Inverter efficiency

LandKurt · December 2011

I put a lot of thought into what inverter to buy and finally decided on and bought a Samlex SSW-1000-12A. It's a reasonably priced pure sine wave inverter with enough power to run my sump pump or fridge. It's a recent model with decent specs for the no load draw, but I'm wondering if it was the best choice after all. I could use some input on what to expect from an inverter.

The cooling fan on the SSW line is load controlled which means it kicks on whether it's needed or not at around 15 or 20 watts of load.

Switched on with no load it draws 8.4 watts according to my Tri-Metric battery monitor. Running just my router, which the Kill-a-Watt puts at 14 watts, the draw is 24.1 watts. That's another watt or two lost to inefficiency - to be expected. The fan hasn't kicked in yet.

Now add a CFL bringing the Kill-a-Watt reading to 40 watts. The loud fan kicks on in the inverter and the battery meter reads a 70.6 watt draw. Adding 26 watts of load increased the draw by 46 watts. That tiny loud fan seems to eat 15+ watts!

I was ready to eat 8 watts or so to the inverter plus about 15% inefficiency, but that 15 watts to a fan is annoying.

When I'm trying to run 30 or 40 watts of networking equipment that extra 15 watts really takes a chunk out of my power budget. I was hoping to find an inverter powerful enough to run my 750 watt sump pump if necessary but efficient enough to run network equipment 24x7. Am I asking the impossible? Maybe I should have gone with Samlex's older PST models with a temperature controlled fan. That probably wouldn't have had to kick on much with a light load.

BB. · December 2011

Re: Inverter efficiency

1,000 watts sounds a little low to run a 750 watt sump pump or a typical refrigerator...

Have you tried running them yet (actually starting?).

-Bill

icarus · December 2011

Re: Inverter efficiency

As Bill suggests, your inverter may be too small. Why not consider two inverters? A Suresine 300 for your lighting and networking, plus a different one for the fridge and pump? Also, have you considered running a dc pump, eliminating the inverter loses?

All this depends on how you use the fridge and pump. A fridge load is rather predictable,, but is the sump pump load as predictable?

Tony

LandKurt · December 2011

Re: Inverter efficiency

Yes, I have successfully run both the fridge and sump pump off the inverter, though not at the same time. The inverter is rated for 2000 watt "maximum active surge power". I was worried that would be enough for the sump pump which my Kill-a-Watt meter showed pulling 750 watts, but it works.

If it can handle the sump pump I doubt the fridge gives it much trouble at all since it only pulls 120 watts once it's running. I suppose the surge is multiples of that figure, but I have no way to meter that.

BB. · December 2011

Re: Inverter efficiency

Cool, sounds like you took care in wiring your 12 volt battery bank and have a good set of batteries out there.

-Bill

LandKurt · December 2011

Re: Inverter efficiency

By way of explanation, this is an emergency backup system for when we're without utility power in the suburbs. I decided to upscale the little MSW inverter system that has been useful in past outages. Instead of a 200W MSW inverter hooked to a 20AH battery my new system is a 1000W PSW hooked to 380AH of AGM batteries. The main goal was to run the fridge and a few lights for a day or two.

Running the sump pump is nice, but rarely necessary. We went nine years in this house without the sump pump working properly and never noticed until hurricane Irene this summer put some water in our finished basement for the first time. So the sump may only be necessary for those once in a century events that come along every few years now.

I used 2 AWG wire to cable up the four 6V golf cart batteries and inverter. Maybe that helps with the surge load. There is a 200A master fuse, battery switch, and 150A fuse to the inverter. There is a 30A battery charger and a solar charger on separate fuses. The solar charger is a TriStar MTTP 60 hooked to a pair of SunTech 170W panels.

I got a little carried away creating my backup system. The solar panels and charger are an impractical addition that aren't well balanced to the batteries. It really needs more panels, but maybe I can grow it later.

BB. · December 2011

Re: Inverter efficiency

You did good... Add some more solar panels (based on battery bank capacity):

14.2 volts * 380 AH * 1/0.77 panel+charger derating * 0.05 rate of charge = 350 watts recommended minimum solar panels
14.2 volts * 380 AH * 1/0.77 panel+charger derating * 0.10 rate of charge = 700 Watts nominal
14.2 volts * 380 AH * 1/0.77 panel+charger derating * 0.13 rate of charge = 911 Watts max cost effective

Just some rough numbers--But will give you an idea of where to aim.

-Bill

LandKurt · December 2011

Re: Inverter efficiency

A smaller inverter for running the small loads, like the Morningstar SureSine is a possibility I'll think about. Though that might mean loses from running two inverters at once If I decide I need everything on standby.

Another thing I'm thinking about is running my network equipment off 12V DC straight from the batteries. A lot of it just uses an AC adapter that puts out 12V DC anyway. You could avoid the loss going from DC through inverter to 120V AC through transformer to 12v DC again. Might be worth it if I keep the batteries in the same basement utility room as my networking equipment.

The only problem is one piece of equipment, the main FiOS gateway router, runs off 10V DC. The plug on the router says 10V and the AC adapter says it outputs 10V DC 1.6 A. I've been unable to find a DC to DC 12V to 10V converter. Is that because 10V is close enough to be powered by a 12V battery or is it just a rare choice for input voltage?

One multi-voltage converter I found http://www.powerstream.com/dc6.htm has a 9V setting it says works for 10V devices because "Also most wall-mount adapters are unregulated. So select the closest to your nominal voltage and don't worry about finding the exact voltage."

I could also try building my own converter based on this device - http://www.dimensionengineering.com/DE-SWADJ3.htm that might be a fun project.

mike95490 · December 2011

Re: Inverter efficiency

I'd not power a 10V device from a 12V battery:

Whe the 12V battery gets charged, there is about 14V present, 4v higher than the 10V spec.

I'd instead, look for a DC-Dc converter chip/module to power it.
here's an example, from a quick search
http://search.digikey.com/us/en/products/PQ1CG2032FZ/425-1759-5-ND/458149

niel · December 2011

Re: Inverter efficiency

something like this can work too. in any case the parts need a good heat sink.
http://parts.digikey.com/1/parts/613848-ic-reg-pos-volt-2a-10v-220-l78s10cv.html

LandKurt · December 2011

Re: Inverter efficiency

mike90045 wrote: »

I'd not power a 10V device from a 12V battery:

Whe the 12V battery gets charged, there is about 14V present, 4v higher than the 10V spec.

That's my concern. I know my 12V battery system actually might run at anything from 10V to 15V depending on load, charge level and charger mode. I've certainly seen 14.5 during absorb charge and that would be 45% above spec.

I did read about a certain Netgear router with a 12V DC adapter that uses an internal voltage regulator to make the 3.3V the logic chips needed. It could actually accept anything between 5V and 25V DC to run on. It would be nice if all equipment was that flexible, but I can't count on having that much wiggle room on the 10V requirement on my Actiontec MI424WR router.

john p · December 2011

Re: Inverter efficiency

A simple 12v to 9v converter will do the job at mininum cost. many converters have switchable outputs 5v 6v 9 v:cool:

CDN_VT · December 2011

Re: Inverter efficiency

LandKurt wrote: »

That's my concern. I know my 12V battery system actually might run at anything from 10V to 15V depending on load, charge level and charger mode. I've certainly seen 14.5 during absorb charge and that would be 45% above spec.

I did read about a certain Netgear router with a 12V DC adapter that uses an internal voltage regulator to make the 3.3V the logic chips needed. It could actually accept anything between 5V and 25V DC to run on. It would be nice if all equipment was that flexible, but I can't count on having that much wiggle room on the 10V requirement on my Actiontec MI424WR router.

Mr Kurt

I have used a few of these :
150W DC-DC 10-32V Boost 12-35V Adjustable Power Supply

For 8 $ delivered to your door , I power up my laptop and a few other small items for surfing , like now.

HIH's
I have bought 5 from this seller.
VT

Edit add:

Just a few things I have used.

LandKurt · December 2011

Re: Inverter efficiency

From the description of that device: "DIY an adjustable on-board power supply, you just input DC 12V, then you can get output DC 12V-35V (adjustable), But the output voltage can not below the input voltage ."

Since I'm trying to reduce the battery voltage to supply a 10V device that device won't do the job. I've already ordered a PowerLine 2000mA Universal DC Adapter that can output 9V. Hopefully that will be close enough.

That Boost device might be helpful in powering a Dell laptop that needs 19V. A down converter for the router and an up converter for the laptop would give me a very efficient way to reach the net.

Inverter efficiency

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