Can I use a battery charger to bypass inverters power saving mode?

[Kamis]

Hi guys!
First time poster, long time solar/battery enthusiast

I recently finished building an offgrid system for our family cottage. Its main components are 16 200ah Lifepo4 batteries in series (with a BMS), a 48v 5kva inverter/solar charger, 660W of solar panels, a breaker panel and some 230V outlets. This is the inverter/charger: https://www.aliexpress.com/item/327...exp_id=5139b3eb-e415-4325-af92-c354b6ed039d-0

Everything works fine so far except I have a few issues with the inverter (I know, cheap & Chinese). The inverter has a power saving mode that can be activated/deactivated through settings. When it's not on power saving mode, the inverter gets quite hot on the top and I'm a little worried to leave it unattended like that. And of course it uses alot more energy too (around 55W instead of 10W on standby). On standby mode it stays pretty much at ambient temperature and even under load it doesn't get hot because the fans kick in. Several other people in my family will use the cabin as well and some of them are getting old and I want to keep the operations as simple as possible for them. About 6 years ago I also built a smaller 12VDC system, which takes care of all the LED lights and phone charging. The new 230VAC system is mainly going to be used for bigger loads such as a coffee maker, a microwave, a kettle etc. For these reasons I would like to keep the inverter ALWAYS on stand by mode.

So what's the problem? For the inverter to wake up, it needs quite a significant load. I haven't got to test it accurately yet, but I'd guess it's something like 100-200W. Even though the 12V system is good for phones/tablets/lights, my family members would like to charge their laptops, cordless drills, cameras etc. that require 230VAC.

So I thought maybe I could build a circuit, where a separate say 100-200W "dumb load" will be turned on for as long as someone needs to load their drills and whatnot. Then I thought why not use a 4amp 16S lifepo4 battery charger as a dumb load to minimize the losses and charge most of the energy back into the batteries. I tried to google this but found nobody doing it so is there something obvious that I'm missing with the idea? If I were to do this battery -> inverter -> back to battery circuit as my dumb load, what kind of safety issues should I consider?

Thanks for taking time to read my post.

 

[Wellbuilt]

Inverters get hot ?
If you can keep your hand on it it should be ok .
In warm weather I have a small fan blowing on my system .
My Internal fan will turn on if I’m only using a little power lites tv it mite be a 60 amp load .
10watts is low for a Chinese inverter in search mode .
I can adjust the watts that my inverter will turn on at , I think I’m at 10 watts
If I turn on my led kitchen lites the inverter will lite it up

 

[Kamis]

It sure would be nice to have an adjustable power setting for waking up the inverter but mine unfortunately doesn't work like that. :/

Does anybody know if my plan to use a few amp lifepo4 58,4v battery charger to recharge my batteries would be a reasonable solution? My goal is to get the inverter to wake up even with smaller loads and preferably not to waste energy with 200 watts worth of incandescent light bulbs while doing that. :D

 

[Kamis]

Hi! I drew a diagram for you to hopefully demonstrate what I'm thinking about.

Problem summary: Inverter has a power saving mode that will not detect small loads (under 100W).

Can anybody confirm this would work or not before I order the battery charger? Am I also correct about using a battery charger as a dummy load will be more efficient than light bulbs, because it would recycle the same energy while still drawing sufficient amount of power from the inverter for it to wake up from power saving mode?

I'd really appreciate some help guys!

 

[wattmatters]

I have pretty much the exact same inverter in an off-grid set up.

Mine is for house backup power and runs the pool pump. I noted when the inverter is in power saving mode and the pool pump controller is in idle mode (i.e. the pump is not running) it would show an error on the pump controller display, which I interpreted as a low voltage error or something similar.

In any case the pump controller didn't like the supply with the inverter in energy saver mode. So I just leave the inverter in normal mode.

Mine doesn't do much overnight, AC loads are ~10W give or take (pool pump controller + a Raspberry Pi) plus whatever the inverter needs. It's rated to draw 45W but hard to say how much it actually draws.

As to getting hot, mine barely gets warm. It has an internal temperature sensor. This is the temp reading over the past 24 hours and past 7 days:




Indeed it's cool enough on top that I leave the Raspberry Pi sitting on top of the inverter without qualm.

 

[Kamis]

I'm going to test my plan this weekend unless someone points out it's a bad idea. I'd really appreciate If anybody could comment weather my diagram will work as planned or not. Or is the circuit somehow unsafe, for example is it going to cause a short or something?

 

[Doug]

If I were considering this, I would be careful about the grounding of the inverter compared to the charger. What happens if the inverter is positive ground and the charger is negative ground, or vise-versa, or some other difference between the devices resulting in a difference in ground? Perhaps an isolated inverter or charger would solve this issue, if these items are available. Perhaps an isolated 1:1 transformer before the charger, or an isolated DC-DC converter after the charger would break any grounding loops. At the moment you have a loop through the inverter and charger and I don't know what this would do. It would be highly dependent on the devices involved. If you do wish to try a smoke test, at the very least you should have multiple fast acting fuses at multiple points through the loop and you should monitor currents and relative voltages and ensure that they're as expected. I would not be surprised if you blew up something with this test, so be prepared for that and don't expect the fuses to save your equipment, though they may stop a fire. If you're on a budget and can't afford to replace your equipment, don't do it!

I see you're trying to load the inverter so that it remains on and available for other loads without a waste load. The simplest option is a somewhat useful load, a light, a heater etc that is productive for your situation and get more solar or whatever input to cover that load.

Another option is to get a second battery, charge that through the inverter and then disconnect it, and reconnect it using a DC-DC charger to return (some of) that energy back to your main battery, then cycle this. If you did this, I would recommend a multi-pole (i.e. switch + and -) 1-off-2 or 1-2 switch (must be break-before-make) that ensures that the charger from the inverter or DC-DC converter cannot be connected at the same time and save you manually transferring cables (such a repetitive action could one-day result in a careless mistake). A switch on a timer would do it automatically. I don't know if the recovered energy after conversion losses would be worth this effort for manual switching or cost for automatic switching. A side benefit is that you would have a second battery which could be used as a backup should there be an issue with the first battery.

For anything other than the simple load & increased supply option above - this would become a complex system and could be hazardous to others if they didn't understand the connections before tinkering with it, or a careless mistake as mentioned already. Interlocks to prevent mistakes can help, knowing that they further increase complexity. Is it worth it?

 

[Kamis]

Thank you Doug for very good points. Some kind of loop / short circuit was exactly what I was afraid of, but couldn't quite figure out myself (and still can't) how the circuit would behave in practise.

I guess I will have to settle for some kind of timer switch that will operate some kind of dummy load although I really can't think of anything useful right now.

The second battery option sounds interesting but you are right, it could result in over complications and possibilities of user errors.