Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Vikelf

Hi,

I am in the design phase of a simple test system. I wanted to add panel meters to view my input and output for my own understanding and curiosity.

Here's what I would like to see:

1) PV Array ---> Volt Meter #1 / Amp Meter #1 ==> Charge Controller

2) Charge Controller --> Volt Meter #2 / Amp Meter #2 ==> Battery Bank

3) Battery Bank --> Volt Meter #2 / Amp Meter #2 / AH #1 ==> Inverter (Xantrex prowatt SW1000)

4) Battery Bank --> Volt Meter #3 / Amp Meter #3 / AH #2 ==> DC Load


Are there panels or Charger controllers in place that can provide this information? (planning a 400W 12v system small 100-200AH 12v Battery bank)

What is better Analog or Digital panel meters? (I understand it's easier to read the digital)

Which uses more power and which one can stay in an always "on" state?

Where do I need a Shunt?

Where do I need fuses? (what size)

MPPT or PWM?

What inverter would you recommend? (Not looking to run anything more than a few lights and handheld shop tools for short period of time)


Any input greatly appreciated!

Cariboocoot

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Better charge controllers like Outback and MidNite will show you Volts and Amps in and out. Beyond that, measuring battery Voltage 'again' is redundant, although you may want to measure it at loads to check for Voltage drop. It is not really a measurement that needs continual monitoring.

Likewise current from the battery to any DC load can be measured. For high current items you will need a meter that utilizes a shunt. If you want to keep track of Amp hours in and out of the battery as well, then you are looking at a battery monitor such as Bogart's Trimetric or Pentametric or Outback's FNDC system.

All of this costs money. It would help if you could explain why you want to measure power at certain locations and what amount of power you expect to need to measure. For small system it is possible to use simpler, less expensive measurement devices.

BB.

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Do you want to "log" the data on a computer? Or just look at the gauges several times a day?

Also, if you are digitally logging, you can, for example with the Charge controller output and Battery logging--Take the difference between charge controller and battery bank to figure out the balance that is going to the loads.

For logging with an MPPT charge controller--The Rogue 12/24 volt 30 amp MPPT charge controller will give you the digital charge controller data (direct connect, no dongles required).

-Bill

Vikelf

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Cariboocoot,

Thanks for the response, I'll try my best to explain.

As I am new and I have an issue with reading and understanding versus doing and learning, I will spend more money to figure it out in the long run.

So I want to understand what the PVs are delivering (what the charge controller sees), what the charge controller outputs (what the battery sees), and what the load sees..

I can purchase several simple DC analog panel amp meters and volt meters or digital versions for a lot less than a large charge controller ...I think . Since this is mainly for a simple learning project, I felt that a small expense of $15 per dual meter Volt/Amp or $6 for separate was justified. Yet, I am sure there are better solutions out there for what I am trying to see. If I can get it to fit my goal then I am willing to modify the design in order to accommodate it. ie Charger Controllers with Monitors or standalone monitors.

It would be nice to have several monitoring points, just don't know the best solution for the design. Any input on the digital vs analog panel meter?

Btw, I did look at the monitors you mentioned, they appear very intelligent but it seems I can accomplish the same thing at 50% of the cost and without have to cycle buttons. /shrug
The monitors maybe doing more than what I realize. Nevertheless, I will investigate it more if not for this system but for the large system down the road.


Open to any suggestions

Vikelf

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Bill,
I don't think I will spend time logging on this system. It's mainly a learning tool. I will plan to log/trend my "full size" system down the road.

Since I am not always home, I plan to have an IP PTZ camera setup to monitor the system (the wife is not reliable!) . In this way, I think the larger Digital or Analog panel meters maybe more useful.

BB.

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Hmmm... Even the Charge Controllers usually "assume" conversion losses (i.e., they measure the output current directly and then estimate the input current from the array). Voltage is "simple to measure". DC Current measurements usually requires a precision resistor/shunt (extra costs, extra losses).

If you were just wanting to make manual measurements, an inexpensive DC Current Clamp meter is nice--It allows you to quickly measure DC (and AC) currents by just moving the meter from wire to wire. However, the problem with active current probes is they drift after a few minutes and need to be re-calibrated (usually reset to zero current) to stay accurate.

But otherwise, DC Shunts and Panel Meters appear to do what you want. Note that these systems use non-linear wave forms (sine squared current wave forms, modified square waves for AC inverters, etc.). You need True RMS reading meters to measure these electrical circuits "accurately"... A typical charge controller's power measurements are only accurate to ~5% (sometimes as far out as 10%--both errors in voltage and current measurements make power measurements even more inaccurate).

-Bill

NorthGuy

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Vikelf wrote: »

So I want to understand what the PVs are delivering (what the charge controller sees), what the charge controller outputs (what the battery sees), and what the load sees.

This is a little bit more complicated. There's a difference between what panels are capable of delivering at current conditions (which is a function of insolation available and panels) and what they're really delivering (which depends a good deal on the charge controller).

When you measure charge controller input, you only measure the later enitity, not the former.

Vikelf

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

NorthGuy,

I guess I don't understand. I am assuming whatever Voltage and Amperage that I see from the PV array is just that regardless of the "Watts In" reported by the Charge Controller.
This way I can better understand the losses...it's a small price <$50 to setup for me gain a little knowledge. Again, this is for a small project (~ 1KW) so for me learning hands on is the most important aspect.

I may not have a complete grasp of the subject but if everything is connected up and operating. I would assume I could insert test points.

Cariboocoot

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Northguy is referring to the difference between a panels potential power output and what you will actually receive on a battery-based system. Basically, if the battery & loads do not need the full power the panels are capable of you will not read that power level because it is not being realized.

So you may have a panel capable of 100 Watts at midday, but because the loads are low and the battery charged the output could be only 25 Watts; there is no place for the power to go so it doesn't materialize.

On a grid tie system there is always a place for the power to go so you would always read the full amount of power the panels are capable of at that moment.

Reading the power levels (Volts and Amps) at various points in a system doesn't really tell you much. You can work out from it, for example, how much power is being lost to wiring or the charge controller or determine how much power is going to the batteries from the controller and how much to loads. But in essence it is not something that needs constant monitoring.

For a small scale project you are better off using a DMM and taking readings at 'junction points' for any given time during the day rather than setting up multiple meters to watch the in and out all the time. Perhaps the biggest advantage would be had by measuring the current to and from the battery and to loads, so that you could weigh the controller output against battery input/output and load draw. The Voltage will be relatively stable within the circuit, unless you have long or undersized wires which would result in excessive V-drop under loaded conditions.

Vikelf

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Cariboocoot,
I understand now and the DDM makes sense as well. I guess I may have had more "want" than "need"...just figured it would look very professional with several panel meters, lol.

Question: What happens to the power that is generated but has no place to go? Generally speaking, Are LVD charge controllers good for a <30VDC lighting project? I assume it has limits on what it will allow as in amps. Should these types of draws be connected directly to the battery or should something like this be used: Sunlight 10amp 24vdc

thanks!

Cariboocoot

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

A fully illuminated panel that has no load on it produces no power. In order for the power to be realized there has to be a circuit for the power to go through. Likewise if the load is not 'maximum' neither will the power generated.

It is similar to loading a generator: it has the potential (Voltage) with no load on it, but the power (V*A=W) doesn't exist without the load. When you 'load up' a generator you will hear the engine rev as it pulls more fuel to increase engine power to meet the electrical demand.

The charge controllers with 'LOAD' terminals on them will have a current limit for those terminals. it is usually the same as the controller's output max, but sometimes less. Providing the loads do not exceed the current rating it works fine. Some of these have light control as well; the ability to turn on the load when the PV power output is indicative of night.

Inverters or other heavy load should not be connected to these terminals.

Vikelf

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Cariboocoot wrote: »

A fully illuminated panel that has no load on it produces no power. In order for the power to be realized there has to be a circuit for the power to go through. Likewise if the load is not 'maximum' neither will the power generated..

Ok, so if there is nothing to charge, the circuit is basically OPEN? As if it were not even connected? The load closes the circuit generating a load? Does that make sense or am I looking at this all wrong?

Cariboocoot

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Vikelf wrote: »

Ok, so if there is nothing to charge, the circuit is basically OPEN? As if it were not even connected? The load closes the circuit generating a load? Does that make sense or am I looking at this all wrong?

That is correct: charge controllers 'pulse' to maintain the Voltage setting on their output, connecting and disconnecting the panels as needed to keep the right level for the charge stage.

So during Bulk the connection is ON, sending as much current as the panels can provide as the battery charges and Voltage rises. When Absorb Voltage is reached the controller begins 'turning the panels on and off' to keep that Voltage, including against the varying current demands of any loads. Float stage functions the same, except at a lower Voltage point.

Loads connected to the LOAD terminals (if provided) are actually connected to the battery, through low Voltage disconnect and/or daylight controls.

NorthGuy

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

Vikelf wrote: »

I am assuming whatever Voltage and Amperage that I see from the PV array is just that regardless of the "Watts In" reported by the Charge Controller.

The controller has a "choice" to take more or less energy. This may be on purpose (e.g. controller dosn't take energy when batteries are full), or because the controller is incapable of taking full energy.

One good example is PWM controller. It extracts less energy than the MPPT controller, but losses inside the controller are very small. If you measure V*I on the output and compare to V*I on the input, you will get much higher efficiency measurement for PWM. [Given 'proper' Vmp on the array for the system.] - 'Coot

zoneblue

Re: Panel Meters (Volt/Amp) Digital or Analog? Monitoring?

My 2c would be that if you are going to the trouble of monitoring you may as well be able to harvest the data. The cost of shunts and panel meters would be about the same. The system we are working on (http://code.google.com/p/theblackboxproject/) is relatively inexpensive, but requires some computer savy.

If you want to measure several shunts, then, adding an analog interface board (eg cai webcontrol or simialr). However if you have or are thinking about having a midnite classic in your system, then it will very soon be able to measure most all of the voltages and currents that matter. The main reason to go with your own shunts would be to qualify the ccs numbers.