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Old 07-02-2015, 09:25 PM   #1
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Measuring your solar systems effectiveness

I recently installed a 400w system in my restored Airstream. It seems to work very well, but I'm looking for hard data to support that observation.
I bought a couple of inexpensive DC watt-meters off of Amazon whose specs seemed good to do the job, but when they came in it was obvious they were not up to the task. The system should generate somewhere in the vicinity of 2kw-hrs of energy on an ideal day. I am looking for an inexpensive metering system to monitor the energy going into the system from the solar panels and also to monitor the DC usage through the fuse panel. Does anyone know of a good piece of hardware for doing this. I expect to have to use 2 units to accomplish this... one for "IN" and the other for "OUT".
I purchased a pair of "60Volt 100Amp" "Watt Meter"... but they have 14 gauge wires for the in and out and 100Amp would require considerably larger wire than that... approximately equal to 10 14 gauge wires. I could build a 9x shunt to make these meters actually do what they advertised, but I don't trust them to be accurate given their mis-advertisement. They were specifically made for RC (Radio Control) batteries and probably do a great job there... but the 100Amp value is peak amperage and is only for a very short interval... Typical current is in the range the 14 gauge wire can handle.
I could get away with putting both of these in parallel on the output of my 2 solar charge converters which should max in the vicinity of 28 amps. This is ok to get initial numbers, but I want a permanent system that I can use to track the performance and my fuse distribution panel is capable of delivering up to 100Amps. The second problem is that they have no reset button and need to be unpowered to be reset. This is not so easy since they can be powered from either the solar panel or the batteries. I basically need to incorporate a pair of connectors into the circuit that allows me to insert this device in or to take it out and plug the wires together without it. Again doable but not something I want permanently installed.
So if any of you know of a reasonable DC watt meter alternative I can use I will be all ears.

Chuck
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Old 07-06-2015, 04:10 AM   #2
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Perhaps these DC inline wattmeters will work for you? They are fitted with power-pole connectors so if you fit your connections also with power-pole connectors you should be able to remove the meter and restore the connections with the appropriate adapters.

DC Inline Watt Meter and Power Analyzer, Powerpole Ends [WattMeter-PP] - $49.99
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Old 07-06-2015, 09:04 AM   #3
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Not sure this would be in your plan but the solar controllers from BlueSky do exactly what you want with their IPN remote. It shows amps to the the batteries, net real time consumption, and has totalizers for amps in, amps out, high and low voltage. Those can be reset from the panel on demand. A simple meter like the Powerpole (good units by the way) doesn't have a computer in them to do the logging.
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Old 07-06-2015, 10:47 PM   #4
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See if this is what you want. Just google it " Trimetric 2025 "
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Old 07-07-2015, 12:27 AM   #5
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I believe that the Tri Metric meter with a 100 amp shunt will do what you want to do. It will measure down to .01 amps when used with a 100 amp shunt. That is total amps in or out of the battery. It also is an accurate DC voltmeter. In addition, and most useful, it will give you either amp hours used or % of charge remaining when measuring the battery capacity.

Blue sky has a similar unit but I think only built into their solar charge controller.

At any rate the Tri Metric will give you all the information you need. Around $200 with the shunt.
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Old 07-07-2015, 01:53 PM   #6
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Here's another choice. I've installed several of these.



Xantrex 84-2030-00 LinkLITE Battery Monitor
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Old 07-07-2015, 03:25 PM   #7
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14 gauge wire is good for 15 amps at 120 volts which is 1800 watts. The meters are rated for 60x100 = 6000 watts. Your photo array is only 400 watts which is 33 amps at 12 volt; even if the array delivers 28 volts you won't exceed the amperage rating. I assume you have a charge controller after the solar panel. What size is the wiring from your array? I'll bet it isn't 6 or 8 gauge., and even they are not big enough for 100 amps.
No matter what the meters were designed for, it seems they are rated way over the power available from the solar panel.

I doubt you will pull 100 amps from the batteries. That would kill a 100 amp-hour battery (theoretically) in an hour. The battery will likely develop high resistance after a few minutes so the scenario of 100 amps draw from house batteries is probably not viable.
If you don't have a ton of money in the meters and also can't return them then set it up temporarily away from flammable structure and try it.

JCW
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Old 07-07-2015, 10:40 PM   #8
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My array should max out at slightly under 30 amps... If I use one each on both of the controllers it will not exceed the 15 amp current rating of #14 wire. Currently my unit is parked under the trees while I am finishing it up so my max amperage is under 10 amps.
In this configuration I am monitoring with one watt meter and using the other to test specific loads for their power usage. The original vent fan pulls 60-70 watts.
This is the extent to which I can check so far. I found a document which pertains to these meters in general. They all seem to use the same IC as the intelligence.
I can reset the display by momentarily shorting the 2 outside pins of the 3 pin connector or by cutting the 12v supply. These units measures the current thru the ground leg so breaking the power to it is fairly simple. Only one of the plus (red) wires needs to be attached to power it up. I can make these 2 meters I bought work for my particular setup with one for each of my pair of 200w solar legs. I want that info anyways since they are mounted at different angles on the 2 sides of the curved roof.
I can use another metering solution to monitor the power out through the distribution panel. That will not count the power that can be consumed via the 2kw inverter I installed... that can peak at 800amps (draw) for a very short period before it will shut down. I used #0 welding wire for the DC backbone and it has separate wires to 2 pairs of batteries. This is essentially 2 #0 wires in parallel to 4500W of energy storage.
I can run the inverter for 2+ hrs at max output and I should not have to worry about heat becoming a problem in the wires... the inverter may be another issue depending upon ambient temperature.
Thanks to everyone for your suggestions. The first meter is the same chip-set as what I have... the other 2 I'm looking into.
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Old 07-07-2015, 11:21 PM   #9
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Ouch...

All of the other units mentioned are pretty expensive... The blue sky one looks like it is a remote panel for their solar charge controller. I already have a Xantrex remote for my inverter which will give me essentially the same stuff as the xantrex battery health meter. The Tri-metric unit is too pricey though probably would work.
I can add a parallel shunt to the one in the watt meter I bought cheaply and also calculate the power as a simple ratio. I could make it carry 1/10th of the current load and simply multiply the display by 10. I would need to open one of these units up and figure out what shunt was used... then buy 9 more to put in parallel with the meter outside. Simple, but probably not that easy to accomplish with all of these units are all made in China.
The data I found was for a unit called "Doc Wattson".
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Old 07-08-2015, 09:25 PM   #10
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A little bit of detail...

Quote:
Originally Posted by JCWDCW View Post
14 gauge wire is good for 15 amps at 120 volts which is 1800 watts. The meters are rated for 60x100 = 6000 watts. Your photo array is only 400 watts which is 33 amps at 12 volt; even if the array delivers 28 volts you won't exceed the amperage rating. I assume you have a charge controller after the solar panel. What size is the wiring from your array? I'll bet it isn't 6 or 8 gauge., and even they are not big enough for 100 amps.
No matter what the meters were designed for, it seems they are rated way over the power available from the solar panel.

I doubt you will pull 100 amps from the batteries. That would kill a 100 amp-hour battery (theoretically) in an hour. The battery will likely develop high resistance after a few minutes so the scenario of 100 amps draw from house batteries is probably not viable.
If you don't have a ton of money in the meters and also can't return them then set it up temporarily away from flammable structure and try it.

JCW
Your analysis sounds like these meters can handle a 6 kw load... they can, but only for a few milliseconds at a time. If you tried to do that for much longer than that you would "let the smoke out" of the unit, as we jokingly say in the engineering community. 14 AWG wire is rated for 15 amps DC or AC current. It can handle more but its temperature will rise as a function of the current passing through it. As the temperature rises, the resistance increases which increases the voltage drop in it... this in turn drops the current in the wire if the voltage is not increased. This acts to self protect the wire, though it can get hot enough to melt the insulation off of it. It can handle a duty cycle load as long as the average current is close to the 15 amp number up to a point... a 10x rate (150 amp) will probably cause the wire to liquefy even for an instant. We used to do this in electronics shop by charging up a capacitor bank and then shorting it with a couple feet of fine solder... The wire would turn white hot in an instant and the tiny beads it turned into would hop all over the place for a few seconds. The shop teacher wasn't impressed... or at least that was his job to look like he wasn't... but he could tell we did learn something about electricity in his class.
These meters we are talking about are all based around an IC chip and a corresponding shunt. The chip measures the voltage difference across the shunt and converts it to a current... It takes many measurements per second and then uses those measurements to calculate all of the figures it displays.
Peak Current, Peak Voltage, Peak Wattage, Average Current, Average Voltage, Average Wattage, Instantaneous Voltage, etc. It also keeps track of the total wattage over time by adding up all of the wattage calculations.
I want mine to last a long time so I don't want to push it past its safe operating conditions... hence the 15 Amp continuous rating I'm using based upon the wire gauge. Hopefully I haven't bored anyone with this long winded reply.

By the way... Making IC chips like these is what I do for a living... and that is why I understand what they do so well. You probably own a cell phone or computer with a chip I helped to engineer.

Chuck
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Old 07-08-2015, 11:06 PM   #11
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More info...

The below site has a lot of info on these meters... answers some of the questions in detail... Turns out adding a parallel external shunt won't work... but there are other shunts available to increase the capability of this meter. Requires cracking the case and un-soldering the internal shunt and then using an external one instead. Voids the warranty, but the units are available for under $20 so who really cares. I could not figure out who actually makes the chip set. I can order a 100 amp external shunt and use the correct size wire to handle a 100 amp load for some pretty short money. I will probably do that for the supply side of my DC electric panel. The unit will support up to 50 amps continuous if the black leads to and from the unit are kept cool... so using one full time for the power from the 400 watts of panel is probably OK.

Meter Special Modifications
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Old 07-09-2015, 07:33 AM   #12
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Thanks for the clarification Chuck
Should have done a little basic Electrical 100
Still I'm unclear as to why the meter is rated that way if it is impractical to use it.

This post is probably not the place to discuss that!

JCW
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Old 07-09-2015, 08:56 PM   #13
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Ordered external shunt.

I ordered the external shunt... Costs more than the meter but is still well worth the additional capability. Even it comes with a de-rating notice if it is not properly cooled. 66% of rated value in still air. I will be mounting it on the wall so it should provide some convective cooling. I should be able to push it to 75 amps continuous with no problems or inaccuracies. I doubt that I will actually maintain a draw of that sort for any length of time. I feel really good about its long term prospects. I still need to order a couple more of these units for general use and as spares just in case. I can get them through Amazon Prime for under $15 each.

I've uploaded a few pictures of my system and its installation... hopefully I've posted them correctly so that they will be visible.

Chuck
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Old 07-09-2015, 10:38 PM   #14
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Just in case...

If you are wondering about that aluminum thing my solar charge controllers are mounted to well here are a few more details:

I hand made the new refrigerator duct out of aircraft aluminum... here are a few pictures of that project.

1) the place it is going in.
2) the finished fabrication of the duct... it was a lot of work.
3) Using aircraft cleco's to hold it in place.
4) Installed.

I should probably gather up all of the de-construction and construction photos and put together an album to put on here (in their own thread) from start to finish... there are hundreds of the de-construction process alone taken to be able to remember where everything goes. I didn't really need them even after waiting 7 years to re-construct it but they were there just in case.
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