Powerwall voltage

Korishan

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Wolf said:
Another thought is a BMS for your 7s45p pack. You will have to find a BMS that will handle the amperage you are requesting and also have a shunt trip or some cut off when the pack voltage is ~21V. Also when recharging you will need to be able to balance the pack and have an upper limit cutoff so you don't overcharge the battery.

He's relying on the inverter to low voltage cutout. Not an idea situation. I agree with Wolf that you should use a proper BMS to handle this instead of letting the inverter just shut off at low battery voltage. Not only can it be configured with alarms to let you know you are getting low on power, but it could also allow you to switch over to an alternate power source "before" you loose battery power. Also, it would allow you to start charging the battery back up before it become too dead.

Sean said:
youlasty said:
2000w isnt enough for my air heater tho :{, ugh not like it matters anyway

What type of air heater is it ?

Must be REALLY cold if he needs 2000W heater at full blast the entire time :p
 

Redpacket

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Some things to keep in mind:
- an inverter that says "modified wave type" is basically a stepped squarewave output, these are typically cheapies at best
- the harder you charge & discharge + deeper your discharge cells, the shorter they will last
- at the charge/discharge rates you're thinking, you may only get a few hundred cycles from the cells
- like suggested above, balancing with a good BMS is critical (your pack WILL fail early without it)
- when you work a pack hard like you're planning, more balancing is needed
- space heating is generally not a good idea unless you already have a huge system due to massive energy demands
- reverse cycle air-con is more efficient (unless outside temp < 0 degC)

Most of us on the forum here don't run things anywhere close to how you're suggesting for the above & other good reasons....
 

youlasty

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Sean said:
youlasty said:
2000w isnt enough for my air heater tho :{, ugh not like it matters anyway

What type of air heater is it ?

it is a fan heater search it up, it uses 2000w continious but it needs a extra watt jump start like with all appliances
 

Sean

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Using resistive air heating is daft, especially one rated at 2kW - running that from a battery is double daft.

Perhaps investing in an air to air heat pump might be a better purchase before the storage system ?

Along with lots of insulation .....
 

youlasty

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Sean said:
Using resistive air heating is daft, especially one rated at 2kW - running that from a battery is double daft.

Perhaps investing in an air to air heat pump might be a better purchase before the storage system ?

Along with lots of insulation .....

thanks for the help yall, decided im gonna go for 420cells 7s60p for 4kwh and a bigger inverter

will be draining them at 1c, 3amps which is very low.

output will be like 4000w which can power so much stuff and thats low drain on the batteries
 

prepared1

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Does this site have tutorials that the OP could be directed to read first, before making up his/her mind?
 

floydR

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Look at the last post from the OP they decided on a 7s60p close to 2 years ago
later floyd
 

daromer

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It was just a spammer who bumped the thread so lets leave it to a rest. I cleaned out the spam.
 

yamanpal20

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I am confused here. I mean the average standard discharge of a 18650 is ~1A with potential busts into the 5 to 10 Amp range.
at a standard discharge of 1A a 3000mAh battery would last you 3hrs and a 7s36p pack would deliver 36A for 3 hrs.
 

Redpacket

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Generally running an air heater from your batteries with a small system like yours (& even a larger system) is a really bad idea.
Trying to pull the massive currents you've calc'd for a sustained time will smash the batteries & your system won't last well at all.
For a short, few minute burst, eg boil a kettle or use microwave, it's OK.
At anything like 10A discharge, the cells will be very stressed, even if they are rated for it. Eg power tool (eg a tradie) or vaping cell use, the cells/packs often only last a year or two.
 

chuckp

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Yes, that's correct.
Loosely speaking yes, your cell has a storage capacity of 3000mAh that’s not the same as usable capacity, if you discharge your cells to say 20% then you only have a usable capacity of 2400mAh. Also if you don’t achieve a full charge that will further reduce your usable capacity.
 
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