PIP-4048MS and PIP-5048MS inverters

[PlanB]

Site; (noun) that location where stuff developed & tested at another location exhibits a range of behaviours hitherto unseen.

I love the idea of the legacy system shedding some light on the new system while you reworked it, Murphy has a delicious sense of irony too.

[paulvk]

For those with lead acid batteries some in depth reading
http://orbit.dtu.dk/fedora/objects/orbi ... 66/content

[baal]

Hello all really enjoyed reading all the posts on the pip-4048ms inverter and rom hacking which i found very interesting, i thought it was pretty good till it died yesterday in 45 degree heat, I myself have one of these i bought it in march 2015 and well found my self here cause after a few months use its broken , the solar side which has 8x 250w 24v (37V oc) panels in series of 2 panels and four parallel connected is no longer even being seen by the inverter so something died in the mppt solar charger as the voltage is there and i checked all the panels, the AC inverter part still works in making power and grid side charger still works but no solar charge which is really upsetting considering im in a caravan completely off grid, which means the only charging i can do is via the generator attached to the grid side, and it cant really cope with running the air conditioner which sucks just as we started having 40+ degree days and it becomes an oven in the caravan.
I was hoping that someone would have documented a similar problem with the solar mppt charger and posted a solution , perhaps someone has a dead pip-4048 inverter that still has a working mppt solar charge controller ?
It really could not happen at a worse time as im sure its going to take at least a month to get a replacement and until then im basically without power and i have to sort this out quick as i have my 5yo son for a few days over christmas no power is going to be a problem when he wants to play xbox

I was thinking perhaps i would just go get a solar charge controller and hook that up , jaycar have one called a sunstar 50A mppt controller dont know how good they are but perhaps i hook one of them up to just solve my no charge issue for the moment but at $849 which is almost as much as pip-4048ms maybe out of my budget surely something out there cheaper that i can get reasonably quickly to rectify my current dilemma, any suggestions ?

Ive a background in electronics and computers but it maybe some surface mount ic thats died that detects the solar connected i need a circuit diagram and some kinda miracle to repair it .

please help me

[offgridQLD]

45c ambient temps perhaps a lot more where it's located in - on the van? Out of interest is there a big black finned heat sink on the top of your pip or is it the newer style with a smooth top surface?

Don't pay $800 for a Jaycar solar charger. That's way overpriced for what you are getting.

Where are you located ? I assume SA or VIC. Edit: I see now your in Melbourne, couldn't see that info on my phone.

Kurt

[coulomb]

Alas, I've never heard of the Solar Charge Controller (SCC) dying, and I've never seen even a partial schematic diagram.

For a really quick and dirty emergency solution, I'd consider connecting the PV arrays (after the breakers of course) directly to the battery. Definitely disconnect from the inverter-charger first. This gives no MPPT, which isn't too bad with 2S panels, but it also means NO VOLTAGE REGULATION. That means you need to keep an eye on the voltage all the time. When the voltage is high, use your breakers (get some if you only have fuses now) to disconnect the PV panels for a while.

You might also need to check for the battery heading towards low voltage, and adjust the air conditioner to keep essential loads (Xbox ) going, since the lack of MPPT will lose you some solar energy.

The SCC is quite separate from the rest of the inverter-charger. So you could take it out and check for anything obvious, including loose connectors along the way. Look for capacitors with their tops bulging. If you find one or two and attempt to replace them, make sure they jave adequate voltage and temperature ratings (try for 105'C gor example). Also try to get low ESR versions. You might be very lucky at Jaycar, but you might do better with RS components or element14. RS still have free shipping for small orders, I believe. You might even be able to beat the Christmas break, but it sounds unlikely. Check the index for the posts on capacitor replacement for more clues.

I hope this gets you through this hot spot, so to speak.

[coulomb]

I've heard of people buying spare main boards from MPP Solar, so you might also be able to buy an SCC on its own for reasonable money.

[paulvk]

As a quick fix maybe http://www.lowenergydevelopments.com.au ... -Regulator
Check with them that it does not go above 60volts when it charging
After looking at the instruction sheet it seems you can set the max charge voltage so this unit should work OK

[Johny]

Hi Sean. Your details say you are in Melbourne but it sounds like the weather we have had in the past few days in central Victoria. Roughly where are you?
As coulomb says, if you are going to be "home" most of the time, connect the panels directly (via a good DC CB) to the batteries and monitor the voltage manually. Disconnect when you have to leave it for a while. Given the hot(ish) weather to come in the next week or so you won't lose to much power without the MPPT. 'Tis a tad bad for your batteries if you don't watch carefully though.

[offgridQLD]

It should be under warranty if you only purchased it in March this year.

Though that doesn't help your immediate issue....powerless Xmas.


I think it would take a good week or so to get a replacement sent over under warranty. Having a backup solar charge controller if your living completely off grid Is a smart Idea. Even a back up inverter.

Though finding one at a good price locally this time of year is the challenge.

Kurt

[solamahn]

I have bought a few scc pcb. USD90 from mppsolar.

[PlanB]

I'm getting some strange results on a 6 box system with a nominal 70kwh of usable storage. Takes 4 hours to charge from 52.4v to 58.4v at 15kw then 15mins from 58.4v back to 52.4v at 7kw discharge. I've validated all the data coming out of the boxes is correct, can't figure out why the discharge doesn't last for 8 hrs (over the same voltage range as the charge) instead of just a quarter hour. Still what's a factor of x32 amongst friends?!
Some days I think about giving up electronics/software & doing landscape gardening instead. I guess that field of endeavour has it's share of head scratching too?

[paulvk]

PlanB
What type and Ah are the batteries

[offgridQLD]

If that's your voltage under a 7kw load and it's a 48v nominal lead acid battery.

I don't think you can really draw any conclusions from the two kind of unrelated voltage points. One under charge and others under load.

Kurt

[Johny]

I tried to find a better graph but this one should do. If you look at the charge/discharge for a particular rate (say C/20) you can see the hysteresis effect. It shows that Voltage doesn't tell you much (all by itself).

[weber]

I'm getting some strange results on a 6 box system with a nominal 70kwh of usable storage. Takes 4 hours to charge from 52.4v to 58.4v at 15kw then 15mins from 58.4v back to 52.4v at 7kw discharge. I've validated all the data coming out of the boxes is correct, can't figure out why the discharge doesn't last for 8 hrs (over the same voltage range as the charge) instead of just a quarter hour. Still what's a factor of x32 amongst friends?!

You haven't been very forthcoming about what you're working on here, Mr B. I think we need our curiosity slaked before we could possibly help you with this. And a description, based on your experience, of how to set up parallel PIPs without blowing them up (what not to do) will soon be really useful to Coulomb and I.

You have to take into account what current, temperature and state of charge your four voltage measurements are made at. You have voltage rise or sag due to charge or discharge current interacting with resistance and electrochemical hysteresis. The resistance is due to cables, contactors, shunts, bolted connections and cell internal resistance. Cell internal resistance should be the most significant part, and that depends on temperature and state of charge. The electrochemical hysteresis is about 60 mV per cell for LiFePO4, so that's about 1 volt for a 16 cell battery. That's how much we expect the battery voltage to fall in going from a small charge current to a small discharge current. It's all in those papers Johny found on voltage vs SoC for LiFePO4.

If you've only been once up and once down, this can explain it. Since at the start of the charge phase, with charge going in, 52.4 V would be quite a low SoC. But at the end of the discharge phase, with current coming out, 52.4 V would be quite a high SoC. But if you're saying you have closed the loop and recharged again after the 15 minute discharge and it still took 4 hours to get back to 58.4 V, then either there's an awful lot of heat somewhere that you're somehow failing to notice, or you've altered the laws of physics, or your measurements are wrong.

Some days I think about giving up electronics/software & doing landscape gardening instead. I guess that field of endeavour has it's share of head scratching too?

Yes. But a shampoo under a hot shower gets rid of those bugs.

[PlanB]

The cells are Sinopoly LFP500AHA, I got asked to write some box monitoring code by a mate with ambitions in alternative energy. The subsequent charge/discharge cycles are all 15min so I just don't understand batteries all that well I guess (there is much better correspondence between cell voltage & SOC on the Leaf).

Re boxes in parallel. Blow up the first set, smile meekly, ask for a 2nd set & be more careful with the wiring, especially the battery wiring. Boxes won't let you parallel the inverter outputs with the #28=PAL cmd unless you have the inverter switch on the box underside off (makes sense when you think about it).

[baal]

thanks for the quick replies
Its working again !
I went back on the roof disconnected the panels and tested each one and found some fool (that would be me ) had wired up the connectors on one of the panels in the wrong polarity as i changed the mc2 connectors to mc3 connectors must have got one set around the wrong way oops, lucky each string had a blocking diode so no damage anything , re-checked all the voltages and polarities as i hooked them back up and now it works.
Gees i feel like an idiot, how i missed that i dont know it was hot so i think i claim heat stroke
anyways its all working getting about 1.9kw and its overcast so i am a happy camper.

I think i will have to look into the lithium batteries as the agm ones i currently use are pretty week , any one hooked up one of thoes telsa powerwalls to a pip-4048 i believe they are a 48Volt unit for the 10kva version might be cheaper .

thanks again

[Johny]

Great to hear Sean!
Don't worry about doing something like that - we've all done similar (or worse)!
It's just great that your back on track with some electricity over Christmas.

You kind of didn't mention the bit about climbing around the roof on a swelteringly hot day.

[baal]

yes mine has the big black heatsink on the top , my only disappointment with it was really the size of the pv connector a bigger one would have been nice and the watchpower software is not all that great, will look at getting it connected to a linux box and log the data to SQL make a nice html front end server for it latter with some remote control features.

but i am all up and working again now, happy days !

[paulvk]

I am working on a server for the inverters using Atmel AVR have the server working sending pages from SD card and or flash , responding to commands , operating external hardware , reading ADC ports and sending data back and forth via rs232 I just have to write the interfacing commands to the inverters.
See here for the project
http://www.mcselec.com/index2.php?optio ... ic&t=12358
I choose not to use a device running a full operating system like the Pi because I want full control of the software and it does not have all the ports as do the AVRs designed to control hardware.

I have already have a remote access via rs232 using other hardware so I can monitor my systems that are 200Km apart.
But its taking a while as I have too many things to do.

[weber]

Hi PlanB,

Yes. Batteries are complicated, but you should be able to implement my simplified (sounds better than "crude") model in your software, that will be Good Enough (TM). We have done so in our BMS, at the cell level.

Introduction

The model takes instantaneous voltage, current and cell temperature, and one constant that you have to obtain from a measurement of voltage sag under load, at a known cell temperature. From those it estimates what the open circuit voltage of the cell would be, which can then be compared with thresholds chosen from published graphs so as to keep operation within a safe range of states-of-charge (SoC).

Of course if you're doing this only at the whole-battery level, you need to ensure that your cells remain top balanced and that they have capacities that don't differ by more than say +-5%.

Yes. Nissan Leaf cells (and pretty much any Li chemistry other than LiFePO4) has a far more linear voltage vs SoC curve than LiFePO4.

The OCV Estimation Method

Here are the best of the papers Johny found. Take a look at their voltage vs SoC graphs for single LiFePO4 cells.

http://www-personal.umich.edu/~hpeng/DSCC2013_Weng.pdf
See figure 2 on page 3.

http://www.cse.anl.gov/us-china-workshop-2011/pdfs/batteries/LiFePO4%20battery%20performances%20testing%20for%20BMS.pdf
[Edit: Broken link above replaced by download/file.php?id=1410]
See the graph on the left of page 15.

Notice how there are two flat sections. One from 40% to 70% SoC and the other from 80% to 95% SoC. These make it impossible to use voltage to tell the state of charge within those ranges. But if all you want to do is tell when you're at 100% SoC and when you're at a chosen lower threshold such as 20% or 30% SoC, then it's doable.

But these graphs show only what happens at very slow rates of charge and discharge. They do not take into account rise or sag due to internal resistance.

So that's the first thing to take care of. Let's say the battery internal resistance (from the point of view of the PIP) is 6 milliohms, then if the PIP measures the voltage as 52.4 V when it is pulling 140 amps from the battery, the open circuit voltage would be 52.4 + (140 x 6/1000) = 53.24 volts. If you divide that by 16 you get an average cell voltage of 3.33 V. If you look that up on one of those charts, using the discharge curve (the lower one), you'll see that this could be anywhere between 80% and 95% SoC.

On the other hand, if you are charging at 300 amps and you read exactly the same voltage (52.4 V) then you can calculate the open circuit voltage to be 52.4 - (300 * 6/1000) = 50.72, which is an average cell voltage of 3.16 V. We can look this up on the charge curve (the upper one) and find that it is around 6% SoC.

So don't use the measured voltage to test against your thresholds for full and empty. Use estimated open circuit voltage which is:

estOcVoltage = measuredVoltage - measuredCurrent * intRes
where a negative current is a discharge.

So how do we measure internal resistance. We do this during commissioning: Make sure the battery is in one of those flat areas -- either 45 to 65% or 85 to 90% SoC (a half hour rested voltage of 52.8 V or 53.5 V). We record the battery temperature. Then we put a light load on it (5 to 10%), wait maybe 5 seconds for the voltage to stabilise, then record the battery voltage and current readings from the PIPs. Then increase the load (to 50 to 100%), wait another 5 seconds, and repeat the measurements. The internal resistance is obtained as:

intRes = (voltageA - voltageB) / (currentB - currentA)

If in doubt, err on the low side for your internal resistance estimate. Divide by the number of cells in series, to get the resistance per cell.

But we're not quite done, because this is not quite Good Enough (TM). That's because internal resistance (IR) varies enormously with cell temperature. The second of those papers above has a horrendous cubic approximation of the IR versus temp curve for a specific cell, but this is really dopey. It's as if they have never heard of Arrhenius' equation. The internal resistance can be approximated much more simply as the sum of a fixed component and an Arrhenius component.

intRes(T) = intResFixed + intResArrhenius(T)

For typical battery temperatures an Arrhenius component approximately halves for every 10 degree rise in Celsius temperature T. So it can be approximated as:

intResArrhenius(T) = intResArrhenius(T0) / 2^((T - T0)/10)
where T0 is any reference temperature at which we know the Arrhenius component of IR to be intResArrhenius(T0).

But we can't directly measure the two components, although the fixed component dominates at high temperatures and the Arrhenius component dominates at low temperatures. Ideally we'd measure the IR at two widely spaced temperatures (at least 10 degrees apart, preferably 20). But we often don't have that luxury.

So I make yet another "simplifying" approximation. I assume that the two components happen to be equal at 10°C, for no other reason than that's what we find in that second paper above. So now we can write

intRes(T) = intResFixed * [1 + 2^(1-T/10)]
where T is the cell temperature

So we calculate (during commissioning) the approximate fixed component from the measured value, using the inverse of the above function.

intResFixed = intRes(T0) / [1 + 2^(1-T0/10)]

So if we happened to measure it at 10°C we'd divide the measured value by 2 to get the fixed component. If we measured it at 20° we'd divide by 1.5, and at 30°C, 1.25.

Summary

So the procedure is to periodically read the battery voltage, current and temperature. If you don't have actual battery temperature, ambient temperature is probably usable, but only for these systems that operate at 0.5C or less. Then use the temperature, and your intResFixed constant, to estimate the internal resistance according to:

intRes(T) = intResFixed * [1 + 2^(1-T/10)]

Then use this internal resistance to estimate the open circuit voltage according to:

estOcVoltage = measuredVoltage - measuredCurrent * intRes(T)

Then compare the estimated open circuit voltage against the thresholds you have chosen from those charts linked above. e.g.
3.23 * 16 = 51.7 V for 25% SoC, and
3.47 * 16 = 55.5 V for 100% SoC.

One thing you'll notice about those two papers. Although they agree on the shapes of the curves and the voltages of those flat areas, they don't quite agree on what voltages should be considered 0% and 100% SoC. This is somewhat arbitrary, but it would be nice if the industry could choose something and agree on it.

[offgridQLD]

"they don't quite agree on what voltages should be considered 0% and 100% SoC. This is somewhat arbitrary, but it would be nice if the industry could choose something and agree on it."


It would be nice.

I feel the battery industry is one with the most wife's tails that get repeated enough that it some how becomes fact. Among other cross referencing of rules from other chemistry even variations of a particular chemistry that all get in the way of the simple science and factual data.

At times it almost feels like the people making the batterys have managed to put a battery together and sell it but don't really fully understand all the ins and outs of the beast they have created them self.

It then takes a 3rd party to do all the testing to come up with some results and rules.



Kurt

[paulvk]

baal
The battery that gives you the most for money spent are the Trojan T105s and a watering kit to make filling with water easy.
Now if you look around every now and then good second hand AGM/VRLAs do come up cheap just have to do the research to find their age and history.

As an example http://www.ebay.com.au/itm/Deep-Cycle-Y ... SwT5tWPvd3
Transport is also not that expensive cost me $170 per pallet (20 per pallet of these) Melb to Syd

[offgridQLD]

"The battery that gives you the most for money spent are the Trojan T105s"

Most what.....

Most Backache's.
Most sulfation.
Most generator run time.
Most acid burns in your levis.
Most saggy voltage.


sorry Just being silly,

though cost isn't a big factor with lithium's going forward. Value when you look at them making usable power over time they are competitive with many added benefits.

Kurt

[PlanB]

Thnx for the detailed reply Dave, I don't have cell temperature & your comment "If you don't have actual battery temperature, ambient temperature is probably usable, but only for these systems that operate at 0.5C or less" suggests I need it since this system runs at room temperature (charge & discharge rates are both less than 0.3C so the pack isn't warm to the touch). I can maybe try your approach with a known temperature on the day & see how it works I guess?

I was going to declare the pack fully charged when it hits 58.4v at the end of the first cycle then coulomb count from there to get SOC for any given 24 hr period.

What would be really nice would be an equation for those cell voltage vs %capacity graphs. Have you noticed how the basic curve shape remains constant even though the graph bounces up & down with temperature, discharge rate, etc? If we knew the line equation we could just use dV/d% to infer SOC from rate of change of pack voltage.