MPPT solar controller and LiFePO4 battery for backpacking

[karrak]

i think the batteryspace battery would be a better fit because of its higher charge voltage cutoff of 15.6V. My reasoning is that at 14.2V, the GV-5 won't charge that battery to capacity, so the battery won't disconnect. Am I close? Can anyone comment on the quality of the batteryspace battery?

The SOC(State of Charge, i.e. how full the battery is, where an SOC of 100% is full) versus the voltage that you charge an LFP battery to is a function of the battery chemistry and is pretty much the same regardless of the battery manufacturer. If you charge an LFP battery to 13.8 volts and wait for the charge current going into the battery to go to zero the battery will be 100% charged regardless of the manufacturer. If you charge the battery at a higher voltage it will get to 100% full quicker, but charging at the higher voltage will decrease the lifespan of the battery. You really do not want to leave a 12 volt LFP charging at more than 14.6 volts. 14.2 volts is OK.

As long as the charge controller keeps the charge voltage at 14.2 volts you will be OK, even with your current battery.

Even if your battery disconnects because it is badly out of balance, as long as you have another load on the GV5 the output voltage from the GV5 will stay at 14.2 volts.

I have contacted Genasun's distributor in Australia. The first response didn't answer my question so I have sent another email asking for clarification of their answer.

Simon

[Dave C]

You all have been very generous with your time in providing a lot of great information. Now let's see if I've learned anything here... I've been looking at this battery made by K2 and this one, sold at batteryspace.com. Of these two, i think the batteryspace battery would be a better fit because of its higher charge voltage cutoff of 15.6V. My reasoning is that at 14.2V, the GV-5 won't charge that battery to capacity, so the battery won't disconnect. Am I close? Can anyone comment on the quality of the batteryspace battery?

[Sunking]

I answered Pulse Code Modulation. But I worked with it in radios for years....

Understood. But when it comes to Lithium Battery Modules it means Protection Circuit Module. If you see a Lithium Modular Battery with Charge and Discharge leads, it has a PCM and will say it in the description. Here is an example of one. If you were to back up a page on the website, you can see quite a few of them. With a Charge and Discharge port, you can bet the battery has a HVC and LVD. No other reason to have separate charge and discharge ports. Not something you want to use with a solar charge controller because no controller is made to operate at Zero volts.

[Mike90250]

What the hell do you think PCM means..........

I answered Pulse Code Modulation. But I worked with it in radios for years....

[solar pete]

I am sure there are others from Australia, I think solar pete hails from here.

I resemble that remark

[karrak]

I'm fairly settled on the idea of ordering another GV-5, but what would you recommend as an alternative?

Sorry I can't help you there. The GV-5 should be OK if you place another load on it while you are charging the LFP battery. When I get some time in the next few days I will send an email to Genasun and Bioenno to see if I can get their thoughts on this problem. Hopefully I will get an answer from someone who has some technical knowledge.

In the U.S. we're just called "hikers" or "backpackers", but I do like the sound of "bushwalker". I've never been to Australia, but will check into the Bibbulmun track if I go there. Are others besides you in this forum also based in Australia? Are you a bushwalker?

I am sure there are others from Australia, I think solar pete hails from here.

Yes, I am a bushwalker, my walking is usually limited to less than two weeks at a time. I have walked the whole Bibbulmun track in stages. It is a great walk! Very well resourced with huts and water every 20km. Other great walks are the Overland Track in Tasmania and the Larapinta Trail in Central Australia.

Besides my interest in backpacking, there's also a fair amonunt of disaster preparedness involve I this for me. The world is becoming more and more "interesting" every day.

Yes, with all the human stupidity evident at the moment I find it hard to be optimistic about the future.

Simon

[Dave C]

If you can't find an MPPT controller to match the GV-5 specs without the annoying problem that the GV-5 has there are ways of getting round the problem.

I'm fairly settled on the idea of ordering another GV-5, but what would you recommend as an alternative?

With your weight requirements, am I right in thinking you are a long distance bushwalker? Have you heard of the Bibbulmun track?
Simon

In the U.S. we're just called "hikers" or "backpackers", but I do like the sound of "bushwalker". I've never been to Australia, but will check into the Bibbulmun track if I go there. Are others besides you in this forum also based in Australia? Are you a bushwalker?

Besides my interest in backpacking, there's also a fair amonunt of disaster preparedness involve I this for me. The world is becoming more and more "interesting" every day.

[Sunking]

How the hell do you know this is the case, have you disassembled the Bioenno battery in question or have access to the circuit diagram of the battery?

What the hell do you think PCM means. Let me educate you

PCM = Protection Circuit Module

Here is a supplier with a lot of 12 volt lithium batteries. Most of them have PCM.

[Sunking]

Would the BMS be sophisticated enough to test if a load has been connected?

Very doubtful. LVD's just monitors cell or pack voltages, not current.

Would the presence of a load affect whether or not the battery disconnects?

It should. The controller needs a load, some current flowing to maintain controlled voltage regulation

What kind of load would you recommend connecting to the battery terminals? What kinds of complications would that introduce?

Any load. It does come with a catch. It drains the battery. All your issues revolve around a battery with a HVC circuit disconnecting the charger. How do I know you have HVC and LVD? Because your battery says it does. In your case the term PCM = Protection Circuit Module. . Here is another battery similar to yours, a 4S 6.6 AH with two ports, a charge port and discharge port with PCM. Sound familiar?

What battery would you recommend?

One without a HVC circuit. Your battery module has a HVC as part of the PCM. It is unnecessary automation which causes more problems than it is worth in my opinion. It makes it incompatible with Solar. I assume you want something modular in a box right? Something on the lines of a Power Stream 12 volt 7 AH LiFe battery. They are drop in replacements for AGM batteries in Alarm Systems. It has a crude BMS with balance boards and LVD. However no HVC and will work just like a regular battery. It can be charged as high as 1C and discharged at 2C continuous. It will work with any solar charge controller or battery charger made for lead acid. Ideally you want a CC/CV charger set to 13.8 to
14.6 volts. Just what the Doctor ordered.

[karrak]

Solar MPPT controllers are not designed as Switch Mode Power Supplies. They must have a load to operate into. To make them behave like a SMPS would require more circuitry and expense for something that is not required or needed.

I beg to differ, maybe I am wrong and the basic operation of commercial MPPT controllers is radically different from what I designed, which I doubt but I would call the main power circuitry of an MPPT controller a Buck Switch Mode Power Supply with the primary feedback control loop being controlled by the output voltage, and a secondary control loop being to maximise the power obtained from the solar panels. They do not necessarily need a load to operate but as jflorey2 has already said the control electronics usually get their power from the load (in this case the battery) with the exception of the Genasun GV-5 which seems to get its power from the solar cell.

But who am I to make such a statement, I am the idiot who doesn't know what i am doing or saying, even though I have designed and built my own MPPT controller over five years ago which is still working just fine.

For those that are interested here is the circuit diagram of the power electronics of my MPPT controller, look familiar?
SolarControllerPower.pdf

Take any MPPT controller you want and try it. Disconnect the battery with bright Sunshine on the panels. One of three things is going to happen:

1. Voltage out will rise to Vin.
2. Let the magic smoke out and never work again.
3. Spills all the ones and zeros out going stupid.

What do you have to loose to prove me wrong? I can tell you without a doubt a Genasun will rise to Vin or about Voc of the panel. It clearly states that in their documentation. Most others will let the magic smoke out, or go stupid. Try it if you got the balls to do it.

There are a few different scenarios when disconnecting the battery from my controller when the output from the solar panels is at its maximum

1. Battery not full and controller providing maximum amps to battery

This is the one that you are getting excited about and would be a challenge to the controller. In my case the voltage control feedback loop would be too slow to stop the output voltage going above its programmed level but my HVD software would detect this and turn off the switching FETs as soon as this condition was detected. This would still be too slow and the output voltage could rise to the Voc of the solar panels, which could be as high as 40 volts. I am fairly sure that all the electronics that would be subjected to the 40 volts is rated at a higher voltage so I can't see any damage happening. The voltage would then drop fairly rapidly due the power consumption of the controller electronics. I am not sure if it would drop to zero or whether the control electronics would start regulating the voltage again.

2. Battery full and controller providing little or no current

It is likely under this scenario that the voltage control feedback loop would be able to keep the output voltage under the HVD trigger and the controller would continue to provide regulated power to the output, although the regulation would suffer.

[karrak]

Would this kind of circuit allow a BMS, when wired to a controller, to block incoming charge current while allowing outgoing current to flow to a load? Or, in a case like mine, is it likely that the disconnect at full charge is like an open a switch, in which case this circuit, if employed, controls the direction of current flow only when the switch is closed?

Current can only flow in one direction at a time, it doesn't go into the battery and out of it at the same time. If you have a load connected to the battery at the same time as it is being charged the current will go directly from the controller to the load, bypassing the battery. If the load draws more current that the controller will provide the load will take current from both the controller and the battery.

In theory you could operate the switch circuit so it would only switch current in one direction at a time but due to it not working well like this you probably wouldn't do it. You would either have is switched on to allow current flow in both directions or switched off so no current can pass.

Simon

[Dave C]

See this article for more information http://electronics.stackexchange.com/questions/79028/understanding-two-mosfet-with-sources-connected"] http://electronics.stackexchange.com/questions/79028/understanding-two-mosfet-with-sources-connected[/URL]

Would this kind of circuit allow a BMS, when wired to a controller, to block incoming charge current while allowing outgoing current to flow to a load? Or, in a case like mine, is it likely that the disconnect at full charge is like an open a switch, in which case this circuit, if employed, controls the direction of current flow only when the switch is closed?

[karrak]

I understand your point. Whether or not the battery will reconnect is unknown. But I don't think the 18V OCV has any causal effect on the disconnect--I think it's purely a result of the disconnect. After the initial disconnect, the battery would reconnect briefly 4 times. Maybe the battery voltage was slipping briefly below 14.6V? Would the BMS be sophisticated enough to test if a load has been connected? Would the presence of a load affect whether or not the battery disconnects?

You are correct. I can't say for sure because I don't have enough facts about the battery but I would think that when all the individual cell voltages dropped below 3.65 volts (overall battery voltage 14.6V) the BMS would reconnect the battery to the connector. The Genasun would then charge the battery a little more until the BMS detected an overvoltage and disconnected the battery again, and so on and so on.

By disconnecting the Genasun controller from the battery the voltage at the connector will drop down to below the cutoff voltage and the BMS will reconnect the battery to the connector. Placing a suitable load on the Genasun controller will make sure that it keeps the voltage regulated.

What kind of load would you recommend connecting to the battery terminals? What kinds of complications would that introduce?

I wouldn't connect the load to the battery terminals but to the load terminals on the Genasun controller as it is this that is causing the problems. All it would need would be a small 1/4watt or 1watt resistor. The value of this would be dependent on how much load the Genasun needs to keep its voltage regulated. I would try a 1/4 watt 10kOhm first. If this didn't work try a 1kOhm 1/4 watt and if this doesn't work try a 330Ohm 1 watt resistor.

Simon

[karrak]

Your battery with two ports has a HVC on the input, and LVD on the output. Both input and output are the point electrically across the battery, but use a relay contacts to open/close the two paths.

How the hell do you know this is the case, have you disassembled the Bioenno battery in question or have access to the circuit diagram of the battery?

I doubt very much you will find any relays in the battery. The BMS is more likely two FETs back to back being controlled by a circuit that detects if the cell voltages are too high or low. See this article for more informationhttp://electronics.stackexchange.com...rces-connected

Don't you ever learn from your mistakes, remember this?

Many battery Manufactures make 12 volt LFP batteries as drop in replacements for Pb and most do not have any type of BMS other than a LVD Relay. That includes the almighty A123 LFP 12 Volt Car Battery. Why would a manufacture do that without a BMS? Because it is NOT NEEDED.

and the reply,

WHOA That statement is complete BS....totally untrue. How to you pretend to know what is inside that battery? Tell you what....you tell us what's in there, and then I'll post a picture of one torn down and we can all see how full of it you really are. Your trousers are ablaze.

By the way, wb9k is the head of the warranty labs at A123systems.

[Dave C]

But his battery will never reconnect when the controller output goes to 18 volts with an Open Circuit.

I understand your point. Whether or not the battery will reconnect is unknown. But I don't think the 18V OCV has any causal effect on the disconnect--I think it's purely a result of the disconnect. After the initial disconnect, the battery would reconnect briefly 4 times. Maybe the battery voltage was slipping briefly below 14.6V? Would the BMS be sophisticated enough to test if a load has been connected? Would the presence of a load affect whether or not the battery disconnects?

What kind of load would you recommend connecting to the battery terminals? What kinds of complications would that introduce?

What battery would you recommend?