you can not

U understand, I am going to have to wait until I see it before I can make plans. I like the idea of picking it off at the transfer switch though. Assuming there is space close by I can mount a box with a breaker. I'm thinking this through and the worst case is it is 120 and we go with a single 40 amp breaker. He'll have to pick an EVSE with a variable 120 output that can send a 32 amp pilot to the car so the car knows what to pull. It's not exactly what he wants (half as fast) but for what he needs it to do as as often as he needs it to do it it should work. ....but lets hope it is a 240 output.
gutfelt
Explorer
Nov 08, 2017
John & Angela wrote:
gutfelt wrote:
does a 12K unit have a 50 amp feed (4 wire) or 30 (3 wire)like a 8K?? if it has a 50 amp feed just like the shore power you could tap in to the system fairly easy
if its the same as a 30amp 8K you wont get 240V nohow

Thats the kind of thing I would like to find out BEFORE we start working on this. I have heard various versions of this. I need 240 volts to make it work the way he wants or he'll be stuck with essentially what I have (120) but at higher current. EVSE's will run fine on 120 but most have a 12 amp pilot signal to the car when running on 120. There are some that send a 32 amp pilot to the car on 120 but obviously it is still half the speed of 32 amps at 240. I need somebody to measure across the breakers on a coach with a 12K Onan. Takers??

John
Like I suggested if the 12K has two 120V( hot) outputs like a 50 amp shore power has You can get your 240 if It only has one like a 30 amp system then you can not
MrWizard
Moderator
Nov 08, 2017
Every RV 1800 RPM Onan i have looked at had dual windings
But they were parallel connected inside the generator connections
For 120v
You will most likely need access to stator winding outputs
Break the parallel connections rewire in series for 230v
And possibly have to rebalance the circuit breaker circuits
The voltage regulator is set up for 120v and only senses one of the two output windings, to control the feild voltage on the rotor

Once you set the Onan for 230v output, then that is what you will have going to the breaker box, no way to get 120v only , except by using only one leg of the output for the house
So it will now be a stick house normal 230v input to breaker box
Acampingwewillg
Explorer II
Nov 08, 2017
Can't really comment on the Onan 12 kw but I do have a Power Tech 10kw and Yes, you could tie into 240 volt at the Genset or Transfer switch fairly easily.
enblethen
Nomad
Nov 08, 2017
Get the exact model number of the Onan genset.
This will tell whether it is two legs of 120 or 120/240.
Ivylog
Explorer III
Nov 08, 2017
Both the 10K &12K are 240V four wires generators.