PIP-4048MS and PIP-5048MS inverters

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Post by weber » Wed, 05 Nov 2014, 17:10

T1 Terry wrote:My thoughts were to arrange the panels in 2 rows of 9 panels in parallel, series linked at one end or both ends with blocking diodes on the positive output from each panel. This way all the unshaded panels in the A parallel row will feed into the common conductor but the blocking diodes will prevent the shaded panels from draining any of the current back into themselves causing cell damage and wasting the energy generated. This then feeds into the common conductor connected to the negative of the B parallel row. The positives from the B row also have blocking diodes and feed into the common positive conductor linked to the solar controller.
There is no need for blocking diodes with parallel panels or strings subject to partial shading. As I mentioned above, a shaded panel is cooler, so the voltage drop of its equivalent diodes is higher. It turns out that the power lost due to the small current that it does shunt from parallel unshaded panels is about the same as what would be lost due to the voltage drop of blocking diodes. So it's better to omit the blocking diodes and eliminate another source of failure.
Looking at the image in the photo, the shade does not move squarely across the roof so a series string of 2 cells bottom to top would be effected by partial shade on the lower panel but full shade on the upper panel rendering zero output from that series string.
Right. Which is why I figure it is better to place all the panels of a string as close together as possible (i.e. side-by-side in the same row), so that advancing shade takes out the whole string before it starts on the next one, so at least one, and often two, strings are unshaded at any given time.
The controller method you have chosen to use senses the average voltage and current from all the series strings and makes a calculation based on this averaged reading, not individual reading from each series string. By using 3 panels in series the strings in full sun will call the shots so to speak, the series strings with partial shade will not have the voltage or current output to compete and their output will be effectively blocked.

It's true that the unshaded strings will call the shots voltage-wise and therefore any string with even one fully-shaded cell (and I do mean "cell", not panel) will contribute zero. But this goes just as much for strings of 2 as it does for strings of 3, except that in the former case a single shaded cell means only losing the output of 2 panels instead of 3. So that is one benefit of your suggestion.

With strings of 3, if only one panel was shaded in three out of the six strings then the MPPT could reduce the array voltage and get 2/3 of the array power instead of only half. However I admit that such a shading pattern is fantastically unlikely. So strings of 3 do not help with the shading issue as I mistakenly stated earlier. They just reduce the amount of cable required and the number of circuit breakers required (from 5 to 3).

Unfortunately I cannot physically lay the panels out in two rows of 9. But even if I could, and if I were to connect them as 9 strings of 2 with cross ties (or two parallel-blocks-of-9 in series) as you suggest, I do not see any advantage in putting one parallel block in one row and the other parallel block in the other row as the north row will be far more prone to shading than the south row, since the trees are to the northeast and northwest.

I worry that, although you know better, you may still be thinking of solar panels as voltage sources like batteries, instead of current sources with a string of (non-ideal) diodes shunting them. I know it was a hard habit for me to break.

From an earlier post of yours:
This way any part of any panel in the "A" paralleled group can have shade across it but the output from the unshaded panels still feeds into the parallel cabling so any of the "B" unshaded panels can utilise the input from the paralleled 24v nom. supply to produce the required 48v nom. to charge the batteries.
Sure, the voltage will still be there, but in the example below (where ">" means shaded), current will still be limited to that of one panel, and hence power will be limited to that of one string, whether the cross-ties are there or not. Do you agree?
        A     B
   1 +-[>]-+-[_]-+
 ----|     |     |----
   2 +-[>]-+-[_]-+
     |     |     |
   3 +-[_]-+-[_]-+
BTW It probably isn't necessary for you to quote my very long posts in their entirety for me to know what you are responding to. I worry that others may find it annoying to have to scroll through my ravings all over again.
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Post by offgridQLD » Wed, 05 Nov 2014, 17:35

+1 on the long winded Quote. I was starting to get a little dizzy scrolling though it on a Iphone trying to find the actual responses hidden in there Image


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Post by PlanB » Sun, 09 Nov 2014, 00:51

Is anyone else having issues with the box returning to factory defaults? I've set up the user battery option with mains charging limited to 2A a couple of times only to have it jump back to AGM charging at 20A.

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Post by Adverse Effects » Sun, 09 Nov 2014, 01:53

Last edited by Adverse Effects on Sat, 08 Nov 2014, 15:35, edited 1 time in total.

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Post by weber » Sun, 09 Nov 2014, 02:14

[Edit: The following excellent information was actually posted by Coulomb, from my computer. -- Weber]
Adverse Effects wrote: its the 4048 4000W BUT it seems that its also listed at 5KVA
Yes, a little confusing. I think inverters are often quoted at a power factor of 0.8, so the headline number (in this case 5000 VA or 5.0 kVA) is more impressive than the actual power output (4000 W or 4.0 kW). I suppose it's nice to know that the IGBTs or MOSFETs will circulate the current required for an 0.8 power factor load, such as an induction motor. But you can only draw 4 kW plus losses from the battery side. (the extra kVA just circulates from the DC bus capacitors to the motor and back to the capacitors again 100 times per second, with some losses of course).

In short: the model most of us are talking about is rated at 4000 W and 5000 VA.

So you could connect a 4000 W heater (power factor 1.0) and run it all day, or a 5000 VA motor with a power factor of 0.8 (drawing real power of 0.8 x 5000 = 4000 W). [ Edit : assuming that the continuous power rating is realistic. ]
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Post by PlanB » Mon, 10 Nov 2014, 23:18

Just curious which graph you got the 76%=3.32v balancing point from a few pages back weber?

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Post by weber » Tue, 11 Nov 2014, 01:07

PlanB wrote: Just curious which graph you got the 76%=3.32v balancing point from a few pages back weber?

It's from this paper that Johny found, that these powerpoint slides are based on.
http://www.cse.anl.gov/us-china-worksho ... %20BMS.pdf
See pages 11, 12, 13 and 15.

The graph on page 15 suggests it is more like 3.325 V.
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Post by PlanB » Tue, 11 Nov 2014, 03:01

So for a cell cycled between 20% & 80% SOC only about 0.1v difference? Or just 1.6v for a 16 cell pack. That's less than the voltage drop typical of 1C discharge.

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Post by weber » Tue, 11 Nov 2014, 03:59

PlanB wrote: So for a cell cycled between 20% & 80% SOC only about 0.1v difference? Or just 1.6v for a 16 cell pack. That's less than the voltage drop typical of 1C discharge.

Right. But when floating/balancing at 76% SoC using our BMS, the charge current will be throttled back to the balance current of 800 mA which is around 0.005C for a 180 Ah cell. So voltage rise due to internal resistance will be around a millivolt per cell and can be ignored.

The low end of the cycle can be determined by coulomb counting. The capacity of the smallest cell, and hence the battery, could be determined by an occasional excursion all the way down to 2.8 volts, which can safely be considered empty, even at 1.2C (the peak load of the PIP-4048MS on a 180 Ah battery) and at temperatures as low as 15°C. This might be done annually, or every 365 cycles.
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Post by weber » Fri, 21 Nov 2014, 04:06

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Post by offgridQLD » Fri, 21 Nov 2014, 04:24

Looking at the yellow case it looks to be a different model not the 24v version of the pip4048. That said I'm not sure if it has any Common layout, or construction defects.

I know the ridgidity or lack of suport of the caps was something I noted when I poked around in my pip4048.

Don't particular kinds of loads make the caps vibrate at particular freqancys or at least try to if they are unsupported.

Kurt

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Post by Adverse Effects » Fri, 21 Nov 2014, 04:32

weber wrote: Reports of a fault in a 24 V model
https://brandon314.wordpress.com/2013/0 ... er-review/
"This entry was posted on April 1, 2013 at 11:14"

so its an old post

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Post by weber » Fri, 21 Nov 2014, 04:45

Sorry. Yes, my mistake. That's in the LC series, not the MS series. I think that means it has a low frequency transformer.
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Post by T1 Terry » Fri, 21 Nov 2014, 15:21

weber wrote:
PlanB wrote: So for a cell cycled between 20% & 80% SOC only about 0.1v difference? Or just 1.6v for a 16 cell pack. That's less than the voltage drop typical of 1C discharge.

Right. But when floating/balancing at 76% SoC using our BMS, the charge current will be throttled back to the balance current of 800 mA which is around 0.005C for a 180 Ah cell. So voltage rise due to internal resistance will be around a millivolt per cell and can be ignored.

The low end of the cycle can be determined by coulomb counting. The capacity of the smallest cell, and hence the battery, could be determined by an occasional excursion all the way down to 2.8 volts, which can safely be considered empty, even at 1.2C (the peak load of the PIP-4048MS on a 180 Ah battery) and at temperatures as low as 15°C. This might be done annually, or every 365 cycles.

3v under a 1C load is very close to 0% SOC, not completely discharged but at the end of the advertised capacity. I would be looking at a system that disconnected non essential loads at around 20% SOC and a warn at 25% SOC, this way the fridge/freezer remains safe along with emergency lighting, this is how we set up caravans and motorhomes and the odd off grid set up. The warning alarm gives plenty of time to either fire up an auxiliary power source or minimise usage if it's in a quite time like after sun down or the middle of the night Image

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Post by offgridQLD » Fri, 21 Nov 2014, 18:21

I would agree on that voltage under that load though sustained 1C loads are not usually associated with off grid power systems.

The system in question is 180Ah x say 53v - 9500w load! that's never going to happen for any period of time with a 4000W inverter .

Typical off grid homes idle loads would be more like 50 - 300w depending on the system in question though by the sounds of it this one is going into a home with very frugal usage. Most likely would only see a few spikes of a few thousand watts throughout the day. Usually around short active times in the kitchen breakfast and dinner.

I always find it funny trying to relate the power electronics and baterys of our EV's to offgrid power electronics and batterys. Just how Huge the demands are from a Ev. I get all impressed when I see my PV pumping in 7000w. Or loading up my inverter to see 6000w output.

Then I back the Imiev out of the driveway and pull 20,000w followed by a roll down the street and regen pumping 30,000w into the batterys as I let off the accelerator. Amassing numbers when you try and relate the two.

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Post by PlanB » Sat, 22 Nov 2014, 01:58

Good point, I never did the sum to realise 1C is pretty unlikely for this. Makes the performance of battery management systems in EVs, where 1C or 2C is likely, look good.

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Post by T1 Terry » Sat, 22 Nov 2014, 13:41

PlanB wrote: Good point, I never did the sum to realise 1C is pretty unlikely for this. Makes the performance of battery management systems in EVs, where 1C or 2C is likely, look good.

Battery management for house battery has very different requirements to EV battery management. These cells behave differently under light discharge and the cell capacity makes a huge difference to cell balancing using the discharge method or shuffle transfer. 0.5 amps will balance a 40Ah or 60Ah cell, but useless for a 400Ah to 1,000Ah cell. This requires a completely different management method, combine that with solar charging that can be any where from a trickle to over 100 amps yet only available for around 3hr in winter yet up to 10 hrs in summer and the EV battery management system would not even close to being up to the task.

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Post by weber » Sun, 23 Nov 2014, 05:16

T1 Terry wrote:Battery management for house battery has very different requirements to EV battery management. These cells behave differently under light discharge and the cell capacity makes a huge difference to cell balancing using the discharge method or shuffle transfer. 0.5 amps will balance a 40Ah or 60Ah cell, but useless for a 400Ah to 1,000Ah cell. This requires a completely different management method, combine that with solar charging that can be any where from a trickle to over 100 amps yet only available for around 3hr in winter yet up to 10 hrs in summer and the EV battery management system would not even close to being up to the task.
Our BMS has 0.8 A bypass and will be used with 180 Ah cells. I assume you're thinking of BMSs that don't control the charge current (except OFF or ON). Ours will attempt to throttle the charge controller back to the bypass current when the first cell is full, by using the serial input to the PIP-4048MS to send commands that reduce the absorb and float voltages.
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Post by T1 Terry » Sun, 23 Nov 2014, 10:57

The trick is reducing the current down to 0.8 amps yet charging all the other cells, at the same time. Even a 0.1% out of balance equals a difference at that time of 1.8Ah between the highest and lowest cells and that will take a continuous 2 1/2 hrs to correct with a 0.8a discharge balancer. In the mean time the system is still in operation so the only time that imbalance will be seen is at the top of the charge, good luck with getting 16 cells within 0.1% balance during that period Image. As soon as you stop the charging the load will drop the high cell voltage and the 0.8a balancing will stop as the cell will no longer register the high voltage required to activate the discharge balancer circuit, so you won't get a 2.5hr crack at rebalancing the cells during the 5 peak sun hrs solar charging you get during summer, to make matters even worse, that's only 2.5 peak sun hrs during winter.

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Post by offgridQLD » Sun, 23 Nov 2014, 14:27

Terry,
      Are you trying to suggest that 400ah+ lifepo4 cells in a offgrid aplication can't be top balances (to within aceptable levels say 10-20mv) using PV charge controllers and 800ma or so cell top balancing boards.

If so I would have to disagree and can link to some examples of people who have been susesfully doing it in Au for years. With detailed data logging of just how well its working.In fact what they are finding is after a fine comissioning ballance by hand. Once the cells are in operation powering there home .Is a very short absorb stage (triggering their ballancers)is needed to complete the balancing to satisfactory levels (around 20 mins).There just isn't much to correct. Some are just Setting a Eq charge once a week for 1hr at the balancing voltage they desire.The cells just don't drift much under light C loads and modest DOD levels.

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Post by T1 Terry » Sun, 23 Nov 2014, 15:36

48v 16 cell systems Kurt? 4 cell 12v system will stay in balance without any form of balancing attached, so the balance boards work fine on these Image 24v systems can be an issue, 48v system are most definitely an issue at the top end of the charge. If you are telling me you have witnessed 48v 400Ah systems that will remain within 10mV to 20mV at 3.6v yr after yr I'd be very interested in any information you have.

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Post by antiscab » Sun, 23 Nov 2014, 15:38

offgridQLD wrote: The cells just don't drift much under light C loads and modest DOD levels.


If they have never been overdischarged (been below 2v) than they don't drift at all

If you use a BMS like the ZEVA one, the shunts latch for some hours after charging stops (you can program how long for and such)

you don't need to be charging to do balancing - but you should start out with a balanced pack in the first place
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Post by offgridQLD » Sun, 23 Nov 2014, 16:31

" If you are telling me you have witnessed 48v 400Ah systems that will remain within 10mV to 20mV at 3.6v yr after yr I'd be very interested in any information you have."

Im not saying some adjustment to the absorb time (or time spent balancing) isn't need if conditions change to much. Say a week of unseasonaly bad weather and high demand high DOD might require a extension of the absorb time. Though on average he is finding from 15min to 30min is all that is needed. so if you don't mind a little more time than is really necessary in absorb then a good 30min or a tad longer should cover it without to much user intervention. Though I think his aim was to keep the time spent at balancing voltages to a minimum to extend the life of the cells.


Lots of info spread across a forum but this thread has some details. Basically he started out with 16x400Ah blue sky energy/calb cells configured as 2p 8s with two cell balance boards for each 2p cell but soon after upgraded his inverter to 48v and reconfigured the cells to 16s 1p - 48v one one cell balance pr cell.

http://forums.energymatters.com.au/sola ... c5108.html

My personal view is its not the number (10mv - 20mv - 30mv) that's so important or worth being to pedantic about. More that it doesn't keep drifting over time. 5mv that becomes 500mv over a year isn't good but 50mv that stays that way all year is fine. We are just trying to avoid a exponentially larger drift in individual cell SOC.




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Post by weber » Sun, 23 Nov 2014, 17:45

T1 Terry wrote: The trick is reducing the current down to 0.8 amps yet charging all the other cells, at the same time. Even a 0.1% out of balance equals a difference at that time of 1.8Ah between the highest and lowest cells and that will take a continuous 2 1/2 hrs to correct with a 0.8a discharge balancer.
Bzzzt. Factor of 10 error. 0.1% difference would be 0.18 Ah and take 15 minutes to correct. But no-one cares about a 0.1% imbalance, so I'll just take your point as still applying to a 1% imbalance (which we barely care about).

We will manually balance them to better than 0.1% before they go into off-grid service, by leaving them charging from the grid at 0.8 A for as long as it takes. After that, the main cause of imbalance I've found is the variation in current drawn by the individual CMUs. But this variation is typically less than 1 mA. That should only require an average of 2 minutes balancing per day at 800 mA.
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Post by PlanB » Mon, 24 Nov 2014, 02:40

Dave is it one of your cell top modules that will throttle the absorb & float voltages? If I took your cmds in on an RPi serial port & echoed them to the 4048 (so we can maintain our serial connection) then echoed the 4048 response back at you would your wait for ACK timing be generous enough to allow this to happen transparently?

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