converter/inverter

pedropedro Registered Users Posts: 11
Hi guys and gals. I'm converting a bus into an rv and have a 440ah battery bank, 2 210 watt panels, a xantrex mppt 60, an exeltech 12v 1100 watt inverter and a 45 amp progressive dynamics converter. We plan on both on and off grid stays so my original thought was to use the converter to supply the DC panel when plugged in, but now I'm thinking maybe the converter would be unecessary and add more compexity to the electrical system.

Anyone using a converter and inverter on the same battery bank?

Comments

  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: converter/inverter

    Be careful with some of the converters. They are sometimes only single stage battery chargers. If it is a 3 stage charger, then I would keep in.

    Now for the inverter, if it is a XP1100, you can get a transfer switch option for it. This way, when the converter is hook to shore power, the inverter switches over automatically.
  • pedropedro Registered Users Posts: 11
    Re: converter/inverter

    I bought one equipped with a 3 stage charger so as not to cook the batteries... easily.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: converter/inverter

    I've seen it mentioned in a couple of places, that when a converter/charger is supplying a load, it should be run in two-stage mode.

    Here is a mention of it from a Samlex converter/charger manual:

    http://www.samlexamerica.com/customer_support/pdf/Manuals/SEC-1260A_SEC-1280A_SEC-2440A_Manual_Mar2009.pdf

    Page 15:

    "CAUTION!

    3 stage charging is recommended for charging stand-alone unloaded batteries (there is no load connected to the battery when it is being charged). If a load is also connected simultaneously, a part of the charger’s output current will be diverted to this load. Thus, the charger may remain locked in Stage 2 if the current drawn by the load is more than the preset value of threshold current determining change over from Stage 2 to Stage 3 .This will lead to overcharging and loss of electrolyte.

    For charging a battery when a load is also connected simultaneously, Stage 2 voltage should be same as Stage 3. Select “Loaded Battery” with the help of DIP Switches (5) – See under “Selecting the Type of Battery and Charging Stages”."


    It is also mentioned here (last paragraph):

    http://www.donrowe.com/battery_charger/samlex_document.html



    As to your original question: Yes, for my RV I run an inverter *and* a charger. The charger is an old one and will be getting swapped out later for most likely an Iota running in two-stage mode (two-stage is the default for the Iotas without the IQ4 module).

    For directly feeding a DC panel - I wouldn't. I would (and do) run a charger to supply the power to the battery, and run the 12v loads off the battery. Just make sure that your converter/charger is bigger than the loads so that you have extra to charge the battery.
  • pedropedro Registered Users Posts: 11
    Re: converter/inverter

    Why not supply the DC panel directly from the converter when we're tapped into shore power?

    Thanks for your advice.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: converter/inverter
    pedro wrote: »
    Why not supply the DC panel directly from the converter when we're tapped into shore power?

    You could, but you have to take into account that you want to charge the batteries as well.

    For simplicity you just wire the loads to the DC panel, then wire that to the batteries - then just wire the converter/charger to the batteries. Done deal.

    Same with the solar - you rig up your solar and connect the solar charge controller to the batteries.

    The loads are one thing, the chargers are another, the batteries are in the middle. In essence, you ARE supplying the DC panel directly from the converter because the converter is putting out enough to run the loads *while* it charges the batteries.

    Which is why it is referred to as a converter/charger - it does both.
  • pedropedro Registered Users Posts: 11
    Re: converter/inverter

    I was thinking it would be easier on the batteries if I kept the loads off them when I was tapped into shore power by supplying the DC panel via the converter. Another question I have is whether there is a conflict with charging a single battery bank from multiple sources at the same time, e.g. alternator/solar, converter/solar.
  • vcallawayvcallaway Solar Expert Posts: 157 ✭✭✭✭✭
    Re: converter/inverter

    Aren't the IOTA's designed to work in this mode?
  • BB.BB. Super Moderators, Administrators Posts: 30,510 admin
    Re: converter/inverter

    Regarding your converter/charger... Many times, these converters require a battery to be connected, or there is a lot of "ripple" in the output (perhaps, just a rectified sign wave for the very simple units). Trying to power your DC panel with the converter and the battery disconnected may give you problems (on my old RV, the lights go dim and the 12 volt radio does not work).

    Regarding multiple chargers on one battery bank... If each charger is properly configured and connected, then there should be no problem. Each will turn off according to its setup.

    The one issue may be if you equalize your battery bank. Some 12 volt devices don't like the 15-16 volts that may be present when a battery is equalized. It would be best if you disconnect/switch off all loads/chargers/devices except the charger and the batteries are are doing/being equalized. Also, any 12 volt loads present may interfere with equalization (equalization current is usually fairly low--Loads may "siphon" the current for their own needs).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: converter/inverter
    vcallaway wrote: »
    Aren't the IOTA's designed to work in this mode?

    Yes, the Iotas are two-stage by default with an RJ jack that you can plug an included doohickey into to select the voltage (13.6 or 14.2). Or you can plug an IQ4 module into that jack and turn it into a multi-stage charger (3 plus EQ).

    What I *don't* like about the IQ4 is that it automatically does an EQ weekly...I will be using AGM and I do NOT want them EQ'd at all.

    Moot point anyway since I'll be charging with loads connected so two-stage seems best for my rig.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: converter/inverter
    pedro wrote: »
    I was thinking it would be easier on the batteries if I kept the loads off them when I was tapped into shore power by supplying the DC panel via the converter.

    I don't think so. From what I've seen on the forums, the biggest killer of batteries is over discharging and/or under charging.

    To do what you've described, you would need a converter to run the DC loads, and a battery charger as well to charge the batteries. Or, you would have to switch back and forth using the unit as a converter sometimes and a charger other times.

    It would be much simpler and easier to just use the converter/charger to do both. Also, whenever you are connected to shore power (or running a generator) the converter would be charging the batteries. Even if it just keeps them topped up while it's running the DC loads that is still "a good thing".

    As long as the converter/charger puts out more than the DC loads, then you won't be drawing down the batteries at all because the converter/charger will supply all the DC loads and still have some left over for charging the batteries.


    Also, batteries have a life span which is measured in "cycles". You might take a battery down 20% (80% charged) say 3000 times, but that same battery might only last 1000 cycles if you take it down 50%. It might only last 150 cycles if you take it down 80%.

    If you have say 40a DC loads, and a 45a converter/charger, then whenever you are plugged in you will be charging the batteries. Keeping them topped off is the best way to keep them alive the longest.
  • pedropedro Registered Users Posts: 11
    Re: converter/inverter

    Thanks dwh and others for your responses. I believe the converter/charger I have (progressive dynamics 9200 series) is designed to supply power to the devices and charge the batteries at the same time.

    Here's where my brain is going into slow mode: Scenario #1--I have solar and an alternator. If I'm running the landscape of this fine country, should I be utilizing the alternator (not huge for a bus, 100amp) or would the panels (420watts through a mppt 60) possibly suffice to give the batteries enough juice to keep a couple devices hummin'. Ya, I know, it's called math. And, if I'm charging with the alternator, which I suspect most would recommend, I assume I need to disconnect the controller or install an expensive transfer swith?

    Scenario #2--I'm at the park, I'm cheap like you and don't want to pay for electrical hook-ups, so the sun's doing what it does but I, like you am cheap, and undersized my system, therefore junior's nintendo is literally breaking the battery bank, so I tap shore power. Do I disconnect the flow from the controller to the batteries so the incoming ac can be converted to charge the batteries, or somehow seperate dc from ac, e.g., solar supplying dc, shore separately supplying ac so I would need a transfer switch for the inverter not to conflict with the converter as n3qik recommended, or just tell junior game times' over?

    I'm looking for harmony, but my ignorance keeps bringing me to chaos.
  • BB.BB. Super Moderators, Administrators Posts: 30,510 admin
    Re: converter/inverter

    My 2 cents, leave it all connected together. You have good quality product and it should all play nicely (except during equalization).

    The alternator is usually not a big charging factor for RV's... The resistance of the wiring harness and issolation switch usually limits it to a few 10's of amps. And, a standard alternator really cannot output a hundred amps for any more than a few minutes is unlikely unless it is designed for the job (such as a Balmar).

    If you want to make use of your alternator power (because you have long drives)--using a inverter on your vehicle battery, run an 120 VAC cord back to the RV and connect to an AC battery charger will probably pump more current than the DC link would.

    In the end, watching battery state of charge and water levels is your best guide as to how much load/charging works out. (~75-90+% is normal range; time below <75% State of Charge is fixed the next day with external charging/reduced load until >75%; and anything below <50% is rare and quickly fixed with firiing up the genset and/or paying for shore power).

    If you have not yet done it--Get a Battery Monitor of some sort. It will really help you manage your battery capacity and teach the others to look at the Monitor and decide what to do (suggestions, pick your numbers/actions for your needs):
    • >90% battery full (get >90% at least once per week)
    • 80%<90% everything OK
    • 50%<75% reduce loads, start genset/shore power next day (as needed)
    • <50% Start Generator/Connect shore power
    • <20% Something is wrong. Turn off all loads and call Dad or Mom.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: converter/inverter

    I was worried about the multiple-charging-sources question myself at one time. Then realized it isn't a big deal! (As long as you have good components, as BB pointed out.) I was worried about one charger "pushing" power into another and damaging it, but the battery "pushes back" just the same as another charge source would.

    I have since had all kinds of sources on my battery bank at the same time. Solar from an MPPT charge controller on my main array, another small PWM charge controller on the Harbor Freight panels, a small wind turbine with its own built-in controls, and even an Iota AC battery charger.

    During bulk charging, it's not a problem. they'll all contribute what they can as the voltage slowly climbs. When you reach absorb voltage, the devices with the lower setpoint (or that measure a little higher voltage than the others) will "drop out" sooner. At that point they won't really contribute anything but it also doesn't hurt them - they're just waiting for the last device to finish bulk/absorption and the battery voltage to drop to float.

    And I also keep my loads on the battery bank full time. There's always power flowing through the whole system one direction or another.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: converter/inverter
    pedro wrote: »
    so I would need a transfer switch for the inverter not to conflict with the converter

    They don't conflict - in fact, they work together.

    Figure a 300w inverter at 12v can draw 31.25a. If you are running it purely from a 30a converter/charger without a battery (you would need one with a good regulated output, such as the Iota) then you could potentially draw every bit of the 30a that the converter/charger can put out.

    But if the 300w inverter could go to say a 400w peak load, you can't get there because the converter/charger doesn't put out enough.

    Now, if you have the battery in the middle, and again, a 300w inverter and a 30a converter/charger, then IF you draw the full 300w, you would actually be drawing all that the 30a converter/charger can put out, as well as 1.25a from the battery.

    With a 400ah battery bank, you could do that for nearly 100 hours before you hit 25% battery drain (or 75% full or 75% SoC (state of charge)). At that point, it would be a great idea to drop the loads to some point below 30a so that the converter/charger can start increasing the battery's charge.

    Letting a lead/acid battery sit partially discharged is definately unhealthy for it. Even sitting at a 75% SoC for a few days WILL cause some small bit of sulfation - and when you get enough sulfation, the battery will need replacement.

    This is why it's a good idea to let the converter/charger handle the DC loads *and* charge the battery at the same time - since you are powering the converter/charger with AC anyway, you might as well put whatever juice you can into that battery.


    Also, having that battery there, if for some reason you peak your inverter momentarily at 400w, then the inverter will have enough current available on the input side since it can make up whatever extra it needs (over and above what the converter/charger supplies) by taking it from the battery.


    At the same time, if there is sunlight on your PV panels, then that will *add* to the available current. So say a 45a converter/charger and 15a solar will add up to a total of 60a available. If you are drawing off 30a of that for DC loads, then the extra 30a will be available to charge the batteries.

    Same with the vehicle alternator. Say it's putting out 30a at highway speeds, and the solar charger has sun and is putting out 15a. Then you have a total of 45a available - minus whatever loads - to charge the batteries.


    The conflict which is normally resolved by a transfer switch, is a conflict of *incoming* AC. For instance on my rig, I have a shore power connection, and a generator.

    My transfer switch is manual - I plug my shore power cord into the generator. If there is shore power I unplug the cord from the gen and plug it into the shore power. There can never be a situation where my little AC breaker box is getting power from the gen and the shore power at the same time (it would be quite dangerous to back feed AC from shore power into the generator).
  • pedropedro Registered Users Posts: 11
    Re: converter/inverter

    So when I'm dry camping, the inverter supplies the AC panel, which in turn supplies the converter, which in turn supplies the DC panel and charges the batteries? If so, wouldn't my 1100watt inverter which is essentially suppllying the AC and DC (via converter when dry-camping) be a bottlekneck point in the system?
  • BB.BB. Super Moderators, Administrators Posts: 30,510 admin
    Re: converter/inverter
    pedro wrote: »
    So when I'm dry camping, the inverter supplies the AC panel, which in turn supplies the converter, which in turn supplies the DC panel and charges the batteries? If so, wouldn't my 1100watt inverter which is essentially supplying the AC and DC (via converter when dry-camping) be a bottleneck point in the system?

    You do not want to do that... It is approaching a perpetual motion machine setup (Inverter powering converter to recharge battery bank that is supplying power to the Inverter which is powering the converter...).

    The AC inverter output needs to not power your converter... Most likely, you will need a separate Inverter AC sub-panel to power those loads that make sense to run from batteries (efficient lighting, small fan, TV, etc.).

    Any large loads (converter, A/C, etc.) should come from the shore power/AC Generator power input.

    One decision you will have to make is whether or not you will want some sort of AC transfer switch to power the Inverter Sub-Panel with shore/generator power or continue to use battery power). Ideally, you would want an AC transfer switch to disconnect the inverter's output and connect the sub-panel to your AC main panel (shore/gen powered).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: converter/inverter

    I like the transfer switch as this places all of the 120 VAC loads to shore power. This gives the inverter a chance to cool down.

    Buy going converter (120VAC) -> battery (12VDC) -> inverter (120VAC), you are doing a double conversion = less efficiently.

    The plus side of this would be if there is poor shore power, you would never know as the battery would absorb any problems.

    Each way has its pluses and minuses.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: converter/inverter

    Shore power or generator supply AC.

    Converter/charger takes that AC and converts to supply DC loads, and also charges the batteries.

    Solar charge controller also charges the batteries.

    The inverter is a DC load, it gets its power from the batteries (and/or the battery charging systems if they are getting power and feeding the batteries).

    What you described above is a "round robin" - battery to inverter to converter/charger to battery...that's a no go. You can't take power out of the battery, shuffle it around some electronic gadgets and then dump it back in. Well, you probably could, but all you'll end up with is a complicated way to drain the battery.


    Keep in mind, you have two separate systems - AC and DC. The DC consist basically of batteries and chargers and some loads, the AC consists of...well a breaker panel and some wiring and some loads.

    The inverter is *one way* of supplying the AC - by taking power from the DC. Another way to supply AC is by shore power. Another way is by generator. To choose between the various ways of supplying the AC panel, you use one or more transfer switches.


    You *can* wire it so that all the AC loads are fed from the inverter, and the inverter is fed from the batteries and the batteries are fed by one or more of the charging systems. That's the simplest way, and if there aren't a bunch of big AC loads, that's how I'd do it.


    Or, you can wire it so that *when there is shore or gen power* the AC loads run from that instead of draining down the batteries.

    This can be done either by;

    A) wiring in a transfer switch (AC panel gets power from inverter OR incoming shore power depending on which way you flip the switch),

    B) using an inverter with a built-in transfer switch. Some inverters will run from shore power if it's available and if not then they'll use the batteries.


    Then if you also have a generator, you need to have another transfer switch to choose between shore or gen.

    So that would be rigged like:

    Shore Power + Generator -> Transfer Switch 1 inputs (choose which "external AC")

    Transfer Switch 1 output + Inverter -> Transfer Switch 2 inputs (choose "external AC" or "inverter")

    Transfer Switch 2 output -> AC panel


    EDIT
    [NOTE: You can only use the converter/charger when there is "External AC". When bookdocking, your only way to charge the batteries would be either solar, engine alternator or generator (the generator is External AC and would run the converter/charger).]
  • pedropedro Registered Users Posts: 11
    Re: converter/inverter

    I must've mistunderstood you in your earlier post. I think I'm dialed in now; I rigged up a manual transfer switch for shore/dry camping selection, so any shorts or circular shenanigans will be avoided.

    Thanks everyone for your help.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: converter/inverter
    pedro wrote: »
    So when I'm dry camping, the inverter supplies the AC panel, which in turn supplies the converter, which in turn supplies the DC panel and charges the batteries? If so, wouldn't my 1100watt inverter which is essentially suppllying the AC and DC (via converter when dry-camping) be a bottlekneck point in the system?


    Hrmmm. Ya know...now that I've slept on it I realize that I left something out. The above statement is correct - as long as there is sufficient power coming in from the solar.

    In that situation it would be:

    solar -> battery -> inverter -> converter/charger -> battery

    So, while there would still be a round-robin, as long as there was enough current from the solar to overcome the losses of the inverter and converter/charger, the battery would still charge up...albeit MUCH more slowly.

    The whole (battery -> converter/charger -> battery) loop would do nothing except drain current from the battery.

    But it would function...


    I also see a source of confusion; The converter/charger IS an AC load...but, it must be turned off when the AC is running from the inverter (to prevent the loop). It should only be turned on when the AC system is running from "external" power.



    [NOTE: I think pedro has it figured out. I added this just for completeness sake and for whoever stumbles over this thread down the road...]
  • pedropedro Registered Users Posts: 11
    Re: converter/inverter

    The mind is quite a design--I've awoken to my share of epiphanies dwh. I ended up going with three switches, with one bar connecting all three of their switch levers. The inverter switch is reversed in relation to the others, so when it's in the on position, the other two (converter/shore) are in the off position. Poor mans' manual transfer switch I guess.

    Thanks again.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: converter/inverter

    There is another way to make a poor man's transfer switch and have it be automated. You can use a contactor, and wire it so that it is energized when there is shore power. When it's off it connects the generator to the AC panel, and when plugged into shore power, the coil is energized and it connects the shore power to the AC panel, thereby disconnecting the generator.

    There was a guy on here recently who did just that. He linked to his web site where it shows how he did it. Lemme see if I can find it...

    Okay, here's the thread:

    http://forum.solar-electric.com/showthread.php?t=6238

    And here's the page where is shows his home built auto transfer switch:

    http://www.jackdanmayer.com/truck_projects_and_improvements.htm#The%20120-volt%20System

    scroll down until you see the caption: "DPDT 30 amp relay used to auto-switch to shore power. Click on these to enlarge."

    Just below that is a pic of the relay.

    http://www.jackdanmayer.com/images/Electrical/Transfer_relay_x.jpg

    Just below the pic of the commercially made transfer switch is the explanation:

    "To the right of the inverter is a 30 amp DPDT relay with a 120-volt coil. Any good electric supply house should have them. The relay takes as input the 120-volt inverter output and the shore power line. The shore power also feeds the coil, so when shore power is available it will always be favored. A cover is available for the relay, and I recommend spending the extra $20 to get it. I covered the entire area with a plexiglass panel so the power lugs are protected, but the relay cover would probably be better. The relay cost $27 without the cover."


    EDIT: Okay, so his particular application is switching the feed to the AC panel from inverter to shore power, but you can do the same thing switching from gen to shore. (In my description in a previous post, his setup would be transfer switch 2. You could use another of the same thing as transfer switch 1 (gen or shore), just wire it so that the coil is energized by incoming shore power - when there is no shore power it will be on gen, and when there is neither shore or gen, it will be on inverter.)
  • vcallawayvcallaway Solar Expert Posts: 157 ✭✭✭✭✭
    Re: converter/inverter

    I'm using a pair of the IOTA switches as part of my backup power.

    Mine are setup so grid power takes priority. That means that the relay is energized pretty much 24/7. Before installing I emailed IOTA asking if there would be any issues with duty cycle wiring this way. This is the response:
    No problem. There are many customers who use our transfer switches this way. As long as utility power is present, the relays will stay locked in. When the utility power goes away, the relays will switch to your inverter until the utility comes back on.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: converter/inverter
    vcallaway wrote: »
    I'm using a pair of the IOTA switches as part of my backup power.

    Mine are setup so grid power takes priority. That means that the relay is energized pretty much 24/7. Before installing I emailed IOTA asking if there would be any issues with duty cycle wiring this way. This is the response:

    Aye, good point - duty cycle is a factor.

    I've rebuilt many contactors, and the rebuild kits normally come with new contacts and springs. I've never yet had to replace an electromagnet in a contactor.

    http://www.grainger.com/Grainger/contactor-repair-kits/starters-and-contactors/electrical/ecatalog/N-8f7?op=search
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