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Old 27-07-2016, 10:35   #5296
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Using micro-inverters on each panel would in effect be the same as using one small MPPT controller per panel...except the AC output would have to sync with an inverter sine wave to contribute to AC loads.

Makes more sense to put the energy into the batteries (DC) and then use as needed via the inverter....
I have found some white papers on Enphase's site, and using their micro-inverter batteries in a generator/solar installation is certainly complicated.

What to do about shading? Maybe use the micro-inverter equipped panels to only feed a battery charger charging conventional LiFePO4 DC batteries. Then AC loads are handled from the batteries through an inverter.
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Old 27-07-2016, 10:45   #5297
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I have found some white papers on Enphase's site, and using their micro-inverter batteries in a generator/solar installation is certainly complicated.

What to do about shading? Maybe use the micro-inverter equipped panels to only feed a battery charger charging conventional LiFePO4 DC batteries. Then AC loads are handled from the batteries through an inverter.
By using multiple smaller panels and independent controllers, only the shaded panels lose output. The other panels keep trudging along. It's the same as the Enphase concept (separate panels feeding common buss) except DC vs. AC.

Absolutely no point in trying to go AC from the panels...the panels are DC and good MPPT controllers are about 98% efficient to the batteries. No way going to AC then back to DC will be as efficient.

Of course there is some inefficiency loss from the batteries through the inverter to the AC loads, but at least it's from the stored energy from the panels.
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Old 27-07-2016, 15:12   #5298
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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There's a thread running where someone actually tested panel shading. A little shade on one panel (they used two panels, both in series and parallel), and production was cut in half. Any shade on both panels and production was cut even more sharply.

Well, I have an arch that's going to shade some part of the array most of the time (relocating the arch will not be easy), so I have gotten interested in Enphase's micro-inverter system. As noted above, the micro-inverters on the panels seem to limit the loss of production due to shading to the proportion of the array shaded. I can live with that. Then they have their micro-inverter AC batteries. How charging happens is not clear. But as I am going to have a mostly AC boat, this whole get-up might make sense for me, if I can figure it out.
Sometimes you need to cut through the marketing BS. Go back to this and think about it:
  • A panel is normally made of a string of cells. If you shade one cell, anywhere, it stops producing power and effectively interrupts the string, which happens to be the whole panel (at least in your reference above)
  • If the panel is shaded and not producing DC power, there isn't more power to be extracted by turning it into AC using micro-inverter gizmos...
On a solar roof installation, for economic reasons, the panels are usually wired in series, which results in high-voltage systems. 1000VDC at the inverter input is nothing uncommon. Shading one cell on one panel can bring the output of the entire system down - at least in theory - more about this below.
Using micro-inverters allows the power to brought down from the roof in parallel using light gauge cabling: it makes the installation more shade tolerant while keeping the cost of the copper down.

This problem doesn't exist on a boat where the best configuration is always paralleling the panels. Turning storable DC power into un-storable AC power makes absolutely no sense, unless you have no storage needs, like when you feed it back into the grid.

When it comes to shading, most panels have at least one or two bypass diodes: if there is a high resistance shaded area over say one half of the panel, current from the other (working) half can flow through the diode instead and bypass the bad half. Bypass diodes are not of much use on boats, because the voltage from half a panel is typically not high enough for charging, but it works in large series installations like solar roofs.
However, if you are prepared to pay, you can get panels with one bypass diode per cell, and that is a little bit better for small shaded areas.

If you are going to hang around the tropics and you design your system capacity for full sun everyday and you effectively design shade into it, you just shot yourself in the foot - when you think about it.

If you design for cloudy days, which means a combination of sufficient panel area and modest consumption, then you are working with diffuse ambient light and - within reason - there is no shade. In full sun, shade would reduce the output, but it would still be higher than effectively needed, so you might decide that you don't care.

There is an easier way than relocating your arch: cut it off at the base and throw it overboard. Seriously. Stern arches have become one of those ubiquitous necessities of cruising yachts. They add weight over the stern, put the boats out of trim, create a considerable amount of windage with very unpleasant implications and they are ugly.
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Old 27-07-2016, 16:14   #5299
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Sometimes you need to cut through the marketing BS. Go back to this and think about it:
  • A panel is normally made of a string of cells. If you shade one cell, anywhere, it stops producing power and effectively interrupts the string, which happens to be the whole panel (at least in your reference above)
  • If the panel is shaded and not producing DC power, there isn't more power to be extracted by turning it into AC using micro-inverter gizmos...
On a solar roof installation, for economic reasons, the panels are usually wired in series, which results in high-voltage systems. 1000VDC at the inverter input is nothing uncommon. Shading one cell on one panel can bring the output of the entire system down - at least in theory - more about this below.
Using micro-inverters allows the power to brought down from the roof in parallel using light gauge cabling: it makes the installation more shade tolerant while keeping the cost of the copper down.

This problem doesn't exist on a boat where the best configuration is always paralleling the panels. Turning storable DC power into un-storable AC power makes absolutely no sense, unless you have no storage needs, like when you feed it back into the grid.

When it comes to shading, most panels have at least one or two bypass diodes: if there is a high resistance shaded area over say one half of the panel, current from the other (working) half can flow through the diode instead and bypass the bad half. Bypass diodes are not of much use on boats, because the voltage from half a panel is typically not high enough for charging, but it works in large series installations like solar roofs.
However, if you are prepared to pay, you can get panels with one bypass diode per cell, and that is a little bit better for small shaded areas.

If you are going to hang around the tropics and you design your system capacity for full sun everyday and you effectively design shade into it, you just shot yourself in the foot - when you think about it.

If you design for cloudy days, which means a combination of sufficient panel area and modest consumption, then you are working with diffuse ambient light and - within reason - there is no shade. In full sun, shade would reduce the output, but it would still be higher than effectively needed, so you might decide that you don't care.

There is an easier way than relocating your arch: cut it off at the base and throw it overboard. Seriously. Stern arches have become one of those ubiquitous necessities of cruising yachts. They add weight over the stern, put the boats out of trim, create a considerable amount of windage with very unpleasant implications and they are ugly.
Thanks for your help. I have abandoned the Enerphase solution, and have moved on to the next bit of black magic, SolarEdge power optimizers. As I am no longer looking at the Enerphase AC batteries, I will not trouble this thread further. I will mention that the boat in question is a power cat, with an arch over the cabin roof, which is where the panels must live.
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Old 27-07-2016, 17:34   #5300
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Thanks for your help. I have abandoned the Enerphase solution, and have moved on to the next bit of black magic, SolarEdge power optimizers. As I am no longer looking at the Enerphase AC batteries, I will not trouble this thread further. I will mention that the boat in question is a power cat, with an arch over the cabin roof, which is where the panels must live.
If you are really hell-bent on spending money on gadgets... when you match a 33/36-cell panel to a 14V battery (charging), there often isn't a lot of room to "optimise" anything. In the tropics, panels run quite warm during the day and the voltage at the MPP isn't much higher.
When conditions are really poor, MPPTs can consume most of the power produced by the panels to run, leaving little or nothing for charging: the claimed efficiency of "98%" (which is always measured in the best possible conditions of course) effectively becomes about "0%" (this one seldom advertised) just when you most need the power.

We were having a drink on a sailing cat last winter when the owner mentioned his panels weren't charging. It was a dull rainy day, so we poked around with a multimeter for a few minutes and the culprit was quite obvious. When I disconnected the expensive big brand magic MPPT box and remote display, the array immediately started charging. It was modest, but much better than nothing. Sure, on a cool sunny day, the MPPT was making a small improvement, except that there is no real need for it then.
In order to have any real value, a MPPT converter needs to have the smallest possible intrinsic consumption: this means not buying it oversize for a start. Even then, gains are not all that impressive against a well-designed installation.
If you have the real-estate, using the MPPT budget to buy more panels is always a winner by a very long margin.

Match your panels to your system voltage, wire them all in parallel, source a PWM regulator (or a few smaller ones) without heatsink (i.e. designed for efficiency, not built down to a cost) and enjoy the lowest cost, simplest design and maximum performance when you need it.
If you want to marry that with lithium cells, beware of overcharging in combination with voltage ripple problems. The simpler, older-style switching regulators are the safest as they switch on peak voltage, not average.

Powerboats and multis in general certainly have more options with solar.
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Old 06-08-2016, 07:50   #5301
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I'm setting up my Victron bvm 702 today for my 540ah lifepo4 bank and I can't remember or seem to find what the Peukerts number the community is using. I want to say it was 1.1 but I'd rather be sure than guess and constantly be getting incorrect readings.

If anyone can shed some wisdom that would be much appreciated!

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Old 06-08-2016, 13:28   #5302
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I'm using 1.1 and so far it's worked well.

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Old 06-08-2016, 14:27   #5303
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I'm using 1.1 and so far it's worked well.

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That's what I settled in on after two yrs of use....
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Old 06-08-2016, 15:07   #5304
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I love this thread. Thank you all for providing a great resource provided by real life experts. I have a simple question. Researching I have come across 1,000 AMP litho 4 batteries. My question is is worthwhile over sizing and using a single battery rather than lower storage that needs to cut off power adding sources when storage limits are met? I know it's probably a silly question so please forgive me in advance. Thanks.
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Old 06-08-2016, 20:05   #5305
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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My question is is worthwhile over sizing and using a single battery rather than lower storage that needs to cut off power adding sources when storage limits are met? I know it's probably a silly question so please forgive me in advance. Thanks.
There are no silly questions.

With lithium you always need a way to cut off charging when full even if battery Ah is big compared to A from charging source (because self discharge and various inefficiencies are much lower).

That said, it is not difficult to accomplish that. With lithium and fractional C charging rates you do not need an absorption phase, just a cutoff when hitting voltage X will do.

That means that with lithium you do not NEED to oversize capacity but you CAN do it to deal with cloudy days, because lithium batts will not suffer from PSOC cycling.


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Old 06-08-2016, 21:57   #5306
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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There are no silly questions.

With lithium you always need a way to cut off charging when full even if battery Ah is big compared to A from charging source (because self discharge and various inefficiencies are much lower).

That said, it is not difficult to accomplish that.
Since I'm over two years now with my 400AH LiFePO4 KISS set-up, it's worth mentioning that a simple way to keep your LiFePO4 batteries from being overcharged without the expense and clap-trap of a BMS/High Voltage Cut Offs etc. Simply set the charge voltage of your various charging devices (Solar/Wind/Battery Charger/Alternator) at a level that can do them no harm. I started out at 13.4v, but over the years have comfortably walked my voltage up to 13.6/13.7v. Once the battery voltage hits that level, there is no longer a driving force to push Amps into the battery bank and the charge stops.

Heretic...Witch...Flat Earther....

Ya ya ya...I've hear all the panic about how I will fry my battery bank, blow it up and kill myself and kids, even contribute to the death of baby fur seals. But after two years with this bone simple system I have seen no measurable decrease in battery capacity, cell drift or drama.

So that takes care of the top end, for the low end that's even easier. I may not know my wedding anniversary date or my kids birthdays but I know the voltage status and Amp hour counter status of my battery bank. That is just something every cruiser knows to keep an eye on so if I'm seeing things getting low, I start the generator if the Solar isn't doing the job for me.

Now I do have audible Low voltage and high voltage alarms (the only time they have went off is when I test them) and I have a cell log giving me the individual cell voltages, that is topped off with an inlet and outlet Amp counter. Done...that's it.

Now I'm not posting this to throw stones at the full BMS computer control guys that interface their battery bank over the internet, I love them and think it is cool to follow along. I'm just sharing this info for the guys like me out there that want to keep things simple and save some cruising kitty cash. I may be a heretic, but the kids are almost out of high school and I'm heading back to Mexico if my battery bank don't explode and kill me first.
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Old 07-08-2016, 07:01   #5307
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by campr View Post
I'm using 1.1 and so far it's worked well.

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That's what I settled in on after two yrs of use....
Thanks gentlemen, I got it setup. Just need to bring the batteries back up to full and I'll do a manual sync on the BMV and be right as rain!

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Old 10-08-2016, 10:05   #5308
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Hi all,

I would like to get some advise on adding to my existing LifePo4 batteries. I have 600ah LifePo4 battery bank and feel the need to add 200ah more capacity as I am headed across the pacific and beyond and my boat is a bit of a power hog.

The bank is in great shape all 100ah cells and 3 years old now with no problems. My concern is I can't get these cells anymore and I would have to add a different brand and I am concerned about them becoming imbalanced with newer cells of a different manufacture and possible capacity differences. Anyone have any experience with doing something similar?

The other possibility would be for me to sell the existing 600ah bank and start fresh with a larger bank. Might be a good deal for someone interested in getting into LifePo4 tech.

Any advise would be greatly appreciated.

Cheers,

CJ
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Old 10-08-2016, 12:34   #5309
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Thanks gentlemen, I got it setup. Just need to bring the batteries back up to full and I'll do a manual sync on the BMV and be right as rain!

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1.1 for Peukert is essentially an AGM Peukert (Lifeline, Odyssey etc.) and it will cause counting errors. At the loads we are drawing these banks at Peukert is essentially 1.0 - 1.03.

No matter what you do these Ah counters will get out of sync if not regularly reset to 100% SOC. The batteries are very, very predictable and Ah counters were designed for lead acid..

The best performance I have come up with so far is Peukert of 1.0 and charge efficiency set to 100% to avoid any negative counting on the recharge.. Remember a Peukert for a a flooded battery of 100Ah is based on a 5A load. A LFP battery is rated at either .5C or 1C load so a 5A load and a flooded Peukert factor simply does not work well...
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Old 10-08-2016, 12:48   #5310
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Here's the dangerous lithiums exploding when being crushed:

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