Feeding 48v, stepped up from 12v battery, intopower station MPPT SCC input?

[Dave in AZ]

Thought this was best place to ask about issues on burning out a power station input. Moved it here.

I want to use a 12v 100Ah LiFePO4 battery to feed my power station, thus increasing its capacity a bit.
I have a Pecron e1500LFP, it has a 32-95v 700W input for mppt solar charge controller. It also has a 12-18v 100W max separate mppt scc input, but that took 17 hrs to drain battery as it went between 65w and 100W input.

I want to use the 700W input, and use a 12 to 48v step up converter to get battery voltage up to input range. I have seen folks reference using step up converters often when discussing boosting a solar panel array to meet inlut specs.

However, I have also seen a ton of cautions on burning out power stations or mppt SCCs by going over voltage spec. Then on the step up converter, it had a note that said, "do not connect to mppts or inverters". And one review said theirs randomly went from 48v output to 120, which is bad! I've also read of folks burning up their Starlinks after using a 12 to 48v step up to feed them.

So, are these step ups a problem for feeding an mppt? Is it an automatic NO due to unreliable voltage or failures on outputs?

Here are the product notes, which seem cut and dried, but again I read here suggestions all the time to hook these to solar panels and batteries...
Note:
* Never connect to solar panel, PWM/MPPT charge controller, inverter or wind turbine.
* Never charge the battery. Keep good air convection.
* Never reverse the polarity.
* Use the enough big cable to avoid the voltage drop.
Application:
12V DC battery as input power to 48V DC appliances as output load.

Here is the unit I was looking at

Cllena DC/DC 12V to 48V Boost Converter 10A 480W Step Up Voltage Regulator Module Car Power Supply Voltage Transformer (Input 10V-16V) https://www.amazon.com/dp/B0CKRX92Q...ann_lstpd_CT0XJNJ6KX4SQZ66VK46&language=en_US

 

[Andrewr05]

If you buy something and it's sole purpose is to give you a regulated output voltage and in the description they can't even guarantee you that it even will give you a regulated and stable output then I wouldn't touch it with a 10-foot pole.

That being said what you are describing is perfectly capable of being done and lots of people do it.

But you need to buy a boost converter that is guaranteed to be regulated.
Bumping up to 48V is a lot to ask for a cheap unit though, you are likely going to want to stay with just 24V or expect to pay a lot more for a decent boost converter.


Your best bet though would be to just get a 48V battery.

 

[JBertok]

For 12V DC PoE ethernet switches, check out Netonix. They make industrial and DIN mount DC-powered networking gear that has the DC-DC voltage converting built-in for both active PoE+ and 24V passive PoE. Been using their gear for many years, it's all very robust.

 

[Dave in AZ]

For 12V DC PoE ethernet switches, check out Netonix. They make industrial and DIN mount DC-powered networking gear that has the DC-DC voltage converting built-in for both active PoE+ and 24V passive PoE. Been using their gear for many years, it's all very robust.

Nothing in your post made a single bit of sense to me. I even went to Netonix page and looked at their switch. I have zero idea how your comment applies to what I asked:
Feeding a 12v LiFePO4 battery into a mppt solar charge controller rated for 32-95v, 700W and 15A max. I want to convert 12v battery output to 48v, 700W. Or any voltage 36 to 80 really, but 700W.

How do 1A ethernet security switches apply to that?

 

[JBertok]

Since mentioning powering a Starlink with 48V, that would be accomplished with Power over Ethernet, and presumably a DC PoE power injector. I posted a solution to powering a Starlink, or any Passive or active PoE device, safely from a 12V DC power source.

https://netonix.com/index.php/ws-12-250-dc.html

 

[DIYrich]

I have a Pecron e1500LFP, it has a 32-95v 700W input for mppt solar charge controller.

The risk is that the mppt will try to vary the voltage to increase the output of the step up converter. Make sure that you design a system to supply at least 700w, so the mppt doesn't try to overload it.

 

[Dave in AZ]

The risk is that the mppt will try to vary the voltage to increase the output of the step up converter. Make sure that you design a system to supply at least 700w, so the mppt doesn't try to overload it.

I guess I don't understand how an mppt does its job. How can the scc input vary the voltage being received from a battery? And what is the risk of a 48v input on a 32-95v mppt, is there any chance it could vary the 48v coming from a battery up enough to risk the 95v input limit? Or could it cause issues with the 12v to 48v converter, is that the risk? If so, I don't understand how it would affect the converter. Thx for any explanations!

 

[JBertok]

I can give you some background on the mode of operation of an MPPT.
Maximum Power Point Trackers utilize the voltage vs. current output curve characteristics of the PV array to regulate their output to the battery.

A PV specification label provides details from which a power output curve can be extrapolated:
"Isc" or short-circuit current, is the rated maximum amperage at zero volts short-circuit.
"Voc" or open-circuit voltage, is the rated maximum voltage at zero amps.
"Vmp" and "Imp" are the Voltage and Amperage rated outputs at maximum wattage. This voltage will always be less than Voc, and the amperage always less than Isc.

When a MPPT needs to taper off the power it's sending to the battery, instead of pulsing output like a Pulse-width-modulated charger would, it uses its variable DC-to-DC conversion capability to allow the array voltage to rise. Rising array voltage results in a tapering off of the current the array is capable of putting out. Current falls off at a greater rate than voltage rises, so the result is a reduction in wattage coming from the array. The closer the MPPT moves the PV voltage toward the Voc of the panels the more the current will fall off.
By observing the voltage of the PV input of a MPPT, you can get a sense of how much PV capacity the MPPT is actually using. If the voltage is close to Vmp*n (n=panels in series) then it's fair to say the MPPT is harvesting the maximum available potential of the PV. If that input voltage is highe, the MPPT has tapered off its output.

The problem with connecting a battery to the input side of the MPPT (with MPPT function enabled) that it is not possible to prevent the rated limitations of the MPPT from being exceeded - especially current. An MPPT is programmed to vary the input voltage to find the sweet spot where Voltage and Amperage are yielding the maximum wattage. Above and below that maximum power point with a PV panel/array, available wattage decreases rapidly. It looks like a peak in the middle of that voltage and current relationship curve. A battery would not respond the same way to having its voltage pulled down. The battery doesn't have a maximum power point peak in its power curve like a PV panel does, the available output wattage keeps going up the more the voltage is pulled down. You can't overload a PV panel, but every battery can be. The MPPT would keep lowering voltage seeing that it can extract more and more current, right up to a point of hitting a limit and/or overload. In your case you'd be overloading the DC-to-DC converter; there is no way to tell specify to the MPPT what the limits are of that converter. A quality MPPT would fault out at that point, a lesser one just goes up in smoke. The MPPT rating in play here is the maximum input Isc, or short-circuit current for the PV input. That is same technical limitation that also defines a limit to how much PV overprovisioning an MPPT can handle.

If your MPPT has the ability to turn off the maximum power point tracking functions and hard set a fixed voltage to the "PV" input, you can make this work with a DC-to-DC step up converter from your 12V battery like you envision. By measuring the amount of current going through your DC-DC converter you can change that hard voltage setpoint until the current flow is safely within the operating margins of the full duty cycle rating of your converter or MPPT - whichever is lower. Start with a high voltage (54V+) and gradually bring it down incrementally while making observations and measurements of that power flow. I might get heckled for this, but I can just about promise it will work fine as described as long as you're staying below the limits of both the converter and the MPPT circuit.

 

[JBertok]

Edit: thinking about this more, you might run into a problem with MPPT, assuming the MPPT function can be disabled in favor of a hard-set voltage, where the "PV" input voltage from the DC converter might not adequate at 48V. I saw you mention the 32-95V input spec of the MPPT, but generally the PV input has to be a certain minimum voltage greater than the battery voltage for a charge cycle to begin. It might be worth looking for a converter that can output 60 or even 72V.

 

[Dave in AZ]

Edit: thinking about this more, you might run into a problem with MPPT, assuming the MPPT function can be disabled in favor of a hard-set voltage, where the "PV" input voltage from the DC converter might not adequate at 48V. I saw you mention the 32-95V input spec of the MPPT, but generally the PC input has to be a certain minimum voltage greater than the battery voltage for a charge cycle to begin. It might be worth looking for a converter that can output 60 or even 72V.

Thanks so much for your in depth reply, I learned a bunch