MPPT solar controller and LiFePO4 battery for backpacking

[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.

[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

[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.

[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.

[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]

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]

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.

[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.

[Dave C]

The KX3 can't handle more than 15V, including transients, even when powered off. So I'm going to have to be able to switch between either panel connected or load connected, never both at the same time. I think I need some kind of double-throw ON-OFF-ON switch that has no common connection, so I can choose between two independent circuits or turn them both off, It seems like it should be pretty straightforward to find this, but I haven't found one yet. It needs to be IP65 rated.

Sorry for the lame electronics 101 question. I think I would use a DPDT switch, permanently connect the common connectors, and connect the panel and the load to the controller through the appropriate connectors on the switch.

[karrak]

The KX3 can't handle more than 15V, including transients, even when powered off. So I'm going to have to be able to switch between either panel connected or load connected, never both at the same time. I think I need some kind of double-throw ON-OFF-ON switch that has no common connection, so I can choose between two independent circuits or turn them both off, It seems like it should be pretty straightforward to find this, but I haven't found one yet. It needs to be IP65 rated.

Sorry for the lame electronics 101 question. I think I would use a DPDT switch, permanently connect the common connectors, and connect the panel and the load to the controller through the appropriate connectors on the switch.

I thought you might get a reply like that from the radio manufacturer.

Maybe an easier solution might be to try putting a load resistor on the GV5 output so it always has a load on it regardless whether the battery is connected or not. May I suggest you try an experiment by placing a 330 Ohm 1 Watt resistor across the output of the GV5 and see if it an keep the output voltage regulated at 14.2V.

A specification for your battery meter might be:
Bidirectional current and voltage logger that hooks up to smartphone or computer via bluetooth.
Logger has to be low power consumption and preferably go to very low power standby mode when battery is not being used.
Smartphone and computer software to display battery SOC and voltage.

Don't think anything like this exists, just an idea.

Simon

[Dave C]

I thought you might get a reply like that from the radio manufacturer.

Maybe an easier solution might be to try putting a load resistor on the GV5 output so it always has a load on it regardless whether the battery is connected or not. May I suggest you try an experiment by placing a 330 Ohm 1 Watt resistor across the output of the GV5 and see if it an keep the output voltage regulated at 14.2V.

A specification for your battery meter might be:
Bidirectional current and voltage logger that hooks up to smartphone or computer via bluetooth.
Logger has to be low power consumption and preferably go to very low power standby mode when battery is not being used.
Smartphone and computer software to display battery SOC and voltage.

Don't think anything like this exists, just an idea.

Simon

I will be interested to see what happens when I test with a resistor. But I don't think a 1W resistor, connected at all times, is a good solution, as it will drain the battery.

At this point, floating the battery is not guaranteed safe with this controller. So, I'm setting up a project box that will contain a Watt's Up power meter and two DPDT ON-OFF-ON switches, one to connect either the panel or the load to the controller or disconnect both, and the other to reverse polarity at the power meter (to allow it to monitor either charging or discharging current) or disconnect it. I've wanted to house my fuses and other wire connections in a sealed box of some kind anyway, and I think this box will add less than a pound.

Your power logger sounds like a nice project. Wish I had time to get up to speed and experiment. Let me know if you come up with something like this.

Is there any LFP battery that would allow a controller to remain at some small current above zero at CV? From what I've learned here, I would say no. If my thinking is correct, then I question Sunking's reasoning that it would be possible to find a battery that would keep this controller from going to panel voltage. Of course, I'm willing to learn if I'm wrong.

[Dave C]

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.

Thanks for the suggestion. I think it also has some kind of voltage limiting feature, but I think it's for low voltage, not high.

[Sunking]

Is there any LFP battery that would allow a controller to remain at some small current above zero at CV? From what I've learned here, I would say no.

OK then you have not learned a thing or listened over the week. Any drop in replacement LFP battery will do it. Again the issue is your battery disconnecting when charged. A drop in replacement does not do that. They work just like any Pb battery. This one here is 12 volt 4.5 AH lithium battery made for alarm panels that use a Float Charger. You can even buy them for a car battery. It wil float at 13 to 14.6 volts and does not take any special charge or solar ccharge controller. Note it looks like any AGM battery with just one set of terminals. No separate charge and discharge port. There are hundreds of them for sale, all you gotta do is look.



Here is another one in your size.



Here is a hint: Look for 12 volt Lithium Alarm panel and motor cycle batteries.

[Dave C]

OK then you have not learned a thing or listened over the week. Any drop in replacement LFP battery will do it. Again the issue is your battery disconnecting when charged. A drop in replacement does not do that. They work just like any Pb battery. This one here is 12 volt 4.5 AH lithium battery made for alarm panels that use a Float Charger. You can even buy them for a car battery. It will never disconnect itself from the charger under any circumstances . Note it looks like any AGM battery with just one set of terminals. No separate charge and discharge port. There are hundreds of them for sale, all you gotta do is look.

If that battery allows a controller to stay above 0A at CV, then it would keep the GV-5 from going to panel voltage. I'll take another look. Thanks. I hope there are very detailed specs.

[Sunking]

If that battery allows a controller to stay above 0A at CV, then it would keep the GV-5 from going to panel voltage. I'll take another look. Thanks. I hope there are very detailed specs.

The battery just needs to stay connected PERIOD. That is what you do not understand. A solar panel and charge controllers are current sources. It requires the battery to turn it into a VOLTAGE SOURCE so the Controller can regulate the voltage. You have been given all your options. Pick one.

1. If it were me I would just connect the radio to the GGV5 Load Port, or Battery Discharge Port, turn it on, leave it on, walk away and call it good. It will work just fine.
2. Get a battery that is compatible and does not disconnect itself from the controller.

Take your pick. It is not that difficult. The resistor idea may or may not work but comes with a catch. It uses precious power you cannot afford. A 12 volt 4.5 AH battery only has 54 watt hours with only 44 usable. If that resistor burns 1 watt, you are using 50% of the capacity of the battery in a day making useless heat. That is on top of what the radio uses. A recipe for a dead battery.