inverter voltage shut down before battery bank voltage goes below 30% dicharge

[musselbeach]

Hi I have been looking for a way to automatically turn off the DC supply to the invewrter before the battery bank dicharges below 30%. I see there are controllers that have a voltage high and low setting output for doing just that. My question is does a MSW inverter care if the DC supply is shutt off and on with out turning off the load switch???

[OperaHouse]

If you are thinking about switching the power to the inverter, forget it.  Just parallel a relay on the on/off switch of the MSW inverter.  Please note that this line also monitors the voltage and using a form of electronic switching with a few fractions of a volt drop may cause the inverter to shut down at a much higher voltage.

[musselbeach]

thank you for your input but I do not quite understand what you mean by: "Please note that this line also monitors the voltage and using a form of electronic switching with a few fractions of a volt drop may cause the inverter to shut down at a much higher voltage."
When you shut off an inverter by the switch does it shut down all DC voltage draw because it says in the instruction it draws power even when nothing is connected to the output or idle??

[musselbeach]

I have reread your advise again and I think I know what you are saying? The switch mechanism I was thinking off was to switch a 12 volt solinoid to interup the DC power input but you say not to do it that way but swich the inverter off the normal way by parralleling the switch but the contacts are still on Maybe you ment in series that would break the cct. ??
 

[oztules]

"parralleling the switch but the contacts are still on Maybe you ment in series that would break the cct. ??"

Unless of course you leave the manual switch off.....then the relay assumes full control. Turn the relay off and you have manual control. If you series it then you have no manual control in case of a relay failure etc.



maybe?

............oztules

[rossw]

A solenoid beefy enough to break the full-load current of your inverter will have a quite substantial coil current - very likely well in excess of the standby draw of the inverter.
Normally-closed solenoids will be somewhat hard to come by in my experience, which would mean using a solenoid that's powered all the time the inverter is... not very efficient!

As for detecting the battery voltage - the voltage of a battery that's 30% discharged, but supplying only a light load, will be far higher than the same battery 30% discharged but supplying a larger load.

Eg, a 12V battery supplying 1 amp might be 12.8 volts at 30% discharge, but could be as low as 12.3 volts while only 10% discharged when supplying 20 amps.
Determining when to shut down, based purely on battery voltage, isn't going to achieve your aim.

[musselbeach]

In most battery info I come across says that you should not allow your battery bank to discharge right down and to recharge at about 30-40% discharge to a float level to save your batteries live span, so unless you are monitoring your battery bank condition and switch the load off manually how is the best way of accomplishing this automatically??Anyone have any ideas>

[rossw]

In most battery info I come across says that you should not allow your battery bank to discharge right down and to recharge at about 30-40% discharge to a float level to save your batteries live span, so unless you are monitoring your battery bank condition and switch the load off manually how is the best way of accomplishing this automatically??Anyone have any ideas>

They're quite right, but overly-simplistic systems are unlikely to achieve your goals.
It might work if you have a fairly constant load, but not if you have variable, changing loads.

Measuring cells specific gravity is one way to do it.
"Watt-counting" - ie, counting how many watt-hours come out of the battery, and subtracting how many watt-hours go back during charging, is a reasonably accurate way of keeping a "fuel gauge" of charge in batteries. It's not perfect, as batteries require more energy to recharge than you take out, so there will be a progressive accumulated error, the counter will need to be "reset" from time to time.

[musselbeach]

Maybe it is just better to measure your wattage use over time and recharge on a time period when the Watt hour capacity of your battery bank has used up say 50 %??

[ChrisOlson]

In most battery info I come across says that you should not allow your battery bank to discharge right down and to recharge at about 30-40% discharge to a float level to save your batteries live span, so unless you are monitoring your battery bank condition and switch the load off manually how is the best way of accomplishing this automatically??Anyone have any ideas>

When you say 30-40% are you talking 60-70% SOC (State of Charge) or 30-40% SOC?  If you're talking about only using 30-40% of the bank's capacity, IMHO, that's treating the batteries pretty nice.  If you're talking 30-40% SOC, you're working them a little hard.

I like 50% SOC as the bottom end, and that's what my battery manufacturer recommends.  Unless you have a more advanced inverter that can monitor that sort of thing and take measures (such as starting a standby gen) when the parameters are reached, I think you're pretty much down to monitoring it manually and taking the necessary measures yourself.

There are some good battery monitors out there, like the Bogart Engineering Trimetric, that will tell you what you need to know.  But making something like that automatic based on voltage is kind of hard to do without a more advanced inverter.  As Ross pointed out, loaded voltage vs at-rest voltage are two different things when determining remaining battery capacity.  For instance, I have my inverters set up to start my standby gen if the bank falls below 24 volts for more than 2 hours, and bring it online within 15 minutes if the bank drops below 23.2.  The reason I do that is because, technically, 24.0 volts is 50% SOC.  But when there's a good load on the inverters it's not usual to see it drop down to 23.5 volts when there's no incoming power.  But if I take all the load off it, it might recover back up to 24.5 volts.  That voltage after the bank recovers is called the "at-rest" voltage, and that's what you have to use to determine approximate SOC.

So unless you have a good handle on what your loads are to know when 50% SOC is reached with the bank under normal load, and have an inverter that you can program to take the appropriate measures, it's really a stab in the dark.

Believe me, I know where you're at because I lived with a system like yours for many years.  I never did find a decent way to make it automatic until I finally bought a more advanced inverter that is designed to take care of that sort of thing without manual intervention.
--
Chris

[musselbeach]

Thank you for all that info guy's as it saves me a lot of expermenting trying to acheive the imposible, so it is manual monitoring and recharge the battery bank at 50% capacity. That what I will keep doing.

[ChrisOlson]

Thank you for all that info guy's as it saves me a lot of expermenting trying to acheive the imposible, so it is manual monitoring and recharge the battery bank at 50% capacity. That what I will keep doing.

One thought before you give up totally on making it automatic, and this something I learned later ---

Does your inverter have a battery charger in it?  If it does, there's a little box made by Morningstar called the "RD-1 Relay Driver".  That box is more than a relay driver - it's really a programmable logic module that can activate relays based on battery voltage and timers.  It can do many of the things that more advanced inverters can do as far as starting generators and/or turning on grid power to an inverter that has a built-in charger.  It could also, technically, turn on an external battery charger.  But I don't like that scheme because it's not very efficient to charge a bank with an external charger with AC grid power, then convert the DC back to AC with an inverter.  If your inverter has a built-in charger, then it probably also has a built-in transfer switch to switch loads over to grid or gen power while the bank is charging.

That little RD-1 is programmable with Moringstar's MSView software and a laptop with a serial cable, and it can do things like activate a relay with a 2 hour timer below your set point (or however you program it).  More info is on the thing here:
http://www.morningstarcorp.com/en/relay-driver

Disclaimer: I am not involved with Morningstar, or promoting their products.  I just have two of these things - one that controls my water heating loads, and the other that does an orderly shutdown of my RE system in the event of an over-voltage situation.  And I've been very happy with their reliability, flexibility in what they can do and be used for, and ease of use.
--
Chris

[musselbeach]

No I do not have an inverter with those extras but I have a couple of differnent controllers and one of them has a user output with voltage on/off settings that can be used to do what ever switching one wants with added relays etc. the controller canbe found at
http://www.tlgwindpower.com/ccontrollers.htm
I use a transfer switch to switch my house load from inverter to gererator. That is why I wanted to be able to automatically switch the inverter off when the battery bank reached 50% discharge which would then switch the transfer switch to the gererator in turn charge the battery bank.

[clockmanFRA]

Hi musselbeach,
I am doing a Multi battery LVD, (Low voltage disconnect) and using an Arduino Mega board as the controller, it also stores the voltages to a 2GB removable data card so you can analyze the information on your PC.
At first i am setting the LVD at 12.20v per 12v battery 20 off, but this LVD shut down voltage can easily be reset to a different voltage.

On my inverter i have put a relay operated switch on the off button, so the fans can still run and the inverter shut down properly.

Its a UK sustainability forum and i have a good chap who is helping with the PIC programming.
http://www.navitron.org.uk/forum/index.php/topic,15541.0.html

[ghurd]

If you have a reasonable sized battery for the load and charging amps,
The basic idea is this,

(thats the inverter switch pulled out of the inverter... I can't find the original post by snake21 I made the sketch for)


Many inverters specifically say not to disconnect and connect the battery when the load is operating.
Even if they do not say it, controlling that many amps mechanically is not a good idea.
G-

[musselbeach]

Thank you very much for that info. I am using a controller that can be found at  http://www.tlgwindpower.com/ccontrollers.htm                                                                                 http://www.tlgwindpower.com/ccontrollers.htm  it has a user ON and user OFF ajustable voltage and I was thinking of setting it at 24volts to turn a relay on/off  wired in parallel to the inverter switch as I have a 24v battery bank and at 24 volts it should be at 50% charge +/- 10%?
Do you not think this would work? I know the battery bank voltage varies as load varies but it should be close enough so that batteries can be charged to float voltage and then the inverter would kick in again.  I am an out dated electrical technologist took his training in 1960 and my electrical profession was in front end design of Microwave Radios.
not to much up on the new electronid's wizardry.
Ron

[ghurd]

Are you using it as a charge controller for the wind and solar system?

If you are, then no.  It looks like it could be used as a dump load controller, or an LVD, but not both at the same time.

24V LVD is far too low in a 24V system.

Here is where the confusing stuff gets confusing and complex.
A 24V battery is half dead at about 24.4V
Totally dead at 23.8 to 24V, depending on what chart you choose to believe.

OK.  You have it set to 24V to make up for surges.  But what if there are no large surges?  Then the battery gets ruined with small loads.

There are some simple work-arounds that may be suitable, but we do not know enough about your system to give any guesses on what would be a good idea to try.
G-

[musselbeach]

I have a 1000 surette battery bank charged by a 500 w TLG wind turbine and 1000 watt solar aray controller see web site
http://www.mwands.com/index.php?main_page=product_info&cPath=4&products_id=450
I have a propane 7 kw generator and transfer switch to charge the battery bank and Cottage when not on a 5000 MSW inverter.
The inverter is the primary power for the cottage which only reguires about 1500 watts as all major appliances run off propane.
So I also have this controller http://www.tlgwindpower.com/ccontrollers.htm  which I was going to use for the switch mode using the on / off termanels to do the switching of the inverter by parralleling the of/on switch Which I can set the voltage to recharge the battery bank. When the inverter goes off the transfer switch switches to generator power.
Hope that gives some light on what I am tring to do as I am now monitoring them by wattage use over time (400 amp hour use) and a battery charge condition meter and manually switch the transfer switch.

[ghurd]

I think you are assuming those items are accurate, and fast, and temp compensated, and will play well together.
I am not sure what to make of the controller you mentioned a few days ago.
The other one is a relay driver with blinky lights.

I do not see how they could play well together, on a regular basis, reliably, or efficiently.
RossW said the same thing in different words, above.
G-

[musselbeach]

maybe what I need is a http://www.windandsun.co.uk/Data%20Sheets/Morningstar/RD_DataSheet.pdf to do the switching. I could also switch the transfer switch because it only needs 12vdc, this would switch the cottage load to the generator an also charge the batteries. That would leave the inverter in idle. How would that be??

[ChrisOlson]

That's actually the box I pointed out earlier in this thread.  Folks can make fun of being it's just a "relay driver".  But I wish Morningstar would call it a RD-1 Programmable Logic Controller instead.  It has four output channels, programmable timers that go up to 18 hours, and can turn on or off just about anything, including complete wind systems and solar arrays, based on high or low voltage set points.

Anything you can turn on or off with a relay, it will run or control, including auto gen-start functions.

If you're going to use an RD-1 to start a generator, it only requires one output channel for a two-wire gen, and two output channels for a three-wire gen (a three-wire gen will have sustained ignition on two wires and crank on one - so you have to drive two relays).  With a diesel, on some gens you can use two wire (one glow/stop, and one crank).  On some diesels it might take three output channels (preheat, crank, stop).

One thing the RD-1 does not do is crank lockout on gen voltage/freq sense.  So it does not have programmable retries on gen start.  Technically, if the gen doesn't start so you get a voltage increase, the RD-1 is going to re-try a gen start after the timers you have programmed into it expire.  But I don't like that.  So for that reason, I only recommend them for two-wire gens that have a built-in controller on the gen.  If you have a three or four wire gen and it starts reliably, then it might work OK.  But it will keep the starter engaged on gen start for the crank time you have programmed into it.  This normally kicks the starter drive off the flywheel and it may not hurt anything.  But I don't like that function of it.  It is best suited to two-wire generator start systems.
--
Chris

[musselbeach]

Yes you did and thank you for that I just could not find who gave to me (sorry) I tryed to find it but I have been on a few sites trying to get differant views on things. I find its best to ask people who have been there and done that rather than spinnig ones wheels. It looks like it will do the job but I all ways like to explore other ideas before making a commitment.
Do you think my idea of switching the transfer switch is better than trying to switch the inverter off and on which wound trigger the transfer swich?

[musselbeach]

I might add that the generator has it own controller to handle the starting as it is a Generac system. The controller has a 220vac input transformer (no center tap) to 12vdc to supply the switching relay and run the contol module. My inverter will supply the 220v and when it shut down the transfer switch switches the cottage load from the inverter to the generator and the generator will also charge the batteries. but if I put a relay in series with the 220v and drove it by the Morning star monitor switch I could turn it off that way. ?

[ChrisOlson]

My inverter will supply the 220v and when it shut down the transfer switch switches the cottage load from the inverter to the generator and the generator will also charge the batteries. but if I put a relay in series with the 220v and drove it by the Morning star monitor switch I could turn it off that way. ?

Yep.  Your gen sounds either a CorePower or Guardian series, and you can start it with a simple relay with the RD-1.

You're definitely better off to flip the transfer switch (Generac EZ Switch?) with it instead of killing the inverter.  Just leave the inverter run.
--
Chris

[musselbeach]

Thank you I think that would be the simplest way as well I will try that once I order the RD-1.

[ghurd]

Folks can make fun of being it's just a "relay driver".  But I wish Morningstar would call it a RD-1 Programmable Logic Controller instead.  

Anything you can turn on or off with a relay, it will run or control, including auto gen-start functions.

I do not recall anyone making fun of it.
It is what they say, and it does what they say.
They do not call it a charge controller, because it would be pretty crappy in that capacity.

MorningStar is honest, and they call it a 'Relay Driver", because it IS a 'relay driver'.

PLC is an entirely different device.

My '89 Camry did have a computer in it, but it could not check email or make a word document.
Nobody called an '89 Camry a 'computer'.
Same idea.

[ChrisOlson]

Yes, I think that distinction is good.  It is not a charge controller but it has capability to control system functions based on voltage or temperature input that few other things can do at the same price.

While it will start and stop a generator, I think it is limited in that capacity.  There are two reasons you would want to start a generator on an off-grid power system - load control and low battery SOC.

On the load control issue, only an inverter can do that properly.  The RD-1 has no way of knowing how much load is on the system.  So there's no way it can bring a gen online for peak load management.

On the low battery SOC issue, it can start a generator using basically the same timers and parameters than an inverter would use to auto-start a gen.  However it can only shut the gen off based on either a high voltage set point or a timer.  With an inverter controlled generator, the inverter will do a full proper charge (bulk and absorb) on the bank, then shut the gen off when absorb is done.

So, IMHO, it's not the perfect gen controller.  But I think in this case it will work fine being that the OP has a two-wire start generator.  After a few charge cycles he will get an idea of how many hours it takes to fully charge the bank once the gen comes online, and program a timer in the RD-1 to shut the gen off based on that.

Just as an example of something else it can do - I have one of my RD-1's configured for temp input on one channel, with a temp sender on my generator.  If it gets below 5° F the RD-1 activates a relay and turns on the block and oil pan heaters on the gen to keep the block and oil warm for cold weather starting (both heaters powered by 120 VAC power).

So even though they call it only a "Relay Driver", it's a pretty sophisticated little box.  And also one of the more useful (and versatile) devices I have found for high level system control.
--
Chris