inverter help please

notsobright
notsobright Solar Expert Posts: 247 ✭✭
hi all,

I want to figure out whats the best inverter for my limited RV system:

two 40w keocera panels
one 100ah AGM batt
morning star sunsaver duo controller

Im wondering is a pure sine wave a nesessity for a PC or laptop and what would be the maximum inverter output I could go with?

I'd like to be able to run a circular saw or other power tools very briefly, is that possible with my system?

Im thinking a 600w MSW might be OK?


also looking for high quality, what are the top brands?

thanks in advance for your help and suggestions.

Comments

  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: inverter help please
    hi all,

    I want to figure out whats the best inverter for my limited RV system:

    two 40w keocera panels
    one 100ah AGM batt
    morning star sunsaver duo controller

    Im wondering is a pure sine wave a nesessity for a PC or laptop and what would be the maximum inverter output I could go with?

    I'd like to be able to run a circular saw or other power tools very briefly, is that possible with my system?

    Im thinking a 600w MSW might be OK?


    also looking for high quality, what are the top brands?

    thanks in advance for your help and suggestions.

    As always, the answer is...it depends.

    First, use battery tools. I'm about to buy Ryobi 18v because they have a battery charger that plugs into a cigarette lighter for about 30 bucks at Home Depot. I noticed long ago that a 120v Makita battery charger running off a MSW inverter didn't do a great job charging the batteries, but I also had a charger that plugged into 12v that *did* do a great job.

    A good worm drive circular saw that draws 10 amps at 120v will draw 100 amps at 12v. You have a 100ah battery, drawing it down below 50% will shorten its life - so you could run that saw for 1/2 hour (total intermittent run-time) tops.

    And actually...going down to 50% DoD (depth of discharge) will shorten the battery's life, so to give it a nice long life, you should try to not drain it more than 25% before recharging it - which means 15 minutes use of that saw.

    (Yes, there are smaller saws, that was just a handy example.)

    I've run my laptop off a 200w MSW I have in my camper. It works fine - but for how long...I don't know. There was a discussion about that on this forum a while back, and since then, I've been checking and I notice that the power brick gets *significantly* hotter when running on the MSW than it does when plugged into grid power. Other people have burned out their power bricks pretty quickly on MSW.

    If I were you, I would probably go with one of these:

    http://store.solar-electric.com/mosu300wasiw.html

    True sine wave, great efficiency, 300 watts continuous, 600 momentary, no fan - you just mount it on a decent heat sink...and a remote on/off switch so you can turn it off when you don't need it.

    I would wire it to a standard receptacle placed to be handy to your laptop, and put the on/off switch right next to that receptacle. Even better, use a twist timer for the on/off switch in case you forget to turn it off.
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
    Re: inverter help please

    I am considering that inverter as Ive read good things about it.

    I have some dewalt cordless tools and their 12v to 18v charger but I would like to get an inverter that would allow for some extream usses in emergency situations only.

    I dont really need high wattage but I would like to be able to have plenty of power if needed even if its only for a few minutes.


    basically Im wondering whats the largest inverter I can get away with on my limited system.


    I understand a pure sine wave is best for extended usage but for emergency purposes Im thinking a MSW inverters should be OK and better than not having one at all.

    thanks

    BTW I allready have a PowerStar 200w/2a single outlet inverter which will run a laptop but Ive had isssues tranfering data from card readers into the laptop and loosing my data (photos) other than that it is OK, Im unsure if it is modfied sine wave or not allthough I suspect it is. oddly enough its made in Scotland!
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: inverter help please

    Running a circular saw from a small battery and inverter is not going to work very well. I suggest for the long run look at the MorningStar TS 300 pure sine wave inverter. Will deliver 300 watts with a 600 watt surge.

    I suggest that you buy a cordless tool set, like the Hitachi cordless circular saw. I bought mine thinking it was a toy, but for most small projects, I can leave one battery on charge from the inverter and use one battery. I wouldn't frame the whole house that way, but I have sided many with one. Pretty nice little saw for not a lot of money.

    I just fire the genny when I need my big 13 amp worm drive.

    Tony
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: inverter help please
    basically Im wondering whats the largest inverter I can get away with on my limited system.

    Depends.

    Let's say you want to power that 10a saw in my previous example.

    10a x 120v = 1200w

    Okay, you'd need a 1200w inverter that could handle whatever the overload is when the saw starts.

    And with intermittent use - a cut here a cut there - you could run that saw for up to 30 minutes total before you take the battery down below 50%.

    If you want to use Tony's 13a Skil, then:

    13a x 120v = 1560w

    So you'd need a 1600w inverter that can handle the startup overload.

    Since it would draw about 30% more, you could run that saw for a total of maybe 20 minutes before you battery is 50% down.


    Starting with the inverter:

    600w @ 120v = 5 amps

    So you could run loads up to 5 amps on the 120v side (better be a small saw).

    5a @ 120v = 50a @ 12v

    So you could, again, run those loads for about a half hour before your battery was 50% drained.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: inverter help please

    Start with the small system... Other than cost ($260 vs $26 for TSW/MSW 300 watt 12 volt inverter)--you should be pretty happy with the small system. Light, cheap, reliable.

    If you need more power--Get a Honda eu2000i for ~$900 delivered. You will get a nice 15 amp 120 VAC "socket" that will run from ~4-15 hours on 1.1 gallons of gasoline (depending on load).

    A couple 5 gallon gas cans, filled with fuel stabilizer and changed 1-2 per year--will give you quite a bit of power... Enough run a fridge and a few lights/radio for 100-150 hours... Run 12 hours per day, that will last you 8-12 days in an emergency.

    About 4-5 years ago I looked at solar for my home--either Grid Tied (cheap and very efficient) or Hybrid/Off-grid system (less efficient, expensive, battery replacement every 7-15 years)...

    I went with GT Solar and a Honda eu2000i + 20 gallons of stored fuel (change once per year with my car).

    We get so little in the way of power failures here--that the more expensive system just did not make sense (last power failure that lasted more than a day or so was 50+ years ago).

    -Bill

    PS: If you need a large genset for specific loads (well, large saw, etc.) get one of those cheap 5kW gensets and only run it when I needed the large amount of power.... Otherwise, keep it turned off and use the solar or Honda for longer term emergency power.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
    Re: inverter help please

    hey guys, thanks for the help!

    I just recieved my suresine 300 (Thanks NAWS) its alot bigger than it looks in the photos!

    Ive called morningstars tech line and left a message but mabey someone here knows the answer.

    schematics call for earth ground input and being seperate from battery negative but Im using (or planned to use) this in my RV. what do I do for ground? I dont want to drive a stake in the ground everywhere. do I just leave it un connected or ground to chassis/batt. neg?

    thanks
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: inverter help please

    Notso,

    You are right, it is bigger and heavier than it looks on paper. I think you will be happy with it.

    It is just my opinion, but I think I would ground the 12vdc side to the frame of the RV, and ground the 120vac side to the RV frame as well. I think it is going to work fine in either case. I am trying to think of a reason why that would be un-save. The reality is that 120vac coursing through RVs and vehicles presents their own sets of grounding issues. In most RV situations that I know about, the 120vac side grounds back through to the generator frame while on genny power. While plugged in it grounds back through the ground wire in the hook up cable.

    In your case the power would be grounded back to the battery/inverter just as though it was a genset.

    I'm sure that others with better knowledge will chime in with what is perhaps the "right answer".

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: inverter help please

    As Tony says... there is no one right answer. My houghts on the options:

    1. Ground the "Neutral" per NEC (North American Electric Code). This is done for "safety" reasons... If the "hot" touches a grounded metal object--pops fuse/breaker and circuit is "safe". Problem is that now if User touches "hot" and "ground", can get electrocuted. So, create GFI (Ground Fault Interrupter Breaker). Now if User (or anything) shorts >5 mAmps from Hot to Ground--the GFI will open and make circuit safe. Not a bad solution to several issues.

    There are also some devices that "assume" neutral is bonded (some AC Fixtures, some spark type auto ignitors for stoves/ovens/etc.)... Floating the output (or wiring Hot/Neutral backwards) can make the devices unreliable for fail to operate.

    2. Float the AC Output (not to code). This can actually be safer and cheaper. If the end user touches either AC Leg and Ground--there is no current flow--so no shock or worse. If one Leg of the AC circuit is shorted to ground (bad insulation)--It is just like #1 without a GFI connection. If both are shorted together or to ground, then the breaker/over current circuit shuts the Inverter Down. Note--while one Leg is shorted--the output is no longer isolated to ground and a User can get a shock--unless a GFI is installed.

    My two cents... If this is just a small installation and you don't have any traditional non-CFL florescent fixtures or auto-spark ignitors (and such)... Don't bother grounding the "neutral"--if your wiring is OK (cord, permanent wiring not shorted to ground)--you are actually safer.

    If, you need 100% code safety (insurance) and will be working in a wet location--Put a GFI breaker (or get a GFI cord set) on the inverter circuit that will be used in wet areas...

    Note, the GFI will only pass self test if the Neutral is grounded back at the inverter (and you have a three wire cord set / circuit with Hot, Neutral, and ground).

    Was that too confusing and did little to help?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: inverter help please

    I think Bill has it dialed. Much as I hate GFCI breakers/recepticals it probably the best all around solution. Leaving the neutral ungrounded is a pretty good option as well. In my system, I have the ground bonded back to the neutral buss bar in the AC load center, but as of now that neutral buss bar is NOT grounded. The reason for that is that I had my building ground tied the neutral as well as the roof mounted PV, the tall vertical radio antenna and the steel chimney. My thought was that a lightning strike near the roof top stuff would feed right back down into the neutral, creating more problems than it solved. My plan, some time in the future (when I get around to it!) is to carry that neutral ground to a separate ground location on a separate grounding conductor. My issue is how to separate these wires enough so as not to provide a direct lightning path INTO the house.

    Tony
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
    Re: inverter help please

    BB, thats exactly the type of info I needed, and much more helpful than MorningStars tech. he wasnt sure but put me on hold for a minute then came back and said just wire both earth grounds (the input side (DC) and output side (AC) all together (tied in with the negative batt./chassis ground) but he didnt seem really certain.


    I think I'll get a GFI since I plan to have an external outlet (flip-open covered receptical) and theres a chance I might need some AC outdoors in wet conditions.


    icarius, why do you dislike GFCI? what are its cons?


    unfamiliar territory for me, is the GFCI just the recepticals with built-in reset switches?


    thanks again
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: inverter help please

    GFI's are available as breakers for a panel, as an outlet assembly (and one outlet GFI can be wired to protect other outlets down stream). They are also available as a 3 foot extension cord with a "GFI" bump in the middle (usually sealed pretty well against rain).

    The only "downsides" -- You can't just run an "isolated" circuit (floating neutral) with GFI (it can work without grounded neutral--but the self test will not function because it can't "ground fault" the hot lead--since a floating circuit won't ground fault).

    If you use GFI--typically, you will only want to use one "GFI" per outlet... What you don't want is one GFI breaker for the whole home (possible for a cabin type installation)... Somebody trips the GFI at a sink outlet--and throws the whole cabin into darkness (because the one GFI killed all of the AC power).

    So--forget the GFI for fixtures and inside connections... And think about it for sinks/outside/wet areas for safety. And--you may want two or more GFI's--If your hand drill "faults"--it does not take out the work lamp (for example).

    For me in outdoor use (non-sink outlets)--I just bought the 3 foot GFI equipped extension cord... Then I can use it when and where I want to.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: inverter help please

    I don't like GFCIs for a variety of reasons. Nuisance trips, poor quality leading to failure (and hassle) Nearby lightning creating short lives.

    I do think there is a place for GFCIs, I just think they are "over prescribed" so to speak.

    Tony
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: inverter help please
    BB. wrote: »
    If you use GFI--typically, you will only want to use one "GFI" per outlet... What you don't want is one GFI breaker for the whole home (possible for a cabin type installation)... Somebody trips the GFI at a sink outlet--and throws the whole cabin into darkness (because the one GFI killed all of the AC power).

    -Bill

    I'll add a couple of notes to the GFCI discussion...

    * You can feed multiple GFCI units from the same branch circuit - in parallel. But do not wire the feed to one GFCI from the *load* side of another GFCI. They will both act flakey and trip at odd times.

    * Unfortunately, I noticed years ago that a lot of new housing construction does exactly what Bill describes above - everything in the house/apartment/condo/townhouse which must be GFCI protected, is tapped off the load side of a single 15a GFCI unit, which is usually a GFCI receptacle (not a breaker) and is commonly found in the garage.


    I agree with tying the AC ground to the vehicle frame, for the reasons stated in previous posts.
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
    Re: inverter help please
    dwh wrote: »
    I'll add a couple of notes to the GFCI discussion...

    * You can feed multiple GFCI units from the same branch circuit - in parallel. But do not wire the feed to one GFCI from the *load* side of another GFCI. They will both act flakey and trip at odd times.

    sounds like a plan, where could I find a brief schematic for wiring two GFCI's in parallel? I have the basic idea but want to avoid the former example you mention.

    basically I want to come out of the SS300 into two GFCI recepticles. so I take it I can ground the input side of the SS300 (Batt./DC side) to chassis AND use two GFCI's on the output/AC side?


    thanks again!
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: inverter help please
    sounds like a plan, where could I find a brief schematic for wiring two GFCI's in parallel? I have the basic idea but want to avoid the former example you mention.

    Here's a page with some diagrams:

    http://www.do-it-yourself-help.com/wiring_receptacles.html

    Under the section, "Wiring GFCI Receptacles", there is one diagram which shows a GFCI with a receptacle attached to the load side. That is fine and proper.

    Do NOT do that with two GFCIs (one connected to the load side of another) or they'll misbehave.

    The second diagram in that section shows how to properly wire two GFCIs on the same branch circuit - i.e., in parallel.


    Also worth a mention, in that second diagram, neither GFCI has anything connected to its "load" terminals - thus they aren't protecting anything "downstream". It doesn't have to be that way. You can wire up two GFCIs in parallel, and then tap off the load side(s) of either/both and *also* protect additional receptacles.

    That would be a combination of both diagrams.


    Also note that receptacle-type GFCIs are a bit counter-intuitive as regards the connections. It's not a requirement, but it is a common practice when wiring receptacles, to wire the *incoming* to the top terminals of the receptacle, and the *outgoing* to the bottom.

    However, as you can see in the diagrams, on most GFCIs the feed is at the bottom and the load is at the top. I've seen them hooked up backwards and people wondered why they didn't work.

    So make sure you actually read what is stamped on the back of the unit before you hook it up.

    basically I want to come out of the SS300 into two GFCI recepticles. so I take it I can ground the input side of the SS300 (Batt./DC side) to chassis AND use two GFCI's on the output/AC side?


    thanks again!

    Yes.

    If you aren't going to use > 15a, then you could just use one GFCI and tap the second receptacle off the load side of the GFCI.


    To answer a question you asked earlier:
    unfamiliar territory for me, is the GFCI just the recepticals with built-in reset switches?

    A GFCI is a simple device to understand - if you know what a "clamp meter" is (clamps around the wire to measure current). The one I have is a 30 year old "Amprobe" analog:

    http://www.testequipmentdepot.com/amprobe/clampmeters/rs1-3.htm

    Imagine a device with two tiny clamp meters in it, one around the hot, and one around the neutral. As long as they detect equal current then the flow is going in and back out along the proper path.

    But say the current is going in on the hot, but not going back out the neutral - then the current might just be flowing through a person (or dog or whatever) to ground.

    When the GFCI detects an imbalance between hot and neutral, it trips a little internal breaker. The "test" button simply creates an imbalance to make sure the device is working.

    You can also test a GFCI with a standard "Wiggy" type device (solenoid tester) by sticking one probe in the hot hole and one in the ground hole. If the GFCI is working, it will detect the imbalance and trip the internal breaker.

    https://www.grainger.com/1/1/63069-wiggy-61-065-tester-voltage-120-240-600-dc-25-60-cat-iii-600v.html


    There are receptacles with built-in GFCI, and there are also breakers which have it built-in - you can tell these because they have a white wire coming off them to connect to neutral, which regular breakers don't have. (EDIT: And a "test" button.)


    By necessity these devices are pretty sensitive and can trip quite easily. This makes them a pain, since anything plugged into them which makes too much electrical noise, or maybe leaks a bit to ground (which might not even be dangerous) will set them off. Also, since they are sensitive, they tend to fail and need replacement fairly frequently.

    Every year or two I had to replace the one in my mom's bathroom that she used daily for her hair dryer. Right at the beginning I discovered that there were 2 outdoor receptacles tapped off the load side of that GFCI - so I wired the in and out together and tapped off a pigtail to feed that GFCI, then I replaced the two outdoor standard receptacles with GFCI receptacles.

    That way, when the one in the bathroom failed, it wouldn't screw up the timers on the outdoor low-voltage landscape lights.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: inverter help please

    And, GFI's are probably a waste to wire to indoor light fixtures and sockets. GFI's can be flaky (false trips, fail over time) and only put them in where they will do some good (typically, electricity + water).

    There is another type of breaker... Arc Fault Circuit Interrupters. Designed to detect not only over current (which tends to be slow to trip breakers) but arcs from shorts that may not even exceed breaker rating.
    The 2008 National Electrical Code (NEC) will require arc-fault circuit interrupters (AFCIs) throughout new homes in the U.S. So, your new construction should now incorporate ground-fault circuit interrupters (GFCIs) that trip on an unbalance between line and neutral, basic circuit breakers that trip on gross faults, and AFCIs that trip on arcs.

    AFCIs are "don't burn the house down" protection, as opposed to the "don't electrocute yourself" protection provided by GFCIs. They were developed because regular circuit breakers have relatively slow tripping times that may not catch arcs, which are generally characterized by short bursts of excess current (see the figure).

    The trick to designing an AFCI is to enable it to distinguish between legitimate arcs, such as those from motor brushes, and dangerous arcs like those in a conduit that's been damaged during a renovation or in a worn appliance cord. While AFCIs aren't new, they've been improved, and the expanded code requirements have trigged a public-awareness campaign by the National Electrical Manufacturers Association (NEMA).

    AFCI history starts with the 1999 NEC, which required AFCIs for all branch circuits that supply 125-V, single-phase, 15- and 20-A receptacle outlets in bedrooms starting in 2002. The 2002 NEC extended the AFCI requirement to all bedroom outlets, such as lighting, receptacles, and smoke alarms. The 2005 NEC respecified AFCIs, reducing current levels and requiring the detection of series arcing in a conductor in addition to parallel arcing across conductors...
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
    Re: inverter help please

    I just got a 3' GFCI extension that has three outlets that I plan to remove the male plug and wire input side direct and I also got a standard GFCI receptical for inside. both are rated at 15a. the ext. GFCI will be closest to the inverter so that will be first in the circut. does this sound relatively acceptable? actually Im not sure I can do this... Im sure I'll have more questions later about this.

    right now I have some mechanical issues Im working on so I can get right into it at the moment.

    cant wait to get this all wired up! including the 130w panel I'll be ordering next week.

    also considering a 200-250 ah AGM to replace my 98ah and since I have the SS Duo controller I can still charge both of them seprately but at the same time.

    I also have the engine starting battery that I plan to switch between it and the 98ah batt. on the secondary side of the SS Duo. that circut is done allready, I added a switch in preperation for charging an external battery when both the onboards were full.

    should be a pretty decent RV set-up when I get everything working. I also plan to run an AC ext. cord into the house for some stuff just to cut down on grid use.

    I think I will be wanting to incorporate one of those volatage sensing relays being mentioned in other threads so that I can maintain three batteries automatically LOL well mabey..
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: inverter help please

    I am not sure I understand why you are cutting up a GFI extension cord and adding an external GFI outlet...

    And, AGM batteries do not like high voltage/equalization... Make sure you "shared" controller can be set appropriately (maybe AGM settings, and you manual equalize just the flooded cell battery bank when needed).

    For charging "other batteries" from your PV house bank... You might look at the Xantex Echo charge controller... Basically turn on at 13 volts and charges connected batteries up to 14.4 volts--then limits current.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
    Re: inverter help please

    Im using the extension cord as the external outlet for now and one indoor GFCI outlet inside. I'll change the cord part to a standard outdoor outlet later but this will help me get it working. I havnt decided where to mount a permanant outlet yet.

    I dont have any battery "banks" only singles. I have the sunsaver duo controller which splits the charge for two batteries. I have added a manual switch off one side of the controller that I can divert the charge to another battery but I'd like to make the switch automatic when the second battery is fully charged so it will start charging a third battery, I'd also like it to cut back off when the secondary battery drops below a certain charge.
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
    Re: inverter help please

    OK, I have the SS300 all wired up including the two GFCI outlets. I skipped the ext. cord idea and wired in a switch to the outside GFCI to be able to turn it off.

    BTW after reading the SS300 install manual it actually specifies GFCI outlets only.


    it also seems I could theoretically just run one wire to the outlets and use the chassis ground for nuetral but I went ahead and ran both wires just to be safe but since Im using chasis ground on both sides of the SS300 Im pretty sure you could just run one wire to the AC outlets and ground them locally.

    the AC output fuse is only 3 amps as per factory specs and thats a tiny wire, hard to belive it can supply 300 watts and upto 600 peak.

    Ive lots of experience with DC wiring but not so much with AC but everything seems to be working OK using a common (chassis) ground. I was a little aprehensive doing this, for some reason it just seems wrong to mix AC and DC ground but like I said everything seems to be working.



    I should have a new KC130watt panel from NAWS by the end of the week too so now I just need a good battery. Ive posted some questions about a couple of 8Ds Im considering in the review section so if anyone has input on them please post it thanks.

    now looking for recomendations on a larger Modified sine wave inverter for use with tools, air conditioner, microwave, etc. and info regarding powering those with a MSW Inverter.

    probably in the 1750-2000 watt range.

    thanks again, again for everyones help and suggestions! Im enjoying learning here and experimenting with solar power. new hobby, I just wish it wasnt so darn expensive!
  • mustapha
    mustapha Registered Users Posts: 1
    Here is a simple diagram how to wire a multiple gfci 


    more diagram gfci wiring