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Thread: Need help hooking up second inverter to batteries and to circuit breaker box.

  1. #1

    Default Need help hooking up second inverter to batteries and to circuit breaker box.

    Hello, I have a simple 12 volt system, and I have one inverter hooked from the 5 12 volt batteries to the AC breaker box. Can anyone tell me how to hook up another inverter to the system. Do I attach the wires from the new inverter to the same place they are attached to the circuit breaker box? The original are hooked up to the large screws in the box. Also, do I attach the new inverter to the batteries at the same place, or other terminals? I have enough power in my batteries for my Staber washer, but the inverter I have just isn't enough, although it used to work. My charge controller says the batteries are fully charged though, when the inverter does its alarm. Thanks.

  2. #2
    Join Date
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    Default Re: Need help hooking up second inverter to batteries and to circuit breaker box.

    If your battery bus is wired correctly (heavy wires of equal length to each string of batteries)... Then yes, attach the second inverter to the same bus point (each inverter + lead should have a fuse/breaker rated for 1.25x the maximum continuous current you plan on using--And, of course, the wire should be the same rating or higher).

    However--If this used to work and does not now--And the inverter is having a low input voltage alarm--Your battery bank (and/or wiring) may be having some issues.

    Have you checked the wiring for voltage drop under load (looking for poor connections/corroded cables), more or more cells/batteries at low voltage under load and/or higher than rest of bank voltage when charging (open/shorted cells).

    Have you checked/logged temperature corrected specific gravity for each cell?

    I like to recommend using a DC Current Clamp DMM (this one is "good enough" for a start--very safe, quick, and easy way to measure AC or DC current flow). Under heavy load and heavy charging, check that each string of batteries is carrying its "fair share" of current (again looking for poor connections, open/shorted, cells, failing/sulfated cells, etc.).

    Double check that your parallel batteries are wired in a "balanced" configuration (such as this website).

    Batteries do fail over time--3-5 years is "OK" for golf cart batteries. Better batteries may last 8-10 years... Fork lift batteries can last upwards of 20 years.

    However, it is also very easy to kill a battery bank in months/weeks/days with poor operating practices. Over/under charging, not refilling with distilled water every ~1-2 months, taking batteries near dead.

    We can discuss your present setup and, perhaps, make some suggestions--If you are having problems with battery life.

    Also, 12 volt battery banks have a practical limit on output current... When you get over ~100 amps (100 amps*12 volts = 1,200 Watts), the copper cabling/breakers/fuses/etc. are pretty expensive to manage this level of current--And voltage drop issues limit how far you can send the low voltage power.

    If you are already looking at a new inverter--You may wish to look at 24 volt inverters too (or even 48 volts).

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  3. #3

    Default Re: Need help hooking up second inverter to batteries and to circuit breaker box.

    Quote Originally Posted by taraxacum45 View Post
    Hello, I have a simple 12 volt system, and I have one inverter hooked from the 5 12 volt batteries to the AC breaker box. Can anyone tell me how to hook up another inverter to the system. Do I attach the wires from the new inverter to the same place they are attached to the circuit breaker box? The original are hooked up to the large screws in the box. Also, do I attach the new inverter to the batteries at the same place, or other terminals? I have enough power in my batteries for my Staber washer, but the inverter I have just isn't enough, although it used to work. My charge controller says the batteries are fully charged though, when the inverter does its alarm. Thanks.
    Whoa! Brakes on!

    You definitely do not connect the AC output of the two inverters at the same place in the AC breaker box. There are only a few inverters meant to be "stacked" like this.

    If your washer need a bigger inverter, dedicate the output of that inverter to the washer. Turn off both when not in use to avoid wasting power keeping an inactive inverter running.

    Now here's another thing: you have five batteries in parallel on a 12 Volt system. The chances of this working well are pretty slim. Unless the wiring is perfect and correct they will not share current evenly. This not only means they won't charge the same, but also that some may not be "contributing their fair share" for running the loads.

    Please provide more details about your system. if you are thinking of adding a second inverter it might be time to go up to 24 Volts and solve a lot of problems all at once. If we know all the specs we can advise on the practicality of making the change up.
    Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  4. #4

    Default Re: Need help hooking up second inverter to batteries and to circuit breaker box.

    The batteries are not old, we got them from a UPS business, I guess they keep them for battery backup in case of power outage, but were never used, and they replace them every year. They are blue, sealed, and they seem to keep a charge well. Could I check them by unhooking each battery, and checking the voltage? My present inverter is only a 1000 watt one, which is not enough to run my heavy upholstery sewing machine, so we wanted to add the 750 watt inverter we already had. But perhaps we should just buy a 2500 watt inverter? We have little money, and our system is as simple as it gets, as we also have little know how. Our lights are all 12 volt, and I buy 12 volt bulbs for them, knowing we are poorer in the winter, and if we have no money when inverter dies, we still have lights and 12 volt pump for water. My pc is laptop, being charged directly from the batteries. We rarely use the tv, for rare dvds. For the AC, the only use is a blender, the washer, and if we had a larger inverter, my huge upholstery sewing machine, and the once a month movie. What would I do with 24 volt, since my stuff is 12 volts? Or is there an inexpensive changeover to 12 volt for them? Thanks so much for your time.

  5. #5

    Default Re: Need help hooking up second inverter to batteries and to circuit breaker box.

    Quote Originally Posted by taraxacum45 View Post
    The batteries are not old, we got them from a UPS business, I guess they keep them for battery backup in case of power outage, but were never used, and they replace them every year. They are blue, sealed, and they seem to keep a charge well. Could I check them by unhooking each battery, and checking the voltage?
    For judging SOC reliably by Voltage the battery to has set for several hours with no current going in or out. Keep in mind they may be fully charged and in good shape, but that doesn't mean they will perform well hooked up all in parallel like that. Since they are UPS batteries they may be gel, which are not ideal for RE application (a difference between staying in Float most of the time and occasionally discharged as needed vs. daily cycling).

    My present inverter is only a 1000 watt one, which is not enough to run my heavy upholstery sewing machine, so we wanted to add the 750 watt inverter we already had. But perhaps we should just buy a 2500 watt inverter?
    There is no way of combining the AC output of these two inverters for the same load. If the 1kW unit will not run the machine you need a bigger inverter to accomplish that. It may actually be capable of it if there are no other load demands and the batteries are wired up perfectly and it is not an MSW type inverter. Do you have any specs on the machine as far as its power requirements? Best case: get a Kill-A-Watt meter and measure what it uses when run on a source capable of operating it (such as a generator if grid is not available).


    We have little money, and our system is as simple as it gets, as we also have little know how. Our lights are all 12 volt, and I buy 12 volt bulbs for them, knowing we are poorer in the winter, and if we have no money when inverter dies, we still have lights and 12 volt pump for water. My pc is laptop, being charged directly from the batteries. We rarely use the tv, for rare dvds. For the AC, the only use is a blender, the washer, and if we had a larger inverter, my huge upholstery sewing machine, and the once a month movie. What would I do with 24 volt, since my stuff is 12 volts? Or is there an inexpensive changeover to 12 volt for them? Thanks so much for your time.
    Sometimes it's a matter of "if you've got to have the inverter anyway you might as well run everything from it". Your DC plan is a good one for the "no inverter" contingency.

    I think you should investigate the battery bank wiring first. Ideally each battery should have its own wires (equal length for each) connecting to common positive and negative bus bars before going to any equipment. All attach an image of two battery strings sharing common connection to give you an idea what I mean. The wire size is important too; if it is too small it will cause too much resistance and cause Voltage drop by the time it reaches the inverter.
    Attached Images Attached Images  
    Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  6. #6

    Default Re: Need help hooking up second inverter to batteries and to circuit breaker box.

    Click image for larger version. 

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ID:	5651 I have attached a picture of my batteries. I hope it comes out. I know, probably enough to make one like yourself to wince. As you can see, some are together with same size and length heavy wires, but others are together with copper pipes made into connectors. Which is better, or should we scrap it all and use something else? Oh, and I just noticed my name next to my name, is "new guy" , wrong, would be "new gal". :) Thanks so much for your help. I love internet.

  7. #7
    Join Date
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    Default Re: Need help hooking up second inverter to batteries and to circuit breaker box.

    You may be having problems with the jumper cable style clamps... They usually will not make good enough connections to operate anything much over a few hundred watts of inverter power.

    You should really bolt up the power cables instead. (the overall wiring could use a bit of help too).

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  8. #8

    Default Re: Need help hooking up second inverter to batteries and to circuit breaker box.

    Okay, I've seen worse wiring. No, really. Of course it was usually all burnt up on account of being so wrong.

    Couple of things. First, what you have there is "laddered" wiring: all connected together like rungs on a ladder. Here's some diagrams of wiring methods. #1 is what you've got, sort of, and it's no good. #3 would be best for you, but you probably could make up #2 easiest. http://www.smartgauge.co.uk/batt_con.html

    Second, I see "alligator clips" making connections. These are very unreliable and can not handle the full current capacity of the wiring. You need to make solid connections to the batteries with bolt-down lugs.

    As for the 'pipe wiring' it is surprisingly good for carrying current. Tends to be a pain mechanically though, and is a big open short hazard. If I were you I'd move all the pipe to the negative side, and sheath it with some old hose or tubing as much as possible.

    These few changes could go a long way towards improving the current and Voltage available to the inverter, which should make it perform much better.

    Don't get to flustered over being called "new guy"; the tags are automatically generated by the forum software and it has no way of determining gender.
    Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  9. #9

    Default Re: Need help hooking up second inverter to batteries and to circuit breaker box.

    Okay, so what should I use/buy for the batteries to join them, and what else have I done wrong? (the overall wiring) When you said to bolt up the power cables, were you talking about the clamped on inverter cables? And that I should just bolt them to the batteries instead? Thanks so much.

  10. #10
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    19,648

    Default Re: Need help hooking up second inverter to batteries and to circuit breaker box.

    Take a look at 2manytoyz's website--1/2 way down. He has lots of pictures and discussions as his solar power setup evolved.

    http://2manytoyz.com/

    Much of his work was Do It Yourself...

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

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