Watt meter for DC loads

solarabcd
solarabcd Solar Expert Posts: 38 ✭
in Off Grid Solar & Battery Systems #1
Any recommendations for a DC watt meter with similar functions as the 'Killawatt' meter. It needs to be able to store accrued watts or at least amps for up to a week and compatible with 48v system. Google is not being my friend in finding one...
Thanks
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #2
    Re: Watt meter for DC loads

    Trimetric is about the only thing that comes close at lowest cost that I can think of.

    Somewhat dependent on what you are trying to accomplish.

    Trimetric unit will give you A-Hrs consumed but no track record of what the D.C. voltage has been.

    The Trimetric unit is measuring average amps, not r.m.s. amps. If your load is a sinewave inverter you can convert with a simple multiplier.

    You could buy a DataQ DI-158U USB four channel ADC with a shunt and make your own calculations in Excel.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,649 admin
    #3
    Re: Watt meter for DC loads

    There are Battery Monitors:

    NAWS sells these
    Victron Energy (recommended a few times here)
    RC-Electronics (simple AH/WH DC versions for Radio Control gadgeteers)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: Watt meter for DC loads

    At ~ $140 the Tri-metric provides nearly all the battery monitoring one would ever need.

    Tony
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  • solarabcd
    solarabcd Solar Expert Posts: 38 ✭
    #5
    Re: Watt meter for DC loads

    From what I read in the manual the Tri metric data logging only records charge and max an min figures. Not many out there seem to allow you to just monitor individual loads for an extended period of time like a basic AC Killawatt meter. Something that you could rock up to a site, plug and play, leave it for a week or month to audit the loads and assess the power draw in real time not necessarily monitoring battery charging.
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  • dak664
    dak664 Registered Users Posts: 14 ✭✭
    #6
    Re: Watt meter for DC loads

    I have not tried it, but the Killawatt can be modified to measure DC, running off a nine volt battery. There is some suggestion that it overheats above ~13 amps in this mode.

    http://endless-sphere.com/forums/viewtopic.php?f=2&t=7785&p=118308
    http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=1428&p=24780
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,649 admin
    #7
    Re: Watt meter for DC loads

    The problem with DC logging of current is you have two choices... 1) is to cut the wire and add a shunt. And 2) clamp a current probe on the wiring and monitor the DC clamp probe.

    1) is reliable and accurate--and a pain because you have to "cut the wire" and bolt in a large current shunt. No additional power required.

    2) is easy, but over time can be quite inaccurate (zero tends to drift with DC current clamps. Also, you need to power the current probe (9volt battery will probably last quite a long time).

    In either case, you now need to develop/purchase some sort of logging meter...

    Laptop computers take power to run for one week (if you are already monitoring an off-grid solar system, you may not have power to spare).

    Some Fluke (and others I am sure) offer data logging--so you could use a current shunt and monitor the output voltage with a Fluke for a week (not cheap).

    If all you want is a Kill-a-Watt type function, the Amp*Hour/Watt*Hour meters seem to be reasonably priced.

    If you want to get more fancy, there is the Tweet-a-Watt which adds an XBee wireless transceiver to the K-a-W.

    The XBee also has an Analog to Digital converter built in--Perhaps you can make your own XBee wireless monitoring system with an external shunt. I think the T-a-W will give you a good starting point.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solarabcd
    solarabcd Solar Expert Posts: 38 ✭
    #8
    Re: Watt meter for DC loads

    Thanks for the replies and info. My first point of call was the RC world and on second view the watts up meter does actually accrue watts. Most seem to be just an instantaneous read out.

    Cheers
    :D
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #9
    Re: Watt meter for DC loads
    solarabcd wrote: »
    From what I read in the manual the Tri metric data logging only records charge and max an min figures. Not many out there seem to allow you to just monitor individual loads for an extended period of time like a basic AC Killawatt meter. Something that you could rock up to a site, plug and play, leave it for a week or month to audit the loads and assess the power draw in real time not necessarily monitoring battery charging.

    Trimetric TM2020 records cumulative A-Hrs (between manual resets). In a mixed charging/discharging situation it would report net results of goes-in minus goes-out current. My system is primarily a UPS function and I use this to keep tabs on battery health as my 1200 A-Hr battery array typically shows -10 A-hrs per day to maintain float current.

    The TM2025 has a Serial data output.
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  • cfcw
    cfcw Solar Expert Posts: 25 ✭
    #10
    Re: Watt meter for DC loads

    I am new to solar and have been experimenting. I purchased both a "watts up" meter and "Doc Watson" meter. Both seem to be accurate, within a few ma from my Fluke meter. They monitor: volts, watts, amps, peak amps, voltage minimum, and amp hours consumed. The main difference is that the Doc Watson store much higher values in usage where the watts up is "rolls over" after 65 Ah. I believe they handle a max of 100 amps surge,fifty amps continuous. The only thing I don't like is the small wires leading (#14 I think)in and out of the meter. These have been very educational for me, I've been using them to get real world numbers from various loads, and see how positioning and light shading affect panel output. It is supposed to work up to 60 volts

    http://www.powerwerx.com/tools-meters/doc-wattson-meter-dc-inline.html
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