Can You Use Light Bulbs to Supply a Test Load?

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a0128958
a0128958 Solar Expert Posts: 316 ✭✭✭
in Solar Beginners Corner #1
(I have enjoyed reading and learning a lot from these forums. Thanks to all of the people who selfishlessly have contributed their knowledge.)

If I were to do some experimentation with one or two 225 watt (DC) modules, what could I use to serve as an inexpensive test load?

For example, hooking up one module to at least a 225 watt load to understand the effects of shading on one or more module cells. Or hooking up a couple of panels in parallel to at least a 450 watt load to understand the effects of shading on a partial module.

I.e., incandescent light bulbs are inexpensive. Could a couple of 200 watt incandescent bulbs be hooked up to a single 225 watt module to serve as a reasonable test load?

I think the fundamental question is, do incandescent bulbs dissipate the same amount of watts, regardless of an AC or DC source connected to them?

Incandescent bulbs are the only inexpensive test load possibility I can think of. Anything else? The toaster from my kitchen?

Thanks.

Best regards,

Bill
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #2
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    When you say 'modules' I assume you mean PV panels.

    Incandescent lights can work but it depends on PV panel voltage. You will only consume the bulbs rated wattage when 120v is applied. They are not linear so at 60v they will not be half the rated power. The hotter the tungsten (higher the voltage), the higher its resistance. At low appled voltage where the tungsten does not get very hot the resistance can be 3 to 4 times lower.

    PV panels act like illumination based current sources clamped by shunt diodes on each cell.

    If you drag the voltage below the Voc - 20% your in the constant current range. This will be close to the same current as if you do a short circuit current measurement.
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  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    #3
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    Re: Can You Use Light Bulbs to Supply a Test Load?
    RCinFLA wrote: »
    When you say 'modules' I assume you mean PV panels.

    Incandescent lights can work but it depends on PV panel voltage. You will only consume the bulbs rated wattage when 120v is applied. They are not linear so at 60v they will not be half the rated power. The hotter the tungsten (higher the voltage), the higher its resistance.

    RC, this is very helpful.

    Sorry, yes, I mean PV panels when I said 'modules.'

    OK, I've now learned the incandescent light bulb is not a linear resistance with respect to voltage.

    I assume a toaster is the same way, since it's a tungsten element also.

    Any ideas for an inexpensive test load at approximately 30 VDC at 16 amps (i.e., up to about 500 watts DC)?
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #4
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    Actually I think toaster are nichrome wire. It is better versus voltage because the nichrome is not run that hot (tungsten bulb run at like 1700 deg C)

    If you take the bottom off and run a fan through it, a toaster might not be too bad a dummy load. Only issue is a toaster runs at about 1000 watts so resistance might be too low for what you are trying to do.

    At 30 vdc a toaster would draw less then 4 amps. Got four old ones around?
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    rc,
    don't look now, but i think your ham is showing.:p:p
    "a toaster might not be too bad a dummy load."
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #6
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    WB4FRS, but not been active for years.

    Thanks for reminding me, license needs to be renewed in 2010.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    glad i helped and i've been inactive for about a year or so now myself so don't feel bad. i have issues with antennas right now and no help if i were to make the big purchases to correct it. very involved and it kills me that i can't do what i used to do physically.
    enough said as i don't want to hijack the thread.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #8
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    Re: Can You Use Light Bulbs to Supply a Test Load?
    niel wrote: »
    glad i helped and i've been inactive for about a year or so now myself so don't feel bad. i have issues with antennas right now and no help if i were to make the big purchases to correct it. very involved and it kills me that i can't do what i used to do physically.
    enough said as i don't want to hijack the thread.

    At 52 I stopped climbing my 50' tower. With the help of 2005 hurricane which broke it in half, I welded a hinge and cantilever strunt so I can fold it over with a cable winch.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #9
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    Hair dryers make a decent load, about ~12 ohms
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #10
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    A good choice would be a couple car batteries... Setup for 12 or 24 volts to do your measurements. Will stop the variations in output voltage which will further confuse the issue. I assume that you are not going to leave the batteries connected for hours/days at a time--But want to just take a few quick readings at a time.

    To keep the batteries from over charging, you could attach your loads, or even inverters with AC lamps, to keep the battery voltage a bit more stable and not fry the battery if your testing is for longer periods.

    12 volts for Vmp=17, 24 volt for Vmp~34 volts, etc.

    The DC Amp*Hour/Watt*Hour meters from here look like they would be very handy for your testing instead of having to have two meters (volt/amp) and a calculator handy to convert to AH or WH.

    12 volt (RV) Filament lamps can be used as a constant current sink in a pinch (not real accurate, but may be close enough for your work). Not sure you would want to pay $4 per 60 watt 12 volt bulb just for a little bit of testing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    I used to have some audio test resistors that were 300 Watts & 8 Ohms. Big ceramic tubes wound with wire and coated. Bet you can't find anything like that these days, but it would work well for such testing.

    I hate being so out-of-date.:cry:
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  • tvengineer
    tvengineer Solar Expert Posts: 31 ✭
    #12
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    anything that is designed to run off of a cars cigarette lighter and supply heat..
    I'm sure they still make those coffee warmers, etc....

    but I agree with a previous poster.. use some batteries.. and get some use from the power you are generating :-)

    Louis
    formerly KD5XE :-)
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #13
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    Happen across these power resistors at a reasonable price.

    http://www.mpja.com/prodinfo.asp?number=17788+RS
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  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    #14
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    These responses are particularly helpful - much appreciated.

    Didn't realize wirewound resistors that can dissipate 100+ watts of heat, in a linear manner, were so inexpensive. Wish I had a small supply of these, that I could connect together in series/parallel.

    The car battery suggestion is very creative. Bill is right, using these would eliminate voltage fluctuations and allow for better focus on simply current changes. Yes, I'm looking to do things that take just a few minutes - not some kind of permanent setup. Wish I had a couple of batteries laying around (versus removing them for a period of time from our vehicles).

    The mission is to not spend any money and simply use what might be laying around the house.

    I thought about the hair dryer, but, it has a motor in it. I'm assuming it's an AC motor, that might be damaged if presented with 30 VDC.

    Many thanks!

    Best regards,

    Bill
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #15
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    A lot of hair driers have universal motors (brushed motors)... They are cheap and turn fast. Should work fine on DC.

    The switch in the handle may only work a few times under DC switching current (if you are > 60 VDC or so). So--use a throw-a-way drier.

    Regarding batteries--perhaps you can borrow a couple from a recyclers--they don't have to be good batteries to supply some sort of load.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    #16
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    Bill, thanks!

    Best regards,

    Bill
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #17
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    Re: Can You Use Light Bulbs to Supply a Test Load?

    Niel,

    When I saw, "Dummy Load", I thought the same thing.

    Ron, RENEW UR License this year ! Much easier to do that than re-test later.

    You know this, 73 Vic K6IC
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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