PIP-4048MS and PIP-5048MS inverters

non-EV Solar, Wind and other renewable power sources
non-EV batteries and other energy storage stuff
Forum rules
Important!
This forum is for discussion of Non-EV matters.
User avatar
coulomb
Site Admin
Posts: 3728
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

PIP-4048MS inverter

Post by coulomb » Mon, 21 Dec 2015, 13:31

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.
Last edited by coulomb on Mon, 21 Dec 2015, 02:34, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
coulomb
Site Admin
Posts: 3728
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

PIP-4048MS inverter

Post by coulomb » Mon, 21 Dec 2015, 13:57

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.
Last edited by coulomb on Mon, 21 Dec 2015, 02:58, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

paulvk
Groupie
Posts: 185
Joined: Fri, 23 Oct 2015, 23:45
Real Name: Paul
Location: Sydney

PIP-4048MS inverter

Post by paulvk » Mon, 21 Dec 2015, 14:01

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
Last edited by weber on Mon, 21 Dec 2015, 03:45, edited 1 time in total.

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

PIP-4048MS inverter

Post by Johny » Mon, 21 Dec 2015, 14:12

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.
Last edited by Johny on Mon, 21 Dec 2015, 03:27, edited 1 time in total.

User avatar
offgridQLD
Senior Member
Posts: 1825
Joined: Tue, 23 Jul 2013, 16:05
Real Name: Kurt
Location: Fleurieu Peninsula, SA

PIP-4048MS inverter

Post by offgridQLD » Mon, 21 Dec 2015, 14:17

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
Groupie
Posts: 121
Joined: Thu, 18 Jun 2015, 00:09
Real Name: Julian Leach
Location: PNG

PIP-4048MS inverter

Post by solamahn » Mon, 21 Dec 2015, 14:23

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

User avatar
PlanB
Senior Member
Posts: 465
Joined: Sat, 16 Jan 2010, 15:24
Real Name: Kris McLean
Location: Freemans reach
Contact:

PIP-4048MS inverter

Post by PlanB » Mon, 21 Dec 2015, 15:04

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
Groupie
Posts: 185
Joined: Fri, 23 Oct 2015, 23:45
Real Name: Paul
Location: Sydney

PIP-4048MS inverter

Post by paulvk » Mon, 21 Dec 2015, 15:12

PlanB
What type and Ah are the batteries

User avatar
offgridQLD
Senior Member
Posts: 1825
Joined: Tue, 23 Jul 2013, 16:05
Real Name: Kurt
Location: Fleurieu Peninsula, SA

PIP-4048MS inverter

Post by offgridQLD » Mon, 21 Dec 2015, 15:33

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
Last edited by offgridQLD on Mon, 21 Dec 2015, 04:34, edited 1 time in total.

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

PIP-4048MS inverter

Post by Johny » Mon, 21 Dec 2015, 15:47

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).

Image

User avatar
weber
Site Admin
Posts: 2601
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

PIP-4048MS inverter

Post by weber » Mon, 21 Dec 2015, 15:48

PlanB wrote: 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. Image 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.
Last edited by weber on Mon, 21 Dec 2015, 04:52, edited 1 time in total.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
PlanB
Senior Member
Posts: 465
Joined: Sat, 16 Jan 2010, 15:24
Real Name: Kris McLean
Location: Freemans reach
Contact:

PIP-4048MS inverter

Post by PlanB » Mon, 21 Dec 2015, 18:54

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).
Last edited by PlanB on Mon, 21 Dec 2015, 07:55, edited 1 time in total.

User avatar
baal
Noobie
Posts: 6
Joined: Mon, 21 Dec 2015, 06:32
Real Name: Sean
Location: Melbourne

PIP-4048MS inverter

Post by baal » Mon, 21 Dec 2015, 19:48

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
To see a World in a Grain of Sand And a Heaven in a Wild Flower, Hold Infinity in the palm of your hand And Eternity in an hour. - William Blake

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

PIP-4048MS inverter

Post by Johny » Mon, 21 Dec 2015, 20:12

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.

User avatar
baal
Noobie
Posts: 6
Joined: Mon, 21 Dec 2015, 06:32
Real Name: Sean
Location: Melbourne

PIP-4048MS inverter

Post by baal » Mon, 21 Dec 2015, 20:46

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 !
To see a World in a Grain of Sand And a Heaven in a Wild Flower, Hold Infinity in the palm of your hand And Eternity in an hour. - William Blake

paulvk
Groupie
Posts: 185
Joined: Fri, 23 Oct 2015, 23:45
Real Name: Paul
Location: Sydney

PIP-4048MS inverter

Post by paulvk » Mon, 21 Dec 2015, 21:42

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.
Last edited by weber on Mon, 21 Dec 2015, 10:57, edited 1 time in total.

User avatar
weber
Site Admin
Posts: 2601
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

PIP-4048MS inverter

Post by weber » Tue, 22 Dec 2015, 01:13

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" Image 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.
Last edited by weber on Mon, 21 Dec 2015, 15:36, edited 1 time in total.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
offgridQLD
Senior Member
Posts: 1825
Joined: Tue, 23 Jul 2013, 16:05
Real Name: Kurt
Location: Fleurieu Peninsula, SA

PIP-4048MS inverter

Post by offgridQLD » Tue, 22 Dec 2015, 01:35

"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
Groupie
Posts: 185
Joined: Fri, 23 Oct 2015, 23:45
Real Name: Paul
Location: Sydney

PIP-4048MS inverter

Post by paulvk » Tue, 22 Dec 2015, 02:14

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

Last edited by paulvk on Mon, 21 Dec 2015, 15:45, edited 1 time in total.

User avatar
offgridQLD
Senior Member
Posts: 1825
Joined: Tue, 23 Jul 2013, 16:05
Real Name: Kurt
Location: Fleurieu Peninsula, SA

PIP-4048MS inverter

Post by offgridQLD » Tue, 22 Dec 2015, 02:46

"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

User avatar
PlanB
Senior Member
Posts: 465
Joined: Sat, 16 Jan 2010, 15:24
Real Name: Kris McLean
Location: Freemans reach
Contact:

PIP-4048MS inverter

Post by PlanB » Tue, 22 Dec 2015, 02:51

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.

User avatar
weber
Site Admin
Posts: 2601
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

PIP-4048MS inverter

Post by weber » Tue, 22 Dec 2015, 04:04

If it's in aircon you can ignore temperature and just use a fixed IR.
PlanB wrote:I was going to declare the pack fully charged when it hits 58.4v
That would certainly guarantee it was full since it corresponds to 3.65 V per cell. But in general you don't need to go that high. Reasons not to go that high are to increase the life of the cells and to avoid any cells going to the destructive 4.3 V if they are not well balanced. How are they balanced? If you're using EV-power CMUs then you will need to go to that high for them to do any balancing.
at the end of the first cycle then coulomb count from there to get SOC for any given 24 hr period.
Coulomb counters will drift. You should reset it to 100% every time it goes to 58.4 V. But I assume that usually only happens once a day anyway.

Coulomb counting is the only way to give the user any idea of the SoC when it is between 40% and 95%. But using the coulomb counter to protect the cells from overdischarge is a bad idea, due to the aforementioned drift, and the cell capacity will reduce over time. Protection should be based on voltage (preferably estimated open circuit voltage). If you're happy to let the cells go down to an average of 5% SoC (which means if there is a +-5% variation in cell capacity, some will be at 0% and others at 10%) then you can just use measured voltage, as you can with your high 100% voltage, because you're so far down the steep part of the curve.

But if you want to prevent cells from regularly going any lower than 20% SoC then you will need to compensate the voltage for current times IR, and compensate the IR for temperature.
What would be really nice would be an equation for those cell voltage vs %capacity graphs.
It's in Weng, Sun and Peng, the first reference I gave above.
http://www-personal.umich.edu/~hpeng/DSCC2013_Weng.pdf
Table 1 equation 6 combined with Table 3 right column.
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.

An interesting idea. You can see this plotted in Lu, the second reference I gave above.
http://www.cse.anl.gov/us-china-worksho ... %20BMS.pdf
Left hand graph on page 12.

One look at that graph should convince you that this is useless for detecting anything other than > 100% and < 10%. It is constant in the range 20% to 40% and has the same value in this range as it has in the ranges 75% to 78% and 99% to 100%.
Last edited by weber on Mon, 21 Dec 2015, 17:09, edited 1 time in total.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
offgridQLD
Senior Member
Posts: 1825
Joined: Tue, 23 Jul 2013, 16:05
Real Name: Kurt
Location: Fleurieu Peninsula, SA

PIP-4048MS inverter

Post by offgridQLD » Tue, 22 Dec 2015, 13:27

Capacity loss over time is something I haven't accounted for in my personal offgrid lithium system. I have LVD at cell level. Though I was thinking the other day my little capacity display that resets to 400ah - 100% SOC each time I reach float starts to have less credibility as the years go on.

That said I never did a full capacity sweep in the beginning so who knows if the cells were over 400Ah new at low C discharge rates.

Would be nice if there was a formula you could use to even roughly predict capacity loss using averages, temp, cycles and so on.

Kurt




User avatar
baal
Noobie
Posts: 6
Joined: Mon, 21 Dec 2015, 06:32
Real Name: Sean
Location: Melbourne

PIP-4048MS inverter

Post by baal » Wed, 23 Dec 2015, 05:28

now again looking at my battery situation ...
I picked up my batteries second hand at $40 each they are powerware VRLA battery PWHR12280W4FR with a float voltage of 13.5 - 13.8V , which were used in some big ups for a hospital and changed at 3years regardless of condition so i figured i would pick the ones that had the highest voltage under load and bought 8 out of the 30 odd they had there thinking that they still had plenty of life left in them, and with a battery tester they all seemed to hold a respectable voltage under test load, so i thought they will do for the moment, i currently have 8 in total hooked up two sets of 4 in series at around 54 Volts ,

I have been running a couple of the desulfator devices found on ebay and im not sure if they really do anything but some of the advertising where they showed battery cells from a battery before and after and it looked impressive and for only $50 thought i would give them a go.

i calculate i have 4 batteries in series so Ah is the same as the battery about 75Ah plus another 75Ah in the other set of 4 so in parallel so about 150Ah at 52Volts, sound right ?
never really understood what that is suppose to mean i can pull one amp for 150hours ? thus 15amps theoretically for 10hrs ( that would be great ), no that cant be right cause i get maybe an hour out of them at 15Amps if its been a good solar day.

mind you it does not last long when you pull 15amps to run the ac which pulls ~800W on the inverter hmm thinking about the numbers the batteries must be nackered 15amps for 1hr is 15ah from what suppose to be 150ah , oh well they lasted 2 years for $350 thats no so bad.

New battery time ...
Ggoing 6 volt so all in series, 4 on each side of the van, mind you its 230kg of weight but on my 30ft caravan thats only a small part of the 3500kg capacity, but you have to think about that too, i built battery boxes just behind the axles on each side which seemed the best place for the weight.

What do people think about these Crown 225 batteries ?
http://www.ktbattery.com/components/com ... CR-225.pdf

8 batteries at about $200 a battery $1600

6volt x8 = 48V
225Ah at c20
and the bit i like the most is they are about the same size as the old ones so should fit in my boxes ( i hope )

lithium batteries would be great if i could afford them but i may have to wait till i find some really cheap .

Battery balance ..
after some reading of posts here in particular the ones about the lithium battery system, i concluded that i need to implement some battery balance system for the 8 batteries, perhaps some system that I can use again in the future on a lithium system would be great. Ideally I would really like to have some computer integration on the system to monitor the batteries so as to perhaps be able to remote view and control the system down the track, suggestions for battery balance solutions are very welcome .

I was looking at some basic battery balance systems like this one on ebay http://www.ebay.com.au/itm/251906187493 which may do the job but does not really give me any remote data but maybe a good short term solution, even after extensive searching i am struggling to find some kind of battery bank management system, perhaps i have to build one from scratch, was thinking with the battery balancer from ebay i could hack them sending the led signals to a basic data capture device with a usb interface to monitor data on the computer.

there is also this battery balancer ( http://www.ebay.com.au/itm/26213462072 ) but it does not have any leds which makes me think how would you even know its working .

Surely theres a device out there that can monitor all the batteries and send the data to a computer with relative ease, perhaps an adrino project, I guess if its not ridiculously expensive why re-invent the wheel.

sorry for the thesis :) ( and the bad spelling )

Sean
To see a World in a Grain of Sand And a Heaven in a Wild Flower, Hold Infinity in the palm of your hand And Eternity in an hour. - William Blake

User avatar
baal
Noobie
Posts: 6
Joined: Mon, 21 Dec 2015, 06:32
Real Name: Sean
Location: Melbourne

PIP-4048MS inverter

Post by baal » Wed, 23 Dec 2015, 05:51

on the battery topic ..

while the size is going to mean new battery boxes which is no big deal, what are peoples thoughts on going with 4 bigger 12v batteres like these

http://www.ebay.com.au/itm/4WD-SOLAR-WI ... SwYHxWHGNv

260Ah at c20
$450 x 4 $1800
63kg a battery gees im going to need a forklift to lift them .
4 would be(250kg)

10 year design life sounds good to me
To see a World in a Grain of Sand And a Heaven in a Wild Flower, Hold Infinity in the palm of your hand And Eternity in an hour. - William Blake

Post Reply