Power transfer issue and proper charge rate

twvette · December 2017

Here is the setup in my RV used for dry camping with electric fridge for reference:

Magnum MSH3012M - Hybrid 3000W inverter/charger
Magnum MW-ARC - advanced remote
Magnum ME-BMK - battery monitor kit

Outback FLEXmax 80 (FM80) - MPPT solar charge controller 80a
GoPower 160W solar panels x6 - 960W total solar

Trojan J305H-AC batteries x4 - 720aH battery bank 12V

This is a new system and entire rig AC is connected to the inverter. We watch satellite TV so we like to always have power so dont have to search for satellites each time want to turn TV on. Have had several occassions now where the power is interrupted. It most often happens at night when have been on battery only power and start the generator in which it then also starts to run the battery charger. Had my charger set to 100% which charges at about 100-120amps. The satellite and TVs will turn off and turn back on immediately so seems like there is a very brief power interrupt. If I bump this down to say 70% or if I remember to turn the charger feature off this does not seem to happen. This problem sometimes also occurs when I turn the generator off which is even stranger to me. Another interesting point of input is does not seem to happen during the day and I suspect somehow the incoming solar is helping compensate but cant make full sense of this. Note, the batteries are never below 75% and under 20Amps being drawn by entire rig so don't think its an issue with lower power to begin with.

It seems to me there is some sort of issue transferring power when a good load is put on the system or removed. Don't know if I might be overlooking a setting in the Magnum to help with this but if not only thing I can think of is use a small UPS to ensure my satellite TV system does not see the interruption, but that is one more thing to remember to turn off when storing my RV.

A secondary question is what charge setting do I need for my system? I was thinking 100% but maybe this is too much at 100-120A and will harm my batteries at some point?

Estragon · December 2017

100-120a charging is about right for your bank. It will basically only take what it needs, and current will taper off once the charger reaches absorb voltage.

The power loss issue is likely the internal tranfer switch. It will be a "break before make" relay, which is to prevent cross-connecting the two AC sources. The break may be short enough that some loads may keep running sometimes (eg from power stored briefly in capacitors in the device).

To get around this, you could run a UPS as you've said, or you could consider running the satellite off a separate smaller inverter, such as a Morningstar 300w PSW. The small inverter would be unaffected by the big inverter transfer switch, and would have the added benefit of a much smaller self-consumption rate. Running the 3kw inverter to keep the sat system awake probably uses ~ 40-45w or so on top of the load draw itself, vs a fraction of that for a small inverter.

twvette · December 2017

Thanks.

Did some deeper reading of the manual and found there are a few settings in the Magnum that I will try. The most promising one appears to be turning the Search Watts feature to Off so there is no interruption to low draw loads as it specifically mentions satellite receiver sensitivity. I am not sure if currently Off or at its default of 5 watts.

This is all still a little strange to me as the way I understand this special hybrid inverter and how it was wired is that would always be connected to batteries through the inverter and if AC input is detected it just adds to the power available and otherwise just charges the batteries with the exception of the air conditioners, but apparently there still is some true switching going on.

Will mess with a few settings next trip and if no luck will just go with a very small UPS power strip. It is a little unfortunate as had a smaller inverter I was previously using prior to this new setup only for the satellite and TV but it was removed to get everything on the one inverter as it always needs to be on for my electric only fridge regardless and thus not a second inverter with some small extra draw. In theory there is not supposed to be any switching issues to ensure the satellite stays on with new system so hopefully just a setting.

Will probably turn down my default charging rate to give me about 70 amps to ensure not too much juice when turn on the generator during the day when also getting good solar (up to 60 amps) as it is now my understanding these two charging sources are additive. Seems my system would be smart enough to see an existing high charge from solar or other external source and scale back but not sure it is doing this. Any further input here appreciated as I don't want to charge too fast and create too much heat in batteries.

Estragon · December 2017

I'm not very familiar with that inverter - others may be if more help with settings. I did have a look at a manual though, and it refers to a 16ms transfer time - maybe one AC cycle so it switches at the 0v crossing?

That's probably fast enough to keep some equipment going, but may depend on how much power the device is using at the time.

The assist feature likely works by adding battery/inverter power to incoming AC if needed to power large loads, unless there is another charge source (eg solar) and fully charged batteries. In that case, it appears to use incoming AC current to supplement the available inverter current. Cool feature, but doesn't solve to 1 cycle transfer time issue, as the incoming AC has to be connected and qualified for the feature to operate.

Power transfer issue and proper charge rate

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