Charging house batteries from the generator

[quietglow]

Hey all,

I was on a weeklong trip last week in which I finally was sitting in a single spot for more than 24 hrs, and I noticed that running the my generator does not appear to charge the house batteries. I suspect it's a setting I am not aware of in the Magnum ME-RC control panel that I am not aware of. I took a look at the unit's manual, but did not see anything about source selecting (i.e. alternator vs generator vs shore) mentioned.

So if I plug into shore power, the Magnum display shows "bulk" or float charging automatically. If I am not plugged in and I run the generator and have the breakers on, the generator runs the microwave, a/c etc. But if the generator is running, I do not get bulk/float charging. The house battery charges normally when the van is running.

Any suggestions on how to get the house batteries to charge off the generator?

Photo of the sitting location (deep in the Ottowa NF in the UP)

 

[1der]

What does the RC display show while on gen power? Is it "Charger Standby" ?

 

[quietglow]

Is it "Charger Standby" ?

No, the screen and lights are no different than when the gen is off. Charge light is not lit, and if I press the "charge" button, nothing happens. Notably, if I press the "inverter" button, the inverter does come on. Now, I can't remember if I have tried pushing the charge button while the inverter and generator are running, but I'll try that.

 

[Scalf77]

Now, I can't remember if I have tried pushing the charge button while the inverter and generator are running, but I'll try that.

When running on the generator you shouldn't need the inverter to be on. Are you sure that the AC isn't coming from the inverter and not the generator? It is possible that you are not getting any input from the generator, not just charging. That would still be an issue but make more sense.

 

[Big_ern_101]

How is the generator wired up? Is it built-in or something you carry with you?
Is the solution as simple as connecting the generator output to the shore power input?

 

[quietglow]

When running on the generator you shouldn't need the inverter to be on. Are you sure that the AC isn't coming from the inverter and not the generator? It is possible that you are not getting any input from the generator, not just charging. That would still be an issue but make more sense.

Generator is def contributing: I ran the air con for several hours over the last week with the generator running. If you don't have the generator running, it'll take a full house battery below 12.2 in just a few moments (my house batteries are getting old). For some reason, it's just not charging the house batteries.

 

[quietglow]

How is the generator wired up? Is it built-in or something you carry with you?
Is the solution as simple as connecting the generator output to the shore power input?

The generator is a Cummins propane model and it's mounted to (and wired into) the vehicle.

 

[Scalf77]

The generator should go to a transfer switch or AC selector input switch. This should happen on the incoming AC lines to the inverter/charger. What model number Magnum Inverter/charger do you have? It could be possible you have a dual input model. I suspect that you have a automatic transfer relay, that defaults the generator when there is power available. I guess I would check the output of the generator and see what kind of power it is putting out.. Do you have the magnum automatic generator start module, although I don't see it causing this issue.

Have you tried the charger with the generator running but no other high AC loads. There are settings to limit charging if load is to high, I would have to look into the Magnum data, as I haven't had a Magnum unit for a while.

 

[quietglow]

The generator should go to a transfer switch or AC selector input switch. This should happen on the incoming AC lines to the inverter/charger. What model number Magnum Inverter/charger do you have? It could be possible you have a dual input model. I suspect that you have a automatic transfer relay, that defaults the generator when there is power available. I guess I would check the output of the generator and see what kind of power it is putting out.. Do you have the magnum automatic generator start module, although I don't see it causing this issue.

Have you tried the charger with the generator running but no other high AC loads. There are settings to limit charging if load is to high, I would have to look into the Magnum data, as I haven't had a Magnum unit for a while.

Yeah, all the time I've been messing with it, I've been running it with the generator on and no load. I think the thing I am looking for is the transfer switch, which I agree is likely automatic. The inverter is an MS2812 and the schematics in the manual def show an external ac selector. I don't see any mention of that in my SMB documentation, but there is a bunch of it so I am still hunting. The van is in for maintenance this week, but I am going to do some sleuthing when I get it back.

 

[Scalf77]

The MS2812 does have dual AC input, but that should not be used for generator input. I guess I would check the VAC drop voltage setting, that generally is set lower for generator use and find the transfer switch.

 

[quietglow]

So I finally found the "schematic" in the SMB manual which references this:

Given that, I think the transfer switch is working fine. All AC stuff works fine on the generator and when on shore power. I think the question I now have (and can't test because the van isn't here) is whether the house batteries charge on shore power either. I have never tested this, and I would have no reason to know because if I have shore power available at a campsite, I normally roll up and plug in. In this scenario, the house batteries are full because I was just driving. I am going to bet that they currently do not.

So now the part I don't understand: what does the job of getting shore power (and, really, gen power) to the house batteries? The SMB attached schematic doesn't show where that happens.

 

[Scalf77]

That schematic is wrong, they just changed the converter into a invert/charger. Two different things. You need to merge the two of these together. Must be their cartoon artist wasn't available for a correct update. The Generator would be one input of a transfer switch, shore power the other input. The output of the transfer switch would be wired to the input of the Invert/charger.

It would be a major screw up, but I guess I would check they didn't wire the transfer switch on the output side of inverter/charger. It would fit your symptoms

 

[quietglow]

they just changed the converter into a invert/charger

This is the missing piece. I don't see anything at all in my docs about a converter. And they have the original manuals for everything else (i.e. the Blue Sea isolator, the inverter etc). Do you know anything about the specs of converters that SMB uses/has used? My van is a Fresno build, and I know they have done things differently, especially concerning the electrical system.

 

[Scalf77]

You shouldn't have a converter, as you have a larger charger built into the Inverter/charger. If you have a inverter/charger the converter should be removed.

 

[quietglow]

You shouldn't have a converter, as you have a larger charger built into the Inverter/charger. If you have a inverter/charger the converter should be removed.

So I am confused -- this is where an accurate schematic would be swell. The SMB docs are ancient and don't get close to matching my rig in other areas as well.

120 comes in from shore and generator and go to a transfer switch. The transfer switch automatically picks the live one and sends that to the inverter/charger. It also, I assume, connects that to the breaker box. Then the inverter/charger decides whether to use that 120v to charge the batteries or not? If it decides to, it converts the 120 into DC and charges the battery? Is that an accurate depiction of the setup?

If so, two things:
1. The transfer switch is working, because it's getting 120 from both generator and shore to the breaker box and all the things connected to it. The house AC runs fine off both shore power and generator.
2. If the transfer switch is correctly wired to the inverter/charger, then it seems like the issue is (as several have pointed out!) with the inverter charger deciding to actually charge the house batteries. Which means I prob should RTFM for the charger control. I'll bet there is some voltage limiter there set incorrectly.

edit: a third thing. the inverter/charger has an AC input breaker. If that is tripped I think it would yield this same result. That will be the first thing I check when I get the van back from service.

Also, the house batteries DO charge fine when the van is running. I am going to assume that's because in the default configuration (as mine still is in), when you turn the key on the van, the battery isolator automatically joins the house and starting batteries. There's a long discussion about this (and whether it's a good idea) in Tim's build thread. So when my van is running, the default is to have all batteries joined, so the alternator is charging them all without anything to do with the above systems.

 

[Scalf77]

I can try to draw up a proper schematic later on today.

The Inverter/Charger will pass thru the AC on the input (be it Shore or generator) to the output. The charger is internal to the inverter/charger. The output of Inverter/charger will go to your breaker box..

Charging the house batteries via alternator /ACR while running will have no impact.

You will need the Manual for both the inverter/charger and the Magnum Remote, as the information is really set via the remote.

 

[Scalf77]

Here is drawing that shows the relationship of generator / shore power / transfer switch to inverter/charger. It should be a little clearer.

 

[quietglow]

Here is drawing that shows the relationship of generator / shore power / transfer switch to inverter/charger. It should be a little clearer.

View attachment 1325820

Wow that is magnificent! And it answers several of my questions about routing. At this point, I am betting that I have a blown breaker on the inverter itself. I may have the van back this afternoon and will take a look.

 

[quietglow]

I am back to being stumped.

I got the van back and realized there are no breakers on this model on the inverter. So I plugged it into shore power, and the control unit shows that it's float charging, just as it should. I changed zero and turned on the generator (after unhooking the shore power) and the control unit does not indicate charging. With the generator running, I turned on the inverter and then the air con, and I ran it for 10 min. This would have nuked the battery if the air con wasn't running on generator power.

I have no idea how this can be possible give the schematic. The inverter/charger is clearly getting AC from both the generator and the shore power. And it clearly can convert it to DC to charge the batt (does so on shore power) and it can clearly get the generator power to the appliances.

From the standpoint of the inverter/charger, it shouldn't know the difference between the generator and the shore power, if the transfer switch is working correctly, right?

 

[Scalf77]

You need to check the output of he generator versus the house input. Generator output can be dirtier and lower than shore power. You might need to check the VAC drop voltage setting, sometimes this needs to be set lower to accommodate generator power.

There is a resettable breaker for the input, but it must be on as it works for shore power.