Trouble with a Chinese 4000W "pure sine wave" Inverter.  - Page 1
Forum section: electronics / general

author: Fflint
author_rank: Frequent Contributor
timestamp: February 21, 2022, 09:30:55 am
content: A while ago I bought a Chinese 4kW "pure sine wave" Inverter for my DIY emergency house power system. I'm in the process of installing PV, but for the time being main energy source is a gas generator that charges 320Ah (12V) lead acid battery bank (via a 1200W charger-ex-computer-PSU).The inverter is used to provide nice clean power to all the electronic devices including led lighting in the house. The battery capacity is sufficient to run half a day without charging and the intended use is only few times per year when a tree lands on my power supply line so lead acid is perfectly fine (as 99% of the time it sits at full charge).However, the inverter seems to measure the battery voltage wrong. The measurement depends on the current draw. At almost zero current draw it measures 0.3V under. At 100A it is almost 1V under! (I'm using short 25mm sq. cables so it is not a drop on the cables). Consequently the battery low voltage cutt off activates too soon. There are no user changeable settings outside on this inverter.So I'm looking for anyone that may have a schematic for this inverter as it is a very popular model sold under many names. It looks like this:My model is 4kW, but they are all very similar. Alternatively perhaps you've experienced a similar issue with an inverter and you would like to share your experience?Also for the curious below I show a difference how the AC waveform looks from my cheap gas generator and from this inverter (both with about 1kW loads).The generator:The inverter:

author: nctnico
author_rank: Super Contributor
timestamp: February 21, 2022, 11:05:28 am
content: Likely there is some voltage drop across the fuses inside (I assume you have measured the actual voltage drop over the cables?). However, for prolonged battery life it would be better to add an extra battery in parallel if you need to get longer runtimes.

author: Fflint
author_rank: Frequent Contributor
timestamp: February 21, 2022, 11:46:10 am
content: Quote from: nctnico on February 21, 2022, 11:05:28 amI don't think adding an extra battery would help. My power bank is massively oversized for what I need as is. I'm really just using the top 5%~10% of it with this inverter :-(The inverter cuts off at around 11.6V when >150Amps are drawn. The load only lasts for 2 minutes or so (a well pump) and then it is off for over an hour. If the inverter really cut off at 10.5 that would be ideal as I plan to run those batteries down to 12.0V (no load). The battery bank internal resistance is such that it drops about 1V per 150A or so. So even when the batteries are 90% full (12.6V) a well pump starts. The voltage drops to 11.6V under heavy load, but the inverter sees 10.6. The pump runs a minute or so, battery bank drops 0.1V and the inverter cuts all the power due to low voltage cutt off. I have to run to an outside building to power cycle it. By the time I get there the battery voltage has recovered to 12.6. After I power cycle it. The pump continues. The actual voltage is about 11.8 while the inverter sees 10.8V.It is a completely silly design if there is 60 miliohms of extra resistance there by design, but it seems it is. If the voltage meter was simply uncalibrated the current consumption wouldn't matter. It would always read some amount off.I'm not sure there are fuses inside (I would hope so!). I did measure the drop on the cables and it is below my meter's sensitivity even at over 100A (measured with a heater).If there are fuses there they should be rated at over 300A. Perhaps whatever holds them is corroded? I have to look inside that inverter at some point.I contacted the seller asking for a schematic, but I'm not holding my breath.60miliOhms is a lot of resistance. Could it happen as a result of a bad solder joint? All bad solder joints I saw before simply didn't work. Also, whatever causes this resistance should heat up. There is over 100W of heating if there is 1V at over 100A. If it was a bad solder joint it should be burned and it should be clearly visible (I hope). However, there is no burning smell at all. It seems to work fine minus the bad voltage measurement.

author: nctnico
author_rank: Super Contributor
timestamp: February 21, 2022, 02:01:43 pm
content: So basically your problem is when the load peaks.Maybe you can open up the inverter to see if there is a problem in there. Still I think that drawing so much current from a lead-acid battery isn't a good idea. As you already experienced, the internal resistance makes the voltage drop a lot. Adding extra batteries can lower the total internal resistance from the batteries though but I agree these things don't grow from trees and cost serious money.A long time ago I put a 2kW inverter in the booth of a car with 25mm^2 wires running to it (4 meters or so) to power a bunch of computers. I had a bigger battery and bigger alternator mounted in that car. Nevertheless, when running stationary (waiting for a traffic light) the inverter would cut out every now and then. However, I designed this system to run from mains and only have the inverter on while the engine is running so I had already included a UPS to bridge the periods without mains. So the system could already deal with the inverter dropping out.All in all, if you can't get the voltage drop fixed, a better approach would be to go for a 24V DC or 48V DC setup. That will reduce your voltage drop by half or even by 4. Although 48V can become tricky to switch due to arcing.

author: Fflint
author_rank: Frequent Contributor
timestamp: February 21, 2022, 02:34:58 pm
content: Quote from: nctnico on February 21, 2022, 02:01:43 pmThanks for advice. This system was built to be "as cheap as possible" with hope it will never actually need to be used. Alas, a bunch of trees landed on my supply line and I got an estimate from the power company they'll fix it not in the usual couple of hours, but in a week. So long enough to be inconvenient, but not long enough to be getting new batteries etc.Regarding drawing 150A out of lead acid batteries. Perhaps you're thinking about car batteries. These are not those. I have 4 tractor batteries (6V) 160Ah, 1200 CCA each. So basically a bank of 320AH rated at 2400CCA. 200A is peanuts for that battery bank. I would love to be able to go with 48V system (mainly because I have lots of 48V devices already), but those tractor batteries were the ones I had on hand. Also I bought the 12V inverter long time ago so that's what I'm stuck with for better or worse.If those power cuts will keep happening with some frequency I'll have to reassess.I've done few measurements inside. Unfortunately all my meters are not that great when it comes to measuring single miliohms, but I attached a load that drew ~150A of current and I measured the voltage drop.I measured a total of 0.6V per side (+/-) so 1.2V total. This was measured where the voltage meter is mounted. In addition to the drop the meter has an error of approximately 0.25V, but it is just the displayed value. The cutoff seems to be affected only by the voltage drop.Out of that 0.6V per side over half (0.35) happens before the voltage enters the inverter. ~0.2V happens on connectors. I think the cables and clamps are responsible for approximately 0.15V.Then inside the device there are 6 40A automotive fuses. I'm surprised they used only 240A fuses. Those fuse sockets are crimped so tight it is impossible to remove them without damage. Still, I measured only ~0.1/0.15 there. And remaining 0.2 is unknown (I couldn't get to the underside without detaching the radiator.So hopefully over half of this voltage drop is in my control. I can use 50mm.sq. Welding cables which will improve the voltage by up to 0.2V (total). Then I'm not sure what would be the best way to improve the connectors. Perhaps sanding them down will help? Also instead of crimped on eyelets I'll try soldered on.

author: nctnico
author_rank: Super Contributor
timestamp: February 21, 2022, 02:48:45 pm
content: I'd keep the crimped connectors. Soldering usually is worse compared to crimping.

author: jonpaul
author_rank: Super Contributor
timestamp: February 21, 2022, 04:00:30 pm
content: bonjour, just seeing this,4kw from , 12V = 333ASo, looking at the Chinese inverter, I doubt that the conductors, switches, transformer or connections can handle ever 1/2 load at 12VI would use a 24 or 48 V battery, specifically designed for high continous discharge current, and buy a high quality inverter specific for this hard service.You get what you pay forBon chanceJon

author: Fflint
author_rank: Frequent Contributor
timestamp: February 21, 2022, 05:27:31 pm
content: Quote from: nctnico on February 21, 2022, 02:48:45 pmOK, how about brazing? (with brass, not silver)Quote from: jonpaul on February 21, 2022, 04:00:30 pmI haven't posted an inside photo yet, so unless you have a similar model, how can you know it'll not handle half the load :-)When I bought it I tested it with a 2.5kW heater (for up to 5 minutes at a time, swapping batteries and running again). So it can handle more than half of the rated load no problem at all. It didn't get hot, just warm to the touch (it has builtin fans). The fans didn't kick off immediately. Maybe after 30s of 2.5kW. Additionally I used it with this and other heaters to test capacity of some lead acid batteries. I never crossed a 3kW barrier though.I mentioned 6 40A automotive fuses. From my experience such fuses don't blow up immediately after their rated current is reached. They activate at more. I don't know how much more, but I wouldn't be surprised with 150% so that puts the fuses in the ballpark of 333A you mentioned.I took few internal photos. Here they are:Input side:Output side:When I bought it (for slightly over $100) I thought I would be happy if it did 2kW. In this it surpassed my expectations, but I didn't expect it will have a voltage drop and a resulting 11.5V cutoff. Anyway it seems I'm able to get rid of half of that voltage drop so it's fine.I bought a "Chinese 4kW" when in actuality I need ~1.5kW. In fact it is more like 200W most of the time, 500W for a couple of hours and short bursts (up to 2 minutes) of 1kW.So I have no need for actual 4kW.im perfectly happy running high consumption loads such as my electric oven, an inductive hob, microwave, kettle directly off the generator. It is just loads such as computers (laptops), TVS, networking equipment (WiFi etc) and LED lights I need an inverter for.Coming back to 24V/48V system and special batteries... Well, let me say this. In 7 years that I own this property I had a number of power cuts I can count on one hand. The worst one in last few years lasted from midday till late night same day. So under 12h. It is extremely unusual to have a power failure like I'm having now that lasts many days, but I can't complain too much. I have my backup power. Most of my neighbours don't.If I was going to invest in battery power it would be lifepo to better utilise (future) PV produced power. The emergency system is just that. Emergency power, used very rarely, to run essential loads such as a well pump, lighting, laptops, mobile phone chargers etc.And that's just a small section of the medium voltage power line that feeds my area:Yes there aretwotrees on the section of this line, lus a third one cut on the ground.

author: f4eru
author_rank: Super Contributor
timestamp: February 21, 2022, 07:59:48 pm
content: With that huge amount of power, you should really go to 48V or more.For safety, you should probably not go over 48V.The innards of this inverter look like a 500W unit, not more-> put it in the trash, buy a real one, "not from China"

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 21, 2022, 09:12:38 pm
content: Does the internal switch switch the 12V to the controls or is it a logic level signal? If it directly switches 12V, a small boost converter can be added with a lower undervoltage lockout point.The more direct way is to find the voltage sense divider and adjust the values.

author: Fflint
author_rank: Frequent Contributor
timestamp: February 21, 2022, 11:12:06 pm
content: Quote from: f4eru on February 21, 2022, 07:59:48 pmTo the "put it in the trash" I say this is completely bonkers. I can understand the unit is a bit overrated, but "put it in the trash and buy a real inverter" is pretty close to a troll...My grid power is back on. During the 3 days it was off, this "made in China" "looks like 500W" unit and my cheapest possible 4 6V tractor batteries allowed me to run the generator for a tenth of the time I would run it otherwise. I estimate over 3 days I "saved" $114 (yes, gas/petrol is that expensive in Europe, if I run the generator 24/7 it would've cost about $40 per day = $1.4 per liter for 30l). So the inverter paid for itself in savings in its first use.As for "not from China". Good luck getting anything not made in China these days. Most things that make claims like "German made" or "Made in USA" unless they are milspec they will have 90% of their internals "made in China".What huge amount of power? 1kW or 2kW? Huge in comparison with what?Don't look under the hood of your (Ice) car if 1kW at 12V is scary :-) I recently replaced a 200A charging fuse in my car. Yes that's a 200A 12V (14.4 to be exact) charging fuse that was blown like nothing by the alternator. And let's not start talking about hydraulic pumps that run off 12V or AC units that run off 12V. Power is voltage times current. A hundred Watts is a hundred Watts. Regardless if it is 1V times 100A, or 1000V times 0.1A. Sure conductor sizes vary, other things have to be considered, but in the end that's what it is.Using 12V with a couple of kW of power is perfectly reasonable. We're not talking about a system comprised of hundreds of batteries where the increased weight of copper conductors required by low voltage would negatively affect the cost of the system to the point of higher voltage being more cost effective. There is under a meter total 12V wiring here and it doesn't even get warm (currently 25mm.sq, will be replaced with 50mm.sq welding cable).12V lead acid has been a choice in small (few kW) UPS systems for ages, because it is the best choice when all factors including the cost/benefit are considered.To "the innards look like a 500W unit" please do post pictures of a 4000W unit that does in your opinion look like it is indeed 4000W or tell us specifically what in that inverter looks undersized by 4 times in your opinion (I already mentioned fuses are 1.5 times under size).BTW it is a 240V unit. If it was 120V I agree the AC side would have to use much heavier gauge wire and a more robust receptacle. For 240V,a 5cm run of those wires I say this not ideal, but probably fine.There are 12 to-220 and 4 to-247 devices there. There are 1kW to-247 mosfets like IXFH320N10T2 for example that are 100V and 320A each. Just by counting them one can't tell if these are 1000W or 100W devices.Quote from: NiHaoMike on February 21, 2022, 09:12:38 pmYou have to be kidding meHow big of a switch it would have to be to reliably switch over 300a repeatedly? Definitely bigger than one shown :-)This is a microprocessor controlled device. One could find how it measures the source voltage and boost it as you said, but there may be a less invasive method available.It has parameters programmed in. Also there are two buttons inside. Perhaps it is possible to change some settings with those buttons, but before messing with it at this level I was hoping to be able to simply fix the voltage drop. If I can't I would first dump the content of the flash firmware for backup just in case.Just the one seller on Aliexpress I bought the unit from sold almost a thousand of them. I can't be the only one interested in re-programming, upgrading, hacking of those units. Just go buy a $1k unit instead, then spend another $1k on batteries is contrary to what I want to achieve with this hobby :-)Editoh look. It is actually rated at 2kW continuous, 4kW peak.So it is not overrated at all.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 21, 2022, 11:31:11 pm
content: Quote from: Fflint on February 21, 2022, 11:12:06 pmA common configuration is to have the switch control the power to the control circuit, which is a few watts at most.

author: Fflint
author_rank: Frequent Contributor
timestamp: February 21, 2022, 11:42:21 pm
content: Quote from: NiHaoMike on February 21, 2022, 11:31:11 pmI didn't realise that's what you meant. OK, It is likely that's how it is done.

author: f4eru
author_rank: Super Contributor
timestamp: February 22, 2022, 07:59:23 am
content: Quote from: Fflint on February 21, 2022, 11:12:06 pmNo. It is not. It is experience.I have a Friend having exactly the same experience.He went through 5 different inverters from different brands and shapes, all from China.1st inverter : 12V 3kW. Exploded at 1.5kW. repaired the mosfets. exploded again at 1kW.2nd inverter : 12V 5kW. Exploded at 1.5kW. not repairable.3nd inverter : 24V 5kW. Exploded after 2 months. Repaired. Re-exploded after some time.4 and 5 Inverter : similar.Now he's looking for repurposing an old UPS, with quality parts.This should not explode.He learned his lesson, after spending much too much on garbage hardware.QuoteThat is very very very different situation.Typical 200 A currents in a car are only happening for 10s200A for 5 minutes is a very different situation, from the cooling of the wires.200A for 1 hour is another higher ballpark again.Don't expect a system dimensionned (or obviously misdimensionned, like this inverter) for a few seconds to last when in constant use.Each wire must be tripled in section when going to higher duty time.

author: Fflint
author_rank: Frequent Contributor
timestamp: February 22, 2022, 09:09:21 am
content: Quote from: f4eru on February 22, 2022, 07:59:23 amHmm, wow. That's a pretty bad run. 5 bad units one after another...It would be interesting to learn why they exploded? Dodgy, used parts? Bad assembly? Perhaps a dodgy seller selling rejects "fixed" with stripped parts?Mine appears to be fine for now(other than the voltage drop). My elderly parents have another unit (only 1.2kW) they use continously throughout the summer in their summer house. It has been fine too.I can't see any obviously used parts inside, bad hand soldering etc. I'm not particularly happy with use of automotive fuses, but overall my impression of the unit is not bad.What happened then, did the seller honor the warranty and refund your friend? Some dodgy sellers "recycle" returned units hoping someone will not test it for a long time. Perhaps your friend was a victim of such dishonest seller?However, such strings of failures happen to budget manufacturers unfortunately. A good example would be an inductive hob made by a popular brand I bought few years ago. It broke down and was sent to be repaired under the warranty 3 times. Then it was swapped with another unit of slightly different type by the manufacturer and that new unit broke down after 3 months. I didn't even go through warranty again I simply bought a different brand that has been in continuous use for last 2 years and is still fine.Any assessment of Chinese inverters has to include the price. Buying anything is always a bit of a gamble. Before I bought that particular inverter I checked the sellers feedback and internal photos one of other buyers posted. I liked what I saw so I bought it.(I can't recommend the seller named as the brand name of my inverter on Aliexpress, because recent comments claim he sells stock he doesn't have).There is also the matter of usage. Those inverters don't have the best cooling. At 2kW continuous my inverter would probably be fine only in low ambient temperatures (below 5C).Anything over and I would recommend additional forced air cooling if one intends to run it at continuous rated power.

author: nctnico
author_rank: Super Contributor
timestamp: February 22, 2022, 11:15:28 am
content: Cooling is a good point. I don't see any fins on the heatsinks at the inside that help the fans moving heat from the MOSFETs. I recon this inverter is about 85% efficient so at 2kW output power you may have around 350W of heat dissipation.

author: Fflint
author_rank: Frequent Contributor
timestamp: February 22, 2022, 01:40:47 pm
content: Quote from: nctnico on February 22, 2022, 11:15:28 amThere aren't any fins, just some shallow serrations, but why such low efficiency estimate? There are published mosfet inverter designs that are 97% efficient. Personally, based on it just getting warm at 2.5kW load (5 minutes) I would estimate its efficiency as definitely better than 90%. Perhaps even 95%. The manufacturer doesn't state it.

author: nctnico
author_rank: Super Contributor
timestamp: February 22, 2022, 01:56:50 pm
content: 85% is typical for a forward converter to boost the voltage. But maybe it uses a more efficient resonant converter design.5 minutes may not be enough to reach the maximum temperature. There is quite a bit of aluminium to heat up. I'd let it run for at least half an hour and then check the temperature.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 23, 2022, 05:59:59 am
content: Interesting case study of typical scam inverter:http://ludens.cl/Electron/chinverter/chinverter.html

author: f4eru
author_rank: Super Contributor
timestamp: February 23, 2022, 10:19:12 am
content: My friend did not have the knowledge to ge this deep in the design, he basically replaced parts, improved thermals, restested, etc...The 5 failed inverters were over the course of several years, some failed quickly enough he could get a refund, but generally a lot of waisted time and money on trash parts.Very interesting findings in this link !Yes, it is really a pity that those things have bad design overall.I think the companies producing them are used to take a reference design, slap it together, outputs something approximately OK, so they ship it.This methodology may often work, but does absolutely not work with inverters. Inverters are very hard to do right.Thermal design, overload behavior and protection, EMC design, safety elements, robustness against load transients, stability, etc....All of those are not covered by a simplistic application note or reference design, and are just critical to a real life device.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 23, 2022, 10:50:47 am
content: They know very well they are selling nonfunctional designs.The mere point of building crap like this is that if they send a brick (or sand-filled casing) instead, customer would definitely claim and win for money back.With a unit which seemingly "works" for a day or two, or even weeks, this is a lot harder for a customer to show.

author: Fflint
author_rank: Frequent Contributor
timestamp: February 23, 2022, 02:31:28 pm
content: Quote from: Siwastaja on February 23, 2022, 05:59:59 amOh my...It has been over 10 years since the above was written so I would hope truly shady companies went out of business and those that at least try making their products better managed to learn something.On Aliexpress there are few ways to cause problems for the seller if they sell crap described as great products. Usually if one reviews comments and reviews one is relatively safe.However, while reading this I was looking at pictures of my inverter and unfortunately some problems raised in this article are still present. Specifically the lack of any fins on the inside of the case where airflow happens. Lack of air inlets. All devices with heatsinks being held in a very dodgy arrangement (see below).Also, no grounding whatsoever (I actually assumed it is by design, for the installer to take care of. I grounded the case and the negative terminal of the battery.)I haven't noticed any increase in radio noise generated by the inverter. I did run a ham radio transceiver on it for an hour or so.There have been some improvements. The filters the author replaced are now equipped with exact same bigger cores he showed (did they read his article?). The single filter capacitor on the high voltage DC side is still a single one, but it is a much better quality one and bigger (220uF, 450V, low ESR).Also the pcb layout differs in some places. Extra capacitors were added on the low side of the dc-dc converter. His inverter has 6 dc-dc sections, mine has 3. I haven't gone that deep into it to check if there is current limiting and balancing on the high voltage DC side. The optocouplers troubles must have been resolved(or masked) , because I've used my inverter for long-ish periods of time and no smoke appeared. The room temperature was quite low at around 5C, but it did get pretty warm to the touch so if the same optocouplers issues were present it should have blown up.At least this article gives me lots of ideas of things to check.Also, I mentioned before my parents have a similar inverter (1200W) and they have been using it whole summer with no issues.So hopefully the situation is much better now than it was in 2009, but I'll not know until I do proper in depth analysis of the inverter.Edit: Does anyone know anything about the quality of other Chinese inverters. For example on-grid transformerless designs etc? They are very popular in Europe.

author: ejeffrey
author_rank: Super Contributor
timestamp: February 24, 2022, 10:13:52 am
content: As far as I know all inexpensive 12 V inverters in that sort of form factor are extremely overrated in the same way as cheap speakers listed as "400 watt PMPO" when it is powered by a 12V 2A power brick. Or a "9 hp" shop vacuum that runs on a 120v/15A circuit.I don't know if there is a different channel to get cheap but honestly rated small inverters. I would be happy to buy that "5000 watt" inverter if it clearly said that it was 2000 watt for 30 seconds, sustained power of 400w or whatever it could actually do. The problem is that there is no real way to verify trustworthyness of ratings.

author: nctnico
author_rank: Super Contributor
timestamp: February 24, 2022, 11:15:14 am
content: Quote from: Fflint on February 23, 2022, 02:31:28 pmActually it is not as bad as you think. Using clamping plates together with silicon rubber is quite common in all kinds of equipment. The rubber can deform a bit as well so mounting isn't that critical.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 24, 2022, 02:12:27 pm
content: The clamping shown is exactly the correct way. You can only clamp two parts, this way, using a single clamping bar, but this is what they do.But it's hard to say if it's done properly. In the link I posted (ludens.cl), the problem was the wrong mounting point, too low, near the bottom part of the transistor case. TO220 requires clamping from quite high up. It's hard to say from the images if there is a gap or not. It's probably fine.

author: Fflint
author_rank: Frequent Contributor
timestamp: February 25, 2022, 12:56:46 pm
content: Ok, so the mounting is probably fine. There is no visible gap. A piece of paper can't be inserted there.

author: Swake
author_rank: Frequent Contributor
timestamp: February 25, 2022, 06:00:06 pm
content: First: 5000W is a model number and probably in no way a reference to the potential power that the device can handle.Second: The first name of Watt in China is certainly not James. No, in fact it is a completely different unit compared to how we know it. So far I haven't been able to find a trustfull description or reference or conversion formula, as it seems there even might be many different bases.