IPM Failures

[icecap]

Anybody else out there having 'IPM' failures, on DC inverter heat pumps, due to voltage surges?

If yes, how have you resolved this issue?

Looking forward to some feedback!

Icecap:(

[paul_h]

Can't say I've had an IPM failure due to power surges. The one's I work on filter the AC voltage, run it through a diode bridge to get DC, then filter it again, so power surges don't normally affect IPMs. I've even had condenser fans on the same filtered DC voltage short out, and that doesn't affect IPMs, so I can't see how a mains AC surge would. A mains surge would blow the main AC filter board first if it's bad enough to affect a IPM thats filtered at the end of the line on the DC circuit
The only things I've seen blow IPMs are dodgy compressors, overheating, faulty IPMs or the local fauna shorting them out. I suppose other faulty components like condenser fans or anything else that runs of the DC circuit could (the active DC filter, IPM signal, other sensors, TX valve, choke coil could as well)
Is the IPM control just dying or are the diodes that feed the compressor shorting out?

[icecap]

I don't think that the diodes are shorting out. The actual fault (my manufacturer informs me) is an open circuit N-W. The manufacturer is giving me 3 possible reasons for the 'IPM' failures: -

1) Overload voltage damage: I haven't checked the compressor but it is a brand new unit and the unit works fine for up to a couple of weeks and then the 'IPM' fails. Surely if the compressor was faulty it wouldn't run for that length of time?

2) Overload current damage: The compressor operates at between 1.5 - 3.5 amps which is well within its limit.

3) Static damage: Can't comment on this one - don't know how it applies?

Could the components be overheating - heatsink problem? The unit is installed in a small server room and is swithed on constantly. Can constant opearation cause problems (obviously the unit will cycle offand on as normal)?

[Thermatech]

In the inverter post you advise computor room aplication.
1/ Does the outdoor unit have 'low ambient fan speed control' ?
2/ Is the system precharged for a set lenght of interconnecting refrigeration pipe ?
3/ Does the system have a indoor unit coil frost prevention function ?
4/ Does the inverter board have any over current protection ?

As the system is cooling 24/7 it will be operating during cool night time outside ambient temperature. If it does not have any low ambient control then it will slug liquid refrigerant back to compressor suction, compressor will over amp & result in possible damage to inverter board especially if it does not have any proper over current protection.
If your system is installed back to back the refrigerant charge may be excessive. On many cheap split systems it is best to remove some charge with very short interconnecting pipe run because they do not have a suction accumulator for excess refrigerant.
Often the computor room will have very low humidity because the system is constantly removing moisture from the air. This will result in the indoor unit coil frosting because almost all standard split systems are not designed for operation in low humidity conditions.
Premium ac split systems will have a coil frost prevention function which will protect the compressor from sluging back liquid which would again cause excessive amps. But the inverter may not be able to cope with constant stop start every few mins due to coil frost prevention. Some times the inverter circuit components are border line & can fail when worked hard.
Computor room aplication makes standard split systems work harder than just about any other aplication.

[icecap]

Hi thermatech, Thanks very much for your views! I will confirm information tomorrow. By the way, I have the same problem with another unit serving a conservatory which is only operated during the day time.

[icecap]

Hi Thermatech,

Sorry for the delay but I've only just received the info from the manufacturer. Here are the answers to your questions: -

1) The outdoor units have low ambient fan speed control.

2) The units are precharged for up to a 7m separation distance but the actual pipe runs are 9m.

3) The indoor units have an indoor coil frost protection function.

4) The inverter board has over-current protection.

I look forward to your views.

Thanks in advance!

[p_p]

Hi Icecap

Who's the manufacturer?




PP

[icecap]

Hi PP,

The manufacturer is Galanz who are one of the top 4 manufacturers in China. They manufacture mainly 'Own brand' products for other companies and their products are distributed all over the world.

I think we have established now that the problem isn't caused by voltage fluctuations as I originally thought. I am due to receive some new PCB's from them early next week with an accessory (not sure what the accessory is) and I will fit and see what happens.

I will update next week!

icecap

[Thermatech]

Manufacturer can do a simple low cost up grade by supplying an extra surge resisitor for fiiting on site.

Sometimes manufactures will sail very close to the wind & base inverter design on 230 - 240 v a/c power supply but we often have 250v a/c & this can push inverter circuit components over the edge when they are already boarder line.

How does the indoor coil frost prevent fuction on this system operate. Does it stop compressor or just slow it down ?

If the unit is stop / start every few mins & 24/7 operation & higher than rated supply voltage then the inverter circuit coponents may be working harder than the manufacturer has allowed for.

Dont forget the units will most likely have been designed for domestic / residential application.

We have seen some far east manufactures claim units have lots of functions but when you actually test system it turns out they do not have those functions at all.
They will hide behind small print. 'specification can change without notification'

Tell us,,,, How much labour allowance is this munufacturer paying for you to do all the return visits to site ???

[frank]

Manufacturer can do a simple low cost up grade by supplying an extra surge resisitor for fiiting on site.

We've just had an Hitachi RAV6 lose the compressor, which we have replaced, and then we found that the PM board was fried, now we find that the control PCB is also fried.

Got one of these Varistors with the new PM board and I hope it works as the customer is starting to think that we don't know what we are doing??:rolleyes:

Hitachi Tech Support just keep us replacing pcb boards after we replace the previous one until we (hopefully) get there.

Is this the modern way of doing it or do we need to become electronic engineers?

As this unit was fitted just over a year ago, do you think we could claim warranty for the compressor, PM board and now the control board, as we are told that " when the PM board fails it can take the control board and the compressor" ??
I'm sure there will be dozens of excuses why they won't honour the warranty - obviously, all of them will be my fault. :D

[icecap]

Hi Thermatech,

If the indoor coil sensor senses a predetermined minimum temperature then after a delay period if the temperature hasn't recovered it will gradually reduce the compressor speed/capacity to lift the evaporating pressure/temperature to acceptable levels. This function works satifactorily as I have spent a lot of time monitoring these systems (operating pressures/temeratures, air on and off temps on indoor and outdoor units, compressor current consumption) etc... They do operate very well generally!

I am having this problem on a conservatory application as well which will only operate during the day/evening and then switched off at night. The IPM on this system lasted 70 days.

I am getting zilch labour allowance for my many hours spent on site at the moment but I'm not holding my breath on getting anything in the future!

I will ask about the maximum operating voltage.

Speak Soon.

[icecap]

Hi Frank,

I was speaking to some friends of mine who work for Axair Climate (Hitachi Agents) regarding my present problem and they mentioned that Hitachi have had problems as well and have developed new IPM's. Not sure what the problem was but looks like it could be similar to the problems I'm facing at the mo.

My gut feeling now is the unpredictable voltages that we can have here in the UK (as Thermatech stated).

I am meeting Axair tomorrow and will try and delve more into Hitachi's IPM problems.

Seak soon.

[paul_h]

Is this the modern way of doing it or do we need to become electronic engineers?
Already on my way there. I've got myself a butane soldering iron and often replace blown varistors that happen after all too frequent power surges, relays that are soldered to the PCB, burnt out tracks and dry solder joints.
Most people here replace the PCB after a power surge, but often the older boards are pricey and had to get. So I cut out the varistor, replace the fuse and test, if it still works, I solder in a $1 varistor, after all that's what they're there for.
The board has a fuse that blows if high current (ie. component fault in the a/c), but won't blow just if there's high voltage. We all know high voltage can fry electronics but the fuse can't protect against that. So these varistors are put across active and neutral and are normally open circuit. If voltage gets above ~400V, they short, which causes the fuse to blow and protect the chips on the PCB. Why bother haven't that protection if we just chuck the board out after a surge anyway?
I'm talking general power/filter PCBs here, not IPMs though.
edit:
Even if you just cut the varistor out and don't bother with the soldering job, the board will work fine without it. So worse case senerio, even if you were going to chuck the board out, the chips will live to the next power surge until they fry (without the varistors protection). So you are halving the amount of boards you go through.
edit2:
Might be worthwhile on units that you suspect are breaking due to power surges to downgrade the standard 470V varistor to a 300v one, or the manufacturers making a solderless replacable varistor so we can change them like a fuse.

[basti]

We've just had an Hitachi RAV6 lose the compressor, which we have replaced, and then we found that the PM board was fried, now we find that the control PCB is also fried.

Got one of these Varistors with the new PM board and I hope it works as the customer is starting to think that we don't know what we are doing??:rolleyes:

Hitachi Tech Support just keep us replacing pcb boards after we replace the previous one until we (hopefully) get there.

Is this the modern way of doing it or do we need to become electronic engineers?

As this unit was fitted just over a year ago, do you think we could claim warranty for the compressor, PM board and now the control board, as we are told that " when the PM board fails it can take the control board and the compressor" ??
I'm sure there will be dozens of excuses why they won't honour the warranty - obviously, all of them will be my fault. :D

Put external varistor's outdoor unit's power input terminal. That will protect power surges. Varistors are cheap and very easy connect.

[frank]

Put external varistor's outdoor unit's power input terminal. That will protect power surges. Varistors are cheap and very easy connect.
That's what we have now done - as advised by Hitachi.

As this unit is just over a year old do you think we could claim against warranty. It sounds like a design fault to me.