Help with automatic low battery switchover to mains - Electronic Circuits Projects Diagrams Free

dannix · 13th April 2008, 09:31 PM

Hi,

I am working on a circuit to automatically switch over from a solar charged battery to rectified mains when the battery voltage drops to 10.5v.

Please see attached schematic.

I am concerned that when the op-amp comparitor de-energises the relay due to low bat voltage the relay will switch the load to rectified mains, as the load is removed from the bat the bat terminal voltage will rise and switch back and forth causing relay chatter. I am unsure how to overcome this so would appreciate some assistance.

If I have gone about this completly the wrong way let me know, I am not as experienced as some of you guys!

Many thanks

I should point out that the rectified mains will in fact go through a commercial buck - boost DCDC convertor for full regulation, this is capable of 8-24v in with regulated 12v out.

Boncuk · 14th April 2008, 05:43 AM

Hi dannix,

assuming the battery is a lead-acid-battery you can use a window discriminator to acivate and deactivate the relay.

Set the low trip point to 10.5V and the high trip point to at least 12.5V. That leaves 2V to play with and certainly no relay flutter.

Boncuk

dannix · 14th April 2008, 05:55 AM

a what?

However I think I solved it by swapping the inputs and putting an invertor between the comparitor output and the transistor., finally a 250k resistor from the invertor output to the - input of the comparitor for histresis. It works in simulation but I have yet to test on breadboard.

Boncuk · 14th April 2008, 09:38 AM

Quote:

Originally Posted by dannix

a what?

The "what" is a combination of two comparators one with a low set point and the other with a high setpoint.

Within the window everything is valid and passes. Outside the window it is discriminated!

Hans

dannix · 14th April 2008, 03:54 PM

Hi, I still don't follow, think its time to research good old google

jbarnaby2000 · 14th April 2008, 07:19 PM

Hi dannix,
I know this is way off topic here, but what did you use to draw up and test your circuit??

Thx

dannix · 18th April 2008, 10:32 AM

Hi, sorry for the delay!
I used livewire pro, its drag and drop style with a simulator (not always most acurate but can help avoid simple mistakes)

dannix · 18th April 2008, 10:35 AM

Quote:

Originally Posted by Boncuk

The "what" is a combination of two comparators one with a low set point and the other with a high setpoint.

Within the window everything is valid and passes. Outside the window it is discriminated!

Hans

That actually makes sense now I re-read it. It was 5am at the end of a night shift when I 1st read it! :S

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14th April 2008, 05:43 AM	(permalink)
Boncuk	Hi dannix, assuming the battery is a lead-acid-battery you can use a window discriminator to acivate and deactivate the relay. Set the low trip point to 10.5V and the high trip point to at least 12.5V. That leaves 2V to play with and certainly no relay flutter. Boncuk

14th April 2008, 05:55 AM	(permalink)
dannix	a what? However I think I solved it by swapping the inputs and putting an invertor between the comparitor output and the transistor., finally a 250k resistor from the invertor output to the - input of the comparitor for histresis. It works in simulation but I have yet to test on breadboard.

14th April 2008, 03:54 PM	(permalink)
dannix	Hi, I still don't follow, think its time to research good old google

14th April 2008, 07:19 PM	(permalink)
jbarnaby2000	Hi dannix, I know this is way off topic here, but what did you use to draw up and test your circuit?? Thx

18th April 2008, 10:32 AM	(permalink)
dannix	Hi, sorry for the delay! I used livewire pro, its drag and drop style with a simulator (not always most acurate but can help avoid simple mistakes)