PIP-4048MS and PIP-5048MS inverters

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Post by offgridQLD » Thu, 30 Oct 2014, 22:54

Tomorrow night I will power up my pip4048 through one of my shunt meters.

I thought I already did this when I first got the unit but thinking back I might have just done the same as you guys with a quick check with the clamp meter and mixing up the test I did on a old UPS I tested with the shunt.

Anyhow Unless some one gets to it first. I will report back tomorrow night with a number from the shunt meter.

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Post by offgridQLD » Sat, 01 Nov 2014, 05:37

I just ran the PIP4048 through a shunt meter and for kicks my clamp meter at the same time.

Numbers are in on idle consumption.

43.9W though after it was on for 5 min or so it settled down to 41-42W fluctuating.
Image

clamp meter surprisingly agrees with the shunt at 0.93A.
Image

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Post by 7circle » Sat, 01 Nov 2014, 06:05

Does the standby power drain vary once the PIP4048 is supplying a Load.
Say it supplies a 500W load .. does it take 550W from the Battery?
Or say its just a 100W Load does it need 150W or less?
If part of the Standby power is to just keep the output transformer magnitized it may be of little consequence if you have lighting or small loads running over night.

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Post by offgridQLD » Sat, 01 Nov 2014, 06:13

I will test that for you in the morning.

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Post by T1 Terry » Sat, 01 Nov 2014, 10:37

That was what we found with the unit we've been running, the light in the fridge draws 75w, the 50 watts for the standby load and 25w for the bulb, yet up near full power the losses are less than 10% over all. If they were only ever running light loads the losses would be significant, but when they are doing their thing the losses are part of the normal 10% inefficiency that you normally factor in when using an inverter anyway.
Are you running the variable fan speed option or full on/off option? Buggered if I can remember where that was in the scroll through menu, but it is in there some where.

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Post by offgridQLD » Sat, 01 Nov 2014, 13:08

We are talking about idle consumption not eficancy at full load and for this eficiant off grid home that there unit will be going in idle consumption is important as that's what it will be doing most it the time in a 4kwh/day house. Im still backing that that 42w idle will be carried through no matter what the load and will find out offer breakfast.


90% eficancy under load (if that's what it is ) isn't that flash .

The variable fan setting sounds intereating. I will say when playing with my unit last night (battery conected ) the fans didn't come on. Well I couldn't hear any fans so perhaps this variable fan speed is the key ?

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Post by weber » Sat, 01 Nov 2014, 15:45

7circle wrote: Does the standby power drain vary once the PIP4048 is supplying a Load.
Say it supplies a 500W load .. does it take 550W from the Battery?
Or say its just a 100W Load does it need 150W or less?
If part of the Standby power is to just keep the output transformer magnitized it may be of little consequence if you have lighting or small loads running over night.

Some terminology: The max 50 watts we're talking about here is usually called "no-load power" or "idle power". That's the input power when the inverter is producing a 230 Vac sine wave but no load is connected to its output.

Thanks for measuring this, Kurt. Good to see it's a little lower than the specs allow.

"Standby power" is the input power when it is powered up from the battery, but is not producing a sine wave. They claim max 15 watts in that case. This is also called "load sensing" mode. This manufacturer calls it "power saving" mode.

Once the inverter is supplying a load, the difference between DC input power and AC output power can no longer be called standby power or no-load power. It is called the "power loss" or just the "loss".

The loss will never decrease as the load increases. For low loads it will at best remain constant.

Yes, part of the idle power is to keep the transformer magnetised, although in this case it isn't an output transformer. It's a high frequency transformer used in the middle, to boost the voltage, which is then switched by output IGBTs to produce the 230 Vac sine wave.

I would guess that most of the extra 35 watts used in idle mode as opposed to standby mode, would be core losses in that transformer (mostly hysteresis loss). Some of it would be gate charge and discharge power to the switching devices.

But this is of enormous consequence if there are small loads running over night.
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Post by T1 Terry » Sat, 01 Nov 2014, 16:51

weber wrote: But this is of enormous consequence if there are small loads running over night.

This was the part I was trying to get at, just not doing a very good job of it. The fridge draws power 24/7 running the defrost heater around the door seal and a few bits keeping the electronics alive so there is always that load as a min. Once the unit starts to do it's thing, the percentage of the idle current reduces, but while at light load it is a high percentage of the current being used.
The higher $$ units have an adjustable output that must run a mini inverter to supply 50w or so, no idea of the actual value, as soon as this load is exceeded the main inverter is powered up. These units have a much smaller "idle current" but the $$ difference between these units and the ones we are looking at here will buy quite a few extra solar panels, so the added cost for efficiency alone is not economically justified, sometimes you just need to live with these things and build the system with this inefficiency in mind.
Have I taken this full circle yet? Image

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Post by offgridQLD » Sat, 01 Nov 2014, 20:20

Yes Terry, when working out efficiency at different inverter loads the idle consumption becomes less of a % factor in the sum. It's always good to read into the efficiency % listed for a inverter as they always list peak efficiency lets say 93% (often not telling you at what % of load that is )Usually the better brands list the efficiency at various load % say 10% load 20% load and so on all the way up to 100% load.

Just for kicks I made A small video showing the idle consumption of the PIP4048 and how running a identical AC load to the (42w) DC idle consumption results in the sum of the two at the battery. Rather than what was suggested. Just nice to clear that one up as the theory has been suggested a few times before on other forums.

Anyhow the results where as expected in the video.

https://www.youtube.com/watch?v=U9hdg_w ... e=youtu.be

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Post by T1 Terry » Sun, 02 Nov 2014, 03:50

Good vid putting the myths to bed Kurt. Was all the noise the fan running or the inverter fans as well? The one... well none of the ones we have fitted up will start the fans up that loud on such a light load so I'm guessing it was just the pedestal fan making all the noise.

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Post by weber » Sun, 02 Nov 2014, 06:07

Coulomb and I pulled all the PCBs out of the inverter today and traced the battery voltage sensing circuitry in both the inverter and the MPPT charger. We have scaled the voltage by 10% (52.8 V will be read as 48 V) in the inverter/genset-charger. The PV-MPPT-charger had us on a wild goose chase for quite some time, following what turned out to be sensing for the morning-wakeup bootstrap supply, based on the PV input voltage being a few volts above the battery voltage. But we eventually found its battery voltage sensing too. However some aspects of it are still mystifying and we have not done the modification there yet.

It seems that the MPPT charger in the PIP-4048MS is the same as the one in their standalone MPPT charger model PCM60X.

Its manual is here:
http://mppsolar.com/manual/PCM60X-MPPT-3KW.pdf.

This has some efficiency test results that answer one of the questions we were considering many posts back.
http://www.mppsolar.com/v3/catalogs/60X ... 20Test.pdf

It seems I won't be able to make toast in the "toast-rack" heatsink on top of the PIP-4048MS (the MPPT heatsink). It shows that when charging the battery at 60 amps, 53 volts, the loss is 72 watts with a PV array voltage of 60 volts, and 91 watts with a PV array voltage of 100 volts (where I plan to operate it, to allow for shading). That's a 28% increase in heat. Hopefully manageable. Hopefully it will just back off the current if it gets too hot.

This MPPT has its own PC software for monitoring and changing settings, called MPPTracker. The software manual is here:
http://www.mppsolar.com/v3/catalogs/60x ... manual.pdf

We were surprised that they haven't used the remote voltage sense (Kelvin) input of the MPPT. This can be enabled by the software, as can the temperature sensor input for those charging lead-acid.

There is no external access to the serial comms port of the MPPT when it forms part of the PIP-4048MS. Instead it appears that the processor in the inverter-proper passes on any relevant settings to the MPPT.

Since I need to run 3 x 72-cell panels in series to allow for loss of voltage due to partial shading by trees, I was concerned about the possibility of exceeding the maximum of 145 volts on frosty dawns. On page 18 of the standalone MPPT manual it claims to have "Protection: Solar high voltage disconnect", which was quite a relief to read. But then Coulomb and I went looking and couldn't see any devices to implement that on the MPPT in the PIP-MS. The MOSFETs are only rated at 150 V and the input capacitors are rated at 160 V.

There are two relays (in parallel) for disconnecting it from the battery, but none for disconnecting it from the PV array. Perhaps those were off-board in the PCM60X, and are not provided in the PIP-MS.
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Post by weber » Sun, 02 Nov 2014, 06:17

In http://www.mppsolar.com/v3/catalogs/60x ... manual.pdf on page 15 in diagram 4.11 you can see there is an option to set the "Battery C.V. charge time" in minutes. So perhaps this is sent to the MPPT by the processor in the inverter-proper. If so it could be intercepted and modified by an added microcontroller having two UARTs, inserted into the serial link between these two devices.
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Post by offgridQLD » Sun, 02 Nov 2014, 13:44

Nice work guys Image

That's interesting that the PCM60X has more user control over the charge setting.Yet they dulled it down and don't take advantage of it in the PIP4048.

I noticed the two green inputs on the pip4048's mppt charger board one labeled (temp) or something along those lines. Just how to make it use the input was the road block for me. (not that you need it for lithium's)


"I'm guessing it was just the pedestal fan making all the noise."

Yes Terry it was just the pedestal fan I was using as a AC load.

I can confirm my units fans do come on if it just sits there powered for some time. Yesterday It was powered up in my shed for several hrs (no ac load) ....I forgot to turn it off Image anyhow the shed was about 35deg c and the fan was on when I noticed I had forgot to shut it down.

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Post by coulomb » Sun, 02 Nov 2014, 15:06

offgridQLD wrote: I can confirm my units fans do come on if it just sits there powered for some time.

I think our fans might have taken hours to come on too. What surprised us was the heat that came out then. I guess there is a fair bit of thermal mass in the heatsinks and other metalwork, but eventually 42 W will exceed what unassisted convection can cope with.
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Post by T1 Terry » Sun, 02 Nov 2014, 15:58

weber wrote: Coulomb and I pulled all the PCBs out of the inverter today and traced the battery voltage sensing circuitry in both the inverter and the MPPT charger. We have scaled the voltage by 10% (52.8 V will be read as 48 V) in the inverter/genset-charger. The PV-MPPT-charger had us on a wild goose chase for quite some time, following what turned out to be sensing for the morning-wakeup bootstrap supply, based on the PV input voltage being a few volts above the battery voltage. But we eventually found its battery voltage sensing too. However some aspects of it are still mystifying and we have not done the modification there yet.

Any chance of a photo showing where the voltage sensing section is? Hopefully they use the same circuit lay out for their 24v units as well as these are far more practical for use in motorhome house battery set ups.
Interesting the 20w waste heat increase when converting a higher solar input voltage, something the MPPT supporters have been denying being the case, but simple logic said it must as there is so much more heat sink and/or forced cooling required in an MPPT controller compared to a PWM controller.

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[Moderator note: Weber's reply to this post has been moved to the PIP inverter repair and hardware modifications topic.]
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Post by offgridQLD » Sun, 02 Nov 2014, 18:09

"something the MPPT supporters have been denying "

I think you will find most people will say the opposite to some degree depending on the design of the MPPT charge.


Still the few watts (say 40 -100w) depending on the size of the array and the efficiency of the mppt controller. Is way better that giving up 20,30 , 50v of charge potential X the current that could be 100's of watts going to wast in a PWM charge


For example batterys charging at 55V PV at 120V at 5 Amps that's 65V the PWM charger is throwing away (this is putting things very simple but for the sake of the explanation I think ok)

In the above example
275w PWM
600w MPPT

Take 1 or 2% off the 600w your still way in front just a warm charge controller.


So I'm sure giving up the few % loss to heat to be able to make use of that extra voltage is a good deal.

While some 48v PWM charges can accept more that say 60V (I think my old plasmatronic PL40's could go over 100v input) they will never be able to make any use of that extra voltage. So you need to match your PV as close to your max charging V as possible. (taking into account a few variables so insure your get the voltage you need under all conditions)

The issue is as arrays get bigger and bigger that few % lost as heat can add up on a 4000 - 5000+ watt array going into one small controller. So the difference between a 2% loss and a 4% loss could be manageable vs making toast.

Kurt
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Post by weber » Sun, 02 Nov 2014, 22:10

[Moderator note: This continues on from Weber's previous post which has been moved to the PIP inverter repair and hardware modifications topic.]

It pains me to say this, given that Coulomb and I expended so much effort on it yesterday, but I don't think we need to change the voltage sensing after all.

The reason I wanted to do it was so the BMS could cause the inverter to cut off if any one cell went below say 2.8 volts. It would do this by sending a command to the inverter to raise the inverter's low voltage cutoff to something that was higher than whatever the total battery voltage happened to be at the time. Because total battery voltage is the thing the inverter uses to decide when to cut off.

It would be possible that all other cells might be at 3.3 volts, giving a total of 52.3 volts. But the highest low-voltage cutoff point that we can set is 48 volts. Hence the idea of changing the voltage scaling so it reads 52.8 volts as 48 volts.

When Coulomb left yesterday, he suggested that what I should do next, to try to solve the mystery of the 1/4, 1/7, 1/13 diffamp gains, was to power up the MPPT on the bench and see what voltages were actually sent to the microcontroller. Even 48/13 = 3.7 V seems too high, let alone 48/4 = 12 V. We had to be missing something, and that would affect what we needed to do to scale the reading to match the change we'd made to the inverter. It's possible that MPPT is using an offset scale.

I tried connecting 48 V to its battery input, but the op-amps did not get power. I eventually figured out that it was probably not going to turn on until (a) it heard from the main microcontroller in the inverter and (b) it saw enough voltage on its PV input. So I pretty much had to put everything back together and wire it to PV and batteries, but the differential amplifiers are not accessible when it is mounted on its heatsink, so I'd have to take it all apart again to modify it, and that was not easy. That's when I started casting about in desperation. "There must be another way", I thought.

At first I thought, "The BMS could just turn off the battery isolation contactor." But that would not only prevent the batteries from being further discharged, it would also stop them being charged.

But it turns out there is another way the BMS can command the inverter to stop discharging the battery. It can set the battery voltage at which the loads are switched from the inverter to the "utility", which in this case means the generator (which won't be running as it is manual start).
See item 12 on page 17 of http://www.mppsolar.com/manual/PIP-MS%201-5K%20manual.pdf
And page 16 of Johny's protocol manual, for the PBCV" command. http://forums.aeva.asn.au/uploads/293/HS_MS_MSX_RS232_Protocol_20140822_after_current_upgrade.pdf

Switching the loads away from the inverter is pretty much the same as cutting it off. Not sure why I didn't realise that before.

But the maximum voltage you can set for that is 51 volts. Is that high enough? If we let our worst cell go as low as 2.5 V that means the others would need to average lower than (51-2.5)/15 = 3.23 V. Could they be higher? Yes, although it isn't likely. But can we do better? Isn't there a way we can just tell the inverter to switch the loads to the "utility" irrespective of battery voltage?

If there is, I can't see it.
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Post by T1 Terry » Mon, 03 Nov 2014, 03:20

offgridQLD wrote: "something the MPPT supporters have been denying "

I think you will find most people will say the opposite to some degree depending on the design of the MPPT charge.


Still the few watts (say 40 -100w) depending on the size of the array and the efficiency of the mppt controller. Is way better that giving up 20,30 , 50v of charge potential X the current that could be 100's of watts going to wast in a PWM charge


For example batterys charging at 55V PV at 120V at 5 Amps that's 65V the PWM charger is throwing away (this is putting things very simple but for the sake of the explanation I think ok)

In the above example
275w PWM
600w MPPT

Take 1 or 2% off the 600w your still way in front just a warm charge controller.


So I'm sure giving up the few % loss to heat to be able to make use of that extra voltage is a good deal.

While some 48v PWM charges can accept more that say 60V (I think my old plasmatronic PL40's could go over 100v input) they will never be able to make any use of that extra voltage. So you need to match your PV as close to your max charging V as possible. (taking into account a few variables so insure your get the voltage you need under all conditions)

The issue is as arrays get bigger and bigger that few % lost as heat can add up on a 4000 - 5000+ watt array going into one small controller. So the difference between a 2% loss and a 4% loss could be manageable vs making toast.

Kurt

Sorry, I can't see the logic of generating a higher voltage so you can loose some of the generated current via heat through a device designed to reduce the voltage to what was desired in the first place Image Surely logic says if you eliminate the extreme voltage differential and limit it to the desired level required for good current flow the system is far less complex and far more efficient.
56v is the required max voltage at the terminals of a 48v nom. battery, a 4v differential between panel voltage and terminal voltage will facilitate good current flow. 24v nom. panels have a Vmp of approx.30v at genuine operating temp, that's 60v with 2 panels in series, so what sense is there in putting 3 panels in series and then loose part of that in the device required to reduce the voltage to the same as 2 panels would have produced?
I've already posted how to work around the shade effect efficiently so that reasoning is gone, so what other reason could there be?

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Post by offgridQLD » Mon, 03 Nov 2014, 03:40

Terry,
      In a ideal world where the panels you are using match the voltage you want to charge at spot on then that might work out fine though if you want to charge flooded lead acid you need a good 60+ volts for charging and EQ and they need to be able to do that under all conditions the panels will see.
Often the panels that represent good economic value don't always match up perfectly with your batterys charging voltages.

The biggest advantage is Unless you want spend a lot of money on copper wire often arrays are some distance from the battery. You can use smaller gauge wire and higher voltage over long runs.

A small thing is even when you do match the panels as close as you can to get a good charge voltage (In a shade free install basically making sure you have just enough voltage to charge in the hottest conditions)
You loose some power when its cold as the panels would have been chosen to cover the hottest day So more voltage than you can use for your PWM chargers and wasting power on a cool morning.


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Post by weber » Mon, 03 Nov 2014, 04:41

T1 Terry wrote:Sorry, I can't see the logic of generating a higher voltage so you can loose some of the generated current via heat through a device designed to reduce the voltage to what was desired in the first place Image Surely logic says if you eliminate the extreme voltage differential and limit it to the desired level required for good current flow the system is far less complex and far more efficient.
56v is the required max voltage at the terminals of a 48v nom. battery, a 4v differential between panel voltage and terminal voltage will facilitate good current flow. 24v nom. panels have a Vmp of approx.30v at genuine operating temp, that's 60v with 2 panels in series, so what sense is there in putting 3 panels in series and then loose part of that in the device required to reduce the voltage to the same as 2 panels would have produced?
I've already posted how to work around the shade effect efficiently so that reasoning is gone, so what other reason could there be?

Terry, You seem to be missing the fact that an MPPT controller doesn't simply "lose" voltage (as a PWM controller does), an MPPT controller turns excess voltage into additional current.

As Kurt said, if your system is designed so it has just enough voltage to fully charge your battery in the hottest weather (as you suggest) (say 60 volts at 20 amps), then in colder weather under the same irradiance it will have more voltage available than you need (say 66 volts at 20 amps). An MPPT controller will turn that 10% extra voltage into 10% extra current and thereby give you 60 volts at 22 amps (OK maybe only 21.5 amps because of losses), but a PWM controller will just waste that extra voltage in the panels and still only give you 60 volts at 20 amps.

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Post by weber » Mon, 03 Nov 2014, 05:41

Terry, the following paper confirms that your practice of total cross-connection of strings of solar panels does indeed reduce losses due to partial shading.
https://hal.archives-ouvertes.fr/file/i ... ame/17.pdf
However it does not quantify the effect. Nor does it consider the cost or complexity of the extra wiring and its overcurrent protection.
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Post by T1 Terry » Mon, 03 Nov 2014, 13:32

weber wrote: Terry, You seem to be missing the fact that an MPPT controller doesn't simply "lose" voltage (as a PWM controller does), an MPPT controller turns excess voltage into additional current.

As Kurt said, if your system is designed so it has just enough voltage to fully charge your battery in the hottest weather (as you suggest) (say 60 volts at 20 amps), then in colder weather under the same irradiance it will have more voltage available than you need (say 66 volts at 20 amps). An MPPT controller will turn that 10% extra voltage into 10% extra current and thereby give you 60 volts at 22 amps (OK maybe only 21.5 amps because of losses), but a PWM controller will just waste that extra voltage in the panels and still only give you 60 volts at 20 amps.

Once the system is designed to produce enough input to equal the output plus a bit to get the system back to full after non optimum days, then any gain due to reduced operating temp and use of a complex controller will achieve what? The battery fully charged 20% earlier in the day? I can't see where this is of any advantage.
The system must be designed around the fact the cell efficiency will be less during the hottest part of the yr, summer, yet the system load is likely to be the highest due to air cond use for extended periods. An MPPT controller can not improve this hot panel output, it only optimise output when the panels produce more due to colder operating conditions, but this is in excess to the systems designed requirements and as it has no other value such as resale to the grid, it becomes surplus to requirement, so of no value at all.

As far as reduced copper costs due to reduced cable size, not sure what the cost balance is here as the cabling must now handle a much higher voltage alone with additional fusing/breaker costs to accommodate this higher voltage. As the MPPT controller will not handle a full series string voltage, there has not been a great reduction in the required cabling volume, so the reduced costs would be minimal I would think.

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Post by offgridQLD » Mon, 03 Nov 2014, 14:30

Terry,
       I think having excess production and no place to to put it is a inherent problem with most off grid systems due to the sizing the system get you through the middle of winter.

the answer to that is build or buy a Electric car and you will always have a place to put it Image

If anything the MPPT will allow you to get away with a slightly smaller array and still get through winter due to more performance when its cool.

I don't see why there is all this negativity towards a MPPT controller. It's not like they are any more expensive now days . I sold two plasmatronics PL40's secondhand (when pricing them to set a 2nd hand sale price) I was shocked at what the new cost was. You can purchase a good brand name 80 - 90A MPPT controller with way more features for the same cost. So the cost argument isn't really there anymore. Perhaps 5 - 10 years ago when MPPT untis where two - three times more expensive.

I will add to that the unit I run at 80V input can pump out max output all day from a 4000w array and its still runs cool. fans hardly cycle at all. So its not like heat is a big issue if the voltage is kept reasonable.

Perhaps we should start a different thread MPPT vs PWM, although it's been done to death on most offgrid forums and I'm a little over it Image.

I only picked my particular charge controllers predominantly because I liked all the inbuilt remote (online) monitoring features so I could monitor and control my system over the net and in general its a adaptable controller with great support.

MPPT or PWM use what works for you and what product your happy with

Kurt





Last edited by offgridQLD on Mon, 03 Nov 2014, 03:44, edited 1 time in total.

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PIP-4048MS inverter

Post by weber » Mon, 03 Nov 2014, 16:31

T1 Terry wrote:Once the system is designed to produce enough input to equal the output plus a bit to get the system back to full after non optimum days, then any gain due to reduced operating temp and use of a complex controller will achieve what? The battery fully charged 20% earlier in the day? I can't see where this is of any advantage.
There are so many misconceptions here about fairly basic stuff, and this is somewhat off-topic, but here goes:

There is no such thing as "plus a bit to get the system back to full after non-optimum days". It's not unusual to have a whole rainy week where the output of your PV array is only 10% of what it is on the best days. Since we can't afford to have a week's worth of battery storage, your "plus a bit" would be plus about 900%. So what we do is design the system to balance its initial cost against the cost (including the environmental and social costs) of backup sources -- typically burning fossil fuels, or the inconvenience of voluntary austerity during those times.

So there will always be times when the extra power available from an MPPT will be useful. And on good days, having your (lead-acid) batteries reach full charge earlier does increase their life. And as Kurt says, the extra cost of an MPPT is no longer significant.

The only reasons I can come up with not to use an MPPT are if you want to have more chance of fixing it yourself if it breaks down, or if you need to locate it somewhere where the extra heat would be a problem, and so you find it preferable to waste even more power as heat in your panels instead.
The system must be designed around the fact the cell efficiency will be less during the hottest part of the yr, summer, yet the system load is likely to be the highest due to air cond use for extended periods. An MPPT controller can not improve this hot panel output, it only optimise output when the panels produce more due to colder operating conditions, but this is in excess to the systems designed requirements and as it has no other value such as resale to the grid, it becomes surplus to requirement, so of no value at all.
None of my customers run aircon off-grid. They design or modify their homes not to need it. But yes, refrigeration loads are higher in summer. But of course in winter the days are shorter so the available solar resource is lower and lighting loads are higher. In Brisbane, an unshaded array tilted north at 27.5 degrees receives on average 30% less energy per day in May, June, July, compared to Dec, Jan, Feb. And the saving on refrigeration in winter does not typically amount to anything like 30%. So an MPPT can help make up that winter shortfall.

Even on a clear midsummer day your panels are only at their hottest during the middle couple of hours. Either side of those hours the panels are cooler so there is extra power that can be harvested by an MPPT, which may allow a slightly smaller array or extend your battery life.
As far as reduced copper costs due to reduced cable size, not sure what the cost balance is here as the cabling must now handle a much higher voltage alone with additional fusing/breaker costs to accommodate this higher voltage. As the MPPT controller will not handle a full series string voltage, there has not been a great reduction in the required cabling volume, so the reduced costs would be minimal I would think.
All UV stabilised solar cable that I am aware of is good for 600 volts DC. And thanks to the explosion in the grid-connect market, DC fuses and circuit breakers are no longer very expensive. And the higher the array voltage, the fewer strings you need and therefore the fewer string protection devices you need. In fact if you have two strings or less you don't need any string protection, although you still need array cable protection from the battery.

For a given array power and cable route length, the amount of copper required to maintain the same percentage volt drop and hence the same percentage power loss, goes down as the square of the voltage. i.e. if you can double the array voltage you only need 1/4 of the copper.

Yes, the specific MPPT in the PIP-4048MS is very poor in this regard since it barely allows a 1.5 times increase in nominal array voltage over battery voltage, but most MPPTs allow at least 2 times. Phew. Back on topic at last. Image
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PIP-4048MS inverter

Post by offgridQLD » Mon, 03 Nov 2014, 17:05

So you mentioned in a earlier post that you might shy away from modifying the voltage reading circuit to fool the the inverters set point for LVD.

Are you thinking now of just having some kind external control over LVD and just leaving the battery V readings/setpoints inside the inverter as is?

When you first mentioned making changes in the inverter. My initial reaction was. Once you started fooling one reading in the inverter it could be a knock on effect where all other voltage dependent set points would need compensating one way or another. Perhaps adding work/complexity to achieve the initial simple task LVD.

Or am I lost where you going with this or the initial reason for the tweak?

Kurt
Last edited by offgridQLD on Mon, 03 Nov 2014, 06:13, edited 1 time in total.

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