MPPT solar controller and LiFePO4 battery for backpacking

[jflorey2]

Thanks for the suggestions. Can an inline meter measure current flow in both directions? From what I've seen, I think the answer is no.

The Cycle Analyst will measure current flow in both directions. It is intended for small EV's (like electric bikes) that do regen braking, so it can measure power flows in both directions, into and out of the battery.

Also, clamp-on meters capable of DC will often measure current bidirectionally. I have a B+K Precison 367A clamp on ammeter that reads in both directions.

[SunEagle]

I do not know of any in-line meters that work well with reverse current flow.

Most of the meters I use are high end like the Fluke and Dranetz. They will provide data that shows a negative kw rate which it a great indicator that the CT's have been hooked up backwards.

Although one of my projects was at a high school with a 1MW solar array. It was interesting to see the usage go backwards and subtract the wattage used during the daytime and then go back to purchasing power late afternoon and at night. We actually had to use 2 meters and a specific time frame to determine the true total load being consumed at the school.

[Dave C]

Unfortunately unless the meter can be programmed to recognized bi-directional current flow, then no it can't. Some will read a negative kw usage went it is sent in the reverse direction other meters may show a positive usage because based on it's programming, all current flows are additive.

Thanks. Actually, one of the descriptions that I read indicated that the unit would be damaged if current flow were reversed. One that indicates readings, either positive or negative, with reverse flow would be okay, because the controller's status would indicate which way it's flowing. Any examples of ones that work like this?

Here's an FAQ for the Watt's Up meter. Reverse flow won't damage this one, and bi-directional measurement can be done with two meters.

[SunEagle]

Thanks for the suggestions. Can an inline meter measure current flow in both directions? From what I've seen, I think the answer is no.

Unfortunately unless the meter can be programmed to recognized bi-directional current flow, then no it can't. Some will read a negative kw usage went it is sent in the reverse direction other meters may show a positive usage because based on it's programming, all current flows are additive.

[Dave C]

Thanks for the suggestions. Can an inline meter measure current flow in both directions? From what I've seen, I think the answer is no.

[solar pete]

I had a look, seems to me you two have different opinions, thats ok with me. Dont see why you cant argue nicely, cheers.

[SunEagle]

Easy Peazy. Us RC modelers do this every day. So dang many I do not know where to start. But here is a good place to look. Prices range from $5 to $40.

This is the one I have. Max voltage = 60 volts, and 100 amps. For $38 it will do:

Functions:
Battery Cell/Voltage Checker
Battery Internal Resistance Checker
Watt Meter (Amps/Watts/Volts)
Servo Tester
Optical Tacho
Temp Gauge
Thrust Calculator
Battery Internal Resistance Meter

That is one great meter. I also have it and glad I purchased one.

[Sunking]

I would like to add a digital panel meter to monitor either voltage and current or just voltage. Is it advisable to monitor current? If so, should I monitor the charge or discharge side? I think charge current would be more variable so of more interest.

Easy Peazy. Us RC modelers do this every day. So dang many I do not know where to start. But here is a good place to look. Prices range from $5 to $40.

This is the one I have. Max voltage = 60 volts, and 100 amps. For $38 it will do:

Functions:
Battery Cell/Voltage Checker
Battery Internal Resistance Checker
Watt Meter (Amps/Watts/Volts)
Servo Tester
Optical Tacho
Temp Gauge
Thrust Calculator
Battery Internal Resistance Meter

[jflorey2]

I would like to add a digital panel meter to monitor either voltage and current or just voltage. Is it advisable to monitor current? If so, should I monitor the charge or discharge side? I think charge current would be more variable so of more interest.

Monitor voltage and current at the _battery._ That's the thing you have to take care of.

There are plenty of devices available that will do this. Powerwerx makes a device (watt-meter and power analyzer) that will monitor voltage and current and track coulombs in for about $50. All Electronics has a volt+amp meter for about $12. Both draw power, of course, so make sure you do not kill your battery while using them. Both are also one-way.

If you want to get fancier, ebikes.ca has a power monitor (Cycle Analyst) that will monitor bidirectional power flow for about $120.

[Dave C]

Dave what you need to understand about Karrak is he is here only for one purpose and one purpose only. To harass me. He has admitted so in writing. Go look for yourself. Page 3 midway down.

Now ask why the mods allow him to stay? He even starts threads to harass me.

I see that this is difficult for you. None of us are above this kind of conflict. Personally, faith in God and prayer help me to deal with life's difficulties better than I would otherwise. I wish you peace and security to deal with the challenges that face you.

[Dave C]

Gentlemen, thank you. You've been extremely generous with your time and expertise. It would have taken me a very, very long time to get to the required information without your assistance.

You've helped me to make a decision about the controller and battery. Now I have one more set of project-related questions that's not specifically within the scope of solar power.

I would like to add a digital panel meter to monitor either voltage and current or just voltage. Is it advisable to monitor current? If so, should I monitor the charge or discharge side? I think charge current would be more variable so of more interest.

I'm looking at this panel multimeter, which requires a separate 4.5 ~ 30V power supply. The meter's negative power lead would connect either to nothing or to a "buck circuit (module) negative". Would the controller be the buck circuit they're referring to? Instead of connecting to a buck circuit, should the power supply's negative terminal be wired to the meter's common ground?

Measuring just voltage would be easier with a meter that requires no additional power supply.

[Sunking]

Dave what you need to understand about Karrak is he is here only for one purpose and one purpose only. To harass me. He has admitted so in writing. Go look for yourself. Page 3 midway down.

the only reason I am posting on the other forum is to counter the gospel according to Sunking

Now ask why the mods allow him to stay? He even starts threads to harass me.

[Sunking]

Wrong, yet again. If there is no load on the output of the power circuit in the MPPT controller the capacitors in the output stage of that circuit will hold the voltage at whatever voltage they have been charged up to. With a load on the output the voltage will slowly go down..

Complete rubbish. If you had really every built a MPPT controller, then you know they all use a Constant-On-Buck Converter. Just about every MPPT Controller including the GV5 uses a TI LM5019MR 100V, 100mA Constant On-Time Synchronous Buck Regulator. Go look at the data and application sheets. None of the Buck Regulators made by TI or Fairchild are capable of 0% On Time. There is no need to. Read the Control Overveiw:

The LM5019 buck regulator employs a control principle based on a comparator and a one-shot on-timer, with the output voltage feedback (FB) compared to an internal reference (1.225V). If the FB voltage is below the reference the internal buck switch is turned on for the one-shot timer period, which is a function of the input voltage and the programming resistor (RON). Following the on-time the switch remains off until the FB voltage falls below the reference, but never before the minimum off-time forced by the minimum off-time one-shot timer. When the FB pin voltage falls below the reference and the minimum off-time one-shot period expires, the buck switch is turned on for another on-time one-shot period. This will continue until regulation is achieved and the FB voltage is approximately equal to 1.225V (typ)

It is a plain as the nose on your face. Read it, MINIMUM OFF-TIME. That means never goes to ZERO

[Dave C]

Your radio will be just fine. If it has been built to plug into a 12 volt power source like a battery with an attached charger the radio designers should have take into account issues like voltage transients. The voltage figure in the radio operator's manual will be the maximum operating voltage that the radio should operate at. This is less than the absolute maximum voltage at which damage will occur. Also and here I actually agree with Sunking, having the radio turned on and providing a load for the GV5 when the Bioenno's BMS disconnects the battery will mean the GV5 should be able to maintain the voltage regulation.

Simon

This is good news, and the fact that you two agree on this is a help. I'll confirm with Elecraft. But before I trust my radio to this setup, I'll test with a resistor.

[karrak]

Unfortunately, with all due respect, your abrasive delivery and your unwillingness to adjust your course when new or different information becomes available make me question your advice.

Edit: However, you have provided valuable information. Your explanation of the term "float" is much appreciated.

I agree that some of the information that Sunking provides is useful, but there is so much that is just plain wrong. This might be OK if Sunking would accept when he is wrong, learn from his mistakes and be prepared to listen to what others are saying, but in the year that I have been writing on this forum I see no evidence of this or that he is prepared to change.

The problem is that if Sunking is challenged in any way the treads where he is being challenged just degenerate to the point where it is hard to extract any useful information from all the dross, so the useful information is lost. Maybe this is his strategy, I don't know.

Simon