Dropping 2 volts to fool the inverter

lazzalazza Posts: 330Solar Expert ✭✭✭
HI Forum

Similar to my post on the chinese charge controllers. As we've been having some battery failures I've noticed an issue with the small Victron inverters 800VA and 1200VA.. which perform very well, but are not, however, programmable with regard to low voltage cut-off. It appears that they bring up the alarm at around 11V (12V system) or 22V (24V system), but dont actually shut-off until so low that the batteries are horrendously low at 9.2V for 12V systems and 18.4V for 24 volt systems!!

see page 8 on the pdf (page 4 of the manual):http://www.victronenergy.com/upload/documents/Manual%20-%20Phoenix%20Inverter%20800VA%20and%201200VA_rev%2001_EN_NL_FR_DE_ES.pdf

The failures have been in 24 volt systems where owners have abused the system (against all our advice of course) I suppose one of the 12V batteries cant supply the current and goes into reverse charge, destroying that battery and frying the other.

I will be talking to the manufacturer, but I know that these models are not programmable. So I was wondering if I could put some form of device before the inverters so that the inverter thinks the system 2V lower than it really is? Thus it will shut down at 11V instead of 9V! And hopefully save the batteries and give better warning to the owner..... any suggestions??

Cheers
Larry

Comments

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Dropping 2 volts to fool the inverter

    Probably the easiest thing to do is connect a Voltage controlled switch to shut the inverter off at whatever LVD you choose.
  • BB.BB. Posts: 28,034Super Moderators, Administrators admin
    Re: Dropping 2 volts to fool the inverter

    Some inverters have remote on/off inputs (typically a 12 volt very low current signal--ground/open or similar switching).

    You can combine that with a Victron Battery Monitor (some Xantrex battery monitors also have remote alarm contact--don't know if they are still being made/sold) -- Program the monitor to "turn on" at 50% state of charge and "turn off" at 80% SOC (or turn on a warning light/buzzer/bell to alert the folks--Use to start a genset, etc.).

    You could put a standard AC relay (or solid state relay) connected to the Victron Battery Monitor (or DC voltage controlled switch) on the output of the Inverter--Divide your circuits into two load banks... One with heavy loads you can interrupt on low battery and another one you cannot (some lights, phone, cell chargers, etc.). At least you can limit how fast they "crash" the batteries.

    If you want to switch DC loads--BlueSea makes some interesting relays that (I guess) have a small motor to turn them on and off--They do not draw power when not charging states:

    http://www.bluesea.com/products/category/Solenoids/ML-Solenoids

    BlueSea also has some interesting load interrupting relays--Don't know if they would work for your needs or not:

    http://www.bluesea.com/products/category/Automatic_Charging_Relays

    The problem with many marine products that may meet your needs is that they are only available in 12 or 24 volt devices--Very few 48 volt devices.

    The issue with using battery voltage as a disconnect signal--You might take a battery to 11.5 volts during heavy loads (or even 10.5 starting a well pump), but not let the battery go below ~12.0 volts on resting (no loads). Also you may need to thermally compensate the set point (if batteries are exposed to a wide range of temperatures). 11.5 volts with 1-5 minutes or so of time delay is probably as good as "one size fits all" set point.

    A battery monitor with an alarm? Even a simple one:

    http://www.solar-electric.com/mnbcm.html

    I am never sure you can accurately estimate a battery bank's capacity purely on voltage profile--But that is what Smart Gauge says they can do (as I understand):

    http://www.smartgauge.co.uk/smartgauge.html

    And it includes a programmable output too... May not be a bad device for your needs (alarm/load control if battery bank is in distress).

    In the end, what is it you want to do?

    Alert the owner, automatic shutdown to protect batteries (nobody there, save them from themselves), and/or let you know that the bank has been abused and the battery replacement costs should be carried by the owner of the system?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Dropping 2 volts to fool the inverter

    the real problem is not the lvd, it's an overtaxed battery. nobody should be dependent on an lvd to prevent overdrawing on their batteries. most likely it needed more in battery ah to begin with and you should not be drawing down your batteries below 50% soc.
  • boBboB Posts: 952Solar Expert ✭✭✭✭
    Re: Dropping 2 volts to fool the inverter

    Well, there is certainly a voltage which you can definitely say that the batteries are basically discharged and the load (inverter) should shut off... That is, unless it is just a large surge temporarily dragging the voltage down. Resting voltage or battery voltage averaged over a long(ish) time should be a good metric for that turn off point.

    What voltage does the Victron shut off at ? I would think he/they would have had a fairly decent LVD set point, if not adjustable.

    boB
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: Dropping 2 volts to fool the inverter
    niel wrote: »
    you should not be drawing down your batteries below 50% soc.
    Have to agree with that! If the customer has to depend on inverter lvd to protect his batteries, then he is already ruining his batteries.
    Seems there are some folks who just cannot grasp how they should treat their off grid system, and they refuse to listen. Perhaps they'll listen after they replace their batteries a few times? Probably not - - they'd likely just say they were being sold junk.
    Yes I'm frustrated. I'm frustrated because I see my cousin going through the same thing with his family. They just don't get it. And unfortunately, neither really does he. And it lands in my lap because I provided assistance in the initial phase. :grr
  • lazzalazza Posts: 330Solar Expert ✭✭✭
    Re: Dropping 2 volts to fool the inverter

    HI

    Yes it is a case of owners (or tenants which is worse) just ignoring all the advice and pushing the systems beyond their limits. The trouble is when this happens when the batteries are still within guarantees... and its' a shame the Victron inverters dont have a higher shut-off point.

    looking at LVD and battery monitors etc... the trouble is that these type of installations are shoe-string ones, and the customers are haggling over 50€ here or there. It's a very tough market. Thus installing extra equipment like the Victron battery monitor just isnt financially viable for us.

    Hence why I was just thinking of a high power diode or something to trick the Victron to shut off a bit earlier.

    In response to Bill, we just want the inverters to shut off a bit sooner, not interested in policing the installation... data loggers etc would be lovely, but will push up prices

    Cheers
    Larry
  • Blackcherry04Blackcherry04 Posts: 2,490Solar Expert ✭✭✭
    Re: Dropping 2 volts to fool the inverter

    I install a automotive LED volt meter that is bright with 1/2 digits that blinks at 12 volts and is pretty obnoxious as a signal that they best start charging, it's available in 12 or 24 v.

    http://www.intellitronix.com/voltmeter-gauges.html


    Here is a disconnect, probably costs more than a cheap inverter.( $90 USD )

    http://www.colehersee.com/home/item/cat/206/48510/
  • NorthGuyNorthGuy Posts: 1,925Solar Expert ✭✭
    Re: Dropping 2 volts to fool the inverter

    How about a generator? If you have an off-grid system, you got to be without power quite often if you don't have a generator. You certainly can over-build the system to avoid generator, but it'll make it much more expensive than the generator. It is impossible to over-load a system with a generator.

    It should be impossible to damage a properly designed system even without a generator. There must be safety alarms and disconnects. IMHO, a system where batteries get killed just because people used too much power is not properly designed. If you sell them to your clients because such systems are cheap, you're doing them a great disservice. And if customers overdraw the power and kill the batteries, they should not be blamed for that.
  • lazzalazza Posts: 330Solar Expert ✭✭✭
    Re: Dropping 2 volts to fool the inverter

    To clarify for some of the comments. I understand we are not looking at best practice- I dont complicate my life and business for fun. I normally ask the forum for clever, cheap solutions as I know there some great brains out there :)!. It may frustrate some members because it seems like we're bodging, but I'll explain it:

    Bottom line is that we're dealing with poor people, living in the countryside..... we're trying to get workable systems on a shoe-string- it's that or they have no electricity. This part of Spain has over 40% unemployment.

    We can tell them it's not ideal til we're blue in the face... but it doesnt change the situation. Hence why I am looking to minimize risk, at a minimum cost... or they'll go with the cowboy down the road who puts in the cheapest chinese inverter and they'll be even worse off.

    One day maybe we'll be doing state-of-the-art installations... hope springs eternal ;)
  • NorthGuyNorthGuy Posts: 1,925Solar Expert ✭✭
    Re: Dropping 2 volts to fool the inverter

    I'm sure your clients will find it beneficial to spend 20-30 euros for protecting switches/buzzes.

    You can use a really inexpensive relay module to do buzzing or switching.

    For example http://www.ebay.com/itm/Voltage-control-relay-timer-delay-switch-overvoltage-under-voltage-protection-/271253504988

    I'm not endorsing this particular one. Nor do I know anything about it. This is just an example.

    Or, if you can solder, you can make your own with fixed voltage setting and the kind of relay that you need. If you need many and buy parts in bulk, it might be really cheap.
  • BB.BB. Posts: 28,034Super Moderators, Administrators admin
    Re: Dropping 2 volts to fool the inverter

    I kind of figured that what was happening...

    It is the problem with unintended consequences. The customer has a battery warranty that may replace the battery even if the customer took the battery dead (it makes the battery supplier/mfg. look terrible because they are "blaming the customer" for the battery failures). And a customer that needs some electricity and there is a battery that is 1/2 full of energy. Even if they have a generator--That takes expensive fuel--And that battery is still 1/2 full.

    You need to put something in place to provide some deterrence for customers to not "kill" the battery bank. But what customer is going to pay extra to restrict their use of the system's available energy.

    Short of selling them batteries for 20% less and no warranty (or very short 90 day warranty)--I am not sure what would be a good answer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lazzalazza Posts: 330Solar Expert ✭✭✭
    Re: Dropping 2 volts to fool the inverter

    HI guys

    Exactly a deterrent is what I need, for the customer to protect themselves from system failure within 2 years and to protect us from having the nightmare of dealing with warranty issues for batteries. The trouble is, simple persuasion through logic goes in one ear and out the other .. at the end of the day, the tendency of the majority of system users is to keep pulling more and more... "oh it works great, i'll try putting in a small electric heater, a that works, now the aircon, great now I'll light a football stadium!"

    ... but as northguy has suggested, a 20 or 30 € extra is feasible- i'll look into these LVD options.

    On another point.. we recovered a battery pair from a failed battery (within warranty and in this case I really dont think the owner are to blame).. one has obviously lost a cell, the other has been a bit fried. It has a resting voltage about 12.6V now, around 12.9V... it seems to hold energy though... is this a usual situation?

    Cheers
    Larry
  • BB.BB. Posts: 28,034Super Moderators, Administrators admin
    Re: Dropping 2 volts to fool the inverter

    A single failed cell in a bank with multiple batteries in parallel can be very difficult to detect with "normal" operational meters...

    Get a shorted cell, and the rest of the batteries in the string get over charged (and can discharge the rest of the bank in bad weather).

    Get an open cell, and that string simply stops participating. And the cells in the rest of the string can start sulfating after a month or so.

    Somebody that is keeping track of their battery bank with a hydrometer (check/log every cell once a month, log cell/individual battery voltage once a month, and use a DC current clamp meter during heavy charging/discharging to make sure that all strings are sharing their loads properly) will probably see the bad cell before the rest of the bank is damaged.

    Of course, when everything is working well--who checks. :p

    So--My recommendation for smaller systems with "no maintenance".

    Keep it at 12 volts and use large AH capacity cells for single string battery banks. If anything goes wrong (one/shorted cell), the system will shut down until it gets help. If you have individually replaceable cells--At least you have less "good lead" to replace.

    Future recommendation for larger systems? Decades ago (pre Internet, pre-personal computers), individuals and companies that owned turbo-prop air craft had an FAA requirement for inspections (I don't remember the details)--Something along the line that they had to have the engines partially torn down once every 2,000 hours of flight time for inspection--Or, if they had a "certified" ongoing functional inspection they could postpone a tear down until the ongoing functional inspection showed a problem...

    The functional inspection was once every 50 hours of flight time, they had to be at a certain altitude and throttle setting--Then wrote down the exhaust gas temperatures, fuel flows, oil pressures, RPMs, Torque, etc... They would mail in the post card and my friend would enter the data and send then a report back (b-monthly???) that showed their engines' performance against the rest of the fleet and against min/max operating zone lines. If the engine exceeded any limits, it was time for service...

    I was wondering if you could do the same thing... Charge them 50 Euro every 6 months for a physical inspection or have them mail in (or post on a web site) their SG readings for each cell, Battery or Cell voltage, Bank Voltage, bank temperature, string current, etc. at 7pm once a month (you want them to do the inspection themselves--The charge once or twice a year is the incentive for them to do it themselves)--And "postpone" the inspection (and extend their battery warranty another 6 months--or whatever) while everything looks "OK".

    Longer term, I have looked at USB data loggers (they are getting cheaper). Put one on the battery bank (over all voltage) and require it for any battery warranty replacement requests. Even a 32,000 point logger will record 4 years of day at one sample per hour. Problem is that most (I have found) use a lithium battery that needs replacement every year. There are other data loggers out there--Perhaps there is one that will take 6-48 volts from the battery bank, to run.

    Ideally, I would like to see a battery logger per cell (or at least, per battery)... That would tell you a lot more (but $50 per battery is probably too much for any but the largest AH capacity battery). You could run into issues with corrosion for cabling/per battery/cell loggers too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ChrisOlsonChrisOlson Posts: 1,807Banned ✭✭
    Re: Dropping 2 volts to fool the inverter
    lazza wrote: »
    Bottom line is that we're dealing with poor people, living in the countryside..... we're trying to get workable systems on a shoe-string- it's that or they have no electricity. This part of Spain has over 40% unemployment.

    We can tell them it's not ideal til we're blue in the face... but it doesnt change the situation

    lazza,

    This might not help with the problem. But in life there are things that are reasonable and things that are not. In my experience dealing with people, if they have something handed to them on a silver platter it is unlikely that they will take care of it. So when they wreck what they were given, then stand with outstretched hand because they want more, that is human nature.

    You can never make something fool proof when you're dealing with fools. They will find a way around it because they have nothing to lose. So IMHO, with this type of situation you have to make it so they have something to lose if they don't care of it. Like telling them, "OK, you were told, you did not do what you were told - sorry, but we are taking your equipment and putting it in someplace where the people will take care of it."

    It only takes a couple days for the word to make the rounds that, "hey - you know this free electric system we got? If we don't care of it we'll lose it and have nothing." In short order people take care of what they are given, because if they don't, they'll lose it.
    --
    Chris
  • lazzalazza Posts: 330Solar Expert ✭✭✭
    Re: Dropping 2 volts to fool the inverter

    HI Guys

    Thanks for the recommendations.. I'll have a good think about it and see if an effective solution can be found. Data loggers would be great combined with LVD would be a great second step, if available at good prices.

    Cheers
    Larry
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