Batteries

Hi Mex,

The Tesla home battery pack is 400 volts dc--obviously it needs to be "married" to something that brings it to 240 AC. There has been nothing but silence about how this is done and what the cost is.

Once we are at 240 volts AC, getting to 120 volts AC should be fairly simple.

MEXICOWANDERER wrote:
"Bringing 400vdc Down to 120vac"

Am I missing something here?

A high voltage thyristor circuit that can handle >300 volts used to cost a king's ransom. Simple devives were bad enough. High wattage circuits were like diamonds. Double the size - square the price.

But times are changed...can someone point me to a 400vdc bucker?

"Bringing 400vdc Down to 120vac"

Am I missing something here?

A high voltage thyristor circuit that can handle >300 volts used to cost a king's ransom. Simple devives were bad enough. High wattage circuits were like diamonds. Double the size - square the price.

But times are changed...can someone point me to a 400vdc bucker?

I'd assume that if I had Lithium batteries, I'd also have a computer assisted charger. The voltage tolerances with Li are very tight. Progressive Dynamics already has Lithium battery chargers. A solar controller would have to have the same output and voltage sensing attributes.

jrnymn7 wrote:

Naio wrote:

jrnymn7 wrote:

Yep, and the interesting thing about LiFePo4, is they do not require Full Charge or Floating... so one would have to re-think their solar charging set-up, and have it stop charging once the bank was at say 90%.

I don't believe in the "one size fits all" approach to solar, so I plan on switching things around, occasionally. For example, I won't need 280w of pointed mppt solar during the summer, so I will likely run one flat 140w panel on pwm. But come the colder, darker months, I will run 2 panels pointed mppt. It was considering the charging of lithium batts that got me thinking about dragging out the charging time to suit how much charging was actually needed.

Forgive my ignorance, but why would it be worth the trouble to swap out panel and controller? What would be the benefit?

It would only be a simple matter of switching around some wire connections. The advantage would be not overly charging the bank, unecessarily. The sloar30 pwm I'll be using has the same setting for abs and float. If the bank was full by say noon, it would charge at Vabs until I could deal with it, several hours later, after work. By slowing the charging process, by lowering the charge rate, I could effectively drag out the charging time to say 5pm. Simply put, I just don't need 16 amps for 10-12 hrs a day, to replace say 40Ah's usage. I could just use an mppt year round, and let it float the bank most of the time in summer, but I'm also interested in comparing the performance of the two methods.

Come late fall/early spring, using mppt will be of necessity, as I will likely need to supplement the 280w system with either gen charging and/or by adding an additional 100 watts or so of portable solar. And yes, I could go with a larger array from the get go, but the portable could come in very handy at times as well.

Cloudy rainy weather does a real number on panel Isc, so mppt does much better under such conditions, while in hot weather, panel voltage takes the hit, so pwm can actually do better. Much of my reconfiguring will be in the interest of research... seeing first hand what works best in any given situation.

Thank you very much for explaining :). I am just starting to learn, and didn't know that about pwm vs mppt.

pianotuna wrote:
Hi 2oldman,

Naw, just bring the 400 DC to 120 volts AC and power a standard 13.6 volt converter.

Ah, good point, PT. A megawatt power supply would do very well in that situation.

Naio wrote:

jrnymn7 wrote:

2oldman wrote:
No matter the power curve, ya still gotta put all that energy back!

Yep, and the interesting thing about LiFePo4, is they do not require Full Charge or Floating... so one would have to re-think their solar charging set-up, and have it stop charging once the bank was at say 90%.

I don't believe in the "one size fits all" approach to solar, so I plan on switching things around, occasionally. For example, I won't need 280w of pointed mppt solar during the summer, so I will likely run one flat 140w panel on pwm. But come the colder, darker months, I will run 2 panels pointed mppt. It was considering the charging of lithium batts that got me thinking about dragging out the charging time to suit how much charging was actually needed.

Forgive my ignorance, but why would it be worth the trouble to swap out panel and controller? What would be the benefit?

It would only be a simple matter of switching around some wire connections. The advantage would be not overly charging the bank, unecessarily. The sloar30 pwm I'll be using has the same setting for abs and float. If the bank was full by say noon, it would charge at Vabs until I could deal with it, several hours later, after work. By slowing the charging process, by lowering the charge rate, I could effectively drag out the charging time to say 5pm. Simply put, I just don't need 16 amps for 10-12 hrs a day, to replace say 40Ah's usage. I could just use an mppt year round, and let it float the bank most of the time in summer, but I'm also interested in comparing the performance of the two methods.

Come late fall/early spring, using mppt will be of necessity, as I will likely need to supplement the 280w system with either gen charging and/or by adding an additional 100 watts or so of portable solar. And yes, I could go with a larger array from the get go, but the portable could come in very handy at times as well.

Cloudy rainy weather does a real number on panel Isc, so mppt does much better under such conditions, while in hot weather, panel voltage takes the hit, so pwm can actually do better. Much of my reconfiguring will be in the interest of research... seeing first hand what works best in any given situation.

Hi 2oldman,

Naw, just bring the 400 DC to 120 volts AC and power a standard 13.6 volt converter.

pnichols wrote:
Us RV'ers don't need all of these fancy configurations using lithium ion battery technology.

What we're going to need is a DC-DC converter to bring that 400vdc down to 12.5. Either that or battery->inverter>-charger->coach.

"RV amp hours per cubic inch is KING"

... a perfect argument for going LiFePo4. Half the size and 1/3 to 1/4 the weight.

Hi,

No, it can be drawn down to 100% (but probably has a 20% capacity that you can't "reach".)

2oldman wrote:
So I'm going to assume the 10kwh Tesla battery should only be drawn down 50% also.