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Blown Inverter (Mecer IVR-1200LBKS 1200VA + Mecer LiFePO4 200AH)


The_Scrutineer
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 Inverter link https://www.comx-computers.co.za/IVR-1200LBKS-specifications-126908.htm

Battery link https://www.communica.co.za/products/batt-12-8v200-li-mcr

 

The short version of this story is 2 year old inverter switched from a single 120AH AGM a single LiFePO4 and the inverter went bang bang and tripped the DV within 10 hours. 

I have 2 questions:
1. Why?
2. Any suggestions on a replacement inverter? This Mecer https://mhn.co.za/shop/mecer-1200va-1000w-12v-w-mppt-inverter/ has "lithium" in the manual https://mhn.co.za/wp-content/uploads/2021/01/Mecer-IVR-1200-2400-MPPTinverter-only.pdf compared to 90% of inverter manuals which dont say anything specfic about lithium.

=========================

The Details
- Mercer IVR-1200 purchased together with a SoSolar 120AH battery in Jan 2019. 
- Setup was Mains plug into Ellies surge protector into the inverter. Load usually 150W flatscreen plus 180W laptop plus sundry (cellphone charger, LTE modem etc).   
- Run time went from 2 hours to less than 30 minutes and the decision was to upgrade to more AH. Initial choice was an AGM but the higher cycle life of a Lithium battery was too tempting to pass on.

Given the heat/fire issues with the LiFE battery I was super paranoid about it catching fire.

- Hooked up the LiFe battery.
- No issues (as in the various components were tested for heating via touch ie cables, battery terminals, the sides and top of the battery).
- Charged it up. No issues
- Switched off mains to test discharge and duration. After 4 hours the inverter was indicating remaining charge as somewhere above 75%. 
- Switched mains back on. Battery recharged in about 1 1/2 hours. Happy days. 

- Roughly 30 minutes after recharging completed, there was a bang and the plug phase tripped on the DV board. 
- On return and inspection there was a burning smell in the room.
- Checked the battery, cable, terminals, 240V AC running into and away from the inverter.
- Everything in order.
- Eventually touched the top of the inverter. It was very warm. Sniff sniff at fan exit vent. Very strong burning smell.  

- Reconnected the inverter to mains and switched on. No drama. Plug phase on DV board trips.
- Conclusion? RIP inverter

- No idea if the battery was affected as I do not have a tester (or 2 wires and a 12V lightbulb)

Worth noting that 
- despite the inverter having a variety of alarms, none of them triggered
- the surge protector on the mains didn't blow and is working
- nothing on the load side of the inverter blew (flat screen TV, laptop, hard drive, cellphone chargers etc)
- The battery comes with screw in bolts and washers.  The washers were placed between the cable lug and the bolt and not between the cable lugs and the battery terminals

 

Other Details
There is some "minor" stuff including:

The inverter is supplied with cables. The lugs on the cables are asymmetrical so I think its M5 for the inverter end and M8 for the battery end. This was not noticed until yesterday when the battery bolt was too big for the lug on the live terminal.  I elected to get around this by screwing on the bolt and using the washer and battery terminal to grip the cable lug on the assumption that any issues with flow of current would result in heating.
Later on when measuring the lugs and bolts to order a replacement cable I noticed the lug on the negative terminal was big enough for the bolt and then realised its small lugs for the inverter and big lugs for the battery.  I switched everything around, reconnected and later everything went bang bang.

Washers. For reasons I dont recall and possibly ignorance on purchase I placed the washers on the inverter end of the cable between the lug and the terminal.  This is incorrect but doesn't seem to have been a problem.  When switching around the battery cables yesterday, I switched the order to bolt, washer, lug, inverter.

Cable connection from inverter to battery  was both cables running down from the inverter. After swapping around the lugs for the live cable I switched to have both cables running up, over and down to the battery

 

Edited by The_Scrutineer
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5 hours ago, 87 Dream said:

The only way to know is to open up the said blown inverter & take some pics as evidence. Pretty sure you will find the problem immediately & actually you might be able to bring it back to life. Where are you based?

87

This is the inverter that blew up. No real signs of damage but something went wrong.

IMG_20210617_092617.jpg

IMG_20210617_093917 (1).jpg

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2 minutes ago, The_Scrutineer said:

This is the inverter that blew up. No real signs of damage but something went wrong.

IMG_20210617_092617.jpg

IMG_20210617_093917 (1).jpg

 

These kind of UPS style inverter/chargers have a limit on battery size. I have a Mecer UPS that I tried to hook up to 2x 200Ah batteries in parallel and it luckily beeped and shut itself down when I tried to switch it on.

My guess is the lithium battery you put on there blew the protection circuit or caused a short somewhere else. These "old school" units weren't built for that kind of discharge capacity.

The new one you are eyeing out will be fine, as it specifically mentions lithium in the manual.

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2 hours ago, tetrasection said:

These kind of UPS style inverter/chargers have a limit on battery size.

My understanding is that the inverter has no idea how big your battery is. All it sees is the voltage between the terminals and all it can do is apply load and pull current. As long as the battery supplies that, it doesn't mind what the source is. Differences in batteries are far more applicable when it comes to charging voltages and currents. But this is generally to the detriment of the battery, such as charging too slowly for a large capacity battery or over charging if the charge voltage is too high.

Something that could have happened here is one of the cells in the battery went high and the battery BMS disconnected it. Inverter might have taken exception to that and popped a fuse or something worse. Sounds like the damage occurred when the battery was close to or fully charged? Unfortunately the loud bang and smell of burning don't give me much hope it's the fuse....

There are many examples of people running these inverters with these Mecer lithium replacements with no problems (mybb forum has lots, my brother has been running a very old 24V for a few weeks), so I think you either got unlucky or something else has happened.

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4 minutes ago, JaseZA said:

My understanding is that the inverter has no idea how big your battery is. All it sees is the voltage between the terminals and all it can do is apply load and pull current. As long as the battery supplies that, it doesn't mind what the source is. Differences in batteries are far more applicable when it comes to charging voltages and currents. But this is generally to the detriment of the battery, such as charging too slowly for a large capacity battery or over charging if the charge voltage is too high.

You can't connect 2000Amps to a 700w inverter. There is definitely a current limit. And if that current is beyond it's overcurrent protection range it will blow or blow a fuse.

Like I said, the UPS I have will take a single battery but not 2 batteries in parallel. Luckily that was still in the range where it could still beep and turn off. If I had connected 16 batteries in parallel it would have been toast.

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1 minute ago, tetrasection said:

You can't connect 2000Amps to a 700w inverter.

The thing is the inverter controls the current. It determines the load, not the battery. Plus, most normal deep cycle LA battery can deliver in excess of 1000A in a dead short anyway. 

I have no idea why your UPS doesn't like 2 batteries in parallel. If they are well matched it should just see it as a single larger battery.

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4 minutes ago, tetrasection said:

You can't connect 2000Amps to a 700w inverter. There is definitely a current limit. And if that current is beyond it's overcurrent protection range it will blow or blow a fuse.

This is determined by your load not the battery size. Batteries do not request current, they will just sink or source it.

 

3 hours ago, The_Scrutineer said:

This is the inverter that blew up. No real signs of damage but something went wrong.

IMG_20210617_092617.jpg

IMG_20210617_093917 (1).jpg

Are you able to check the mosfets on the heat sinks and the MOV? The MCB tripping means that something is short circuited and this is normally the incoming MOV or a mosfet bank. MOVs age with each over voltage event they experience so it's possible this one has just reached the end of it's life. If it's the mosfets look for cracking on the case of each mosfet, you will need to take them out of circuit to test properly if you don't see anything visually.

For the MOV test the resistance between it's legs. It should be open circuit.

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17 minutes ago, JaseZA said:

The thing is the inverter controls the current. It determines the load, not the battery. Plus, most normal deep cycle LA battery can deliver in excess of 1000A in a dead short anyway. 

I have no idea why your UPS doesn't like 2 batteries in parallel. If they are well matched it should just see it as a single larger battery.

 

I'm guessing it's got to do with inrush current?

Quote

A large inrush current can cause the following:

Damage to input filter capacitors
Blow out of the main fuse
Contact failure (and reduction in current carrying capacity) due to arcing and pitting

 

Edited by tetrasection
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On 2021/06/17 at 10:13 AM, 87 Dream said:

Wow, she still looks in good shape. If you have a multimeter can't you see if there is still voltage on the battery terminals? Where are you based I know a repair centre to that can assist but only if you in Gauteng close to Randburg. If you elsewhere then I guess some closer self inspection of the unit might be needed.

87

The multimeter arrived 13.29 volts on the LiFEPO4 battery. Tried to measure amps and there was sparkles so I assume I am not supposed to do that.

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A conceptual question

So far every manual I have looked at does not say "do not connect more than x AH battery to this inverter"

1.2KVA divided by 12 volts = 100amps. Does this therefore mean the max battery that can be attached is 100AH?  If multiple batteries are attached in parallel would you not then have 200AH to consume, with only 100AH of ... I dont know the correct term... so will say electrical pressure

So as a thought experiment,  if you have 2 x 100 liter JoJo tanks raised 2m off the ground. Each has a pipe and the two pipes run to ground level and are joined and fed into a tap

Alternatively you have 1 x 200 litre JoJo tank, raised 2m off the ground. It also has a pipe running to a tap at ground level

Would the 200 litre tank not create twice gravity fed pressure vs the 2 x 100 litre tanks?

(logic being if F= ma where Mass is the water and 
acceleration is gravity, with the 2 x 100 litre tanks its 100kg x 1G whereas a single tank is 200kgs x 1G. 

Replace water with batteries and the tap with an inverter and conceptually an inverter has to hold back twice the electrical pressure with a 200AH battery than with 2x 100AH batteries)?

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36 minutes ago, The_Scrutineer said:

Tried to measure amps and there was sparkles so I assume I am not supposed to do that.

Definitely don't do that - most multimeters are only rated to 10A. If you just connect it across the battery terminals it will short the battery, allowing VERY large currents and popping the multimeter fuse.

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35 minutes ago, The_Scrutineer said:

So as a thought experiment,  if you have 2 x 100 liter

Looking at electricity like water flow actually works very well. Pressure=Voltage, Flow=Current.

Batteries in parallel are like two 100L tanks sitting next to each other, 2m above the ground. The pressure is the same at the tap except you can now allow twice as much water to flow out before it's empty (200L vs 100L). You also have two taps so your flow rate can be twice as high.

Batteries in series is like having both 100L tanks at 4m but only having a single pipe! So now your pressure is doubled, you have the same quantity of water (200L) but you're trying to push that through a single tap, so you have reduced flow rate.

This analogy isn't perfect though - in theory they're very thin tanks so the pressure doesn't drop very much as you drain them. 

43 minutes ago, The_Scrutineer said:

(logic being if F= ma where Mass is the water and acceleration is gravity, with the 2 x 100 litre tanks its 100kg x 1G whereas a single tank is 200kgs x 1G. 

Hmm, right thinking but there is an actual formula for this: P = Rho x G x H where P=Pressure, Rho=density, G=Acceleration due to Gravity and H=Height. As you can see, there is no mass - this is because pressure isn't changed by how much water, just how high it is above the ground. 

48 minutes ago, The_Scrutineer said:

If multiple batteries are attached in parallel would you not then have 200AH to consume, with only 100AH of ... I dont know the correct term... so will say electrical pressure

So Ah (Amp-Hours) is a measure of energy quantity. Basically it's how many amps can be delivered for an hour. 100Ah = 100A for an hour. Adding more batteries increases the total energy. 

 

Sorry, this turned into a lesson far more quickly than I imagined! Hopefully it's a little bit helpful. I'm also sure there are much more qualified people here to explain this! Hopefully they'll correct anything I've gotten horribly wrong.

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21 hours ago, tetrasection said:

I'm guessing it's got to do with inrush current?

Sorry, missed your reply! As far as I know, in-rush current is the initial current the inverter pulls to fill the capacitors. In theory capacitors can fill at incredibly high currents so if there is nothing to slow the rate down, it can damage the inverter. It's why it is always advisable to connect your batteries via a resistor (can be a light blub) the first time to slowly charge the capacitors. Again, 100ah vs 200ah batteries both have very high short circuit currents versus the safe current for the inverter, so I'm not sure it would make a difference.

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1 hour ago, JaseZA said:

Sorry, missed your reply! As far as I know, in-rush current is the initial current the inverter pulls to fill the capacitors. In theory capacitors can fill at incredibly high currents so if there is nothing to slow the rate down, it can damage the inverter. It's why it is always advisable to connect your batteries via a resistor (can be a light blub) the first time to slowly charge the capacitors. Again, 100ah vs 200ah batteries both have very high short circuit currents versus the safe current for the inverter, so I'm not sure it would make a difference.

Perhaps the lithium battery provides the current more instantly, like a brick wall rather than a wave?

I've seen posts about people blowing their inverters with lithium batteries but never with LA?

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1 hour ago, 87 Dream said:

At least your battery is still in working order. So not all is lost.

Did you manage to check the fuses I mentioned earlier the 5 X 40A ones under the plastic shield material?

87

Combination of the tight component packaging and unable to remove the plastic shield means I couldn't get to the fuses. Also unable to see any signs of scorching.

There is a DC current of about 1.16V across the  inverter DC terminals which would imply that not all the fuses are blown (I think)

Edited by The_Scrutineer
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1 hour ago, JaseZA said:

Looking at electricity like water flow actually works very well. Pressure=Voltage, Flow=Current.

Batteries in parallel are like two 100L tanks sitting next to each other, 2m above the ground. The pressure is the same at the tap except you can now allow twice as much water to flow out before it's empty (200L vs 100L). You also have two taps so your flow rate can be twice as high.

Batteries in series is like having both 100L tanks at 4m but only having a single pipe! So now your pressure is doubled, you have the same quantity of water (200L) but you're trying to push that through a single tap, so you have reduced flow rate.

This analogy isn't perfect though - in theory they're very thin tanks so the pressure doesn't drop very much as you drain them. 

Hmm, right thinking but there is an actual formula for this: P = Rho x G x H where P=Pressure, Rho=density, G=Acceleration due to Gravity and H=Height. As you can see, there is no mass - this is because pressure isn't changed by how much water, just how high it is above the ground. 

So Ah (Amp-Hours) is a measure of energy quantity. Basically it's how many amps can be delivered for an hour. 100Ah = 100A for an hour. Adding more batteries increases the total energy. 

 

Sorry, this turned into a lesson far more quickly than I imagined! Hopefully it's a little bit helpful. I'm also sure there are much more qualified people here to explain this! Hopefully they'll correct anything I've gotten horribly wrong.

Thank you for this. No stress on the lesson, its good to pick things up as I go along.

So basically from the above, the flow rate for 1 x 200AH battery versus 2 x 100AH batteries is practically identical?  

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44 minutes ago, 87 Dream said:

Unless you can reach these I think you will always have your doubts.

What is your plan if action with this unit? Will you try to repair or will you look to upgrade? I have never owned this very small type of inverter Model but was always inquisitive on their quality & longevity. How long have you had this unit & how close to its design limits did you run it? 

87

Back in the day I had a workshop made 1000W inverter that was very heavy and robust with no fan cooling.  No issues with that one. Never blew, never overloaded. Lacked info. It was either on or off 😂

The Mecer is decent enough. I wasn't in the room when things went wrong so until an electrician takes a look that will be a mystery. Will have it repaired at some point and use as a backup.

Pros
- It has a range of alarms which appear to work
- I am super impressed that it did not damage anything on the input or output leg when it blew
- During operation battery charge and % Load is displayed in 25% increments. I have mixed feelings about this because readings would change depending on load. So a given higher load may reflect 25%. Reduce the load and the battery capacity would increase to 50% so its more of a hybird percentage of fully charged running time available sort of thing. In some ways this is handy. At the same time its difficult to judge depth of discharge or battery condition
- It seems to handle device start up power draw quite well. I suspect that it can handle 1000W - 1500W. In my experience when a high load is added to a running inverter there is a momentary change in the buzzing sound. This inverter didn't seem to have it
- Grid to Inverter change over is as fast as it needs to be
- It displays AC in and AC out digitally in volts. This is handy in terms of measuring the state of the grid connection. There will be times when its running 240V+ and others where its running below 230V which is usually a good sign that our substation is about to trip
- It charged the Lithium battery to what based on voltage looks like 90% which is decent enough considering the 1.2V? difference in voltage between LA and LiFEPO4.  

Cons
- The fan runs in inverter mode. Fan noise is an irritation
- When charging the fan runs faster. Bigger irritation
- Fan is loudest when charging at 20A. This is preferable to what can be long charging periods at 10A
- The on/off function is a button and not a switch. For me this is a big irritation and design flaw when working on the cables. Its very easy to bump it and I still have PTSD from the spark when I reconnected the battery!

Overall? I dunno, I would give it a 7.5/10. Downsides being the noise and the lack of indicators for battery health. Overall I am starting to think Mecer is a little underrated. Have used a variety of Mecer devices over the years. They may not be best of breed, however from a value (utility vs cost) perspective I have no issue and say we should look to buy "local" more often.  The sticker says "made in China" which is a bit disappointing.

There is a decent review video on YouTube (not by me) 


 

Edited by The_Scrutineer
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