Second powerwall, what do I need?

Follow up for anyone who is interested, with one question.

I have proceeded to add 3 additional Powerwalls, now have a total of four 48 volt walls, each with 1400 18650 Lithium ion cells, most from old modems and medical packs, some from used laptops. Total of 5600 cells. A ton of hours of work, but all done.

I repurposed 9 additional 280 watt solar panels to help charging the system, and this has done very well, using a lot less grid power to recharge the Powerwalls using super off-peak grid, $0.015 per kWh.

I temporarily added another solar charge controller, another PCM60X, rated for up to 3.2 kW, producing up to 60 amps output. What I noticed was that each of the 9 panels was hooked up to a separate PCM60X charge controller, and I never saw over 1.5 kW of input from the solar panels on either of the chargers. I then decided to try hooking ALL 18 panels up to a single PCM60X charger. Thus far, in the middle of winter, I have seen a single time point in mid afternoon in full sun that was 3.16 kW of solar input. Question is...will I exceed the 3.2 kW limit as the sun gets higher in the sky as summer approaches, and if so, will I FRY my single PCM60X unit? What will happen to the solar charger if it exceeds the specifications for an hour of the day? Is there some redundancy built-in?

If this is dangerous, then I could simply split the system again and put my second PCM60X back in service, with each of the 9 panel arrays attached to a dedicated charge controller. Wonder what others have done???
 
Fantastic - a lot of fun to read about your progression in building up the system. It was similar for me as well - step by step and before you know it you'll be powering the whole house :)

>will I exceed the 3.2 kW limit as the sun gets higher in the sky as summer
If winter is 3.16 then it seems pretty likely to me.

Some comments:
1) Not sure why you don't like running both PCM60X(s) - its perfectly OK to have multiple Charge Controllers charging a single battery bank.
Add 3 or 4 or... as long as the battery / control box / wiring can handle the incoming amps its OK.

2) Seem like PCM60X would answer this question for you? For example, I use Midnite Solar Charge controllers and they allow you to limit output amps (amps -> battery) which is implemented by limiting amps coming in... so you can overload the PV input to a significant degree and it will just ignore it.

3) Side note: I have circuit breakers just before the power goes into the charge controllers.... which is mainly for safety when I work on them but I did trip these when I got 'too much' input during some experiments. Perhaps you could add some circuit breakers if most days are OK but you want protection for a couple of unexpectedly sunny days?

Personally, I'd shoot for #1 - design/scope the system for year-round operation.
 
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OffGridInTheCity said:
Fantastic - a lot of fun to read about your progression in building up the system. It was similar for me as well - step by step and before you know it you'll be powering the whole house :)

>will I exceed the 3.2 kW limit as the sun gets higher in the sky as summer
If winter is 3.16 then it seems pretty likely to me.

Some comments:
1) Not sure why you don't like running both PCM60X(s) - its perfectly OK to have multiple Charge Controllers charging a single battery bank.
Add 3 or 4 or... as long as the battery / control box / wiring can handle the incoming amps its OK.

2) Seem like PCM60X would answer this question for you? For example, I use Midnite Solar Charge controllers and they allow you to limit output amps (amps -> battery) which is implemented by limiting amps coming in... so you can overload the PV input to a significant degree and it will just ignore it.

3) Side note: I have circuit breakers just before the power goes into the charge controllers.... which is mainly for safety when I work on them but I did trip these when I got 'too much' input during some experiments. Perhaps you could add some circuit breakers if most days are OK but you want protection for a couple of unexpectedly sunny days?

Personally, I'd shoot for #1 - design/scope the system for year-round operation.
Click to expand...
Just saw 3.34 kW and 57 amps output from the PCM60X this afternoon. No way to throttle it back with software, but do have breakers in the combiner box that precedes the charger. Not sure how much the single PCM60X can handle?

Maybe adding the second charger is a good idea?
 
Manual, page 13 shows a software setting to limit current to between 10A ~ 60A ("Settings Program 01").

I have 3.2kWp PV panels connected to a eSmart3 60A charger with, but software limited to 45A. Runs a lot cooler. I lose some PV energy on very sunny days, but on such days the battery gets enough charge anyways.
 
To add: Don't know for sure about the PCM60X, but usually with such chargers, you can attach way more solar panels than the manufacturer recommends, as long as you stay under the max voltage limit. The 60A (or whatever) output limit also limits how much power it takes from the solar panels. The only issue is that the charger will potentially run much longer periods at 100%, which may reduce the lifespan of the charger, so setting a slightly lower limit may be a good idea. Particularly true with Chinese devices that are often designed with much less tolerance to save costs.
 
All great responses! Essentially have 18 x 280 watts or 5.04 kW of solar panels attached to a charger with maximum input rated at 3200 watts for 48 volt battery system. Maximum output is 60 amps. Due to each 9 panel array getting greater power at different times of the day, am essentially seeing around 60% of their potential output at peak sun today. That will likely go to 65-70% as summer approaches. Still the maximum output is 60 amps, but concerned about overheating and potential charger failure due to exceeding the recommended maximum solar input of 3200 watts.

Probably best solution is to use both chargers, each attached to 9 panel array, and throttle back the maximum output in amps as appears to be appropriate and this may extend the charger life.

Also with the 57 amp maximum output today, my battery bank charged to what my Batrium battery management software showed 101.5% charge and was attempting to limit the charge on multiple packs.

This has been a good experiment, only way to actually see what total output in watts and amps would be!

Thanks again for the input!
 
drspeakman:

Sounds like you are working your way through this. Would like to share part of my "journey" of learning the last couple years. I still need to learn a lot. Started by researching battery backup systems, because our project was far from being done, and the PV panels would be last to go into the system. (Building new house mostly by myself) Our goal was, and is backup for power outages. Right now, a large portion of the US has rolling blackouts, snow storms, etc. And bitter cold temps....

Decided on recycled auto packs, like BMW, etc, and ESS batteries, like Samsung. Do not want to assemble 18650 cells. Our batteries are nominally 24 volts or 48. Bear with me here...I think your situation is similar to mine...

Spent a couple years reading about all the main brands like Outback, Schneider, Magnum, Victron, etc. Also looked at lots of inverters available sitting in warehouse, like the Delta H6. Looked at PIPs. Phocos, Exeltech, etc. I called ALL of the companies and talked with owners, tech managers, service techs, etc. This also goes for people like Midnite Solar.

In our case, the local utility pays about 2 cents per KW if you sell back to them, and sells kw for 16 cents. We have huge industrial loads during he day, much lower at night. Our utility does have a plan where you sign up for a year at a time, and get a 60% discount from 7:01pm, to 6:59 am, but pay 150% for energy used from 7am to 7pm. I may do that plan in the future, if they still have it, and use my batteries during the day, charge at night. I decided not to grid connect, for a couple reasons:

1. It doubles the price of the system due to having to hire pros, and additional markups.
2. They keep raising the base charge for being connected, so even if you sell back to them, the base charge is still there, and even reduces your contribution more.
3. The whole rapid shut-down issue.
4. DC off-grid while maintaining a normal grid connection seemed to be more efficient, especially because we committed to serious battery backup.
5. DIY allows you to buy better equipment, for some outlay of cash.
6. I'm willing to go downstairs, and manually disconnect from the grid, and turn on systems to back up loads. Thinking was that later in the game, we can modify this if we choose.

Wanted to buy the Magnum for a long time. Great inverters. But the ones I heard had a whining noise that hurt my ears.
Found that getting any tech info from Schneider was nearly impossible, so crossed them off the list.
Really like the Radian system, but the inverter is just part of the stuff you need to buy to make it all work. Displays, connection devices, really adds to the cost.
Considered just buying some inverters like Victron, or Exeltech, and making a couple discrete battery systems with a 1000-2000 watt inverter, attach a small homemade panel, plug in your loads direct. Then you still need charge controllers, etc when you have PV panels. The all in one boxes are cheaper.

In the end, I did what OffGridinTheCity did...separated most of our loads into 3 Square D panels. I do this work myself, and would highly advise you to learn how to do your own wiring. It is much easier than all the stuff you have to learn about DC, batteries, etc. It will save you a lot of money, you can customize it, and spend your cash on more batteries, or solar. Also, the whole panel becomes a "critical load panel". I actually have 4 panels, and they will all route to a 5th panel that will be located upstairs at the point of entry, that includes 1 large disconnect.

I bought Victron Quattro 48v. Have now decided to build a second, independent battery bank at nominal 24 volt. Am either going to buy another Victron, or a Phocos. Check out the 24v, 3000w unit or the 48v, 5000w unit. They appear to be well made, support is in US. Basically, they look to me to be a better PIP. German engineering, made in China. They do everything like many other hybrid units. Price is great.

One comment: Many, many people buy Victron because of their connectivity, data logging, apps, etc. Not me. I bought it because their history is making reliable units for things like boats, off-shore, off grid, etc. I don't want to sell to the utility, don't want panels on my roof like most installations here, and want to be able to take a large portion of my investment with me if I move again. So, going ground mount, discrete panels, multiple sources of inverters. As usual, your mileage may vary.....best of luck!
 
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