Battery protection automatic cut-off

[ecusolar]

I'm planning to install a battery guard, something like the Morningstar driver relay but that solution is a little pricy for the objective.

Does someone know of a simple, cheap way to shut down the inverter at a PERSONALIZED voltage?

I was reading of an automotive gadget at about 50 USD but it's fixed to 12V.

The inverter does it also but at about 10.5V what is far to much in my opinion, I don't wanna open that thing and try out all potenciometers till finding the right one, maybe I never get the right and blow the whole thing, lol.

All that happens if you are a cheap bastard , some Xantrex inverters can adjust the shut off position.

Thanks for any hint

Joe

[Sunking]

Well a lot of inverters have auto shutdown.

[ecusolar]

Yeah, but they shut down when they want, not when I want.

I would like to cut-off at 11.6V about.

There must be some cirquits that can drive a relay to personalize the voltage.

[ecusolar]

If we can find a cheap but reliable gadget could be very useful for DIY projects.

For example you could use one to switch to a grid inverter when your batteries are fully charged for not to waste the solar production.

A generator battery could give an alarm when discharged cause of few use etc.

It hurts having a diesel generator and when you need it, the bloody starter battery is dead.

There are simple battery monitors that show a different LED depending on the charge, those could drive a relay instead of the LED

[Mike90250]

This becomes a mind set problem. You start with a set of training batteries and you have to learn not to kill them. You need to monitor your power usage, and delay high power stuff till an afternoon after your batteries are out of the BULK mode. Things that you want to not run at night or early AM, put a timer on them.

[Sunking]

I would like to cut-off at 11.6V about.

You need to rethink this a bit because it is flawed. You never want to go below 50% DOD which for Flooded Lead Acid batteries is 2.033 volts per cell, so for a 12 volt battery is 12.2 volts.

At 100% DOD or 0% charge is 1.966 vpc or 11.8 volts for a 12 volt battery. At 11.6 is well beyond completely discharged at rest.

[Mike90250]

It's also very hard to set a cut-off point, because the cell voltage is lower, depending on the drain at the time. You need to let the battery bank idle for about 2-3 hours before the voltage is a good indicator of State Of Charge.

[ecusolar]

I'm sure it can be done

Thanks friends.

Your posts gave me more reasons to worry about a good gadget as most cheap inverters cut at 10.5V.

Temporally I solved the problem with a Morningstar PS30 charge/load controller which cut-off at 11.4V.

I have a conversation with a company in UK which offers a personalized LVD gadget with time delay for about 20 USD.

I really would love to have a simple circuit to drive a voltage driven relay, other use would be the folks that have a DJ in car, it would not be the first time I see them at Saturday night asking for a jump start.

[ecusolar]

You need to rethink this a bit because it is flawed. You never want to go below 50% DOD which for Flooded Lead Acid batteries is 2.033 volts per cell, so for a 12 volt battery is 12.2 volts.

At 100% DOD or 0% charge is 1.966 vpc or 11.8 volts for a 12 volt battery. At 11.6 is well beyond completely discharged at rest.

That's exactly the reason for a unit I'm thinking of, the controllers and inverters cut-off to late, Mike and Dereck.

I want a unit that is personalizeable like the Morningstar relay driver but in a more economic way.

Sorry if I'm thinking out of the box.

Joe

[Sunking]

Sorry if I'm thinking out of the box.

Joe you are actually asking very good questions. You are starting to gain experience and asking the right questions.

As you hav e noticed many charge controllers have LVD outputs, some are programmable. Problem is if you use the LVD output severely limits output current, so serving large loads like an inverter is just not possible.

As Mike stated using SOC (state of charge) voltages is practically useless for live operating systems, and only useful for rested batteries of several hours which is not practical.

I do not know of any add on devices on the market made to do what you want. For an example a black box that is installed say between the batteries and inverter. I know some inverters have built in LVD and some of the higher end models can be programmed.

Now with that said if you have time to do homework, have mechanical and fabrication skills, they are pretty easy to make. It involves a few electronic discreet components to kake a voltage comparator to operate a relay to open the circuit when a low voltage is detected, and reconnect when the voltage is higher.

Do a little research on Google for voltage comparator circuit or even Low Voltage Disconnect circuits. Heck if i was not so busy and had time I could find or design one quickly, but it would be up to you to build at your own risk.

Maybe a guy by the name of John p might see this and probable already has a few as they are a common circuit as most just use a single Integrated Op-Amp, a few passive components like resistors and zener diodes, and a driver transistor to operate a relay. The trouble you could yourself into is not knowing what size wire to use to handle high currents safely and end up burning up you work or worse. Nothing is more frustrating working for hours, than letting out the magic smoke.

One last mote, there might even be such a product on the market. It is just something I have not ever looked for or had a need for it as most of my work is with telephone companies which hate LVD devices.

As for economics, you are going to have to bite the bullet and ask yourself which is more important. Sacrificing your battery or buying insurance to maximize battery life. IMHO a good LVD is a wise investment. So my recommendation is to purchase a quality inverter with built in programmable LVD.

[ecusolar]

Thanks Dereck and Mike

Thanks for the complete reply Dereck.

What Mike said makes sense, I can have 11V under load, cut the load and the battery is coming back to let

[Sunking]

[QUOTE=ecusolar;20396] What Mike said makes sense, I can have 11V under load, cut the load and the battery is coming back to let

[ecusolar]

Yup, I'll wait for what this guys can offer, hope it's OK to link there: http://www.reuk.co.uk/Low-Voltage-Ba...t-Circuits.htm

I'm waiting for a reply to my request, will let you know what they say.

[Naptown]

You need to rethink this a bit because it is flawed. You never want to go below 50% DOD which for Flooded Lead Acid batteries is 2.033 volts per cell, so for a 12 volt battery is 12.2 volts.

At 100% DOD or 0% charge is 1.966 vpc or 11.8 volts for a 12 volt battery. At 11.6 is well beyond completely discharged at rest.

Grid tie guy here
But when the inverter is under load wouldn't the voltage be lower than the voltage at rest and setting the cut out point lower under load would be the same as a higher at rest voltage?

[Sunking]

Grid tie guy here
But when the inverter is under load wouldn't the voltage be lower than the voltage at rest and setting the cut out point lower under load would be the same as a higher at rest voltage?

Yes sir, it is called SAG. Batteries have internal resistance, thus voltage drop proportional to the amount of current and resistance of the battery.