efficiency of inverter

[hockeyoligist2]

This is a kind of strange thing, I ran across at a friends house last weekend. He has a well and he had disconnected the pump from the regular power supply, put in a receptacle, plugged in a battery charger connected to two 12 V batteries, and put a small inverter to change back to 120v to power the pump.
He did this because he has frequent power outages (POCO Side) and he wants to have water when he needs it.
How efficient could this be? I suggested putting a relay in that would switch it over when the power drops out. But he said it would cost about the same. Any one know a formula to give him the facts?

 

[charlie b]

Not sure I follow. You need the batteries to power the pump during a utility outage. You need the inverter to get the 120VAC. You need the charger, and you need to keep it in a ?trickle charge? mode, in order to keep the batteries charged.

So what is the difference, in terms of components, between his version and yours? It seems to me that his would power the pump at all times, with or without the utility being available, via the charger and the inverter. Your version would keep a trickle charge on the batteries, and would add a relay to switch over the power from the utility to the inverter. So you are adding a component, and therefore not saving money on components.

What am I missing in this installation?

 

[coulter]

You might save a little money, just because of the power lost through the efficiency of the charger and the inverter when the utility was available. If they were both 90%, you would be losing 19% of the power going into the charger.

As charlie said, you still lose the trickle charge power.

 

[hockeyoligist2]

The way that I am seeing it. The pump runs, draws down the battery's , then the charger has to recharge the batteries, while he has power. where if he had a relay it could be a trickle charge until needed. Due to converting to 12V dc then back to 120V ac, wouldn't he be using more power? (in my opinion he would) But with a simple relay he would be running direct until needed. I may be wrong, I'm not real familiar with inverters. But from what I'm thinking you get a loss converting ac-dc then dc-ac?

 

[dsteves]

Some inverters will protect the load and the batteries by shutting themselves off if the DC bus drops below a prescribed level. In that circumstance the inverter would have to be disconnected from the battery and reconnected, or switched off and on again (accomplishing the same reset) to get the inverter to work again.

Under that circumstance, the pump wouldn't work until the reset got done and the batteries were sufficiently charged.

If the sump pump was busy during an outage, you'd probably want it working when commercial power was restored, regardless of battery condition. I'd wire up something to unload the inverter during normal power availability. The reset cycle, if necessary with his particular inverter, might be accomplished by enabling the inverter with a delay-off timer powered [on] the commercial side.

That's a neat idea; around here the hardware store will sell you a backup pump that runs on 12V. You provide the deep-cycle battery and the trickle charger.

Dan

 

[robbietan]

there will be a drop in efficiency, since there will be losses from the ac-dc conversion and at the dc-ac conversion.

 

[RayS]

I wouldn't want a hi-current charger constantly connected to a battery, (that's the bigger power loss) and would not want the pump constantly running on inverter power (nasty waveform can eat lesser insulation)

I'd try a good UPS with a supplementary battery. That way, it runs mostly on line power without power loss, and the battery is kept properly charged, with a stepped up charge rate after useage. Make sure it has a high enough VA rating to start the pump- the bigger sizes are getting much more affordable.

 

[boater bill]

The inverter system sounds like an improvised UPS. Wouldn't having batteries under charge continuosly create an outgassing situation and have the battery fail pretty quickly? I like the idea of a UPS just have enough amps for startup load on the pump motor.

 

[tallgirl]

The inverter system sounds like an improvised UPS. Wouldn't having batteries under charge continuosly create an outgassing situation and have the battery fail pretty quickly? I like the idea of a UPS just have enough amps for startup load on the pump motor.

It the job of the charge controller to make sure that doesn't happen. I'm friends with a guy who I think has a patent a charge controller. I'll have to sit down with him and see what interesting stories he has to tell.

The short answer is that there are ways to keep that from happening. The long answer is that after I chat with this guy I may go file a few of my own as I couldn't find the one I was looking for ...

 

[catchtwentytwo]

I think there might be problems getting a UPS that'll handle a motor (something like this was recently discussed in this forum APC-UPS sq wave to sine wave ). The 12 volt powered sump pump package seems best. Or maybe a bilge pump.

 

[hockeyoligist2]

The inverter system sounds like an improvised UPS. Wouldn't having batteries under charge continuosly create an outgassing situation and have the battery fail pretty quickly? I like the idea of a UPS just have enough amps for startup load on the pump motor.

The charger he is using is electronic. It goes off when the batteries are charged. The 12v batteries he is using are deep cycle "boat type". He said he has had this setup for over a year now and hasn't had any trouble.

 

[tallgirl]

The charger he is using is electronic. It goes off when the batteries are charged. The 12v batteries he is using are deep cycle "boat type". He said he has had this setup for over a year now and hasn't had any trouble.

He still needs to be sure to test the batteries (and that includes with a real load tester, not just a voltmeter or hygrometer ...) on a regular basis. Lead acid batteries have a limited life and sitting around waiting on the power to fail limits that further.

 

[hockeyoligist2]

His doesn't sit long, his power goes off every Sunday for a while. And usually 2 other times a week. He lives at the end of the line, his neighbors are on a different POCO. He finally got tired of complaining so he set up this system. The way it is set up every time the pump runs it drains the batteries some. Since he is going directly from charger to batt. to inverter.

He is happy with it, I was just thinking it may save a little power if he put in a heavy duty relay to switch from regular power to the inverter. Instead of using the inverter full time.

 

[W6SJK]

He is happy with it, I was just thinking it may save a little power if he put in a heavy duty relay to switch from regular power to the inverter. Instead of using the inverter full time.

In other words, you want to convert his pseudo online UPS arrangement (well, not exactly online) to an offline UPS. Yes, it would be more efficient.

 

[coulter]

Wet lead acid batteries are happiest floating on line. Discharge cycles are what shortenes the life.

carl

 

[coulter]

I wouldn't call it a "pseudo UPS". I's say it was engineered to fit his equirements. Most of the UPSs I deal with are a rectifier, battery bank, inverter, static switch, and a bypass switch.

carl

 

[dave_asdf]

He is happy with it, I was just thinking it may save a little power if he put in a heavy duty relay to switch from regular power to the inverter. Instead of using the inverter full time.

with constant use of the charger/inverter i would assume he'll have to replace them more often also.

 

[hockeyoligist2]

with constant use of the charger/inverter i would assume he'll have to replace them more often also.

my thinking too....

 

[brian john]

Flooded lead acid batteries have a limited life depending upon many things, Temperature-heat shortens a batteries life typically above 77 degrees F, deep cycle discharges, or many short cycle discharges, cheap chargers with AC ripple, lack of electrolyte (Acid).

As for efficiency power in power out, you have an idea what the motor draws at FLA (nameplate) and measure input current to his system under operation. This would give a rough idea of power loss.