Help...Newbie in town...two cheap inverters on one battery bank ?

Pangea
Pangea Registered Users Posts: 16
Greetings from Japan...Canadian living in Japan...I have recently purchased a 50 watt (17.60volts) and 100 watt (18 volts) solar panels and two 12 volt batteries wired in parallel at 115 amps each adding (i guess) to 230 amps. a 20 amp pwm charge controller (and a partridge in a pear tree) . ( panels are not too expensive here 50 watt at around 50 bucks and the 100 at around 90 bucks)

I also bought a cheap 450 watt inverter. I can run a a single house fan or the lap top computer on it. However if I try both the buzzer on the inverter starts ... I figured two batteries at 115amps each should handle the load ... So I thought if I attach another 500 w inverter to the load on the PWM charge controller would that be ok ?

I figure that it would just drain the batteries faster ...( but not sure) I have read the two blogs about two inverters on this site and it seems that I can...( Something about grounding and something about the pulse in the wires ? )

Please any advice would be most appreciated...:confused:

Also If this is not the right place to make this post ...I do apologize in advance...

Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?
    Pangea wrote: »
    I also bought a cheap 450 watt inverter. I can run a a single house fan or the lap top computer on it. However if I try both the buzzer on the inverter starts ... I figured two batteries at 115amps each should handle the load ... So I thought if I attach another 500 w inverter to the load on the PWM charge controller would that be ok ?
    I figure that it would just drain the batteries faster ...( but not sure) I have read the two blogs about two inverters on this site and it seems that I can...( Something about grounding and something about the pulse in the wires ? )
    It all depends on how much power the computer and fan are drawing. And on the wires from the batteries to the inverter.
    A 450 watt inverter could handle a 50 watt computer power supply (laptop sized) and a 400w fan. Or it could handle a 150 watt computer power supply (desktop) and a 300w fan.
    But 450 watts at 12 volts is going to be almost 40 amps, so you need some seriously large wire between the batteries and the inverter, and it should be short even then.
    You need to know just how much the computer and the fan draw and also measure the voltage at the batteries and at the inverter when running them both.
    Finally, the computer power supply may be drawing large current peaks just at the extremes of the AC voltage swing, and this will draw more current from the inverter than the power alone would indicate. The inverter will trip out on high current even if it is only part of each cycle.

    If your cheap inverter is a Modified Square Wave output rather than a Sine Wave output, the current peaks will be even worse and the fan motor may not be very happy either.
    SMA SB 3000, old BP panels.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Welcome to the forum.

    You've got a few problems it seems.
    As inetdog said much depends on what the loads are drawing. But two things to avoid: adding a second inverter and/or attaching an inverter to the charge controller's LOAD terminals. Here's why:
    A second inverter will have its own power consumption, effectively increasing the load on the batteries. This won't make anything better.
    No inverter should be connected to LOAD terminals because they are current limited, usually at 20 Amps which is only 240 Watts.

    Now onward. On a 12 Volt system wiring size is critical. If it is not large enough the Voltage at the inverter input will drop under load, possibly to the point of triggering th low Voltage alarm. It sounds like this is happening. It also makes a difference how the wiring is connected with two batteries. For optimum performance see method #2 on the Smart Gauge page: http://www.smartgauge.co.uk/batt_con.html

    Another thing: if the batteries are not fully charged they will not be able to operate at the higher end of their Voltage range. If all you are charging 230 Amp hours of battery with is two panels totaling 150 Watts they aren't being properly charged. That much panel probably would handle 85 Amp hours @ 12 Volts. Together they might make 8.5 Amps; a mere 3.6% rate - far below the recommended 5% no load minimum.

    As it is if the batteries are fully charged they'd have about 1.3 kW hours of stored power. 150 Watts of panel would only supply perhaps 500-600 Watt hours, or about half what the batteries are capable of.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Also remember a 450 watt 12 volt supply will use nearly 45 amps DC at maximum load. Connections need to be bolted with heavy enough wire to support the current. Generally "alligator" or "jumper cable" type clips/clamps are not "good enough" to carry these higher current reliably.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    And you do not want to draw off more than 50% of the batteries power ie keep above 50% DoD, depth of discharge, nor go below 50% SoC, state of charge.

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Pangea
    Pangea Registered Users Posts: 16
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    First ....Thank you Inetdog, Cariboocoot, BB, and Westbranch...I am truly grateful to you all for taking the time to answer my plea...and Second...

    Holy Smokes talk about getting over my head... Here I taught I knew what I was doing...Ha! don't know squat...Well at least now I know more on what to look into and LEARN more...cheers for the intel....

    I have a few questions and please answer if and when you have some time...I will direct them to each reply for consistency. One thing Is there a good resource or book that I should read first ?

    thank you all again

    Oh...This is the article/web page that got me started with my current set up...http://www.treehugger.com/solar-technology/inexpensive-diy-solar-power-the-600-kit.html

    perhaps they needed to explain a tut more ...?
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?
    Pangea wrote: »
    Is there a good resource or book that I should read first ?

    Not kidding, possibly the very best resource you'll find anywhere is this very forum with it's many sections and topics of discussion.
    Books can be of value, but they often reflect the personal opinions of the author, which may or may not be correct and not misleading. This forum provides the opportunity for ideas, thoughts and information to be vetted.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    For a bunch of solar/conservation related information, this thread has a lot of information:

    http://forum.solar-electric.com/showthread.php?5556-Working-Thread-for-Solar-Beginner-Post-FAQ

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Oh goody: a solar "kit".

    Begin MOCK MODE:

    Part 1: How To Waste Your Time, Effort, And Money Building Panels From Rejected Cells Found On E-bay. You can build your own homemade panels for around 5-6 times as much as a commercial panel costs, and it will have a very high percentage rate of failure (if it works at all) probability with the added detraction of no warranty.

    Part 2: Throw away more money on an AIMS MSW inverter.

    End MOCK MODE.

    That article is out of date in its information, overly simplistic, and useless.

    1kW of good panels can be counted on for 2 kW hours of electric in some locations, but the particular location will determine how much power you can actually realize. To make flat statements that "so much" panel will run "this" for "so long" is inaccurate. For one thing, loads run off the batteries, not the panels. The panels recharge the batteries.

    The batteries mentioned: two 92 Amp hour 12 Volts totaling 184 Amp hours. The most they would supply would be about 1 kW hour AC. They would serve longer at half that rate. You wouldn't need 1 kW of panels to recharge them either: more like 315 on a PWM controller.

    MSW inverters are pretty much a waste of money these days. The pure sine wave versions have come down in price to where they are a better deal as they will handle any type of load providing the power requirement is met.

    Expressing the system in terms like having $55 to spend on wiring ... Not good. Every system is different, and you don't know what the wiring needs to be until the rest of it is planned.

    Perhaps the worst statement in the article is this: "... it is relatively easy to expand ..."
    In a pig's eye it is. Half the questions I answer have to do with expansion and how difficult it is to do once you're locked in to a lower system Voltage. Then there's the problem of finding equipment now that is compatible with what you bought then: panel specs tend to change often these days and mixing them isn't always possible. Most of the time expansion is a matter of starting all over again.

    My advice: read the forum, ask questions whenever you like. That's why we're here. An active forum full of engineers, technicians, installers, and people with experience is going to be far better than any single source written by one person.
  • Pangea
    Pangea Registered Users Posts: 16
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Thank you for your reply.

    Do you mean the inverter should be within arms length of the charge controller ?

    It is a cheapee for now ...MSW

    I thought by pressing the reply button the reply would pop out by the person who posted the reply in the first place ...SO the above question is / was for
    inetdog...but all are welcome

    I have read the post http://www.smartgauge.co.uk/batt_con.html and will remedy the batteries...Good to know...

    I guess I will ask the questions here ... no point in posting a bunch of posts

    Cariboocoot you explained that the batteries are not being sufficiently charged , the PWM light does go yellow but if I switch the loan off for a while (like an hour in the day time ) then the light goes back to green...I thought that meant that the batteries had charged ? Should I leave them alone for a few days...also you explained not to run the inverter from the load part on the charge controller ...Should I run it off the batteries directly ? I will not attach a second inverter as you had explained...thank you for that...

    As regarding the wire thickness...( I am sorry but I only know metric) it is 2mm solid copper wire used usually for AC wiring in homes...To be safe I have put the batteries outside and ran wires from the charge controller into the apartment where I have attached the MSW inverter then the appliances ...I have checked the voltage at all the intervals and there seems to be very little loss in volts from the panels to the inverter ? perhaps I should be checking for amps and not volts ? The panels seem to read around 12 volts even on a cloudy day...Perhaps I do not know how to use the meter properly...( I read I can use the volt meter to measure the battery charged state, is that correct ?)

    Thank you for the encouragement to query here rather than getting any book ... Thank you again...
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    The inverter should be close to the batteries as they are what power it. The longer the wire between batteries and inverter the greater the Voltage drop under heavy current loads and the more likely there will be trouble (such as the Voltage at the inverter falling below the cutoff point even if the batteries are charged).

    Next to the "Reply" button is one that says "Reply With Quote"; that will quote that post in your reply.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    12 VDC is a "pretty low voltage". So, you do not want to pull (or charge) too much power or your copper cables become huge (large diameter)--Which is expensive and difficult to work with.

    And, usually, you want the DC cables short--To keep voltage drop low.

    Usually, we suggest 1) measure your loads; 2) conserve your loads (less power needed means smaller/cheaper off grid power system); 3) design your system to support the loads; 4) shop for hardware that will meet your needs; 5) spend money.

    Off grid power systems can be "expanded" a bit--But, in general, it is much better to define your loads to be supported, then design/build the system. There are many reasons that it is very difficult to expand a system... For example, a 1,200 watt AC inverter will draw (worst case):

    1,200 watts * 1/0.85 inverter efficiency * 1/10.5 cutoff voltage = 134.5 Amps

    And since many "good" inverters will run at 2x rated power for a few seconds (surge current support), you are looking at 2x134.5 amps = 269 amps through that cabling/back to the battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Pangea
    Pangea Registered Users Posts: 16
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Greetings all...question...in order to expand my battery bank...the batteries should be close to the same age and have the same voltage and amps ? I have two marine type 12 volt 115amp batteries/ so if I were to add a third then it should be exactly the same ...from what I have read...Also I am aware that I need more panel for the batteries that I have presently ...

    Also for those who had replied before , I have completely rewired my setup and have the inverter right by the charge controller but it is connected directly to the batteries and not the load section on the charge controller...Also the batteries are reconnected to allow a same level recharge...Thank you for the advice it was not in vain...

    I used the multimeter to check the output of the inverter and it fluctuates something fierce...26 to 58 to 74 to about 86 volts of AC...I don't think that is good ...ANY kind words of wisdom...?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?
    Pangea wrote: »
    Greetings all...question...in order to expand my battery bank...the batteries should be close to the same age and have the same voltage and amps ? I have two marine type 12 volt 115amp batteries/ so if I were to add a third then it should be exactly the same ...from what I have read...

    In general, Marine Batteries make poor deep cycle batteries (they are a compromise between automotive/truck batteries and true deep cycle batteries). If you are cycling the batteries deeply (using 25% or more of their capacity), at some point you should think about getting true deep cycle batteries. "Golf Cart" type 5 volt ~220 AH batteries can be pretty nice and cheap for smaller off grid power systems.

    Mixing ages of batteries will work... It can cause new batteries to "age down" to the older batteries. And/or you could end up with having to diagnose/replace batteries one or two at a time--So you end up with more maintenance on your part (i.e., if batteries last 3 years, every year or two you will have to replace at least one battery--plus failing batteries can place more strain on the remaining "good batteries". Usually, it is "less work" to just replace all batteries at the same time and have the bank last its X years between replacement.

    Similar issues with replacing with non-similar batteries (size, type, even brand/models)--Batteries may not properly share charging/discharging currents. So wear/usage/available energy/aging may not be optimal.
    Also I am aware that I need more panel for the batteries that I have presently ...

    So, assuming 12 volt at 3x 115 AH battery bank, with 5% to 13% rate of charge:
    • 345 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 1/0.05 rate of charge = 325 Watt array minimum
    • 345 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 1/0.10 rate of charge = 650 Watt array nominal
    • 345 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 1/0.13 rate of charge = 845 Watt array "cost effective" maximum
    I used the multimeter to check the output of the inverter and it fluctuates something fierce...26 to 58 to 74 to about 86 volts of AC...I don't think that is good ...ANY kind words of wisdom...?

    Something does not sound right. If you plug a 100 watt filament lamp into the AC inverter--How does the bulb function? Look normal brightness? Is the light steady?

    I would suspect the meter (good meter, good batteries if digital meter?). Are you making good electrical connections? Are you using the AC scale? MSW type inverters read "low AC Voltage" with most less expensive DMM type meters (not a sign wave output).

    And the inverter DC power input wiring is all bolted up? No "alligator clamps" or jumper cables (many inverters will fail to work reliably if not bolted up/solid connections with heavy copper cabling).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Pangea
    Pangea Registered Users Posts: 16
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Thank you Bill for your reply and thank you for calculating the panel wattage figures...That has given me a good idea on how much panel output I will need...In regards to the panels I have a question...Is it possible to mix panel watts and voltages...I have read that the volts should be roughly the be the same...

    Currently I have a 50 watt panel at 17.6 volts at 2.84 amps and a 100 watt panel at 18 volts at 5.6amps.

    I wish to add another 100 watt panel at 15.84 volts at 7.69 amps...the battery bank is 12 volts. Is that all right to do or not ?

    I have read that there will be some loss because the panel is at 15.84 volts . I also read that there will be some backwash of energy to the panels. The panels all have blocking diodes so that shouldn't be a problem...

    In regards to the batteries the price is nuts here in Japan for real deep cycle batteries like the one for golf carts( at least from the ones that I have found) Hence the Marine ones though they are not ideal. Surprisingly, panels are not too expensive like about 100 dollars for a 100 watt panel...

    thanks again
  • Pangea
    Pangea Registered Users Posts: 16
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?
    BB. wrote: »
    Something does not sound right. If you plug a 100 watt filament lamp into the AC inverter--How does the bulb function? Look normal brightness? Is the light steady?

    I will try but I don't have an incandescent bulb at the moment( I use energy saving ones at home). I have a cheap digital multimeter. I had it set on LOW AC setting and tried it on my wall outlet which it kept a steady 101.6 volts ( Japan uses 100 Volts instead of 110 or 115 )... I am not sure what does BOLTED UP mean ? I have 3.5 mm wire connecting the inverter to the battery.( not alligator clips) Is there a way of taking a pic and posting it ? Might be easier to explain to what the heck i have done...
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    In this case "bolted up" means solid connections on the DC wiring. Good connections are important to keeping the DC input Voltage steady under loads. It's easy for resistance to go high and on 12 Volt systems it can cause big problems.

    Your 3.5mm wire is roughly 7 AWG, which is good for around 60 Amps tops or 720 Watts from the inverter. The closer the current draw is to this level, the greater effect any loose connections or high resistance points will have. If you can't get steady output Voltage with no load on the inverter, something is seriously wrong. At that point you start checking everything, from the resting Voltage of the batteries to the Voltage difference between them and the inverter input.

    BTW, adding another panel whose Vmp is only 15.84 is not going to help much: by the time its output goes through wiring the Voltage it supplies will be less than the battery charging point. This is why "12 Volt" panels have a Vmp of 17-18.

    You can upload digital pictures by clicking "Go Advanced" and "Manage Attachments". Use the "Basic Uploader" to find the file on your computer, send it to the server, and include it in your post.
  • Pangea
    Pangea Registered Users Posts: 16
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Attachment not found.Attachment not found.Attachment not found.Attachment not found.Attachment not found.Attachment not found.
    the grey wire with the black marker on the left top is wire coming from the panels.

    the other grey wire goes into my apartment from the inverter...

    the battery wires come in from the right top side into a 15 amp ac breaker.


    the two larger panels are attached in parallel at a another breaker . that wire goes about 7 meters into the PWM. Good / Bad I don't know...I hope ok...

    I am running DC voltage from the LOAD on the charge controller to a cigarette plug and a wire going into my apartment to charge cell phones...

    Thank you Cariboocoot

    I have tried the 100 watt light test and it shone without a waver of any kind...Good I supposed...I did check the DC voltage on all the connections and batteries...about 12.48 this morning. that includes the connection to the inverter...Now I have included some pics ( bloody mess of wires I agree) of my set up and a pic from the Japanese book on solar setup...I realize it is in Japanese but I feel that you will know what you are looking at ...( diagram and all)

    I treid both of my cheap inverters and they both fluctuate ...one less than the other but they do...However no more low power alarm...which is good...But one of the inverters has a light to indicate that electricity is being received , and it was on even though I had shut the battery flow off...so

    ...I was wondering Are the panels in fact sending DC to the inverter bypassing the batteries? I believe they are ... I have checked on other post it seems to be ok to do but do not know for sure...

    Sadly I have made the purchase of the 100watt/ 15.84 volt panel off yahoo auction japan...I can always sell it myself ...

    Also can you please direct me how to wire everything properly if by dumb luck i have not done so the first time ?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Okay that wiring could do with a bit of re-work. ;)

    Think like this: you have four separate but inter-acting circuits: The first is the PV's to the charge controller, the second is the charge controller to the batteries, the third is the batteries to the inverter (and other DC loads), and the fourth is the AC wiring. Each of these will have its own Voltage and current ratings and needs to be wired accordingly (including circuit protection).

    Basic wiring rule: it has to be large enough to A). carry the maximum expected continuous current and B). conduct the Voltage over distance under load without incurring too much Voltage drop. The circuit protection is then determined by the wire size.

    Right now the DC out of the controller and in to the inverter is wired together. This won't "bypass the batteries" exactly, but it's the same size wiring and probably shouldn't be. If the controller is 30 Amps, then the most current seen on that circuit (#2) would be 30 Amps. That on the inverter translates to (30 * 12) approximately 360 Watts. Is that a 500 Watt inverter or a 1500 Watt inverter? Either way, the 10 AWG that would work for the charge controller output is too small for the inverter draw. This can cause Voltage drop under loads. At 500 Watts the wire size should be at least 8 AWG, and larger is always better on an inverter.

    So what you're looking to do is:

    1). Circuit from panels to charge controller. If more than two panels in parallel each should have its own fuse. Wire sized to handle combined current of panels and (especially important here) not lose too much Voltage over distance.

    2). Circuit from charge controller to batteries. Wire and circuit protection to handle maximum current. Voltage drop is usually not an issue here so long as the distance is kept to a minimum. Fuse/breaker according to controller's rating.

    3). Circuit from batteries to DC loads including inverter. This will be two circuits for you; one wire set and fuse/breaker large enough to handle the inverter and another for your DC chargers. Voltage drop can be an issue here especially for he inverter as it will draw a lot of current at maximum power. It is best to have the fuses/breakers near the battery so that if one does blow there is not a lot of "live" wire about looking to make a short circuit and cause more trouble.

    4). AC lines. Standard household wiring practices apply here.

    Does this help?
  • Pangea
    Pangea Registered Users Posts: 16
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Thank you Cariboocoot...I will try to re wire everything once more...I see you are from BC...My mom lives in North Vancouver..Once again thank you for taking the time to explain everything...There wouldn't be any diagram or schematic available ? I am a bit more of a visual learner but no probs if there isn't...
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    It's a bit difficult to draw diagrams because I'd have to do a new one for each system. Otherwise I'd be drawing "basic" diagrams which could get misinterpreted - and inevitably someone would say "you left out ..."

    Although I know I should draw some of these basic diagrams and then "just point". :roll:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help...Newbie in town...two cheap inverters on one battery bank ?

    Just treat the batteries as the "heart" of your system.

    For a first approximation. Design the charging system to battery connection first. Wire size/lengths (keep short and neat). Long/small diameter wire can cause excessive voltage drop which will cause the batteries to charge slower. Here a 0.05 to 0.10 volt maximum drop (with maximum charging current) between controller and battery bank is a good aim point.

    Then design the Battery to AC Inverter connection. AC inverters can take a lot of current and need heavy connections back to the battery bus (low voltage drop again). For a 12 volt system, designing for a ~0.5 volt maximum drop is good for DC inverter wiring.

    The battery wiring (if more than one battery is connected) has to be able to manage the worst case current (loads and inverters, etc.). Generally all the battery connections come to a single + and - point. That is the "bus connection". All positive wires that leave that point should have a fuse or circuit breaker to protect down stream wiring from over current (breakers and fuses protect the wiring from over heating). You may have a 20 amp fuse for your solar array, and a 60 amp breaker/switch for your AC inverter (so you can turn off the inverter when not needed), etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset