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Ridiculous cooling design of Axpert clone inverter


Gerald_D

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I am new to Axpert (clone), but not new to inverters and chargers in general. Yesterday I connected a Must PV1800 3kW 24V and had a chance to observe this thing in action. There are 2 fans at the bottom, big one and small one - they blow air out, downwards. The air inlets, both sides of case are near the top - 290 punched holes, each 3mm diameter. The internal heatsinks are oriented for vertical airflow.

1. Natural convection on a wall mounted system is upwards - the fans fight this and pull air downwards. Why not make the fans suck in at the bottom and blow out the top?

2. the 290 punched holes have less cross-section area than the fans - they are a restriction. Needs more or bigger holes. (small holes have edge throttling effects on their sharp corners too)

3. Both fans do not run together. Often they run independently. When only one fan runs, the easiest inflow of air is through the fan that is not running - this air bypasses the heatsinks! Once this thing is out of warranty I will force both fans to run together (and increase the intake at the top). Probably also turn the fans over and reverse the airflow to go upwards. Might get away with then reducing the fan speeds and the noise.

4. The wiring connections are high off the wall and right next to the fan - how does one do a neat trunked installation without obstructing the airflow?

 

Okay I am just blowing off steam after a frustrating day, sorry. (another ridiculous asian thermal design is the very popular DALY BMS for lithium batteries - two fake plastic fans on top acting as a blanket on the aluminium case!)

WhatsApp Image 2022-09-28 at 15.34.31.jpeg

WhatsApp Image 2022-09-28 at 15.34.30.jpeg

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22 minutes ago, Gerald_D said:

The air inlets, both sides of case are near the top - 290 punched holes, each 3mm diameter. The internal heatsinks are oriented for vertical airflow.

They copied the Axpert design perfectly. Bug compatible!

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1. Natural convection on a wall mounted system is upwards - the fans fight this and pull air downwards. Why not make the fans suck in at the bottom and blow out the top?

Why indeed. I reversed the fans in mine.
 

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2. the 290 punched holes have less cross-section area than the fans - they are a restriction. Needs more or bigger holes. (small holes have edge throttling effects on their sharp corners too)

This contributes to the Axperts staying hot. And the capacitors aren't rated for long life. I'm told that the clone capacitors are even worse. I replaced the critical ones in mine with long life capacitors; 5000h from memory. Originals were 2000h.
 

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3. Both fans do not run together.

Oh. That's an "improvement" over the original design. I agree that it makes things worse.
 

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4. The wiring connections are high off the wall and right next to the fan - how does one do a neat trunked installation without obstructing the airflow?

You put the inverter(s) in a box that has good ventilation. Trunking comes neatly out of the outer box. Yes, it's a major pain, and probably doesn't make sense for a indoor install.

Edited by Coulomb
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It is amazing that the extremely simple concept of convection and "hot air rises" seems to be missed...
I used to have an Infinisolar that originally had dual fans at the bottom, thankfully blowing up, but when the inverter when in for repairs and to have the fans replaced I got the unit back with the fans blowing down, as in yours @Gerald_D, and were also significantly lower air flow capacity. When I complained I was told they were the same as the original spec fans and also installed as per the original manufacturer instructions (yeah right). I immediately turned the fans over but due to the much lower air flow the inverter still tended to get pretty hot so I made a box to fit the top of the inverter and added 2 higher powered fans in that box and setup a smart switch with a temperature probe to turn the top fans on/of at defined temperatures. It solved my hot inverter issue but certainly wouldn't really want that on a new installation, wasn't very pretty...

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The most ridiculous part of the design is having 2 fans side-by-side and only running one at a time. With a 1kW load, the small fan runs continuously, the big one is idle. Testing with piece of thin paper it can be seen that most of the inlet air is coming from the idle fan, not from the top inlets. Thus the heatsinks are bypassed. On top of that, some of the warm air coming out the small fan goes back into the idle big fan. When Utility is charging the battery, only the big fan runs, sucking a lot of its air in through the idle small fan. At a 2.4kW load, both fans are running. I am happier to run the inverter at 2.4KW rather than 1kW.

I am trying to think of a discreet fix to get both fans to run together, but mechanical engineering is my field, not electronics. Any suggestions? 

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Thanks for sharing this.

I have a similar MUST model (PH1800). I will probably reverse the fans too.

Just wondering if you found a solution to Ground-neutral bonding with your MUST inverter ? I still haven't installed mine because I'm having a hard time finding a solution for when grid is up but inverter is working off battery/solar.

 

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  • 1 month later...
9 hours ago, jeddles said:

is it possible to reverse the fans without breaking the warranty?

You have to open the case (take off the front cover), and that usually means cutting a sticker that has the manufacturing date on it. It's then pretty obvious that your passion fingers have been in there.

So: no, not really.

But once you do that, take out the serial comms board (if present, designs vary) and you can swap the fans without taking out the main board. Fan Rectification.

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  • 10 months later...
2 hours ago, Coulomb said:

I would say so. There has to be a limit obviously, but I doubt that the power supply is that close to its limit.

Ok, so I infer the PWM driver is not the power carrying function. The 12VDC supply is? Meaning the PWM input to the fan is just a logic/control function, and its driver current capability does not matter? 

Edited by BritishRacingGreen
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  • 8 months later...
On 2022/09/28 at 5:06 PM, Coulomb said:

This contributes to the Axperts staying hot. And the capacitors aren't rated for long life. I'm told that the clone capacitors are even worse. I replaced the critical ones in mine with long life capacitors; 5000h from memory. Originals were 2000h.

Hi @Coulomb

Some of the forum posts, including yours, have inspired me to replace the capacitors in my inverter once the warranty runs out. Also, thanks for sharing the service manual.

When you refer to the critical capacitors, which ones are you referring to? Would it be the DC-AC ones, or the ones close to the MOSFETs? 

 

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11 hours ago, Logic said:

When you refer to the critical capacitors, which ones are you referring to? Would it be the DC-AC ones, or the ones close to the MOSFETs? 

The ones near the MOSFETs (rated at a bit above battery voltage, e.g. 63V) are the most important, since they protect the MOSFETs from ringing due to unavoidable wiring inductance. 

The bus capacitors don't seem to be as critical, as the IGBTs seem to be tougher, and the voltage margin is higher. Also, the supplied capacitors seem reasonable in quality, and are also rather expensive. 

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On 2024/06/25 at 3:48 AM, Coulomb said:

The ones near the MOSFETs (rated at a bit above battery voltage, e.g. 63V) are the most important, since they protect the MOSFETs from ringing due to unavoidable wiring inductance. 

The bus capacitors don't seem to be as critical, as the IGBTs seem to be tougher, and the voltage margin is higher. Also, the supplied capacitors seem reasonable in quality, and are also rather expensive. 

Thanks @Coulomb
I appreciate your advice. I'm glad to hear not all of the capacitors are not seen as bad/problematic.
I'll plan for upgrading the capacitors by the MOSFETs once the warranty runs out. If it was your unit, would you just upgrade those capacitors or the MOSFETs (or anything else) as well?

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5 hours ago, Logic said:

If it was your unit, would you just upgrade those capacitors or the MOSFETs (or anything else) as well?

I have had those capacitors and the MOSFETs upgraded on both of my units.

Now that the MOSFETs have a higher voltage rating, I probably would not not update them now. But those capacitors, yes.

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3 minutes ago, Coulomb said:

I have had those capacitors and the MOSFETs upgraded on both of my units.

Now that the MOSFETs have a higher voltage rating, I probably would not not update them now. But those capacitors, yes.

Thanks!

When you say now that the MOSFETs have a higher voltage rating, are you referring to your units or the newer Axpert inverters that are sold?
So, I'll plan to replace the capacitors, and if the MOSFETs don't have much headroom above the battery's maximum voltage, I'll upgrade them as well.

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2 minutes ago, Logic said:

When you say now that the MOSFETs have a higher voltage rating, are you referring to your units or the newer Axpert inverters that are sold?

Both. Mine are so old that they were before the "64 V mania", and came with 75 V MOSFETs. With the higher maximum battery voltage (they don't all go to 64 V any more, but way higher than my 58.4 V), they started using 80 V MOSFETs, I believe. All new models seem to come with 80 V MOSFETs now, though I'm not sure what the fatter MOSFETs are rated at. Now the schematics are loading very slowly, so I can't check.

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35 minutes ago, Coulomb said:

Both. Mine are so old that they were before the "64 V mania", and came with 75 V MOSFETs. With the higher maximum battery voltage (they don't all go to 64 V any more, but way higher than my 58.4 V), they started using 80 V MOSFETs, I believe. All new models seem to come with 80 V MOSFETs now, though I'm not sure what the fatter MOSFETs are rated at. Now the schematics are loading very slowly, so I can't check.

Thanks, glad to hear it's better with the newer units. Depending on the price, it might be a good idea to just go ahead and replace it anyways. But I'll leave that for when the warranty expires.

On another topic, did your inverter come with the dust filters? If it did, did you move them to the bottom when you changed the direction of the fans?

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I don't know if a friend advised you to reverse the fans to push the air up But it may be a good idea to place two additional fans at the upper openings to expel hot air out Yes, there will be double the noise But you can use a thermal control chip that speeds up or slows down the fans depending on the temperature and not as designed for loads above two kilowatts.

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