Do invertors and convertors play well together?

halfwright · June 2012

I have installed a samlex PST-150S-12A inverter and a Morningstar TS-MPPT-45 in my fifth wheel trailer, along with 4 6 volt batteries.

What seems to be happening is the convertor is charging the batteries off the 120 system just like it was shore power. I have 12 volt wires showing 35 amps when the GFI cicuit breaker is on. I have removed the GFI outlet in the bathroom because the invertor has built-in GFI cuicuts. Do I need to remove the convertor? I wired the invertor into the breaker box. The ampereage in the 12 volt wires does vary with the charger output. It goes lower as the charging rate does. The 12 volt wires at the box do get slightly warm, but not hot.

BB. · June 2012

Re: Do invertors and convertors play well together?

I am not sure I understand--If the AC input to the AC to DC Converter of the RV is tied to the AC Inverter's AC output--Then, yes, I would believe that you will see the DC converter charging the battery bank while the AC inverter discharges the same battery bank (and overall, since there are around 10-30% losses involved in all of this, the battery bank will go flat relatively quickly).

Normally, the AC input to the DC Converter would be connected to the shore power AC input only.

And the AC system on the RV would either be tied 100% to the AC output of the AC inverter, or, you would use an AC Transfer Switch (manual or automatic) to switch the AC circuitry to either the Inverter's AC output or Shore Power AC.

This is not always an "obvious" choice of how to connect everything... And adding an AC generator and/or an Inverter/Charger to the mix makes things more complex. Here is one short thread about connecting an Inverter with automatic AC transfer switch:

Powermax Auto Transfer Switch Morningstar Suresine standby mode issue

-Bill

halfwright · June 2012

Re: Do invertors and convertors play well together?

I have the inverter wired to the breaker box. I had assumed that the converter was wired into it also. I am able to just unplug the inverter to protect it from shore power. I guess I will set up a knife blade switch or something like that to isolate the converter from solar power from the charger. what the heck! I am retired have have plenty of time to piddle with stuff like this. Just wish I had the knowledge and money. Thank you for your help and advise.

BB. · June 2012

Re: Do invertors and convertors play well together?

Be really careful with Inverters and other sources of AC power... Connect an AC off grid inverter to some other source of AC power (generator, shore power), and you will, at the very least, let the magic smoke out.

Normally, a true "transfer switch" is setup to prevent, even accidental, connecting two (or more) AC sources together in parallel (mechanical design of the switch, interlocks, etc.).

And--Neutral bonding of AC wiring and AC inverter (and generator) outputs is an entire thread in itself. Again, done incorrectly with the "wrong equipment", and you can lots of smoke released into your space.

-Bill

halfwright · June 2012

Re: Do invertors and convertors play well together?

We (my wife and I) will be in your part of the country in about 6 weeks or so. We are going full time in this cursed fifth wheel that I have put the solar panels on. First trip--from Denver CO to Las cruces NM to see family--then across to San Diego and up the Coast Highway to Canada. Then, across to Glacier NP. I will probably let the magic smoke out of several things before this is all over.

Again, thanks for your help.

Jim45D · June 2012

Re: Do invertors and convertors play well together?

When I installed my inverter into my RV I did have problems with the converter playing a active part. Then I found this. I disconnected the convertor, and never any more erratic problems.

halfwright · June 2012

Re: Do invertors and convertors play well together?

Jim,

Where did you wire the inverter into the 120 volt system?

Jim45D · June 2012

Re: Do invertors and convertors play well together?

I had installed a sub-panel close to the inverter with it's own breakers. From there I used heavy duty well wiring to go from the sub-panel underneath the coach, weaving in and out of available crevices, chassis voids, and eventually up the wall via a sewer breather pipe, then to the main breaker panel. I connected it to the breaker bar there. Avoiding the A/C breakers. Do disconnect that converter. With the proper solar configuration you'll never need it. You don't necessarily need the sub panel box. I just did it as an added safety feature.

halfwright · June 2012

Re: Do invertors and convertors play well together?

For those following this thread, let me tell you what I have found. On my unit, the converter plugs into the back of the breaker box. I assume this is some type of sensor telling it when 120 volts are present. There are two 8 (???) gauger wires running off the 12 volt side of the breaker box to the batteries. My cure is going to be cutting the hot wire between the converter and the breaker box and installing a toggle switch. I am going to mount it next to the inverter so that when I turn off the inverter for shore power, I can turn on the converter, and vice versa.

BB. · June 2012

Re: Do invertors and convertors play well together?

I am not sure you are talking about the DC or AC breakers boxes... Make sure that you don't make the "system" too complex. You don't want to make it so that somebody can cause a safety problem "ever" if a wrong switch is connected (reason for interlocks and purpose designed transfer switches).

From what little I know, AC to DC converters are pretty simple. AC in and DC out (basically just a battery charger). So, they should pretty simple to wire up.

-Bill

vtmaps · June 2012

Re: Do invertors and convertors play well together?

halfwright wrote: »

I am going to mount it next to the inverter so that when I turn off the inverter for shore power, I can turn on the converter, and vice versa.

Bill's comment is on point. Let me put it somewhat more bluntly: I think your inverter is wired improperly, and maybe dangerously. You shouldn't have to turn off your inverter when you connect to shore power. There should be a transfer switch so that the inverter is disconnected when you are on shore power. There are several simple ways to do this. It is slightly less simple to have the transfer switch also deal with the converter, but it should be done.

Perhaps I misunderstand what you have done. Do you know what will happen if you connect to shore power and forget to turn off the inverter?

--vtMaps

Jim45D · June 2012

Re: Do invertors and convertors play well together?

The toggle switch will work; as long as you don't forget to switch it on and off. But, you will forget, everyone does. As BB pointed out it's just a battery charger. I don't know what your's charges at, but mine on it's best day was around 4 amps. Good luck.

Shadowcatcher · June 2012

Re: Do invertors and convertors play well together?

Modern converters can charge a 125AH battery in three to four hours adjusting the charge voltage to feed back from the battery. Mine is a Progressive Dynamics and the way I handled the situation is that I used a 30A DPDT switch and one side is AC from the Sure Sine and the other is the shore power to the Circuit barkers.

Do invertors and convertors play well together?

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