Inverter switch on circuit

[Capt Slog]

The title and intro say it all really.

I'm looking for a circuit that I could add to an existing inverter to make it turn on when there is a demand.  I'm hoping to run my mains powered lights from a small inverter but don't want it on all the time if I can help it.

The lights are all CFL, and so I'm hoping the initial 'demand' isn't that great, in that I'm not calling for enough power to start a tumble dryer, just one 11w bulb at first instance.

I have searched by the way, but it's not easy when you don't know quite what it's called.

Is there anything easy I can build?

Thanks

[DamonHD]

Wireless remote control?

Rgds

Damon

[rippersoftware]

Check out the set of pictures in this thread.  This is using a Ghurd controller as a LVD.

http://www.fieldlines.com/story/2008/7/5/222655/9638

[Capt Slog]

Thanks guys but that's not what I want.

I have just realised though....

 if I want the inverter to switch 'on' when it feels a load, it must also have to switch 'off' when it doesn't or some preset time after load.  It's obviously more complex than I first thought.

.

[scottsAI]

Capt Slog,

One CFL,

rewire circuit to use 12v CFL, cost $15 each is good price.

Second option is to rewire for 12v and use a small inverter on each CFL.

Ebay you can find small inverters for less than $10 each w/ship.

Beware many small inverters only supply 5w for cell phone. Read carefully.

Switch is on the 12v side for both solutions.

Have fun.

[ghurd]

Might be called "load sense" or "sleep mode".

Yes, turning it On is a lot easier than turning it Off.

I have a couple that do it.  1000 and 1200W.  750W is the smallest with it I can think of (TrippLite PV750FC).

Takes a long time to turn on.  1/2 or 3/4 second? (Long time with a drill or saw)

Stays on a while with no load.  7 seconds?

Both are long enough to think it was broken.

I expect it is a nightmare to do.

G-

[Capt Slog]

I expect it is a nightmare to do.

Ok, that's good enough for me, thanks Ghurd.  If it was easy I'd have a go, but when those in the know say no, I'll believe it.  :-)

.

[Capt Slog]

Thanks scottsAI, good ideas both, and not ones I'd considered.  At the moment I do run some 12v around the house, but it's quite light cable as it's only supplying LEDs reflector lamps.  I'll have a look at whats available here, but it could get prohibitively expensive, epecially when the power company sends me free CFLs now and then. (4 this week)

The inverter I have is 150w continuous, and uses 150mA at rest, so I suppose the loss isn't to much to stand, I'll see.

.

[ghurd]

The mother of all stupid ideas?

The existing light cable from the main battery, to a 7AH SLA near the light.

Inverter on the SLA.

Maybe a diode (voltage loss) on the wire between batteries to keep the SLA voltage down around SLA voltages.

Just a thought.

G-

[SparWeb]

"I'm looking for a circuit that I could add to an existing inverter to make it turn on when there is a demand."

When you put it that way, it makes me think you bought the wrong inverter.  There are models for sale with "sleep mode" that go into stand-by when there is no demand.  You can even control the threshold at which they "wake-up", and how often they check for a new load (eg 1/60sec or up to 1 second delay).

[boB]

Yes, all decent inverters have a search mode that does this and is built in from the start.

If you want to make an inverter do this that doesn't have search mode, you will need

to make an oscillator to turn the inverter on every few seconds at least and use a current sense circuit to see if some minimum amount of current is being drawn, and then the inverter can stay on until the current drops below the threshold.

Not too hard to do if you have some circuit skills and some time and patience.

boB

[scottsAI]

Capt Slog,

The idea is to put the switch on the DC side so no 150ma stand by losses. Zero.

Do the math it adds up big time on a small system. Bigger system maybe not so important with one small inverter.

I designed the power system for a hunting lodge. The inverter losses were too large, so was looking at the 12v CFL, at the time they cost $20 each. Then realized one for the entrance was OK, but not for the rest of the system. Found on eBay two 75w inverters for $13, ended considering 12v CFL.

Free or $2 CFL + inverter can compete against 12v CFL.

Power testing 18w for CFL in 120vac. Using inverter was 20w, acceptable.

Inverters offer the freedom to use any wattage CFL, many of the 12v CFL are low wattage like only 11watts. Large rooms like 23w CFL. One large CFL is more efficient than two lower wattage CFL.

Have fun,

Scott.