Author Topic: DC Relay/switch question  (Read 988 times)

Offline vardaman

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DC Relay/switch question
« on: April 27, 2018, 08:02:20 AM »
Can someone point me in the right direction about what type of relay/switch I need?

I have an inverter that will alarm if the voltage falls below about 8vdc. So can I put a relay or some other switch before the inverter that will switch off completely at a set voltage so that the inverter just goes off and doesn't see the low voltage.

Any help would be greatly appreciated!

Offline Carl

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Re: DC Relay/switch question
« Reply #1 on: April 27, 2018, 01:49:39 PM »
  A low voltage disconnect can be had for typical 12 or 24 volt operation,you must pick one to handle your current needs for the inverter ....move inverters with low voltage warning are at 10.8 volts for 12 volt systems and the amperage depends on the power your system needs.

https://www.amazon.com/s/ref=nb_sb_ss_c_1_30?url=search-alias%3Daps&field-keywords=12+volt+low+voltage+disconnect&sprefix=12+volt+low+voltage+disconnect%2Caps%2C403&crid=3ROLXPPEBOSJ5&rh=i%3Aaps%2Ck%3A12+volt+low+voltage+disconnect

Offline vardaman

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Re: DC Relay/switch question
« Reply #2 on: April 27, 2018, 02:53:02 PM »
Will these work without a battery in the system?
« Last Edit: April 27, 2018, 02:59:34 PM by vardaman »

Offline Carl

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Re: DC Relay/switch question
« Reply #3 on: April 27, 2018, 05:00:47 PM »
Will these work without a battery in the system?

Help me understand...you want a battery-low voltage protection circuit that works in a circuit without a battery???
Seriously,with such a question,I think you should hire a professional to work on your project. While it is only 12 volts,it can kill or cause much damage and mayhem.

  I worry as no inverter I know of has an 8 volt warning and most ,of any power capability,have automatic low voltage shutdown at 10.5 to 11 .2 volts under load.

Offline vardaman

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Re: DC Relay/switch question
« Reply #4 on: April 27, 2018, 06:38:47 PM »
I didn't say I needed a battery low voltage protection circuit, you did. I said I needed a relay or a switch. I'm not using batteries. It runs when the sun is shining, that's all I need for it to do.

Offline Fixit

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Re: DC Relay/switch question
« Reply #5 on: April 27, 2018, 10:20:32 PM »
Trying to picture what you want . Is this a direct grid the system ? Or maybe sense you install solar hot water systems intended for pump run on a SHWS .

Offline FreeThinker

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Re: DC Relay/switch question
« Reply #6 on: April 28, 2018, 04:23:26 AM »
I'm a little confused as well, sounds like you want a relay or switch that opens the contacts at some voltage level above 8vdc?  Regardless, maybe this will help.

Quote
Pick up voltage (also defined as pull in voltage, or must operate voltage): As the voltage of a de-energized Relay is increased, this is the value at or below which all contacts must function.

Drop out voltage (also defined as release, or must release voltage): As the voltage on an energized Relay is decreased, this is the value at or above which all contacts must return to their de-energized position.

Then use the search feature at Mouser (https://www.mouser.com/Electromechanical/Relays/_/N-5g31?Keyword=Electromechanical+Relays&FS=True) to find a relay (you'll need to read the data sheets) that has a "Pick up / must operate" voltage that will keep the relay contacts closed at your normal operating voltage, and that has a "Drop out/must release" voltage of about 8v (or whatever voltage you want the contacts to open at).

Offline Carl

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Re: DC Relay/switch question
« Reply #7 on: April 28, 2018, 06:07:01 AM »
I didn't say I needed a battery low voltage protection circuit, you did. I said I needed a relay or a switch. I'm not using batteries. It runs when the sun is shining, that's all I need for it to do.

In this type system. a low voltage disconnect ...the BATTERY would be replaced by the solar panels.