Inverter recommendations

robd

Greetings all. First post from a lurker.
This may be a loaded question.
I have recently completed a solar installation on my RV (26' TT) with the intent of being mostly off grid.
I have 490W of panels, Morningstar MPPT-45 and 220AH of deep cycle GC batteries. 2 more batteries are planned as soon as I can figure out where to put them!
I am looking for suggestions for an inverter.
As my battery voltage will very possibly exceed 15V during equalization or normal charge in cold weather, I will need something that will continue to function up to at least 15.5V.
I plan on using a Morningstar Suresine 300 for my entertainment and bedroom outlets but need something for the rest of the rig. My wattage requirements are fairly moderate. I really only need to run the microwave, a toaster and a coffee maker (seperately of course) so probably something in the 1500 - 2000 watt range. Also Modified Sine will probably be just fine for this.
I also do plan to tie it directly to the breaker panel and as the rig will be plugged in occasionally some sort of transfer switch will be in order.
Samlex has a couple of possibilities. The ST1500-212 and while a bit bigger that I need, there is also their PSE-12275A.
Xantrex also have a couple of possibilities but I figured I would ask here for any other recommendations/suggestions.

Thanks -Rob-

Cariboocoot

Re: Inverter recommendations

Welcome to the forum Rob.

A little problem with these two statements:
"My wattage requirements are fairly moderate. I really only need to run the microwave, a toaster and a coffee maker."

Those items aren't all that moderate in power consumption. They are all over 1kW, which means about 100 Amps draw on a 12 Volt system. Frankly that will be rough one 220 Amp hours of battery or even 440 (which you don't have quite enough solar to support, btw). I'm not saying it won't work, but you will need to use very big 4/0 wire and keep the runs short because under load the V-drop is going to be heavy.

You're right to be concerned about the inverter shutting down from over Voltage when the system tops 15V during charging; many of them will. Samlex is one that will handle it and they are not high priced either. You might want to go for 2kW version though, as it will not 'work as hard' to supply that big Wattage. You may also need a pure sine for the microwave; some can be picky about waveform. Unfortunately you can't tell in advance.

Do you have a budget on this? It might be better to go with one sine wave inverter instead of two separate inverters (unless you want the safety of redundancy). One choice: http://www.solar-electric.com/samlex-pure-sine-wave-inverter-pst-2000-12.html

Some things that are bound to be mentioned: ditch the electric cookery, go with 24 Volt. Both don't actually fit your criteria as I see it so I'm not going to go into detail about them.

robd

Re: Inverter recommendations

Cariboocoot wrote: »

Welcome to the forum Rob.

Those items aren't all that moderate in power consumption. They are all over 1kW, which means about 100 Amps draw on a 12 Volt system. Frankly that will be rough one 220 Amp hours of battery or even 440 (which you don't have quite enough solar to support, btw). I'm not saying it won't work, but you will need to use very big 4/0 wire and keep the runs short because under load the V-drop is going to be heavy.

Do you have a budget on this? It might be better to go with one sine wave inverter instead of two separate inverters (unless you want the safety of redundancy). One choice: http://www.solar-electric.com/samlex-pure-sine-wave-inverter-pst-2000-12.html

Thanks for the reply Cariboocoot.
Not argueing (yet ) but even at 1500 watts consumption, these devices only run for a few minutes max. Well except the uwave which we don't use all that much and certainly not for long. If they run for say 10 minutes, even at 1500 watts thats only approx. 20AH or less than 10% battery capacity of our existing 220 AH.
I have a battery meter (Bogart) so we do keep an eye on what we use. All of our heavy usage will be first thing in the morning (toast and coffee mainly) so given reasonable weather most if not all of that should get replaced.
The plan behind two inverters was to be able to keep the big one shut off except when needed. I know the MS 300 has very low idle requirements so I was planning to just leave it on.
-Rob-

Cariboocoot

Re: Inverter recommendations

The total Amp hours consumed isn't the problem: it's the draw while they are on. We're talking 100+ Amps here, which will pull Voltage down. Possibly to the point where the inverter shuts off for low Voltage. And also understand that the 220 Amp hours is @ the "20 hour" rate: as you increase the current draw you decrease the over-all capacity. You are looking at a ~10X increase in current over what is used to determine that capacity @ 20 hours. As a rule-of-thumb discharge rate should not be much more than 2X charge rate. You're looking at 5X, a significant difference. For the time that current is being drawn the battery capacity is effectively less. Drawing first thing in the morning also means drawing at the point when the batteries have been discharged the most; another hit on the capacity available.

Again, it will work but it has the potential for causing trouble.

vcallaway

Re: Inverter recommendations

I'm running a Xantrex 2k ProWatt SW inverter with 4 6v GC batteries. I can run my big microwave for small stuff but it really draws the batteries down. It draws 1400w when running. We just simply changed our cooking habits to not use the microwave or any other heavy electric load when running on battery power. I even make my coffee using a tea kettle and french press. Actually like that better anyways.

I used 2/0 cables to connect the inverter and they are only about 3' long. Anything less and I get a voltage drop with that load. My inverter was switched on a couple of years ago and has only been switched off a couple of times when I was doing maintenance. I've been very happy with it.

silvertop

Re: Inverter recommendations

vcallaway wrote: »

I'm running a Xantrex 2k ProWatt SW inverter with 4 6v GC batteries. I can run my big microwave for small stuff but it really draws the batteries down. It draws 1400w when running. We just simply changed our cooking habits to not use the microwave or any other heavy electric load when running on battery power. I even make my coffee using a tea kettle and french press. Actually like that better anyways.

I used 2/0 cables to connect the inverter and they are only about 3' long. Anything less and I get a voltage drop with that load. My inverter was switched on a couple of years ago and has only been switched off a couple of times when I was doing maintenance. I've been very happy with it.

We also try to limit large loads on batteries only. I have a Panasonic inverter microwave that has power levels (10 levels) with sun we run at 100 / on batteries 40 and it only pulls 590 watts. This will slow cooking but works very well........

westend

Re: Inverter recommendations

As posted, your microwave will suck the voltage of 220ah bank very hard while on inverter. For an average microwave you'll need 2000w of sine wave inverter to pull the load. The Panasonic microwave units can run on considerably less. FWIW, I bought and attempted to run a Samlex Pure Sine 600w, powering a small dorm fridge. The Samlex would not overcome the locked rotor draw, even though that was within the surge rating of the inverter. I installed a 1000w Xantrex SW Pure Sine and it does run the fridge without problem. Your toaster and coffee pot will be resistive loads so any inverter rated to a bit over the draw of those appliances will work. The microwave may not get along well with a MSW inverter. Good luck with your inverter install!

robd

Re: Inverter recommendations

Thanks for all the input folks. I am planning to add more battery capacity in the near future and will make sure I do it a way to maximize their efficiency.
On another topic, I would like to ask about wiring on the AC side. I have read, seen and heard conflicting information about the best way to do this. In my installation the inverter will need to be located at the front of the unit while the shore power connection is at the rear. The existing converter and breaker panel is about halfway back. I do want to install a transfer switch of some sort.
Is it a) normal and b) legal to use a normal NEMA 5-20R plug into the inverter or must an inverter that suports a hard wire connection be used?
-Rob-

Blackcherry04

Re: Inverter recommendations

robd wrote: »

Thanks for all the input folks. I am planning to add more battery capacity in the near future and will make sure I do it a way to maximize their efficiency.
On another topic, I would like to ask about wiring on the AC side. I have read, seen and heard conflicting information about the best way to do this. In my installation the inverter will need to be located at the front of the unit while the shore power connection is at the rear. The existing converter and breaker panel is about halfway back. I do want to install a transfer switch of some sort.
Is it a) normal and b) legal to use a normal NEMA 5-20R plug into the inverter or must an inverter that suports a hard wire connection be used?
-Rob-

I always set up my Inverters installs on pigtails with plugs so they can be plugged around in a RV or Boat in case of a outage. Most all the factory installs come that way also. It wouldn't be up to code in a home.

vcallaway

Re: Inverter recommendations

I had the same wiring issue.

I ran conduit down the frame with some flex at each end. Wanted to protect the wiring from the elements and road debris. Mounted a 30a RV plug inside the storage bay where my cord is. I just plug the shore cord in there. My RV has a transfer switch between shore cord and generator. Not really any need for an automatic switch to be added as well.

Just make sure you have a way to turn off or unplug your converter/charger when running on inverter. Mine is located in the same bay so it is easy to just unplug it when I plug in the inverter.

westend

Re: Inverter recommendations

If you're going to hardwire into a subpanel and use a transfer switch, I would hardwire the inverter to the subpanel. Depending on the schema of the inverter, you may end up with usable receptacles at the inverter, too, if that is a consideration. I can't recall if there is any legal restriction against using a plug to the inverter for the subpanel connection but I wouldn't consider it best practice. The risk of the connection becoming energized can't be totally eliminated and if the male plug is loose, it could spell problems.

Shadowcatcher

Re: Inverter recommendations

From what I have been able to find Magnum and Morningstar appear to be the only ones able to handle more than 15 V.

Cariboocoot

Re: Inverter recommendations

Shadowcatcher wrote: »

From what I have been able to find Magnum and Morningstar appear to be the only ones able to handle more than 15 V.

Most of the "better" inverters will (Outback up to 17.5 on their 12 Volt models) and the Samlex as I mentioned before. Exeltech will go to 16.

The "El Cheapos" are the ones that will scream and shut down over 15 Volts. Always check the specs. If they won't tell you, don't buy it.

solar_dave

Re: Inverter recommendations

Cariboocoot wrote: »

Most of the "better" inverters will (Outback up to 17.5 on their 12 Volt models) and the Samlex as I mentioned before. Exeltech will go to 16.

The "El Cheapos" are the ones that will scream and shut down over 15 Volts. Always check the specs. If they won't tell you, don't buy it.

This is why I am buying Samlex, high voltage cut off is 16.5 on the 12V 1000watt model
Exceltech as well
XP-1100/12Vdc low=10.4/10.6Vdc* median=13.8Vdc high=16.5Vdc
* is buzzer alert level.

Rybren

Re: Inverter recommendations

It's important to note that not all models of Samlex inverters have a high voltage cutoff of 16.5V. Check the specs before buying. The PST-1500 (12v and 24V) have the higher cutoff (and hardwire capability)

robd

Re: Inverter recommendations

Thanks everyone for your comments and suggestions. You have given me lots to think about.
One other thing I was wondering. When I do this install, I would like to isolate the Air Conditioner and Converter/Charger from the rest of the system such that they can only operate when connected to shore power.
Would something like what is shown in the attachment be permitted? I am mostly concerned around what I call the input panel. The idea is that it would become the mains panel and the existing breaker panel in the converter would become the sub panel. In my unit the DC side of the converter is easy to isolate.

Thanks

Attachment not found.