Off griding my cooler

[LeftyRight]

I am trying to understand this whole Solar thing so please excuse my novice point of view. I have a swamp cooler that I am trying to change to a solar powered appliance. The thing uses a 2 speed 110v motor to spin the squirrel cage and separate pad motors to rotate them. The surge current is 19 amps and 6 amps to run. So how do I look at the circuit?

My electrician said that I should look into changing the main motor to DC and run a small inverter for the pad motors. I want to have batteries in the circuit so I would need all the appropriate charging maintenance electronics and all but it’s the battery capacity that I do not understand for the big surge event. I’m thinking that 720 watts are correct to deal w/ the 6amp constant supply from the PV panels that would be needed so the batteries aren’t drained during the days need for cooling.

It’s my first circuit to try to isolate and take off the grid so any help would be great, thanks ahead of time.

[niel]

actually in a battery operated system you could keep the original motors and such and use a pure sine wave inverter to run it. the inverter will add a tad more power draw of 10-20% depending on the inverter.

your big problem may not be surge depending on how long it is you need to run the swamp cooler. the extra capacity you need in the batteries to run long term will most likely be able to absorb any start surges.

before we go on here with the batteries i do question the going off grid part for if you have the grid you can operate a gt solar system to offset the draw from the swamp cooler with less cost to you and more efficiency. in light of the high 120vac draw that long term this would create a huge off grid system. anything less inhibits you from running it as much as you need to. at least staying grid tied enables you to run it anytime and you can even build up your gt system over a longer time-period.

i see you managed to get on board ok.

[BB.]

Welcome to the Forum LeftyRight,

And yes, posts appear when you hit submit (no moderation holds).

Regarding your question. You can measure loads with a Kill-a-Watt meter (for 15 amp 120 VAC plug in appliances). Because we also need to know how many watts*hours per day of energy use. Name plat ratings usually are not accurate enough--And while we need to know surge current to size inverters/battery banks--The average power used per day is needed too.

Next, off grid solar power is not cheap... In the end, it costs around $1 to $2+ per kWH for off grid power (cost of parts, replacement batteries every 5+ years, etc.).

So, just converting an appliance to off grid solar will usually not save money.

There are options--Like getting a DC configured swamp cooler which will also use much less power (and move a bit less air too). And then you have the choice of only running it when the sun is up (solar panels only), or evening/morning too (need batteries).

Batteries and inverters add a lot of cost to power systems. And from a pure wallet point of view, looking to make your existing system more efficient (changing motor to Permanent Magnet type with VFD--variable frequency drive--examples) could save you money by reducing your power needs and avoiding the whole off grid cost model.

If you want off grid for emergency power--Generators are sometimes better for short term outages (few days to week outage). For long term outages, then solar can be helpful.

But, otherwise, if your utility supports Grid Tied solar power systems--They are the cheapest and most reliable choice for alternative power--But GT PV systems (no batteries) do not supply emergency power.

Questions? How would you like to proceed?

-Bill

[Cariboocoot]

Welcome to the forum. Glad to see you got the posting thing to work.

How did you come up with those current numbers? Usually you can not detect the surge current of a motor.

I would not go in for trying to modify the cooler. Probably more trouble than it's worth.

To take it off grid you will need to have batteries. Not many things can be directly powered by solar panels. Those that do will function only when the panels put out power. That's not a good choice for a cooler.

As for sizing the batteries you have a matter of comparing Watts on the AC side to Watts on the DC side. If the cooler draws 6 Amps @ 120 VAC is 720 Watts, but when converted to DC you will have conversion inefficiency and also the inverter's consumption to deal with. So the 720 Watts becomes 800 Watts and the inverter will consume a further 20 Watts (you will not be able to run this device off a small, low-power inverter as its running power is high and its motors will have a significant surge demand). Thus on the DC side you need to supply 820 Watts.

Now comes the time factor. How long does the cooler run consuming this power? Will the inverter be on all the time? This much load operating all the time is a huge amount of Watt hours: 820 * 24 = 19,680 Watt hours per day. This is why it's a good idea to use a Kill-A-Watt and see how many Watt hours it typically uses in a day. It probably is not nearly 20kW hours.

Once that number is determined you can pick the best system Voltage and battery bank size.

How are we doing so far?

[BB.]

Forgot to add a link to a Kill-a-Watt meter so you can see what we are talking about.

-Bill

[LeftyRight]

Thanks for everyone's responses so far :) but this whole solar deal should be a simple operation from where I'm at on trying to take one of my grid hungry money vacumes off the grid. I had my electrician target each of my circuits at the service from the breakers and we turned each circuit on and watched the ammeter to see the current spike to get the reality of the load at start up of the swamp cooler main motor. What I am not understanding is why is this any different then running a bench grinder on solar power from a battery farm to stabilize the load and spike issues? It's only one circuit that I'm trying to take off the grid so it should be pretty straight forward. Please be gentle I only kind of liked my electronics class when I was into racing engines in school some 30 yrs ago and I didn't give it much attention then so now I'm paying the price.

[Cariboocoot]

It isn't any different: starting a motor is starting motor. How much it demands is what makes the difference.

First up: inverter size. To handle that 19 Amp spike (good way to get a measurement, btw) you need to be able to supply 19 Amps * 120 VAC = 2280 Watts on start-up. A good inverter capable of such a surge load would handle it. That would include an inverter with a running rating of 2kW + or a 1kW inverter with a better than 2X surge rating sustainable long enough to get the motor started.

Second: enough battery capacity to supply that momentary surge without the Voltage dropping and the inverter shutting down. This should not be a problem either, providing the system Voltage is high enough and the capacity is there to meet the Watt hour demand.

The specs on this swamp cooler are not unlike those of an air conditioner. In fact some of the A/C units tested lately for the forum appear to be better.