What size inverter would be good for a small shop

ericksericks Registered Users Posts: 10
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What size inverter would be good for a small shop. right now i have a 2500 watt Aims it runs all of my hand tools but won't run any of my larger shop tools.
I need something that will run band saw and other large shop tools all are 110 volt. What would be a good Inverter that can handle inductive loads. without breaking the bank.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: What size inverter would be good for a small shop

    It is a good question... One issue with the AIMs (and other, typically, 12 volt inverters) is that they have a high output rating, but may not be capable of the rated output.

    Sometimes it the "fault" of the inverter (even many "good ones" have issues with running at over 80% or so of rated power), it can also be the wiring (running a 20 amp load at 120 volts is 200+ amps to 400 surge amps through the 12 volt wiring), or even the fault of the batteries (a small battery bank--imagine trying to crank your engine for 15-20 minutes at a time--won't happen).

    There are devices that can help reduce starting loads--Variable Frequency Drives--These will soft start and even provide variable frequency drive to the motor (0-400 Hz or so)... If the motor is either a 3 phase motor or has an external start capacitor.

    Otherwise, it is back to basics. What tools do you want to run and their ratings (amps, volts, peak current, etc.).

    What size/type battery bank do you have (12/24/48 volt, AH rating, flooded cell, storage/agm/gel)?

    Is this an off grid shop? Battery backup? Portable?

    Solar panels+Charger? Backup AC generator?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ericksericks Registered Users Posts: 10
    Re: What size inverter would be good for a small shop

    Well I have 4 - 45 watt solar panels with a 500 watt 30 amp charge controller I made wind generator running into a 7 amp charge controller with a 50 amp diode to keep power from back feeding the wind generator both run into a bank of 6 - 12 volt deep cycle battery's. which runs the 2500 watt power inverter.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What size inverter would be good for a small shop

    I hate to be the bearer of bad news, but there's a lot wrong with that system (not just the AIMS inverter).

    Six 12 Volt batteries in parallel? That is a bad idea; pretty much impossible to keep the current evenly distributed between all six. It's also likely 600-ish Amp hours of capacity, and four 45 Watt panels will not do much for charging that; it's about 600 Watts short. Those are probably HF panels too; notorious for not meeting their specifications.

    I know; you're going to say it works. It works for now, so long as the panels can 'put back' the power used and the battery bank hasn't slid too far down in capacity from chronic deficit charging.

    That wind turbine; does it have any mechanical furling/braking? Is there a diversion controller and dump load? Is it actually contributing anything? Or is it in danger of flying apart in a high wind?

    Not intending to be mean here, just pointing out some rather significant shortcomings to what you've got. From there it's much easier to know what to change and how to change it to get the long-term dependable system you want.

    As for what size inverter you need, that is simple; look up the power demand of the biggest (combined) load. That sets your inverter size. And from that and the amount of Watt hours you expect to use (very difficult to predict with a shop) you can pick the best system Voltage for your needs. Pretty safe to say 12 Volts won't be it. :D
  • PhotowhitPhotowhit Solar Expert Posts: 5,023 ✭✭✭✭
    Re: What size inverter would be good for a small shop

    A Prosine 1800 watt inverter will run a 1 1/2 horse Delta table saw, I haven't stressed it yet, but fired up and cross cut soft 2X.

    How big are your batteries? AmpHours?
    What gauge is your battery cable?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • ericksericks Registered Users Posts: 10
    Re: What size inverter would be good for a small shop

    Thank you for the info.

    So what battery set up would work best an what solar panels also. And yes to all the above on the wind generator. We don't get much wind but when we do it puts a trickle charge into the system. Winter is the time the wind generator works best.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: What size inverter would be good for a small shop

    Cariboocoot is right re too small panels for the loads, and the 6 batteries in parallel etc.
    All that aside, my experience confirms Photowhits endorsement of the Prosine 1800/12 inverter. It has no trouble with my 12 amp cut off saw, and laughs at the 8 amp bandsaw. BUT, it requires heavy and short cables between batteries and inverter, very good solid electrical connections AND well charged batteries, strong enough to supply what the Prosine will demand.
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: What size inverter would be good for a small shop

    Can you tell us a bit more about your loads/power needs? Also, the hours of use per day is important. A power saw run 15 minutes per day as a hobby is much different than running tools 6-8 hours per day for a production shop.

    Also--If the heavy loads are "temporary" (say building a home or a cabin)--Then sometimes a generator is the better solution (plus perhaps a small solar power system for lights, radio, computer at night).

    Or would you like us to pick a midrange inverter and show you the math for designing the battery bank and the charging system around it?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ericksericks Registered Users Posts: 10
    Re: What size inverter would be good for a small shop

    Yes lets pick a midrange inverter an go from there.
  • ericksericks Registered Users Posts: 10
    Re: What size inverter would be good for a small shop

    My battery's are 125 amp hour each. with 10 gauge cables i made them so that the length from each battery would stay short.
  • PhotowhitPhotowhit Solar Expert Posts: 5,023 ✭✭✭✭
    Re: What size inverter would be good for a small shop

    10 gauge or 1/0?

    10 gauge I think is good for 20 amps or about 220 watts at 12 volts.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • PhotowhitPhotowhit Solar Expert Posts: 5,023 ✭✭✭✭
    Re: What size inverter would be good for a small shop

    Some of the other things your fighting are voltage drop with a 12 volt system, and the Aims inverter is likely 85% 'peak' efficentcy so just figure adding 20%+ to any loads, and likely your m=not able to run things due to low voltage? Do you get a code when the inverter fails?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What size inverter would be good for a small shop

    If you were to use the maximum continuous capacity of that 2500 Watt 12 Volt inverter at nominal battery Voltage it would be roughly 210 Amps on the DC side. 1/0 AWG would have trouble with that, and you'd probably want 4/0 to manage the V-drop and current demand properly.

    This is one of the reasons for going up to 24 Volts; it cuts the current demand in half for the same Watts. Another reason is the ability to store up Watt hours as more Volts rather than more Amp hours (with the associated current sharing problems).
  • ericksericks Registered Users Posts: 10
    Re: What size inverter would be good for a small shop

    Thank you so much for this info.
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: What size inverter would be good for a small shop

    You are looking at shop power--And I assume fairly significant loads running for longer periods of times (pumps, compressors, as well as table saws, joiners/planers etc. And, there are a bunch of inverters in the $1,700 to $2,200 range--Start with a somewhat bigger inverter/battery bank and then see how this matches against your needs/expectations/bank account...

    You won't hurt my feelings if you say cut the price by 1/2--Just a point on paper for discussion (we are all volunteers here except the Admin--Wind Sun), so we do not have any dogs in the hunt based on what you eventually choose (or where you purchase the equipment). We do start with our host because they are a good wholesaler/retailer with good pricing and service--and to support them for the "free" support of this forum (that they created--not any of us).

    Start with a nice 2kW inverter with 120 VAC output. Also, this is an Inverter/Charger--So you can plug your genset into the AC power input for backup power during poor weather/heavy operation--genset will run the loads and also recharge your battery bank (note prices are from our host's website--Just putting in prices for information--and they will change over time):

    wind-sun_2241_27787643Magnum MS2012 2000 Watt Sine Wave inverter w/charger
    Regular Price: $2,149.00; sale price: $1,719.20


    I would choose 48 volts as this is the most cost effective for larger power systems (less copper for wiring, solar charge controllers can manage larger arrays without having to buy more controllers at the higher voltage). But to keep the system costs bit less of a shock, I will start with 24 volt battery bank. Note there are larger inverters for not much more money here too--But the will need much larger battery banks to support those higher output ratings--No longer a "midrange" system.

    So, assuming flooded cell battery bank (cheaper, rugged, a bit more forgiving of mistakes)--We have two numbers to look at... The maximum sustained power (watts) and maximum surge power. Sizing the battery bank based on power would give us:
    • 2,000 Watts * 1/24 volts battery bank * 1/0.85 inverter efficiency * 8 hour battery discharge rate = 784 AH @ 24 volt battery bank

    Yes, this is a large battery bank--But very easy to cut down if you, for example, only want 1,000 watt maximum continuous output--Cut the battery AH by 1/2 to 392 AH @ 48 volts--Anyway, to continue.

    The rough maximum surge current from such a battery bank would be:
    • 24 volts * 784 AH * maximum surge = 7,526 watt maximum surge (well more than this inverter can supply)

    Next, we would want to recharge this battery bank with solar power... The normal recommendation is around 5% to 13% rate of charge, which would be:
    • 784 AH * 29 volt battery bank charging * 1/0.77 panel+charger deratings * 0.05 rate of charge = 1,476 watt array minimum
    • 784 AH * 29 volt battery bank charging * 1/0.77 panel+charger deratings * 0.10 rate of charge = 2,953 watt array nominal
    • 784 AH * 29 volt battery bank charging * 1/0.77 panel+charger deratings * 0.13 rate of charge = 3,839 watt array cost effective maximum

    And, such solar arrays on a reasonably sunny 4 hour of "noon time equivalent" power per day (by the way, where will system be--You are currently posting from Europe--Some areas have notoriously poor sunshine at times):
    • 1,476 watt array * 0.52 system derating * 4 hours of sun per day = 5,018 WH = 5.0 kWH per day
    • 2,953 watt array * 0.52 system derating * 4 hours of sun per day = 10,039 WH = 10 kWH per day
    • 3,839 watt array * 0.52 system derating * 4 hours of sun per day = 13,048 WH = 13 kWH per day

    And you need a charge controller--A high end MPPT charge controller, such as the Midnite Classic 150 volt can output a maximum of 94 amps at 24 VDC--(around $610). A single controller could manage (again, cost effectively) a solar array of around:
    • 94 amps * 29 volts charging * 1/0.77 panel+charger deratings = 3,540 watt rough maximum cost effective array @ 24 volt battery bank

    So a single "large" MPPT charge controller can handle most of the suggested configurations above (300 watts less than the 13% rate of charge array--not a big difference).

    Now--You can see that the loads will guide us to battery bank sizing, which then forces the solar array size (for proper charging).

    If you average loads are only 1kW continuous, and you only need 2.5 kWH per day--You could cut the battery bank and solar array by 1/2 and still have more than enough battery bank for starting surge for the battery bank.

    Anyway--All of the above gives you some ideas and what a "generic" system could do if you expected to run it at its limits.

    The simplest way to reduce cost would be to limit the typical maximum inverter to 1,000 watt maximum continuous load (around 1 HP) and cut battery bank AH and Array Wattage by 1/2...

    You could also save money by going with an Inverter Only and use a separate AC battery charger (grid or backup genset).

    And--A big driver in this system is the questions of how many kWH per day you will be running the system.

    A smallish off grid energy efficient home/cabin can be pretty comfortable on 3.3 kWH per day (I would use this number as the dividing line between "smallish" and "larger" off grid power system)--And this system is larger than that--So if you need to use power for your living area too--You might want to add those power requirements for your shop too.

    Also, as I asked before, the actual amount of kWH per day from any solar array is very dependent on where the system will be installed and how much sun you get (by season). it is very easy for some folks to get less than 2 hours per day of sun in winter (far north, lots of cloudy weather)--And others to get >6 hours per day (high desert, far north, no-marine layers, etc.).

    Hope this helps.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ericksericks Registered Users Posts: 10
    Re: What size inverter would be good for a small shop

    when ever i work in the shop the system works just fine up to 8 hours at times. it runs small hand tools the system runs my small bench top band saw 4.5 " angle grinders small drill press hand drills and so on. it will run my 2x42 " belt grinder where it gets week is like my chop saw and bigger 110 stuff. and i"m using 4 0 battery cables.
  • ericksericks Registered Users Posts: 10
    Re: What size inverter would be good for a small shop

    Outstanding this helps a bunch Thank you so much for this info.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What size inverter would be good for a small shop

    ericks; get yourself a Kill-A-Watt meter and measure the power demands of the tools you've got. It will help you make decisions about what inverter & such to get.

    Here's some data from my own shop (taken from other posts):
    I just ran my 10" Skil tablesaw through my UPM meter. The saw is rated as 13A @ 120 VAC. The start-up was 4.9 Amps (118 Volts here). I pushed a piece of wood through it and loaded it fairly well: 8.6 Amps / 952 Watts.

    Small "pancake" compressor used to power air nailers: 12.4 Amps, and basically held peak from start-up (against pressure). 1372 Watts - sucked the line Voltage down from 118 to 112!

    6 gallon ShopVac: 6.5 Amps. 744 Watts.

    2.5 HP Skil circular saw: 8.3 Amps. 928 Watts (while cutting wood).

    Black & Decker reciprocating saw: 6.6 Amps. 750 Watts (while cutting wood).
  • mike95490mike95490 Solar Expert Posts: 8,469 ✭✭✭✭✭
    Re: What size inverter would be good for a small shop

    For starting tools, motors, such, you should run a 48V system, in my opinion. the monster XW6048 runs anything connected to it. I left space in my power room, to add a parallel inverter, but it looks like its just wasted wall space. Now i'm thinking of buying my replacement inverter now, and just storing it.
    Big tools need big power.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: What size inverter would be good for a small shop
    ericks wrote: »
    My battery's are 125 amp hour each. with 10 gauge cables i made them so that the length from each battery would stay short.
    ericks wrote: »
    and i"m using 4 0 battery cables.

    I am confused... just how have you wired your batteries?

    On the subject of system voltage and parallel batteries... if you use a higher voltage it is easier to avoid parallel batteries... for example four of your batteries in series (48 v) has the same energy storage as four batteries in parallel (12 v).
    read: http://forum.solar-electric.com/showthread.php?14674

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: What size inverter would be good for a small shop

    "2.5 HP Skil circular saw: 8.3 Amps. 928 Watts".
    Those kind of specs really make me wonder if they were invented by the same folks who dream up the power producing claims for all those little wind turbines - - - - -
    On the other hand, the motors in these saws would be awesome candidates for use in perpetual motion machines. :D
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What size inverter would be good for a small shop
    "2.5 HP Skil circular saw: 8.3 Amps. 928 Watts".
    Those kind of specs really make me wonder if they were invented by the same folks who dream up the power producing claims for all those little wind turbines - - - - -
    On the other hand, the motors in these saws would be awesome candidates for use in perpetual motion machines. :D

    It's a common con; the HP rating of the motor given as mechanical at stall, which is about as useful as a chocolate hammer. :p

    Two-point-five electrical HP would be about twice those Watts and have a tendency to trip the breaker. Actually my old 2 HP B&D used to do just that!
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