EMS measuring higher voltage than generator producing

**Hpangle** · 08-05-2019, 07:15 PM

We are dry camping at an NFS campground, and when hoking up our Honda 2000 generator, the EMS (50 amp) shows E3, 135 volts. When measuring at the generator, the meter indicates 127 volts. How is the 5th wheel gaining voltage? We have had the rig about a month, and all worked prior, using 50 amp shore power, 20 amp shore power. We have gen prep, and was told by dealer that the EMS is after the transfer switch. We don’t have an onboard generator. Any ideas?

**D2Reid** · 08-05-2019, 10:06 PM

Bad EMS.

I recently learned that my external EMS that was showing high voltage has an adjustment on it. But when I measured the voltage at the pedestal I found the EMS to be reading the voltage correctly and shutting down appropriately. 135v.... Because it was accurate I didn't pursue the adjustment procedure.

I know that this wasn't much actual help, at least you know you are not along in experiencing a problem like this.

**Luv2Ski** · 08-06-2019, 04:33 AM

Regarding the meter you're using, is it a true RMS type? If so, there's a good reason why it may not agree with the EMS if the generator isn't putting out a pure sine wave.

Are they in agreement when measuring pedestal voltage? Make sure the loads are minimized when you do this test so there's little to no voltage drop.

**Luv2Ski** · 08-06-2019, 04:46 AM

Originally Posted by Hpangle

...We have gen prep, and was told by dealer that the EMS is after the transfer switch.

In your case, it shouldn't matter whether the EMS comes after the transfer switch or before it if you're feeding the generator output to the shore power receptacle on your RV.

**Keebler** · 08-06-2019, 04:54 AM

One positive comment about your EMS if it is a Progressive Industries. I had an issue with mine reading incorrectly and they sent me a new one. Replacement process was easy and didn't cost me a penny. Impressive service.

**Hpangle** · 08-06-2019, 10:27 AM

d2Reid,
Thanks for the info. I didn’t see any adjustment in the manual, so will call Progressive for details on the adjustment procedure.

Luv2Ski,
The meter I am using is a digital Fluke, so I am pretty sure it is a rms, and our Honda 2000 is either a pure or modified sine wave. Since I am measuring the generator voltage at the plugs, there are no loads, other than the meter. And thanks for the comment about the transfer switch. This is my first experience wit a transfer switch, and was wondering if something inside it might be loose or whatever. And we are feeding the generator into the shore power cable, via dogbones.

Keebler,
Great idea, but in my case, the EMS was purchased and installed as part of purchase agreement, so we don’t have superficial paperwork showing proof of purchase. But, I am going to call them and see what they can do.

Thanks for the quick replies, cell/internet service doesn’t exist where we are camped, so drive out once a day to check.
Harold

**gbkims** · 08-06-2019, 07:13 PM

Originally Posted by Hpangle

And we are feeding the generator into the shore power cable, via dogbones.

Wondered if both the EMS L1, L2 are reading the same high 135V.
Using a dogbone adapter should put the same voltage onto L1 & L2, then to the EMS, so I'd expect them to have nearly the same reading.
The EMS HW50-C has individual voltage adjustments for L1 and L2 on its internal circuit boards that can be tweaked if the readings don't match within a few volts.
Seems 135V is quite a bit off for a reading, so perhaps something to do with the generator to RV connection, which I don't know what that would be.

**Luv2Ski** · 08-07-2019, 12:23 AM

Harold,

Fluke meters have a great reputation. Yours is probably dead nuts accurate. I love my Fluke 117 and I know it's spot on after checking it against a calibration source I have access to.

Instead of feeding the RV from a 120v generator outlet, have you tried feeding it from a 120v house or RV pedestal outlet? I'd be curious if the Fluke meter and the EMS would be in agreement then or at least close to it. Like you said, the Fluke is probably true RMS. I'd wager the EMS voltage monitor circuit isn't. Having a pure sine source from a utility makes the measurements apples to apples. That's the setup I'd suggest if/when you do adjustments to the EMS.

**Hpangle** · 08-07-2019, 03:24 PM

Update: Problem is solved. I contacted progressive tech support and they talked me thru the adjustment. But first I rechecked the generator voltage at the plug going into the 5th wheel, then I removed the EMS cover, and applied power and checked both hot lines in and they showed the same voltage as the generator. And the EMS still showed the high voltage. I then adjusted the EMS reading to match the generator output.
Thanks to all for the help!
Harold

**howson** · 08-07-2019, 04:43 PM

Originally Posted by Hpangle

Update: Problem is solved. I contacted progressive tech support and they talked me thru the adjustment. But first I rechecked the generator voltage at the plug going into the 5th wheel, then I removed the EMS cover, and applied power and checked both hot lines in and they showed the same voltage as the generator. And the EMS still showed the high voltage. I then adjusted the EMS reading to match the generator output.
Thanks to all for the help!
Harold

Was it as simple as adjusting one (or both) of these potentiometers?