power shut off

[thirteen]

Don't most inverters have a voltage shutdown when the power supply is lower than required? If so are they adjustable? I've never had one apart. The ones I have seen are usually black and melted and good for srap.

[DamonHD]

Hi,

*Some* do, and none of those that I happen to have looked at are adjustable.  And usually the claimed set-points are far lower than I would be comfortable with in terms of damaging (lead-acid) batteries.

Rgds

Damon

[Steadfast]

Glenn Hurd is working on creating a switch to do that for me...

http://www.fieldlines.com/index.php/topic,146979.0.html

[ghurd]

13,

Does the inverter have a rocker switch?
If so, it is a pretty easy modification.

The type with a membrane push button switch are not so straight forward.


I believe inverter LVDs are intended to protect the inverter, not the battery.
That often works out well for me when I am trying to operate something with a long startup surge, and using undersize jumper cables between the battery and inverter.  If the inverter went LVD at 12.2V or 11.9V, then it wouldn't get the power tool started.
G-

[thirteen]

I am going to buy a new inverter next spring and am looking for information on there use for battery protection.  I'll have a 24v system. I'll also be getting new batteries and solar panels. What I use now is old batteries and I think it is an old Victor inverter 12v. I'm trying to find a relay or sensor to break the battery power supply if the voltage drops below safe operating usage from the batteries to the inverter. A person would have to manually reset it. I was thinking of a spring  connected to a switch on a soleniode could work with a simple set of pionts.  I will be gone 2-3 months at a time and with some of my kids going up there while I'm gone there may be a problem show up. I would not like to come back to a barbaqued control house.

[Flux]

Yes most of the modified square wave inverters do have a low volt cut off and also a high limit. This gives some protection to the battery and to the inverter but it's not foolproof.

The lv cut off is usually round 10v and the idea is based on a low charged battery supplying full load with a bit of drop from the cheap cables usually supplied. At the trip point in this case the battery is probably safe enough. The same is not true if you run the inverter on light load for hours until the thing trips out, under these conditions trhe battery will be way discharged and most likely damaged.

The only true reference for state of charge measuring battery volts is on open circuit after standing for some time. It is near impossible to get a decent idea of state of charge when on variable loads.

A more intelligent Lv disconnect would need a set point determined by the load current and it would be battery specific and would need to take into account the wiring volt drop. I am sure you can make something better than the built in protection on the inverter but for normal use for the intended purpose the protection is good enough when used as intended for portable power supplies.

Flux

[OperaHouse]

The problem is once you reach the upper or lower limit the inverter will latch off and will have to be manually reset.  At $16, a UNO is pretty cheap and the development system is FREE.  Just add a couple of parts like a relay placed in parallel with the rocker switch and the inverter can be turned off and restarted again automatically when things are back to normal.  Read my frifge control post.

[Xan]

i bought was was claimed to be "an awesome low frequency pure sine wave inverter that could start difficult loads". It turned out what this thing really was is a UPS. It is true it is low freq. But it has a horrendous no load draw - 2Amps - pretty high  for a 12 volt 500 watt inverter. So it seemed to me the only practical place to use it was for the washing machine. That way it could be turned on only when a wash was being done thereby mitigating the issue of the high no-load draw.

I needed to turn it on and off remotely. What it had was TWO membrane push buttons one each for on & off, which is kind of common for UPS type devices I have found. I determined that how these worked was that the "On" button pulled a line to the MPU high, and the "Off" button pulled that same line low. It also proved to be the case that holding the On button in once it was started did nothing else and caused no problems, and also that the Off button would "take over" if you pushed it - even if you were pressing the On at the same time.

It was simple then to wire a relay that would switch this control line to either high when it was energised on low when it wasn't. I took these high & low voltages from the same place that the push buttons did to avoid any unexpected (and potentially damaging) situations.

And ever since then it has been running like this really well. The inverter is out in the power shed and it can be remotely switched on & off from the laundry room.

I thought this info might be useful to someone else trying to do a similar thing.