Tesla Batteries

You obviously don't have a clue. That's ok, get some professional system advice. Surely there's an off-grid newsgroup with actual relevant experience.

DO NOT COBBLE TOGETHER YOUR OWN BATTERY CHARGER. Batteries are the most expensive part of the system. You want to make them last as long as possible. Get a charger configured to interface with your EXACT source and battery configuration.

DO NOT BELIEVE THE POWER CONSUMPTION RATINGS ON THE PRODUCT STICKER. Do the math with real numbers. An electric heater with 1200W on the panel can reasonably be expected. to consume 1200W. Most other things have non-unity power factor and can have a significant effect on the numbers you need to calculate. Don't expect to be able to use more than half of your battery capacity. Solar panels are rated for noon on a summer day with perfect solar tracking. On a rainy winter day, you don't get much at all.

A system that keeps you up and running thru a week-long blizzard is gonna cost you WAY more than you think. Don't try to plan it a piece at a time. Determine the exact requirements. Get a quote on a professionally installed system. Start with the most expensive parts and see if you can whittle it down to full DIY, or whether you can effectively purchase some of the system parts.

Cobbling together a system that doesn't meet your needs is a big waste of money.

Some texting bitch wrecked my first Volt about two year ago, if the insurance company had let me keep the hulk I'd ship you that one to play with!

You can pick up 48V 45 ampere/hour surplus individual pack modules off eBay relatively cheap, tho (it takes about eight of these to make a full pack for the car)

Forget that idea. Assuming you mean the Tesla PowerWall 1, 2, or 3, these were not designed to power anything. They were designed to reduce your peak power usage (time of use load shifting) thus saving you money on your electric utility bill.

Really? Solar panels power a charge controller. It's the charge controller that charges your battery. Misdesign the charge controller and say goodbye to your battery. There are many more ways to kill a big battery than there are to use it properly, so be prepared to do some careful shopping, designing, and building. Trial and error is a really bad way to design a charge controller.

Also, you'll need to deal with various electrical safety standards. I don't have any idea what is in fashion in the UK, but in the Trumpland, we have NEC Article 690. This is old, incomplete, but is the most readable copy I could find online: Many of the safety features, such as the rapid shutdown and disconnect, can be complexicated and expensive.

Unfortunately, my favorite alternative power magazine ceased publication last month after the deaths of the owners. The online archive of back issues are planned to be available eventually. Meanwhile, the web site is full of relevant articles and information. I suggest you dig through the "project profiles" for design examples worth stealing:

You probably won't appreciate this, but unless you have money to burn on an over-designed monster system, you will find that going off grid involves some substantial lifestyle changes and careful energy management and accounting. Most off-grid failures can be attributed to the owners unwillingness to grind the numbers and make any necessary changes. I suggest you delay designing your system and instead spend some time carefully measuring your current power consumption and calculating your future off-grid power and storage requirements. Also, consider that the further north you live, the more difficult it is to build a usable solar power system.

e.g. this is the size of the array required to supply the energy needs of a small organic farm near me (Boston area); a modest single-family two-story farmhouse, large barn, and a couple other associated out-buildings on about 20 hectares of farmland/fields.

five 25 square meter panels mounted on sun-tracking mounts, a 5-10kW array, maybe.

You have me interested now. I thought in the USA peak power load was typically in mid afternoon when aircon was at full stretch and by implication solar panels also at peak output. Surely the purpose of a Tesla power wall *is* to store any excess solar power to use later in the evening when the sun has gone down (rather than dumping it into the hot water immersion heater - as is common in the UK). A quirk of the feed-in-tariff is that you get paid a premium rate for half of what you generate no matter what you do with it (insane).

ISTR they come in 12kWhr blocks and are notable for being able to withstand being installed outside in the cold (UK never below -15C).

What is the peak discharge rate that they can cope with in practice?

In the UK you would also have to worry about the battery being destroyed during the short grey winter days. There has been less than 10 hours of sunshine since 1/1 and around 8 hours of daylight. The sun doesn't pack much punch when it barely gets 14 degrees above the horizon.

It is worth pointing out that "professionally" designed active radar signs in the UK "please go round the (dangerous) bend" routinely destroy their batteries every winter. And they are a total waste of time - they work brilliantly in mid-summer but are dead in the water a couple of hours after sunset in winter and on every frosty winters morning!

A neighbouring villages cricket pavilion has a solar powered off grid system (because the cost of running mains to it was prohibitive). It seems to work OK but mainly because they only use it in summer.

There are plenty of companies offering solar power systems in the UK but you have to be careful some are scam artists with incredible (and I use the word advisedly) predictions of customer savings on electricity bills that somehow never materialise. Likewise for ground source heat pumps.

The only times I looked at setting up an offgrid supply it turned out to be much cheaper to have a pair of big lead acid SLA's and charge them off site weekly. It was an order of magnitude cheaper than solar power - granted solar PV prices have come down a long way since then.

ies for energy storage. These would be charged from solar panels.

of an AC operated 240 volt one, is that alright ? Will they charge properl y ?

charging them there, but where this is going there are not going to be any charging stations. If a float charge can be maintained it would work. The reserve would certainly be there and it would be a matter of replacing what ever energy is used.

e a towmotor to install the batteries so we can't have them failing soon.

ruck converted to a camper, but it is not going to live at a campground. Pl us I doubt that you can pull enough power from a campground to charge one. Of course the proper fittings can be installed and the thing driven to a ch arging station but we do not want to HAVE TO do that.

arged periodically. Are these batteries like that ?

know, there could be more than one in parallel.

asons. However that could change depending on what kind of information I gl ean about this whole matter.

t what I can and can't do. Constant current is no problem if that's what's needed. But what would be the minimum current ?

a slightly higher voltage than the state of charge dictates, but then can I taper off when it nears full charge ?

, what are the consequences ? If some other type of battery would be more s uitable that can be worked in.

ap. And we don't plan on really draining that much. There will be A/C but t hat will run of a generator. Want cooling go get some fuel for that. It is however not a necessity. We need the necessities to remain away from the gr id practically indefinitely. For example I am sure a propane stove would be nice because electric sucks, plus is less cost effective. But there would be electric alternatives. Intermittent use of things like a toaster oven, e lectric skillet, microwave and all that will be in there. We are aware of w hat kind of power that uses, so propane, as long as it is plentiful or near by would be the norm.

un one on 120 volts. There wouldn't be much running off the inverter but wh at does will want amps. Al the lighting will be low voltage LED, even fans. Just things with a compressor are the problem there.

m to be elusive. For example I could calculate by what the charger pulls at 240 volts in the garage normally and get an idea. But there are specific t hat will be lacking unless I can get the whole setup and test it. That woul d be impractical, we are not buying a whole Tesla, just some batteries. Thu s the question about self discharge, used batteries might not quite have th e capacity as new ones, so two of them might be better. That is of course i f they don't kill each other.

The idea of running all that lot on solar power is simply impractical. The first things people do when designing an off grid solar system is a) list what they think they could get away with using, as you have b) calculate what that would cost. Utter expletives. c) work out how they could run a way more frugal load. Anything & everything that can avoid using electricity must do so. The rest needs to be superefficient. Then it might be doable.

Secondly, I don't know the cost of Tesla batteries but would be surprised i f they were cheaper than lead acids. Homemade lead acids are not impossible .

A simpler constant current charger? Ha. At a minimum you need MPPT & a prop er charging algorithm.

Calculate your daily energy use is the next move.

NT

No wonder.

Take a look at

Also remember the air mass (AM) losses due to the low sun angle, when only a half or quarter solar intensity is available. Thus a "100 W" panel will produce 25-50 W in December even with optimal orientation and this is available only 2 h/day on average.

Speaking of used batteries. Tesla battery is around $300/kWh. Leaf battery is around $200/kWh. Leaf battery would be better deal, as long as you don't fast charge it too much.

I am wondering if Tesla would sell real model 3 with smaller battery, I.e. 50 kwhr. No way they can sell for $35k otherwise.

That sounds more like a 15 to 20kW system, or about 2x larger than mine. My roof annually generates enough power for my power-hungry house (including electric hot water and 5kW heat pump to heat house above 40-deg F). Maybe a system 2x larger could handle a small farm.

BUT, given cloudy dark days and winter, I absolutely depend on banking my extra summer power into the grid, with net-metering. I use average 30kWh. If off-grid, I'd want at least 10 days of backup, or a 300kWh storage system. Smaller ones need not apply.

That is not advice.

system advice. "

That is advice. Of course that is why I am here. I figured someone might kn ow about these things.

I really want to avoid that like the plague. I know there is more to it tha n a constant current source.

Do the math with real numbers. "

I know about power factor. The problem with real numbers is obtaining them. I tend to figure worst case. So he has this fridge in mind that is rated 3 .5 amps running and 6 amps to start. I think it reasonable to assume that t he starting current is going want close to the 720 watts, but in run it is not going to be 400 watts. Thing is, worst case scenario just figure the 40

cost you WAY more than you think. "

I am not sure what this guy thinks it is going to cost, but if he is not af raid of buying Tesla batteries I doubt he intends to be penny wise and poun d foolish.

installed system. "

Might, or maybe from one of the places that sells them. But it seems to me that whatever they put together could be enhanced.

you can whittle it down to full DIY..."

Sounds like a plan.

money. "

That's why I'm here.

eBay relatively cheap, tho (it takes about eight of these to make a full pack for the car) "

We are still in the figuring out the need stage. Part of it can be changed, like a DC fridge is alot more expensive and usually too small, but a bigger invertor and a bit more battery ? Might be worth it.

Those individual pack modules, from what ? Tesla or something else ?

Damn at looks big. You say 10 KW ? Hmmm. good reason for the A/C to be on the generator for sure.

That's another question. I doubt they like to run into a short circuit.

e were not designed to power anything. "

I had to look that up. No, what he was considering is using actual Tesla ca r batteries.

I understand that. But one of the main questions I guess I didn't phrase ri ght is if a Tesla CAR battery can be charged slowly, because it is not what you can get form the 240 volt line in the garage. No matter what charge ra te the controller would set, the input must be greater than the output. (ex cept in that other universe) Would it hurt to charge too slowly ? The only reason to even think about designing a charger it because it may be that th e normal charger cannot be run on too low a current, or voltage depending.. . Perhaps the usual charger with a bypass to get it to a certain point wher e it will rune ? Something like that.

This is new to me, but I don't scare easily. My main concern is the life of the batteries, after the power demands are met.

really bad way to design a charge controller. "

Which is why I am here. How much does it take to charge these things ? I me an, what do they LIKE ?

If I have to go store boughten so be it. But, well you know. Do those specs exist somewhere on the net or are they a trade secret or something ? If no t, maybe a regular charger could be bought and what it does measured. In fa ct just having that could come in handy. Maybe it barely keeps up, and if r un down takes a week to charge. But then there is the option to just drive up to a charging station and boom, there's the power again. Would like to a void that if possible but to have the option is good.

And of course he wants to be off the grid but on the net, that is a whole n ew ball of wax, though I know it can be done.

I copied all those links and will read them later. (before doing anything o f course)

instead spend some time carefully measuring your current power consumption ..."

Problem is there is no current power consumption to measure. We are discuss ing all kinds of options for that. For example he probably will want a micr owave, if we do that a modern fridge ain't shit. In no way do I pretend wan t to put pencil to paper without a hell of alot more information. I also kn ow that there are needed numbers even before contemplating a store boughten system. Off the shelf so to speak.

more difficult it is to build a usable solar power system. "

He intends to go mostly south. There will be A/C but that will be separate on a generator. In fact a big enough generator might even run an AC operate d charger as rated... Hmmm.

a salvage Chevrolet Volt, a la:

"It will buff out"

I've always wanted a compacted compact car:

A random tangent - the safe-ing procedure for a Mitsubishi i-MieV electric car where the battery pack has been damaged in a crash or otherwise is the vent plugs are to be removed from the pack and the entire car lifted up with a forklift and deposited in a pool of de-ionized water to soak for a few days.

Not kidding it does say this in the service manual.

There's not "more to it"! You absolutely do not want a constant current source under any circumstances.

I know only what I've read from other people who probably don't know what's actually going on in a Tesla charger either. I'd suggest that the charger has some minimum power requirement just to make the electronics and safety features of the charger work.

Unless you have some inside proprietary information, I'd suggest you use the TESLA charger designed for that exact battery. That means you're gonna need a way to get sunlight into whatever voltage and current the charger wants.

Vendors misrepresent to generate competitive advantage.

Get a Kill-A-Watt meter and measure stuff.

I made a measurement on your behalf. A 100W-equivalent LED light bulb measured 16W and 16VA. A different 100W-equivalent LED light measured 16W and 20VA.

Inverters are rated in W and VA. That 25% extra VA can make a big difference in what your inverter can tolerate. Depends on the degree of misrepresentation the inverter vendor can tolerate.

If you add up all your demand, you'll find that you cannot afford a solar system that lets you run everything at once. That gives you some interesting problems. What do you want to happen if you're running the coffee pot and the refrigerator clicks on and overloads the system? Do you want your power system in a limit-cycle oscillation when the propane heater is trying to start? What do you want to happen when it's early sunny morning and the batteries are flat? Is that different from what happens when it's cloudy out? You will decide to have a backup generator. How are you gonna predict when to run it? Do you want it to run at 7AM if the day is expected to be sunny? cloudy?

I waste a LOT of time helping someone with that attitude. He ventures into areas where he hasn't a clue and can't be dissuaded by facts. He thinks he can do everything better than the professionals. I'm always digging him out of holes he got into. Reading your posts over the long term suggests that you two should meet.

If you stick with an experienced vendor, it's likely that you won't be able to do a lot better. I predict that you'll decide you can do it cheaper. Maybe you can, but I've got experience with people who try to do that, including me, and have decided that it's often a fool's errand.

I've never pulled the trigger, but I've pondered off-grid and solar in scenarios from staying put and going mostly off grid all the way to post-apocalyptic existence.

The first question to answer is why you're doing it. Exactly what are you trying to accomplish? It's easy to get tunnel vision and ignore the possibility that a minor change in the objective can make a BIG difference in the execution. "Just because I can" is best left to areas where you have significant experience.

One important thing to consider is, "how easy is it for someone to vandalize or steal my solar system?" Most people ignore questions like this because they think the probability is low. Probability makes good sense when sizing a sewer system or writing an insurance policy. In an individual situation it's either 0 or 1. There ain't no in-between.

What are the parameters of your situation? If your scenario predicts easily available propane, you might consider running everything possible from that. If your scenario predicts the failure of civilization and roving gangs plundering everything in sight, maybe you won't have propane...or solar panels when they get finished with you.

In a propane situation, you may decide that your best option is a bank of 12V Lead Acid batteries and a small solar system and inverter. Maybe 48V, but that creates portability issues for devices. Maybe a propane powered generator.

My attempt here is to suggest that, how you charge a Tesla battery, is WAY down your list of issues to resolve.

In my case, I couldn't come up with any scenario that resulted in lower energy costs. Yes, there are people who have favorable grid power buy-back situations...until they become no longer available. That didn't work for me.

There are lots of sources for info on solar insolation. This is one such

I've seen charts that disclose just how much solar energy you can get by month, on average...but you still need SIGNIFICANTLY more to ride out cloudy periods.

"insolation " is your keyword.

Don't ignore wind. If you have it, it can be a major addition to power, especially at night.

I'm a believer in simulation. Go out to the breaker box and turn off all except one 15A circuit. Run some extension cords to get everything you use running off that circuit. See how you feel after a month of that.

If you have a smart meter, you can probably put an IR sensor on that and measure the time between light pulses. When the time gets shorter than the duration that represents the maximum power you'll have available, sound a horn. A short horn blast represents an excess that you might be able to ride out for a short time. A continuous horn says, "turn something off."

I've helped engineer small combination wind/solar systems to put on mountain tops. Believe me, it's WAY more complex that it seemed at the start.

Are we having fun yet?

Pretty close, around 500A for 100Kwh Tesla and 120A for 24kwh Leaf.

The problem is the unstable power from solar panels. Li polymer battery does not like too many cycles. It might be better to first charge into LA or AGM battery, then transfer to LiPo

Depending on the SOC (State Of Charge), it could be 500A down to 10s of A (not sure the exact number). For Leaf, it's 120A down to 5A, when close to fully charged.