Running a step down transformer off of an off grid 120v inverter?

imcloud

I need to run a 120vac in 5a 30vac out step down transformer, can I do that with my 120 v system, I have a 1000 watt 12v-120 v inverter, 2 100ah batteries, and a 200 ish watt solar panel.  but the system doesnt pull 30vac 5 a all the time, more like 1.5 to 2 a constant...

BB.

Yes, it can be done. The big question is how much energy (Watts*Hours per day) your subsystem uses (and possibly look at running it from 12 or 24 VDC--If practicable).

Using a Kill-a-Watt Hour type meter will help you figure out how much energy per day your subsystem will take:

https://www.solar-electric.com/kiacpomome.html

-Bill

imcloud

I was told by the company that sells the inverters that an inverter wont run a step down transformer?  This is for an irrigation control.  I used inverters before and they make 120v 60hz and never had a problem running anything, including pcs and laptops so I cant understand why they would say it wouldnt work?

Horsefly

Sounds like it may be a modified sine wave (MSW) inverter, which would likely play havoc with any attempt to go through a step down transformer.

Estragon

The waveform could well be an issue, but would likely depend on the transformer circuitry. For example, a laptop steps 120v down to 5v, 3v, etc internally, but the ac is rectified to dc as part of the process.

A square or ragged MSW supply may saturate a transformer core designed for PSW only?

imcloud

what type would you guys recommend?  

Estragon

Something like a Morningstar 300w sine wave inverter (sold by our hosts).

There may be other ways to do it, but based on what you've told us, that's what I would do.

imcloud

will 300w be enough?  the transformer in the controller says 24vac 4.2a and 7vac 3.2a max...

mike95490

imcloud said:

will 300w be enough?  the transformer in the controller says 24vac 4.2a and 7vac 3.2a max...

Now this is 2 transformers , or one transformer with 2 windings ?

I run a 24v sprinkler timer off a transformer just fine, last 5 years, pure sine inverter

imcloud

its 1 transformer with 2 windings, so there are 4 low voltage wires coming out and going to the control..  Hey I want to thank everyone for responding thus far, thanks a lot for the help guys I really do appreciate it, its a lot of money to invest on a whim and I will feeel a lot better about it with some experienced know how behind my purchase...

Horsefly

If this transformer with the voltage / current ratings you've quoted is the only thing you will run off the inverter, 300W will be more than enough.

mike95490

24vac 4.2a and 7vac 3.2a

24 x 4.2 = 100.8 watts
7 x 3.2 = 22.4
123.2 watts total, well within the Suresine 300 rating

Estragon

Those numbers are likely outputs - 120v input would be somewhat higher, but should still be well within limits even with really inefficient transformer. Unlike some cheap inverters I've used, the MS will easily do rated output, and handles surges to about double rated.

imcloud

the input says 120v 5a

imcloud

sorry correction its 120v 2.8a

imcloud

I can get a decent deal on a samlex pst 600 12   will that be a decent option

mcgivor

The Samlex is a good inverter for your needs, much better than the cheap unknown  offerings, it at least is UL listed, and has a real warranty.

imcloud

I am going to try that inverter and see if that will work our for me...  I will do 2-100w panels, with a charge controller, 2 100ah batteries, and the samlex inverter...  Is there anything else I will need?  I was told that the panels need to be mounted at 18* pointing south, is that accurate?

BB.

Really need to understand your loads... And remember that your AC inverter is a load itself--They can draw ~6 watts to 20-40+ Watts for the larger inverters.

For example, 200 Watts of panels

http://www.solarelectricityhandbook.com/solar-irradiance.html

Hartford
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 63° angle from vertical or 27 degrees from horizontal:
(Optimal summer settings)

Jan	Feb	Mar	Apr	May	Jun
2.91	3.73	4.50	4.80	5.20	5.53
Jul	Aug	Sep	Oct	Nov	Dec
5.42	5.16	4.71	3.92	2.88	2.61

So, for September, you would get around:

• 200 Watts * 0.52 system eff * 4.71 hours of sun (average Sept sun) = 490 Watt*Hours per day
• 490 WH per day / 24 hours = 20 Watts average power

And remember, that a 300 Watt Morning Star inverter draws 6 watts just turned on (tare load). And you should not plan on using 100% of predicted power every day (some days more, some days less).

200 AH of storage batteries, for long term/off grid usage, suggest 50% max discharge and 2 days of storage:

• 200 AH * 12 volts * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 510 WH per day
• 510 WH per day / 24 hours = 21 Watt average AC load

And, again, if you leave the inverter running 24 hours per day, ~6 watts * 24 watts = 144 WH per day inverter losses

-Bill

myocardia

imcloud said:

I will do 2-100w panels, with a charge controller, 2 100ah batteries, and the samlex inverter...  Is there anything else I will need?

You're gonna need considerably more panel, to be able to recharge 200 ah worth of batteries. Of course, 200ah worth of batteries is nowhere near enough to be able to power an almost 150 watt AC load 24/7. Unless you're only wanting to power this load for 60-90 minutes per day, you're going to need a ton more batteries, and a commensurate amount more solar panels.

imcloud

wow Bill, thanks, OK so if I understand that correctly, I will have around 500 watts per day and the converter itself would use 150 of them leaving me with around 350watts per day...  So I really would need to know how many watts per day my control uses total while irrigating and sitting idle...    
Am I understanding that correctly?  The max the control can pull is 2a at 120v so that is 240w ?  would that be 240w so with that math I would need 5760 watts just to run the control?  In reality the control is going to be running at about 1/4 of its capability and only for around 5 hours a day.  But I wont know what that costs in Watts until its setup and running....

Horsefly

imcloud said:

wow Bill, thanks, OK so if I understand that correctly, I will have around 500 watts per day and the converter itself would use 150 of them leaving me with around 350watts per day...  So I really would need to know how many watts per day my control uses total while irrigating and sitting idle...    
Am I understanding that correctly?  The max the control can pull is 2a at 120v so that is 240w ?  would that be 240w so with that math I would need 5760 watts just to run the control?  In reality the control is going to be running at about 1/4 of its capability and only for around 5 hours a day.  But I wont know what that costs in Watts until its setup and running....

There is an important distinction you probably are missing:  Watts is an instantaneous measure of power. When you integrate power over time, you get energy which is expressed (for purposes here) as watt hours.  What Bill gave you was that you will be producing around 500 watt hours per day. 

I think I still don't understand what loads you are running on this transformer. However, if the loads connected to the transformer are off, the transformer will not be drawing much power on the primary side. I don't know what "1/4 of its capability" means.  As Bill said, you need to better describe what you are doing. 

imcloud

this https://www.hunterindustries.com/sites/default/files/OM_ACC_EM.pdf
is running 20 of these for 15m each a day so total is 1 running for every 15m for 5 hours...  just in the summer, not when its raining obviously... the 151's...

https://www.hunterindustries.com/sites/default/files/br_pgv_1in.pdf

Horsefly

On first glance I can't tell what the nominal power consumption of the controller is. It says what the max power is (1.2A at 120VAC), but I'm sure it is way less than that. The valves you are pointing to clearly say they have an inrush current of 350mA (which will be only for a fraction of a second when the valve is first turned on), and 190mA holding (when the valve is open). If you really only have one valve open at a time, all the valves will be consuming nominally 190mA at 24VAC, which is less than 5W. I'm guessing that the controller will consume way less than the spec, since it looks like you can have it run all the valves at once.  Anyway, I'd bet you are using less than 20W total for the 5 hours, and that only totals 100 watt hours. 

Is this system in use now, but you just want to move it to solar? If so you can actually measure how much 120VAC current it is consuming. 

imcloud

so the controls specs are -

• Transformer Input: 120/230 VAC, 50/60 Hz, 2A max at 120V, 1A max at 230V
• Max AC Current Draw: 120 VAC, 2 Amps; 230 VAC, 1 Amp (max computed with all programs running and optional accessories installed)
• Transformer output: 24 VAC, 4A, at 120 VAC
• Decoder Line (path) output: 34 V peak-to-peak
• Decoder Power draw: 40 mA per active output 

And the valves, which will there are 20 of, and the program is going to be simple 20 valves, on 1 at a time for 15 minutes each only for 1 cycle each..  so 20 starts with 5 hours of run time, the valve specs are...

• 24 VAC solenoid – 350 mA inrush, 190 mA holding, 60 Hz (North America) – 370 mA inrush, 210 mA holding, 50 Hz (most international locations)...

thats the only thing it will run...

imcloud

tomorrow I am going to go to a facility that has one of these controllers running, Im gonna put a kill a watt meter on it and see what it is pulling when at idle, when opening a valve, and when running...

imcloud

I am also thinking about putting a timer on the system if I have to, what if I cut the stand by losses by shutting off the inverter for the off times?   the controllers manual says ----
Power Failures ........................................................................ The ACC’s real time clock is independent of external power or the 9 VDC battery, and will keep time during a power failure of virtually any length. When external power is restored, the ACC will still have the correct time and will be ready to irrigate. Quick Start................................................................................ A Power Outage message will be stored in the Alarm Log, with time of the outage. Another log is stored when power is restored.


so I am thinking if I cut the power and then restart it before and after the 5 hr cycle my off times will not draw any energy from the cells...

imcloud

using something like this https://www.amazon.com/MISOL-Controller-display-program-programmable/dp/B0090MTLFO/ref=sr_1_4?ie=UTF8&qid=1504706174&sr=8-4&keywords=12v+timer
unless that may cause an issue with the inverter needing to be started before the load?  in which case the inverter will have to run all the time and I can shut the clock off with a 120v timer switch, depending on the losses..  or 2 timers, 1 12v that turns on a few minutes before the 120v...

BB.

Just to be clear: 1x Controller and 20x valves, 1x valve at a time?

-Bill

imcloud

yes that is correct and each valve for 15minutes 1 time a day

BB.

I would suggest sizing the system to run the loads (transformer+inverter) 24x7 (don't cycle the inverter and use the 9 volt backup battery). Keep the system "simple". (for example, can somebody program the unit when on 9 volt power, or do they have to turn on the AC power, etc.).

Also, I did not size the system for winter operation (less sun). If you shut down the system for 3 months of winter--Then sizing the array/battery bank for when you have more sun will keep the system smaller/less expensive.

-Bill