Hello,
I bought a MPP LV2424 Hybrid (green unit) thinking that, based on other forum posts, that the unit would bond Neutral to Ground when operating in battery mode.
My intention was to use this device to feed a generator transfer switch so I could move loads between utility power and the inverter output. The transfer switch does not switch neutrals or grounds, which means that the neutral and ground from the inverter would still be bonded in the service panel regardless.
Before connecting it all up, I took a voltmeter and measured AC voltage from Hot to Neutral and got the expected 120v, but from Hot to Ground I found about 56v volts, and the same from Neutral to Ground. Battery negative also appears to be tied to inverter ground, because I get about 56 volts AC from battery negative to neutral, and about the same from battery negative to hot.
I have a multimeter with a scope function and it appears to be a 60hz sine wave, not just random noise that's showing up as 56v to a dumb meter.
Why am I seeing this? Even if the neutral is floating I wouldn't expect to see a voltage potential between the inverter case / ground and the neutral conductor, especially not 56v. I'm concerned bonding N/G risks shorting part of the inverter output stage and since the manual doesn't explicitly deal with this issue, I am unsure how to proceed. This symptom feels eerily familiar - something I ran into years ago with cheap modified sine wave units that spit out two square waves each responsible for half of the AC cycle. Bonding N/G on those units would either make the battery terminals live or blow their output stage.
I also realize that when on battery and connected via a transfer switch, I would *not* want the inverter to bond N/G (otherwise there would be a ground loop, since it is also bonded at the service panel). In this case, having it not bonded is a blessing, but I'm still concerned about the 56v from the negative terminals to the case/ground/battery negative, and that bonding them might blow the output or otherwise damage it.
Working it out in my head, if Inverter Neutral, Inverter Ground and DC negative are bonded, and that is bonded to earth ground, everything should be at the same potential but I can't help think I'm missing something. I have also seen advice to bond Input N to Output N to ensure no ground loops occur when connected to utility power (and eliminate the need to bond downstream of the inverter), but I have also seen other forum threads where people claim MPP does not support this.
What would be much cleaner would be if the unit had an internal bonding relay and a configuration option to determine when to bond N/G, but it doesn't.
MPP support have been unresponsive to my e-mail requests for the last 5 days beside the initial automated e-mail response. I've half a mind to return it while still in the 30 day period and just get a Samlex EVO or similar with manual that clearly outlines the device's N/G behavior, but I thought I'd at least get some feedback in case I'm missing something.
Thanks,
Brett.
I bought a MPP LV2424 Hybrid (green unit) thinking that, based on other forum posts, that the unit would bond Neutral to Ground when operating in battery mode.
My intention was to use this device to feed a generator transfer switch so I could move loads between utility power and the inverter output. The transfer switch does not switch neutrals or grounds, which means that the neutral and ground from the inverter would still be bonded in the service panel regardless.
Before connecting it all up, I took a voltmeter and measured AC voltage from Hot to Neutral and got the expected 120v, but from Hot to Ground I found about 56v volts, and the same from Neutral to Ground. Battery negative also appears to be tied to inverter ground, because I get about 56 volts AC from battery negative to neutral, and about the same from battery negative to hot.
I have a multimeter with a scope function and it appears to be a 60hz sine wave, not just random noise that's showing up as 56v to a dumb meter.
Why am I seeing this? Even if the neutral is floating I wouldn't expect to see a voltage potential between the inverter case / ground and the neutral conductor, especially not 56v. I'm concerned bonding N/G risks shorting part of the inverter output stage and since the manual doesn't explicitly deal with this issue, I am unsure how to proceed. This symptom feels eerily familiar - something I ran into years ago with cheap modified sine wave units that spit out two square waves each responsible for half of the AC cycle. Bonding N/G on those units would either make the battery terminals live or blow their output stage.
I also realize that when on battery and connected via a transfer switch, I would *not* want the inverter to bond N/G (otherwise there would be a ground loop, since it is also bonded at the service panel). In this case, having it not bonded is a blessing, but I'm still concerned about the 56v from the negative terminals to the case/ground/battery negative, and that bonding them might blow the output or otherwise damage it.
Working it out in my head, if Inverter Neutral, Inverter Ground and DC negative are bonded, and that is bonded to earth ground, everything should be at the same potential but I can't help think I'm missing something. I have also seen advice to bond Input N to Output N to ensure no ground loops occur when connected to utility power (and eliminate the need to bond downstream of the inverter), but I have also seen other forum threads where people claim MPP does not support this.
What would be much cleaner would be if the unit had an internal bonding relay and a configuration option to determine when to bond N/G, but it doesn't.
MPP support have been unresponsive to my e-mail requests for the last 5 days beside the initial automated e-mail response. I've half a mind to return it while still in the 30 day period and just get a Samlex EVO or similar with manual that clearly outlines the device's N/G behavior, but I thought I'd at least get some feedback in case I'm missing something.
Thanks,
Brett.
