What is needed to switch and inverter on/off

[force9BOAT]

Hello,

I've spent an hour looking at inverters on the Internet but I can't find exactly what I want.  I want a low/high voltage switch that will cut power to the inverter when my 24V battery drops to about 22V and then will cut back in again after battery voltage comes back up to about 24V.  I want this function to be automatic and occur before the inverter's own low voltage alarm comes on.

Most inverters have their own low voltage cut-off but only after the battery voltage has gone lower than I want to allow it and also only after an audible alarm has been sounding for a long time.  I want to avoid both of those events.  Also I want to be able to control when the system comes back on and I want it to be automatic.  

Can someone point me to such a contorller?

Thank you,

Rob

[whirlybird]

Do you have any electronic skills if you do, My friend Adelaide does just that with

A couple of resistors and a simple relay. Very cheap and it works.

I am sure he will read this and get back to you, I would want to complicate it with a PIC chip or some such device.

Have fun.

Whirlybird.

[pyrocasto]

I may need something like that as well as my inverter's switch quit working, so it stays on at all times now. :S

[Opera House]

I hate crude solutions, but for those who want one.......  Common relays have a pull in of abput 65% of their rated voltage and drop out at about 20%.  As an example, I pulled a 5V relay out of the pile and it pulled in at abour 3.2V and dropped out at 1V.  If you put a 20V zener in series with the coil, this circuit wil pull in at about 23V and drop out at about 21V. For a little fine adjustment, two 1N4002 diodes can also be placed in series and raise those two voltages another 1.5 volts.  Measuring the resistance of the coil you can also place a resistor in series to raise the operating voltage of the coil.  In this case the coil resistance is 65 ohms.  Adding a 33 ohm resistor (50%)in series will increase the difference between the on/off voltage from about 2V to 3V.  A lot of trial and error.  The zener can be replaced with an adjustable zener LM431 (three lead device) and a pot to make it adjustable.    

[force9BOAT]

Whirlybird,

I am very interested in your friend's setup.  Please ask him to describe it for me in detail.  I need to know what to buy and how to set it up.

Thank you,

Rob

[dinges]

Somewhere in your inverter, there should be a potmeter (or a few resistors) that set the threshold at which the inverter should switch off due to low voltage.

This potmeter may be clearly marked on the board. If it's instead a few resistors, you could play with the values of these too. They should be somewhere near an opamp.

Unless it's a potmeter that needs adjusting, you may need the schematic to find out how the low-voltage switching is done and how to modify the threshold.

I've done the same once with a PC power supply, without schematic. Took some reverse engineering, bit of calculating and experimenting, but it worked in the end. Not easy (for me) though.

But ýou may be lucky, in that it is just a potmeter that you can adjust.

BTW, DON'T start turning just about any potmeter you see. Be absolutely sure you've got the correct one, otherwise you will do more damage than good!

Peter,

The Netherlands.

[Experimental]

Hi Rob,

   Just want to give you a caution about this -- shutting down or starting your inverter, when under load, can lead to inverter damage!!

   All loads, should be shut off first on the cheep models, but this may not be true on the more expensive, and heavy duty models ...

   I,m not going to test mine to find out though , just thought it would be something to think about !!!     Cheers, Bill H.......

[cyplesma]

maybe set up two relays.

one to act has the power on/off switch and the second to cut the supply to the inverter.

that means that the on/off switch has to have a smaller threshold.

both relays off

battery (source) power supply starts at zero

when supply reaches 22/23 volts supply relay switches on

wait to turn on inverter on/off relay (replaces switch) when supply reaches 23/24 volts

so at this point you have the inverter able power a load.

when supply voltage drops to 22/23 volts turn inverter on/off relay OFF.

when supply voltage drops to 21/22 volts turn off the supply relay.