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something that can protect a battery from 100% Empty

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toxsick

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Hello,

I want to protect my battery from a low voltage condition switching off a relay!

I would like to have feature as a minimum, from Most Important!

1. Low & High must be Variable.. (set Low at 11.2v / High at 13.4v)
2. I would like to be able to use in 12v & 24 v systems
3. temporary battery LOWS, a cache type idea (safe to goto 10v for 5-10 seconds without trigger)


the relay is not important as the simple relay in the circuit will just Power a LARGE pack of 30+A relays

I have seen several systems but they cost 2-3 hundred bucks.

does anyone here know of something like this that's is simple to build?

thanks every1...
Shaun
 
You have several options you can take. Build a simple battery monitor circuit using discreet components like using operational amplifier circuit configured as a window comparator. Anytime your battery was outside the "window" you determine you could open/close a relay slaved to other relays.

Another aproach would be using a simple PIC chip that was programmed to output when programmed limits were exceeded (below or above). This is how I would do it.

Either method would require a small handful of components and relatively inexpensive (including a slave relay under maybe $20.00 USD).

Ron
 
You have several options you can take. Build a simple battery monitor circuit using discreet components like using operational amplifier circuit configured as a window comparator. Anytime your battery was outside the "window" you determine you could open/close a relay slaved to other relays.

Another aproach would be using a simple PIC chip that was programmed to output when programmed limits were exceeded (below or above). This is how I would do it.

Either method would require a small handful of components and relatively inexpensive (including a slave relay under maybe $20.00 USD).

Ron

thanks ron sounds really good...

i dont know about designing circuits.. but I can follow a circuit diagram pretty well if the components are basic i'd find them at the local shop and put them on a custom board if anyone out there is willing to help I'd appreciate that so very much!

if there issomeone willing to help.. is it possible to use least amount of parts
 
Hello,

I want to protect my battery from a low voltage condition switching off a relay!

...

Look at this. Uses my favorite part, the LM431 You might be able to eliminate the relay. The PFET can switch several amps...
 

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thanks so much for your interest & help, I dont know much by looking at components.. that circuit can do as asked at the top.. I.E. 1.2.3.!!!
 
Well initially you listed the requirements as:

1. Low & High must be Variable.. (set Low at 11.2v / High at 13.4v)
2. I would like to be able to use in 12v & 24 v systems
3. temporary battery LOWS, a cache type idea (safe to goto 10v for 5-10 seconds without trigger)

Since you mentioned High & Low limits I suggested using a Window Comparator where for example you could have a slave small relay energized between 11.2 V (Low Limit) and 13.4 V (High Limit). Anytime the limits, high or low were exceeded the system would drop out. That part is easily done with several components. Additionally tossing in a delay is not a problem, meaning if the system goes out of limits for several seconds it won't drop out the relay. You could likely configure a 555 timer in there for a delay and if limits return to in limits during delay nothing will happen. You would need a version for a 12 Volt system and a 24 Volt system.

The second option I proposed would be to use a PIC chip. Using a simple micro controller would be easy but would require programming the PIC. Overall likely fewer parts but programming would initially be needed.

The other circuit proposed by MikeMl would also work but I think it would only shut down for a low voltage condition so you may need another redundant circuit for your over voltage if that is important. I really like how he did that but he can better comment on his design.

Just My Take
Ron
 
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You don't need a window. Use the OP amp as a Voltage Level Detector. What you do in use I believe the positive input to set a reference voltage. You can make it adjustable by using a variable resistor (3 prong type). Tie one side to the positive supply voltage and the other side to ground. Then connect the wiper to the positive input of the OP Amp. Now you can adjust the level. Then your battery will go into the negative input of the OP Amp. When the voltage drops below the reference (variable resistor) the output will switch.
 
You don't need a window. Use the OP amp as a Voltage Level Detector. What you do in use I believe the positive input to set a reference voltage. You can make it adjustable by using a variable resistor (3 prong type). Tie one side to the positive supply voltage and the other side to ground. Then connect the wiper to the positive input of the OP Amp. Now you can adjust the level. Then your battery will go into the negative input of the OP Amp. When the voltage drops below the reference (variable resistor) the output will switch.

Yes, a simple comparator will work just fine but... the original post calls out a high and low level. He wants to work within those levels or a range of "Low & High must be Variable.. (set Low at 11.2v / High at 13.4v)". He has an under volt and over volt condition. What is suggested above is a simple non inverting comparator which will work just fine when the battery voltage drops below a threshold determined by the pot, however, it won't respond to an overcharge (over voltage) condition. That is why I suggested a window comparator and not using a non inverting input comparator.

Ron
 
No problem. :) I tend to do the same thing.

Ron
 
I'm curious though. Why does he want the window? Maybe he wants to use it with a charger too.

That would be my only guess. Maybe to be used with a charging system and he is concerned about over voltage? I guess only he can answer that directly. It would be simpler with just a shutdown of the load on under voltage. I also thought about latching a shutdown because once the load is removed the battery voltage can creep up above the limit and the thing can engage the load again.

Ron
 
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