PIP-4048MS and PIP-5048MS inverters

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PIP-4048MS inverter

Post by weber » Fri, 03 Feb 2017, 21:43

The litz wire just arrived for the PIP PWM-blocking inductor.

It gives me some satisfaction that although I was forced to order it in cave-man units, as 20 feet of 32AWG x 100, it arrived on a spool with the only writing being "0.2x100, 7m", hand written.

Fortunately its overall diameter is about 2.9 mm, as I estimated it would be, from a table given by another manufacturer. See PDF page 7 of
http://edge.rit.edu/edge/P10022/public/ ... zSpecs.pdf
I allowed for 3.0 mm dia in my winding diagram and experiments, so hopefully all will go to plan.

It appears to be made as 5 bundles of 20, which is OK, so long as there is some randomisation of the 20 in each bundle, so that no strand spends too long in the middle.
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Post by weber » Sat, 11 Feb 2017, 00:52

I still haven't rewound the inductor, but I've planned out how to do it. One problem is that the insulating enamel on the litz wire is only half the thickness of the original. So although I need to have three layers of winding in the middle of the toroid to fit all 64 turns, I don't want turns with a large voltage difference to touch one another. And in particular, I want a decent gap between the two ends of the winding. This has the added benefit of minimising inter-winding capacitance which might otherwise allow some PWM to bypass the inductance.

I came up with the following scheme that you might call "3 steps forward 2 steps back". The turns are all parallel to each other as they pass thru the inside of the donut, but they criss-cross like crazy on the outside, as you can see in the "unrolled" view on the right. No wires that touch are more than 5 turns apart.

Only one half of the winding is shown. The two halves are identical. It makes sense to start at the middle of the winding and hence the middle of the length of wire, so that you only have to pull a maximum of 3.5 metres of wire through the hole each time, instead of 7 metres.

Image

I thought I'd post this now, so after I try to put it into practice, and post a photo of the result, you can all have a good laugh about "the best laid schemes o' mice an' men".
Last edited by weber on Fri, 10 Feb 2017, 19:34, edited 1 time in total.
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Post by offgridQLD » Sat, 11 Feb 2017, 18:26

350 attempts later .......Image

Perhaps it just looks visually tricky in the drawing. Hopefully a slow and methodical approach gives you the outcome your looking for.

The results will be interesting.

ps, I did get my wire in the post, though just 3m of it.

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Post by paulvk » Sat, 11 Feb 2017, 18:50

Why not put some high temp tape between layers to improve insulation, it also makes winding the next layer much easier I have found.

On another note with all this hot weather I have been running my one inverter system with 61 amps shown on the solar input even had three AC units running at once on Friday for about 4 hours 3000watts, ambient temp was 32C and 45C on the heat sink with both 100mm fans (xtra cooling) on the sides at the top going.

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Post by offgridQLD » Sat, 11 Feb 2017, 19:30

Paulvk, So the 100mm fans at the top are they sucking hot air out

as in you have flipped over the bottom stock fans to pull air in from the bottom and blow it to the top? then assisted by the two external fans pulling the hot air out the top?

Or are the stock bottom fans in the original orientation blowing hot air out the bottom.

I spun the two stock fans over to blow upwards but from what i can tell with my hand(not very technical) it feels like a lot of heat is gathering at the top of the unit now. large black heat sink warm (without Pv connected and top of the case warm. Even with the inverter doing very little work.

Perhaps feeling heat being expelled and radiating from the case is bette than being trapped inside the unit. Though I cant help but feel the unit felt cooler with the bottom fans in the stock orientation.

Not that it really matters as my pip has a air conditioner blasting 22C air at it from 5 feet away.

Energy efficient Solar powered Air conditioners are great. We have 3 going at the moment to. One keeping the power electronics cool at 22c and two keeping us cool in the house at 24c.It's about 38c outside The Pv chargers and inverters are brushing off the piddly little 1200w load with the ubundant sun. Actually one charge controller shut down and went to rest as it was bored with no work to do Image

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Post by paulvk » Sat, 11 Feb 2017, 20:27

Yes fans flipped at bottom and the two at the top drawing air out.
Note they are 48v all metal fans drawing 250ma run by a temp control with its probe in the top of the heat sink.
Its 34c here now, 49c showing on temp control it turns them on at 42c and off at 34c.
They are only screwed on over the vent holes at the top but now as warranty is up I am going to make full size holes which will increase air volume, will also block the holes in the back so that the air has to come from the bottom up through the heatsinks.

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Post by solamahn » Sat, 11 Feb 2017, 22:18

I have gone back to leaving fans in factory orientation. I find that having the fans blow upwards can cause condensation to form on the inside of the inverter.
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Post by offgridQLD » Sat, 11 Feb 2017, 22:27

I always thought condensation formed when warm moisture laden air hits a cold surface.

So warm moist air is getting sucked into the base of the pip yes i can see that happening in a humid environment but it would be hitting a warmer surface with the hot components inside the PIP

am I missing something?

What where the signs of the moisture. water droplets on the charge controller at the top? or just signs of corrosion?

[ Edited Coulomb: corrected trivial spelling mistake. ]







Last edited by coulomb on Sat, 11 Feb 2017, 16:58, edited 1 time in total.

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Post by solamahn » Sun, 12 Feb 2017, 02:27

I think it is water droplets caused by the pressure difference across the fans in a humid environment.
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Post by coulomb » Sun, 12 Feb 2017, 03:56

Tejota wrote: 32 param is bulk charging time. Options: Automatic (default) or time (5-900 minutes)

Tejota, I'm interested in how parameter/setting 32 is supposed to work.

My reading of the firmware is that it is intended to be a *maximum* absorb time. So if you set 20 minutes, the absorb phase could last for anything from 10 minutes to 20 minutes, depending on if and when the current falls below a threshold for 10 minutes without exception.

Can I ask what is the source of your information? I can't find any manual that mentions setting 32.

In another post, you state that setting 32 could be used for equalisation. I suppose that during equalisation, the current will be high, so it's unlikely that the battery current will fall below the threshold before the time on the absorb setting has expired, but it might. Perhaps that's OK for equalisation, I'm not very experienced with lead acid batteries. Does the documentation mention equalisation? Is this perhaps its primary function?
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Post by weber » Sun, 12 Feb 2017, 20:11

offgridqld wrote:350 attempts later .......
Ha ha. Good one.
ps, I did get my wire in the post, though just 3m of it.
Sorry I messed you around with this, Kurt. But it turned out to only need 5.9 metres. And you got the 0.2 mm x 100 strand litz wire, right? So if it works, and you decide to do it, you can just buy another 3 metres and solder them together and heatshrink the join, and start the winding with the join on top.
paulvk wrote:Why not put some high temp tape between layers to improve insulation, it also makes winding the next layer much easier I have found.
Sounds like a good idea, Paul. But I enjoyed the challenge of designing a winding that would also minimise interwinding capacitance. And I'd already wound it by the time I read your post.

You can see the result below. I think it turned out quite well. That's a piece of 3 mm polycarbonate epoxied in at the bottom as a separator. The biggest problem while winding it was the roll-curl. It made the wire want to kink as I was pulling it through, for the first 15 turns or so on each side. So next time I'd try to overbend it in reverse as I unwind it from the roll, to try to straighten it before starting winding.

ImageImageImage
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Post by offgridQLD » Sun, 12 Feb 2017, 21:54

Looking good,
             Not as jammed packed as I was expecting. Good to know that joining two rolls of wire is OK.




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Post by weber » Tue, 14 Feb 2017, 06:10

Coulomb and I installed the rewound inductor and reassembled the PIP today. Here are some photos.

ImageImage ImageImage Image

Sadly, we have to say it really wasn't worth the trouble. It only runs about 10 degrees cooler. We measured the hottest spot at 89°C after running with no load for over 2 hours. The previous version ran at more than 100°C.

We also measured the power consumed from the battery with the inverter running, but no AC load, at 69 W. Unfortunately we didn't measure the consumption of this specific inverter before rewinding the inductor with the litz wire. But the received wisdom was that it was, in general, 50 W. However, it seems very unlikely that we've increased the no-load power consumption at the same time as making the inductor run a little cooler.
Last edited by weber on Mon, 13 Feb 2017, 19:19, edited 1 time in total.
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Post by offgridQLD » Tue, 14 Feb 2017, 14:52

Thanks for giving it a go guys!

I appreciate the effort and expense involved. Bugger looks like there is more to the PIPs 50w baseline metabolism Image

I have measured two pips as just under 50w (48w) with a little shunt based dc power meter. 69w is 40% more consumption.

Perhaps the new inductor runs cooler as it dissipates the heat better due to better air circulation around the wire surface.

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Post by weber » Tue, 14 Feb 2017, 16:44

I think the exposed surface area of the winding is much the same as it was before. It might even be less than it was. So although the high no-load power consumption of the inverter as a whole may be a mystery, I'm pretty sure the lower temperature of the inductor is due to lower power dissipation in it.

It seems likely that most of the remaining losses in the inductor are hysteresis losses in its core. If it happens to be going a little too far towards saturation, it might benefit from removing a few turns, otherwise such losses may be unavoidable. By the way, the inductance measured the same as the original, using Coulomb's meter.

I expect the other major loss in the inverter will be hysteresis loss in the core of the high frequency transformer used in the 50 V to 400 V bidirectional DC-DC converter. But its temperature can't be easily measured with the SCC in place over it. Nothing can be done about that loss either, except such tricks as running a lower PWM frequency at low loads, which may result in annoying audible tones coming from the inverter.

It's not inconceivable that by reducing the equivalent series resistance of that inductor at PWM frequencies, I've increased the losses somewhere else. But I can't think of where that might be. Nor can I think of a mechanism for it.

It's possible the Voltronic engineers knew exactly what they were doing in not using litz wire for this one inductor, or perhaps they tried the same experiment I just did, and got the same result.

[Edit: Axpert engineers -> Voltronic engineers]
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Post by weber » Tue, 14 Feb 2017, 18:16

I have a bigger problem than inverter power losses right now. I have the loss of an inverter. Sigh.

When I turned on the 1200 W vacuum cleaner for about the fifth time, to remove the dust from drilling the holes for the rewound inductor in the spare PIP, I heard a pop from the PIP that was powering the vacuum cleaner, and another pop a second later. So I hit the big red button that disconnects it from all energy sources (battery, solar and utility). And after establishing that there was no smoke or flames I powered it up again briefly and saw the familiar fault code 9 which is "Bus soft-start failed".

So after reassembling and testing the spare PIP (which is now the main PIP), we disassembled the blown PIP and found the usual failed MOSFETs on the battery side of the DC-DC converter. All eight MOSFETs in one half-bridge (in parallel groups of 4) had their gates shorted to their drains, and had consequently blown several components in their gate drive circuitry as well.

It's nice that they have upgraded from the earlier IRFB3307 to IRFB3077 that have nearly half the on-resistance, and a pulsed current rating of 850 A instead of 510 A, but they are still only rated for 75 V! I really don't think their problem was ever their current rating. They need to use 100 V MOSFETs.

I earlier recommended the 100 V IRFB4310Z and installed them pre-emptively in one of Kurt's PIPs, along with higher-voltage-and-longer-life capacitors. But they only had the same on-resistance and pulsed-current ratings as the IRFB3307. I feel obliged to match, or nearly match, the ratings of the IRFB3077 now, in a 100 V device. I'll let you know what I come up with.
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Post by offgridQLD » Tue, 14 Feb 2017, 18:31

Hopefully some good luck from now on.

That upgraded pip of mine has to deal with a lot surge loads as its main duty now is powering the shed. Particularly the car hoist the spike is significant more so when started under a few ton load. The 16cfm air compressor and a few other things give it a real workout.

Will probably go pop now I have talked it up Image
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Post by andys » Tue, 14 Feb 2017, 19:44

ouch Weber. how old was this unit?

Any idea how exactly would they be seeing anywhere near 75V?

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Post by weber » Tue, 14 Feb 2017, 21:37

andys wrote: ouch Weber. how old was this unit?

Any idea how exactly would they be seeing anywhere near 75V?
Hi andys. It was built in October 2015, but it has only been in use for about 6 months. Admittedly a hot 6 months. I suppose that could have aged the capacitors (Jamicon WL-series 3300 uF 63 V 105°C 2000 hour) sufficiently that they were no longer able to adequately control voltage spikes on the MOSFETs.

I don't know for sure that they are failing on overvoltage, but when you look at their current specs and the fact that there are 4 in parallel, it's very hard to see how 4 MOSFETs capable of 150 A each could be over-current on the start surge of a 1200 W vacuum cleaner, even if the start surge was 10 times that power. Whereas a MOSFET would only need to have more than 75 volts on it for 10 microseconds to take it out. So I am imagining a voltage spike caused by the sudden change in current through stray inductance between the MOSFET and its DC bus capacitors, or possibly the voltage control loop undershooting followed by overshooting.
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Post by weber » Tue, 14 Feb 2017, 22:38

Here's my post from 2 years ago, about upgrading battery-side MOSFETs and caps.
viewtopic.php?title=pip4048ms-inverter& ... 332#p56103

Here are five low-cost 100 V MOSFETs that may be suitable for replacing the existing IRFB3077s. None are more than $5.00 AU or $3.50 US. Most are available from more than one of Digikey, Mouser, Element 14 or RS Components.
MDP1921, TK100E10N1, AOT290L, CSD19535KCS, SUP70040E.

My search has been far from exhaustive. I haven't looked at Mouser at all, and my efforts with Element14 and RS Components were cursory. But I need to get back to work on other things, so I'd be pleased if anyone else can suggest other options, or tell me why any of those above are not suitable, or which they think is the best choice.
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Post by paulvk » Wed, 15 Feb 2017, 00:56

I found these caps 3300uF SLPX332M080A9P3 @20KhZ ESR-0.076 Ripplel-4.04A 80V 100V surge size 22 x 50 3000h at 85C & full ripple element14 1604359 I am thinking of using them.
I have had 3 AC units running off my one PIP system with SCC at 61amps during this time a 1hp pump ran twice as well with no problems so its strange that a 1200w load caused a problem.
I wonder if the lead acid wet cells 225Ah T105s also soak up spikes have less than 1 meter of 50mm welding cable in each leg.
Would lithium with BMS have the ability to absorb spikes?

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Post by weber » Wed, 15 Feb 2017, 01:51

Hi Paul, I agree a 22 mm diameter cap will just fit, although the existing are 18 mm diameter. And height isn't a problem. And they have the right lead spacing (10 mm). And 80 V is a good rating. Ripple current close to the original. I note that every rated hour at 105°C is worth about 4 hours at 85°C. But the real killer is that their ESR is about 5 times greater than the original. It is the ESR, or more precisely the high frequency impedance (which includes the effect of ESL), that is important in this application. The capacitance doesn't really matter. The 80 V caps I put in Kurt's PIP were only 1800 uF, but they had the required low HF impedance.

It's good that we have the option of up to 22 mm diameter now. When I did Kurt's the pairs of caps were so close together there was no option other than 18 mm. So it should be easier to find an 80 V cap with a HF impedance of 15 milliohms or less, now.

The LiFePO4 (160 Ah) battery has a low internal resistance (about 16 milliohms), and we use double 50 mm² cable to connect it, with the battery in shelves directly below the inverter.
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Post by offgridQLD » Wed, 15 Feb 2017, 03:30

Could there be something particular about that vacume cleaner load that caused the voltage spike. The few vacumes I have pulled apart look to have very crude motors.


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Post by weber » Wed, 15 Feb 2017, 04:04

offgridQLD wrote: Could there be something particular about that vacume cleaner load that caused the voltage spike. The few vacumes I have pulled apart look to have very crude motors.

Yes Kurt, it could have been brush arcing. That inverter ran that vacuum cleaner many times over the past 4 months. Coulomb also pointed out to me yesterday that there is an element of Russian-roulette about where the 50 Hz sine wave is at, when the motor is turned on.

I should also mention that we were running firmware in it that we had patched. We've ported our bug-fix and LiFePO4 changes to version 72.70 and were testing it. But our patches have nothing to do with any low-level operations such as gate drive or fast voltage-control loops, and the patched firmware had been operating successfully for two days during which the vacuum cleaner was used several times, not to mention the microwave, kettle and fridge. But no other major appliances were in use at the time of the failure. The load just before the vacuum cleaner was turned on would have been 200 to 400 watts.
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Post by andys » Wed, 15 Feb 2017, 16:32

Now pondering installing "soft start" circuits to my big loads, seems easier than replacing blown components.

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